Annals of Oncology 1:421-426, 1990. © 1990 Kluwtr Academic Publishers. Printed in the Netherlands.

Original article CGS 16949A, a new aromatase inhibitor in the treatment of breast cancer A Phase I study K.R. Beretta,1 K. Hoeffken,2 S. Kvinnsland,3 P. Trunet,4 H.A. Chaudri,4 A.S. Bhatnagar,4 A. Goldhirsch1 & F. Cavalli1 1

Servizio Oncologico Ticinese, Ospedale San Giovanni, Bellimona, Switzerland;2 University Clinic, West Germany Tumor Center, Essen, West Germany; 3 Regionsykehuset, Trondheim, Norway;4 C1BA-GEIGY Limited, Basel, Switzerland

Summary. Forty-six postmenopausal women with either locally advanced or metastatic breast cancer were treated with the aromatase inhibitor CGS 16949A in three different daily doses (0.3 mg, 0.6 mg and 0.9 mg total daily dose). 41 patients (89%) were pretreated by endocrine treatment for metastatic disease; 30 of these 41 were also pretreated with chemotherapy. Of the remaining 5 patients (11%) 3 were previously treated with chemotherapy alone and 2 were not pretreated. Evaluable sites of disease were: skin and soft tissue (including local recurrence) in 34, bone in 31, lung in 14 and viscera in 13 instances, respectively. 1 PR (3%) and 9 stable diseases (24%) were observed in the 37 patients assessable for response. All but two of these results were observed in the 0.9 mg group. Time to progression was 14 months for the patient showing a PR, and the median time to progression for those with stable disease was 6 months (range 6 to 23 months). Plasma estradiol and estrone levels were measured in patients receiving the daily dose of 0.6 mg (n = 4) and 0.9 mg (n = 15). The estrone levels decreased from a mean of 23.1 pg/mL (SD 17.1) to 10.5 pg/mL (SD 6.6) in the 0.6 mggroup and from 21.2 pg/mL (SD 18.9) to 9.1 pg/mL (SD 5.5) in the 0.9 mg-group within 4 days of drug administration (p < 0.0001 from baseline in both groups, with no significant difference between doses). Plasma estradiol levels decreased from 12 pg/mL (SD 12.6) to 6.0 pg/mL (SD 3.6) in the 0.6 mg-group and from 9.5 pg/mL (SD 6.5) to 6.1 pg/mL (SD 2.6) in the 0.9 mg-group (p < 0.01). The suppression of estradiol and estrone was maintained during the subsequent measurements on days 8 and 29 in the 0.9 mg group (n = 14). There was no significant change over time in cortisol levels, nor was there any significant difference between the three doses at any given time. Toxicity was mostly mild and consisted mainly of loss of appetite (7/46 = 15%), fatigue (5/46 = 11%) and nausea (4/46 = 9%) at all three dose levels. We conclude that the aromatase inhibitor CGS 16949A is well tolerated within the ranges tested and does not affect the cortisol level. Although, as observed by others, suppression of plasma estrone might be enhanced by higher doses of CGS 16949A, some antitumor effect can already be seen with 0.9 mg daily. Key words: CGS 16949A, aromatase inhibitor, advanced breast cancer, Phase I trial

Introduction CGS 16949A, a tetrahydroimidazo-pyridine derivative, is a very potent non-steroidal inhibitor of aromatase activity in vitro, effectively blocking the conversion of androgenic precursors to estrogen in an aromatase enzyme preparation derived from human placental microsomes [1]. It was found to be 400 times more potent than aminoglutethimide [1]. In vitro progesterone, corticosterone and aldosterone production are inhibited at concentrations 5000, 3000 and 35 times higher, respectively, than those for estrogen [2, 3]. The drug has been found to be 300-800 times more potent than aminoglutethimide in reducing the growth of hormone-dependent DMBA-induced rat mammary tumors [4]. Inhibition of the aromatase enzyme may be achieved by two approaches: steroids used as substrates for the enzyme activity interfere with androgen aromatization by binding to the aromatase at the active site to inactivate the enzyme (type I aromatase inhibitors) [5, 6], and non-steroidal com-

