Efficacy and safety of talazoparib (TALA) or physician's choice of therapy (PCT) in United States patients (pts) with HER2- germline BRCA1/2-mutated (gBRCAm) locally advanced/metastatic breast cancer (LA/MBC) in the EMBRACA study

1044

Background: TALA is a poly(ADP-ribose) polymerase (PARP) inhibitor approved in the US for HER2- g BRCAm LA/MBC. Approval was based on results from the Phase 3 EMBRACA trial comparing efficacy/safety of TALA (1 mg/d) to PCT (capecitabine, eribulin, gemcitabine, vinorelbine) in HER2- g BRCAm LA/MBC pts. This analysis describes outcomes in US pts included in the pivotal study. Methods: Clinical findings from US pts enrolled in EMBRACA were analyzed. Pt characteristics, progression-free survival (PFS), objective response rate (ORR), clinical benefit rate (CBR), and safety/adverse events (AEs) were among the parameters assessed. Results: Of 431 randomized pts, 156 pts (36%) were from the US (TALA: 99; PCT: 57). Pt characteristics were balanced, although a higher percentage in the TALA arm had more poor prognostic features (eg, triple-negative breast cancer, disease-free interval < 12 mo, and more disease sites). TALA improved PFS, ORR, CBR, and duration of response (DOR) vs PCT (Table). 22% of pts in the TALA arm had a continued objective response at month 12 vs 0 pts in the PCT arm. The most common AEs in the TALA arm included anemia, neutropenia, thrombocytopenia, fatigue, nausea, alopecia, and headache; hematologic grade 3/4 AEs occurred more often than nonhematologic AEs. Conclusions: In US pts with HER2- g BRCAm LA/MBC, TALA demonstrated significant improvements in outcomes vs PCT with a manageable safety profile. Clinical trial information: NCT01945775. [Table: see text]

Clinical and safety outcomes of TALAPRO-2: A two-part phase III study of talazoparib (TALA) in combination with enzalutamide (ENZA) in metastatic castration-resistant prostate cancer (mCRPC)

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Background: TALA is a dual-mechanism PARP inhibitor that inhibits PARP catalytic activity and traps PARP on DNA. ENZA is a novel hormonal therapy approved to treat castration resistant prostate cancer. TALA + ENZA may improve clinical outcomes for men with mCRPC. However, TALA, is a substrate for efflux drug transporters P-gp and BCRP. Prior to the initiation of TALAPRO-2 part 1, the in vivo effect of ENZA on exposure of P-gp and BCRP substrates, such as TALA, had not been evaluated. Methods: TALAPRO-2 part 1 was designed to determine TALA starting dose based on safety and pharmacokinetics (PK) evaluation of TALA + ENZA. Pts were ≥18 yrs of age, had ECOG PS ≤1, with no prior systemic treatment for mCRPC. The starting dose of TALA in the first 13 pts was 1 mg once daily (QD) + ENZA 160 mg QD (1 mg QD cohort). Based on safety review of prespecified target safety events and PK data, TALA dose was reduced to 0.5 mg QD; additional pts were treated with a starting dose of TALA 0.5 mg QD + ENZA 160 mg QD (0.5 mg QD cohort). Results: 19 pts were enrolled in part 1 (1 mg QD cohort, 13; 0.5 mg QD cohort, 6). The median (range) age was 71 yrs (52-82). As of the analysis cutoff date, the median treatment duration was 25 and 11 wks for the 1 mg QD and 0.5 mg QD cohorts, respectively. Treatment-emergent adverse events (TEAEs) occurred in 19 pts. The most common TEAE, anemia, occurred in 76.9% and 33.3% of pts in the 1 mg QD and 0.5 mg QD cohorts, respectively. TEAEs that led to TALA dose reduction occurred in 6 pts (46.2%) and 0 pts in the 1 mg QD and 0.5 mg QD cohorts, respectively. In the 1 mg QD cohort, target safety events were reported for 7 pts (53.8%) vs 0 in the 0.5 mg QD cohort. 92% and 100% of pts had a 50% decline from baseline in PSA in the 1 mg QD and 0.5 mg cohorts, respectively, demonstrating preliminary anti-tumor activity. PK data showed that ENZA increased TALA exposure and that TALA 0.5 mg QD + ENZA maintained similar TALA exposure to that achieved with 1 mg QD monotherapy. Conclusions: TALA 0.5 mg QD + ENZA 160 mg QD had a manageable safety profile in pts with mCRPC and will be the starting dose for the randomized portion of TALAPRO-2. Clinical trial information: NCT03395197.

