Abstract OT2-01-03: A phase 1/2 study of once-daily oral VT-464 in patients with advanced androgen receptor (AR) positive triple negative (TNBC) or estrogen receptor (ER) positive breast cancer (BC)

Abstract

Abstract VT-464, an oral dual lyase-selective CYP17 inhibitor and AR antagonist (wild-type and mutated forms [e.g., F876L and T877A]), is in multiple Phase (Ph) 2 studies as treatment for men with castration-resistant prostate cancer (CRPC). VT-464 inhibits the growth of multiple BC cell lines in vitro including MCF7 (ER(+)/AR low), tamoxifen-resistant MCF7, and MDA-MB-453 (ER(-)/AR(+)) in a dose-dependent manner and with greater potency/efficacy than enzalutamide (submitted, Ellison et al., 2015). A subset of TNBC and most ER(+) BC express AR, making them potential targets for VT-464 since it directly inhibits both androgen/estrogen synthesis and AR transcriptional activity. Objectives: The primary objective of Ph 1, now enrolling, is to establish the once-daily dose of VT-464 in women. Secondary objectives include safety, PK and efficacy endpoints, including determination of clinical benefit rate (CBR) which is the primary objective of Ph 2. Exploratory objectives include the determination of the extent of AR expression and signaling in breast tissue and to evaluate the relationship of expression with VT-464 effects on circulating tumor biomarkers, circulating hormones and clinical outcomes. Study Design: This study is an open-label, single arm, Ph 1/2 study of VT-464 in women with AR(+) TNBC or ER(+)/HER2 normal unresectable locally advanced or metastatic BC. Ph 1 will follow a modified 3+3 Fibonacci design with cohort expansion to 6 patients following a single DLT in the first 28-days of treatment. Approximately 2-3 dose-levels will be explored in Ph 1. Ph 1 start dose will be the MTD for men with CRPC. AR(+) TNBC and ER(+)/HER2 BC cohorts will be expanded in Ph 2 using the MTD from Ph 1. Ph 2 will follow a Simon's two-stage design with pre-determined futility parameters. Eligible patients will have ER≥1% BC or AR≥1% (as determined by central IHC testing using the Dako antibody) TNBC. ER(+) patients must be postmenopausal and must have received at least 1 prior line of endocrine therapy. Additional eligibility criteria include: ≥ 18 years of age, ECOG PS ≤ 1, unresectable locally advanced or metastatic BC, available representative tumor specimen to enable correlative science. Treatment Plan: Eligible patients will receive VT-464 once-nightly with dinner in a continuous dosing schedule. Adverse events and concomitant medications will be collected from the time of signing of informed consent until 30 days after end of study visit (EOS). Safety labs will be monitored monthly through EOS. Dense PK will be collected after the first dose of study drug in Ph 1 and single morning samples collected approximately every two cycles thereafter in Ph 1 and Ph 2 until EOS. Blood samples for steroids, circulating tumor DNA and circulating tumor cells will be collected through Cycle 2 and then at EOS. Tumor biopsy will be collected at baseline and at disease progression. Radiographic response will be assessed every 8 weeks and EOS. Patient Accrual: Accrual is ongoing with 12-18 patients expected to be enrolled in Ph 1. Citation Format: Gucalp A, Hudis C, Norton L, Patil S, Kurman MR, Eisner JR, Moore WR, Traina TA. A phase 1/2 study of once-daily oral VT-464 in patients with advanced androgen receptor (AR) positive triple negative (TNBC) or estrogen receptor (ER) positive breast cancer (BC). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr OT2-01-03.