miR-640 Enhances Abemaciclib Sensitivity by Suppressing CDK Inhibitor Resistance-Associated Genes in Breast Cancer Cells.

We investigated the potential of miR-640 to downregulate CDK4/6 inhibitor resistance-associated genes and evaluated its apoptotic, anti-metastatic and anti-proliferative effects, both alone and in combination with abemaciclib in breast cancer cells. miR-640 was identified via GSE126125 dataset analysis. Targets were predicted using miRDB, TargetScan and TargetMiner, filtering for resistance-associated genes. MTT assays determined IC50 values for abemaciclib and combinations. Functional effects were evaluated in MCF7 and MDA-MB-231 cells through Annexin V, cell cycle and wound healing assays. Target gene expression was quantified by RT-qPCR. Successful transfection significantly upregulated miR-640 (~50-fold). The miR-640/abemaciclib combination strongly inhibited migration, induced apoptosis and triggered cell line-specific phase arrests (S and G2/M in MCF7; G0/G1 in MDA-MB-231). Gene expression analysis showed significant downregulation of a comprehensive resistance network (including CDK4/6, CDKN2B, WNT7B, MAP3K1 and AURKA) in MCF7 cells. In MDA-MB-231 cells, PDK1, CDK6, CDKN2B, SMAD2, ZFP91, MAP3K1 and AURKA were significantly suppressed. This study identifies miR-640 as a potent tumour suppressor that resensitises breast cancer cells to CDK4/6 inhibition. By post-transcriptionally downregulating key resistance genes, miR-640-alone or additively with abemaciclib-suppresses proliferation and migration while inducing apoptosis, emerging as a promising combinatorial therapeutic strategy.