Mol Imaging Biol (2014) DOI: 10.1007/s11307-014-0800-x * World Molecular Imaging Society, 2014
RESEARCH ARTICLE
BAY 1075553 PET-CT for Staging and Restaging Prostate Cancer Patients: Comparison with [18F] Fluorocholine PET-CT (Phase I Study) Mohsen Beheshti,1 Thomas Kunit,2,5 Silke Haim,1 Rasoul Zakavi,3 Christian Schiller,1 Andrew Stephens,4 Ludger Dinkelborg,4 Werner Langsteger,1 Wolfgang Loidl2 1
Department of Nuclear Medicine and Endocrinology, PET-CT Center Linz, St. Vincent’s Hospital, Seilerstaette 4, Linz, 4020, Austria Department of Urology, Prostate Center Linz, St. Vincent’s Hospital, Linz, Austria 3 Nuclear Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran 4 Piramal Imaging GmbH, Berlin, Germany 5 Department of Urology, Paracelsus Medical University, Salzburg, Austria 2
Abstract Purpose: (2RS,4S)-2-[18F]Fluoro-4-phosphonomethyl-pentanedioic acid (BAY1075553) shows increased uptake in prostate cancer cells. We compared the diagnostic potential of positron emission tomography (PET)-X-ray computed tomography (CT) imaging using BAY1075553 versus [18F]f luorocholine (FCH) PET-CT. Procedures: Twelve prostate cancer patients (nine staging, three re-staging) were included. The mean prostate-specific antigen in the primary staging and re-staging groups was 21.5±12 and 73.6±33 ng/ml, respectively. Gleason score ranged from 5–9. In nine patients imaged for preoperative staging, the median Gleason score was 8 (range, 7–9). PET acquisition started with dynamic PET images in the pelvic region followed by static whole-body acquisition. The patients were monitored for 5–8 days afterward for adverse events. Results: There were no relevant changes in laboratory values or physical examination. Urinary bladder wall received the largest dose equivalent 0.12 mSv/MBq. The whole-body mean effective dose was 0.015 mSv/MBq. There was a significant correlation between detected prostatic lesions by the two imaging modalities (Kappa=0.356, PG0.001) and no significant difference in sensitivity (P=0.16) and specificity (P=0.41). The sensitivity and specificity of PET imaging using BAY1075553 for lymph node (LN) staging was 42.9 % and 100 %, while it was 81.2 % and 50 % using FCH. The two modalities were closely correlated regarding detection of LNs and bone metastases, although BAY1075553 failed to detect a bone marrow metastasis. Degenerative bone lesions often displayed intense uptake of BAY1075553. Conclusions: BAY1075553 PET-CT produced no adverse effects, was well tolerated, and detected primary and metastatic prostate cancer. FCH PET-CT results were superior, however, with respect to detecting LN and bone marrow metastases. Key words: BAY1075553, FCH, PET-CT, Prostate cancer, PSMA
Correspondence to: Mohsen Beheshti; e-mail: [email protected]
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Introduction
P
rostate cancer is the most commonly diagnosed cancer
and the second leading cause of death in men in the United States [1]. In Europe, 417,000 new cases were diagnosed in 2012 [2]. Although prostate-specific antigen (PSA) is well established as a screening tool and a sensitive marker during assessment of prostate cancer, it suffers from unacceptable specificity and is not able to localize the malignancy or determine its extent. Hence, a biopsy is needed to sample the prostate to obtain multiple needle cores. Biopsy, however, is associated with a substantial number of false-negative results, often leading to re-biopsy. Accurate diagnosis and defining the extent of a prostate cancer is of great importance for determining the appropriate therapeutic approach. Molecular imaging has become an essential tool in cancer research, clinical trials, and routine medical practice. At present, positron emission tomography (PET) in combination with X-ray computed tomography (CT) plays a pivotal role among the molecular imaging modalities, providing noninvasive, quantitative, real-time information. Currently, several PET radiotracers have been introduced to depict the intraglandular malignancy in the prostate as well as extraglandular infiltration [3–8]. PET-CT using C-11- and F-18-labeled choline has demonstrated good diagnostic performance in the assessment of recurrent prostate cancer [4, 9]. In the preoperative setting, however, it cannot differentiate malignant disease from inflammatory processes or benign prostatic hyperplasia [5]. In addition, because of the limited resolution of PET-CT scanners, it has low sensitivity for detecting small (i.e., G5 mm) lymph node metastases [5]. Prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II, is a type II integral membrane protein. It has been well established as a highly specific marker for prostate cancer cells. Elevated expression of PSMA is seen in all prostate cancers, although the highest levels are found in high-grade, hormone-refractory, and metastatic disease [10–14]. PSMA expression has also been identified in the neovasculature of solid tumors [15]. The most common nonmalignant tissues with PSMA expression include prostate epithelium and, to a limited extent, the brush border cells of the duodenum, kidney proximal tubules, breast epithelium, neuroendocrine cells in colonic crypts, and brain [14–16]. Imaging studies with PSMAspecific small molecules in humans have shown accumulation in lacrimal and salivary glands as well [17, 18]. This favorable restricted expression profile suggests that PSMA would be an excellent target for detecting prostate cancer and marking it for treatment. Many approaches using PSMA have been introduced for therapeutic and diagnostic purposes. ProstaScint® (7E11C5.3) was the first monoclonal antibody used to detect
prostate cancer [19]. It was not able to bind to viable cells, however, because it targets an intracellular epitope of PSMA. Recently, several monoclonal antibodies that bind to the external domain of PSMA have been developed [18, 20–24]. Among them, (2RS,4S)-2-[ 1 8 F]fluoro-4phosphonomethyl-pentanedioic acid (BAY1075553) has shown promise in the assessment of PSMA-positive prostate cancer for preclinical investigations [24]. In the present prospective study, we compared the diagnostic potential of PET-CT imaging with BAY1075553 as a novel PET tracer versus [ 18 F]fluorocholine (fluoromethyl-dimethyl-2hydroxyethylammonium [FCH]) PET-CT. It is the first such study conducted in humans.
Materials and Methods Patients This prospective phase I study was approved by both the institutional ethics committee and the routing committee of the province. Written informed consent was obtained from all patients. Twelve patients with a mean age of 66.9±7.8 years (range, 53– 82 years) and mean PSA level of 34.5±29.2 ng/ml (normal range, G2.5 ng/ml) were studied. Nine patients were imaged for preoperative staging. The other three patients were imaged postoperatively because there was biochemical evidence of recurrence. Their Gleason score ranged from 5 to 9. In the nine patients imaged preoperatively, the median Gleason score was 8 (range, 7– 9). Their mean PSA level was 21.5±12.0 ng/ml. Inclusion and exclusion criteria are shown in Table 1. Pelvic lymphadenectomy was performed in all nine patients in the preoperative setting. All 12 patients were monitored clinically from 24 h before BAY1075553 administration to 5–8 days afterward. Monitoring included physical examination, electrocardiography, and laboratory parameters of various organs. Adverse events were documented. The patients’ characteristics are shown in Tables 2 and 3.
Procedures BAY1075553 and FCH were synthesized on site. The radiochemical purity was 995 % as analyzed by thin-layer chromatography. Synthesis, pharmacokinetics, and radiation dosimetry of each tracer has been described in previous studies [24, 25].
Biodistribution and DosimetryBiodistribution and dosimetry for F-18 radiolabeled BAY1075553 were determined based on PETCT image data from two healthy subjects. Image quantification, kinetic modeling to determine residence times, and dosimetry analysis were performed by CDE Dosimetry Services, Inc., TN, USA, ordered by Bayer Healthcare Pharmaceuticals, Berlin, Germany (present correspondence: Piramal Imaging GmbH, Berlin, Germany). Whole-body PET image data for the two healthy subjects were obtained using F-18 radiolabeled BAY1075553 at approximately 0.5, 6, 16, 150, and 330 min after injection. Image data were
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Table 1. Inclusion and exclusion criteria for participating patient in the study Inclusion criteria
Exclusion criteria
1. Written informed consent
1. Any concurrent severe and/or uncontrolled and/or unstable medical disease which could compromise participation in the study 2. Acute renal insufficiency of any intensity 3. Active inflammatory bowel disease within the last 6 months 4. Acute prostatitis requiring medical treatment within the last 6 months 5. A non-urologic bacterial infection requiring active treatment with antibiotics within 3 months
Males ≥18 years of age Life expectancy of at least 3 months Serum PSA value above normal Creatinine, TSH, AST, ALT, ALK-phosphatase, and bilirubin in norm levels within 2 weeks before any imaging with contrast agents (e.g., gadolinium, Visipaque) 6. Patients with
2. 3. 4. 5.
Primary prostate cancer Adenocarcinoma GSc≥3+3 (at least 2 biopsies) Previous MR u/o FCH PET-CT positive; no treatment in between; max. interval 6 weeks All imaging ≥3 weeks after tumor biopsy Prostate cancer recurrence Advanced cancer disease and a high likelihood to LN metastasis, ideally scheduled to undergo explorative pelvic lymphadenectomy Previous MR u/o FCH PET-CT positive; no treatment in between; max. interval 6 weeks Adequate recovery (excluding alopecia) from previous therapy
6. Active other malignancy (except basal cell or squamous cell skin cancer) within the last 2 years 7. Body weight 9350 lbs (approx. 165 kg) 8. Symptomatic rectal stenosis 9. Unmanaged claustrophobia 10. Patients with primary prostate cancer only: androgen ablation within 3 months before planned treatment 11. Known sensitivity to the study drug or components of the preparation 12. Hints for drug abuse/dependence, life time history of alcohol abuse/ dependence 13. Subject is in custody by order of an authority or a court of law 14. Subject is a relative of the investigator, student of the investigator, or otherwise dependent 15. Subject has completed participation in another clinical study involving administration of a therapeutic investigational drug in the preceding 4 weeks; previous assignment to treatment in this study 16. Unwillingness or inability to comply with the protocol 17. Subject fulfils criteria which in the opinion of the investigator preclude participation for scientific reasons, for reasons of compliance, or for reasons of the subject’s safety 18. Hematological or biochemical parameters that are outside the normal range and are considered clinically significant by the investigator, in particular, the presence of hepatitis B virus surface antigen (HBsAg), hepatitis C virus antibodies (anti-HCV), or human immune deficiency virus antibodies (antiHIV); minor deviations in lab parameters that are considered by the evaluating physician to be not clinically significant with respect to safety or interpretation of study results are not considered an exclusion criterion
attenuation-corrected at the imaging site and were quantified based on the Medical Internal Radiation Dosimetry (MIRD) 16 methodology (CDE) to determine kinetic data for all organs that show significant activity uptake. Dosimetry estimates were created via kinetic modeling of the quantified image data to determine residence times and the standard MIRD methodology. A urinary bladder voiding interval of 1.0 h was utilized.
