Computational and experimental repositioning of quinoline analogues as KSP inhibitors: insights from free energy landscape and PCA analysis

Eg5 is a mitotic kinesin motor protein essential for the formation of bipolar spindles during cell division. Its inhibition disrupts mitosis, leading to cell cycle arrest and apoptosis in cancer cells. This makes Eg5 a promising target for chemotherapeutic interventions, especially in cases resistant to traditional treatments. In this study, a drug repurposing strategy was employed to design and synthesise quinoline-based Schiff base derivatives as potential Eg5 inhibitors. These compounds were subjected to in vitro biological evaluations, including cytotoxicity testing against the human breast cancer cell line MDA-MB-231 and the normal mouse fibroblast cell line L929 using the MTT assay. Enzymatic assays targeting Eg5 were also conducted. Among the synthesised molecules, compound (5) demonstrated significant Eg5 inhibition in enzymatic assays, with an IC₅₀ of 2.544 ± 0.810 µM in the Malachite Green assay and 4.03 ± 2.027 µM in the steady-state ATPase assay, and moderate inhibition against triple-negative breast cancer cells (MDA-MB-231). Computational studies, including molecular docking, molecular dynamics simulations, and MM/GBSA free energy calculations, were performed to analyse binding interactions. ADMET properties were predicted using the QikProp module. The findings suggest that targeting mitosis through Eg5 inhibition may offer a strategic approach in chemotherapy, potentially enhancing treatment efficacy.