Essential Role of DNA Methyltransferase 1–mediated Transcription of Insulin-like Growth Factor 2 in Resistance to Histone Deacetylase Inhibitors

Abstract

<b>Purpose:</b> Histone deacetylase inhibitors (HDI) are promising anticancer therapies; however, drug resistance limits their efficacy. Here, we investigated the molecular mechanisms underlying HDI resistance, focusing on the mechanism of HDI-mediated induction of insulin-like growth factor 2 (IGF2) based on our previous study.<b>Experimental Design:</b> The methylation status of CCCTC-binding factor (CTCF)-binding sites in the <i>IGF2/H19</i> imprinting control region (ICR) were determined by methylation-specific PCR and bisulfite sequencing. The effectiveness of single or combinatorial blockade of DNA methyltransferase 1 (DNMT1) and histone deacetylase (HDAC) was evaluated using cell viability assay and patient-derived tumor xenograft (PDX) model.<b>Results:</b> HDAC inhibition by vorinostat increased acetylated STAT3 (K685), resulting in transcriptional upregulation of <i>DNMT1</i> DNMT1-mediated hypermethylation of CTCF-binding sites in the <i>IGF2/H19</i> ICR decreased CTCF insulator activity, leading to a transcriptional upregulation of <i>IGF2</i> and activation of the insulin-like growth factor 1 receptor (IGF-1R) pathway in cells with acquired or <i>de novo</i> vorinostat resistance. Strategies targeting DNMT1 diminished the <i>IGF2</i> expression and potentiated vorinostat sensitivity in preclinical models of lung cancer with hypermethylation in the <i>H19/IGF2</i> ICR. The degree of ICR hypermethylation correlated with vorinostat resistance in patient-derived lung tumors and in patients with hematologic malignancies.<b>Conclusions:</b> DNMT1-mediated transcriptional upregulation of <i>IGF2</i> is a novel mechanism of resistance to HDIs, highlighting the role of epigenetic deregulation of IGF2 in HDI resistance and the potential value of the <i>H19/IGF2</i> ICR hypermethylation and DNMT1 expression as predictive biomarkers in HDI-based anticancer therapies. <i>Clin Cancer Res; 23(5); 1299-311. ©2016 AACR</i>.