Design, Synthesis, and Biological Evaluation of Indazole-Based PLK4 Inhibitors

Abstract

PLK4 (Polo-like kinase 4), a member of the serine/threonine protein kinase family, serves as a central regulator of centriole duplication and plays a critical role in eukaryotic mitosis. Overexpression of PLK4 in multiple cancer types underscores its potential as a therapeutic target. In our previous studies, compound 28t demonstrated acceptable kinase inhibitory activity but exhibited poor cellular activity. Consequently, 28t was selected as a lead compound for further optimization. Through functional group migration and rational drug design strategies, we conducted structural modifications that ultimately yielded 23 novel indazole-based PLK4 inhibitors. Among these, compound C05 exhibited exceptional kinase inhibitory activity (IC50 < 0.1 nM). At the cellular level, C05 demonstrated potent antiproliferative effects against IMR-32 (neuroblastoma), MCF-7 (breast cancer), and H460 (non-small cell lung cancer) cell lines, with IC50 values of 0.948 μM, 0.979 μM, and 1.679 μM, respectively. Notably, compound C05 demonstrated favorable kinase selectivity towards PLK4 among the 10 kinases tested, achieving an inhibition rate of 87.45%. Further pharmacological experimental studies, including apoptosis induction, cell cycle arrest analysis, and clonogenic formation experiments, revealed that C05 outperformed the positive control LCR-263 in both potency and efficacy. Western blot analysis demonstrated that compound C05 effectively suppressed PLK4 autophosphorylation at 4 μM. Unfortunately, compound C05 demonstrated poor metabolic stability in human liver microsomes (HLM), exhibiting a short half-life (T1/2) of 2.69 minutes under standard incubation conditions. Notwithstanding the suboptimal metabolic stability, the compelling biological activity profile of compound C05 warrants further structural refinement.