Oral squamous cell carcinoma (OSCC) has remained a disease with poor survival for decades. Current treatment options such as targeting EGFR has had limited success. We hypothesize that inhibiting compensatory pathways in combination with EGFR signaling may result in greater efficacy. To identify synergistic combinations with EGFR-targeted therapy, we introduced Genome-scale CRISPR-Cas9 KnockOut (GeCKO) libraries into OSCC cell lines. CRISPR-Cas9 generates individual genetic knockouts through targeted gene editing. We used a pool of CRISPRs targeting over 18,000 genes to perform genome-scale screening for drivers of sensitivity to EGFR-targeted therapy. Upon selection of the OSCC GeCKO pool, we identified gene knockouts in the FGFR pathway that increased sensitivity to the EGFR inhibitor gefitinib. Using resazurin viability assays we tested combinations of EGFR and FGFR inhibitors in 14 OSCC cell lines. Six/14 (43%) of the cell lines were responsive to the combination, indicating that the FGFR pathway is an alternate mechanism of resistance to EGFR-targeted therapy in some tumors. We advanced an OSCC cell line to test in vivo by establishing subcutaneous cell line xenografts in mice. After treatment for 21 days, the mice receiving the combination of EGFR and FGFR inhibitors, gefitinib and BGJ398, had significantly smaller tumors than mice receiving vehicle or either monotherapy. These results suggest targeting EGFR in combination with its compensatory pathway such as FGFR signaling could be effective in vivo. While OSCC remains a common and frequently lethal cancer, there is great potential for the development of novel 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 is a common compensatory mechanism to EGFR inhibition, and that targeting EGFR and FGFR in combination has efficacy in an in vivo model. Overall, targeting compensatory mechanisms in combination with EGFR-targeted therapy could generate novel, beneficial treatment plans for patients with OSCC.
Citation Format: Megan Ludwig, Andrew Birkeland, Sai Nimmagadda, Sue Foltin, Aditi Kulkarni, Hui Jiang, Thomas Carey, John Chad Brenner. Genome-wide CRISPR screen identifies potential therapeutic combination of EGFR and FGFR inhibitors in oral cancer [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 964.