Abstract 5910: Oncolytic gene editing therapy for the treatment of pediatric rhabdomyosarcoma
Authors: Phelps Michael P. , Yang Heechang , Patel Shivani , Chen Eleanor 
Published: August 2018

The inability to directly target many tumor oncogenes remains a major challenge for current cancer therapy. Small molecule inhibitors targeting these potent cancer genes have had limited success, therefore a new therapeutic approach is urgently needed. Recent advances in high efficiency gene editing technology have shown remarkable promise for the ability to destroy tumor oncogenes by targeting the genomic DNA (gDNA) of cancer cells. Unlike traditional small molecule inhibitors, cancer gene editing therapy is not sensitive to modifications in protein structure and can target any potential cancer gene. Gene editing therapy can also be rapidly adapted to the unique genetics of individual patients, providing the flexibility needed to target essential genes in rare cancers or individuals with relapsed tumors, for which there is no treatment options. Despite promising developments in this technology, major challenges remain in establishing an effective gene therapy delivery system, as well as improving cancer specific gene editing selectivity. To help overcome these challenges, we have developed high efficiency CRISPR/Cas9 gene editing approaches targeting the activated RAS oncogene in embryonal rhabdomyosarcoma (ERMS) and the PAX3/FOXO1 fusion gene in alveolar RMS (ARMS). Rhabdomyosarcoma is an aggressive pediatric sarcoma characterized by myogenic differentiation arrest. We demonstrate that targeting the exons of these driver oncogenes can effectively regress human RMS tumor xenografts in mice, using a tamoxifen- inducible gene editing approach. We also used a tumor-specific gene editing strategy to target the activating point mutation found in the NRAS and HRAS oncogenes as well as the breakpoint in the PAX3/FOXO1 fusion gene. We employed CRISPR systems from both Streptococcus pyogenes and Staphylococcus aureus to expand the number of genetic mutations that can be targeted in cancer cells. Finally, to test the therapeutic viability of cancer gene editing technology we engineered myxoma replicating oncolytic viruses with the CRISPR/Cas9 gene editing components, targeting both NRAS and PAX3/FOXO1 oncogenes. Myxoma virus is a non-integrating rabbit DNA poxvirus capable of selectively replicating in cancer cells with reduced anti-viral response. Our approach seeks to synergize the tumor selectivity of myxoma oncolytic viral replication with CRISPR/Cas9 technology, to create a novel cancer gene editing therapy that can be customized to the unique genetic mutations found in each cancer patient. While we have examined this technology on RMS tumors, the approach could also be widely applied to a number of different cancer types, creating one of the first customizable cancer therapies.

Citation Format: Michael P. Phelps, Heechang Yang, Shivani Patel, Eleanor Chen. Oncolytic gene editing therapy for the treatment of pediatric rhabdomyosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5910.