TALAPRO-2: Part 2 (P2) of the placebo-controlled phase 3 study of talazoparib (TALA) with enzalutamide (ENZA) in metastatic castration-resistant prostate cancer (mCRPC)

TPS5092

Background: ENZA is approved to treat men with CRPC. TALA is a poly(ADP-ribose) polymerase (PARP) inhibitor that inhibits PARP1/PARP2 and traps PARP on DNA, preventing DNA damage repair (DDR), and causing cell death in BRCA1/2-mutated cells. TALA is approved in the US to treat germline BRCA1/2-mutated HER2- locally advanced/metastatic breast cancer. A combination of TALA with ENZA in mCRPC may improve clinical outcomes. TALAPRO-2 (NCT03395197) is a 2-part study to evaluate the efficacy, safety, pharmacokinetics and (patient) pt-reported outcomes of the combination treatment. The focus here is on P2 of TALAPRO-2. Methods: Approximately 860 pts are planned to be enrolled in P2 from multinational sites. Pts are aged ≥18 years, have asymptomatic/mildly symptomatic mCRPC, Eastern Cooperative Oncology Group performance status ≤1, no brain metastases, and have not received taxanes/novel hormonal therapy (NHT). P2 is a randomized double-blind study that will evaluate safety, efficacy, and pt-reported outcomes of TALA (0.5 mg QD) + ENZA (160 mg QD) vs placebo + ENZA (160 mg QD). Pts will be randomized to 1 of 2 treatment groups: TALA + ENZA, or matching placebo + ENZA. Randomization will be stratified by prior treatment with NHT for castration-sensitive prostate cancer (CSPC) or prior treatment with taxane-based chemotherapy for CSPC (yes/no) and DDR mutation status (deficient vs. nondeficient/unknown). The primary endpoint is radiographic progression-free survival (rPFS), defined as time to progression in soft tissue per RECIST v1.1 or in bone per PCWG3 criteria or death. The key secondary endpoint is overall survival (OS). Efficacy will be assessed by radiography every 8 weeks up to week 25 and every 8-12 weeks thereafter. The analyses of rPFS will be compared between TALA in combination with ENZA and placebo in combination with ENZA by using a 1-sided stratified log-rank test. OS will be evaluated separately in the all comers and the DDR-deficient populations. Pt recruitment is ongoing. Results: n/a. Conclusions: n/a. Clinical trial information: NCT03395197.

Outcomes of talazoparib (TALA) versus physician's choice of chemotherapy (PCT) in patients (pts) with advanced breast cancer (ABC) and a germline BRCA (gBRCA) mutation by line of chemotherapy (CT) in the EMBRACA trial

1071

Background: The PARP inhibitor TALA was approved in the US for treatment of g BRCA-mutated ABC based in part on the EMBRACA study. Understanding the outcomes of EMBRACA pts relative to prior CT is a current unmet need. Methods: EMBRACA was a randomized Phase 3 trial comparing TALA 1 mg daily vs PCT (capecitabine, eribulin, gemcitabine, vinorelbine) in g BRCA-mutated ABC. Clinical outcomes were assessed by line of prior CT for ABC in intent-to-treat (ITT), triple-negative breast cancer (TNBC), and hormone receptor-positive (HR+) breast cancer cohorts. Results: 431 pts were randomized (ITT; TALA 287; PCT: 144). TALA was generally more effective than PCT across efficacy endpoints regardless of line of CT (Table). For the ITT population, TALA improved progression-free survival (PFS) and objective response rate (ORR) vs PCT for each line of CT assessed. Other prespecified subgroups (TNBC and HR+) will be presented. Conclusions: In pts with g BRCA-mutated ABC, TALA demonstrated improvements in clinical outcomes compared with PCT regardless of prior lines of CT. Clinical trial information: NCT01945775. [Table: see text]

First-in-human study of MM-141: A novel tetravalent monoclonal antibody targeting IGF-1R and ErbB3