PET-CT ImagingAll patients underwent BAY1075553 PET-CT imaging followed by FCH PET-CT the next day. Imaging was performed on an integrated PET-CT system (Discovery LS; GE
Medical Systems, Milwaukee, WI, USA) that consisted of a fullring PET scanner with a 14.6-cm transverse field of view and an inplane resolution of 4.8 mm full width at half maximum at the center of the field of view. All PET-CT scans were acquired in twodimensional mode (4 min emission per bed position) and were reconstructed with standard reconstruction ordered-subset expectation maximization iterative algorithm (two iterative steps) and were reformatted into transverse, coronal, and sagittal views. All patients fasted for at least 4 h before each examination. Preparation of study subjects consisted of inserting a suitable indwelling intravenous catheter into a large vein (e.g., antecubital vein), preferably in the subject’s nondominant arm. Correct
Table 2. Pre-operative staging: patient’s characteristics and imaging findings in both BAY1075553 and FCH PET modalities ID
Age
PSA (ng/ml)
Gleason score
T stage
N stage
PLND (number)
Positive (pathology)
FCH LNM
BAY1075553 LNM
FCH BM
BAY1075553 BM
1 2 3 4 5 6 7 8 9
65 64 68 71 70 66 70 56 63
6.9 20.8 21.1 15.5 35.0 22.6 5.6 23.0 43.0
7 7 7 8 8 8 7 9 8
pT3b pT2c pT3b pT3b pT2c pT3a pT2c pT3b pT3a
pN0 pN0 pN1 pN0 pN0 pN0 pN0 pN1 pN0
4 3 15 5 12 11 8 9 1
0 0 3 0 0 0 0 2 0
0 0 1 0 0 0 2 2 1
0 0 0 0 0 0 0 1 0
0 0 g 0 0 0 0 0 0
0 0 g 0 0 0 0 0 0
PLND pelvic lymph node dissection, LNM lymph node metastasis, BM bone metastasis, g generalized
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Table 3. Recurrent disease: patient’s characteristics and imaging findings in both BAY1075553 and FCH PET modalities ID
Age
PSA
Primary Gleason Score
Primary T Stage
Primary N Stage
FCH LNM
BAY1075553 LNM
FCH BM
BAY1075553 BM
1 2 3
53 75 82
110,6 47,3 63,0
5 6 8
pT3a pT3a cT2-3
pN0 pN0 cN0
4 4 5
0 4 2
0 2 0
0 2 0
LNM lymph node metastasis, BM bone metastasis
localization of the indwelling cannula must be ensured by test injection of normal saline solution prior to injecting the study drug. A radioactive dose of 300 MBq ±20 % for BAY1075553 and 4.07 MBq/kg body weight for FCH were administered as slow intravenous bolus injections lasting up to 60 s. After injecting the study drug, the cannula and injection system were flushed with 10 ml saline solution. Acquisition started 30 s after the injection. Dynamic PET images were acquired in the pelvic region for 12 min (8×30 s and 8×1 min per frame) to assess the early perfusion pattern of each tracer and overcome the effect of urinary activity in the bladder. Static whole-body acquisition from the thigh to the base of the skull was then performed. Delayed static acquisition was performed for abnormal tracer uptake 90–120 min after injection. For BAY 1075553, the required mass dose to obtain an image (as extrapolated from preclinical studies) was ≤100 μg. For this study, the safety margin at a maximum mass dose of 100 μg BAY 1075553 per patient was 91,000, which was derived from the “no observed effect level” determined in preclinical studies in toxicology and safety pharmacology. A typical radioactive dose of 2-deoxy-2-[18F]fluoro-D-glucose used for an oncological scan is about 350 MBq for an adult human. This study aimed at showing that, following a single intravenous injection of 300 MBq ±20 % (total quantity of BAY 1075553, ≤100 μg), the PET tracer would selectively accumulate in prostate cancer tissue and allow adequate diagnostic performance compared with that seen with [18F] fluorocholine in primary and recurrent disease. The CT portion of the BAY1075553 PET-CT procedure was performed after intravenous infusion of 100 ml ionic contrast medium with high beam current modulation (120–330 mA). In FCH PET-CT study, the CT portion was performed with low beam current modulation (80–120 mA) for localization and attenuation correction. The reformatted, transverse, coronal, and sagittal views were used for interpretation.
Image Interpretation and Data AnalysisTwo experienced nuclear medicine specialists who were aware of the patient’s history jointly interpreted all of the PET scans. They also had access to the CT and PET–CT fusion images for morphological correlation and localization of pathological PET lesions. Images were read using advanced PET-CT review software (Advantage Windows, version 4.4; GE Medical Systems), which allows simultaneous scrolling through the corresponding PET, CT, and fusion images in the transverse, coronal, and sagittal planes. A lesion was considered pathological when the focal tracer accumulation was greater than the background activity. Bone lesions were considered malignant depending on their anatomical localization (e.g., posterior aspect of the vertebral body and pedicle) and/or characteristic morphological changes (e.g., cortical destruction). Discrete FCH uptake only in inguinal lymph nodes was
interpreted as possible reactive FCH uptake [26, 27] and therefore was excluded from data analysis. Semi-quantitative analysis of the abnormal radiotracer uptake was performed using the maximum standardized uptake value (SUVmax) within the volume of interest, which was manually placed over the pathological lesions on the static whole-body images. The final diagnosis of positive PET lesions was based on histopathological findings and/or follow-up imaging studies (i.e., FCH, [18F]NaF PET-CT, and/or magnetic resonance imaging) for at least 6 months (range, 3–12 months). In the follow-up studies, pathological lesions on PET studies were considered malignant if (1) they showed persistent uptake or increased activity with corresponding morphological changes on CT and clinical evidence of disease progression, or (2) after treatment, there was decreased tracer uptake with clinical regression (suggesting a treatment response).
Histopathological CorrelationCorrelating the imaging results with histopathological findings was performed based on sextant biopsy templates. For evaluating local tumor involvement, the prostate gland contour was identified on the PET images based on corresponding CT images. The defined prostate volume on PET images was extracted using a software program provided by the manufacturer (Advantage Windows 4.4, GE Medical Systems). Based on the sextant biopsy template, the extrapolated prostate volume was divided equally into basal, middle, and apical thirds on each side. The segment with the highest tracer intensity was selected for the correlation with the sextant and with maximum tumor involvement histopathologically. PET-CT findings were correlated with histopathology results for patients who underwent lymphadenectomy. Postoperative histopathological evaluation of lymph nodes consisted of a standard protocol of step sections in 250-μm sequences (conventional hematoxylin–eosin staining) and immunohistochemistry of each step. The results of BAY1075553 PET in the prostate gland were compared with histopathological findings in 12 segments (apical, middle, and basal thirds, each divided into four segments of right, left, anterior, and posterior).
Statistical Analysis Univariate analysis was performed to assess the variables and frequency tables. Quantitative variables were defined as the mean± SD and were compared in different groups using the independent t test. The paired ttest was used to compare quantitative variables in a paired group. Sensitivity and specificity were calculated using data collected from PET studies on per-patient and per-lesion bases. Kappa coefficient was calculated for comparison of two techniques.
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Pearson’s correlation coefficient was calculated for correlations between different quantitative variables. SPSS software version 16 (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis. A value of pG0.05 was considered to indicate statistical significance in all comparisons. Statistical analysis was undertaken on both patient-based and lesion-based analyses.
Results Biodistribution, Dosimetry, and Safety In the reported data by CDE Dosimetry Services, Inc., for two healthy subjects, on average, the organ receiving the largest dose was the urinary bladder wall at 0.43 rem/mCi (0.12 mSv/MBq) followed by the kidneys at 0.36 rem/mCi (0.098 mSv/MBq). The whole-body mean effective dose (International Commission on Radiological Protection, ICRP-103) was 0.054 rem/mCi (0.015 mSv/MBq). No adverse clinical reactions, abnormal laboratory findings, or side effects were detected during the 5–8 days after intravenous administration of BAY1075553. None of the patients showed any reaction to the CT contrast agent. Physiological BAY1075553 uptake was observed in salivary glands and, because of its renal excretion, in the urinary tract. Intensive tracer accumulation was noted in the urinary bladder during both dynamic and static acquisitions, which affects assessment of the prostate gland. In general, marked tracer uptake was also seen in degenerative bone lesions. Tracer uptake was also increased in sclerotic vessels. The liver, pancreas, spleen, gastrointestinal tract, and bone marrow showed no noticeable physiological uptake. Dynamic images were performed from pelvis in all patients. The mean SUVmax in dynamic images of FCH PET study was 4.0±1.1 and increased significantly to 7.0± 1.6 in whole-body static images (PG0.001). This pattern was also seen in BAY1075553 PET study. Mean SUVmax was increased from 4.2±1.7 in dynamic to 5.7±2.5 in the static images (P=0.02). Time of bladder activity was significantly shorter in BAY1075553 PET (2.7±0.98 min) compared with FCH PET (5.7±1.4 min, PG0.001).
Lesion-Based Approach Overall, 108 segments in the prostate glands were analyzed. Histopathological analysis showed that, in three patients, all 12 segments of the prostate gland were involved, whereas four to nine segments were involved in the other patients. Histological evaluation showed that 71 segments were infiltrated. BAY1075553 PET was able to identify 41 positive segments correctly, whereas 49 segments were positive on FCH PET. Using histological examination as the gold standard, BAY1075553 PET gave false-positive results in six segments compared with seven false-positive segments found by FCH PET. BAY1075553 PET showed a sensitivity and specificity of 49.3 % (37.3–61.3 %) and 83.8 % (67.3–93.2 %), respectively, in the detection of primary prostate cancer (95 % confidence interval). Sensitivity and specificity for FCH PET were 59.1 % (46.8–70.0 %) and 81 % (64.2–91.4 %), respectively. The sensitivity and specificity of BAY1075553 PET in apical segments were 50 % (30.3–69.6 %) and 90 % (54.1–99.5 %), respectively. The corresponding percentages for FCH PET were 42.5 % (23.9–62.8 %) and 80.0 % (44.2– 96.4 %), respectively. In middle segments they were 40.0 % (21.8–61.1 %) and 63.6 % (31.6–87.1 %) for BAY1075553 PET and 68 % (46.4–84.2 %) and 72.7 % (39.3–92.6 %), respectively, for FCH PET. In basal segments, the sensitivity and specificity were 60 % (36.4–80.0 %) and 93.7 % (67.7– 99.6 %) for BAY1075553 PET and 75.0 % (50.5–90.4 %) and 87.5 % (60.4–97.8 %) for FCH PET. Comparison of BAY1075553 and FCH PET showed that there was a significant correlation between the two methods (kappa=0.356, pG0.001). No significant difference was noted in the sensitivity (p=0.16) or specificity (p=0.41) of the two imaging modalities for detecting primary intraglandular lesions. The same was true for the sensitivities of the two techniques in the apical (p=0.3), middle (p= 0.051), and basal segments (p=0.22). Also, there was no significant difference between the specificities of the two methods (p90.2).
Lymph Node Assessment
Primary Tumor
Patient-Based Approach BAY1075553 PET had 50 % sensitivity for detecting lymph node involvement with 100 % specificity. FCH had 100 % sensitivity and 83.4 % specificity.
