Successes and limitations of targeted cancer therapy in breast cancer.

Peters S, Stahel RA (eds): Successes and Limitations of Targeted Cancer Therapy. Prog Tumor Res. Basel, Karger, 2014, vol 41, pp 15–35 (DOI: 10.1159/000355896)

Successes and Limitations of Targeted Cancer Therapy in Breast Cancer Giuseppe Curigliano · Carmen Criscitiello Early Drug Development for Innovative Therapies Division, Department of Medicine, European Institute of Oncology, Milan, Italy

Abstract

We can no longer consider breast cancer as a single disease. Several breast cancer subtypes can be defined by genetic array tools [1–3] or approximations to this classification using traditional clinical-pathological features [4–7]. Molecular subtypes have different risk factors [8, 9], natural histories [10–12] and different sensitivity to sys-

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Breast cancer is not a single disease. Specific biological processes and distinct genetic pathways are associated with prognosis and sensitivity to chemotherapy and targeted agents in different subtypes of breast cancers. As a consequence, breast cancer can be classified by molecular events. A primary challenge for future drug development in breast cancer will be to distinguish genes and pathways that ‘drive’ cancer proliferation (drivers) from genes and pathways that have no role in the development of cancer (passengers). The identification of functional pathways that are enriched for mutated genes will select subpopulation of patients likely to be sensitive to biology-driven targeted agents. The selection of driver pathways in resistant tumors will permit to discover a biology-driven platform for new drug development to overcome resistance. We are moving in the era of stratified and personalized therapy. Personalized cancer therapy is based on the precept that detailed molecular characterization of the patient’s tumor and its microenvironment will enable tailored therapies to improve outcomes and decrease toxicity. However, there are numerous challenges we need to overcome before delivering on the promise of personalized cancer therapy. These include tumor heterogeneity and molecular evolution, costs and potential morbidity of biopsies, lack of effective drugs against most genomic aberrations, technical limitations of molecular tests, and reimbursement and regulatory hurdles. Critically, successes and limitations surrounding personalized cancer therapy must be tempered with realistic expectations, which, today, encompass increased survival © 2014 S. Karger AG, Basel times for only a portion of patients.

temic and targeted therapies [13–15]. The discovery of ‘genetic signatures’ in breast cancers can provide key insights into the mechanisms underlying tumorigenesis and might prove to be useful for the design of targeted therapeutic approaches [16]. The availability of next-generation human genomic sequencing tools and progress in sequencing and biocomputational technologies will enable genome-wide investigation of somatic mutations in human breast cancers [17] at diagnosis and during their natural history. Genomic sequencing studies focus on the comparison between the sequences found in tumor samples and those of the originating normal tissues or those in the metastatic site of disease. The goal of such comparisons is to identify regions of the genome that differ frequently enough to warrant further investigation for potential causal mechanisms. Also, such studies have the potential to highlight underlying mechanisms of metastasis and resistance to drugs. Breast cancer arises as the result of clonal expansions driven by cells that acquire a selective survival advantage through specific mutations. Genome-wide sequencing studies will therefore identify two specific types of mutations: the ‘drivers’ – those providing a survival and proliferation selective advantage – and the ‘passengers’ – those neutral to the selection process [18, 19]. One of the major goals of the analysis of data from genome-wide sequencing studies is the ranking of genes based on the likelihood that they may be drivers. This a new way in representing the ‘wiring diagram’ of breast cancer [20] identifying all molecular pathways that emphasize the heterogeneity and complexity of human breast cancer, explain mechanisms sustaining proliferation hallmarks of cancer and ‘drive’ tumor progression and resistance to chemotherapy and targeted agents. Identification of ‘druggable’ targets within these pathways represents a challenging platform for new drug discoveries in patients with breast cancer (fig. 1). Molecular characterization of breast cancer subpopulation and molecular screening tools allowed the discovery of multiple oncogenic molecular alterations. A large number of such oncogenic events occur in a small percentage of breast cancer patients and define a specific segment of the disease. Disease segmentation in rare molecular entities is also related to a combination of frequent events [21]. Identification of such molecular events may be crucial to understand molecular mechanisms inducing resistance to first-line therapy. Molecular screening of pathways upregulated in resistant tumors will have a major implication in early drug development.

Endocrine therapy is probably the most important systemic therapy for hormone receptor-positive breast cancer. Hormonal manipulation was the first targeted treatment employed in breast cancer therapy even before the role of the estrogen (ER) and progesterone receptors (PR) had been elucidated. A substantial proportion of pa-

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Curigliano · Criscitiello Peters S, Stahel RA (eds): Successes and Limitations of Targeted Cancer Therapy. Prog Tumor Res. Basel, Karger, 2014, vol 41, pp 15–35 (DOI: 10.1159/000355896)


Luminal A and B Breast Cancer: New Targeted Therapies for the Treatment of Endocrine-Resistant Disease

Tamoxifen

Luminal A

mTOR inhibitors?

