Abstract 2593: A double dose of DNA damage: Overcoming drug resistance using targeted oncolytic viruses
Authors: Taylor R. Jamieson, Carolina S. Ilkow
Journal: Cancer Research (2019)

Abstract Background: Hereditary breast and ovarian cancers make up 5-10% of breast cancer and 10-15% of ovarian cancer cases. These cancers tend to be difficult to treat and progress in an aggressive manner. Poly(ADP-ribose) polymerase inhibitors (PARPi) are a type of drug that targets the DNA repair pathway; many of these drugs are undergoing clinical trials and some are presently in use for cancers harbouring mutations in their DNA repair machinery, such as hereditary breast and ovarian cancers. Unfortunately, numerous patients become resistant to PARPi, leaving limited options for further treatment. Oncolytic or “cancer-killing” viruses are an innovative approach for treating even the most complex cancers. Oncolytic viruses target and destroy cancer cells, leaving normal cells unharmed, all while activating a patient’s own immune system to fight the cancer. Our group has demonstrated that oncolytic rhabdoviruses may be used to deliver therapeutic payloads by encoding targeting sequences to act on genes via RNA interference (such as shRNA). Objective: The aim of this project is to overcome PARPi resistance by engineering cancer specific viruses that will target genes relevant to the DNA repair pathway, sensitizing them to PARPi treatment in a synthetically lethal manner. Methods: shRNA sequences targeting components of the DNA repair pathway have been cloned into the genome of an oncolytic rhabdovirus (a non-targeting control sequence has been inserted into the same virus as well). Prior to encoding shRNA sequences into the virus, validation of these targets was performed using siRNA transfection. Downregulation of targeted genes are being assessed via qPCR and Western Blot analysis following transfection and infection. Cell viability following treatment with PARPi +/- viruses will be assessed by Alamar Blue and Crystal Violet assays. Results: Downregulation of siRNA targeted genes has been validated at the mRNA level via qPCR analysis (Western Blot analysis is currently ongoing). Validation of the newly engineered viruses to show downregulation of their specific gene targets is currently underway. Changes in cell viability for seven unique human/mouse cell lines following treatment with varying concentrations of two different PARPi to establish a dosing scheme for combination therapy with viral infection has been completed. Conclusions and project impact: This project is currently in the early stages of development; however, preliminary experiments testing the combination of siRNA knockdown with PARPi have revealed a significant decrease in cell viability compared to siRNA knockdown or PARPi alone in MCF-7 breast cancer cells. By engineering OVs that specifically replicate in and kill cancer cells while delivering PARPi sensitizing sequences, this combination approach may enhance and expand the utility of oral PARPi therapeutics in numerous cancers with alterations in DNA repair genes. Citation Format: Taylor R. Jamieson, Carolina S. Ilkow. A double dose of DNA damage: Overcoming drug resistance using targeted oncolytic viruses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2593.