Patient-Based Approach Nine patients had local involvement, all of which was detected correctly by both BAY1075553 and FCH PET imaging. Hence, the sensitivity and specificity of BAY1075553 and FCH were both 100 % for local involvement. There was no significant difference in the mean SUVmax values for malignant lesions in the prostate gland examined with BAY1075553 PET (5.6±2.4) or with FCH PET (6.9±1.6) (p=0.9). The PSA levels and mean Gleason scores were not significantly different in patients with positive or negative BAY1075553 or FCH images (p90.1).
Lesion-Based Approach Overall, 68 lymph nodes were resected from nine patients and were examined histopathologically. Altogether, 20 (20/68) malignant lymph nodes were detected by both PET modalities. The sensitivity of FCH was 81.2 %, and its specificity was 50 %. The sensitivity of BAY1075553 was 43.8 % with a specificity of 100 %. The mean SUVmax of the detected lymph nodes was 10.22±3.3 on FCH PET images and 6.84±2.3 on BAY1075553 PET images (p=0.12). The maximum metabolic diameter of the lesions was 19.29±3.9 mm on FCH
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
PET compared with 17.29±2.13 mm on BAY1075553 PET (p=0.29).
Bone Metastases In the patient-based analysis, the sensitivity and specificity of both BAY1075553 and FCH imaging were 100 % for detecting bone metastases, although only two patients had bone metastasis (one during preoperative staging and one with recurrent disease). Because of the generalized bone metastases in the patient being staged preoperatively and positive findings with both imaging modalities, lesion-based analysis was not performed. Nevertheless, FCH PET was able to detected bone marrow metastases that were not depicted by BAY1075553 PET. The mean SUVmax values for bone metastasis were 15.9±1.2 and 14.6±0.7 on FCH PET and BAY1075553 PET, respectively (p=0.5).
Recurrence (Restaging) Both BAY1075553 and FCH PET-CT modalities were applied in three patients with biochemical evidence of recurrent disease (Table 2). None of these patients had local recurrence in the prostate bed. Lymph node metastases were detected in all three patients. FCH PET-CT was able to detect more malignant lymph nodes than did BAY1075553 PET-CT (i.e., 13 vs. 6); however, there was no difference concerning detection of bone metastases between the two imaging modalities in one patient with bone metastases.
Discussion Targeted molecular imaging has been used in recent prostate cancer studies as it is a noninvasive diagnostic modality that allows accurate staging and restaging of the disease. Identifying and targeting membrane-based proteins that specifically overexpress in prostate cancer has been the goal of recent studies [28]. Among them, PSMA has received the most attention because of its expression in the vast majority (990 %) of examined prostate cancers and its higher expression in cancerous prostate cells than in the benign cells [12, 19, 22, 29, 30]. Several studies have demonstrated a correlation between increased PSMA expression and a higher Gleason score. It has also been suggested that PSMA expression levels in the primary tumor can predict disease outcome, but this has not yet been validated as a predictive marker [31, 32]. Thus, PSMA seems to be a potential target molecule for diagnosis and specific prostate cancer therapy. New PSMA-based PET imaging agents are generally divided into three categories: (1) antibodies, (2) aptamers, and (3) low-molecular-weight PSMA inhibitors [33]. Researchers have been working intensively to develop agents in each of the three categories but particularly on low-molecular-weight PSMA inhibitors.
PSMA presides over an enzymatic site in its extracellular domain that contains two zinc ions and is composed of two bundles: the glutamate sensing bundle and the nonpharmacophore bundle [33]. Most small-molecule PSMA inhibitors have zinc-binding components that adhere to a glutamate or glutamate isostere and belong to one of three groups: (1) phosphonates, phosphates, phosphoramidates; (2) thiols; (3) ureas. Most recently published studies working on new imaging agents for prostate cancer that are based on small-molecule PSMA inhibition have focused on the use of either phosphoramidate or glutamate–urea heterodimer scaffolds with various radioisotopes [18, 20–24, 33–38]. BAY1075553 falls into the phosphonate-based heterodimer group. It has shown promise in the preclinical data and was introduced as a novel F-18 labeled radiotracer targeting the PSMA inhibitor for imaging prostate cancer [24]. The quality of PET imaging using BAY1075553 in the lymph node carcinoma cell line derived from a human prostate cancer tumor model compares favorably with preclinical results published previously using an F-18 labeled radiotracer targeting the PSMA inhibitor [39, 40]. BAY1075553 also showed rapid tumor targeting. It is a low-clearance compound with rapid, almost exclusive, renal excretion. It has been shown to be capable of detecting even lowexpressing prostate tumors [24, 41]. In the present prospective phase 1 clinical study, we evaluated the safety, patients’ tolerance, and biodistribution of BAY1075553. We also assessed its potential value for staging and restaging prostate cancer patients. In addition, we compared its performance with that of FCH PET-CT, which is the current established diagnostic modality for preoperative staging of high-risk prostate cancer and for restaging patients with recurrent disease [4, 5]. BAY1075553 proved to be a safe PET tracer with no adverse clinical reactions, abnormal laboratory findings, or side effects for as long as 5–8 days after its intravenous administration. In the nine patients being staged preoperatively, both BAY1075553 PET and FCH PET revealed pathological lesions in the prostate. Neither of the imaging modalities, however, was able to differentiate benign from malignant lesions accurately. BAY1075553 PET gave falsepositive results in six segments and FCH PET in seven segments (Fig. 1). BAY1075553 PET had a sensitivity and specificity of 49.3 % and 83.8 %, respectively, for detecting primary prostate cancer. The sensitivity and specificity of FCH PET were 59.1 % and 81.0 %, respectively. Hence, accurate noninvasive diagnosis of primary prostate cancer using PET imaging remains a dilemma that warrants further research. When assessing lymph node metastasis in preoperative patients, BAY 1075553 PET showed 100 % specificity versus 50 % specificity by FCH PET, but it exhibited only 43.8 % sensitivity compared with 81.2 % for FCH PET. FCH PET-CT was clearly superior for N staging of prostate cancer patients (Figs. 2 and 3). The results of this study
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Fig. 1. Staging preoperative, 67-year-old prostate cancer patient, Gleason score 7, PSA 22.6 ng/ml, prostate volume 42 ml. a Histopathologic results: prostate adenocarcinoma prominently on the right lobe (marked) with only small lesion on the left lobe. b BAY1075553 PET-CT (upper row), FCH PET-CT (lower row). BAY1075553 PET showed focal tracer uptake on the right prostate lobe well correlated with histopathology results (yellow arrow) while FCH PET showed increased tracer uptake on both lobes (false-positive on the left lobe).
confirmed our previous data concerning the value of FCH PET-CT imaging for detecting lymph node metastases in prostate cancer patients [5]. Nevertheless, detection of micrometastases and lymph node metastases G5 mm is still under debate mainly because of the limited resolution of the current generation of PET scanners, which is about 4.8 mm. This limitation may be partly overcome in the near future with the new high-definition PET scanners with the time-offlight concept [42, 43]. These scanners will have an intrinsic resolution of about 2 mm with improvements in the signalto-noise ratio. Dynamic acquisition of BAY1075553 PET did not provide additional information to static images due to early tracer accumulation in the urinary bladder which affects the interpretation of the pelvic lesions. In the patient-based analysis, both imaging modalities were able to detect bone metastases, although only two patients had bone involvement (Fig. 3). Substantially increased BAY1075553 uptake was seen in degenerative bone lesions, which reduced its specificity and may interfere with its diagnostic applications for evaluating bone
metastases (Fig. 4). Lesche et al. also found this pattern in a preclinical study. They reported intense BAY1075553 uptake (∼2.5 % ID/g 60 min after injection) in regions of active bone growth in the skull and long bones that did not increase over time. They concluded that bone uptake was not due to increasing fluoride incorporation upon compound disintegration in vivo, but rather to specific compound binding to bone structures. As expression of PSMA in bone structures is not detectable [14, 44], binding of BAY1075553 may be independent of PSMA expression and might be explained by its phosphonate structure [24]. This pattern of tracer uptake in benign bone lesions, however, was not seen in similar studies performed with other 68Ga-PSMA targeting agents using glutamate–urea heterodimer scaffolds [18]. This finding emphasizes again the relation between the phosphonate component of BAY1075553 and benign bone uptake. The variable performance of BAY1075553 in different areas of the body affected by the same disease is probably related to PSMA expression. PSMA is particularly elevated in aggressive, androgen-insensitive disease and may serve as
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Fig. 2. Biochemical recurrence, 78-year-old prostate cancer patient, Gleason score 8, PSA 8.9 ng/ml, TUR-P, and radiotherapy, increasing PSA under anti-androgen treatment. a BAY1075553 PET MIP. b FCH PET MIP. c Transaxial images of BAY1075553 PET-CT (upper row) and FCH PET-CT (lower row). FCH PET showed marked increased tracer uptake in the abdomen suggestive of pelvine and retroperitoneal lymph node metastases (yellow arrow–lower row) significantly superior to BAY1075553 PET (yellow arrow–upper row).
a better marker for such tumors. For example, PSMAtargeted imaging tracers have been shown in preclinical models to reflect the activity of androgen signaling and the response to taxane therapy [41]. Additional clinical studies are needed to determine the biological behavior of tracers of this class and their clinical applications. Despite the higher specificity of BAY1075553 PET for differentiating malignant from benign intraglandular prostatic disease, it suffers from low sensitivity for detecting malignant primary and lymph node lesions. This is in contrast to preclinical data [24] and other imaging agents
used to assess small-molecule PSMA inhibition focusing on the use of either glutamate-containing phosphoramidate or glutamate–urea scaffolds [45]. Despite the unsatisfactory findings of the current study using PSMA inhibitors based on 2-(phosphonylmethy)pentanedioic acid scaffolds, glutamate–urea–lysine heterodimers may still be the first choice, given their sub-nanomolar binding affinity and impressive in vivo imaging [36–38]. One of the limitations of this study was that BAY1075553 PET-CT was performed with intravenous CT contrast, whereas FCH PET-CT was performed without CT
Fig. 3. Biochemical recurrence, 54-year-old prostate cancer patient, Gleason score 5, PSA 13.9 ng/ml, radical prostatectomy 2003 (T3a N0 M0 R0), local recurrence (2009), biopsy Gleason score 8, elevated PSA under anti-androgen treatment 2,513 ng/ ml. a BAY1075553 PET MIP (left), FCH PET MIP (right): generalized bone and lymph node metastases clearly detectable on both modalities. b Transaxial images BAY1075553 PET-CT (upper row), FCH PET-CT (lower row). FCH PET showed marked increased tracer uptake on retroperitoneum suggestive of lymph node metastases (yellow arrow–lower row) while BAY1075553 PET showed only mild diffuse tracer uptake (yellow arrow –upper row). c Transaxial images BAY1075553 PET-CT (upper row), FCH PET-CT (lower row). FCH PET showed focal tracer uptake on the proximal part of left femur suggestive of bone marrow metastasis (yellow arrow–lower row); however, BAY1075553 PET was negative (yellow arrow–upper row).
