4CAST: A phase 1b dose exploration, open-label, single-center study evaluating the safety of INO-464 in combination with chemotherapy in patients with metastatic breast cancer.

Abstract

e13112 Background: Metastatic triple negative breast cancer (TNBC) has a poor prognosis and the development of new targeted therapies is an area of unmet need. The androgen receptor (AR) antagonist, INO-464, but not abiraterone or enzalutamide, blocks chemotherapy induced cell plasticity to inhibit and primary and metastatic breast cancer (MBC) growth. Single agent INO-464 at a dose of 450mg/d is well tolerated but has low efficacy. Laboratory data demonstrates suppression of metastatic TNBC and an increase in survival with the combination of INO-464 and taxane chemotherapy. Methods: We designed a Phase 1b open-label, single center dose exploration (Part 1) and dose expansion (Part 2) clinical trial of INO-464 450mg/d with docetaxel (IV 75mg/m2 q3wkly) or nab-paclitaxel (IV 100mg/m2 D1/8/15 q4wkly) in any subtype of MBC. The primary objective was to assess the safety and tolerability of INO-464 (450mg/d) and docetaxel or nab-paclitaxel utilizing a rolling 6 design, as well as to determine the maximum tolerated dose (MTD) and the recommended dose of INO-464 to be given with a taxane in the dose expansion study. Secondary objectives included anti-tumor activity and testosterone levels. Results: Recruitment began in August 2022. The cut-off date for this analysis was 19 January 2024. Eight patients have been treated to date and 6 patients were DLT evaluable. All were women with MBC with mean age of 56 (range 48-64) years. Patients had received a median of 5 (range 2 to 7) lines of chemotherapy for MBC. Patient 001 had G3 anaphylaxis due to docetaxel that resolved with adrenaline but came off study and was not DLT evaluable. The protocol was amended to give INO-464 with 1mg of dexamethasone. No DLTs were subsequently observed. Adverse events (AEs) were mostly low grade and chemotherapy related although G2 pneumonitis occurred beyond the DLT period in two patients, one of whom had prior sacituzimab govotecan-related pneumonitis. INO-464-related AEs were G1 fatigue/headache in 4/6 patients. Seven of seven patients had a best response (RECIST1.1) SD, and CA15.3 stability was seen in 4/7 patients. Baseline serum testosterone was detectable in 4/6 patients (range 0.5-1.3 nmol/L, lower limit of detection of <0.5), and remained undetectable or at the lower limit of detection throughout treatment. Conclusions: The MTD of INO-464 is 450mg daily with 0.5mg dexamethasone in combination with docetaxel or nab-paclitaxel chemotherapy. The combination is well tolerated with early efficacy signals. Dose expansion will test the combination in metastatic TNBC with nuclear AR positive breast cancer. Clinical trial information: NCT04947189 .