Normal like

Aromatase inhibitors PI3K and mTOR inhibitors

Luminal B

T-DM1, pertuzumab

HER2 enriched

Neratinib Cisplatin

Basal like

Olaparib, Neratinib UBE2C PTTG1 MYBL2 CCNB1 BIRC5 HSPC150 TYMS MELK KNTC2 CEP55 CDC6 RRM2 ORC6L ANLN KIF2C EXO1 CENPF CDCA1 CDC20 MKI67 CCNE1 GRB7 TMEM45B ERBB2 BLVRA GPR160 FOXA1 MMP11 NAT1 CXXC5 ESR1 SLC39A6 PGR BAG1 ACTR3B MIA FOXC1 MYC KRT5 SFRP1 KRT17 KRT14 BCL2 PHGDH CDH3 EGFR FGFR4 MDM2 MLPH MAPT

Veliparib

tients, despite being ER and/or PR positive, are either primarily resistant to hormone therapies or will develop hormone resistance during the course of their disease. Signaling through complex growth factor receptor pathways which activate the ER is emerging as an important cause of endocrine resistance. Hundreds of new targeted agents in pipeline are actually in development for targeting several signaling pathways in patients with endocrine-resistant breast cancer. Resistance to endocrine therapy can be related to loss of ER expression [22], to ER level decreases over time; gradual loss of E dependence [23], to upregulation of several transcriptional pathways associated with the expression of high HER2 or epidermal growth factor receptor (EGFR) [24], and several other pathways. We are faced with several challenges to personalized cancer medicine: (a) understanding the genetics of each cancer; (b) need to match the right drug with the individual tumor; (c) monitor the response to treatment; (d) design of rational combinations; (e) testing new anticancer agents earlier in disease (neoadjuvant setting). In patients with endocrine responsive disease a ‘real time’ testing of tumor tissue for genotype sequencing would be ideal. Early drug response and development of acquired resistance should be monitored by repeat biopsy of the tumor or, noninvasively, by functional imaging or circulating tumor cell analysis [25]. We will highlight ongoing clinical trials with signal transduction inhibitors in combination with hormonal manipulation as a means to overcome endocrine resistance in patients with breast cancer.

Successes and Limitations of Targeted Cancer Therapy in Breast Cancer Peters S, Stahel RA (eds): Successes and Limitations of Targeted Cancer Therapy. Prog Tumor Res. Basel, Karger, 2014, vol 41, pp 15–35 (DOI: 10.1159/000355896)

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Fig. 1. New and old targeted agents for molecular subtype of breast cancer: targeting pathways to overcome resistance.

Targeting Epidermal Growth Factor Receptor Pathway Several early clinical trials have been conducted with the EGFR tyrosine kinase inhibitors (TKIs) gefitinib or erlotinib either alone or in combination with endocrine therapy. Results from the monotherapy phase II studies with gefitinib in patients with advanced breast cancer were relatively disappointing [26–28]. Two other phase II studies explored the potential benefit for combining either gefitinib or erlotinib with an aromatase inhibitor in unselected patients with ER-positive advanced breast cancer with very low clinical efficacy [29, 30]. In the setting of neoadjuvant therapy for ER-positive postmenopausal breast cancer, a randomized trial of anastrozole alone or in combination with gefitinib given for 3 months prior to surgery showed no improvement in tumor response rate or antiproliferative effect as determined by Ki-67 [31]. On the other hand, a preoperative trial of gefitinib versus gefitinib combined with anastrozole for 4–6 weeks prior to surgery in women with ER+ EGFR+ primary breast cancer reported that combined treatment induced the greatest reduction in tumor cell proliferation [32]. A double-blind placebo-controlled phase II trial of tamoxifen with or without gefitinib was conducted in 290 patients as first-line endocrine therapy in postmenopausal women with ERpositive metastatic breast cancer (MBC) [33], with an increase in progression-free survival (PFS) from 8.8 to 10.9 months (hazard ratio 0.84, 95% confidence interval, CI: 0.59–1.18, p = 0.31) [33]. A second randomized trial of gefitinib and anastrozole versus anastrozole alone in a similar first-line patient population of women with ER positive advanced breast cancer reported a prolongation of PFS from a median of 8.2 months with anastrozole to 14.6 months with the combination (hazard ratio 0.55, 95% CI: 0.32–0.94) [34]. A second randomized phase II trial with the same combination of gefitinib and anastrozole did not show any statistically significant benefit [35]. Table 1 summarizes major clinical trials with anti-EGFR-targeted agents.

A phase II clinical trial of letrozole and the monoclonal antibody trastuzumab in patients with ER+/HER2+ MBC demonstrated a clinical benefit rate (partial response and stable disease) of 50% [36]. Subsequently, the randomized phase II TAnDEM trial in patients with ER+/HER2+ MBC reported a better PFS with the addition of trastuzumab over anastrozole alone (4.8 vs. 2.4 months, p = 00.0016) [37]. Other trials have been conducted with lapatinib, a potent oral TKI of both EGFR and HER2. Lapatinib has been explored in combination with endocrine therapy within a phase III trial of 1,286 patients with metastatic ER+ breast cancer who were randomized to receive either letrozole alone or letrozole combined with lapatinib [38]. In patients with known ER+/HER2+ breast cancer, the addition of lapatinib to letrozole significantly

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Targeting HER2 Pathway

Table 1. Clinical trials combining endocrine therapies with biological targeted agents (anti-EGFR and anti-HER2) in ER-positive breast cancer Clinical setting

Trial phase

Intervention

Clinical end points

Reference

MBC

phase II (n = 15)

anastrozole and gefitinib

response rate no response no stable disease

[29]

phase II (n = 150)

letrozole and gefitinib

clinical benefit 11/20 patients

[30]

response rate 61% anastozole vs. 45% (combination arm), p = 0.067

[31]

MBC

PFS 2.4 months (anastrozole) anastrozole vs. phase III randomized trastuzumab plus vs. 4.8 months (anastrozole plus trastuzumab), p = 0.0016 anastrozole (n = 207)

[37]

MBC

letrozole vs. phase III randomized letrozole plus lapatinib (n = 219)