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Fig. 4. Transaxial images of a BAY1075553 PET-CT and b FCH PET-CT. BAY1075553 PET showed focal increased tracer uptake (ayellow arrow) on an osteophyte on T5 (ared arrow). Hence, BAY1075553 PET showed limited specificity due to nonspecific intense uptake on benign and/or degenerative bone lesions.
contrast enhancement. Contrast-enhanced (CE) CT may affect the PET study in two ways. First, it may affect urinary excretion of the investigational PET tracer. Second, it may cause an increase in the SUV in regions of high contrast concentration when CE-CT is used for attenuation correction. In addition, because of the limited spatial resolution of current PET technology, small-tumor involvement or micrometastases (e.g., tumor diameter G5 mm) might not be depicted. Finally, although the inclusion of 12 patients in the first human study on this subject seems acceptable, it may not fully demonstrate the value of each PET tracer because of the small number of patients.
Conclusion BAY1075553 caused no adverse effects and was well tolerated by all patients. BAY1075553 PET-CT was able to detect prostate cancer in patients with both localized and advanced disease. However, both BAY1075553 PET and FCH PET showed limitations to a similar degree in differentiating malignant from benign prostatic lesions. FCH PET produced results superior to those seen with BAY1075553 PET, particularly with respect to detecting lymph node and bone marrow metastases. BAY1075553 also seems to have limited specificity for detecting bone metastases mainly because of the nonspecific increased uptake in degenerative bone lesions.
Acknowledgments. Piramal Imaging GmbH GmbH, Berlin, Germany, gave financial supported to this study. Conflict of Interest. A. Stephens and L. Dinkelborg are employees of Piramal Imaging GmbH, Berlin, Germany. Other authors have no conflict of interest.
References 1. Jemal A, Siegel R, Ward E et al (2009) Cancer statistics, 2009. CA Cancer J Clin 59:225–249 2. Ferlay J, Steliarova-Foucher E, Lortet-Tieulent J et al (2012) Cancer incidence and mortality patterns in Europe: estimates for 40 countries. Eur J Cancer 49:1374–1403 3. Jadvar H (2009) Molecular imaging of prostate cancer with 18Ffluorodeoxyglucose PET. Nat Rev Urol 6:317–323 4. Beheshti M, Haim S, Zakavi R et al (2013) Impact of 18F -choline PET/ CT in prostate cancer patients with biochemical recurrence: influence of androgen deprivation therapy and correlation with PSA kinetics. J Nucl Med 54:833–840 5. Beheshti M, Imamovic L, Broinger G et al (2010) 18F choline PET/CT in the preoperative staging of prostate cancer in patients with intermediate or high risk of extracapsular disease: a prospective study of 130 patients. Radiology 254:925–933 6. Dehdashti F, Picus J, Michalski JM et al (2005) Positron tomographic assessment of androgen receptors in prostatic carcinoma. Eur J Nucl Med Mol Imaging 32:344–350 7. Kato T, Tsukamoto E, Kuge Y et al (2002) Accumulation of [11C]acetate in normal prostate and benign prostatic hyperplasia: comparison with prostate cancer. Eur J Nucl Med Mol Imaging 29:1492–1495 8. Schuster DM, Savir-Baruch B, Nieh PT et al (2011) Detection of recurrent prostate carcinoma with anti-1-amino-3-18Ffluorocyclobutane-1-carboxylic acid PET/CT and 111In-capromab pendetide SPECT/CT. Radiology 259:852–861 9. Beheshti M, Langsteger W, Fogelman I (2009) Prostate cancer: role of SPECT and PET in imaging bone metastases. Semin Nucl Med 39:396–407
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
10. Wright GL Jr, Haley C, Beckett ML, Schellhammer PF (1995) Expression of prostate-specific membrane antigen in normal, benign, and malignant prostate tissues. Urol Oncol 1:18–28 11. Bostwick DG, Pacelli A, Blute M et al (1998) Prostate specific membrane antigen expression in prostatic intraepithelial neoplasia and adenocarcinoma: a study of 184 cases. Cancer 82:2256–2261 12. Minner S, Wittmer C, Graefen M et al (2011) High level PSMA expression is associated with early PSA recurrence in surgically treated prostate cancer. Prostate 71:281–288 13. Mhawech-Fauceglia P, Zhang S, Terracciano L et al (2007) Prostatespecific membrane antigen (PSMA) protein expression in normal and neoplastic tissues and its sensitivity and specificity in prostate adenocarcinoma: an immunohistochemical study using multiple tumour tissue microarray technique. Histopathology 50:472–483 14. Silver DA, Pellicer I, Fair WR et al (1997) Prostate-specific membrane antigen expression in normal and malignant human tissues. Clin Cancer Res 3:81–85 15. Chang SS, Reuter VE, Heston WD et al (1999) Five different antiprostate-specific membrane antigen (PSMA) antibodies confirm PSMA expression in tumor-associated neovasculature. Cancer Res 59:3192–3198 16. Sacha P, Zamecnik J, Barinka C et al (2007) Expression of glutamate carboxypeptidase II in human brain. Neuroscience 144:1361–1372 17. Barrett JA, Coleman RE, Goldsmith SJ et al (2013) First-in-man evaluation of 2 high-affinity PSMA-avid small molecules for imaging prostate cancer. J Nucl Med 54:380–387 18. Afshar-Oromieh A, Malcher A, Eder M et al (2013) PET imaging with a [68Ga]gallium-labelled PSMA ligand for the diagnosis of prostate cancer: biodistribution in humans and first evaluation of tumour lesions. Eur J Nucl Med Mol Imaging 40:486–495 19. Troyer JK, Beckett ML, Wright GL Jr (1995) Detection and characterization of the prostate-specific membrane antigen (PSMA) in tissue extracts and body fluids. Int J Cancer 62:552–558 20. Galsky MD, Eisenberger M, Moore-Cooper S et al (2008) Phase I trial of the prostate-specific membrane antigen-directed immunoconjugate MLN2704 in patients with progressive metastatic castration-resistant prostate cancer. J Clin Oncol 26:2147–2154 21. Milowsky MI, Nanus DM, Kostakoglu L et al (2004) Phase I trial of yttrium-90-labeled anti-prostate-specific membrane antigen monoclonal antibody J591 for androgen-independent prostate cancer. J Clin Oncol 22:2522–2531 22. Osborne JR, Green DA, Spratt DE et al (2014) A prospective pilot study of Zr-J591/prostate specific membrane antigen positron emission tomography in men with localized prostate cancer undergoing radical prostatectomy. J Urol 191(5):1439–1445 23. Elsasser-Beile U, Reischl G, Wiehr S et al (2009) PET imaging of prostate cancer xenografts with a highly specific antibody against the prostate-specific membrane antigen. J Nucl Med 50:606–611 24. Lesche R, Kettschau G, Gromov AV et al (2014) Preclinical evaluation of BAY 1075553, a novel (18)F-labelled inhibitor of prostate-specific membrane antigen for PET imaging of prostate cancer. Eur J Nucl Med Mol Imaging 41:89–101 25. DeGrado TR, Reiman RE, Price DT et al (2002) Pharmacokinetics and radiation dosimetry of 18F-fluorocholine. J Nucl Med 43:92–96 26. Cimitan M, Bortolus R, Morassut S et al (2006) [(18)F] Fluorocholine PET/CT imaging for the detection of recurrent prostate cancer at PSA relapse: experience in 100 consecutive patients. Eur J Nucl Med Mol Imaging 33:1387–1398
27. Schmid DT, John H, Zweifel R et al (2005) Fluorocholine PET/CT in patients with prostate cancer: initial experience. Radiology 235:623–628 28. Li Y, Cozzi PJ, Russell PJ (2010) Promising tumor-associated antigens for future prostate cancer therapy. Med Res Rev 30:67–101 29. Kallioniemi OP, Wagner U, Kononen J, Sauter G (2001) Tissue microarray technology for high-throughput molecular profiling of cancer. Hum Mol Genet 10:657–662 30. Liu H, Rajasekaran AK, Moy P et al (1998) Constitutive and antibodyinduced internalization of prostate-specific membrane antigen. Cancer Res 58:4055–4060 31. Ross JS, Sheehan CE, Fisher HA et al (2003) Correlation of primary tumor prostate-specific membrane antigen expression with disease recurrence in prostate cancer. Clin Cancer Res 9:6357–6362 32. Perner S, Hofer MD, Kim R et al (2007) Prostate-specific membrane antigen expression as a predictor of prostate cancer progression. Hum Pathol 38:696–701 33. Mease RC, Foss CA, Pomper MG (2013) PET imaging in prostate cancer: focus on prostate-specific membrane antigen. Curr Top Med Chem 13:951–962 34. Nedrow-Byers JR, Jabbes M, Jewett C et al (2012) A phosphoramidatebased prostate-specific membrane antigen-targeted SPECT agent. Prostate 72:904–912 35. Schafer M, Bauder-Wust U, Leotta K et al (2012) A dimerized ureabased inhibitor of the prostate-specific membrane antigen for 68Ga-PET imaging of prostate cancer. EJNMMI Res 2:23 36. Banerjee SR, Pullambhatla M, Byun Y et al (2008) 68Ga-labeled inhibitors of prostate-specific membrane antigen (PSMA) for imaging prostate cancer. J Med Chem 53:5333–5341 37. Chen Y, Foss CA, Byun Y et al (2008) Radiohalogenated prostatespecific membrane antigen (PSMA)-based ureas as imaging agents for prostate cancer. J Med Chem 51:7933–7943 38. Maresca KP, Hillier SM, Femia FJ et al (2009) A series of halogenated heterodimeric inhibitors of prostate specific membrane antigen (PSMA) as radiolabeled probes for targeting prostate cancer. J Med Chem 52:347–357 39. Lapi SE, Wahnishe H, Pham D et al (2009) Assessment of an 18Flabeled phosphoramidate peptidomimetic as a new prostate-specific membrane antigen-targeted imaging agent for prostate cancer. J Nucl Med 50:2042–2048 40. Mease RC, Dusich CL, Foss CA et al (2008) N-[N-[(S)-1,3Dicarboxypropyl]carbamoyl]-4-[18F]fluorobenzyl-L -cysteine, [18 F] DCFBC: a new imaging probe for prostate cancer. Clin Cancer Res 14:3036–3043 41. Hillier SM, Kern AM, Maresca KP et al (2011) 123I-MIP-1072, a small-molecule inhibitor of prostate-specific membrane antigen, is effective at monitoring tumor response to taxane therapy. J Nucl Med 52:1087–1093 42. Conti M (2009) State of the art and challenges of time-of-flight PET. Phys Med 25:1–11 43. Moses WW (2007) Recent advances and future advances in time-offlight PET. Nucl Inst Methods Phys Res A 580:919–924 44. Ananias HJ, van den Heuvel MC, Helfrich W, de Jong IJ (2009) Expression of the gastrin-releasing peptide receptor, the prostate stem cell antigen and the prostate-specific membrane antigen in lymph node and bone metastases of prostate cancer. Prostate 69:1101–1108 45. Foss CA, Mease RC, Fan H et al (2005) Radiolabeled small-molecule ligands for prostate-specific membrane antigen: in vivo imaging in experimental models of prostate cancer. Clin Cancer Res 11:4022–4028
RESEARCH ARTICLE
BAY 1075553 PET-CT for Staging and Restaging Prostate Cancer Patients: Comparison with [18F] Fluorocholine PET-CT (Phase I Study) Mohsen Beheshti,1 Thomas Kunit,2,5 Silke Haim,1 Rasoul Zakavi,3 Christian Schiller,1 Andrew Stephens,4 Ludger Dinkelborg,4 Werner Langsteger,1 Wolfgang Loidl2 1
Department of Nuclear Medicine and Endocrinology, PET-CT Center Linz, St. Vincent’s Hospital, Seilerstaette 4, Linz, 4020, Austria Department of Urology, Prostate Center Linz, St. Vincent’s Hospital, Linz, Austria 3 Nuclear Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran 4 Piramal Imaging GmbH, Berlin, Germany 5 Department of Urology, Paracelsus Medical University, Salzburg, Austria 2
