First-in-human, phase I study of CBP-1008, a first-in-class bispecific ligand drug conjugate (Bi-XDC), in patients with advanced solid tumors.

5556 Background: Folate receptor α (FRα) and vanilloid subfamily member 6 of transient receptor potential channels (TRPV6) are potential promising therapeutic targets due to their high expression level in many solid tumors including ovarian cancer. CBP-1008 is a first-in-class bi-specific ligand drug conjugate targeting FRα and TRPV6 carrying monomethyl auristatin E (MMAE) as payload and is administered by intravenous infusion Q2W. Methods: This phase 1 study includes the dose-escalation of Ia and the dose-expansion of Ib. The phase Ia started with accelerated titration (0.015, 0.03mg/kg) and then switched to 3+3 design (0.12, 0.15, 0.17, 0.18, 0.20mg/kg). Phase Ib dose-expansion study includes 4 cohorts, platinum-resistant high-grade serous ovarian cancer (HGSOC), other sub-types of ovarian cancer such as clear cell ovarian cancer (OCCC) and low-grade serous ovarian cancer, metastatic triple negative breast cancer (TNBC) and other solid tumors. The primary objective is to assess the safety and preliminary efficacy. Results: As of December 8, 2023, 240 patients (phase Ia: n=40; phase Ib: n=200) have been enrolled including 136 HGSOC,17 OCCC, 24 TNBC and 63 other tumor types. Majority of adverse events were mild to moderate. Common (≥50%) treatment-related AEs (TRAEs) were neutropenia, WBC decreased, AST increased, pyrexia, ALT increased and nausea. Grade 3/4 TRAEs (≥5%) were neutropenia (49%), WBC decreased (26.8%), AST increased (5.9%), ALT increased (5.9%), anaemia (5.4%). 41 HGSOC patients at dose of 0.15mg/kg with ≤3 prior treatment regimens, regardless of FRα expression levels were evaluable for efficacy assessment. 13 patients achieved partial response (PR) and 29 patients achieved stable disease (SD). The objective response rate (ORR) and the disease control rate (DCR) were 31.7% and 70.7%, respectively. For 19 patients with FRα expression level 0 to 49%, 6 patients achieved PR and ORR was 31.6%. The longest treatment duration exceeds 13 months. Conclusions: The current result showed that CBP-1008 demonstrated manageable safety profile. Promising antitumor activity was observed in ovarian cancer patients at dose of 0.15mg/kg, especially in platinum-resistant HGSOC patients with ≤3 prior treatment regimens. CBP-1008 has the potential to provide a better treatment option for ovarian cancer patients regardless of FRα expression levels. Clinical trial information: NCT04740398 .