The epidermal growth factor receptor (EGFR) tyrosine kinase signaling pathways regulate cellular activities. The EGFR tyrosine kinase inhibitors (EGFR-TKIs) repress the EGFR pathway constitutively activated by somatic EGFR gene mutations and have drastically improved the prognosis of non-small-cell lung cancer (NSCLC) patients. However, some problems, including resistance, remain to be solved. Recently, combination therapy with EGFR-TKIs and cytotoxic agents has been shown to improve the prognosis of NSCLC patients. To enhance the anticancer effects of EGFR-TKIs, we examined the cross-talk of the EGFR pathways with ataxia telangiectasia-mutated (ATM) signaling pathways. ATM is a key protein kinase in the DNA damage response and is known to phosphorylate Akt, an EGFR downstream factor. We found that the combination of an ATM inhibitor, KU55933, and an EGFR-TKI, gefitinib, resulted in synergistic cell growth inhibition and induction of apoptosis in NSCLC cell lines carrying the sensitive EGFR mutation. We also found that KU55933 enhanced the gefitinib-dependent repression of the phosphorylation of EGFR and/or its downstream factors. ATM inhibition may facilitate the gefitinib-dependent repression of the phosphorylation of EGFR and/or its downstream factors, to exert anticancer effects against NSCLC cells with the sensitive EGFR mutation.
Keywords: ATM inhibitor; EGFR mutation; EGFR-TKI; combination therapy; non-small-cell lung cancer.
© 2016 The Authors. Cancer Science published by John Wiley & Sons Australia, Ltd on behalf of Japanese Cancer Association.