Abstract 3176: The EGFR pathway as the Achilles’ heel for human papillomavirus-induced tumors: EGFR/MAPK pathway inhibitors exhibit antiviral activities and limit tumor growth in vivo

Abstract

Human papillomaviruses (HPVs) are etiological agents of many anogenital and oropharyngeal cancers. HPV[+] oropharyngeal squamous cell carcinomas (OPSCCs) typically respond more favorably to current treatment regimens (including radiotherapy combined with cisplatin or cetuximab, an EGFR monoclonal antibody), than do HPV-negative OPSCCs. The discrepancy in patient outcomes has been attributed, in part, to substantially fewer genetic mutations present in HPV[+] cancers. Paradoxically, an increasing body of literature notes lower EGFR expression in HPV[+] vs. HPV[-] OPSCC. Yet, HPV oncoproteins E5, E6 and E7 each work to increase EGFR signaling, and MAPK-regulated AP-1 transcription factors direct HPV early gene expression. The goal of this work is to test the hypothesis that upon infection, HPV establishes a feed-forward loop with the EGFR pathway to drive viral gene expression independent of EGFR levels. We modeled early neoplasia with cell lines maintaining episomal HPV16 genomes, and cancers using SCC lines with integrated HPV16 genomes. Cells treated with EGF, EGFR inhibitors (cetuximab, erlotinib), or MEK antagonists (PD98059, trametinib) were evaluated for signaling and viral responses. Consistent with our hypothesis, we found increased EGF-dependent EGFR activation levels in HPV[+] cell lines, as well as heightened MEK1/2 activity independent of EGFR activation in HPV[+] cell lines compared to uninfected cells. RT-qPCR revealed that HPV oncogene transcription was enhanced by EGFR activation, whereas EGFR and MEK inhibitors led to significant declines in HPV transcription. In cells with episomal HPV genomes, lower viral genome levels accompanied inhibitor-reduced viral transcription. These data suggest EGFR/MAPK pathway interference leads to anti-viral affects, which are expected to restore p53 and pRb function and prevent tumorigenesis in vivo. As predicted, cell proliferation and tumor growth in NOD/SCID-gamma mouse HPV[+] SCC xenografts were significantly reduced with EGFR and MEK inhibitors. Experiments are underway to quantify the restored function of p53 and pRb in drug-treated cells and determine if these cells become sensitized to lower doses of cisplatin or radiation. In summary, our results reveal HPV infection creates a feed-forward loop with the EGFR/MAPK proliferation pathway, and EGFR and MEK antagonists have anti-viral effects, including reduction in the E6 and E7 oncoproteins needed to maintain the transformed phenotype in vitro and in vivo. Additionally, the ability of the drugs to reduce episomal viral genome levels suggests a potential curative effect if administered prior to viral genome integration. Lastly, this work reveals an anti-viral molecular mechanism which may account for the favorable outcomes of patients with HPV[+] OPSCC treated with cetuximab-radiotherapy. Citation Format: Anastacia M. Griego, Pamela Barraza, Chelin Hu, Agnieszka Dziduszko, Brianna K. Crowley, Helen J. Hathaway, Julie E. Bauman, Michelle A. Ozbun. The EGFR pathway as the Achilles’ heel for human papillomavirus-induced tumors: EGFR/MAPK pathway inhibitors exhibit antiviral activities and limit tumor growth in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3176. doi:10.1158/1538-7445.AM2014-3176