New drugs for breast cancer subtypes: Targeting driver pathways to overcome resistance

Cancer Treatment Reviews 38 (2012) 303–310

Contents lists available at ScienceDirect

Cancer Treatment Reviews journal homepage: www.elsevierhealth.com/journals/ctrv

New Drugs

New drugs for breast cancer subtypes: Targeting driver pathways to overcome resistance Giuseppe Curigliano ⇑ Division of Medical Oncology, Department of Medicine, European Institute of Oncology, Milan, Italy

a r t i c l e

i n f o

Article history: Received 14 June 2011 Accepted 21 June 2011

Keywords: Breast cancer subtypes Molecular classification Targeted agents

a b s t r a c t Breast cancer is not a single disease. Genetic array tools can define several subtypes. Specific biological processes and distinct gene 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 sub-population of patients the will most likely 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. Any of the breast cancer subtypes implies that clinicians should consider cases within the various distinct sub-population in order to properly choose the most personalized therapeutic approach. We will review all new emerging agents targeting the driver pathways within breast cancer molecular subtypes. Ó 2011 Elsevier Ltd. All rights reserved.

Introduction We cannot longer consider breast cancer as a single disease. Several breast cancer subtypes can be defined by genetic arrays tools1–3 or approximations to this classification using traditional clinicalpathological features.4–7 Molecular subtypes have different risk factors,8,9 natural histories10–12 and different sensitivity to systemic and targeted therapies.13–15 The discovery of ‘‘genetic signatures’’ in breast cancers can provide key insights into the mechanisms underlying tumorigenesis and can be proven useful for the design of targeted therapeutic approaches.16 The availability of next generation human genomic sequencing tool and progress in sequencing and bio-computational technologies will enable genome-wide investigation of somatic mutations in human breast cancers17 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 metastatic site of disease. The goal of this comparison is to identify regions of the genome that differ frequently enough to warrant further investigation of potential causal mechanisms. These 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 advan⇑ Address: Division of Medical Oncology, Istituto Europeo di Oncologia, Via Ripamonti 435, 20141 Milano, Italy. Tel.: +39 02 57489788; fax: +39 02 57489581. E-mail address: [email protected] 0305-7372/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ctrv.2011.06.006

tage 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 cancer20 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 drugs discoveries in patients with breast cancer. 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. We will overview all new promising molecules under investigation in all breast cancer subtypes (Fig. 1).

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

Luminal A and B breast cancer: new targeted therapies for the treatment of endocrine resistant disease

monal manipulation as a means to overcome endocrine resistance in patients with breast cancer.

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 patients, 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 are emerging as important causes 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. Clinical clues mechanisms to understand 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 facing 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 could 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 hor-

Targeting EGFR 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 all 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 pre-operative trial of gefitinib vs. gefitinib combined with anastrozole for 4 to 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 firstline endocrine therapy in postmenopausal women with ER positive metastatic breast cancer,33 with an increase in progression-free survival 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 vs. anastrozole alone in a similar first-line patient population of women with ER positive advanced breast cancer reported a prolongation of progression-free survival 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

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G. Curigliano / Cancer Treatment Reviews 38 (2012) 303–310 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 no. patients

Intervention

Clinical endpoints

References

Metastatic breast cancer

Phase II n = 15

Anastrozole and gefitinib

Mita et al.29

Phase II n = 150 Phase II randomized n = 206 Phase III randomized n = 207 Phase III randomized n = 219 Randomized phase II n = 150 Randomized phase II N = 206

Letrozole and gefitinib

Response rate No response No stable disease Clinical benefit 11/20 patients

Smith et al.31

Letrozole vs. letrozole plus lapatinib

Response rate 61% anastozole vs. 45% (combination arm) p = 0.067 PFS = 2.4 mo (anastrozole) vs. 4.8 mo (anastrozole plus trastuzumab) P = 0.0016 PFS = 3.0 mo (letrozole) vs. 8.2 mo (letrozole plus lapatinib)

