GSK-3484862, a DNMT1 degrader, promotes <i>DNMT3B</i> expression in lung cancer cells

DNA methylation alterations, including hypermethylation and silencing of tumor suppressor genes, contribute to cancer formation and progression. The FDA-approved nucleoside analogs azacytidine and decitabine are effective demethylating agents for hematologic malignancies but their general use has been limited by their toxicity and ineffectiveness against solid tumors. GSK-3484862, a dicyanopyridine-containing, DNMT1-selective inhibitor and degrader, offers a promising lead for developing novel demethylating therapeutics. Here, we demonstrate that GSK-3484862 treatment upregulates <i>DNMT3B</i> expression in lung cancer cell lines (A549 and NCI-H1299). Disrupting <i>DNMT3B</i> in NCI-H1299 sensitizes these cells to GSK-3484862, enhancing its inhibitory effects on cell viability and growth. GSK-3484862 treatment induces demethylation at <i>DNMT3B</i> regulatory elements including a candidate enhancer located ∼10 kb upstream of the <i>DNMT3B</i> transcription start site, as well as at the promoter of <i>TERT</i> (telomerase reverse transcriptase), a potential activator of <i>DNMT3B</i> expression. These demethylation events correlate with upregulation of <i>DNMT3B</i> expression. These findings suggest that combining inhibitors targeting DNMT1, the maintenance methyltransferase, with those targeting DNMT3A/3B, the <i>de novo</i> methyltransferases, or using pan-DNMT inhibitors, could enhance anticancer efficacy and reduce resistance.