Abstract Purpose: (2RS,4S)-2-[18F]Fluoro-4-phosphonomethyl-pentanedioic acid (BAY1075553) shows increased uptake in prostate cancer cells. We compared the diagnostic potential of positron emission tomography (PET)-X-ray computed tomography (CT) imaging using BAY1075553 versus [18F]f luorocholine (FCH) PET-CT. Procedures: Twelve prostate cancer patients (nine staging, three re-staging) were included. The mean prostate-specific antigen in the primary staging and re-staging groups was 21.5±12 and 73.6±33 ng/ml, respectively. Gleason score ranged from 5–9. In nine patients imaged for preoperative staging, the median Gleason score was 8 (range, 7–9). PET acquisition started with dynamic PET images in the pelvic region followed by static whole-body acquisition. The patients were monitored for 5–8 days afterward for adverse events. Results: There were no relevant changes in laboratory values or physical examination. Urinary bladder wall received the largest dose equivalent 0.12 mSv/MBq. The whole-body mean effective dose was 0.015 mSv/MBq. There was a significant correlation between detected prostatic lesions by the two imaging modalities (Kappa=0.356, PG0.001) and no significant difference in sensitivity (P=0.16) and specificity (P=0.41). The sensitivity and specificity of PET imaging using BAY1075553 for lymph node (LN) staging was 42.9 % and 100 %, while it was 81.2 % and 50 % using FCH. The two modalities were closely correlated regarding detection of LNs and bone metastases, although BAY1075553 failed to detect a bone marrow metastasis. Degenerative bone lesions often displayed intense uptake of BAY1075553. Conclusions: BAY1075553 PET-CT produced no adverse effects, was well tolerated, and detected primary and metastatic prostate cancer. FCH PET-CT results were superior, however, with respect to detecting LN and bone marrow metastases. Key words: BAY1075553, FCH, PET-CT, Prostate cancer, PSMA
Correspondence to: Mohsen Beheshti; e-mail: [email protected]
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Introduction
P
rostate cancer is the most commonly diagnosed cancer
and the second leading cause of death in men in the United States [1]. In Europe, 417,000 new cases were diagnosed in 2012 [2]. Although prostate-specific antigen (PSA) is well established as a screening tool and a sensitive marker during assessment of prostate cancer, it suffers from unacceptable specificity and is not able to localize the malignancy or determine its extent. Hence, a biopsy is needed to sample the prostate to obtain multiple needle cores. Biopsy, however, is associated with a substantial number of false-negative results, often leading to re-biopsy. Accurate diagnosis and defining the extent of a prostate cancer is of great importance for determining the appropriate therapeutic approach. Molecular imaging has become an essential tool in cancer research, clinical trials, and routine medical practice. At present, positron emission tomography (PET) in combination with X-ray computed tomography (CT) plays a pivotal role among the molecular imaging modalities, providing noninvasive, quantitative, real-time information. Currently, several PET radiotracers have been introduced to depict the intraglandular malignancy in the prostate as well as extraglandular infiltration [3–8]. PET-CT using C-11- and F-18-labeled choline has demonstrated good diagnostic performance in the assessment of recurrent prostate cancer [4, 9]. In the preoperative setting, however, it cannot differentiate malignant disease from inflammatory processes or benign prostatic hyperplasia [5]. In addition, because of the limited resolution of PET-CT scanners, it has low sensitivity for detecting small (i.e., G5 mm) lymph node metastases [5]. Prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II, is a type II integral membrane protein. It has been well established as a highly specific marker for prostate cancer cells. Elevated expression of PSMA is seen in all prostate cancers, although the highest levels are found in high-grade, hormone-refractory, and metastatic disease [10–14]. PSMA expression has also been identified in the neovasculature of solid tumors [15]. The most common nonmalignant tissues with PSMA expression include prostate epithelium and, to a limited extent, the brush border cells of the duodenum, kidney proximal tubules, breast epithelium, neuroendocrine cells in colonic crypts, and brain [14–16]. Imaging studies with PSMAspecific small molecules in humans have shown accumulation in lacrimal and salivary glands as well [17, 18]. This favorable restricted expression profile suggests that PSMA would be an excellent target for detecting prostate cancer and marking it for treatment. Many approaches using PSMA have been introduced for therapeutic and diagnostic purposes. ProstaScint® (7E11C5.3) was the first monoclonal antibody used to detect
prostate cancer [19]. It was not able to bind to viable cells, however, because it targets an intracellular epitope of PSMA. Recently, several monoclonal antibodies that bind to the external domain of PSMA have been developed [18, 20–24]. Among them, (2RS,4S)-2-[ 1 8 F]fluoro-4phosphonomethyl-pentanedioic acid (BAY1075553) has shown promise in the assessment of PSMA-positive prostate cancer for preclinical investigations [24]. In the present prospective study, we compared the diagnostic potential of PET-CT imaging with BAY1075553 as a novel PET tracer versus [ 18 F]fluorocholine (fluoromethyl-dimethyl-2hydroxyethylammonium [FCH]) PET-CT. It is the first such study conducted in humans.
Materials and Methods Patients This prospective phase I study was approved by both the institutional ethics committee and the routing committee of the province. Written informed consent was obtained from all patients. Twelve patients with a mean age of 66.9±7.8 years (range, 53– 82 years) and mean PSA level of 34.5±29.2 ng/ml (normal range, G2.5 ng/ml) were studied. Nine patients were imaged for preoperative staging. The other three patients were imaged postoperatively because there was biochemical evidence of recurrence. Their Gleason score ranged from 5 to 9. In the nine patients imaged preoperatively, the median Gleason score was 8 (range, 7– 9). Their mean PSA level was 21.5±12.0 ng/ml. Inclusion and exclusion criteria are shown in Table 1. Pelvic lymphadenectomy was performed in all nine patients in the preoperative setting. All 12 patients were monitored clinically from 24 h before BAY1075553 administration to 5–8 days afterward. Monitoring included physical examination, electrocardiography, and laboratory parameters of various organs. Adverse events were documented. The patients’ characteristics are shown in Tables 2 and 3.
Procedures BAY1075553 and FCH were synthesized on site. The radiochemical purity was 995 % as analyzed by thin-layer chromatography. Synthesis, pharmacokinetics, and radiation dosimetry of each tracer has been described in previous studies [24, 25].
Biodistribution and DosimetryBiodistribution and dosimetry for F-18 radiolabeled BAY1075553 were determined based on PETCT image data from two healthy subjects. Image quantification, kinetic modeling to determine residence times, and dosimetry analysis were performed by CDE Dosimetry Services, Inc., TN, USA, ordered by Bayer Healthcare Pharmaceuticals, Berlin, Germany (present correspondence: Piramal Imaging GmbH, Berlin, Germany). Whole-body PET image data for the two healthy subjects were obtained using F-18 radiolabeled BAY1075553 at approximately 0.5, 6, 16, 150, and 330 min after injection. Image data were
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Table 1. Inclusion and exclusion criteria for participating patient in the study Inclusion criteria
Exclusion criteria
1. Written informed consent
1. Any concurrent severe and/or uncontrolled and/or unstable medical disease which could compromise participation in the study 2. Acute renal insufficiency of any intensity 3. Active inflammatory bowel disease within the last 6 months 4. Acute prostatitis requiring medical treatment within the last 6 months 5. A non-urologic bacterial infection requiring active treatment with antibiotics within 3 months
Males ≥18 years of age Life expectancy of at least 3 months Serum PSA value above normal Creatinine, TSH, AST, ALT, ALK-phosphatase, and bilirubin in norm levels within 2 weeks before any imaging with contrast agents (e.g., gadolinium, Visipaque) 6. Patients with
2. 3. 4. 5.
Primary prostate cancer Adenocarcinoma GSc≥3+3 (at least 2 biopsies) Previous MR u/o FCH PET-CT positive; no treatment in between; max. interval 6 weeks All imaging ≥3 weeks after tumor biopsy Prostate cancer recurrence Advanced cancer disease and a high likelihood to LN metastasis, ideally scheduled to undergo explorative pelvic lymphadenectomy Previous MR u/o FCH PET-CT positive; no treatment in between; max. interval 6 weeks Adequate recovery (excluding alopecia) from previous therapy
6. Active other malignancy (except basal cell or squamous cell skin cancer) within the last 2 years 7. Body weight 9350 lbs (approx. 165 kg) 8. Symptomatic rectal stenosis 9. Unmanaged claustrophobia 10. Patients with primary prostate cancer only: androgen ablation within 3 months before planned treatment 11. Known sensitivity to the study drug or components of the preparation 12. Hints for drug abuse/dependence, life time history of alcohol abuse/ dependence 13. Subject is in custody by order of an authority or a court of law 14. Subject is a relative of the investigator, student of the investigator, or otherwise dependent 15. Subject has completed participation in another clinical study involving administration of a therapeutic investigational drug in the preceding 4 weeks; previous assignment to treatment in this study 16. Unwillingness or inability to comply with the protocol 17. Subject fulfils criteria which in the opinion of the investigator preclude participation for scientific reasons, for reasons of compliance, or for reasons of the subject’s safety 18. Hematological or biochemical parameters that are outside the normal range and are considered clinically significant by the investigator, in particular, the presence of hepatitis B virus surface antigen (HBsAg), hepatitis C virus antibodies (anti-HCV), or human immune deficiency virus antibodies (antiHIV); minor deviations in lab parameters that are considered by the evaluating physician to be not clinically significant with respect to safety or interpretation of study results are not considered an exclusion criterion
attenuation-corrected at the imaging site and were quantified based on the Medical Internal Radiation Dosimetry (MIRD) 16 methodology (CDE) to determine kinetic data for all organs that show significant activity uptake. Dosimetry estimates were created via kinetic modeling of the quantified image data to determine residence times and the standard MIRD methodology. A urinary bladder voiding interval of 1.0 h was utilized.
