Structure-based design and SAR development of novel selective polo-like kinase 1 inhibitors having the tetrahydropteridin scaffold

Discovery of novel dihydropteridone derivatives as orally bioavailable PLK1 inhibitors with reduced hERG inhibitory activity for acute myeloid leukemia treatment

Polo like kinase 1 (PLK1) is a serine/threonine kinase that plays an important role in multiple phases of the cell cycle, inhibiting its activity has been considered an effective treatment for acute myeloid leukemia (AML). Here, we reported a series of highly potent PLK1 inhibitors. Among them, compound WD6 was identified as the most promising PLK1 inhibitor, with an IC50 value of 0.27 nM and greatly reduced hERG affinity, with 12.78 % inhibition at 10 μM. Compound WD6 displayed significant anti-proliferative activities against MV4-11 (IC50 = 23.3 nM), excellent pharmacokinetic properties (t1/2 = 7.59 h, AUC0-t = 29300 ng h mL-1 and F = 35.1 %), good PPB and low risk of drug-drug interactions. In vivo, oral administration of compound WD6 at a dose of 20 mg/kg effectively suppressed the tumor growth in the MV4-11 xenograft mouse model. Further research indicated that WD6 exhibited excellent kinase selectivity, arresting MV4-11 cells at G2 phase, inducing apoptosis in a dose-dependent manner and down-regulating the transcription of the proliferation-related oncogene c-MYC. These results showed that compound WD6 has the potential to be a promising drug candidate for treating AML.

Fine-tuning probes for fluorescence polarization binding assays of bivalent ligands against polo-like kinase 1 using full-length protein

Polo-like kinase 1 (Plk1) is an important cell cycle regulator that is a recognized target for development of anti-cancer therapeutics. Plk1 is composed of a catalytic kinase domain (KD), a flexible interdomain linker and a polo-box domain (PBD). Intramolecular protein-protein interactions (PPIs) between the PBD and KD result in "auto-inhibition" that is an essential component of proper Plk1 function. Recently, we developed high-affinity PBD-binding inhibitors using a bivalent approach. These ligands contain the low-nanomolar affinity Plk1 KD-binding inhibitors BI2536 or Wortmannin tethered to the PBD-binding peptide, PLH*SpT (H* represents a -(CH2)8Ph group on the histidine side chain π-nitrogen). Due to the extremely high affinity of these bivalent inhibitors, to avoid bottoming out in competitive binding assays, it was necessary to use PLH*SpT in the affinity probe. As reported herein, we have developed fluorescence polarization assays using a new fluorescent probe based on the Plk1 PBD-binding peptide, FDPPLHSpTA. We applied the assay to evaluate the affinities of bivalent inhibitors that possess a variety of PBD-binding peptides having much lower PBD-affinities than PLH*SpT. Tethering BI2536 in these bivalent inhibitors resulted in significant affinity enhancements as compared to the parent monovalent peptides.

Structure-Based Discovery of a Highly Selective, Oral Polo-Like Kinase 1 Inhibitor with Potent Antileukemic Activity

Polo-like kinase 1 (PLK1) plays pivotal roles in cell division and cancer pathogenesis, making it a highly coveted therapeutic target for anticancer strategies. This article reports a series of PLK1 inhibitors developed using a structure-based strategy, culminating in the discovery of compound B31, a novel isoform-specific PLK1 inhibitor with excellent kinome selectivity. In vitro, this compound exhibited superior anticancer potency across a broad spectrum of cell lines, particularly against K562, achieving a remarkable IC50 value of 0.08 nM. In a mouse model harboring subcutaneous K562 tumors, oral administration of B31 at dosages of 10 or 20 mg/kg twice weekly exhibited remarkable antileukemic activity. B31 had minimal impact on HEK293T cells and very weak inhibitory activity against the hERG channel. Furthermore, in the acute toxicity test, this compound demonstrated an extraordinary safety profile even at a dosage of 500 mg/kg, highlighting its potential as a novel antileukemic agent.

Progress with polo-like kinase (PLK) inhibitors: a patent review (2018-present)

INTRODUCTION

Polo-like kinases (PLKs) have five isoforms, all of which play crucial roles in cell cycle and cell proliferation, offering opportunities for drug design and treatment of cancers and other related diseases. Notably, PLK1 and PLK4 have been extensively investigated as cancer drug targets. One distinctive feature of PLKs is the presence of a unique polo-box domain (PBD), which regulates kinase activity and subcellular localization. This provides possibilities for specifically targeting PLKs.