PFS 3.0 months (letrozole) vs. 8.2 months (letrozole plus lapatinib)

[38]

MBC

randomized tamoxifen vs. tamoxifen phase II plus gefitinib (n = 150)

PFS 8.8 months (tamoxifen) vs. [33] 10.9 (tamoxifen plus gefitinib)

randomized anastrozole plus gefitinib vs. phase II anastrozole (n = 206)

PFS 14.6 months (anastrozole plus gefitinib) vs. 8.2 (anastrozole)

anastrozole vs. Early breast cancer phase II randomized gefitinib plus anastrozole (n = 206)

[34]

reduced the risk of progression (hazard ratio 0.71, 95% CI: 0.53–0.96, p = 0.019) and improved the median PFS from 3.0 months for letrozole to 8.2 months for the combination [38]. The double targeting of ER and HER2 may be effective in tumors with endocrine resistance and/or established coexpression of both receptors; this promising strategy of coblockade has now become clinical reality with the recent approval of the combination of lapatinib with letrozole in HER2-positive MBC patients. Table 1 summarizes major clinical trials with anti-HER2 agents.

The phosphoinositide-3 kinase (PI3K) pathway has been identified as an important target in breast cancer research. PI3K pathway is frequently aberrantly activated in breast cancer with mutations occurring in up to one quarter of endocrine-resistant breast cancer [39]. Several agents targeting the PI3K pathway are currently under de-


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Targeting Phosphatidylinositol 3-Kinase/AKT/Mammalian Target of Rapamycin Signaling Pathways in Endocrine-Resistant Breast Cancer

velopment including monoclonal antibodies, TKIs, PI3K inhibitors, Akt inhibitors, rapamycin analogs, and mammalian target of rapamycin (mTOR) inhibitors. Their development is based on the strategy of coblockade; multiple signaling inhibition is mandatory since anti-mTOR agents and PI3K inhibitors may result in the activation of compensatory feedback loops that would result in reduced activity.

PI3K Inhibitors Alterations of signal transduction pathways leading to uncontrolled cellular proliferation, survival, invasion, and metastases are hallmarks of the carcinogenic process. The phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR and the Raf/mitogen-activated and extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathways are critical for normal human physiology, and also commonly dysregulated in human cancers, including breast cancer. In vitro and

20



Mammalian Target of Rapamycin Inhibitors The first agents against the PI3K pathway that were studied in the clinic were rapamycin analogs. Clinical data suggest that mTOR inhibition may play a role in the therapy of endocrine-resistant breast cancer. In the neoadjuvant setting, patients with early ER-positive breast cancer were randomized to receive either letrozole plus placebo for 16 weeks or letrozole plus daily everolimus (RAD001), a rapamycin analogue. The primary end point of the trial was response rate to the combination therapy [40]. Response rate by clinical examination was higher in the everolimus arm than that with letrozole alone (i.e. placebo; 68.1 vs. 59.1%). An antiproliferative response, as defined by a reduction in Ki67 expression to natural logarithm of percentage positive Ki67 of less than 1 at day 15, occurred in 52 (57%) of 91 patients in the everolimus arm and in 25 (30%) of 82 patients in the placebo arm (p < 0.01) [40]. A phase 3, randomized, multicenter study (BOLERO-2) evaluated everolimus in combination with exemestane in postmenopausal women with HR+ HER2− advanced breast cancer that recurred or progressed after previous nonsteroidal aromatase inhibitor (letrozole or anastrozole) therapy (n = 724). Patients were randomized (2:1) to everolimus (10 mg/ day) or placebo in combination with open-label exemestane (25 mg/day). Randomization was stratified according to the presence of visceral metastasis and previous sensitivity to endocrine therapy defined as (1) ≥24 months of endocrine therapy in the adjuvant setting before disease recurrence, or (2) response or disease stabilization for ≥24 weeks after endocrine therapy in the advanced setting. Most patients had bone metastases (76%), visceral involvement (56%), and hormone-sensitive disease (84%). Previous therapy included letrozole or anastrozole (100%), chemotherapy (68%), tamoxifen (48%), and fulvestrant (16%). The primary end point was PFS based on investigator assessment of radiographic studies. At a median follow-up of 12.5 months, median PFS by investigator assessment was 7.4 months for the everolimus plus exemestane arm compared with 3.2 months for the placebo plus exemestane arm (hazard ratio = 0.44; 95% CI: 0.36–0.53; p < 1 × 10–16) [41].

Table 2. Inhibitors of the PI3K3CA pathway under clinical development (either as single agents or in combination) for advanced breast carcinoma or advanced solid tumors Drugs

Target

Current phase of Setting clinical development

BKM120

pan-class I phase II MBC phase III randomized phase III study of BKM120/placebo with fulvestrant PI3K in postmenopausal patients with hormone receptor-positive HER2-negative locally advanced or MBC refractory to aromatase inhibitor

XL147

pan-class I phase II PI3K

study of XL147 or XL765 in combination with letrozole in subjects with breast cancer

CDG-0941 pan-class I phase II randomized PI3K

study of GDC-0941 or GDC-0980 with fulvestrant versus fulvestrant in advanced or MBC in patients resistant to aromatase inhibitor therapy

BYL719

PI3K phase I–II (α-specific)

BYL719 plus letrozole or exemestane for patients with hormone receptor-positive locally advanced unresectable or MBC

BEZ235

phase I–II

pharmacodynamic study of BKM120 and BEZ235 in breast cancer; a phase Ib/II study of BEZ235 and trastuzumab in patients with HER2-positive breast cancer who failed prior to trastuzumab

