Design, synthesis, and biological evaluation of novel molecules as potent inhibitors of PLK1

Polo-like kinase 1 (PLK1) is an attractive therapeutic target for the treatment of tumors, as it is an essential cell-cycle regulator frequently overexpressed in tumor tissues. PLK1 can promote tumor invasion and metastasis, and is often associated with poor prognosis in cancer patients. However, no PLK1 inhibitor has been granted marketing approval until now. Therefore, more potentially promising PLK1 inhibitors need to be investigated. In this study, a series of novel inhibitors targeting PLK1 was designed and optimized derived from a new scaffold. After synthesis and characterization, we obtained the structure-activity relationship and led to the discovery of the most promising compound 30e for PLK1. The antiproliferative activity against HCT116 cells (IC50 = 5 nM versus 45 nM for onvansertib) and the cellular permeability and efflux ratio were significantly improved (PappA→B = 2.03 versus 0.345 and efflux ratio = 1.65 versus 94.7 for 30e and onvansertib, respectively). Further in vivo studies indicated that 30e had favorable antitumor activity with 116.2% tumor growth inhibition (TGI) in comparison with TGI of 43.0% for onvansertib. Furthermore, 30e improved volume of tumor tissue distribution in mice as compared to onvansertib. This initial study on 30e holds promise for further development of an antitumor agent.

Discovery of novel potent migrastatic Thiazolo[5,4-b]pyridines targeting Lysyl-tRNA synthetase (KRS) for treatment of Cancer metastasis

Recently, non-canonical roles of Lysyl-tRNA Synthetase (KRS), which is associated with cell migration and cancer metastasis, have been reported. Therefore, KRS has emerged as a promising target for the treatment of cell migration-related diseases, especially cancer metastasis, although the satisfying chemical inhibitors targeting KRS have not yet been identified. Here, we report the discovery of novel, mechanistically unique, and potent cell migration inhibitors targeting KRS, including the chemical and biological studies on the most effective N,N-dialkylthiazolo [5,4-b]pyridin-2-amine (SL-1910). SL-1910 exhibited highly potent migration inhibition (EC₅₀ = 81 nM against the mutant KRS-overexpressed MDA-MB-231 cells) and was superior to the previously reported KRS inhibitor (migration inhibitory EC₅₀ = 8.5 μM against H226 cells). The KRS protein binding study via fluorescence-based binding titration and KRS protein 2D-NMR mapping study, in vitro concentration-dependent cell migration inhibition, and in vivo anti-metastatic activity of SL-1910, which consists of a new scaffold, have been reported in this study. In addition, in vitro absorption, distribution, metabolism, and excretion studies and mouse pharmacokinetics experiments for SL-1910 were conducted.