Genome-wide DNA Methylation Analysis Reveals <i>GABBR2</i> as a Novel Epigenetic Target for <i>EGFR</i> 19 Deletion Lung Adenocarcinoma with Induction Erlotinib Treatment.

Abstract

<b>Purpose:</b> The past decade has witnessed the rapid development of personalized targeted therapies in lung cancer. It is still unclear whether epigenetic changes are involved in the response to tyrosine kinase inhibitor (TKI) treatment in epidermal growth factor receptor (<i>EGFR</i>)-mutated lung cancer.<b>Experimental Design:</b> Methyl-sensitive cut counting sequencing (MSCC) was applied to investigate the methylation changes in paired tissues before and after erlotinib treatment for 42 days with partial response (PR) from stage IIIa (N2) lung adenocarcinoma patients (<i>N</i> = 2) with <i>EGFR</i> 19 deletion. The Sequenom EpiTYPER assay was used to validate the changed methylated candidate genes. Up- or downregulation of the candidate gene was performed to elucidate the potential mechanism in the regulation of erlotinib treatment response.<b>Results:</b> Sixty aberrant methylated genes were screened using MSCC sequencing. Two aberrant methylated genes, <i>CBFA2T3</i> and <i>GABBR2</i>, were clearly validated. A same differential methylated region (DMR) between exon 2 and exon 3 of <i>GABBR2</i> gene was confirmed consistently in both patients. GABBR2 was significantly downregulated in <i>EGFR</i> 19 deletion cells, HCC4006 and HCC827, but remained conserved in <i>EGFR</i> wild-type A549 cells after erlotinib treatment. Upregulation of GABBR2 expression significantly rescued erlotinib-induced apoptosis in HCC827 cells. GABBR2 was significantly downregulated, along with the reduction of S6, p-p70 S6, and p-ERK1/2, demonstrating that GABBR2 may play an important role in EGFR signaling through the ERK1/2 pathway.<b>Conclusions:</b> We demonstrated that <i>GABBR2</i> gene might be a novel potential epigenetic treatment target with induction erlotinib treatment for stage IIIa (N2) <i>EGFR</i> 19 deletion lung adenocarcinoma. <i>Clin Cancer Res; 23(17); 5003-14. ©2017 AACR</i>.