Abstract 3080: Site-specific conjugation of CPL976H-MMAE enables stable and selective dual targeting of PD-L1 and AXL

Abstract Background: Combining immune checkpoint blockade with cytotoxic chemotherapy has improved survival in multiple solid tumors; however, systemic toxicity and limited response durability remain key limitations. To overcome these barriers, we developed CPL976H-MMAE, a next-generation bispecific antibody-drug conjugate (ADC) that simultaneously targets PD-L1 and AXL. This dual-target approach aims to suppress immune escape and tumor progression pathways while ensuring efficient and precise delivery of Monomethyl Auristatin E (MMAE) directly to the cancer cells. Materials and Methods: CPL976H-MMAE was created with Fc-glycan remodeling and click-chemistry conjugation, resulting in an enhanced molecular stability and a standardized drug-to-antibody ratio (DAR). Target binding and stability of CPL975H-MMAE in serum were assessed by Surface Plasmon Resonance (SPR) after incubation in human, cynomolgus, mouse, and rat sera (7 days at 37°C). Pharmacokinetic and biodistribution studies were performed in MDA-MB-231 cell line xenograft models using LC-MS. Efficacy of CPL976H-MMAE was validated ex vivo in patient-derived xenografts (PDX) representing distinct PD-L1/AXL expression profiles. Potential binding to red-blood-cells (RBCs), MMAE release and its partitioning to RBCs were quantified by LC-MS in rat and cynomolgus species. Results: CPL976H-MMAE retained strong and stable dual-target binding across different species sera, showing highest stability in human and cynomolgus, moderate in mouse, and lowest, but still satisfactory, in rat. ADC binding and MMAE level in RBCs of mouse and cynomolgus species was negligible, even though free MMAE exhibits partial association, further indicating conjugate stability in circulation. Pharmacokinetic analyses revealed a favorable plasma clearance profile and evident, dose-dependent tumor accumulation at 0.8-6 mg/kg, with minimal off-target MMAE exposure. Ex vivo studies confirmed potent cytotoxic activity of CPL976H-MAME in PDXs expressing both high and moderate PD-L1/AXL levels. Conclusions: CPL976H-MMAE effectively merges immune checkpoint blockade with targeted cytotoxicity, addressing both primary and acquired resistance to PD-1/PD-L1 therapies. High serum stability, sustained tumor accumulation, and limited systemic exposure presents CPL976H-MMAE as a formidable and robust bifunctional ADC. Presented data highlight CPL976H-MMAE translational potential for future therapies, especially for patients unresponsive to current immunotherapies. This study was supported by The National Centre for Research and Development ( POIR.01.01.01-00-0429/19) Citation Format: Delfina Popiel,Filip Mitula,Anna Jablonska,Krzysztof Lacek,Natalia Czerwinska,Tomasz Kornatowski,Magdalena Langowska,Sylwia Wieczorek,Bartosz Wiernicki,Damian Kolakowski,Adam Zmyslowski,Tomasz Banach,Joanna Deshayes,Michal Mroczkiewicz,Marcin Zagozda,Joanna Hucz-Kalitowska,Emilia Mroz,Malgorzata Choros,Maciej Wieczorek,Olga Abramczyk. Site-specific conjugation of CPL976H-MMAE enables stable and selective dual targeting of PD-L1 and AXL abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3080.