pounds interfere with the steroid hydroxylation by binding to cytochrome P450, the coenzyme responsible for delivering the OH-groups (type II aromatase inhibitors) [6, 7, 8]. The best-known type I aromatase inhibitor is the 4OH-derivative of androstenedione, 4-OHA (4-hydroxyandrostenedione), the efficacy of which has already been shown in phase II trials [9]. As the cytochrome P 450 is common for several enzymes of the steroid synthesis, like hydroxylases, desmolases and aromatase, the type II aromatase inhibitors are less selective than type I inhibitors [6, 7, 8]. Aminoglutethimide and CGS 16949A are such blockers of cytochrome P450. Aminoglutethimide was initially used for the treatment of advanced breast cancer at doses of 500-1000 mg daily [7, 8, 10], dosages derived from its use for adrenal blockade in Cushing's syndrome. Its administration led to a decrease in plasma cortisol limited to a duration of only 3-7 days due to a so-called "adrenal escape phenomenon", i.e. a ten fold increase in ACTH due to low cortisol serum

422 levels and subsequent abolishment of the drug-induced adrenal blockade [11,12]. With co-administration of hydrocortisone with aminoglutethimide this phenomenon was avoided [13, 14]. It is known that 30-40% of unselected postmenopausal women presenting with metastatic breast cancer respond to hormonal treatments [15, 16]. Aminoglutethimide is used as a secondary endocrine therapy, usually after tamoxifen, and has a similar efficacy. Its choice as secondary treatment is related to the adverse effects at conventional doses [10]. Improved tolerance was attempted through reduction of the aminoglutethimide daily dose [17], and introduction of new, more selective drugs. It has been shown that breast cancer cells accumulate an intracellular concentration of estrogens 10-100-fold higher than plasma [18]. Even ERnegative tumors retain estradiol to reach a 10-fold conTable 1. Patient eligibility, characteristics and pretreatment. No. of patients entered: No. of eligible patients: No. of ineligible patients:

47 46 1 (premenopausal)

Median age Median interval since menopause: Median disease-free time after mastectomy:

64 years (range 35-81 years) 14 years (range 1-37 years)

ER-Stams ER-positive ER-negative ER unknown Sites of disease before treatment. skin soft tissue local recurrence bone lung viscera Number of sites: 1 site 2 sites 3 sites > 3 sites Adjuvant pretreatmenr. adjuvant endocrine therapy adjuvant chemotherapy Pretreatment for metastatic disease: Endocrine pretreatment alone Endocrine and chemotherapeutic pretreatment Chemotherapy alone No pretreatment No of endocrine pretreatments for metastatic disease: 1 endocrine pretreatment 2 endocrine pretreaiments 3 endocrine pretreatments 4 endocrine pretreatments Response to hormonal pretreatment. No. of patients pretreated with hormones CR PR NC PD not assessable

2.5 years (range 0-15 years) 17 10 19 15 8 11 31 14 13 15 18 7

6 11 15

It 30 3 2 41 15 16 9 1

41 4 9 20 4 4

centration over that in plasma [18]. Mechanisms by which aromatase inhibitors may influence the intracellular estradiol availability in hormone-dependent tumor cells are: 1) blockage of the peripheral aromatase, and, hence, lowering of plasma estrone, estradiol and estrone-sulfate (substrates for tumor cell uptake) [6]; 2) inhibition of tumor cell aromatase [6, 19]; 3) increased estrogen catabolism by enzyme induction in liver microsomes [20]. Although it is unclear if the decrease in serum estrone and estradiol is related to clinical response, their levels are used to measure the effects of aromatase inhibitors. The aim of this trial was to show evidence of aromatase inhibition by CGS 16949A in reducing plasma estrone (El) and estradiol (E2) levels without suppressing cortisol production. Unfortunately, unlike in the trials of others [21, 22], the measurement of plasma aldosterone, androgens and urinary steroids was not planned. Furthermore, tolerance of the drug and antitumor activity of the compound were assessed.

