Design, synthesis and biological evaluation of novel benzimidazole-derived p21-activited kinase 4 (PAK4) inhibitors bearing a 4-(4-methylpiperazin-1-yl)phenyl scaffold as potential antitumor agents

A series of novel 6-(4-(4-methylpiperazin-1-yl)phenyl)-1H-benzo[d]imidazole-based p21-activited kinase 4 (PAK4) inhibitors were designed and synthesized based on the structure of lead compound GNE-2861 and that of anticancer inhibitors reported in our previous studies. All target compounds so designed were preliminarily screened in vitro for anti-tumor potency through kinase inhibitory assays and MTT assays, which revealed that most compounds exhibited significant inhibitory effects on PAK4 enzyme as well as prominent antiproliferative activities against four cancer cell models (A549, NCI-H1975, MDA-MB-231 and SK-BR-3) and low damage to healthy cells. In particular, the hit compound 12i was identified as the most effective and rather selective compound both at the enzyme and cellular level. Meanwhile, molecular docking and dynamic studies disclosed that compound 12i could bind to PAK4 stably via multiple interactions applied between the compound and the enzyme. Further mechanism studies indicated that compound 12i could inhibit the proliferation and suppress the migratory potential of MDA-MB-231 cells by inhibiting the phosphorylation of PAK4 and LIMK1, arresting cell cycle in the G0/G1 phase, inducing apoptosis and promoting ROS production. Notably, compound 12i could effectively inhibit triple-negative breast cancer (TNBC) growth with little toxicity in the MDA-MB-231 cell xenograft model. Taken together, in vitro and in vivo results demonstrated that compound 12i possessed high drug potential as an inhibitor of PAK4 to inhibit the growth and metastasis of TNBC.