A phase 1, multi-center, open-label, dose-escalation and dose expansion study of CBP-1018, a bi-ligand-drug conjugate, in patients with heavily treated advanced solid tumors.

Abstract

e15007 Kaiwen Li and Junyan Wu contributed equally to this work. Yehui Shi and Hai Huang are the corresponding authors. Background: Prostate-specific membrane antigen (PSMA) or folate hydrolase 1 (FOLH1) is highly expressed on prostate cancer and folate receptor α (FRα) overexpressed in various malignant tissues which both related to tumor invasiveness. CBP-1018 is a first-in-class bi-ligand-drug conjugate targeting both PSMA and FRα with monomethyl auristatin E (MMAE) as payload. Methods: This phase 1 study included both a dose-escalation and expansion stage. In the dose-escalation stage, an accelerated titration was conducted in single patient at 0.03mg/kg followed by an i3+3 design for dose levels (DLs) ≥ 0.06 mg/kg, Q2W in a 4-week cycle. This stage mainly enrolled patients (pts) with metastatic castration resistant prostate cancer (mCRPC) received a median 3.5 prior lines of treatment. The primary objectives were to evaluate the safety and tolerability, determine dose limiting toxicity (DLT) and maximum tolerated dose (MTD). Additionally, pharmacokinetics (PK) and preliminary efficacy will also be evaluated. Results: As of 24 Nov 2022, 14 pts (12 mCRPC, 1 bladder cancer and 1 ureteral carcinoma) were enrolled at 5 DLs (1 pt at 0.03 mg/kg, 3 pts each at 0.06, 0.08, 0.10 mg/kg, 4 pts at 0.12 mg/kg). No DLTs or drug-related deaths were observed. For 9 pts (64.3%) experienced treatment-related adverse events (TRAEs) ≥ grade 3, most common were neutrophil decrease (35.7%), WBC decrease (28.6%), lymphocyte decrease (14.3%), elevated GGT (14.3%) and hypertriglyceridaemia (14.3%). Among 10 efficacy evaluable pts with mCRPC, 3 SD were observed at DLs of 0.08, 0.10, and 0.12mg/kg, 4 non-PD at 0.06, 0.10, and 0.12 mg/kg, and 3 PD at 0.06 and 0.08 mg/kg. Decrease of prostate-specific antigen (PSA) was detected in 3 pts at 0.10 mg/kg. Overall median PFS was 7.2 months (95%CI, 1.7-9.3) and not reached in mCRPC pts. For PK profile of CBP-1018 and free MMAE, t1/2z was ranged 0.54-1.15 h and 40.28-57.27 h, respectively, no accumulation of both substances after multiple doses. Conclusions: CBP-1018 was well-tolerated at DLs of 0.03-0.12 mg/kg Q2W with no DLTs. Multiple SD were observed at DLs of 0.08-0.12 mg/kg, conferred a promising preliminary antitumor activity in pts with mCRPC. MTD was not reached and dose-escalation to establish the RP2D is continuing. Clinical trial information: NCT04928612 .