Patients and methods From October 1986 to April 1988 47 patients entered the trial. All but one of the patients were postmenopausal women with metastatic breast carcinoma who were considered suitable for endocrine therapy, but who were no longer responding to standard agents. Other inclusion criteria consisted of the presence of metastatic, progressive breast cancer (measurable or not); life expectancy of at least 3 months. Exclusion criteria were second malignant disease, severe renal or hepatic dysfunction, severe heart disease or severe endocrine disorders. Verbal informed consent was obtained from all patients and they were free to withdraw from the trial at any time. Patients who tolerated the drug and had no signs of tumor growth could continue the treatment until progression. Details of eligibility, patient characteristics and pretreatment are given in Table 1. Patients were included irrespective of their ER status. All but one of the eligible patients received one dose level. No patient received either endocrine or chemotherapy within the 2 weeks prior to the start of trial treatment The pretreatment tests of the patients included steroid hormone measurements (estrone, estradiol, cortisol). These were repeated on days 3, 8 and 29. Nine of the 46 eligible patients were not assessable for response because they had no measurable or evaluable tumor parameters (phase I trial) or because the drug was administered for too short a period to allow any evaluation of response. These nine patients were accrued at the beginning of the study and were withdrawn early (after one month) due to impaired performance status. For the others assessment of response was performed at months 1, 2, 4 and 6 and thereafter every 3 months. Response to treatment was measured according to the standard criteria of the UICC with the exception of stable disease which was defined as lasting for at least 6 months. Stable disease of lesser duration was considered as progression. Toxic effects were graded according to the WHO criteria when possible.

423 Table 2. Specification of the El and E2 measurements (A.S. Bhatnagar). Estradiol (E2)

Estrone(El)

Limit of detection:

l-2pg/mL

Z5-5pg/mL

Intra-assay CV*

ll%(5pg/mL) 5.6%(4Opg/mL) 15%(75pg/mL) 12%(40pg/mL)

9%(20pg/mL) 14% (45 pg/mL) 22% (20 pg/mL) 12%(45pg/mL)

Inter-assay CV*

Table 3. Possible adverse effects in 46 patients. No qfpts with clinical adverse effects alone biological adverse effects alone both total

WHO toxicity grade 1 grade 2

• CV = coefficient of variation.

The dosage of CGS 16949A from 0.3 to 0.9 mg total daily, as used in this trial, was selected on the basis of unpublished experimental data. These studies have shown a decrease in El and E2 of 40%-60% which seemed dosedependent within the range of 0.3 to 3.0 mg given as a single dose orally to healthy male volunteers. 13 patients received 0.3 mg CGS 16949A total daily dose (seven 0.3 mg od and six 0.1 mg tid). 14 patients received 0.6 mg daily (eleven 0.3 mg bid and two 0.2 mg tid). 18 patients received 0.9 mg daily (0.3 mg tid). One patient received both 0.6 mg (0.3 mg bid) and in a later phase 0.9 mg daily (0.3 mg tid). Plasma estradiol (E2) and estrone (El) were measured by specific radioimmunoassay (RIA) after extraction from plasma using diethyl ether. The ether extracts were reconstituted in the corresponding assay buffer and aliquots used in the RIAs. Plasma estradiol was measured using a commercial kit (No. ER-150) obtained from Baxter, Merz + Dade, Diidingen, Switzerland, which contains a specific estradiol antibody having negligible crossreaction with estrone and 125-I-estradiol as the tracer. Plasma estrone was measured using a commercial kit (No. RK-E11) obtained from Biihlmann Laboratories, SchSnenbuch, Switzerland, which contains specific estrone antibodies having negligible cross-reaction with estradiol and with 3H-estrone as the tracer. The intra- and inter-assay specifications of the tests used are summarized in Table 2. Plasma cortisol was measured in the three participating centers according to the local established methods. Statistical methods: Hormonal measurements were transformed to logarithms before analysis of variance was carried out (procedure GLM in SAS, Statistical Analysis System, Cary, North Carolina, Version 5.16). Means and standard deviation (SD) reported are in the original units, based on the untransformed values. Time to progression was calculated (in days) using the Kaplan-Meier productlimit method (procedure LIFETEST in SAS). Results Thirty-seven patients were evaluable for response. One (3%) had a partial remission of a locoregional recurrence that appeared after a disease-free interval of 33 months. She had an ER+/PgR- primary tumor and had been treated with adjuvant tamoxifen until 2 months before starting CGS 16949A. This remission lasted 14 months. Nine patients (24%) had stable disease of at least 6 months' duration. Median time to progression was 6 months with a range of 6

