Role of Nicotinamide N-methyltransferase and bone morphogenetic protein 4 in EGFR-TKI-resistance of non-small cell lung cancer cells

Abstract

Lung cancer is considered as the leading cause of cancer-associated deaths worldwide and epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are used clinically as target therapies for lung cancer patients. However, the occurrence of acquired EGFR-TKI-mediated resistance such as gefitinib, remains a major problem in non-small cell lung cancer (NSCLC) treatment and limits their efficacy. Subsequently, various studies are ongoing to investigate the mechanisms of drug resistance and explore the novel therapeutics strategies for NSCLC treatment. The present study suggests the mechanisms of acquired gefitinib resistance using PC9-Gef cells, HCC827-Gef cells, H1993-Gef cells and H292-Gef cells that gained resistance through continuous exposure to gefitinib. Moreover, employing a natural product daphnane diterpenoid yuanhuadine (YD), an antitumor agent, a novel strategy was confirmed to overcome this resistance via modulation the targeted genes. <br/> Accumulating evidence also suggests that microRNAs (miRNAs), a new class of small, nonprotein-encoding RNAs, play a significant role in epigenetically modulating various phenotypic changes in cancer cells. Indeed, miRNAs may affect genetic programs through post-transcriptional silencing of target genes, either by inhibiting the translation of target mRNAs or by promoting their degradation. These actions may lead to the regulation of numerous aspects of cancer biology, including drug resistance. <br/> <br/> Recently, overexpression of Nicotinamide N-methyltransferase (NNMT), a cancer-associated metabolic enzyme, is correlated with various human tumors. However, their precise roles in regulating the development of drug-resistant tumorigenesis are still poorly understood. Herein, establishing EGFR-TKI-resistant NSCLC models indicates that there is a negative correlation between the expression levels of NNMT and miR-449a in tumor cells. Additionally, knockdown of NNMT suppressed p-Akt and tumorigenesis, while re-expression of miR-449a induced phosphatase and tensin homolog, and inhibited tumor growth. Furthermore, YD, significantly upregulated miR-449a levels while critically suppressing NNMT expression. <br/> Bone morphogenetic proteins (BMPs) are a family of signaling molecules that belong to the transforming growth factor-β superfamily and the activation of the BMP-BMP receptor pathway conferred resistance to EGFR-TKIs in lung cancer patients harboring EGFR mutations. Recent studies have also suggested the possibility that small-molecule BMP4 antagonists were able to effectively inhibit the growth of lung cancer cells and chemotherapy-resistant cancer cells. In the present study, in comparison with the gene expression pattern of parental NSCLC cells, acquired gefitinib-resistant cell lines displayed that BMP4 gene was up-regulated in the gefitinib-resistant cell lines. Therefore, the role of BMP4 in EGFR-TKI resistance in NSCLC cells and the dynamic interactions of BMP4 with the tumor microenvironment such as miRNA or fatty acids were also elucidated. <br/> Based on these findings, up-regulation of NNMT and BMP4 or down-regulation of miR-449a expression can be regarded as novel cancer biomarkers of acquired gefitinib resistance and therapeutic targets overcome this resistance. Moreover, YD, which induces the expression of miRNAs while suppresses NNMT and BMP4 expression may be considered as a potential lead compound for the gefitinib-resistant NSCLC.<br/>