Evaluation of potential Myt1 kinase inhibitors by TR-FRET based binding assay

Targeting Protein Kinase, Membrane-Associated Tyrosine/Threonine 1 (PKMYT1) for Precision Cancer Therapy: From Discovery to Clinical Trial

\Protein kinase membrane-associated tyrosine/threonine 1 (PKMYT1), an overlooked member of the WEE family responsible for regulating cell cycle transition, has recently emerged as a compelling therapeutic target for precision cancer therapy due to its established synthetic lethal relationship with CCNE1 (cyclin E1) amplification. Since the first-in-class selective PKMYT1 inhibitor, RP-6306, entered clinical trials in 2021, the field has experienced renewed interest underscored by the growing number of inhibitor patents and the exploration of additional gene alterations, such as KRAS/p53 mutations, FBXW7 mutation, and PPP2R1A mutation, as novel synthetic lethal partners. This perspective summarizes, for the first time, the PKMYT1 structure, function, and inhibitors in both the literature and patent applications reported to date. Compounds are described focusing on their design and optimization process, structural features, and biological activity with the aim to promoting further drug discovery efforts targeting PKMYT1 as a potential precision therapy.

Genome-wide CRISPR screens identify PKMYT1 as a therapeutic target in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with an overall 5-year survival rate of <12% due to the lack of effective treatments. Novel treatment strategies are urgently needed. Here, PKMYT1 is identified through genome-wide CRISPR screens as a non-mutant, genetic vulnerability of PDAC. Higher PKMYT1 expression levels indicate poor prognosis in PDAC patients. PKMYT1 ablation inhibits tumor growth and proliferation in vitro and in vivo by regulating cell cycle progression and inducing apoptosis. Moreover, pharmacological inhibition of PKMYT1 shows efficacy in multiple PDAC cell models and effectively induces tumor regression without overt toxicity in PDAC cell line-derived xenograft and in more clinically relevant patient-derived xenograft models. Mechanistically, in addition to its canonical function of phosphorylating CDK1, PKMYT1 functions as an oncogene to promote PDAC tumorigenesis by regulating PLK1 expression and phosphorylation. Finally, TP53 function and PRKDC activation are shown to modulate the sensitivity to PKMYT1 inhibition. These results define PKMYT1 dependency in PDAC and identify potential therapeutic strategies for clinical translation.

Myt1 kinase inhibitors - Insight into structural features, offering potential frameworks

The cell cycle includes two checkpoint arrests allowing to repair of damaged DNA. Many cancer cell lines exhibit weak G1 checkpoint mechanisms relying significantly more on the G2 checkpoint than do healthy cells. Inhibition of Myt1 kinase (PKMYT1), a forgotten member of the Wee family, cyclin-dependent kinase 1 (Cdk1) inhibitory kinase, target for G2 checkpoint abrogation, whose inhibition forces cells into premature unchecked mitosis resulting in cell death, is a promising concept for anticancer therapy. There are not many inhibitors of this emerging, potentially clinically important kinase. Herein, the valuable insight into structural features and binding mechanisms of diaminopyrimidines, aminoquinolines, quinazolines, pyrido[2,3-d]pyrimidines, pyrazolo[3,4-d]pyrimidines, and pyrrolo[2,3-b]quinoxalines, as well as finally made a general scheme of fragmented structures of Myt1 inhibitors with the enzyme, offer potential frameworks useful for future directions, for further chemical optimizations, in the discovery and the design of novel effective structures, potential therapeutics.

Overexpressed PKMYT1 promotes tumor progression and associates with poor survival in esophageal squamous cell carcinoma

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is one of the most common malignant tumors worldwide and the 5-year overall survival rate remains poor. Protein kinase, membrane associated tyrosine/threonine (PKMYT1) is overexpressed in several cancers and participate in tumor progression. However, the mechanism of PKMYT1 in ESCC is unclear.

PURPOSE

The objective of our study was to demonstrate the the expression and role of PKMYT1 in ESCC.

PATIENTS AND METHODS

  We detected the expression of PKMYT1 in ESCC patients and analysed the correlation with overall survival time and disease-free survival time. Then we detected PKMYT1 expression in ESCC cell lines and immortalized human esophageal epithelial cell line. Down-regulated PKMYT1 was carried out in KYSE70 and KYSE450 cells to invetigate the mechanism of PKMYT1 in ESCC cells.

