Discovery of methyl 3-((2-((1-(dimethylglycyl)-5-methoxyindolin-6-yl)amino)-5-(trifluoro-methyl) pyrimidin-4-yl)amino)thiophene-2-carboxylate as a potent and selective polo-like kinase 1 (PLK1) inhibitor for combating hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related death worldwide and targeted therapeutics exhibit limited success. Polo-like kinase 1 (PLK1), a Ser/Thr kinase, plays a pivotal role in cell-cycle regulation and is considered a promising target in HCC. Here, via structural optimization using both biochemical kinase assays and cellular antiproliferation assays, we discovered a potent and selective PLK1 kinase inhibitor, compound 31. Compound 31 exhibited biochemical activity with IC₅₀ of < 0.508 nM against PLK1 and a KINOMEscan selectivity score (S(1)) of 0.02 at a concentration of 1 μM. Furthermore, 31 showed broad antiproliferative activity against a variety of Cancer cell lines, with the lowest antiproliferative IC₅₀ (11.1 nM) in the HCC cell line HepG2. A detailed mechanistic study of 31 revealed that inhibition of PLK1 by 31 induces mitotic arrest at the G2/M phase checkpoint, thus leading to Cancer cell Apoptosis. Moreover, 31 exhibited profound antitumor efficacy in a xenograft mouse model. Collectively, these results establish compound 31 as a good starting point for the development of PLK1 targeted therapeutics for HCC.