We demonstrated here that the transcription of DNA methyltransferases DNMT1, DNMT3A, DNMT3B and COQ3 genes as well as the histone methyltransferase DOT1, SUV39H1 and SUV39H2 were downregulated in GBK-treated MCF-7 cells (Supplementary Figure 3B), indicating that GBK could inhibit breast cancer progression by reducing the DNA methylation level in the promoters of tumor suppressor genes or the global genome. The gene discussed is COQ3; the disease is breast cancer.