Evaluation of broad spectrum protein kinase inhibitors to probe the architecture of the malarial cyclin dependent protein kinase Pfmrk

Recent progress in development of cyclin-dependent kinase 7 inhibitors for cancer therapy

Introduction: Cyclin-dependent kinase 7 (CDK7) is a part of the CDK-activating kinase family (CAK) which has a key role in the cell cycle and transcriptional regulation. Several lines of evidence suggest that CDK7 is a promising therapeutic target for cancer. CDK7 selective inhibitors such as SY-5609 and CT7001 are in clinical development. Areas covered: We explore the biology of CDK7 and its role in cancer and follow this with an evaluation of the preclinical and clinical progress of CDK7 inhibitors, and their potential in the clinic. We searched PubMed and ClinicalTrials to identify relevant data from the database inception to 14 October 2020. Expert opinion: CDK7 inhibitors are next generation therapeutics for cancer. However, there are still challenges which include selectively, side effects, and drug resistance. Nevertheless, with ongoing clinical development of these inhibitors and greater analysis of their target, CDK7 inhibitors will become a promising approach for treatment of cancer in the near future.

Plasmodial Kinase Inhibitors Targeting Malaria: Recent Developments

Recent progress in reducing malaria cases and ensuing deaths is threatened by factors like mutations that induce resistance to artemisinin derivatives. Multiple drugs are currently in clinical trials for malaria treatment, including some with novel mechanisms of action. One of these, MMV390048, is a plasmodial kinase inhibitor. This review lists the recently developed molecules which target plasmodial kinases. A systematic review of the literature was performed using CAPLUS and MEDLINE databases from 2005 to 2020. It covers a total of 60 articles and describes about one hundred compounds targeting 22 plasmodial kinases. This work highlights the strong potential of compounds targeting plasmodial kinases for future drug therapies. However, the majority of the Plasmodium kinome remains to be explored.

An Update on Development of Small-Molecule Plasmodial Kinase Inhibitors

Malaria control relies heavily on the small number of existing antimalarial drugs. However, recurring antimalarial drug resistance necessitates the continual generation of new antimalarial drugs with novel modes of action. In order to shift the focus from only controlling this disease towards elimination and eradication, next-generation antimalarial agents need to address the gaps in the malaria drug arsenal. This includes developing drugs for chemoprotection, treating severe malaria and blocking transmission. Plasmodial kinases are promising targets for next-generation antimalarial drug development as they mediate critical cellular processes and some are active across multiple stages of the parasite's life cycle. This review gives an update on the progress made thus far with regards to plasmodial kinase small-molecule inhibitor development.

Targeting malaria protein kinases

Malaria is one of the most impacting public health problems in tropical and subtropical areas of the globe, with approximately 200 million cases worldwide annually. In the absence of an effective vaccine, rapid treatment is vital for effective malaria control. However, parasite resistance to currently available drugs underscores the urgent need for identifying new antimalarial therapies with new mechanisms of action. Among potential drug targets for developing new antimalarial candidates, protein kinases are attractive. These enzymes catalyze the phosphorylation of several proteins, thereby regulating a variety of cellular processes and playing crucial roles in the development of all stages of the malaria parasite life cycle. Moreover, the large phylogenetic distance between Plasmodium species and its human host is reflected in marked differences in structure and function of malaria protein kinases between the homologs of both species, indicating that selectivity can be attained. In this review, we describe the functions of the different types of Plasmodium kinases and highlight the main recent advances in the discovery of kinase inhibitors as potential new antimalarial drug candidates.

A structure guided drug-discovery approach towards identification of Plasmodium inhibitors

This article provides a comprehensive review of inhibitors from natural, semisynthetic or synthetic sources against key targets ofPlasmodium falciparum.

Selective inhibitors of Plasmodium falciparum glycogen synthase-3 (PfGSK-3): New antimalarial agents?

Plasmodium falciparum glycogen synthase kinase-3 (PfGSK-3) is one of the eukaryotic protein kinases that were identified as essential for the parasite causing malaria tropica. Although the physiological functions of PfGSK-3 are still unknown, it had been suggested as a putative target for novel antimalarial drugs. The high structural similarity of PfGSK-3 and its human orthologue HsGSK-3 makes the development of selective PfGSK-3 inhibitors a challenging task. Actually, established GSK-3 inhibitors are either unselective or are more potent for inhibition of the mammalian GSK-3. A high throughput screening campaign identified thieno[2,3-b]pyridines as a new class of PfGSK-3 inhibitors. Systematic variation of the substitution pattern at the parent scaffold led to compounds which selectively inhibited the plasmodial enzyme. These compounds also exhibited activity against erythrocyte stages of the parasites. A hypothetical explanation for the selectivity of the new antimalarial compounds was enunciated based on the results of docking a selective inhibitor into a PfGSK-3 homology model and by comparison of the results with an X-ray structure of HsGSK-3 co-crystallized with a similar but unselective compound. This article is part of a Special Issue entitled: Inhibitors of Protein Kinases.

