Toca 511 and Toca FC in patients with gastrointestinal tumors in the Toca 6 study.

TPS880 Background: Toca 511 (vocimagene amiretrorepvec) is an investigational, conditionally lytic, retroviral replicating vector (RRV). RRVs selectively infect cancer cells due to defects in innate and adaptive immune responses found in cancers that support virus replication, and the requirement for cell division for virus integration into the genome. Toca 511 spreads through tumors, stably delivering an optimized cytosine deaminase (CD) gene that converts the prodrug, Toca FC (investigational, extended-release 5-FC) into 5-FU. 5-FU kills infected dividing cancer cells and diffuses and kills surrounding cancer cells, myeloid derived suppressor cells, and tumor associated macrophages, thus reestablishing tumor immunity (Cloughesy et al. Neuro Oncol 2016). In a Phase 1 study, resected high grade glioma tumors expressed CD protein following intravenous (IV) Toca 511.1 In animal models of metastatic colorectal cancer, IV Toca 511 infected metastatic sites, and subsequent 5-FC treatment resulted in decreased tumor size and improved survival (Yagiz et al. Mol Therapy 2015). Methods: Toca 6 is a Phase 1b, multicenter, open-label study (NCT02576665) that aims to investigate changes in immune activity after treatment with Toca 511 & Toca FC in patients with solid tumors, including gastrointestinal tumors. A total of 30 patients who have advanced malignancies, including colorectal and pancreatic cancer, with molecular characteristics that may increase sensitivity to 5-FU or viral infection, or IDH1 mutated solid tumors (e.g., intrahepatic cholangiocarcinoma) will be enrolled. In these patients, Toca 511 is injected IV daily for 3 days, then intratumorally after biopsy. Oral Toca FC is started ~4 weeks later and repeated every 4-6 weeks. Changes from baseline in intratumoral immune activity (infiltrating T-cell subpopulations, B cells, monocytes) at 4 weeks after start of Toca FC are assessed. Contemporaneous peripheral blood is analyzed for effector, memory, Treg, and myeloid lineage cells. Viral RNA, DNA, and CD protein expression in tumor after IV Toca 511 are measured. Safety and efficacy will be determined. Concomitant checkpoint inhibitor therapy may be given following immune activity assessments. The study has enrolled 3 patients. Clinical trial information: NCT02576665.