Tamoxifen vs. tamoxifen plus gefitinib

PFS = 8.8 mo (tamoxifen) vs. 10.9 (tamoxifen plus gefitinib)

Osborne33

Anastrozole plus gefitinib vs. anastrozole

PFS = 14.6 mo (anastrozole plus gefitinib) vs. 8.2 (anastrozole)

Cristofanilli34

Early breast cancer Metastatic breast cancer Metastatic breast cancer Metastatic breast cancer

Anastrozole vs. gefitinib plus anastrozole Anastrozole vs. trastuzumab plus anastrozole

Mayer et al.30

Kaufman et al.37 Johnson et al.38

Abbreviations: PFS, progression free survival; mo, months.

randomised 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.

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.

Targeting HER2 pathway

Mammalian target of rapamycin (mTOR) inhibitors

A phase II clinical trial of letrozole and the monoclonal antibody trastuzumab in patients with ER+/HER2+ metastatic breast cancer 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+ metastatic breast cancer reported a better progression-free survival with the addition of trastuzumab over anastrozole alone (4.8 months vs. 2.4 months, P = 00.0016).37 Other trials have conducted with lapatinib, a potent oral tyrosine kinase inhibitor (TKI) of both EGFR and HER2. Lapatinib has been explored in combination with endocrine therapy within a phase III trial of 1286 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 reduced the risk of progression (hazard ratio 0.71, 95% CI 0.53–0.96, P = 0.019), improving the median progression-free survival form 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 co-expression of both receptors, the promising strategy of co-blockade has been delivered in the clinic with the recent approval of the combination of lapatinib with letrozole in HER2 positive metastatic breast cancer patients. Table 1 summarizes major clinical trials with anti-HER2 agents.

The first agents against the 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 a randomized phase II study 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 analog. The primary endpoint of the trial was response rate to the combination therapy.40 Response rate by clinical palpation in the everolimus arm was higher 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 < .01).40 In another trial in the metastatic setting patients (n = 109) were randomly assigned to receive 75 or 250 mg of temsirolimus (monoclonal antibody against mTOR) weekly.41 Patients were evaluated for tumor response, time to tumor progression, adverse events, and pharmacokinetics of temsirolimus. Temsirolimus produced an objective response rate of 9.2% (10 partial responses) in the intent-to-treat population. Median time to tumor progression was 12.0 weeks. Efficacy was similar for both dose levels but toxicity was more common with the higher dose level.41 Ridaforolimus (MK-8669) in combination to exemestane is actually under investigation in early clinical trials for ERpositive breast cancer progressing to non steroidal aromatase inhibitors.

Targeting phosphatidylinositol 3-kinase/AKT/mTOR signaling pathways in endocrine resistant breast cancer 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 development including monoclonal antibodies, tyrosine kinase inhibitors, PI3K inhibitors, Akt inhibitors, rapamycin analogs, and mammalian target of rapamycin (mTOR) inhibitors. Their development is based on the strategy of co-blockade; multiple signaling

PI3K Inhibitors Pan-PI3K inhibitors include GDC-0941 (Genentech Inc.), that is under investigation in a phase I-II clinical trial, in combination with endocrine therapy and mTOR inhibitors. The XL147 agent is a potent inhibitor of the Class I PI3K family. A phase I/II randomized study of letrozole and XL147 vs. letrozole and XL765 (Exelixis/Sanofi-Aventis), a dual mTOR and PI3K inhibitors, is also planned.