Several human cyclin-dependent kinase inhibitors, structurally related to roscovitine, are new anti-malarial agents

In Africa, malaria kills one child each minute. It is also responsible for about one million deaths worldwide each year. Plasmodium falciparum, is the protozoan responsible for the most lethal form of the disease, with resistance developing against the available anti-malarial drugs. Among newly proposed anti-malaria targets, are the P. falciparum cyclin-dependent kinases (PfCDKs). There are involved in different stages of the protozoan growth and development but share high sequence homology with human cyclin-dependent kinases (CDKs). We previously reported the synthesis of CDKs inhibitors that are structurally-related to (R)-roscovitine, a 2,6,9-trisubstituted purine, and they showed activity against neuronal diseases and cancers. In this report, we describe the synthesis and the characterization of new CDK inhibitors, active in reducing the in vitro growth of P. falciparum (3D7 and 7G8 strains). Six compounds are more potent inhibitors than roscovitine, and three exhibited IC₅₀ values close to 1 µM for both 3D7 and 7G8 strains. Although, such molecules do inhibit P. falciparum growth, they require further studies to improve their selectivity for PfCDKs.

3,6-Diamino-4-(2-halophenyl)-2-benzoylthieno[2,3-b]pyridine-5-carbonitriles are selective inhibitors of Plasmodium falciparum glycogen synthase kinase-3

Plasmodium falciparum is the infective agent responsible for malaria tropica. The glycogen synthase kinase-3 of the parasite (PfGSK-3) was suggested as a potential biological target for novel antimalarial drugs. Starting from hit structures identified in a high-throughput screening campaign, 3,6-diamino-4-(2-halophenyl)-2-benzoylthieno[2,3-b]pyridine-5-carbonitriles were discovered as a new class of PfGSK-3 inhibitors. Being less active on GSK-3 homologues of other species, the title compounds showed selectivity in favor of PfGSK-3. Taking into account the X-ray structure of a related molecule in complex with human GSK-3 (HsGSK-3), a model was computed for the comparison of inhibitor complexes with the plasmodial and human enzymes. It was found that subtle differences in the ATP-binding pockets are responsible for the observed PfGSK-3 vs HsGSK-3 selectivity. Representatives of the title compound class exhibited micromolar IC₅₀ values against P. falciparum erythrocyte stage parasites. These results suggest that inhibitors of PfGSK-3 could be developed as potential antimalarial drugs.

Malarial kinases: novel targets for in silico approaches to drug discovery

Malaria, the disease caused by infection with protozoan parasites from the genus Plasmodium, claims the lives of nearly 1 million people annually. Developing nations, particularly in the African Region, bear the brunt of this malaria burden. Alarmingly, the most dangerous etiologic agent of malaria, Plasmodium falciparum, is becoming increasingly resistant to current first-line antimalarials. In light of the widespread devastation caused by malaria, the emergence of drug-resistant P. falciparum strains, and the projected decrease in funding for malaria eradication that may occur over the next decade, the identification of promising new targets for antimalarial drug design is imperative. P. falciparum kinases have been proposed as ideal drug targets for antimalarial drug design because they mediate critical cellular processes within the parasite and are, in many cases, structurally and mechanistically divergent when compared with kinases from humans. Identifying a molecule capable of inhibiting the activity of a target enzyme is generally an arduous and expensive process that can be greatly aided by utilizing in silico drug design techniques. Such methods have been extensively applied to human kinases, but as yet have not been fully exploited for the exploration and characterization of antimalarial kinase targets. This review focuses on in silico methods that have been used for the evaluation of potential antimalarials and the Plasmodium kinases that could be explored using these techniques.

Selective inhibition of Pfmrk, a Plasmodium falciparum CDK, by antimalarial 1,3-diaryl-2-propenones

The cyclin dependent protein kinases, Pfmrk and PfPK5, most likely play an essential role in cell cycle control and differentiation in Plasmodium falciparum and are thus an attractive target for antimalarial drug development. Various 1,3-diaryl-2-propenones (chalcone derivatives) which selectivity inhibit Pfmrk in the low micromolar range (over PfPK5) are identified. Molecular modeling shows a pair of amino acid residues within the Pfmrk active site which appear to confer this selectivity. Predicted interactions between the chalcones and Pfmrk correlate well with observed potency. Pfmrk inhibition and activity against the parasite in vitro correlate weakly. Several mechanisms of action have been suggested for chalcone derivatives and our study suggests that kinase inhibition may be an additional mechanism of antimalarial activity for this class of compounds.

Drugging the Plasmodium kinome: the benefits of academia-industry synergy

Malaria remains a major killer in many parts of the world. Recently, the development of nonprofit organisations aimed at fighting this deadly scourge incited academic and industrial scientists to merge their expertise in drug-target validation and lead discovery. Expectations are clear: identification and characterisation of new molecules showing high efficacy, low toxicity and little propensity to induce resistance in the parasite. In this context, protein kinase inhibitors represent an attractive possibility. Here, we compare traditional target-based drug-discovery approaches with innovative exploratory paths (parallel screening, cell-based assays, integrated systems biology and allosteric inhibition) and discuss the benefits of acadaemia-industry cooperation. Early characterisation of distribution, metabolism, pharmacokinetic (DMPK) and toxicology parameters are considered as well.