18 7 1 26 (57%)

incresein bilirubin increase in liver enzymes nausea/vomiting increase in creatinine cutaneous (urticaria) cardiac rhythm (palpitations) other possible adverse effects loss of appetite esophageal discomfort orthostan'c syndrome circulatory disturbances edema of leg sleep disturbance fatigue nycturia menstrual spotting increase in lipids increase in uric acid increase in urea hyperkalemia thrombocytosis

1 1"

mild

moderate

2 1 1 2 2 1**

* relationship in 1 case considered as probable. ** rechallenge was negative. • • • in patient with hypoaldosterordsm.

to 23 months. 27 patients (73%) showed progression within 6 months (median 4 months, range 1 to 6 months). A total of 26/46 patients (57%) reported some side effects: 18/46 (39%) had clinically overt adverse reactions, and 7 (15%) showed some biological alteration, and 1 (2%) had both. The most frequent side effects were nausea, loss of appetite and fatigue. Table 3 summarizes the reported side effects. The increase in transaminases in 3 cases could not be attributed to CGS 16949A since the patients had at least one pathological test in pretreatment examinations. One patient discontinued the study after 3 weeks of treatment because of nausea and vomiting, which did not completely disappear after discontinuation of CGS 16949A. In one patient hypoaldosteronism with hyperkalemia, chronic metabolic acidosis and secondary osteomalacia was diagnosed. The syndrome persisted after cessation of CGS 16949A and disappeared with substitution of a mineralocorticoid. In this case an accumulation of CGS 16949A due to chronic renal failure (creatinine 150-200 umol/L) was excluded. Plasma estradiol and estrone levels were measured in patients receiving a daily dose of 0.6 mg (n = 4) and 0.9 mg (n = 15). The measurements were performed by ASB. The estrone levels decreased from a mean of 23.1 pg/mL (SD 17.1) to 10.5 pg/mL (SD 6.6) in the 0.6 mg-group (Fig.

424

I

I

I

I 29

29

Fig. 1. Plasma estrone values (mean ± SD) in 4 patients treated with CGS 16949A 0.6 mg daily (A) and in 15 patients (day 8 and 29: 14 patients) treated with 0.9 mg daily (B). ** p < 0.0001 (vs. basal values).

Fig. 2. Plasma estradiol values (mean ± SD) in 4 patients treated with CGS 16949A 0.6 mg daily (A) and in 15 patients (day 9 and 29: 14 patients) treated with 0.9 mg daily (B). *• p < 0.01 (vs. basal values).

Table 4. Suppression of El and E2 by different aromatase inhibitors. Reference

Drug

Beretta CGS 16949A Santen [21] COS 16949A Stuart-Harris [10] aminoglutethimide + hydrocortisone Bruning[17] low-dose Dowsett[23] aminoglutethimide Dowsett [9] 4-hydroxyandrostenedione

Dose used

0.9 mg/d >2mg/d 1000 mg/d 2x20 mg/d 125 mg bid 125 mg bid 250 or 500 mg q2 w

No.paL

Suppression to % of baseline Estrone

Estradiol

14 12

41%-50% 30%-40%

64%-73% 65%

12 22 40

33% (21-56%) 40% 64.6% ±5.3% 40.3% ± 7.0%

50% (28-68%) 58% 57.6% ±5.8% 26%-^42%

1A) and from 21.2 pg/mL (SD 18.9) to 9.1 pg/mL (SD 5.5) in the 0.9 mg-group (Fig. IB) within 4 days of drug administration (p < 0.0001 for values of day 3 vs. basal values in both groups with no significant difference between the 0.6 and 0.9 mg dose levels). Plasma estradiol levels decreased from 12.0 pg/mL (SD 12.6) to 6.0 pg/mL (SD 3.6) in the 0.6 mg-group (Fig. 2A) and from 9.5 pg/mL (SD 6.5) to 6.1 pg/mL (SD 2.6) in the 0.9 mg-group (p < 0.01) (Fig. 2B). The measurements of estrone and estradiol on day 29 in the 0.6 mg group are not shown in the Figs. 1A

