Abstract B27: Identifying therapeutic combinations with EGFR-targeted therapy through the generation of genome-wide CRISPR-Cas9 knockout libraries in oral cancer cell lines

Abstract

Abstract Oral squamous cell carcinoma (OSCC) remains a disease with poor survival. With recent characterization of the mutational landscape of OSCCs, there is great potential for personalized targeted therapies. However, to date utilization of targeted therapies in OSCC have had limited success with anti-EGFR therapy. Combinations of targeted therapies, which may have greater efficacy by inhibiting compensatory pathways, have not been well studied. To identify synergistic combinations with EGFR-targeted therapy, we introduced Genome-scale CRISPR-Cas9 Knock-Out (GeCKO) libraries into OSCC cell lines. CRISPR-Cas9 generates individual genetic knockouts through targeted gene editing, and by using a pool of CRISPRs targeting over 18,000 genes we can perform genome-scale screening for synergistic targetable pathways. Upon selection of the OSCC GeCKO pool, we identified that knockouts of genes in the FGFR pathway caused sensitivity to the EGFR inhibitor gefitinib. We further investigated the possible synergistic effect of dual EGFR and FGFR inhibition with resazurin viability assays in 14 of our OSCC models. We found 6/14 (43%) of the models were responsive to the combination of EGFR and FGFR inhibition, indicating that the FGFR pathway could be an alternate mechanism of resistance to EGFR-targeted therapy. For further investigation of this combination, we again used CRISPR-Cas9 to generate an EGFR knockout (KO) OSCC cell line. This EGFR KO cell line retains sensitivity to FGFR inhibitors, and we expect that this cell line will be a useful tool in further evaluating the compensatory mechanism of the FGFR pathway. OSCC remains a common and frequently lethal cancer with great potential for the development of personalized targeted therapies. Here, we describe the use of genome-wide CRISPR-Cas9 library to discover the synergistic combination of EGFR and FGFR inhibition. Further investigation suggests the FGFR pathway as a common compensatory mechanism to EGFR inhibition. We hope to use this approach to identify additional compensatory mechanisms of resistance to targeted therapies with the eventual goal of translating these findings to clinic. Citation Format: Megan Ludwig, Andrew Birkeland, Sai Nimmagadda, Sue Foltin, Hui Jiang, Thomas Carey, John Chad Brenner. Identifying therapeutic combinations with EGFR-targeted therapy through the generation of genome-wide CRISPR-Cas9 knockout libraries in oral cancer cell lines [abstract]. In: Proceedings of the AACR Precision Medicine Series: Opportunities and Challenges of Exploiting Synthetic Lethality in Cancer; Jan 4-7, 2017; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2017;16(10 Suppl):Abstract nr B27.