Rationale design, synthesis, cytotoxicity evaluation, and molecular docking studies of 1,3,4-oxadiazole analogues

Background: 1,3,4-Oxadiazole heterocycles possess a broad spectrum of biological activities. They were reported as potent cytotoxic agents and tubulin inhibitors; hence it is of great interest to explore new oxadiazoles as cytotoxic agents targeting tubulin polymerization. Objective: Two new series of oxadiazoles (5a-h and 12a-h) were synthesized, structurally related to the heterocyclic linked aryl core of IMC-038525, NSC 776715, and NSC 776716, with further modification by incorporating methylene linker. Method: The 2,5-disubstituted-1,3,4-oxadiazoles (5a-h and 12a-h) were synthesized by refluxing an equimolar mixture of the intermediates [(4) and (8a-d)] and aromatic aldehydes in water-ethanol system using sodium bisulphite catalyst. The cytotoxicity evaluation was carried out according to the National Cancer Institute (NCI US) Protocol, while the tubulin polymerization assay kits from Cytoskeleton™(bk011p) was used to perform an in vitro tubulin polymerization assay. Results: 2-(5-{[(4-Chlorophenyl)amino]methyl}-1,3,4-oxadiazol-2-yl)phenol (5f) and 2-[(2,4-dichlorophenoxy) methyl]-5-(3,4-dimethoxyphenyl)-1,3,4-oxadiazole (12c) showed maximum cytotoxicity with the mean percent growth inhibitions (GIs) of 71.56 and 72.68 respectively at 10 µM drug concentrations. Both the compounds (5f and 12c) showed superior cytotoxicity than clinically prevalent anticancer drugs, Imatinib and Gefitinib in one dose assay. The compound 12c showed promising results in five dose assay, with GI₅₀ values varies between 1.61 and >100 µM. Furthermore, the compounds, 5f and 12c also inhibited the polymerization of tubulin with, an IC₅₀ of 2.8 and 2.2 µM, respectively. Conclusion: The oxadiazoles reported herein are tubulin inhibitors and cytotoxic agents. These findings will be helpful in future drug design of more potent tubulin inhibitor cytotoxic agents.