PI3K/mTOR

in vivo data suggest the PI3K/AKT/mTOR and Raf/MEK/ERK cascades to be interconnected with multiple points of convergence, crosstalk, and feedback loops. Raf/ MEK/ERK and PI3K/AKT/mTOR pathway mutations may coexist. Inhibition of one pathway can still result in the maintenance of signaling via the other (reciprocal) pathway. The existence of such ‘escape’ mechanisms implies that dual targeting of these pathways may lead to superior efficacy and better clinical outcome in selected patients. Several clinical trials targeting one or both pathways are already underway in breast cancer patients. The toxicity profile of this novel approach of dual pathway inhibition needs to be closely monitored, given the important physiological role of PI3K/AKT/mTOR and Raf/MEK/ERK signaling. In table 2, we report current relevant preclinical and clinical data and discuss the rationale for dual inhibition of these pathways in the treatment of breast cancer patients.

The use of demethylating agents or histone deacetylase (HDAC) inhibitors can reactivate expression of a functional ER in cell lines in which ER silencing exists because of promoter methylation [42]. HDACs are crucial components of the ER transcrip-


21


Targeting Histone Deacetylase

tional complex. Preclinically, HDAC inhibitors can reverse tamoxifen/aromatase inhibitor resistance in hormone receptor-positive breast cancer [42]. In a phase II trial, patients with ER-positive MBC progressing on endocrine therapy were treated with 400 mg of vorinostat daily for 3 of 4 weeks and 20 mg tamoxifen daily, continuously. The objective response rate was 19% and the clinical benefit rate was 40%. The median response duration was 10.3 months (CI: 8.1–12.4) [43]. Targeting Insulin-Like Growth Factor Receptor Insulin-like growth factor-1 receptor (IGF-1R) is a homodimeric receptor tyrosine kinase activated by IGF I/II ligand binding which results in tumor growth and apoptosis blockade [44]. IGF-1R antagonists have been shown to interact with both ER pathways. This crosstalk between ER suggests that IGF-1R may be an attractive treatment target especially for the ‘Luminal B’ breast cancers. This is supported by in vitro experiments showing a synergistic effect when cotargeting the IGF-1R receptor along with anti-ER agent [45]. Moreover, growth of tamoxifen-resistant MCF-7 cells declines when anti-IGF-1R antibody is added to the cells [46]. Several monoclonal antibodies and TKIs are in early clinical development in the treatment of breast cancer. Phase II randomized trials are currently ongoing for patients progressing to nonsteroidal aromatase inhibitors and randomized to exemestane versus exemestane with figitumumab, a fully humanized anti-IGR-1R antibody. In a recent randomized phase II study, the investigational agent AMG 479, a fully human monoclonal antibody against the IGF-1R, failed to revert resistance to hormonal therapy in patients with endocrine therapy-resistant, ER-positive MBC [47]. Indeed, the drug showed a trend toward worse PFS and objective response in a phase II trial [47]. When AMG 479 was paired with exemestane or fulvestrant, patients in the experimental arm had a median PFS of 3.9 months, compared with 5.7 months for patients on exemestane or fulvestrant alone (hazard ratio, 1.17; p = 0.435). In this study, AMG 479 in combination with either fulvestrant or exemestane does not appear to delay or reverse resistance to hormonal therapy in this population of patients with prior endocrine therapy-resistant hormone receptor-positive MBC. Other trials are currently ongoing in hormone-resistant breast cancer patients using TKIs targeting the IGF-1R pathway.

Src is specifically involved in coordinating signaling from the steroid receptors, including the ER and androgen receptor (AR). Multiple studies have shown crosstalk between ER/AR and Src, with ER/AR activation leading to activation of Src, and subsequent Src-mediated cell proliferation [48, 49]. Blocking the interaction

22



Targeting Src Family Tyrosine Kinase

between ER/AR and Src leads to inhibition of downstream cellular pathways, and cessation of cell growth [48]. Several studies have shown associations between resistance to endocrine therapy and both increased levels of Src activity and an increasingly invasive and aggressive tumor phenotype [50, 51]. Given these data, specifically targeting Src may overcome endocrine resistance in hormonally driven cancers. Several inhibitors of Src have been developed. One of the best studied is dasatinib. Dasatinib is a potent oral small molecule inhibitor of the Src tyrosine kinase. Another agent, bosutinib, is an oral dual selective competitive inhibitor of both Src (IC50 = 1.0 nmol/l) and Abl tyrosine kinases, with moderate inhibition of the Axl tyrosine kinase, Eph receptors, and Ste20 family kinases [52]. Multiple other agents with activity against Src, including saracatinib and XL999 are in preclinical or early-phase clinical development. A phase II monotherapy study was open to patients with both ER-positive and/or HER2 positive disease. Of the response-evaluable population from both subtypes, a response rate of 4% was seen, with a clinical benefit rate of 8% in the HER2+ cohort, and 16% in the ER+ cohort. Interestingly, all benefit was seen in patients with ER+ tumors [53]. Another phase II randomized trial was designed for patients with ER positive MBC progressing to nonsteroidal aromatase inhibitors. Patients are randomized to exemestane plus dasatinib versus exemestane plus placebo. The accrual to this trial has just been completed.

