Abstract 5267: Pro-inflammatory CXCL8 signaling potentiates survival of K-Ras mutant colorectal cancer cells

Abstract

Abstract Background: Pro-inflammatory signaling within the tumor microenvironment is proposed to aid tumor progression and metastasis in a number of cancer types, including colorectal cancer (CRC). The pro-inflammatory chemokine, CXCL8 (interleukin-8) has been associated with tumor size, Dukes stage, liver metastasis and overall survival in CRC. This chemokine is expressed by multiple cell types within the tumor microenvironment including tumor cells, innate immune, and vascular endothelial cells. Additionally, the elevated expression of both CXCL8 receptors, CXCR1 and CXCR2, in CRC tumor epithelium relative to normal adjacent tissue indicates that CRC is receptive to both an autocrine tumor-derived stimulus and a paracrine ‘stromal-derived’ stimulus. Objectives: Our first objective was to characterise how mutation of the oncogene K-Ras may regulate CXCL8 expression and signaling in CRC cells in vitro. Secondly, we sought to characterise the importance of CXCL8 in modulating survival of K-Ras mutant CRC cells. Results: Mutation of K-Ras or the catalytic subunit of phosphatidyl-inositol-3 kinase (PI3KCA) is indicated in 35-40% and 15-18% of colorectal adenocarcinomas, respectively. The HCT-116 cell line harbours mutations in both K-Ras and PI3KCA. Basal CXCL8, CXCL1 and CXCR1/2 levels were significantly elevated in K-Ras mutant HCT-116 cells relative to isogenic HKH-2 K-Ras wild-type cells. Treatment with inhibitors of AKT and/or MEK attenuated CXCL8 transcript levels and secretion in K-Ras mutant cells, but conversely increased CXCR1/2 gene expression. Attenuation of CXCL8 gene expression using siRNA demonstrated a concurrent loss of cell viability in CRC cells; this effect was significantly marked in K-Ras mutant HCT-116 cells, consistent with increased dependence of these cells on elevated CXCL8 signaling. Moreover, attenuation of CXCR2 signaling potentiated the sensitivity of K-Ras mutant HCT-116 cells to oxaliplatin and 5-FU. In addressing mechanisms underpinning CXCL8-promoted resistance, treatment with recombinant human CXCL8 was shown to increase expression of anti-apoptotic proteins Bcl-XL and Bcl-2 and furthermore, induce phosphorylation of multiple tyrosine kinases (RTKs) including EGFR, c-MET and FGFR1. Furthermore, blockade of CXCR2 signaling attenuated oxaliplatin-induced increases in anti-apoptotic protein expression in HCT-116 cells. Conclusions: CXCL8 signaling is elevated in K-Ras and PI3KCA mutant cancers. The up-regulation of autocrine CXCL8 signaling is linked to the promotion of cell survival, principally mediated through the inhibition of apoptosis and promotion of RTK signaling. The clinical relevance of CXCL8 signaling in modulating outcome of K-Ras mutant CRC to current treatments remains to be determined. However, CXCL8-directed therapies may be relevant as chemo-sensitizing agents in K-Ras and/or PIK3CA mutant tumors. Citation Format: Laura M. Campbell, Olabode Oladipo, Pamela J. Maxwell, Daniel Longley, Richard H. Wilson, David JJ Waugh. Pro-inflammatory CXCL8 signaling potentiates survival of K-Ras mutant colorectal cancer cells. [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 5267. doi:10.1158/1538-7445.AM2014-5267