384

Background: MM-141 is a novel tetravalent bispecific monoclonal antibody that binds IGF-1R and ErbB3 and blocks both ligand dependent and independent IGF-1R/ErbB3/PI3K/AKT/mTOR signaling. MM-141 potentiated gemcitabine, nab-paclitaxel, docetaxel, irinotecan, tamoxifen, and everolimus in preclinical models. A multi-arm Phase 1 study is ongoing and the monotherapy dose-escalation portion of the study is completed. Hepatocellular carcinoma (HCC) patients were enrolled to an expansion cohort of Arm A to receive MM-141 as a monotherapy. Another arm of treatment combined MM-141 with gemcitabine and nab-paclitaxel. Methods: This is a Phase 1 dose-escalation study evaluating safety, tolerability, pharmacokinetic (PK), and pharmacodynamic (PD) properties of MM-141 as monotherapy (n=15) and in combination with everolimus (Arm B) or with nab-paclitaxel and gemcitabine (Arm C). Three HCC patients in the Arm A expansion cohort received MM-141 as a monotherapy at a weekly dose of 20 mg/kg. These patients underwent mandatory pre-treatment and optional post-treatment biopsies. Patients in the dose-escalation portion of Arm C received MM-141 at a weekly dose of 12 or 20 mg/kg or a bi-weekly dose of 40 mg/kg in combination with gemcitabine (1000 mg/m2) and nab-paclitaxel (125 mg/m2). Results: 15 patients with advanced solid tumors were enrolled into the dose escalation portion of Arm A. No dose-limiting toxicities were observed at any of the studied doses. The safety, tolerability, PK and PD profile support weekly and bi-weekly MM-141 dosing. The Arm A expansion enrolled 3 patients with sorafenib-refractory HCC. The analysis of pre- and post-treatment biopsies confirmed that IGF-1R and ErbB3 are expressed in patients previously exposed to sorafenib, and their levels are decreased after MM-141 exposure. Arm C, combining MM-141, gemcitabine, and nab-paclitaxel in a “3+3” dose-escalation design is on-going. Conclusions: MM-141 was well tolerated as a monotherapy and translational analysis of pharmacodynamic parameters suggest appropriate target engagement. Combination data with gemcitabine/nab-paclitaxel will be presented and preparations for a randomized Phase 2 study in front-line pancreatic cancer are underway. Clinical trial information: NCT01733004.

HER3 as a potential prognostic biomarker in pancreatic cancer

295

Background: HER 3 is revealing itself to be increasingly important in HER family signaling. Understanding the role of HER 3 in pancreatic cancer may shed light on targeted therapy development. Methods: A large human pancreatic cancer tumor tissue microarray (TMA) was established at our institution from 165 patients with pancreatic cancer who underwent surgical resection. The TMA contains two cores from each patient. Clinical information of these patients has been prospectively maintained in a clinical database. Immunohistochemistry (IHC) was performed on the TMA using a monoclonal antibody against HER 3. An independent pathologist blinded to the patient data applied the H score to grade the expression level of HER 3. The association between expression levels of HER 3 and survival were evaluated by the Kaplan-Meyer product limit method and log-rank test, while the optimal cut-off for each marker was determined using the Martingale residuals from Cox proportional hazard models. Results: Out of 165 patients, 136 patients’ tumors were identified to have adequate tumor content for IHC analysis. The group with higher HER 3 levels at the cell membrane (n=50)(H score ≥150) had a superior overall survival compared to the low HER 3 membrane expression group (n=86) (22.5 months vs. 17 months; p=0.036). Interestingly, the group with higher expression levels at both the cell membrane and in the cytosol (n=37) (H score ≥190) had a more striking survival difference compared to the lower group (n=99) (26 months vs. 15 months; p= 0.035). Conclusions: Patients with high HER 3 expression either at the cell membrane only or at both the membrane and in the cytosol have longer survival, perhaps indicating a lower heregulin and inactive HER 3 signaling. Additional biomarker analyses are ongoing. The functional role of HER 3 in pancreatic cancer is being further explored to assist clinical evaluation of HER 3 targeting in pancreatic cancer.