HER2-Positive Breast Cancer: New Targeted Therapies for the Treatment of Trastuzumab-Resistant Disease

Many breast cancer patients with HER2 overexpression do not respond to initial therapy with trastuzumab and a vast majority of these develop resistance to this monoclonal antibody. Several molecular mechanisms leading to the development of trastuzumab resistance have been described, including circulating HER2 extracellular domain [54], loss of PTEN [55], activation of alternative pathways (e.g. IGFR) [56], receptor-antibody interaction block [57] or innate modulation of the immunological response [58]. Identification of upregulated pathways may lead to development of new therapeutic targets that potentially overcome resistance to trastuzumab. Several agents are currently under development to overcome trastuzumab resistance (table 3).

Genetech in collaboration with Roche have recently developed trastuzumab-DM1 (maytansine conjugated to trastuzumab) which is active on HER2-overexpressing breast cancer and also on trastuzumab-refractory tumors. Maytansinoids are very po-


23


Trastuzumab-DM1

Table 3. New targeted therapies for the treatment of trastuzumab-resistant disease Clinical setting Trial phase

Intervention

Clinical end points

Reference

MBC

phase I (n = 24)

trastuzumab-DM1

clinical benefit rate at 3.6 mg/kg was 73% including 5 PR

[61]

phase II (n = 112)

trastuzumab-DM1 3.6 mg/kg

PR 25.9% [62] median PFS 4.6 months

Early breast cancer

pertuzumab/trastuzumab phase III randomized plus chemotherapy (n = 417)

pathological complete response in dual targeting arm 45.8%

[66]

MBC

pertuzumab/trastuzumab phase III randomized plus chemotherapy (n = 808)

PFS 12.4 months in the control group, as compared with 18.5 months in the pertuzumab group

[67]

MBC

phase III single arm (n = 136)

cohort 1: 16-week PFS 59% (22.3 weeks); PR 24% cohort 2: 16-week PFS 78% (39.6 weeks); PR 56%

[70]

neratinib 240 mg/day cohort 1: 66 patients before trastuzumab cohort 2: 70 patients first line

tent anticancer agents originally isolated from plant families: Celastraceae, Rhamnaceae and Euphorbiaceae and later from microorganism-producing antibiotics (Actinosynnema pretiosum) [59, 60]. They are 19-member microcyclic lactams related to amsamycin. The maytansinoid DM1 is 100- to 1,000-fold more potent than anticancer agents in clinical use [59, 60]. The maytansine DM1 binds to microtubules in a manner similar to Vinca alkaloids, but is 20- to 100-fold more potent than vincristine in blocking mitosis [59]. Therefore, the maytansinoid DM1 was conjugated to the humanized HER2 antibody trastuzumab (Tmab, which is a protein) using -S-S(disulfide)-containing linkers (Tmab-SPDT-DM1, Tmab-SPP-DM1, Tmab-SSNPPDM1, Tmab-SSNPP-DM4). The first-in-human phase I, multicenter, open-label, dose escalation study of single-agent T-DM1 in patients with HER-2 positive MBC, who had previously received a trastuzumab-containing chemotherapy regimen, demonstrated that at the maximum-tolerated dose (MTD) of 3.6 mg/kg every 3 weeks, T-DM1 was safe and had considerable clinical activity. The clinical benefit rate [CBR (RR plus stable disease at 6 months)] among 15 patients treated at MTD was 73%, including five objective re-

24



PR = Partial response; SD = stable disease.

sponses [61]. Phase II studies of T-DM1 in patients with HER-2-positive MBC who progressed while receiving HER-2-directed therapy (trastuzumab or lapatinib), or who were previously treated with several lines of chemotherapy have demonstrated an objective response rate, by independent assessment, of 25.9% (95% CI: 18.4– 34.4%). Median duration of response was not reached as a result of insufficient events (lower limit of 95% CI: 6.2 months), and median PFS time was 4.6 months (95% CI: 3.9–8.6 months) [62]. Several randomized clinical trials are actually ongoing in metastatic HER2-positive breast cancer patients. An open-label, phase III trial (EMILIA) compared the safety and efficacy of T-DM1 with that of capecitabine in combination with lapatinib in patients with HER-2-positive MBC previously treated with a trastuzumab-based therapy [63]. Among 991 randomly assigned patients, median PFS as assessed by independent review was 9.6 months with T-DM1 versus 6.4 months with lapatinib plus capecitabine (hazard ratio for progression or death from any cause, 0.65; 95% CI: 0.55–0.77; p < 0.001), and median overall survival at the second interim analysis crossed the stopping boundary for efficacy (30.9 vs. 25.1 months; hazard ratio for death from any cause, 0.68; 95% CI: 0.55–0.85; p < 0.001). The objective response rate was higher with T-DM1 (43.6 vs. 30.8% with lapatinib plus capecitabine; p < 0.001); also results for all additional secondary end points favored T-DM1. Rates of grade 3 or 4 adverse events were higher with lapatinib plus capecitabine than with T-DM1 (57 vs. 41%). The incidence of thrombocytopenia and increased serum aminotransferase levels was higher with T-DM1, whereas the incidence of diarrhea, nausea, vomiting, and palmar-plantar erythrodysesthesia was higher with lapatinib plus capecitabine. T-DM1 significantly prolonged progression-free and overall survival with less toxicity than lapatinib plus capecitabine in patients with HER2-positive advanced breast cancer previously treated with trastuzumab and a taxane. Another first-line trial (MARIANNE) is currently ongoing for the treatment of MBC [64]. This randomized, 3-arm, multicenter study will evaluate the efficacy and safety of trastuzumab-DM1 with pertuzumab or T-DM1 with pertuzumab-placebo, versus the combination of trastuzumab plus taxane (docetaxel or paclitaxel) in patients with HER2-positive progressive or recurrent locally advanced or previously untreated MBC [64].

