Title: Abstract 3307: Induction of autophagy as a mechanism of therapeutic resistance in head and neck cancer
Abstract: Abstract Background: In the curative setting for head and neck cancer (HNC) a commonly used treatment is radiation combined with the anti-EGFR monoclonal antibody cetuximab (CTX). However, despite decades of research into improved treatments, therapeutic resistance remains a major challenge for this malignancy with roughly 40% of patients developing recurrent disease. We are studying the molecular mechanisms by which radiation and cetuximab induce autophagy and how this process can be modulated to improve the efficacy of therapy. Methods: We evaluated a panel of both human papillomavirus (HPV) positive and negative HNC cell lines for autophagic response to both CTX treatment and ionizing radiation (XRT). Induction of autophagy was detected by immunoblot flux assays for LC3 and p62 and by immunofluorescent staining of autophagic vesicles. siRNA knockdown of EGFR, LAMPT4B, ULK1, Beclin1 and others was used to probe the involvement of different signaling molecules. The addition of specific autophagy inhibitors, such as the ULK1 inhibitor SBI-0206965, to CTX or XRT treatment was tested to determine whether the reduction of autophagic response reduced cell survival in a clonogenic survival assay. Induction of apoptosis was analyzed by immunoblot against cleaved Caspase and PARP and AnnexinV staining. Results: Flux assays revealed that both CTX and XRT induced autophagy in a time and dose dependent manner. Immunofluorescent staining of LC3 to identify autophagic vesicles showed that a relatively small fraction of the total cell population is able to induce this response. Specific siRNA knockdown of EGFR and LAMPT4B was able to abrogate the induction of autophagy in response to both CTX and XRT. Involvement of alternative downstream pathways involving either ULK1 and Beclin1 or p53 in response to either treatment is under investigation. To determine whether blockade of cytoprotective autophagy can help overcome therapeutic resistance, we tested specific autophagy inhibitors in combination with either CTX or XRT treatment. The addition of the ULK1 inhibitor to CTX or XRT induced apoptosis as shown by caspase activity, AnnexinV staining, and reduced cell survival in clonogenic assays. Conclusions: Autophagy may play a critical and protective role in how head and neck cancers respond to therapeutic stress. The addition of specific autophagy inhibitors to standard treatments may provide a way to overcome resistance to therapy. Citation Format: Jaimee C. Eckers, Adam D. Swick, Tyler Fowler, Justin Skiba, Kwangok P. Nickel, Randall J. Kimple. Induction of autophagy as a mechanism of therapeutic resistance in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3307. doi:10.1158/1538-7445.AM2017-3307
Publication Year: 2017
Publication Date: 2017-07-01
Language: en
Type: article
Indexed In: ['crossref']
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