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

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. The methylation status of CCCTC-binding factor (CTCF)-binding sites in the 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. HDAC inhibition by vorinostat increased acetylated STAT3 (K685), resulting in transcriptional upregulation of DNMT1-mediated hypermethylation of CTCF-binding sites in the ICR decreased CTCF insulator activity, leading to a transcriptional upregulation of and activation of the insulin-like growth factor 1 receptor (IGF-1R) pathway in cells with acquired or vorinostat resistance. Strategies targeting DNMT1 diminished the expression and potentiated vorinostat sensitivity in preclinical models of lung cancer with hypermethylation in the ICR. The degree of ICR hypermethylation correlated with vorinostat resistance in patient-derived lung tumors and in patients with hematologic malignancies. DNMT1-mediated transcriptional upregulation of 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 ICR hypermethylation and DNMT1 expression as predictive biomarkers in HDI-based anticancer therapies. .