Design, Synthesis and Biological Evaluation of 2-Anilinopyridyl-Linked Oxindole Conjugates as Potent Tubulin Polymerisation Inhibitors

A series of 2-anilinopyridyl linked oxindole conjugates (6a-ad) were synthesized andevaluated for their antiproliferative activity against a panel of four human cancer cell lines viz., HeLa, DU-145, A549 and MCF-7. All the compounds showed very good to moderate anticancer activity against the tested cell lines. Amongst the series, conjugates 6h, 6q, 6r, 6s and 6y exhibited promising antiproliferative activity with IC50 values ranging between 0.7 to 1 mu M selectively against human prostate cancer cell line (DU-145). Interestingly conjugate 6r was twice more potent than E7010 and the flow cytometric analysis revealed that 6r and 6y induced cell cycle arrest at G(2)/M phase. Treatments with 6r and 6y manifested increased protein levels of the G(2)/M marker, cyclin B1. Tubulin polymerization inhibition assay, competitive colchicine binding assay and western blot analysis suggested that they inhibit microtubule assembly formation. Immunocytochemistry revealed loss of intact microtubule structure in cells treated with 6r and 6y. In addition, Hoechst staining and mitochondrial membrane depolarisation assay results further support induction of apoptosis by these conjugates leading to cell death. Molecular docking studies is suggestive of that these conjugates occupy the colchicine binding site of the tubulin and could be considered as potential leads with antiproliferative activity.