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Targeting histone deacetylase The use of de-methylating agents or histone deacetylase inhibitors can reactivate expression of a functional ER in cell lines in which ER silencing exists because of promoter methylation.42 Histone deacetylases (HDACs) are crucial components of the ER transcriptional 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 metastatic breast cancer progressing on endocrine therapy were treated with 400 mg of vorinostat (Merck & Co., Inc., White House Station, New Jersey) 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 (confidence interval: 8.1–12.4).43 Targeting Insulin-like growth factor receptor (IGF-1R) 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 cross talk 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 co-targeting the IGF-1R receptor along with antiestrogen 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 non steroidal aromatase inhibitors and randomized to exemestane vs. exemestane with figitumumab (Pfizer Inc), a fully humanized anti-IGR-1R antibody. In a recent randomized phase II study, the investigational agent AMG 479 (Amgen Inc), a fully human monoclonal antibody against the IGF-1R, failed to revert resistance to hormonal therapy in patients with endocrine therapy-resistant, ER positive metastatic breast cancer.47 Indeed, the drug showed a trend toward worse progression-free survival 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 progression-free survival of 3.9 months, compared with 5.7 months for patients on exemestane or fulvestrant alone (hazard ratio, 1.17; P = .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 metastatic breast cancer. Other trials are currently ongoing in hormone resistant breast cancer patents using TKIs targeting the IGF-1R pathway. Targeting Src family tyrosine kinase 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 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 this 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 (Sprycel, BMS354825;

Bristol-Myers Squibb Oncology). Dasatinib is a potent oral small molecule inhibitor of the Src tyrosine kinase. Another agent, bosutinib (SKI-606, Wyeth), 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 (AZD0530; AstraZeneca) and XL999 (Exelixis) 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 responseevaluable 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 metastatic breast cancer progressing to non steroidal aromatase inhibitors. Patients are randomized to exemestane plus dasatinib vs. 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 (Herceptin, Roche), 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 block57 or innate modulation of the immunological response.58 Identification of upregulated pathways may lead to development on new therapeutic targets that potentially overcome resistance to trastuzumab. Several agents are currently under development to overcome trastuzumab resistance. Trastuzumab-DM1 Genetech Inc., in collaboration with Roche, have recently developed trastuzumab-DM1 (a maytansine conijugated to trastuzumab, RG-3502, T-DM1) which is active on HER2 overexpressing breast cancer and also on trastuzumab-refractory tumors. Maytansinoids are very potent anticancer agents originally isolated from plant families: Celastraceae, Rhamnaceae and Euphorbiaceae and later from microorganism producing antibiotics (Actinosynneme pretiosum).59,60 They are 19-membered microcyclic lactams related to amsamycin. The maytansinoid DM1 is 100 to 1000 fold more potent that anticancer agents in clinical use.59,60 The maytansine DM1, which bind to microtubules in a manner similar to Vinca alkaloids, but is 20–100 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 metastatic breast cancer (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 (SD) at 6 months]) among 15 patients treated at MTD was 73%, including five objective responses.61 Phase II studies of T-DM1 in patients with HER-2 positive metastatic breast cancer who progressed while receiving HER-2-directed therapy (trastuzumab or lapatinib), or who were previously treated with several lines of

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Table 2 New targeted therapies for the treatment of trastuzumab resistant disease. Clinical setting

Trial phase no. patients

Intervention

Clinical endpoints

References

Metastatic breast cancer

Phase I n = 24 Phase II n = 112 Phase II randomised n = 79

Trastuzumab-DM1

Krop et al.61

Metastatic breast cancer

Phase II single arm

Trastuzumab plus pertuzumab

Metastatic breast cancer

Phase III single arm n = 136

Neratinib 240 mg/die Cohort 1: 66 pts prior trastuzumab Cohort 2: 70 pts first line

Clinical benefit rate at 3.6 mg/kg was 73% including 5 partial response Partial response 25.9% Median PFS = 4.6 mo Arm A: 2 pts PR 18 pts SD Arm B: SD 14 pts PFS = 5.5 mo PR = 24.2% Clinical benefit rate: 50% Cohort 1: 16 weeks PFS = 59% (22.3 weeks). PR: 24% Cohort 2: 16 weeks PFS = 78% (39.6 weeks); PR: 56%

Metastatic breast cancer

Trastuzumab-DM1 3.6 mg/kg Pertuzumab 420 mg (arm A) Pertuzumab 1050 mg (arm B)

