PIM1-mediated signalling as a therapeutic target in breast cancer: repurposing venetoclax for targeted inhibition.

PIM1 kinase has emerged as a critical mediator of cancer progression, particularly in triple-negative breast cancer (TNBC), due to its involvement in epithelial-mesenchymal transition (EMT), drug resistance, and cell survival pathways. This study aimed to evaluate PIM1-mediated signalling as a therapeutic target in breast cancer and identify potential repurposed drugs using an integrative in silico and in vitro approach. Protein-protein interaction and pathway enrichment analyses revealed that PIM1 and its interactors are involved in EMT, cell cycle, and drug resistance pathways. Gene expression analysis using Human Protein Atlas data and qRT-PCR confirmed significantly elevated PIM1 expression in MDA-MB-231 (31.4-fold) and EMT-induced MDA-MB-231 (47.69-fold) compared to MCF-7. Structure-based virtual screening of 2,450 FDA-approved drugs and MD simulation identified Venetoclax as a potential inhibitor of PIM1, showing strong binding energy (-206.703 kJ/mol). Further, cytotoxicity assays exhibited a significantly lower IC₅₀ of Venetoclax in EMT-MDA-MB-231 cells (4.41 µM), compared to MDA-MB-231 (42.29 µM) and MCF-7 (19.68 µM). Subsequent western blot analysis showed a 2.39-fold reduction in GSK3β phosphorylation in EMT-MDA-MB-231 cells, validating inhibition of PIM1-mediated signalling. In addition, Mitoxantrone accumulation assay revealed a 1.4-fold increase, suggesting reduced ABCG2-mediated drug efflux. These findings support Venetoclax as a promising inhibitor of PIM1-mediated signalling with selective efficacy against aggressive breast cancer phenotypes. Its dual targeting of EMT signalling and drug resistance highlights its translational potential and paves the way for further clinical development.