Pertuzumab is a novel recombinant humanized monoclonal antibody directed against the highly conserved dimerization domain of HER-2, and as such, it inhibits HER-2 homo- and heterodimerization. Pertuzumab-mediated blockage of HER-2 dimerization inhibits HER family downstream signaling (i.e. the Akt cell survival pathway and the mitogen-activated protein kinase pathway) [65]. In a phase III randomized trial investigating the efficacy and safety of pertuzumab in combination with chemotherapy and trastuzumab was explored in patients


25


Pertuzumab

with HER-2-positive MBC. The combination of pertuzumab plus trastuzumab plus docetaxel, as compared with placebo plus trastuzumab plus docetaxel, when used as first-line treatment for HER2-positive MBC, significantly prolonged PFS with no increase in cardiac toxic effects. The median PFS was 12.4 months in the control group as compared with 18.5 months in the pertuzumab group (hazard ratio for progression or death, 0.62; 95% CI: 0.51–0.75; p < 0.001) [66]. The idea that the combination of pertuzumab and trastuzumab might be a clinically meaningful therapy in MBC came from the single-arm, phase II trial of trastuzumab plus pertuzumab, which demonstrated that the combination was well tolerated and active in patients with HER-2 positive MBC who had progressed during trastuzumab therapy [67]. In this trial, the objective response rate was 24.2%, and the clinical benefit rate was 50%. Cardiac dysfunction was minimal, and no patient withdrew as a result of cardiac-related adverse events. Recently, the combination of pertuzumab and trastuzumab has been tested in HER2-positive patients with newly diagnosed early breast cancer. The NEOSPHERE study (Neoadjuvant Study of Pertuzumab and Herceptin in an Early Regimen Evaluation) is a randomized multicenter phase II study that was conducted in 417 women with newly diagnosed HER2-positive, early, inflammatory or locally advanced breast cancer who never received trastuzumab. Prior to surgery (neoadjuvant treatment), these women were randomized to 4 study arms. The primary end point was pathological complete response (pCR), and the results were: (1) arm A: pCR of 29% for trastuzumab and docetaxel; (2) arm B: pCR of 45.8% for trastuzumab, pertuzumab and docetaxel; (3) arm C: pCR of 16.8% for trastuzumab and pertuzumab; (4) arm D: pCR of 24% for pertuzumab and docetaxel [68]. The findings of the NEOSPHERE study suggested that this new approach was effective for early HER2-positive breast cancer, and suggest the importance of the dual targeting approach in HER2-positive breast cancer.

Neratinib is an orally available pan-ErbB TKI, differing in that it inhibits HER4 as well as HER1/EGFR and HER2 [69]. The efficacy and safety of neratinib were evaluated in a trial including two cohorts of patients with advanced ErbB2-positive breast cancer, those with and those without prior trastuzumab treatment, in an open-label, multicenter, phase II trial. The 16-week PFS rates were 59% for patients with prior trastuzumab treatment and 78% for patients with no prior trastuzumab treatment. Median PFS was 22.3 and 39.6 weeks, respectively. Objective response rates were 24% among patients with prior trastuzumab treatment and 56% in the trastuzumab-naïve cohort [70]. A potential role for the use if neratinib is under investigation in patients with HER2-mutated breast cancers. Emerging agents for treatment of HER2-resistant tumors are reported in table 2.

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Neratinib

Table 4. New targeted therapies for the treatment of TNBC Clinical setting

Trial phase

Intervention

Clinical end points

Reference

Metastatic BRCA1- and BRCA2-mutated breast cancer patients

phase I (n = 60) 22 mutation carriers

olaparib 200 mg twice daily in mutation carried

objective antitumor activity was reported only in mutation carriers

[72]

phase II (n = 54) cohort 1: 27 cohort 2: 27

olaparib 400 mg twice daily: cohort 1 olaparib 100 mg twice daily: cohort 2

cohort 1: overall response rate 41% cohort 2: overall response rate 22%

[74]

Metastatic TNBC patients

phase II randomized (n = 123)

iniparib 5.6 mg/kg plus carboplatin/ gemcitabine vs. carboplatin/gemcitabine

overall response rate 52% in iniparib arm vs. 32 in chemotherapy arm (p = 0.01); median PFS 5.9 vs. 3.6 months (p = 0.01); OS 12.3 vs. 7.7 months (p = 0.01)

MBC

phase II single arm (n = 41)

veliparib 40 mg twice overall response rate daily plus temozolomide 7% PR in BRCA1/2 mutated 37.5%

[76]

[79]

OS = Overall survival.

Ductal Triple-Negative Breast Cancer: New Targeted Therapies for the Treatment of a ‘DNA Repair Disease’

Numerous transcriptional pathways are under investigation to determine how best to target therapies to specific mutations or molecular events in basal-like breast cancers. Each one of these pathways will require careful investigation to assess how important therapeutic interventions along this pathway will be. Table 4 summarizes some targeted agents under investigation for triple-negative breast cancer (TNBC).

