Design and synthesis of imidazo[2,1-b]thiazole linked triazole conjugates: Microtubule-destabilizing agents

A series of imidazo[2,1-b]thiazole linked triazole conjugates were synthesized by using Huisgen 1,3-dipolar cyclo-addition reaction (click chemistry approach) and evaluated for their antiproliferative activity against some human cancer cell lines like, HeLa (cervical), DU-145 (prostate), A549 (lung), MCF-7 (breast) and HepG2 (liver). Among them, Conjugates 4g and 4h demonstrated a significant antiproliferative effect against human lung cancer cells (A549) with IC₅₀ values of 0.92 and 0.78 μM respectively. Flow cytometric analysis revealed that these conjugates induced cell cycle arrest in G2/M phase in A549 lung cancer cells. The tubulin polymerization assay and immunofluorescence analysis showed that these conjugates effectively inhibit microtubule assembly in cell free and cell based (A549) experiment respectively. Moreover, the apoptosis inducing properties were evaluated by Hoechst staining, mitochondrial membrane potential and Annexin V-FITC assay. Further, western blot analysis was performed for proapoptotic protein Bax and antiapoptotic protein Bcl-2 and the results demonstrated that there was up regulation of Bax and down regulation of Bcl-2 suggesting that these compounds induced apoptosis in human lung cancer cells, A549.