Remarks

day 3, 8 and 29 synopsis of 10 reports

day 7

and 2A because of a small number of samples. The two estrone values in the 0.6 mg group on day 29 were 11.2 and 16.2 pg/mL, the two estradiol values 5.1 and 29.0 pg/mL. The suppression of estrone and estradiol was maintained on day 8 and 29 for the 0.9 mg group (n = 14). Cortisol levels were measured in 10/13 patients in the 0.3 mg group, 11/14 patients in the 0.6 mg group and in 15/19 patients in the 0.9 mg group (Fig. 3). There was no significant change over time in cortisol levels nor was there any significant difference between doses at any given time.

425 1200

A

1000

0.3 mg daily

800 600 c

( •—-1 400 200

0 days

3

29

29

Fig. 3. Plasma cortisol values (mean ± SD) in 10 patients treated with CGS 16949A at 0.3 mg daily (A), 11 al 0.6 mg daily (B) and 15 at 0.9 mg daily (C).

Discussion In this Phase I study, 46 in part heavily pretreated postmenopausal women with either locally advanced or metastatic breast cancer were treated with CGS 16949A. Our results show a decrease in the plasma estrone level to 40%-50% and in plasma estradiol level to 65%-75% of the basal value. There was no difference in the decrease in estrone or estradiol from baseline to day 3 between the 0.6

mg and the 0.9 mg group. Santcn et al. recently published their Phase I trial with a dose escalation of CGS 16949A, beginning with 0.6 mg daily and increasing the dose every 2 weeks to 16 mg daily [21, 22]. Maximal decreases in estrone of 30%-40% and in estradiol of 65% of baseline were observed, reached with a dose of 2.0 mg daily (for estrone) and with 0.6 mg daily (for estradiol). One might conclude that with the dose of 2.0 mg daily the lowest plasma estrogen level can be reached without risk of inhibiting cortisol or aldosterone levels. The tolerance of CGS 16949A was good; the subjective toxic effects were mild to moderate and consisted mainly of loss of appetite, fatigue and nausea. No drowsiness was reported. One generalized urticaria was seen under combined treatment with CGS 16949A and allopurinol. A rechallenge with CGS 16949A alone did not lead to any symptoms. One partial response with a duration of 14 months was seen with CGS 16949A 0.9 mg daily, and 9 patients showed stable disease lasting from 6 to 23 months, 7 in the 0.9 mg group, 2 in the 0.6 mg group. The patients treated with 0.3 mg were more heavily pretreated and had a worse performance status than the patients of the 0.6 and 0.9 mg groups. Nine of them were withdrawn early because of worsening peformance status and were therefore not evaluable for response. Furthermore, the evaluable patients treated with 0.3 and 0.6 mg total daily dose had less probability of responding because of their heavier pretreatments in comparison to the 0.9 mg group. The reduction in estrogen levels under treatment with CGS 16949A is comparable to the reduction obtained with other aromatase inhibitors (Table 4). Based on these results, CGS 16949A appears to be well tolerated and safe within the studied doses. It would seem appropriate to conduct extended phase II studies using daily doses of up to 4 mg, and phase HI trials aimed at defining the role of the drug, especially in tamoxifen-resistant tumors; studies comparing CGS 16949A to other hormonal treatments such as tamoxifen have already been activated by some groups. Once the role of CGS 16949A in the treatment of advanced breast cancer is clarified, the use of this non-toxic compound in the adjuvant setting might be feasible.

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Received 6 February 1990; accepted 7 May 1990. Correspondence to: F. CavaUi, MX). Servizio Oncologico Ospedale San Giovanni 6500 Bellinzona, Switzerland