PET-CT ImagingAll patients underwent BAY1075553 PET-CT imaging followed by FCH PET-CT the next day. Imaging was performed on an integrated PET-CT system (Discovery LS; GE
Medical Systems, Milwaukee, WI, USA) that consisted of a fullring PET scanner with a 14.6-cm transverse field of view and an inplane resolution of 4.8 mm full width at half maximum at the center of the field of view. All PET-CT scans were acquired in twodimensional mode (4 min emission per bed position) and were reconstructed with standard reconstruction ordered-subset expectation maximization iterative algorithm (two iterative steps) and were reformatted into transverse, coronal, and sagittal views. All patients fasted for at least 4 h before each examination. Preparation of study subjects consisted of inserting a suitable indwelling intravenous catheter into a large vein (e.g., antecubital vein), preferably in the subject’s nondominant arm. Correct
Table 2. Pre-operative staging: patient’s characteristics and imaging findings in both BAY1075553 and FCH PET modalities ID
Age
PSA (ng/ml)
Gleason score
T stage
N stage
PLND (number)
Positive (pathology)
FCH LNM
BAY1075553 LNM
FCH BM
BAY1075553 BM
1 2 3 4 5 6 7 8 9
65 64 68 71 70 66 70 56 63
6.9 20.8 21.1 15.5 35.0 22.6 5.6 23.0 43.0
7 7 7 8 8 8 7 9 8
pT3b pT2c pT3b pT3b pT2c pT3a pT2c pT3b pT3a
pN0 pN0 pN1 pN0 pN0 pN0 pN0 pN1 pN0
4 3 15 5 12 11 8 9 1
0 0 3 0 0 0 0 2 0
0 0 1 0 0 0 2 2 1
0 0 0 0 0 0 0 1 0
0 0 g 0 0 0 0 0 0
0 0 g 0 0 0 0 0 0
PLND pelvic lymph node dissection, LNM lymph node metastasis, BM bone metastasis, g generalized
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Table 3. Recurrent disease: patient’s characteristics and imaging findings in both BAY1075553 and FCH PET modalities ID
Age
PSA
Primary Gleason Score
Primary T Stage
Primary N Stage
FCH LNM
BAY1075553 LNM
FCH BM
BAY1075553 BM
1 2 3
53 75 82
110,6 47,3 63,0
5 6 8
pT3a pT3a cT2-3
pN0 pN0 cN0
4 4 5
0 4 2
0 2 0
0 2 0
LNM lymph node metastasis, BM bone metastasis
localization of the indwelling cannula must be ensured by test injection of normal saline solution prior to injecting the study drug. A radioactive dose of 300 MBq ±20 % for BAY1075553 and 4.07 MBq/kg body weight for FCH were administered as slow intravenous bolus injections lasting up to 60 s. After injecting the study drug, the cannula and injection system were flushed with 10 ml saline solution. Acquisition started 30 s after the injection. Dynamic PET images were acquired in the pelvic region for 12 min (8×30 s and 8×1 min per frame) to assess the early perfusion pattern of each tracer and overcome the effect of urinary activity in the bladder. Static whole-body acquisition from the thigh to the base of the skull was then performed. Delayed static acquisition was performed for abnormal tracer uptake 90–120 min after injection. For BAY 1075553, the required mass dose to obtain an image (as extrapolated from preclinical studies) was ≤100 μg. For this study, the safety margin at a maximum mass dose of 100 μg BAY 1075553 per patient was 91,000, which was derived from the “no observed effect level” determined in preclinical studies in toxicology and safety pharmacology. A typical radioactive dose of 2-deoxy-2-[18F]fluoro-D-glucose used for an oncological scan is about 350 MBq for an adult human. This study aimed at showing that, following a single intravenous injection of 300 MBq ±20 % (total quantity of BAY 1075553, ≤100 μg), the PET tracer would selectively accumulate in prostate cancer tissue and allow adequate diagnostic performance compared with that seen with [18F] fluorocholine in primary and recurrent disease. The CT portion of the BAY1075553 PET-CT procedure was performed after intravenous infusion of 100 ml ionic contrast medium with high beam current modulation (120–330 mA). In FCH PET-CT study, the CT portion was performed with low beam current modulation (80–120 mA) for localization and attenuation correction. The reformatted, transverse, coronal, and sagittal views were used for interpretation.
Image Interpretation and Data AnalysisTwo experienced nuclear medicine specialists who were aware of the patient’s history jointly interpreted all of the PET scans. They also had access to the CT and PET–CT fusion images for morphological correlation and localization of pathological PET lesions. Images were read using advanced PET-CT review software (Advantage Windows, version 4.4; GE Medical Systems), which allows simultaneous scrolling through the corresponding PET, CT, and fusion images in the transverse, coronal, and sagittal planes. A lesion was considered pathological when the focal tracer accumulation was greater than the background activity. Bone lesions were considered malignant depending on their anatomical localization (e.g., posterior aspect of the vertebral body and pedicle) and/or characteristic morphological changes (e.g., cortical destruction). Discrete FCH uptake only in inguinal lymph nodes was
interpreted as possible reactive FCH uptake [26, 27] and therefore was excluded from data analysis. Semi-quantitative analysis of the abnormal radiotracer uptake was performed using the maximum standardized uptake value (SUVmax) within the volume of interest, which was manually placed over the pathological lesions on the static whole-body images. The final diagnosis of positive PET lesions was based on histopathological findings and/or follow-up imaging studies (i.e., FCH, [18F]NaF PET-CT, and/or magnetic resonance imaging) for at least 6 months (range, 3–12 months). In the follow-up studies, pathological lesions on PET studies were considered malignant if (1) they showed persistent uptake or increased activity with corresponding morphological changes on CT and clinical evidence of disease progression, or (2) after treatment, there was decreased tracer uptake with clinical regression (suggesting a treatment response).
Histopathological CorrelationCorrelating the imaging results with histopathological findings was performed based on sextant biopsy templates. For evaluating local tumor involvement, the prostate gland contour was identified on the PET images based on corresponding CT images. The defined prostate volume on PET images was extracted using a software program provided by the manufacturer (Advantage Windows 4.4, GE Medical Systems). Based on the sextant biopsy template, the extrapolated prostate volume was divided equally into basal, middle, and apical thirds on each side. The segment with the highest tracer intensity was selected for the correlation with the sextant and with maximum tumor involvement histopathologically. PET-CT findings were correlated with histopathology results for patients who underwent lymphadenectomy. Postoperative histopathological evaluation of lymph nodes consisted of a standard protocol of step sections in 250-μm sequences (conventional hematoxylin–eosin staining) and immunohistochemistry of each step. The results of BAY1075553 PET in the prostate gland were compared with histopathological findings in 12 segments (apical, middle, and basal thirds, each divided into four segments of right, left, anterior, and posterior).
Statistical Analysis Univariate analysis was performed to assess the variables and frequency tables. Quantitative variables were defined as the mean± SD and were compared in different groups using the independent t test. The paired ttest was used to compare quantitative variables in a paired group. Sensitivity and specificity were calculated using data collected from PET studies on per-patient and per-lesion bases. Kappa coefficient was calculated for comparison of two techniques.
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Pearson’s correlation coefficient was calculated for correlations between different quantitative variables. SPSS software version 16 (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis. A value of pG0.05 was considered to indicate statistical significance in all comparisons. Statistical analysis was undertaken on both patient-based and lesion-based analyses.
Results Biodistribution, Dosimetry, and Safety In the reported data by CDE Dosimetry Services, Inc., for two healthy subjects, on average, the organ receiving the largest dose was the urinary bladder wall at 0.43 rem/mCi (0.12 mSv/MBq) followed by the kidneys at 0.36 rem/mCi (0.098 mSv/MBq). The whole-body mean effective dose (International Commission on Radiological Protection, ICRP-103) was 0.054 rem/mCi (0.015 mSv/MBq). No adverse clinical reactions, abnormal laboratory findings, or side effects were detected during the 5–8 days after intravenous administration of BAY1075553. None of the patients showed any reaction to the CT contrast agent. Physiological BAY1075553 uptake was observed in salivary glands and, because of its renal excretion, in the urinary tract. Intensive tracer accumulation was noted in the urinary bladder during both dynamic and static acquisitions, which affects assessment of the prostate gland. In general, marked tracer uptake was also seen in degenerative bone lesions. Tracer uptake was also increased in sclerotic vessels. The liver, pancreas, spleen, gastrointestinal tract, and bone marrow showed no noticeable physiological uptake. Dynamic images were performed from pelvis in all patients. The mean SUVmax in dynamic images of FCH PET study was 4.0±1.1 and increased significantly to 7.0± 1.6 in whole-body static images (PG0.001). This pattern was also seen in BAY1075553 PET study. Mean SUVmax was increased from 4.2±1.7 in dynamic to 5.7±2.5 in the static images (P=0.02). Time of bladder activity was significantly shorter in BAY1075553 PET (2.7±0.98 min) compared with FCH PET (5.7±1.4 min, PG0.001).
Lesion-Based Approach Overall, 108 segments in the prostate glands were analyzed. Histopathological analysis showed that, in three patients, all 12 segments of the prostate gland were involved, whereas four to nine segments were involved in the other patients. Histological evaluation showed that 71 segments were infiltrated. BAY1075553 PET was able to identify 41 positive segments correctly, whereas 49 segments were positive on FCH PET. Using histological examination as the gold standard, BAY1075553 PET gave false-positive results in six segments compared with seven false-positive segments found by FCH PET. BAY1075553 PET showed a sensitivity and specificity of 49.3 % (37.3–61.3 %) and 83.8 % (67.3–93.2 %), respectively, in the detection of primary prostate cancer (95 % confidence interval). Sensitivity and specificity for FCH PET were 59.1 % (46.8–70.0 %) and 81 % (64.2–91.4 %), respectively. The sensitivity and specificity of BAY1075553 PET in apical segments were 50 % (30.3–69.6 %) and 90 % (54.1–99.5 %), respectively. The corresponding percentages for FCH PET were 42.5 % (23.9–62.8 %) and 80.0 % (44.2– 96.4 %), respectively. In middle segments they were 40.0 % (21.8–61.1 %) and 63.6 % (31.6–87.1 %) for BAY1075553 PET and 68 % (46.4–84.2 %) and 72.7 % (39.3–92.6 %), respectively, for FCH PET. In basal segments, the sensitivity and specificity were 60 % (36.4–80.0 %) and 93.7 % (67.7– 99.6 %) for BAY1075553 PET and 75.0 % (50.5–90.4 %) and 87.5 % (60.4–97.8 %) for FCH PET. Comparison of BAY1075553 and FCH PET showed that there was a significant correlation between the two methods (kappa=0.356, pG0.001). No significant difference was noted in the sensitivity (p=0.16) or specificity (p=0.41) of the two imaging modalities for detecting primary intraglandular lesions. The same was true for the sensitivities of the two techniques in the apical (p=0.3), middle (p= 0.051), and basal segments (p=0.22). Also, there was no significant difference between the specificities of the two methods (p90.2).
Lymph Node Assessment
Primary Tumor
Patient-Based Approach BAY1075553 PET had 50 % sensitivity for detecting lymph node involvement with 100 % specificity. FCH had 100 % sensitivity and 83.4 % specificity.
