Abstract 4597: A novel immuno-oncology approach: targeting cell-surface mesothelin with a fusion construct containing human granzyme B

Abstract

Abstract Immunological approaches to target tumors have gained considerable traction recently because of excellent clinical results. In addition, targeted treatment with antibody-drug conjugates (ADCs) can also be effective in achieving regression of solid tumors. The challenge for ADCs continues to be efficacy, stability of the construct and development of resistance. We have developed a unique fusion protein composed of 1) a novel human single-domain antibody (SD1) that uniquely targets Region III of the mesothelin glycoprotein and 2) an engineered version of the human serine protease Granzyme B (GrB). Mesothelin is highly expressed in aggressive cancers such as malignant mesothelioma, pancreatic and ovarian cancers, and NSCLC. Granzyme B generates an intense, irreversible pro-apoptotic effect through direct cleavage of caspases, release of cytochrome C from mitochrondria, and cleavage of nuclear matrix. Previous ADCs targeting mesothelin have faced the drawbacks of toxic payloads, formation of neutralizing antibodies, and competition with the serum protein MUC16/CA125. SD1-GrB represents a new class of completely human immunotoxins containing a payload with a unique mechanism of action. Additionally, because of its unique binding properties, SD1 does not compete with circulating CA125 and is not subject to cleavage. The SD1-GrB construct was designed as a homodimer (~200kDa) containing an IgG Fc domain and was expressed using transient-transfection of HEK293E cells. The soluble SD1-GrB was isolated from conditioned media and purified to homogeneity as assessed by SDS-PAGE and Western. Enzymatic activity of the GrB component was assessed by IEPD and found to be similar to authentic, native GrB. Binding to mesothelin was confirmed by surface plasmon resonance. Additionally, binding to the human lung adenocarcinoma cell lines H460 and HCC1703 was demonstrated by ELISA. Initial cytotoxicity (IC50) of SD1-GrB against H460 and HCC1703 was in the 30 nM range. Assessment against a larger panel of cell lines is ongoing followed by in vivo efficacy in a human tumor xenograft model. Our preliminary evaluation of SD1-GrB ADC suggests this construct has a unique mechanism of action and is highly cytotoxic against target cells. This molecule appears to be an excellent candidate for further pre-clinical development as a therapeutic agent. Research conducted, in part, by the Clayton Foundation for Research. Citation Format: Lawrence H. Cheung, Rasheed Tijani, Nasir Khan, Claire Thuning-Roberson, Michael G. Rosenblum. A novel immuno-oncology approach: targeting cell-surface mesothelin with a fusion construct containing human granzyme B [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4597. doi:10.1158/1538-7445.AM2017-4597