Design and synthesis of 1,2,3-triazolo linked benzo[d]imidazo[2,1-b]thiazole conjugates as tubulin polymerization inhibitors

1,2,3-Triazolo linked benzo[d]imidazo[2,1-b]thiazole conjugates (5a–v) were designed, synthesized and evaluated for their cytotoxic potency against some human cancer cell lines like DU-145 (prostate), HeLa (cervical), MCF-7 (breast) HepG2 (liver) and A549 (lung). Preliminary results revealed that some of these conjugates like 5f and 5k exhibited significant antiproliferative effect against human breast cancer cells (MCF-7) with IC₅₀ values of 0.60 and 0.78 µM respectively. Flow cytometric analysis of the cell cycle demonstrated an increase in the percentage of cells in the G₂/M phase which was further authenticated by elevation of cyclin B1 protein levels. Immunocytochemistry revealed loss of intact microtubule structure in cells treated with 5f and 5k, and western blot analysis revealed that these conjugates accumulated more tubulin in the soluble fraction. Moreover, the conjugates caused apoptosis of the cells that was confirmed by mitochondrial membrane potential and Annexin V-FITC assay. Molecular docking studies indicated that these conjugates occupy the colchicine binding site of the tubulin protein.