Patient-Based Approach Nine patients had local involvement, all of which was detected correctly by both BAY1075553 and FCH PET imaging. Hence, the sensitivity and specificity of BAY1075553 and FCH were both 100 % for local involvement. There was no significant difference in the mean SUVmax values for malignant lesions in the prostate gland examined with BAY1075553 PET (5.6±2.4) or with FCH PET (6.9±1.6) (p=0.9). The PSA levels and mean Gleason scores were not significantly different in patients with positive or negative BAY1075553 or FCH images (p90.1).
Lesion-Based Approach Overall, 68 lymph nodes were resected from nine patients and were examined histopathologically. Altogether, 20 (20/68) malignant lymph nodes were detected by both PET modalities. The sensitivity of FCH was 81.2 %, and its specificity was 50 %. The sensitivity of BAY1075553 was 43.8 % with a specificity of 100 %. The mean SUVmax of the detected lymph nodes was 10.22±3.3 on FCH PET images and 6.84±2.3 on BAY1075553 PET images (p=0.12). The maximum metabolic diameter of the lesions was 19.29±3.9 mm on FCH
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
PET compared with 17.29±2.13 mm on BAY1075553 PET (p=0.29).
Bone Metastases In the patient-based analysis, the sensitivity and specificity of both BAY1075553 and FCH imaging were 100 % for detecting bone metastases, although only two patients had bone metastasis (one during preoperative staging and one with recurrent disease). Because of the generalized bone metastases in the patient being staged preoperatively and positive findings with both imaging modalities, lesion-based analysis was not performed. Nevertheless, FCH PET was able to detected bone marrow metastases that were not depicted by BAY1075553 PET. The mean SUVmax values for bone metastasis were 15.9±1.2 and 14.6±0.7 on FCH PET and BAY1075553 PET, respectively (p=0.5).
Recurrence (Restaging) Both BAY1075553 and FCH PET-CT modalities were applied in three patients with biochemical evidence of recurrent disease (Table 2). None of these patients had local recurrence in the prostate bed. Lymph node metastases were detected in all three patients. FCH PET-CT was able to detect more malignant lymph nodes than did BAY1075553 PET-CT (i.e., 13 vs. 6); however, there was no difference concerning detection of bone metastases between the two imaging modalities in one patient with bone metastases.
Discussion Targeted molecular imaging has been used in recent prostate cancer studies as it is a noninvasive diagnostic modality that allows accurate staging and restaging of the disease. Identifying and targeting membrane-based proteins that specifically overexpress in prostate cancer has been the goal of recent studies [28]. Among them, PSMA has received the most attention because of its expression in the vast majority (990 %) of examined prostate cancers and its higher expression in cancerous prostate cells than in the benign cells [12, 19, 22, 29, 30]. Several studies have demonstrated a correlation between increased PSMA expression and a higher Gleason score. It has also been suggested that PSMA expression levels in the primary tumor can predict disease outcome, but this has not yet been validated as a predictive marker [31, 32]. Thus, PSMA seems to be a potential target molecule for diagnosis and specific prostate cancer therapy. New PSMA-based PET imaging agents are generally divided into three categories: (1) antibodies, (2) aptamers, and (3) low-molecular-weight PSMA inhibitors [33]. Researchers have been working intensively to develop agents in each of the three categories but particularly on low-molecular-weight PSMA inhibitors.
PSMA presides over an enzymatic site in its extracellular domain that contains two zinc ions and is composed of two bundles: the glutamate sensing bundle and the nonpharmacophore bundle [33]. Most small-molecule PSMA inhibitors have zinc-binding components that adhere to a glutamate or glutamate isostere and belong to one of three groups: (1) phosphonates, phosphates, phosphoramidates; (2) thiols; (3) ureas. Most recently published studies working on new imaging agents for prostate cancer that are based on small-molecule PSMA inhibition have focused on the use of either phosphoramidate or glutamate–urea heterodimer scaffolds with various radioisotopes [18, 20–24, 33–38]. BAY1075553 falls into the phosphonate-based heterodimer group. It has shown promise in the preclinical data and was introduced as a novel F-18 labeled radiotracer targeting the PSMA inhibitor for imaging prostate cancer [24]. The quality of PET imaging using BAY1075553 in the lymph node carcinoma cell line derived from a human prostate cancer tumor model compares favorably with preclinical results published previously using an F-18 labeled radiotracer targeting the PSMA inhibitor [39, 40]. BAY1075553 also showed rapid tumor targeting. It is a low-clearance compound with rapid, almost exclusive, renal excretion. It has been shown to be capable of detecting even lowexpressing prostate tumors [24, 41]. In the present prospective phase 1 clinical study, we evaluated the safety, patients’ tolerance, and biodistribution of BAY1075553. We also assessed its potential value for staging and restaging prostate cancer patients. In addition, we compared its performance with that of FCH PET-CT, which is the current established diagnostic modality for preoperative staging of high-risk prostate cancer and for restaging patients with recurrent disease [4, 5]. BAY1075553 proved to be a safe PET tracer with no adverse clinical reactions, abnormal laboratory findings, or side effects for as long as 5–8 days after its intravenous administration. In the nine patients being staged preoperatively, both BAY1075553 PET and FCH PET revealed pathological lesions in the prostate. Neither of the imaging modalities, however, was able to differentiate benign from malignant lesions accurately. BAY1075553 PET gave falsepositive results in six segments and FCH PET in seven segments (Fig. 1). BAY1075553 PET had a sensitivity and specificity of 49.3 % and 83.8 %, respectively, for detecting primary prostate cancer. The sensitivity and specificity of FCH PET were 59.1 % and 81.0 %, respectively. Hence, accurate noninvasive diagnosis of primary prostate cancer using PET imaging remains a dilemma that warrants further research. When assessing lymph node metastasis in preoperative patients, BAY 1075553 PET showed 100 % specificity versus 50 % specificity by FCH PET, but it exhibited only 43.8 % sensitivity compared with 81.2 % for FCH PET. FCH PET-CT was clearly superior for N staging of prostate cancer patients (Figs. 2 and 3). The results of this study
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Fig. 1. Staging preoperative, 67-year-old prostate cancer patient, Gleason score 7, PSA 22.6 ng/ml, prostate volume 42 ml. a Histopathologic results: prostate adenocarcinoma prominently on the right lobe (marked) with only small lesion on the left lobe. b BAY1075553 PET-CT (upper row), FCH PET-CT (lower row). BAY1075553 PET showed focal tracer uptake on the right prostate lobe well correlated with histopathology results (yellow arrow) while FCH PET showed increased tracer uptake on both lobes (false-positive on the left lobe).
confirmed our previous data concerning the value of FCH PET-CT imaging for detecting lymph node metastases in prostate cancer patients [5]. Nevertheless, detection of micrometastases and lymph node metastases G5 mm is still under debate mainly because of the limited resolution of the current generation of PET scanners, which is about 4.8 mm. This limitation may be partly overcome in the near future with the new high-definition PET scanners with the time-offlight concept [42, 43]. These scanners will have an intrinsic resolution of about 2 mm with improvements in the signalto-noise ratio. Dynamic acquisition of BAY1075553 PET did not provide additional information to static images due to early tracer accumulation in the urinary bladder which affects the interpretation of the pelvic lesions. In the patient-based analysis, both imaging modalities were able to detect bone metastases, although only two patients had bone involvement (Fig. 3). Substantially increased BAY1075553 uptake was seen in degenerative bone lesions, which reduced its specificity and may interfere with its diagnostic applications for evaluating bone
metastases (Fig. 4). Lesche et al. also found this pattern in a preclinical study. They reported intense BAY1075553 uptake (∼2.5 % ID/g 60 min after injection) in regions of active bone growth in the skull and long bones that did not increase over time. They concluded that bone uptake was not due to increasing fluoride incorporation upon compound disintegration in vivo, but rather to specific compound binding to bone structures. As expression of PSMA in bone structures is not detectable [14, 44], binding of BAY1075553 may be independent of PSMA expression and might be explained by its phosphonate structure [24]. This pattern of tracer uptake in benign bone lesions, however, was not seen in similar studies performed with other 68Ga-PSMA targeting agents using glutamate–urea heterodimer scaffolds [18]. This finding emphasizes again the relation between the phosphonate component of BAY1075553 and benign bone uptake. The variable performance of BAY1075553 in different areas of the body affected by the same disease is probably related to PSMA expression. PSMA is particularly elevated in aggressive, androgen-insensitive disease and may serve as
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Fig. 2. Biochemical recurrence, 78-year-old prostate cancer patient, Gleason score 8, PSA 8.9 ng/ml, TUR-P, and radiotherapy, increasing PSA under anti-androgen treatment. a BAY1075553 PET MIP. b FCH PET MIP. c Transaxial images of BAY1075553 PET-CT (upper row) and FCH PET-CT (lower row). FCH PET showed marked increased tracer uptake in the abdomen suggestive of pelvine and retroperitoneal lymph node metastases (yellow arrow–lower row) significantly superior to BAY1075553 PET (yellow arrow–upper row).
a better marker for such tumors. For example, PSMAtargeted imaging tracers have been shown in preclinical models to reflect the activity of androgen signaling and the response to taxane therapy [41]. Additional clinical studies are needed to determine the biological behavior of tracers of this class and their clinical applications. Despite the higher specificity of BAY1075553 PET for differentiating malignant from benign intraglandular prostatic disease, it suffers from low sensitivity for detecting malignant primary and lymph node lesions. This is in contrast to preclinical data [24] and other imaging agents
used to assess small-molecule PSMA inhibition focusing on the use of either glutamate-containing phosphoramidate or glutamate–urea scaffolds [45]. Despite the unsatisfactory findings of the current study using PSMA inhibitors based on 2-(phosphonylmethy)pentanedioic acid scaffolds, glutamate–urea–lysine heterodimers may still be the first choice, given their sub-nanomolar binding affinity and impressive in vivo imaging [36–38]. One of the limitations of this study was that BAY1075553 PET-CT was performed with intravenous CT contrast, whereas FCH PET-CT was performed without CT
Fig. 3. Biochemical recurrence, 54-year-old prostate cancer patient, Gleason score 5, PSA 13.9 ng/ml, radical prostatectomy 2003 (T3a N0 M0 R0), local recurrence (2009), biopsy Gleason score 8, elevated PSA under anti-androgen treatment 2,513 ng/ ml. a BAY1075553 PET MIP (left), FCH PET MIP (right): generalized bone and lymph node metastases clearly detectable on both modalities. b Transaxial images BAY1075553 PET-CT (upper row), FCH PET-CT (lower row). FCH PET showed marked increased tracer uptake on retroperitoneum suggestive of lymph node metastases (yellow arrow–lower row) while BAY1075553 PET showed only mild diffuse tracer uptake (yellow arrow –upper row). c Transaxial images BAY1075553 PET-CT (upper row), FCH PET-CT (lower row). FCH PET showed focal tracer uptake on the proximal part of left femur suggestive of bone marrow metastasis (yellow arrow–lower row); however, BAY1075553 PET was negative (yellow arrow–upper row).
