Abstract B249: Prolonged cytotoxic activity induced by anti-PSMA x anti-CD3 ADAPTIR™ molecule in the absence of significant cytokine release.

Abstract

Abstract Background: Treatment of metastatic, castrate-resistant prostate cancer (CRPC) remains a highly unmet medical need. We have developed a humanized bispecific ADAPTIR™ (modular protein technology) molecule, ES414, which redirects T-cell cytotoxicity against cells expressing PSMA (Prostate Specific Membrane Antigen), a prostate cancer antigen. In previous preclinical studies, ES414 has been shown to induce cytotoxicity against prostate cancer cells in vitro when measured by target cell lysis and in vivo in multiple mouse xenograft models. ES414 was also previously shown to be well-tolerated in humanized mice and non-human primates. Here, we examine the effects of exposure to ES414 over several days on T-cell function in the presence of PSMA+ target cells.Materials and Methods: Long term cytotoxic activity induced by ES414 against PSMA(+) cell lines in the presence of purified human T cells was followed in vitro by use of high content microscopy. Cytotoxic activity was determined by incorporation of a label such as propidium iodide or 7-aminoactinomycin D. Binding to subsets of peripheral blood mononuclear cells (PBMC) and Fc(gamma) receptor-expressing cell lines was assessed by multi-color flow cytometry. T cells were assessed for activation and proliferation in a similar setting using multi-color flow cytometry. Cytokine release was measured at multiple timepoints using multiplex immunoassays. Results: ES414 selectively bound to T cells, and did not bind to other PBMC subsets nor to Fc (gamma) receptor expressing cell lines. T cells activated by ES414 in the presence of target cells rapidly induced target cell lysis within 4 hours and continued serial lysis for more than 48 hours. Target cell lysis occurred at low effector-to-target cell ratios. In the presence of target cells, ES414 also induced T-cell activation, as measured by upregulation of activation markers, and proliferation, but induced limited levels of cytokine secretion in comparison to control molecules. Conclusions: These preclinical in vitro studies show that ES414 selectively engages T cells, targets T cells towards tumor cells, and induces T-cell activation, with limited cytokine release. Limited cytokine release in the presence of redirected T-cell cytotoxicity is a desirable feature that warrants further investigation of ES414 as a potential therapeutic for CRPC. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B249. Citation Format: Gabriela Hernandez-Hoyos, Toddy Sewell, Padma Ravikumar, Megan Aguilar, John Kumer, David Bienvenue, Catherine J. McMahan, Jane Gross, John W. Blankenship. Prolonged cytotoxic activity induced by anti-PSMA x anti-CD3 ADAPTIR™ molecule in the absence of significant cytokine release. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B249.