Therapeutic potential of targeting polo-like kinase 4

Endoplasmic Reticulum Stress in Acute Myeloid Leukemia: Pathogenesis, Prognostic Implications, and Therapeutic Strategies

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy that poses a significant therapeutic challenge due to its high recurrence rate and demanding treatment regimens. Increasing evidence suggests that endoplasmic reticulum (ER) stress and downstream activation of the unfolded protein response (UPR) pathway play a key role in the pathogenesis of AML. ER stress is triggered by the accumulation of misfolded or unfolded proteins within the ER. This causes activation of the UPR to restore cellular homeostasis. However, the UPR can shift from promoting survival to inducing apoptosis under prolonged or excessive stress conditions. AML cells can manipulate the UPR pathway to evade apoptosis, promoting tumor progression and resistance against various therapeutic strategies. This review provides the current knowledge on ER stress in AML and its prognostic and therapeutic implications.

Harnessing Structure Prediction of Polo-Like Kinase 4 for Drug Repurposing

Polo-like kinase 4 (PLK4) is a centrosome-specific kinase aberrantly expressed in cancers. Drugs inhibiting its catalytic kinase domain are under clinical phase-1/2 trials in patients with different leukemia types. However, the kinase domain of PLK4 shows structural similarity with other kinases. Therefore, drugs targeting the unique C-terminal polo-box domain (PBD) of PLK4 could provide better specificity. The knowledge of domain orientation in a full-length PLK4 structure is imperative for drug discovery. In this work, we utilized ab initio and threading approaches to predict the full-length structure of human PLK4, which was employed for virtually screening the ChEMBL library. Among the hit compounds targeting the unique regions in PLK4, we identified Alectinib, which affects centrosome numbers corresponding to PLK4 levels at centrosomes. The FT-IR analysis also confirmed Alectinib interaction with the PBD. Therefore, this work identifies a chemical scaffold that could be repurposed to target the unique regions of PLK4.

Centrosome biogenesis and maintenance in homeostasis and disease

Recent technological advances in proteomics and microscopy techniques, such as cryo-electron microscopy (cryoEM) and expansion microscopy (ExM), have enhanced our understanding of centrosome structure, biogenesis, and regulation. Here we discuss new insights into centrosome structure, highlight new regulatory mechanisms in centrosome biogenesis, and explore emerging concepts in centrosome maintenance and plasticity across different contexts. Furthermore, we review how centrosome biogenesis and homeostasis are dysregulated in various pathological conditions. We finalise by outlining outstanding questions in the field, how the mechanisms discussed are regulated across multiple contexts, the balance between centriole stability and plasticity, and the therapeutic potential of targeting centrosome dysfunction in disease.

PLK4 inhibition as a strategy to enhance non-small cell lung cancer radiosensitivity

Lung cancer is the leading cause of cancer-related mortality worldwide. Non-small cell lung cancer (NSCLC) is the most common subtype of lung cancer and comprises 85% of cases. Despite treatment advances, local control after curative-intent chemoradiation for NSCLC remains suboptimal. Polo-like kinase 4 (PLK4) is a serine-threonine kinase that plays a critical role in the regulation of centrosome duplication and cell cycle progression and is overexpressed in NSCLC, thus, making it a potential therapeutic target. CFI-400945 is an orally available PLK4 inhibitor currently undergoing clinical trial evaluation. As radiation causes cell death primarily by mitotic catastrophe, a process enhanced by alterations in centrosome amplification, we hypothesized that disruption of the mitotic machinery by inhibition of PLK4 would enhance the effects of radiation in NSCLC. PLK4 inhibition by CFI-400945 resulted in radiosensitization of NSCLC cell lines. In contrast, CFI-400945 had no effect on the radiosensitivity of normal lung fibroblasts. PLK4 inhibition did not affect cell-cycle phase distribution prior to radiation, but rather the combination of CFI-400945 and radiation resulted in increased G2/M cell cycle arrest, increased centrosome amplification, and a concomitant increase in cell death through mitotic catastrophe. Lastly, CFI-400945 treatment enhanced the radiation-induced tumor growth delay of NSCLC tumor xenografts. These data indicate that targeting PLK4 is a novel approach to enhance the radiation sensitivity of NSCLC in vitro and in vivo through potentiation of centrosome amplification and cell death through mitotic catastrophe.