RESULTS

PKMYT1 was up-regulated in tumor tissues and ESCC cell lines, and higher expression of PKMYT1 correlated with poorer overall survival in ESCC patients. Besides, in ESCC cell lines KYSE70 and KYSE450, knocking down PKMYT1 allowed more cells to skip G2/M checkpoint to complete mitosis, which promoted cell apoptosis, inhibited cell proliferation, and prevented the EMT phenotype in vitro. Meantime, we also observed that down-regulated PKMYT1 in ESCC cells suppressed AKT/mTOR signaling pathway. These results demonstrated PKMYT1 may act as an oncogene in ESCC.

CONCLUSION

PKMYT1 plays an crutial role in ESCC progression, downregulated PKMYT1 might inhibit the development of ESCC by AKT/mTOR signaling pathway, and might be a novel target in the treatment of ESCC.

Computer-aided design, synthesis and biological characterization of novel inhibitors for PKMYT1

In the current work, we applied computational methods to analyze the membrane-associated inhibitory kinase PKMYT1 and small molecule inhibitors. PKMYT1 regulates the cell cycle at G2/M transition and phosphorylates Thr14 and Tyr15 in the Cdk1-cyclin B complex. A combination of in silico and in vitro screening was applied to identify novel PKMYT1 inhibitors. The computational approach combined structural analysis, molecular docking, binding free energy calculations, and quantitative structure-activity relationship (QSAR) models. In addition, a computational fragment growing approach was applied to a set of previously identified diaminopyrimidines. Based on the derived computational models, several derivatives were synthesized and tested in vitro on PKMYT1. Novel inhibitors active in the sub-micromolar range were identified which provide the basis for further characterization of PKMYT1 as putative target for cancer therapy.

Regulation of G2/M Transition by Inhibition of WEE1 and PKMYT1 Kinases

In the cell cycle, there are two checkpoint arrests that allow cells to repair damaged DNA in order to maintain genomic integrity. Many cancer cells have defective G1 checkpoint mechanisms, thus depending on the G2 checkpoint far more than normal cells. G2 checkpoint abrogation is therefore a promising concept to preferably damage cancerous cells over normal cells. The main factor influencing the decision to enter mitosis is a complex composed of Cdk1 and cyclin B. Cdk1/CycB is regulated by various feedback mechanisms, in particular inhibitory phosphorylations at Thr14 and Tyr15 of Cdk1. In fact, Cdk1/CycB activity is restricted by the balance between WEE family kinases and Cdc25 phosphatases. The WEE kinase family consists of three proteins: WEE1, PKMYT1, and the less important WEE1B. WEE1 exclusively mediates phosphorylation at Tyr15, whereas PKMYT1 is dual-specific for Tyr15 as well as Thr14. Inhibition by a small molecule inhibitor is therefore proposed to be a promising option since WEE kinases bind Cdk1, altering equilibria and thus affecting G2/M transition.

The glycoglycerolipid 1,2-dipalmitoyl-3-(N-palmitoyl-6'-amino-6'-deoxy-α-d-glucosyl)-sn-glycerol is no inhibitor of the human Myt1 kinase

Previously, a glycoglycerolipid isolated from marine algae was reported to be a potent and selective inhibitor of the human Myt1 kinase, an enzyme involved in cell cycle regulation with great potential as an anti-cancer target. Based on that report, a lot of research effort has been invested by several working groups to synthesize and derivatize this compound. However, reliable assay data confirming the inhibitory potential and the mechanism of action of these glycoglycerolipids are missing so far. Here, based on experimental data and theoretical considerations, we show that the aforesaid glycoglycerolipid 1,2-dipalmitoyl-3-(N-palmitoyl-6'-amino-6'-deoxy-α-d-glucosyl)-sn-glycerol is not an inhibitor of the human Myt1 kinase.

A fluorescence anisotropy-based Myt1 kinase binding assay

Abstract The human Myt1 kinase is a regulator of Cdk1/CycB and, hence, important for the G2/M transition in the cell cycle. It may act as a target for drug development, but suitable assay systems for assessing potential inhibitors are lacking so far. Herein, we describe the rational development of a fluorescence anisotropy-based kinase binding assay. A suitable fluoroprobe based on the tyrosine kinase inhibitor dasatinib was synthesized and tested with Myt1 and several other kinases for control purposes. The probe acted as expected in terms of specificity and reversibility, and a Myt1 assay was set up. Notwithstanding the moderate Kd of the starting compound dasatinib before chemical modification, satisfying Z' factors >0.5 were achieved. A validation with known kinase inhibitors demonstrated the applicability of the assay and led to a reliable ranking of the tested active compounds.