Design, synthesis and biological evaluation of novel diaryl-substituted fused nitrogen heterocycles as tubulin polymerization inhibitors to overcome multidrug resistance in vitro and in vivo

Microtubule-targeting agents (MTAs) are considered as one of the most successful chemotherapy drugs for lung adenocarcinoma (LUAD). However, the clinical application of MTAs is often significantly plagued by multidrug resistance (MDR). To overcome this limitation in the quest of more effective MTAs for tumor therapy, a series of novel diaryl-substituted nitrogenous fused heterocycles were designed, synthesized and evaluated. Through four rounds of structure-activity relationship studies, the benzoimidazole derivative 37 was identified as a potent cytotoxic agent against both paclitaxel-sensitive and -resistant A549 (A549/T) cells, effectively overcoming multidrug resistance of A549/T cells against various MTAs. Mechanistic investigations revealed that 37 could disrupt microtubule assembly and induce cell cycle arrest at the G2/M phase, and hence trigger the cell apoptosis. Furthermore, 37 was found to be a poor substrate for P-glycoprotein (P-gp), a major contributor to multidrug resistance, and could reduce the level of P-gp in resistant cells, thereby effectively overcoming P-gpmediated multidrug resistance. Notably, 37 exhibited higher liver microsomal stability and better water solubility than those of the reference combretastatin A-4 (CA-4). In vivo studies using an A549/T xenograft model demonstrated that 37 significantly inhibited tumor growth without obvious toxicity, outperforming the positive controls CA-4 and paclitaxel. As a novel tubulin polymerization inhibitor, compound 37 is marked by potent anticancer activity and remarkable anti-MDR properties. These salient features, coupled with the low toxicity of 37, would render it quite promising as a lead for further drug development towards clinical treatment of multidrug-resistant LUAD.