CTX-009 (ABL001), a bispecific antibody targeting DLL4 and VEGF A, in combination with paclitaxel in patients with advanced biliary tract cancer (BTC): A phase 2 study.

540 Background: CTX-009 is a novel bispecific antibody that simultaneously inhibits Delta-like ligand 4/Notch-1 (DLL4) and VEGF A, two signaling molecules which play an important role in angiogenesis in the tumor microenvironment. DLL4 is induced by VEGF and acts to the downstream of VEGF, and synergistic effect for dual blockade of both DLL4 and VEGF was evaluated in preclinical models. A phase 1b study assessed the safety, tolerability, pharmacokinetics and efficacy of CTX-009 in combination with paclitaxel or irinotecan in patients (pts) with advanced solid tumors. Encouraging results in the Phase 1b in BTC pts, including two durable Partial Responses (PRs) out of 3 pts, prompted the expansion of the study to include a Phase 2 cohort in which BTC pts are treated in 2L or 3L setting. We present preliminary results from this Phase 2 study. Methods: This open-label, multi-center, single-arm Phase 2 study investigated pts with unresectable advanced, metastatic or recurrent BTC in advanced 2L or 3L setting. Eligible pts were treated with CTX-009 (10 mg/kg IV biweekly) in combination with paclitaxel (80 mg/m 2 IV on Day 1, 8, 15 q4-weekly). The primary objective was to assess the objective response rate (ORR) based on RECIST v1.1. Secondary endpoints included time to treatment failure (TTF), duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety. Results: Overall, 24 pts have been enrolled (IHCC: 9, EHCC: 3, GB: 7, AoV: 5) and as of the data cut-off date (August 12, 2022), the median follow-up duration was 11.8 months (m) (range: 1.6-16.4) and 3 pts remained on treatment. 11 pts were treated in 2L and 13 pts treated in 3L. There were 9 confirmed PRs by investigator’s assessment and ORR was 37.5% (95% CI: 18.8-59.4; 2L: 63.6%, 3L: 15.4%). Median DOR and PFS were 9.4 m (95% CI: 3.5–NE) and 9.4 m (95% CI: 5.4-11.1), respectively. Median TTF was 5.9 m (95% CI: 3.9-9.8) and median OS has not been reached (95% CI: 11.0–NE); the OS rate at 12 m was 53.0% (95% CI: 29.8–71.7). Treatment-related adverse events (TRAEs) of any grade were reported in 100% of pts and TRAEs of ≥ grade 3 were reported in 75% of pts (including one grade 5 pneumonia). The most frequent TRAEs of ≥ grade 3 were neutropenia (50.0%), hypertension (16.7%), anemia (12.5%), and thrombocytopenia (8.3%). Six pts (25.0%) experienced treatment-emergent AEs (confusional state, pulmonary embolism, blood creatinine increased, pneumonia, biliary fistula, and large intestine perforation) that led to discontinuation of the study treatment. Conclusions: This Phase 2 study has shown promising efficacy in BTC pts treated in 2L or 3L setting. TRAE rate based on mode of action was high, but DLL4/VEGF targeting in BTC has a potential of development. Further investigation of safety and efficacy of this regimen is warranted. Clinical trial information: NCT04492033 .