DNA lesions such as single-strand breaks (SSBs) and double-strand breaks are common by products of normal cellular metabolism, and may also result from exposure to harmful environmental agents. Briefly, four DNA repair mechanisms are responsible for repairing these lesions: (a) base excision repair (BER), (b) nucleotide excision


27


Targeting the Poly-Adenosine Diphosphate-Ribose Polymerase Pathway

repair (NER), (c) mismatch repair (MMR), and (d) recombinational repair (with homologous recombination and nonhomologous end joining) [71]. When SSBs occur, they are repaired using the intact complementary strand as a template by BER, NER, and MMR. A key component of the BER pathway, poly-adenosine diphosphate-ribose polymerase 1 (PARP1), is the most important member of the PARP family of enzymes [72, 73]. PARP inhibition leads to accumulation of DNA SSBs and subsequent DNA double-strand breaks at replication forks. These breaks normally are repaired via the homologous recombination double-stranded DNA repair pathway, major components of which are the tumor-suppressor proteins BRCA1 and BRCA2 [73]. PARP1 is upregulated differentially in primary breast cancers, including ERnegative, PR-negative, and HER2-negative (ductal triple negative) breast cancers. Preclinical studies of in vitro activity of PARP inhibitors demonstrated that inhibitory activity was restricted to tumors which were BRCA deficient [73].

Iniparib Iniparib (previously BSI 201; 4-iodo-3-nitrobenzamide) is a drug that acts as an irreversible inhibitor of PARP1 (hence, it is a PARP inhibitor) and possibly other enzymes through covalent modification [76]. An open-label, phase 2 study to compare the efficacy and safety of gemcitabine and carboplatin with or without iniparib, a small molecule with PARP-inhibitory activity, in patients with metastatic TNBC, was conducted. A total of 123 patients were randomly assigned to receive gemcitabine (1,000 mg/ m2

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Olaparib Olaparib, a novel, orally active PARP inhibitor, induced synthetic lethality in BRCAdeficient cells. A proof on concept trial in BRCA-mutated patients assessed the efficacy, safety, and tolerability of olaparib alone in women with advanced breast cancer [74]. Patients had been given a median of three previous chemotherapy regimens (range 1–5 in cohort 1, and 2–4 in cohort 2). Response rate was 11 (41%) of 27 patients (95% CI: 25–59) in the cohort assigned to 400 mg twice daily, and 6 (22%) of 27 [11– 41] in the cohort assigned to 100 mg twice daily [74]. The results of this study provide proof of concept for PARP inhibition in BRCA-deficient breast cancers. Phase I studies are currently ongoing combining cisplatin and olaparib. Agents like platinum salts bind to DNA directly and result in the formation of DNA-platinum adducts and, consequently, intrastrand and interstrand DNA crosslinks that impede cell division. As a consequence, cisplatin may be an effective treatment for patients with hereditary BRCA1-mutated breast cancers. Because sporadic TNBC and BRCA1-associated breast cancer share features suggesting common pathogenesis, a neoadjuvant trial of cisplatin in TNBC was conducted [75]. Six (22%) of 28 patients achieved pathologic complete responses, including both patients with BRCA1 germline mutations; 18 (64%) patients had a clinical complete or partial response in the BRCA1 mutation group. These background data suggest that combination of PARP inhibitors and cisplatin can be potentially very active.

body surface area) and carboplatin (at a dose equivalent to an area under the concentration time curve of 2) on days 1 and 8 – with or without iniparib (at a dose of 5.6 mg/ kg body weight) on days 1, 4, 8, and 11 – every 21 days. Primary end points were the rate of clinical benefit [i.e. the rate of objective response (complete or partial response) plus the rate of stable disease for ≥6 months] and safety. Additional end points included the rate of objective response, PFS, and overall survival [76]. The addition of iniparib to gemcitabine and carboplatin improved the rate of clinical benefit from 34 to 56% (p = 0.01) and the rate of overall response from 32 to 52% (p = 0.02). The addition of iniparib also prolonged the median PFS from 3.6 to 5.9 months (hazard ratio for progression, 0.59; p = 0.01) and the median overall survival from 7.7 to 12.3 months (hazard ratio for death, 0.57; p = 0.01) [76]. Another large randomized trial included 519 women with metastatic TNBC. Patients were randomized to receive a standard chemotherapy regimen (gemcitabine and carboplatin) on days 1 and 8 of each 21-day cycle, with or without iniparib 5.6 mg/kg, which was administered on days 1, 4, 8 and 11 of each 21-day cycle [77]. Patients in the study had received up to two previous lines of chemotherapy in a metastatic setting. The coprimary endpoints were overall survival and PFS [77]. Sanofi-Aventis announced that the trial did not meet the pre-specified criteria for significance for coprimary end points of overall survival and PFS. Veliparib Veliparin (ABT-888) is a potent inhibitor of both PARP-1 and PARP-2 [78]. Preclinical studies showed that temozolomide potentiation by PARP inhibition occurs in TNBC [78]. A single-arm phase II trial of veliparib in combination with temozolomide was conducted in patients who had received at least one prior regimen for MBC [79]. Patients received veliparib (40 mg twice daily on days 1–7) and oral temozolomide (150 mg/m2/day on days 1–5) every 28 days; temozolomide was increased to 200 mg/m2 as tolerated. The primary end point was objective response rate, and secondary end points were PFS, clinical benefit rate and safety and tolerability. Of the 41 patients, 23 had TNBC. Objective response was 7% (one complete response and two partial responses; 95% CI: 2–20%). The rate of stable disease at 16 weeks was 10% (4 patients). When response among all BRCA1/BRCA2 mutation carriers was determined, objective response was 37.5% (one complete response and two partial responses), and clinical benefit rate was 62.5% (n = 5) [79].

There are numerous challenges that need to be overcome to successfully implement personalized therapy in breast cancer. These include biological challenges such as tumor heterogeneity and molecular evolution, technical challenges such as limitations of molecular tests, pharmacological challenges such lack of effective drugs, and regulatory and reimbursement challenges.


