Pilot study of CBX-12 pharmacodynamics in patients with advanced solid tumors.

Abstract

TPS3187 Background: Topoisomerase 1 (TOP1) inhibitors effectively kill a diverse range of tumor cells but have limited clinical utility due to severe off-target toxicities. Targeted therapeutic strategies have been developed to circumvent these limitations, although there remains an unmet need for antigen-agnostic tumor targeting. CBX-12 is a peptide conjugate that uses a novel pH-low insertion peptide (pHLIP) linked to TOP1 inhibitor exatecan to selectively target the low-pH tumor microenvironment and deliver the payload intracellularly. Recently published results of the first-in-human study of CBX-12 (NCT04902872) demonstrated single-agent activity in 4 patients, including a complete response in a patient with ovarian cancer. The predominant reported toxicity was myelosuppression with the most common grade 3/4 treatment-related adverse event being neutropenia in 28.6% of patients. Here we report our new pharmacodynamic (PD) biomarker-driven pilot study of CBX-12 in patients with advanced solid tumors. The primary objective of this study is to assess the effects of CBX-12 on biomarkers of DNA damage response (DDR) in biopsy specimen to establish the degree and duration of CBX-12 target engagement. The secondary objectives are to assess the effects of CBX-12 on TOP1 molecular response; determine any association between tumor TOP1 levels, DDR modulation, and plasma exatecan levels; evaluate the effect of CBX-12 on CD8+ T cell infiltration and activation in the tumor microenvironment; assess the objective response rate using RECIST v 1.1; and assess safety and tolerability of CBX-12. The planned PD endpoints aim to confirm and further enrich knowledge of the mechanisms underlying response or resistance to CBX-12 treatment, and guide future complementary treatment combination strategies. The study results may also help identify future patient populations likely to benefit from CBX-12 treatment. Methods: CBX-12 will be administered intravenously once weekly in 28-day cycles at the recommended phase 2 dose. Mandatory biopsies will be collected at baseline, 24-36 hours post first dose, and on cycle 3 day 1 to assess both short- and long-term effects of CBX-12 on the tumor. Mandatory research blood samples will be collected at specified timepoints for pharmacokinetic, circulating tumor cell, and cell-free DNA analyses. Clinical trial information: NCT05691517 .