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
Fig. 4. Transaxial images of a BAY1075553 PET-CT and b FCH PET-CT. BAY1075553 PET showed focal increased tracer uptake (ayellow arrow) on an osteophyte on T5 (ared arrow). Hence, BAY1075553 PET showed limited specificity due to nonspecific intense uptake on benign and/or degenerative bone lesions.
contrast enhancement. Contrast-enhanced (CE) CT may affect the PET study in two ways. First, it may affect urinary excretion of the investigational PET tracer. Second, it may cause an increase in the SUV in regions of high contrast concentration when CE-CT is used for attenuation correction. In addition, because of the limited spatial resolution of current PET technology, small-tumor involvement or micrometastases (e.g., tumor diameter G5 mm) might not be depicted. Finally, although the inclusion of 12 patients in the first human study on this subject seems acceptable, it may not fully demonstrate the value of each PET tracer because of the small number of patients.
Conclusion BAY1075553 caused no adverse effects and was well tolerated by all patients. BAY1075553 PET-CT was able to detect prostate cancer in patients with both localized and advanced disease. However, both BAY1075553 PET and FCH PET showed limitations to a similar degree in differentiating malignant from benign prostatic lesions. FCH PET produced results superior to those seen with BAY1075553 PET, particularly with respect to detecting lymph node and bone marrow metastases. BAY1075553 also seems to have limited specificity for detecting bone metastases mainly because of the nonspecific increased uptake in degenerative bone lesions.
Acknowledgments. Piramal Imaging GmbH GmbH, Berlin, Germany, gave financial supported to this study. Conflict of Interest. A. Stephens and L. Dinkelborg are employees of Piramal Imaging GmbH, Berlin, Germany. Other authors have no conflict of interest.
References 1. Jemal A, Siegel R, Ward E et al (2009) Cancer statistics, 2009. CA Cancer J Clin 59:225–249 2. Ferlay J, Steliarova-Foucher E, Lortet-Tieulent J et al (2012) Cancer incidence and mortality patterns in Europe: estimates for 40 countries. Eur J Cancer 49:1374–1403 3. Jadvar H (2009) Molecular imaging of prostate cancer with 18Ffluorodeoxyglucose PET. Nat Rev Urol 6:317–323 4. Beheshti M, Haim S, Zakavi R et al (2013) Impact of 18F -choline PET/ CT in prostate cancer patients with biochemical recurrence: influence of androgen deprivation therapy and correlation with PSA kinetics. J Nucl Med 54:833–840 5. Beheshti M, Imamovic L, Broinger G et al (2010) 18F choline PET/CT in the preoperative staging of prostate cancer in patients with intermediate or high risk of extracapsular disease: a prospective study of 130 patients. Radiology 254:925–933 6. Dehdashti F, Picus J, Michalski JM et al (2005) Positron tomographic assessment of androgen receptors in prostatic carcinoma. Eur J Nucl Med Mol Imaging 32:344–350 7. Kato T, Tsukamoto E, Kuge Y et al (2002) Accumulation of [11C]acetate in normal prostate and benign prostatic hyperplasia: comparison with prostate cancer. Eur J Nucl Med Mol Imaging 29:1492–1495 8. Schuster DM, Savir-Baruch B, Nieh PT et al (2011) Detection of recurrent prostate carcinoma with anti-1-amino-3-18Ffluorocyclobutane-1-carboxylic acid PET/CT and 111In-capromab pendetide SPECT/CT. Radiology 259:852–861 9. Beheshti M, Langsteger W, Fogelman I (2009) Prostate cancer: role of SPECT and PET in imaging bone metastases. Semin Nucl Med 39:396–407
M. Beheshti et al.: BAY 1075553 PET-CT as PSMA targeting imaging in prostate cancer
10. Wright GL Jr, Haley C, Beckett ML, Schellhammer PF (1995) Expression of prostate-specific membrane antigen in normal, benign, and malignant prostate tissues. Urol Oncol 1:18–28 11. Bostwick DG, Pacelli A, Blute M et al (1998) Prostate specific membrane antigen expression in prostatic intraepithelial neoplasia and adenocarcinoma: a study of 184 cases. Cancer 82:2256–2261 12. Minner S, Wittmer C, Graefen M et al (2011) High level PSMA expression is associated with early PSA recurrence in surgically treated prostate cancer. Prostate 71:281–288 13. Mhawech-Fauceglia P, Zhang S, Terracciano L et al (2007) Prostatespecific membrane antigen (PSMA) protein expression in normal and neoplastic tissues and its sensitivity and specificity in prostate adenocarcinoma: an immunohistochemical study using multiple tumour tissue microarray technique. Histopathology 50:472–483 14. Silver DA, Pellicer I, Fair WR et al (1997) Prostate-specific membrane antigen expression in normal and malignant human tissues. Clin Cancer Res 3:81–85 15. Chang SS, Reuter VE, Heston WD et al (1999) Five different antiprostate-specific membrane antigen (PSMA) antibodies confirm PSMA expression in tumor-associated neovasculature. Cancer Res 59:3192–3198 16. Sacha P, Zamecnik J, Barinka C et al (2007) Expression of glutamate carboxypeptidase II in human brain. Neuroscience 144:1361–1372 17. Barrett JA, Coleman RE, Goldsmith SJ et al (2013) First-in-man evaluation of 2 high-affinity PSMA-avid small molecules for imaging prostate cancer. J Nucl Med 54:380–387 18. Afshar-Oromieh A, Malcher A, Eder M et al (2013) PET imaging with a [68Ga]gallium-labelled PSMA ligand for the diagnosis of prostate cancer: biodistribution in humans and first evaluation of tumour lesions. Eur J Nucl Med Mol Imaging 40:486–495 19. Troyer JK, Beckett ML, Wright GL Jr (1995) Detection and characterization of the prostate-specific membrane antigen (PSMA) in tissue extracts and body fluids. Int J Cancer 62:552–558 20. Galsky MD, Eisenberger M, Moore-Cooper S et al (2008) Phase I trial of the prostate-specific membrane antigen-directed immunoconjugate MLN2704 in patients with progressive metastatic castration-resistant prostate cancer. J Clin Oncol 26:2147–2154 21. Milowsky MI, Nanus DM, Kostakoglu L et al (2004) Phase I trial of yttrium-90-labeled anti-prostate-specific membrane antigen monoclonal antibody J591 for androgen-independent prostate cancer. J Clin Oncol 22:2522–2531 22. Osborne JR, Green DA, Spratt DE et al (2014) A prospective pilot study of Zr-J591/prostate specific membrane antigen positron emission tomography in men with localized prostate cancer undergoing radical prostatectomy. J Urol 191(5):1439–1445 23. Elsasser-Beile U, Reischl G, Wiehr S et al (2009) PET imaging of prostate cancer xenografts with a highly specific antibody against the prostate-specific membrane antigen. J Nucl Med 50:606–611 24. Lesche R, Kettschau G, Gromov AV et al (2014) Preclinical evaluation of BAY 1075553, a novel (18)F-labelled inhibitor of prostate-specific membrane antigen for PET imaging of prostate cancer. Eur J Nucl Med Mol Imaging 41:89–101 25. DeGrado TR, Reiman RE, Price DT et al (2002) Pharmacokinetics and radiation dosimetry of 18F-fluorocholine. J Nucl Med 43:92–96 26. Cimitan M, Bortolus R, Morassut S et al (2006) [(18)F] Fluorocholine PET/CT imaging for the detection of recurrent prostate cancer at PSA relapse: experience in 100 consecutive patients. Eur J Nucl Med Mol Imaging 33:1387–1398
27. Schmid DT, John H, Zweifel R et al (2005) Fluorocholine PET/CT in patients with prostate cancer: initial experience. Radiology 235:623–628 28. Li Y, Cozzi PJ, Russell PJ (2010) Promising tumor-associated antigens for future prostate cancer therapy. Med Res Rev 30:67–101 29. Kallioniemi OP, Wagner U, Kononen J, Sauter G (2001) Tissue microarray technology for high-throughput molecular profiling of cancer. Hum Mol Genet 10:657–662 30. Liu H, Rajasekaran AK, Moy P et al (1998) Constitutive and antibodyinduced internalization of prostate-specific membrane antigen. Cancer Res 58:4055–4060 31. Ross JS, Sheehan CE, Fisher HA et al (2003) Correlation of primary tumor prostate-specific membrane antigen expression with disease recurrence in prostate cancer. Clin Cancer Res 9:6357–6362 32. Perner S, Hofer MD, Kim R et al (2007) Prostate-specific membrane antigen expression as a predictor of prostate cancer progression. Hum Pathol 38:696–701 33. Mease RC, Foss CA, Pomper MG (2013) PET imaging in prostate cancer: focus on prostate-specific membrane antigen. Curr Top Med Chem 13:951–962 34. Nedrow-Byers JR, Jabbes M, Jewett C et al (2012) A phosphoramidatebased prostate-specific membrane antigen-targeted SPECT agent. Prostate 72:904–912 35. Schafer M, Bauder-Wust U, Leotta K et al (2012) A dimerized ureabased inhibitor of the prostate-specific membrane antigen for 68Ga-PET imaging of prostate cancer. EJNMMI Res 2:23 36. Banerjee SR, Pullambhatla M, Byun Y et al (2008) 68Ga-labeled inhibitors of prostate-specific membrane antigen (PSMA) for imaging prostate cancer. J Med Chem 53:5333–5341 37. Chen Y, Foss CA, Byun Y et al (2008) Radiohalogenated prostatespecific membrane antigen (PSMA)-based ureas as imaging agents for prostate cancer. J Med Chem 51:7933–7943 38. Maresca KP, Hillier SM, Femia FJ et al (2009) A series of halogenated heterodimeric inhibitors of prostate specific membrane antigen (PSMA) as radiolabeled probes for targeting prostate cancer. J Med Chem 52:347–357 39. Lapi SE, Wahnishe H, Pham D et al (2009) Assessment of an 18Flabeled phosphoramidate peptidomimetic as a new prostate-specific membrane antigen-targeted imaging agent for prostate cancer. J Nucl Med 50:2042–2048 40. Mease RC, Dusich CL, Foss CA et al (2008) N-[N-[(S)-1,3Dicarboxypropyl]carbamoyl]-4-[18F]fluorobenzyl-L -cysteine, [18 F] DCFBC: a new imaging probe for prostate cancer. Clin Cancer Res 14:3036–3043 41. Hillier SM, Kern AM, Maresca KP et al (2011) 123I-MIP-1072, a small-molecule inhibitor of prostate-specific membrane antigen, is effective at monitoring tumor response to taxane therapy. J Nucl Med 52:1087–1093 42. Conti M (2009) State of the art and challenges of time-of-flight PET. Phys Med 25:1–11 43. Moses WW (2007) Recent advances and future advances in time-offlight PET. Nucl Inst Methods Phys Res A 580:919–924 44. Ananias HJ, van den Heuvel MC, Helfrich W, de Jong IJ (2009) Expression of the gastrin-releasing peptide receptor, the prostate stem cell antigen and the prostate-specific membrane antigen in lymph node and bone metastases of prostate cancer. Prostate 69:1101–1108 45. Foss CA, Mease RC, Fan H et al (2005) Radiolabeled small-molecule ligands for prostate-specific membrane antigen: in vivo imaging in experimental models of prostate cancer. Clin Cancer Res 11:4022–4028
