Abstract 2396: Development of a new generation of dimeric, highly cytotoxic fusion proteins containing active GrB and VEGF targeting tumor neovasculature: Incorporating IgG heavy chain Fc fragments improves cytotoxicity, stability and pharmacokinetics

VEGF121 is a naturally-occurring splice variant that binds to VEGF receptors R-1 and R-2, which are over-expressed on the endothelium of tumor vasculature but not normal vasculature. The serine protease granzyme B (GrB) is capable of inducing intense cellular apoptosis through both caspase-dependent and caspase-independent multiple-cascade mechanisms. We have previously reported the expression of a fusion protein composed of Granzyme B and VEGF121 (GrB/VEGF121) and its subsequent in vitro and in vivo characterization. Here we report on the development and characterization of GrB-Fc-VEGF, which fuses the two domains via an IgG heavy chain Fc-fragment. We hypothesized that this modification, resulting in a relatively high molecular weight (133 kDa vs 80 kDa) would result in improved in vivo circulation and efficacy. VEGF inter-chain dimerization domains were modified such that dimerization occurred only through the Fc domain. GrB-Fc-VEGF121was expressed in HEK-293E cells under serum-free conditions and purified from the media by immobilized metal affinity chromatography (25 mg/L). Western blotting confirmed incorporation of both VEGF121 and GrB moieties into the construct. Comparison of GrB-Fc-VEGF121 with its expected molecular weight suggests significant glycosylation when produced in HEK293E cells. The enzymatic activity of GrB in GrB-Fc-VEGF121 was comparable to that of human GrB. In vitro studies of GrB-Fc-VEGF121 suggests improved cytotoxicity against cell lines expressing high levels of VEGFR-1 or VEGFR-2, unlike GrB/VEGF121, which targeted VEGFR-2+ cells more efficiently. Thus, the GrB-Fc-VEGF121 produced in HEK293E cells is active and has significant potential as a targeted therapeutic. In vitro cytotoxicity against an expanded panel of cells, internalization, and in vivo pharmacokinetics and efficacy against various tumor models are currently ongoing and will be presented. Research conducted, in part, by the Clayton Foundation for Research. Citation Format: Khalid A. Mohamedali, Lawrence H. Cheung, Ana Alvarez-Cienfuegos, Michael G. Rosenblum. Development of a new generation of dimeric, highly cytotoxic fusion proteins containing active GrB and VEGF targeting tumor neovasculature: Incorporating IgG heavy chain Fc fragments improves cytotoxicity, stability and pharmacokinetics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2396.