Abstract 2476: Bispecific redirected T-cell immunotherapy targeting P-cadherin expressing tumors

Introduction: Strong evidence exists supporting the important role T-cells play in the immune response against tumors. Still, the ability to initiate tumor specific immune responses remains a challenge. We have developed a Dual-Affinity Re-Targeting (DART®) protein engineered with enhanced pharmacokinetic properties to extend in vivo half-life, and designed to engage and activate endogenous polyclonal T cell populations via the CD3 complex in the presence of P-cadherin expressing tumors. We designate this bispecific redirecting T-cell molecule as P-cadherin LP-DART. P-cadherin up-regulation has been reported in various tumors, including breast, gastric, endometrial, colorectal and pancreatic cancers, and is correlated with poor survival of patients. Methods: The P-cadherin LP-DART was stably expressed by CHO cells and purified to homogeneity via standard antibody-purification methods. Functional in vitro studies were performed with a panel of human cancer cell lines and human T cells isolated from healthy donors. In vivo tumor growth inhibition studies were performed in immunodeficient athymic nude or NOD-scid IL2Rgammanull (NSG) mice bearing human tumor cell line- or patient derived-xenografts and human T-cells, and treated with P-cadherin LP-DART. Results: P-cadherin LP-DART exhibited binding to a broad panel of cancer cell lines expressing various levels of endogenous cell surface P-cadherin, and comparable binding to a number of human donor derived T-cells expressing CD3. In the presence of T-cells, this bispecific molecule elicited P-cadherin expression level dependent cytotoxic T-lymphocyte (CTL) responses against the different tumor cell lines, and induced antigen dependent T-cell activation and cytokine release. P-cadherin LP-DART also demonstrated potent in vivo anti-tumor activity against implanted tumor xenografts. Significant tumor growth inhibition was observed across a range of potential indications that express P-cadherin. Measurement of in vivo pharmacodynamic markers support P-cadherin LP-DART mediated CTL infiltration and killing as the mechanism of tumor inhibition. Conclusions: P-cadherin LP-DART displays potent in vitro and in vivo redirected T-cell activity against a broad panel of cancer cell lines expressing a range of cell surface P-cadherin levels. These data support further investigation of P-cadherin LP-DART as a potential novel therapeutic treatment for cancers expressing P-cadherin. Citation Format: Timothy S. Fisher, Adam Roo