Abstract 2104: ERK-dependent IL-6 autocrine signaling mediates adaptive resistance to pan-PI3K inhibitor in head and neck squamous cell carcinoma

Abstract

Abstract Purpose: To investigate resistant mechanisms to NVP-BKM120, a pan-PI3K inhibitor, and potential combination therapies in head and neck squamous cell carcinoma (HNSCC). Experimental Design: A panel of 10 human HNSCC cell lines including NVP-BKM120-resistant HNSCC patient-derived cell lines were used to evaluate the antitumor activity of NVP-BKM120. Patient-derived tumor xenograft (PDTX) models were established from recurrent/metastatic HNSCC patients treated with and resistant to NVP-BKM120. Results: Treatment of NVP-BKM120 led to upregulation of interleukin 6 (IL-6) and subsequent activation of either extracellular signal-regulated kinase (ERK) or signal transducers and activators of transcription 3 (STAT3), resulting in a modest antitumor effects on HNSCC cells. In a subset of cell lines, blockade of IL-6 autocrine signaling with IL-6 receptor (IL-6R) siRNA or IL-6R neutralizing antibody completely abolished constitutive or NVP-BKM120-induced activation of ERK and STAT3 as well as expression of oncogenic factors including Bcl2 and cMYC, resulting in the enhanced sensitivity to NVP-BKM120 with a marked reduction of S phase and significant increment of G0/G1 arrest. Interestingly, trametinib, a MEK inhibitor, significantly reduced NVP-BKM120-induced IL-6 and cMYC upregulation, whereas it had no effect on STAT3 inhibition. Moreover, combination of NVP-BKM120 with trametinib yielded more potent anti-tumor effects than combination with a pharmacologic inhibitor of STAT3 or siSTAT3. Furthermore, combination of NVP-BKM120 with trametinib or tocilizumab, a humanised anti-IL-6 receptor antibody, synergistically suppressed the growth of NVP-BKM120-resistant PDTX models as compared with either agent alone, which was confirmed in two PDTX-derived cell lines. Conclusions: Collectively, these results suggested that IL-6/ERK signaling contributes to intrinsic and adaptive resistance to NVP-BKM120 in HNSCC, providing a rationale for a novel therapeutic strategy to overcome resistance to pan-PI3K inhibitors. Citation Format: Mi Ran Yun, Han Na Kang, Byoung Chul Cho. ERK-dependent IL-6 autocrine signaling mediates adaptive resistance to pan-PI3K inhibitor in head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2104.