Abstract 4108: Targeting IL-6 signaling overcomes cetuximab resistance in head and neck squamous cell carcinoma

Abstract Head and neck squamous cell carcinoma (HNSCC), the sixth most common cancer worldwide, has a five-year survival rate of only 50%. The first targeted agent FDA approved for treatment of HNSCC was cetuximab, a monoclonal antibody targeting the epidermal growth factor receptor (EGFR). Despite EGFR overexpression in up to 90% of HNSCC tumors and ample evidence supporting EGFR as a therapeutic target in HNSCC, the response rate for single-agent cetuximab is below 20%, and resistance to cetuximab-containing therapy remains a major obstacle in the effective treatment of HNSCC. Identification and targeting of mediators of cetuximab resistance is needed to improve patient outcomes. Secretion of the cytokine interleukin 6 (IL-6) has been proposed as a mechanism of resistance to cetuximab in HNSCC, and inhibition of signal transducer and activator of transcription 3 (STAT3), a downstream mediator of IL-6 signaling, has been shown to overcome cetuximab resistance in preclinical HNSCC models. Thus, we hypothesize that IL-6 signaling mediates resistance to cetuximab and that co-treatment with agents targeting the IL-6 pathway will enhance the therapeutic efficacy of cetuximab in HNSCC. We have generated cetuximab-resistant variants of the cetuximab-sensitive HNSCC cell lines Cal33 and PE/CA-PJ49. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis indicated that IL6 expression is increased 3.5- to 8-fold in cetuximab-resistant variants compared to the parental cells from which they were derived. In addition, a colony formation assay revealed that, as expected, cetuximab-treated parental cells formed fewer colonies than vehicle-treated cells, while cetuximab treatment had no effect on the ability of cetuximab-resistant PE/CA-PJ49 variants to form colonies. In contrast, treatment with tocilizumab, an IL-6 receptor-neutralizing monoclonal antibody, markedly reduced the colony-forming ability of the cetuximab-resistant variants, but not parental cells. These results suggest that targeted inhibition of IL-6 signaling may effectively inhibit proliferation in cetuximab-refractory HNSCC cells. Citation Format: Rachel A. O'Keefe, Neil Bhola, Toni M. Brand, Yan Zeng, Daniel E. Johnson, Jennifer R. Grandis. Targeting IL-6 signaling overcomes cetuximab resistance in head and neck squamous cell carcinoma [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 4108. doi:10.1158/1538-7445.AM2017-4108