Abstract 1609: Oncolytic virotherapy for SCLC using immunocompetent mouse models
Authors: Kellish Patrick , Shabashvili Daniil , Rahman Masmudur M. , Reinhard Mary , McFadden Grant , Kaye Frederic , Zajac-Kaye Maria 
Published: July 2017

Background: Small cell lung cancer (SCLC) is an aggressive subtype of lung cancer with few treatment advances over the past 3 decades and poor survival. Locally targeted oncolytic virotherapy employs a viral vector that has selective cytotoxicity for tumor cells and non-toxic for normal cells and tissues. The therapeutic benefit is proposed to arise from an initial viral cytotoxic phase following by host immune responses. Myxoma Virus (MYXV) has been widely tested in Australia to control rabbit populations with no toxicity to humans. MYXV selectively infects mouse and human tumors cells with no cytotoxicity to normal tissues and is a promising oncolytic virotherapy agent that has not been tested in human lung cancer or in clinical trials.

Methods: To study MYXV infection and viral replication in vitro, we utilized human and mouse SCLC cell lines with MYXV engineered with fluorescent reporters. Using an optimized conditional genetically engineered mouse model (GEMM) (Ade-CRE mediated p53/Rb1/p130 null) we examined the effects of intrapulmonary MYXV treatment on SCLC tumors at 5 and 30 days post-MYXV treatment. Survival analysis was determined following intranasal MYXV 3 months post-Ade-CRE induction. We also tested intratumoral MYXV in patient derived xenografts (PDX) and subcutaneous syngeneic allografts in immunocompetent mice.

Results: We optimized a conditional SCLC GEMM using limiting dilutions of intratracheal Ade-CRE to reduce the SCLC foci to simulate human disease and generated mouse SCLC lines from individual clones. We observed efficient MYXV infection, late viral replication, and cytotoxicity in both human and mouse SCLC in vitro. In contrast, we did not detect productive infection nor cytotoxicity in non-tumor cells. Following intranasal MYXV instillation we observed MYXV localized exclusively within lungs at 3 days and no longer detected by 7 days’ post treatment. TUNEL staining of SCLC lesions showed apoptosis and necrosis at 5 days within SCLC and the effect persisted with discrete foci of tumor necrosis 30 days’ post-treatment. There was no toxicity to any mouse tissues. SCLC GEMM treated with intrapulmonary MYXV (n=30) showed a modest but statistically significant prolongation of survival compared to PBS control mice (n=30) (p &lt; 0.05). Direct intratumoral MYXV injections performed on PDX tumors in immunodeficient mice showed efficient infection and late viral replication in all patient samples. We observed extensive tumor necrosis at 7 days, and persisting virus at 10 days’ post treatment. Direct intratumoral MYXV injections performed on allograft tumors in syngeneic immunocompetent mice showed extensive necrosis accompanied by immune cell infiltration into the tumor, and the virus was undetectable 7 days’ post treatment.

Conclusions: We show the potential for MYXV as an oncolytic virotherapy for SCLC with enhanced cytotoxicity in immunocompetent mice suggesting a role for concurrent immune checkpoint therapies.

Citation Format: Patrick Kellish, Daniil Shabashvili, Masmudur M. Rahman, Mary Reinhard, Grant McFadden, Frederic Kaye, Maria Zajac-Kaye. Oncolytic virotherapy for SCLC using immunocompetent mouse models [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 1609. doi:10.1158/1538-7445.AM2017-1609