Virtual screening of natural compounds as selective inhibitors of polo-like kinase-1 at C-terminal polo box and N-terminal catalytic domain

The over-expression of Polo-like kinase-1 (PLK1) is associated with cancer prognosis due to its pivotal role in cell proliferation. The N-terminal catalytic domain (NCD) and C-terminal polo box domain (PBD) of PLK1 are critical for the activity of the protein. Drugs that inhibit PLK1 by targeting these domains are on clinical trials, but so far, none has been approved by FDA. Thus, this study targets the two domains of PLK1 to identify compounds with inhibitory potential. Four validated e-pharmacophore models from NCD (PDB ID: 2OU7 and 4J52) and PBD (PDB ID: 5NEI and 5NN2) were used to screen over 26,000 natural compounds from NPASS database. Hits were identified after the well-fitted compounds were subjected to molecular docking study and ADME prediction. The pIC50 and electronic behaviour of the identified hits selectively targeting NCD and PBD of PLK1 were predicted via an externally validated QSAR model and quantum mechanics. The results showed that CAA180504, CAA197326, CAA74619, CAA328856 modulating PLK1 at NCD, and CBB130581, CBB230713, CBB206123, CBB12656 and CBB267117 modulating PLK1 at PBD had better molecular docking scores, pharmacokinetics and drug-like properties than NCD (volasertib) and PBD (purpurogallin) reference inhibitors. The compounds all had satisfactory inhibitory (pIC50) values which range from 6.187 to 7.157. The electronic behaviours of understudied compounds using HOMO/LUMO and global descriptive parameters revealed the atomic portion of the compounds prone to donating and accepting electrons. In conclusion, the hit compounds identified from the library of natural compounds are worthy of further experimental validation.Communicated by Ramaswamy H. Sarma.

[Mining Polo-Box domain of Polo-like kinase 1 as a new therapeutic target for cancer]

Polo-like kinase 1 (Plk1) is widely regarded as one of the most promising targets for cancer therapy due to its essential role in cell division and tumor cell survival. At present, most Plk1 inhibitors have been developed based on kinase domain, some of which are in clinical trial. However, inhibitors targeting kinase domain face off-target effect and drug resistance owing to the conserved nature and the frequent mutations in the ATP-binding pocket. In addition to a highly conserved kinase domain, Plk1 also contains a unique Polo-Box domain (PBD), which is essential for Plk1's subcellular localization and mitotic functions. Inhibitors targeting Plk1 PBD show stronger selectivity and less drug resistance for cancer therapy. Therefore, Plk1 PBD is an attractive target for the development of anti-cancer agents. In this review, we will summarize the up-to date drug discovery for targeting Plk1 PBD, including the molecular structure and cellular functions of Plk1 PBD. Small-molecule inhibitors targeting Plk1 PBD not only provide an opportunity to specifically inhibit Plk1 activity for cancer treatment, but also unveil novel biological basis regarding the molecular recognition of Plk1 and its substrates.

Identification of a novel Polo-like kinase 1 inhibitor that specifically blocks the functions of Polo-Box domain

Polo-like kinase 1 (Plk1) is a promising target for cancer therapy due to its essential role in cell division. In addition to a highly conserved kinase domain, Plk1 also contains a Polo-Box domain (PBD), which is essential for Plk1's subcellular localization and mitotic functions. We adopted a fluorescence polarization assay and identified a new Plk1 PBD inhibitor T521 from a small-molecule compound library. T521 specifically inhibits the PBD of Plk1, but not those of Plk2-3. T521 exhibits covalent binding to some lysine residues of Plk1 PBD, which causes significant changes in the secondary structure of Plk1 PBD. Using a cell-based assay, we showed that T521 impedes the interaction between Plk1 and Bub1, a mitotic checkpoint protein. Moreover, HeLa cells treated with T521 exhibited dramatic mitotic defects. Importantly, T521 suppresses the growth of A549 cells in xenograft nude mice. Taken together, we have identified a novel Plk1 inhibitor that specifically disrupts the functions of Plk1 PBD and shows anticancer activity.

Discovery of indolizines containing triazine moiety as new leads for the development of antitumoral agents targeting mitotic events

A new family of 3-aroylindolizines bearing a dimethoxytriazine unit in their position 1 was designed, synthesized and evaluated for their ability to inhibit tubulin polymerization and cellular growth in vitro. Compound 39 was the best candidate in the current study with a GI50 value of 870 nM on SNB-75 CNS cancer cells and of 920 nM on MDA-MB-231/ATCC breast cancer cells. The standard NCI Compare results indicated that indolizine 39 may target PLK1 (polo-like kinase 1).