Abstract B29: The role of MYD88-dependent signaling in the anti-tumor efficacy of the EGFR inhibitor erlotinib in head and neck cancer cells
Authors: Simons Andrean L. , Koch Adam T. , Love-Homan Laurie , Stanam Aditya 
Published: May 2015

Abstract
Epidermal growth factor receptor (EGFR) is upregulated in the majority of head and neck squamous cell carcinomas (HNSCC). Unfortunately, the incorporation of EGFR inhibitors (EGFRIs) into the management of HNSCC has not improved long-term survival rates in patients with advanced stage HNSCC tumors. Therefore, the identification and understanding of strategies that will improve the efficacy of EGFRIs may potentially improve patient treatment and survival.
Using microarray analysis, our laboratory has observed a profound increase in genes involved in MYD88-dependent pro-inflammatory pathways in EGFRI-treated HNSCC cell lines compared to their respective vehicle-treated cell lines. Additionally, we have previously shown that EGFRIs induce production of the inflammatory cytokine interleukin-6 (IL-6), leading to the reduced efficacy and acquired resistance to EGFRIs in HNSCC cells. Since MYD88-dependent signaling may lead to IL-6 production and secretion, the purpose of these studies is to determine if MYD88-dependent pathways such as Toll-like receptor (TLR), interleukin-1 receptor (IL-1R) and interleukin-18 receptor (IL-18R) pathways are responsible for the IL-6 production induced by EGFRIs.
We found that knockdown of MYD88 (using siRNA and shRNA) significantly inhibited IL-6 secretion induced by the EGFRI erlotinib in Cal-27 and SQ20B HNSCC cells in vitro, increased the anti-tumor activity of erlotinib in vitro and enhanced the anti-tumor efficacy of erlotinib in a HNSCC xenograft mouse model. These results suggested that MYD88-dependent signaling was involved in IL-6 production and in the reduced efficacy of erlotinib.
In order to elucidate which MYD88-dependent pathway was involved in erlotinib-induced IL-6 production, we investigated the involvement of TLR, IL-1R or IL-18R-mediated signaling. Although TLRs and the IL-18R were expressed and active on our HNSCC cells, we found little to no evidence of their involvement in erlotinib-induced IL-6 production. However, inhibition of the IL-1R through pharmacologic (anakinra) or genetic (siRNA and shRNA transfection) methods significantly reduced erlotinib-induced IL-6 production and increased HNSCC cell sensitivity to erlotinib in vitro. These observations point to the IL-1R/MYD88 pathway being involved in IL-6 production and in the reduced efficacy of erlotinib. We observed a time-dependent increase of IL-1 alpha (IL-1α) but not IL-1 beta (IL-1β) in response to erlotinib treatment implicating IL-1α as the damage associated molecular pattern (DAMP) responsible for activating the IL-1R. Furthermore, suppression of cell death with a pan-caspase inhibitor reduced erlotinib-induced IL-1α secretion.
Finally, human HNSCC tumors were found to have higher IL-1α mRNA levels than matched normal tissue, and comparison of high and low IL-1α expressing HNSCC tumors (from the TCGA PANCAN databank) showed IL-1α to be negatively correlated with survival. Altogether, erlotinib-induced cell death may result in the release of IL-1α which activates IL-1R on adjacent surviving cells resulting in MYD88-mediated IL-6 secretion and the development of acquired resistance to erlotinib. In summary, the IL-1α/IL-1R/MYD88/IL-6 pathway may be responsible for the reduced anti-tumor efficacy of erlotinib and other EGFRIs; and blockade of the IL-1 pathway may improve the efficacy of EGFRIs in the treatment of HNSCC. This work was supported by the grants NIH K01CA134941 and ACS IRG7700434.
Citation Format: Andrean L. Simons, Adam T. Koch, Laurie Love-Homan, Aditya Stanam. The role of MYD88-dependent signaling in the anti-tumor efficacy of the EGFR inhibitor erlotinib in head and neck cancer cells. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr B29.