Abstract 2606: Targeting mesothelin on tumor cells with a novel, completely human fusion construct delivering the serine protease granzyme B

Abstract

Abstract Mesothelin is a cell-surface antigen identified as an excellent cancer-associated target upregulated on numerous tumors, including pancreatic and ovarian cancers, as well as mesotheliomas and lung cancers. Granzyme B is a highly cytotoxic serine protease nominally delivered by immune effector cells to target cells, resulting in induction of cell death pathways that are both caspase-dependent and -independent. We developed a fusion protein (GrB-Fc-SD1) composed of GrB and containing SD1, a novel human single-domain antibody that uniquely targets Region III of the mesothelin glycoprotein. The SD1 and GrB domains are tethered by a human IgG heavy chain fragment which enables dimerization. The fusion protein was transiently expressed in HEK-293E cells in serum-free conditions with a final yield of 5 mg/L. Western blot analysis confirmed the expression of this construct as a homodimer. The GrB enzymatic activity in GrB-Fc-SD1 was similar to that of commercially available human granzyme B. ELISA studies confirmed the specific recognition of the SD1 antibody to mesothelin extra-cellular domain. Biacore analysis confirmed binding of GrB-Fc-SD1 with a dissociation constant between 10−7 and 10−8 M. In vitro cytotoxicity against a limited panel of lung, pancreatic and ovarian cancer cell lines expressing surface mesothelin indicate cytotoxicity in the nanomolar range, while cytotoxicity against mesothelin-negative cells was at micromolar levels. Ex vivo serum stability studies showed excellent stability of GrB-Fc-SD1 at both 4°C and -20°C over ninety days and a half-life of approximately three days at elevated temperatures (37°C). In vivo efficacy studies against Capan-2 xenografts in nude mice using both weekly x 5 and QOD x 5 doses of GrB-Fc-SD1 (130 mg/mg total dose, delivered IP) indicated highly significant efficacy in both dose regimens, with p < 0.001 compared to vehicle-treated mice. Mouse body weights were not impacted at the efficacy doses used in this study, indicating that this dose was non-toxic. Histopathology studies revealed a significant decrease in the percentage of Ki-67+ nuclei in treated tumors compared to controls. These data warrant continued investigation of the protein as a therapeutic candidate. Research supported by H2Biologics. Research conducted, in part, by the Clayton Foundation for Research. Citation Format: Khalid A. Mohamedali, Lawrence H. Cheung, Mihai G. Iurascu, Louis R. DePalatis, Claire Thuning-Roberson, Michael G. Rosenblum. Targeting mesothelin on tumor cells with a novel, completely human fusion construct delivering the serine protease granzyme B [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2606.