Abstract 6305: Bispecific claudin 18.2 and GPRC5D antibodies with potent cell-killing activity for cancer therapeutics

Abstract

Abstract Tumor-associated antigens with little or no expression in healthy tissue are attractive targets for anti-tumor modalities including T cell-engaging bispecific antibodies. CLDN18.2 is a transmembrane adhesion protein undetectable in most healthy adult tissues but highly expressed in gastric, pancreatic, esophageal, and lung cancers. GPRC5D is a G protein-coupled receptor that is absent from most healthy tissues except for hair follicles but expressed on multiple myeloma cells. Both CLND18.2 and GPRC5D are novel oncology targets with no clinically approved therapies against them. Using our discovery platform tailored to complex transmembrane proteins, we have developed bispecific antibodies with the ability to potently kill CLDN18.2-positive or GPRC5D-positive cells. Multipass membrane proteins are valuable therapeutic targets in oncology and other disease areas but are largely inaccessible as antibody targets due to their poor expression, membrane-dependent structure, small extracellular regions, and poor immunogenicity due to sequence conservation. We developed an antibody discovery platform (MPS) that specifically addresses each of these challenges. This platform utilizes advanced immunization techniques including DNA, mRNA, and Lipoparticles (virus-like particles). It also employs chickens as an evolutionarily divergent host species for robust immune responses against conserved targets. Antibodies raised in chickens are directly humanized prior to isolation, reducing the need for downstream engineering. In two separate campaigns, we immunized chickens with CLDN18.2 and GPRC5D and obtained high-titer immune responses. We were successful in isolating high-affinity antibodies specific to each of these targets. Our CLDN18.2 antibodies showed specificity for their target and did not bind the closely related splice variant CLND18.1, which is highly expressed in healthy lung tissue. Additionally, the antibodies showed no binding to ~6,000 other proteins that were screened using a Membrane Proteome Array. A subset of antibodies from both discovery programs were configured as bispecific molecules using a CD3-targeting arm to bring tumor cells into close proximity with cytotoxic T cells that mediate cell killing. The panels of molecules encompassed multiple bispecific formats bearing different stoichiometries, geometries, and sizes to enable identification of lead molecules with favorable activities and safety profiles. Both CLDN18.2 and GPRC5D bispecifics showed potent T cell-mediated cytotoxicity with picomolar potency. They also showed good cytokine release and developability profiles. GPRC5D x CD3 and CLDN18.2 x CD3 bispecifics hold promise as potent and safe therapeutics for different cancer types. Citation Format: Ileine Sanchez, Hayley Roth, Brad Screnci, David Tucker, Nick Molino, Trevor Barnes, Paige Murphy, Kyle Guldner, Tim Phillips, Kristen Shema, Thomas Charpentier, Alyssa Cunningham, Janae Latta, Breanna Tyrell, Meghan Pitts, Carmen Navia, Charles Azuelos, Anna Lobley, Jawhara Karam, Valerie Fiers, Daniela Reyes, Kate Slovik, Alison Snyder, Marianne Assogba, Kai-Ti Chang, Riley Payne, Kyle Doolan, Ross Chambers, Joe Rucker, Benjamin Doranz. Bispecific claudin 18.2 and GPRC5D antibodies with potent cell-killing activity for cancer therapeutics. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6305.