Burris et al.62 Gianni et al.66

Baselga et al.67 Burstein et al.70

Abbreviations: PFS, progression free survival; PR, partial response; Patients, pts; Stable disease, SD; mo, months.

chemotherapy have demonstrated an objective response rate, by independent assessment, of 25.9% (95% CI, 18.4% to 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 progression-free survival time was 4.6 months (95% CI, 3.9 to 8.6 months).62 Several randomized clinical trial are actually ongoing in metastatic HER2 positive breast cancer patients. An openlabel, phase III trial (EMILIA) will compare the safety and efficacy of T-DM1 with that of capecitabine in combination with lapatinib in patients with HER-2 positive metastatic breast cancer previously treated with a trastuzumab-based therapy.63 Another first line trial (MARIANNE) is currently ongoing for the treatment of metastatic breast cancer.64 This randomized, 3-arm, multicentre study will evaluate the efficacy and safety of trastuzumab-DM1 with pertuzumab or T-DM1 with pertuzumab-placebo, vs. the combination of trastuzumab plus taxane (docetaxel or paclitaxel) in patients with HER2-positive progressive or recurrent locally advanced or previously untreated metastatic breast cancer (MBC). Patients will be randomized to 1 of 3 treatment arms (Arms A, B or C). Arm A will be open-label, whereas Arms B and C will be blinded.64 Pertuzumab 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 II randomized trial investigating the efficacy and safety of pertuzumab in patients with HER-2 positive MBC, the only measurable therapeutic benefit observed was a stable disease of a relatively short duration.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 patients withdrew as a result of cardiac-related adverse events. Recently the combination of pertuzumab and trastuzumab has been tested in patients with HER2 positive first diagnosed early breast cancer. The NEOSPHERE study (Neoadjuvant Study of Pertuzumab and Herceptin in an Early Regimen Evaluation) is a randomized multicentre 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 four study arms. The primary endpoint 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 HER2positive breast cancer, and suggest a potential application of the double targeting approach. Neratinib 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 Emerging agents for treatment of HER2 resistant tumors are reported in Table 2. 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. Targeting the poly-(adenosine diphosphate [ADP]-ribose) polymerases (PARPs) pathway DNA lesions such as single-strand breaks (SSBs) and doublestrand breaks (DSBs) 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 repair (NER), (c) mismatch repair (MMR), and (d) recombinational repair (with homologous recombination and

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Table 3 New targeted therapies for the treatment of triple negative breast cancer. Clinical setting

Trial phase no. patients

Intervention

Clinical endpoints

References

Metastatic BRCA1 and BRCA2 mutated breast cancer patients

Phase I n = 60 22 mutation carrier Phase II N = 54 Cohort 1: 27 Cohort 2: 27 Phase II randomised n = 123

Olaparib 200 mg twice daily in mutation carried

Objective antitumor activity was reported only in mutation carriers

Fong et al.72

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%

Tutt et al.74

Iniparib 5.6 mg/kg plus carboplatin/ gemcitabine vs. Carboplatin/ gemcitabine Veliparib 40 mg twice daily plus temozolomide

Overall response rate 52% in iniparib arm vs. 32 in chemotherapy arm (p = 0.01). Median PFS: 5.9 mo vs. 3.6 mo. (p = 0.01); OS: 12.3 mo vs. 7.7 mo (p = 0.01)

O’Shaughnessy et al.76

Overall response rate = 7% PR in BRCA1/2 mutated: 37.5%

Isakoff et al.79

Metastatic triple negative breast cancer patients

Metastatic breast cancer

Phase II single arm n = 41

Abbreviations: PFS, progression free survival; PR, Partial response; Patients, pts; Stable disease, SD; mo, months; OS, Overall survival.

