Design, synthesis and biological evaluation of imidazopyridine/imidazopyrimidine-benzimidazole conjugates as potential anticancer agents

A series of imidazopyridine/imidazopyrimidine-benzimidazole conjugates (11a-t) were synthesized and evaluated for their antiproliferative activity. All of these conjugates showed moderate to improved cytotoxic activity against the human cervical (Hela), lung (A549), prostate (DU-145) and melanoma (B-16) cancer cell lines. Among them, conjugates 11i and 11p showed significant antiproliferative activity against lung cancer cell line A549 with IC₅₀ values 1.48 and 1.92 μM, respectively. Flow cytometric analysis revealed that these conjugates induced cell cycle arrest at G₂/M phase in the A549 cell line leading to caspase-3-dependent apoptotic cell death. The tubulin polymerization assay (IC₅₀ of 11i is 2.06 μM and 11p is 2.26 μM) and immuofluorescence analysis displayed that these conjugates effectively inhibit microtubule assembly at both the molecular and cellular levels in A549 cells. Further, Hoechst staining, caspase-3 activation assay, DNA fragmentation analysis and Annexin V-FITC assay also suggested that these compounds induced cell death by apoptosis. Furthermore, molecular docking studies indicated that these conjugates efficiently interact and bind with tubulin protein. Overall, the present study demonstrates that the synthesis of imidazopyridine/imidazopyrimidine-benzimidazole conjugates as promising tubulin inhibitors with G₂/M phase cell cycle arrest and apoptotic-inducing ability.