(685f) Engineering Multiparatopic Antibody-Drug Conjugates to Enhance Cancer Immunotherapy

Antibody-drug conjugates (ADCs) represent a growing class of therapeutics, with 13 clinically approved molecules, and dozens of others in various stages of development. ADCs typically consist of a disease-specific antibody linked to a toxic drug that kills the target cell. Cancer cells express a variety of surface proteins that suppress the immune system, and these proteins can serve as potential targets for ADC killing. A particular cell surface protein that is highly expressed in multiple cancer types is known as programmed death-ligand 1 (PD-L1). Although its upregulation on tumor cells makes PD-L1 a promising target for ADCs, this protein does not get internalized readily into cells, a critical property that is required in order for an ADC to mediate its cytotoxic function. To address these shortcomings, we engineered a new class of anti-PD-L1 antibodies called multiparatopic antibodies that target non-overlapping epitopes on a single protein target and significantly enhance receptor internalization and receptor degradation. We then leveraged this strategy to engineer novel ADCs targeting PD-L1 that will serve as a powerful new immunotherapeutic platform to treat cancer. In vitro cytotoxicity assays were performed, employing a secondary antibody-saporin conjugate specific to human immunoglobulin G (IgG), which is endocytosed by piggybacking on cell surface antigen-targeted antibodies. Our engineered anti-PD-L1 triparatopic antibody demonstrated more potent cell killing than atezolizumab, an FDA-approved anti-PD-L1 monoclonal antibody. Encouraged by these results, the triparatopic antibody was chemically conjugated with the tubulin inhibitor small molecule drug monomethyl auristatin E (MMAE) to formulate an ADC. Our multiparatopic ADC demonstrated much stronger cell killing potency than atezolizumab ADC that translated to an IC₅₀ enhancement of >100-fold. The triparatopic ADC is being investigated in both in vitro and in vivo studies as an anti-tumor agent. Collectively, our triparatopic ADC approach introduces a promising new strategy to empower ADC efficacy, and will have broad relevance across cancer types.