nonhomologous end joining [NHEJ]).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, PARP1, is the most important member of the PARP family of enzymes.72,73 PARP inhibition leads to accumulation of DNA single-strand breaks 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 ER-negative, progesterone receptor-negative (PR negative), HER2-negative (ductal triple negative). Preclinical studies of in vitro activity of PARP inhibitors demonstrated inhibition of tumor cell growth only if the cell was BRCA-deficient.73 Inhibition of PARP to kill tumor cells selectively, therefore, is a novel approach to cancer therapy (Table 3). Olaparib Olaparib, a novel, orally active poly-(ADP-ribose) polymerase (PARP) inhibitor, induced synthetic lethality in BRCA-deficient 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 six (22%) of 27 (11–41) in the cohort assigned to 100 mg twice daily.74 The results of this study provide positive proof of concept for PARP inhibition in BRCA-deficient breast cancers and shows a favorable therapeutic index for a novel targeted treatment strategy in patients with tumors that have genetic loss of function of BRCA1-associated or BRCA2-associated DNA repair. 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 triple-negative breast cancer (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.

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 II 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 triple-negative breast cancer, was conducted. A total of 123 patients were randomly assigned to receive gemcitabine (1000 mg per square meter of 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 per kilogram of 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 P6 months) and safety. Additional end points included the rate of objective response, progression-free survival, 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 progression-free survival from 3.6 months to 5.9 months (hazard ratio for progression, 0.59; P = 0.01) and the median overall survival from 7.7 months to 12.3 months (hazard ratio for death, 0.57; P = 0.01).76 Another large randomized trial included 519 women with metastatic triple negative breast cancer. Patients were randomized to receive a standard chemotherapy regimen (gemcitabine and carboplatin) on days one and eight of each 21-day cycle, with or without iniparib 5.6 mg/kg, which was administered on days one, four, eight 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 co-primary endpoints were overall survival and progression-free survival.77 SanofiAventis announced that the trial did not meet the pre-specified

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criteria for significance for co-primary endpoints of overall survival and progression-free survival. Veliparib Veliparib (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 triple negative breast cancer.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 metastatic breast cancer.79 Patients received veliparib (40 mg twice daily days 1–7) and oral temozolomide (150 mg/m2/d 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 progression-free survival, clinical benefit rate and safety and tolerability. Of the 41 patients, 23 had triple negative breast cancer. 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% (four 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 Conclusion 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 may be inappropriate for new targeted agents. Resistance to many of traditional and new drugs is a major clinical challenge. The use of high-throughput technologies will help us to understanding the molecular biology of signaling pathways as the roads of the ‘‘genomic landscape’’ of breast cancer. The number of potential driver genes is large, even if more limited is the number of ‘‘driver’’ pathways. Patient selection, rational combination therapies, surrogate markers identification and tumor tissue banking will be key areas of research. Conflict of interest Author has no conflict of interest to declare. References 1. Perou CM, Sorlie T, Eisen MB, et al. Molecular portraits of human breast tumours. Nature 2000;406:747–52. 2. Prat A, Perou CM. Deconstructing the molecular portraits of breast cancer. Mol Oncol 2011;5:5–23. 3. Parker JS, Mullins M, Cheang MCU, et al. Supervised risk predictor of breast cancer based on intrinsic subtypes. J Clin Oncol 2009;27:1160–7. 4. Nielsen TO, Hsu FD, Jensen K, et al. Immunohistochemical and clinical characterization of the basal-like subtype of invasive breast carcinoma. Clin Cancer Res 2004;10:5367–74. 5. Blows FM, Driver KE, Schmidt MK, et al. Subtyping of breast cancer by immunohistochemistry to investigate a relationship between subtype, short, long term survival: a collaborative analysis of data for 10, 159 cases from 12 studies. PLoS Med 2010;7:e1000279. 6. Hugh J, Hanson J, Cheang MC, et al. Breast cancer subtypes and response to docetaxel in node-positive breast cancer: use of an immunohistochemical definition in the BCIRG 001 trial. J Clin Oncol 2009;27:1168–76.

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