Synthesis and Bioevaluation of 3,6-Diaryl-[1,2,4]triazolo[4,3-<i>b</i>] Pyridazines as Antitubulin Agents

Abstract

A series of 3,6-diaryl-[1,2,4]triazolo[4,3-<i>b</i>]pyridazines were designed as a class of vinylogous CA-4 analogues. The easily isomerized (<i>Z</i>,<i>E</i>)-butadiene linker of vinylogous CA-4 was replaced by a rigid [1,2,4]triazolo[4,3-<i>b</i>]pyridazine scaffold. Twenty-one target compounds were synthesized and exhibited moderate to potent antiproliferative activity. The compound <b>4q</b> with a 3-amino-4-methoxyphenyl moiety as the B-ring, comparable to CA-4 (IC₅₀ = 0.009-0.012 μM), displayed the highly active antiproliferative activity against SGC-7901, A549, and HT-1080 cell lines with IC₅₀ values of 0.014, 0.008, and 0.012 μM, respectively. Tubulin polymerization experiments indicated that <b>4q</b> effectively inhibited tubulin polymerization, and immunostaining assay revealed that <b>4q</b> significantly disrupted tubulin microtubule dynamics. Moreover, cell cycle studies revealed that compound <b>4q</b> dramatically arrested cell cycle progression at G2/M phase in A549 cells. Molecular modeling studies showed that <b>4q</b> could bind to the colchicine binding site on microtubules.