Effect of MM-141 on gemcitabine and nab-paclitaxel potentiation in preclinical models of pancreatic cancer through induction of IGF-1R and ErbB3 degradation

289

Background: Gemcitabine, the first-line treatment for pancreatic cancer, has been improved by addition of nab-paclitaxel. However, patient response to this regimen is limited. Oncogenic insulin-like growth factor 1 (IGF-1) and heregulin (HRG) signaling are associated with increased cancer risk and decreased response to anti-metabolites and taxanes. Therefore, we explored MM-141, a novel bispecific antibody that blocks ErbB3 and IGF-1 receptor (IGF-1R) signaling, in combination with nab-paclitaxel and gemcitabine in preclinical models of pancreatic cancer. Methods: Combinations with MM-141, gemcitabine, and nab-paclitaxel were investigated in pancreatic cancer cell lines, in vitro and in vivo. The effects of MM-141, gemcitabine, and nab-paclitaxel on tumor growth and signaling were measured by 3D spheroid growth, ELISA, Western, and mouse xenograft experiments. Results: In vitro studies show that IGF-1 and HRG are potent activators of AKT signaling, leading to increased pancreatic tumor cell proliferation and decreased sensitivity to gemcitabine and nab-paclitaxel. MM-141 inhibits ligand-induced AKT activation, induces IGF-1R and ErbB3 degradation better than a mixture of IGF-1R and ErbB3 antibodies, and sensitizes cells to gemcitabine and nab-paclitaxel, in vitro. In vivo, MM-141 combines favorably with a nab-paclitaxel/gemcitabine regimen, leading to curative outcomes in a subset of treated mice. Conclusions: ErbB3 and IGF-1R co-inhibition is required to inhibit AKT signaling in pancreatic adenocarcinoma cell lines. These receptors are associated with chemoresistance to gemcitabine and nab-paclitaxel, which is abrogated by co-administration with MM-141. MM-141-induced degradation of oncogenic receptor complexes is likely essential to reverse chemoresistance and enhance effects of the nab-paclitaxel/gemcitabine regimen. These data, taken together with wide-spread expression of IGF-1R and ErbB3 in Stage IV pancreatic adenocarcinoma tissue, support clinical exploration of a MM-141/nab-paclitaxel/gemcitabine regimen in frontline metastatic pancreatic cancer. Preparations for a randomized Phase 2 study are underway.

A phase I study of MM-121 in combination with multiple anticancer therapies in patients with advanced solid tumors

2609

Background: MM-121 is a fully human monoclonal antibody targeting the epidermal growth factor receptor family member ErbB3. ErbB3 has been implicated in driving cancer growth and in the development of resistance to conventional chemotherapies across multiple malignancies. Here we present results of an open-label, Phase 1, multicenter, non-randomized, dose-escalation trial which recently completed enrollment evaluating MM-121 in combination with one of the following chemotherapies: Gemcitabine (Arm A, n=11), carboplatin (Arm B, n=11), pemetrexed (Arm C, n=10), or cabazitaxel (Arm D, n=11). Methods: Patients were treated in a dose escalation “3+3” design to assess the safety, tolerability and pharmacokinetics (PK) of MM-121 administered weekly in combination with anticancer therapies in subjects with advanced cancer. Doses were escalated until the maximum tolerated dose (MTD) was identified or the combination was shown to be tolerable at the highest planned doses. Secondary objectives included: Determining the objective response rate, clinical benefit rate, PK and immunogenicity of MM-121. Data summarized are as of 1/17/2013 from a live database. Results: Overall, 43 patients, [22 (51%) female and 21 (49%) male] have been treated with a median treatment duration of 57 days (range 1-302). The median age was 59 years (range 42-84) and patients had received a median of four prior lines of therapy (range 0-13). Common (>20%) adverse events of any grade and causality across all arms included diarrhea (74%), nausea (54%), fatigue (51%), anemia (44%), vomiting (33%), hypokalemia (30%), decreased appetite (26%), thrombocytopenia (26%), peripheral edema (23%), neutropenia (21%), and constipation (21%). Four DLTs were observed: Two in combination with carboplatin (G4 thrombocytopenia and G3 rash), one with gemcitabine (G4 thrombocytopenia), and one with pemetrexed (G4 hyperuricemia). Overall 38 (88%) patients were evaluable for response and the overall clinical benefit rate (PR or SD >18 weeks), is 32% (12/38). Conclusions: MM-121 can be combined at its recommended single agent dose with standard doses of gemcitabine, pemetrexed, and cabazitaxel and adapted doses of carboplatin. Clinical trial information: NCT01447225.