VB6-845d tumor cell killing elicits biologic features of immunogenic cell death

VB6-845d is a Targeted Protein Therapeutic, TPT, that comprises a Fab fragment specific for the Epithelial Cell Adhesion Molecule (EpCAM) genetically fused to deBouganin via a furin protease sensitive linker. DeBouganin (deB) is a de-immunized variant of bouganin, a ribosome inactivating protein (RIP), that when internalized blocks protein synthesis thereby leading to cell death. While all cytotoxic molecules induce tumor cell killing, only some are capable of inducing biological manifestations indicative of immunogenic cell death (ICD). ICD is characterized by the collective appearance of distinct cellular changes termed damage associated molecular patterns, or DAMPs, which play a role in immune cell activation by triggering pro-inflammatory processes. Key DAMPs necessary for defining ICD are cell surface translocation of calreticulin, an endoplasmic reticulum chaperone protein, ATP secretion and release of HMGB1 (high mobility group box 1). To evaluate whether VB6-845d cell killing elicits the hallmark features of ICD, VB6-845d treated tumor cell lines were assessed for the presence of these distinct signaling molecules. In vitro studies showed that VB6-845d cytotoxicity induces the translocation of calreticulin to the cell surface as well as the release of ATP and HMGB1. The expression of other potential immune regulators following VB6-845d treatment was also examined. In summary, the data presented suggests that VB6-845d mediates tumor cell killing by an ICD pathway. The potential cross-priming effect initiated by VB6-845d-induced ICD suggests the use of VB6-845d in combination with immune checkpoint inhibitors may enhance their effectiveness in EpCAM-positive epithelial cancers. Citation Format: Rachelle L. Dillon, Shilpa Chooniedass, Arjune Premsukh, Glen C. MacDonald, Jeannick Cizeau, Gregory P. Adams. VB6-845d tumor cell killing elicits biologic features of immunogenic cell death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2788.