DNA methyltransferases are an essential class of modifiers in epigenetics. In mammals, DNMT1, DNMT3A and DNMT3B participate in DNA methylation to regulate normal biological functions, such as embryo development, cell differentiation and gene transcription. Aberrant functions of DNMTs are frequently associated with tumorigenesis. DNMT aberrations usually affect tumor-related factors, such as hypermethylated suppressor genes and genomic instability, which increase the malignancy of tumors, worsen the prognosis for patients, and greatly increase the difficulty of cancer therapy. However, the impact of DNMTs on tumors is still controversial, and therapeutic approaches targeting DNMTs are still under exploration. Here, we summarize the biological functions and paradoxes associated with DNMTs and we discuss some emerging strategies for targeting DNMTs in tumors, which may provide novel ideas for cancer therapy.

Epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) resistance is a major obstacle in the treatment of non-small cell lung cancer (NSCLC). Epigenetic alterations have been shown to be involved in NSCLC oncogenesis; however, their function in EGFR-TKI resistance remains uncharacterized. Here, we found that an EHMT2 inhibitor, UNC0638, can significantly inhibit cell growth and induce apoptosis in EGFR-TKI-resistant NSCLC cells. Additionally, we also found that EHMT2 expression and enzymatic activity levels were elevated in EGFR-TKI-resistant NSCLC cells. Moreover, we determined that genetic or pharmacological inhibition of EHMT2 expression enhanced TKI sensitivity and suppressed migration and tumor sphere formation in EGFR-TKI-resistant NSCLC cells. Further investigation revealed that EHMT2 contributed to PTEN transcriptional repression and thus facilitated AKT pathway activation. The negative relationship between EHMT2 and PTEN was confirmed by our clinical study. Furthermore, we determined that combination treatment with the EHMT2 inhibitor and Erlotinib resulted in enhanced antitumor effects in a preclinical EGFR-TKI-resistance model. We also found that high EHMT2 expression along with low PTEN expression can predict poor overall survival in patients with NSCLC. In summary, our findings showed that EHMT2 facilitated EGFR-TKI resistance by regulating the PTEN/AKT pathway in NSCLC cells, suggesting that EHMT2 may be a target in the clinical treatment of EGFR-TKI-resistant NSCLC.

Tyrosine kinase inhibitors (TKIs) have demonstrated clinical benefits in the treatment of several tumour types. However, the emergence of TKI resistance restricts the therapeutic effect. This study uses non-small cell lung cancer (NSCLC) to explore the mechanisms contributing to TKI resistance in tumours. Biological phenotypes and RNA microarray expression data were analysed in NSCLC cells with and without TKI pretreatment. Specific inhibitors and siRNAs were used to validate the direct involvement of an AKT/FOXM1/STMN1 pathway in TKI resistance. Patients’ tissues were analysed to explore the clinical importance of FOXM1 and STMN1. In vitro and in vivo studies showed that TKIs induced the enrichment of cancer stem cells (CSC), promoted epithelial to mesenchymal transition (EMT), and conferred multidrug resistance on NSCLC cells in a cell type- and TKI class-dependent manner. Mechanistically, TKIs activated an AKT/FOXM1/STMN1 pathway. The crucial role of this pathway in TKI-induced enrichment of CSC and drug resistance was verified by silencing FOXM1 and STMN1 or blocking the AKT pathway. Additionally, overexpression of STMN1 was associated with upregulation of FOXM1 in advanced NSCLC patients, and STMN1/FOXM1 upregulation predicted a poor outcome. Our findings elucidate an additional common mechanism for TKI resistance and provide a promising therapeutic target for reversing TKI resistance in NSCLC.

Zeste enhancer homolog 2 (EZH2) is highly expressed in various malignant tumors, which could silence tumor suppressor genes via trimethylation of H3K27. Herein was first reported a novel series of pyrrole-3-carboxamide derivatives carrying a pyridone fragment as EZH2 inhibitors. By combining computational modeling, in vitro cellular assays and further rational structure–activity relationship exploration and optimization, compound DM-01 showed powerful inhibition towards EZH2. DM-01 was found to have significant ability to reduce the cellular H3K27me3 level in K562 cells in the Western blot test. Meanwhile, our data showed that knockdown EZH2 in A549 cells resulted in a decrease of cell sensitivity to DM-01 at 50 and 100 μM. DM-01 could also increase the transcription expression of DIRAS3 in a dose-dependent manner, a tumor suppressor in the downstream of EZH2, suggesting it was worth investigating further as a lead compound.