Polo-like kinase 4 accelerates glioma malignant progression and vasculogenic mimicry by phosphorylating EphA2

Vasculogenic mimicry (VM), which involved the formation of vascular-like structures by highly invasive tumor cells, had been identified as one of the mechanisms contributing to resistance against anti-angiogenic therapy in patients with glioblastoma (GBM). Therefore, inhibition of VM formation may serve as an effective therapeutic strategy against angiogenesis resistance. Polo-like kinase 4 (PLK4), a protein kinase, had been linked to the progression of glioblastoma and was associated with an unfavorable prognosis. The integration of proteomics and phosphoproteomics revealed that PLK4 directly activated the PI3K-Akt and MAPK signaling cascades by phosphorylating the Ser901 and Ser897 of EphA2. In addition, EphA2 Ser901 phosphorylating catalyzed by PLK4 significantly enhanced the phosphorylation of its own Ser897 site, which is a hallmark of EphA2 activation. The PI3K-Akt signaling was intricately associated with the progression of VM. Thus, PLK4 influenced malignant progression and VM formation via stimulation of the EphA2 signal transduction. Moreover, the expression level of PLK4 protein positively correlated with the level of EphA2 phosphorylation in glioma tissues. These results highlighted the crucial significance of PLK4 phosphorylating EphA2 in the malignant progression and VM formation in GBM.

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.

Targeting polo-like kinase 1 to treat kidney diseases

Globally, ∼850 million individuals suffer from some form of kidney disease. This staggering figure underscores the importance of continued research and innovation in the field of nephrology to develop effective treatments and improve overall global kidney health. In current research, the polo-like kinase (Plk) family has emerged as a group of highly conserved enzyme kinases vital for proper cell cycle regulation. Plks are defined by their N-terminal kinase domain and C-terminal polo-box domain, which regulate their catalytic activity, subcellular localization, and substrate recognition. Among the Plk family members, Plk1 has garnered significant attention due to its pivotal role in regulating multiple mitotic processes, particularly in the kidneys. It is a crucial serine-threonine (Ser-Thr) kinase involved in cell division and genomic stability. In this review, we delve into the types and functions of Plks, focusing on Plk1's significance in processes such as cell proliferation, spindle assembly, and DNA damage repair. The review also underscores Plk1's vital contributions to maintaining kidney homeostasis, elucidating its involvement in nuclear envelope breakdown, anaphase-promoting complex/cyclosome activation, and the regulation of mRNA translation machinery. Furthermore, the review discusses how Plk1 contributes to the development and progression of kidney diseases, emphasizing its overexpression in conditions such as acute kidney injury, chronic kidney disease, and so forth. It also highlights the importance of exploring Plk1 modulators as targeted therapies for kidney diseases in future. This review will help in understanding the role of Plk1 in kidney disease development, paving the way for the discovery and development of novel therapeutic approaches to manage kidney diseases effectively.

Pan-cancer analysis of polo-like kinase family genes reveals polo-like kinase 1 as a novel oncogene in kidney renal papillary cell carcinoma

BACKGROUND

Polo-like kinases (PLKs) are a kinase class of serine/threonine with five members that play crucial roles in cell cycle regulation. However, their biological functions, regulation, and expression remain unclear. This study revealed the molecular properties, oncogenic role, and clinical significance of PLK genes in pan-cancers, particularly in kidney renal papillary cell carcinoma (KIRP).

METHODS

We evaluated the mutation landscape, expression level, and prognostic values of PLK genes using bioinformatics analyses and explored the association between the expression level of PLK genes and tumor microenvironment (TME), immune subtype, cancer immunotherapy, tumor stemness, and drug sensitivity. Finally, we verified the prognostic value in patients with KIRP through univariate and multivariate analyses and nomogram construction.

RESULTS

PLK genes are extensively altered in pan-cancer, which may contribute to tumorigenesis. These genes are aberrantly expressed in some types of cancer, with PLK1 being overexpressed in 31 cancers. PLK expression is closely associated with the prognosis of various cancers. The expression level of PLK genes is related with sensitivity to diverse drugs and cancer immunity as well as cancer immunotherapy. Importantly, we verified that PLK1 was overexpressed in KIRP tissues and could be an unfavorable prognostic biomarker in patients with KIRP. Hence, PLK1 may serve as an oncogenic gene in KIRP and should be explored in future studies.

CONCLUSIONS

Our study comprehensively reports the molecular characteristics and biological functions of PLK family gens across human cancers and recommends further investigation of these genes as potential biomarkers and therapeutic targets, especially in KIRP.