29


Limitations of Targeted Therapies in Breast Cancer

Tumor Heterogeneity During tumor progression, subclones frequently arise resulting in differences in the proportion and pattern of specific aberrations between the primary tumor and metastases or tumor recurrences. Strikingly, metastases are not necessarily more complex than the primary tumor from which they originated, but can actually lose aberrations that are present in the primary lesion. Molecular Evolution and Resistance The array of clones with particular aberrations can change under both the selective pressure of a targeted therapy and as a result of the mutagenic activity of radiation and chemotherapy. There are two general conceptual approaches to deal with intratumoral heterogeneity and emergence of resistance: in-depth characterization of tumors and recurrence to identify rare and dominant clones, and lowdepth sequential characterization of tumors to identify driver clones. Repeated biopsies at progression can assist in determining whether emergent aberrations could be treatable by specific means. As obtaining multiple biopsies is costly and associated with potential morbidity, surrogates such as molecular imaging or analysis of circulating tumor cells or circulating free DNA are also being pursued in ongoing studies. Undruggable Targets The role of in-depth molecular analysis is to identify molecular aberrations that can be targeted with existing therapeutic strategies. However, many proteins are currently ‘undruggable’, and loss-of-function mutations of tumor suppressor genes, such as TP53, are currently not actionable. However, our drug toolkit is rapidly evolving, and emerging technologies that interrupt protein-protein and DNA-protein interactions, and approaches such as siRNA might potentially render previously undruggable targets druggable.

The identification and validation of markers of sensitivity and resistance are a key step necessary for the implementation of personalized cancer therapy. In early clinical trials generally carried out in heavily pretreated patients with advanced-stage or metastatic disease, patients occasionally demonstrate unexpected responses. Indepth characterization of these ‘unusual responders’ may help to identify important

30



Technical Challenges

biomarkers of sensitivity, within personalized cancer therapy programs. Comprehensive analysis of not only alterations in the genome but also the epigenome, transcriptome, proteome, and gene-gene, protein-protein and genome-environment interactions is likely to have important clinical implications in biomarker development. Need for New Trial Designs Novel clinical trial designs are being developed to identify and validate biomarkers and targeted therapeutics. Independent of the design, access to tissue molecular tumor characterization is a prerequisite for conducting such studies which often is a limiting factor for patient accrual. Biomarker discovery and validation must be integrated into all aspects of drug development, from discovery through to clinical trials. Pharmacological Challenges Although multiple targeted therapies are currently entering clinical trials, it is not yet clear whether these agents have the appropriate specificity, pharmacology and pharmacodynamics to inhibit their therapeutic targets. There is a real risk of abandoning outstanding targets due to studies of therapeutic agents with poor or variable bioavailability, short half-lives or off-target toxicity delivered with inappropriate dosing. Indeed, with very few exceptions, it is not yet known what degree and duration of target inhibition is necessary to develop optimal outcomes.

The ‘wiring diagrams’ of breast cancer subtypes define that the signaling circuitry describing the intercommunication between various pathways should be charted in far greater detail and clarity in order to better understand ‘drivers’ and ‘passengers’. We continue to foresee breast cancer research as an increasingly ‘computational’ science, in which in silico models should predict underlying pathways that sustain cancer progression and proliferation. The selection of patients for targeted therapy remains a challenge because we lack reliable biomarkers to predict activity for most of the targeted agents. Traditional methodologies applied for drug development are likely inappropriate for new targeted agents. Resistance to many traditional and new drugs is a major clinical challenge. The use of high-throughput technologies will help us understand the molecular biology of signaling pathways as the roads of the ‘genomic landscape’ of breast cancer. The number of potential driver genes is large; however,


31


Conclusions

the number of ‘driver’ pathways is more limited. Patient selection, rational combination therapies, surrogate markers identification and tumor tissue banking have become key areas of research. Research efforts should be directed at generating the level of evidence required to make comprehensive testing reimbursable. Until that time, partnerships between academia and industry as well as significant philanthropic support are needed to facilitate comprehensive molecular characterization to demonstrate that it benefits patients.

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Giuseppe Curigliano, MD, PhD Early Drug Development for Innovative Therapies Division Via Ripamonti, 435 IT–20141 Milan (Italy) E-Mail [email protected]


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Successes and limitations of targeted cancer therapy in ovarian cancer.

Successes and limitations of targeted cancer therapy in lung cancer.

Successes and limitations of targeted cancer therapy in colon cancer.

Successes and limitations of targeted cancer therapy in melanoma.

Successes and limitations of targeted cancer therapy in gastrointestinal stromal tumors.

Successes and limitations of targeted therapies in renal cell carcinoma.

Targeted therapy in HER2-positive breast cancer.

Prevention: targeted therapy-anastrozole prevents breast cancer.

Familial breast cancer - targeted therapy in secondary and tertiary prevention.

Triple-negative breast cancer: molecular subtypes and targeted therapy.

Targeted therapy in cancer.

Alternative targeted therapy for early Her2 positive breast cancer.

Targeted therapy in gastric cancer.

Targeted therapy in ovarian cancer.

Biomarkers and Targeted Therapy in Pancreatic Cancer.

Oral targeted therapy for cancer.

[New targeted therapies in breast cancer].

Limitations of Personalized Medicine and Gene Assays for Breast Cancer.

Progestins, breast cancer, and the limitations of epidemiology.

Therapy of breast cancer.

Endoscopic therapy of esophageal cancer: possibilities and limitations.

Biomarker-directed Targeted Therapy in Colorectal Cancer.

Mast Cell-Targeted Strategies in Cancer Therapy.

Targeted nanosystems: Advances in targeted dendrimers for cancer therapy.