AREA COVERED

This article provides an overview of the roles of PLKs in various cancers and related diseases, as well as the drug development involving PLKs, with a particular focus on PLK1 and PLK4. It summarizes the PLK1 and PLK4 inhibitors that have been disclosed in patents or literature (from 2018 - present), which were sourced from SciFinder and WIPO database.

EXPERT OPINION

After two decades of drug development on PLKs, several drugs progressed into clinical trials for the treatment of many cancers; however, none of them has been approved yet. Further elucidating the mechanisms of PLKs and identifying and developing highly selective ATP-competitive inhibitors, highly potent drug-like PBD inhibitors, degraders, etc. may provide new opportunities for cancer therapy and the treatment for several nononcologic diseases. PLKs inhibition-based combination therapies can be another helpful strategy.

Application of a Fluorescence Recovery-Based Polo-Like Kinase 1 Binding Assay to Polo-Like Kinase 2 and Polo-Like Kinase 3

Assay systems for evaluating compound protein-binding affinities are essential for developing agonists and/or antagonists. Targeting individual members of a protein family can be extremely important and for this reason it is critical to have methods for evaluating selectivity. We have previously reported a fluorescence recovery assay that employs a fluorescein-labelled probe to determine IC50 values of ATP-competitive type 1 inhibitors of polo-like kinase 1 (Plk1). This probe is based on the potent Plk1 inhibitor BI2536 [fluorescein isothiocyanate (FITC)-polyethylene glycol (PEG)-lysine (Lys) (BI2536) 1]. Herein, we extend this approach to the highly homologous Plk2 and Plk3 members of this kinase family. Our results suggest that this assay system is suitable for evaluating binding affinities against Plk2 and Plk3 as well as Plk1. The new methodology represents the first example of evaluating N-terminal catalytic kinase domain (KD) affinities of Plk2 and Plk3. It represents a simple and cost-effective alternative to traditional kinase assays to explore the KD-binding compounds against Plk2 and Plk3 as well as Plk1.

Design, synthesis, and biological evaluation of novel dihydropteridone derivatives possessing oxadiazoles moiety as potent inhibitors of PLK1

Polo like kinase 1 (PLK1) is a serine/threonine kinase that is widely distributed in eukaryotic cells and plays an important role in multiple phases of the cell cycle. Its importance in tumorigenesis has been increasingly recognized in recent years. Herein, we describe the optimization of a series of novel dihydropteridone derivatives (13a-13v and 21g-21l) possessing oxadiazoles moiety as potent inhibitors of PLK1. Compound 21g exhibited improved PLK1 inhibitory capability with an IC₅₀ value of 0.45 nM and significant anti-proliferative activities against four tumor-derived cell lines (MCF-7 IC₅₀ = 8.64 nM, HCT-116 IC₅₀ = 26.0 nM, MDA-MB-231 IC₅₀ = 14.8 nM and MV4-11 IC₅₀ = 47.4 nM) with better pharmacokinetic characteristics than BI2536 in mice (AUC_0-t = 11 227 ng h mL^-1vs 556 ng h mL^-1). Moreover, 21g exhibited moderate liver microsomal stability and excellent pharmacokinetic profile (AUC_0-t = 11227 ng h mL^-1, oral bioavailability of 77.4%) in Balb/c mice, acceptable PPB, improved PLK1 inhibitory selectivity, and no apparent toxicity was observed in the acute toxicity assay (20 mg/kg). Further investigation showed that 21 g could arrest HCT-116 cells in G2 phase and induce apoptosis in a dose-dependent manner. These results indicate that 21g is a promising PLK1 inhibitor.

QSAR study of tetrahydropteridin derivatives as polo-like kinase 1(PLK1) Inhibitors with molecular docking and dynamics study

PLK1 is the key target for dealing with different cancer because it plays an important role in cell proliferation. According to the regulation of OECD, a QSAR model was developed from a dataset of 68 tetrahydropteridin derivatives. Three descriptors (maxHaaCH, ATSC7i, AATS7m) were considered for the development of the QSAR model. The reliability and predictability of the developed QSAR model were evaluated by various statistical parameters (r² = 0.8213, r²_ext = 0.8771 and CCC_ext = 0.9364). The maxHaaCH descriptor is positively correlated to pIC₅₀ whereas, the ATSC7i and AATS7m are negatively correlated with pIC₅₀. The QSAR model explains all the structural features and shows a good correlation with the activity. Based on molecular modelling techniques, five compounds (D1-D5) were designed. Molecular docking and dynamics studies of the most active compound were performed with PDB ID: 2RKU. The results of the present investigation may be employed to identify and develop effective inhibitors for the treatment of PLK1-related pathophysiological disorders.

