Abstract A018: Effects of Toca 511 and Toca FC on tumor microenvironment and peripheral blood populations in patients with advanced malignancies

Abstract

Toca 511 (vocimagene amiretrorepvec) is an investigational, conditionally lytic, retroviral replicating vector that selectively infects cancer cells due to cell division requirements for virus integration into the genome, and defects in innate and adaptive immune responses found in malignant tissues that support virus replication. Toca 511 spreads through cancer cells and stably delivers optimized yeast cytosine deaminase (CD) that, upon administration of the prodrug, Toca FC (an investigational, extended-release version of 5-fluorocytosine [5-FC]), converts 5-FC into 5-fluorouracil (5-FU). 5-FU kills infected dividing cancer cells and diffuses to and kills surrounding cells in the tumor microenvironment, including immunosuppressive myeloid cells. In animal models, this depletion of immunosuppressive myeloid cells leads to therapeutically active immunity against tumors. A similarly derived antitumor response may occur in cancer patients, as local injection of Toca 511 into the tumor bed after resection of recurrent high-grade glioma followed by treatment with Toca FC has been associated with prolonged survival and durable complete responses (median duration of follow-up: 37.4+ months); responses were delayed in onset, consistent with time to response for immuno-oncology agents. The current phase 1b, multicenter, open-label study (Toca 6; NCT02576665) is designed to investigate changes in immune activity after treatment with Toca 511 and Toca FC in patients with advanced malignancies. Toca 511 is administered intravenously (IV) daily for 3 days and then as a single injection into metastatic or recurrent tumor. Oral Toca FC is started ~4 weeks later and repeated every 4-6 weeks. Biopsies are obtained prior to and following exposure to Toca 511 and Toca FC treatment to evaluate changes in immune activity, and peripheral blood is obtained contemporaneously for evaluation. The study has enrolled 19 patients to date (colorectal cancer: 15; sarcoma: 2; non-small cell lung and pancreas cancer: 1 each). Treatment has been well tolerated. Viral RNA, DNA, and CD protein expression are observed in tumor after IV delivery of Toca 511. We plan to report on tumor microenvironment remodeling that follows treatment with Toca 511 and Toca FC. Infiltrating T-cell subpopulations, B cells, and monocytes quantified by immunofluorescence from stained formalin-fixed, paraffin-embedded samples will be presented. Additionally, changes in peripheral blood, including T-cell effector, helper/memory, and regulatory populations, and myeloid lineage cells following exposure to Toca 511 alone and following subsequent exposure to Toca FC will be reported. Data from this study will inform future development of Toca 511 and Toca FC alone or in combination with other therapies in patients with solid tumors. Citation Format: Jaime Merchan, Jordi Rodon, Derek Ostertag, Shree Venkat, Arthur Donahue, Peder Horner, Dalissa Tijera, Thian Kheoh, Douglas J. Jolly, Harry E. Gruber, Jolene S. Shorr, Gerald S. Falchook. Effects of Toca 511 and Toca FC on tumor microenvironment and peripheral blood populations in patients with advanced malignancies [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A018.