Estrogen-dependent breast cancer is often treated with the aromatase inhibitors or estrogen receptor (ER) antagonists. Tamoxifen as a major ER antagonist is usually used to treat those patients with ERα-positive breast cancer. However, a majority of patients with ERα positive fail to respond to tamoxifen due to the presence of intrinsic or acquired resistance to the drug. Altered expression and functions of microRNAs (miRNAs) have been reportedly associated with tamoxifen resistance. In this study, we investigated the role of miR-27b-3p in resistance of breast cancer to tamoxifen. MiR-27b-3p levels were remarkably reduced in the tamoxifen-resistant breast cancer cells compared with their parental cells. In addition, miR-27b-3p was also significantly downregulated in breast tumor tissues relative to adjacent non-tumor tissues. Moreover, the expression levels of miR-27b-3p were lower in the breast cancer tissues from tamoxifen-resistant patients compared with that from untreated-tamoxifen patients. Notably, tamoxifen repressed miR-27b-3p expression, whereas estrogen induced miR-27b-3p expression in breast cancer cells. Besides, we provided experimental evidences that miR-27b-3p enhances the sensitivity of breast cancer cells to tamoxifen in vitro and in vivo models. More importantly, we validated that miR-27b-3p directly targeted and inhibited the expression of nuclear receptor subfamily 5 group A member 2 (NR5A2) and cAMP-response element binding protein 1 (CREB1) and therefore augmented tamoxifen-induced cytotoxicity in breast cancer. Lastly, miR-27b-3p levels were found to be significantly negatively correlated with both NR5A2 and CREB1 levels in breast cancer tissues. Our findings provided further evidence that miR-27b-3p might be considered as a novel and potential target for the diagnosis and treatment of tamoxifen-resistant breast cancer.

Background/Aim: Treatment of human non-small-cell lung cancer (NSCLC) often involves uses of multiple therapeutic strategies with different mechanisms of action. Here we found that resveratrol (RV) enhanced the anti-tumor effects of epidermal growth factor receptor (EGFR) inhibitor erlotinib in NSCLC cells. Methods: Cell viability was measured by MTT assay and clonogenicity assay. Western blot was applied to assess the protein expression levels of target genes. Cell apoptosis was monitored by AnnexinV-FITC assay and sub-G1 population assay. Intracellular ROS were measured by flow cytometric analysis. Cell caspase activities were carried out by fluorometric assays. Results: Exposure of H460, A549, PC-9 and H1975 cells to minimal or non-toxic concentrations of RV and erlotinib synergistically reduced cell viability, colony formation and induced cell apoptosis. Furthermore, RV synergistically enhanced erlotinib-induced apoptosis was involved in ROS production. Additionally, co-treatment with RV and erlotinib repressed the expressions of anti-apoptosis proteins, such as survivin and Mcl-1, whereas promoted p53 and PUMA expression and caspase 3 activity. Moreover, the combination was also more effective at inhibiting the AKT/mTOR/S6 kinase pathway. Subsequently, small interfering RNA (siRNA) depletion of PUMA and overexpression of survivin significantly attenuated NSCLC cells apoptosis induced by the combination of the two drugs. Conclusion: Our findings suggested that RV synergistically enhanced the anti-tumor effects of erlotinib in NSCLC cells were involved in decrease of survivin expression and induction of PUMA expression. In conclusion, based on the observations from our study, we indicated that the combined administration of these two drugs might be considered as a novel therapeutic regimen for treating NSCLC.

Chemoresistance is a major obstacle to effective breast cancer chemotherapy. However, the underlying molecular mechanisms remain unclear. In this study, nuclear receptor coactivator 3 (NCOA3) was found to be significantly increased in taxol-resistant breast cancer tissues and cells. Moreover, overexpression of NCOA3 enhanced breast cancer cell resistance to taxol, whereas depletion of NCOA3 decreased taxol resistance. Subsequently, we investigated whether NCOA3 expression was regulated by miRNAs in breast cancer. By bioinformatics prediction in combination with the data of previous report, miR-17 and miR-20b were selected as the potential miRNAs targeting NCOA3. By real-time PCR analysis, we found that miR-17 and miR-20b were significantly reduced in taxol-resistant breast cancer tissues and cells. In addition, we provided some experimental evidences that miR-17 and miR-20b attenuated breast cancer resistance to taxol in vitro and in vivo models. Furthermore, by luciferase reporter assays, we further validated that both miR-17 and miR-20b directly binded the 3′-untranslated region of NCOA3 mRNA and inhibited its expression in breast cancer cells. Finally, both miR-17 and miR-20b levels were found to be significantly negatively correlated with NCOA3 mRNA levels in breast cancer tissues. Together, our results indicated that loss of miR-17 and miR-20b enhanced breast cancer resistance to taxol by upregulating NCOA3 levels. Our study suggested miR-17, miR-20b and NCOA3 may serve as some predictive biomarkers and potential therapeutic targets in taxol-resistant breast cancer treatment.