Polo-like Kinase 1 Inhibitors in Human Cancer Therapy: Development and Therapeutic Potential

Polo-like kinase 1 (PLK1) plays an important role in a variety of cellular functions, including the regulation of mitosis, DNA replication, autophagy, and the epithelial-mesenchymal transition (EMT). PLK1 overexpression is often associated with cell proliferation and poor prognosis in cancer patients, making it a promising antitumor target. To date, at least 10 PLK1 inhibitors (PLK1i) have been entered into clinical trials, among which the typical kinase domain (KD) inhibitor BI 6727 (volasertib) was granted "breakthrough therapy designation" by the FDA in 2013. Unfortunately, many other KD inhibitors showed poor specificity, resulting in dose-limiting toxicity, which has greatly impeded their development. Researchers recently discovered many PLK1i with higher selectivity, stronger potency, and better absorption, distribution, metabolism, and elimination (ADME) characteristics. In this review, we emphasize the structure-activity relationships (SARs) of PLK1i, providing insights into new drugs targeting PLK1 for antitumor clinical practice.

Recent progress in agents targeting polo-like kinases: Promising therapeutic strategies

Polo-like kinases (PLKs) play important roles in regulating multiple aspects of cell cycle and cell proliferation. In many cancer types, PLK family members are often dysregulated, which can lead to uncontrolled cell proliferation and aberrant cell division and has been shown to associate with poor prognosis of cancers. The key roles of PLK kinases in cancers lead to an enhanced interest in them as promising targets for anticancer drug development. In consideration of PLK inhibitors and some other anticancer agents, such as BRD4, EEF2K and Aurora inhibitors, exert synergy effects in cancer cells, dual-targeting of PLK and other cancer-related targets is regarded as an rational and potent strategy to enhance the effectiveness of single-targeting therapy for cancer treatment. This review introduces the PLK family members at first and then focuses on the recent advances of single-target PLK inhibitors and summarizes the corresponding SARs of them. Moreover, we discuss the synergisms between PLK and other anti-tumor targets, and sum up the current dual-target agents based on them.

Small-Molecule Kinase Inhibitors for the Treatment of Nononcologic Diseases

Great successes have been achieved in developing small-molecule kinase inhibitors as anticancer therapeutic agents. However, kinase deregulation plays essential roles not only in cancer but also in almost all major disease areas. Accumulating evidence has revealed that kinases are promising drug targets for different diseases, including cancer, autoimmune diseases, inflammatory diseases, cardiovascular diseases, central nervous system disorders, viral infections, and malaria. Indeed, the first small-molecule kinase inhibitor for treatment of a nononcologic disease was approved in 2011 by the U.S. FDA. To date, 10 such inhibitors have been approved, and more are in clinical trials for applications other than cancer. This Perspective discusses a number of kinases and their small-molecule inhibitors for the treatment of diseases in nononcologic therapeutic fields. The opportunities and challenges in developing such inhibitors are also highlighted.

Small-molecule inhibitors of breast cancer-related targets: Potential therapeutic agents for breast cancer

Despite dramatic advances in cancer research and therapy, breast cancer remains a tricky health problem and represents a top biomedical research priority. Nowadays, breast cancer is still the leading cause of malignancy-related deaths in women, and incidence and mortality rates of it are expected to increase significantly the next years. Currently more and more researchers are interested in the study of breast cancer by its arising in young women. The common treatment options of breast cancer are chemotherapy, immunotherapy, hormone therapy, surgery, and radiotherapy. Most of them require chemical agents, such as PARP inhibitors, CDK4/6 inhibitors, and HER2 inhibitors. Recent studies suggest that some targets or pathways, including BRD4, PLK1, PD-L1, HDAC, and PI3K/AKT/mTOR, are tightly related to the occurrence and development of breast cancer. This article reviews the interplay between these targets and breast cancer and summarizes the progress of current research on small molecule inhibitors of these anti-breast cancer targets. The review aims to provide structural and theoretical basis for designing novel anti-breast cancer agents.

Drug design and molecular docking simulations of Polo-like kinase 1 inhibitors based on QSAR study

Computationally exploring novel potential Polo-like kinase 1 inhibitors using a systematic modeling study.

Design, synthesis and biological evaluation of novel pteridinone derivatives as potent dual inhibitors of PLK1 and BRD4

To develop novel simultaneous inhibition of PLK1 and BRD4 bromodomain by a single molecule, three series of novel pteridinone derivatives were designed, synthesized and evaluated for their biological activity.