Abstract

Antibody based therapeutics targeting mesothelin (MSLN) have shown limited anticancer activity in clinical trials. Novel antibodies with high affinity and better therapeutic properties are needed. In the current study, we have isolated and characterized a novel VH domain 3C9 from a large size human immunoglobulin heavy chain variable (VH) domain library. 3C9 exhibited high affinity [KD (dissociation constant) < 3 nM] and binding specificity in a membrane proteome array (MPA). In a mouse xenograft model, 3C9 fused to human Fc became visible at tumor sites as early as 8 hours post infusion and persisted at the tumor site for more than 10 days. Both CAR-T cells and antibody domain drug conjugations (DDCs) generated with 3C9 were highly effective at killing MSLN positive cells in vitro without off-target effects. The X-ray crystal structure of full-length MSLN in complex with 3C9 reveals interaction of the 3C9 domains with two distinctive residues patches on the MSLN surface. 3C9 fused to human Fc domain drug conjugate was efficacious to inhibit tumor growth in a mouse xenograft model. This newly discovered VH antibody domain holds promise as a therapeutic candidate for MSLN-expressing cancers.