Drug repurposing for the identification of new Bcl-2 inhibitors: In vitro, STD-NMR, molecular docking, and dynamic simulation studies

Background: The anti-apoptotic protein B-Cell Lymphoma 2 (Bcl-2) is a key target for the development of anti-cancer agents, as its overexpression can render cancer cells resistant to chemotherapeutic treatments.Aims and objectives: The current study has systematically evaluated a library of FDA-approved drugs for Bcl-2 inhibition using a drug repurposing strategy via in vitro, biophysical, and in-silico techniques.Materials and methods: In vitro anticancer activity was performed, followed by apoptosis assay. The selected compounds were subjected to Saturation Transfer Difference Nuclear Magnetic Resonance (STD-NMR) spectroscopy, molecular docking, and molecular dynamic simulation for ligand-protein interactions. Key findings: In the initial screening, seventy-five (75) drugs were evaluated against the HL-60 (human blood promyelocytic leukemia) cancer cell line. Among them, paroxetine HCl, carvedilol, clomipramine HCl, and clomifene citrate showed significant anti-proliferative activity (IC50 = 9.733 +/- 0.524, 11.940 +/- 0.079, 12.376 +/- 1.242, and 6.155 +/- 0.363 mu M, respectively), in comparison to the reference drug venetoclax (IC50 = 7.086 +/- 0.041 mu M). This indicated that the test drugs have comparable IC50 values to the standard drug. Furthermore, the drugs were able to induce apoptosis in HL-60 cells. These drugs showed interactions with Bcl-2 protein in STD-NMR analysis. Docking and MD simulation studies further supported the interaction of these drugs with Bcl-2 protein, mainly via hydrophobic contacts leading to stable drug-Bcl-2 complexes. Significance: This study, identifies paroxetine HCl, carvedilol, clomipramine HCl, and clomifene citrate as significant Bcl-2 inhibitors and needs further pre-clinical and clinical studies for potential anti-cancer agents' evaluation.