Abstract 5660: Tumor cell death caused by INT230-6 induces protective T cell immunity

Standard care for many types of cancer involves systemic administration of cytotoxic agents. This may result in low drug concentration at tumor sites, which limits cell killing. More recently it has been shown that cytotoxic formulations designed for intratumoral delivery improve drug efficacy presumably by increasing drug concentration at the tumor site. Furthermore, it has been discovered that the mechanisms of anticancer agents extend beyond direct tumor cell lysis. One major aspect is that cell death often induces an immune response. Different types of cell death such as necrosis, apoptosis and autophagic cell death induced by cytotoxic agents trigger immune responses with varying degrees of inflammation and involving different types of immune cells. The ideal immune responses that may give maximum benefit to patients would be strong and long lasting anti-tumor T cell responses. In this study, a novel, tissue and cell diffusive cytotoxic formulation, INT230-6, was administered intratumorally over 5 sequential days into subcutaneous 300mm3 murine Colon26 tumors. Treatment resulted in regression from baseline of 100% of the tumors and up to 80% complete response (CR). We then analyzed the T cell responses in the protection induced by INT230-6. No animals achieved a CR after CD8 or CD8/CD4 double depletion at treatment onset, indicating a critical T-cell role in tumor regression. Mice with CRs were protected from re-challenge by either subcutaneous or intravenous re-inoculation of the Colon26. The protection was abrogated by CD4/CD8 double depletion prior to the re-challenge, indicating that immunological T cell memory was induced and was necessary for protection. Hence, INT230-6 given locally to treat tumors induces tumor-specific protective T cell immunity. Colon26 tumors express the endogenous retroviral protein gp70 containing the AH-1 CTL epitope. AH-1-specific CD8 T cells were detected in tumors of mice without treatment. However, these highly expressed PD-1. This was consistent with the observation that the PD-1 blockade enhanced the efficacy of INT230-6. Conversely, INT230-6 enhances the efficacy of checkpoint inhibitors. Citation Format: Anja C. Bloom, Lewis H. Bender, Ian B. Walters, Katharine T. Clark, Masaki Terabe, Jay A. Berzofsky. Tumor cell death caused by INT230-6 induces protective T cell immunity [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 5660. doi:10.1158/1538-7445.AM2017-5660