Synthesis of 3-N-/O-/S-methyl-imidazo[1,2-a] pyridine derivatives for caspase-3 mediated apoptosis induced anticancer activity

A library of 49 analogs of imidazo[1,2-a]pyridine with 2-halo, aryl, styryl and phenylethynyl-substitution at C-2 position and N-/O-/S-methyl linkage at C-3 position, have been synthesized and evaluated for their anti-proliferative activity against breast (MCF-7, MDA-MB-231), pancreatic (MiaPaca-2), lung (A549), prostate (PC-3) and colon (HCT-116) cancer cell lines and normal cells (HEK-293). Among the screened compounds, 5b exhibited best anticancer potential in all tested cancer cells with IC₅₀ ranging from 3.5 to 61.1 µM and no toxicity in normal cells. Further, mechanistic study of 5b revealed concentration dependent increased generation of ROS, reduced mitochondrial membrane potential (MMP), surface and nuclear morphological alterations and inhibition of colony formation in HCT-116 cells. Western blot results had shown that the cell death in HCT-116 colon cancer cells was achieved through the induction of apoptosis via upregulation of the PTEN gene and downregulation of AKT pathway. Similarly, 5b treatment induced caspase-3 cleavage which is a hallmark of apoptosis. Molecular docking and binding energy (ΔG) studies of hit 5b with respect to three important cancer targets (EGFR, mTOR and PI3Kα) revealed strong binding of inhibitor with PI3Kα (docking score −6.932 and ΔG −56.297).