Polo-like kinase 1 inhibitors in mono- and combination therapies: a new strategy for treating malignancies

Prognostic model for hepatocellular carcinoma based on necroptosis-related genes and analysis of drug treatment responses

Objective

Recent studies reveal that necroptosis is pivotal in tumorigenesis, cancer metastasis, cancer immunity, and cancer subtypes. Apoptosis or necroptosis of hepatocytes in the liver microenvironment can determine the subtype of liver cancer. However, necroptosis-related genomes have rarely been analyzed in hepatocellular carcinoma (HCC). Therefore, this study aims to construct an HCC risk scoring model based on necroptosis-related genes and to validate its predictive performance in overall survival prediction and immunotherapy efficacy evaluation in HCC, as well as to analyze drug treatment responses.

Methods

This study analyzed clinical information and RNA-seq expression data of liver cancer patients from TCGA public data, identified necroptosis-related genes, and conducted GO and KEGG enrichment analyses. Using Cox regression analysis and LASSO analysis to identify independent prognostic factors, a predictive model was established and validated in clinical subgroups, and correlation analysis with immune cells and ssGSEA differential analysis were conducted. Finally, potential drugs for HCC were screened to explore the drug sensitivity of different subtypes.

Results

We identified 19 differentially expressed necroptosis-related genes and constructed a predictive model with 3 independent prognostic factors through stepwise Cox regression. Validation results from clinical subgroups showed that the constructed model performed well in risk prediction, and ssGSEA differential analysis results were significant. We analyzed 55 immunotherapy drugs, and clustered them by distinct IC50 values to guide drug selection for HCC patients. Notable, Bleomycin, Obatoclax. Mesylate, PF.562271, PF.02341066, QS11, X17. AAG, and Bl. D1870 exhibited significantly different sensitivities in different subtypes, providing references for clinical practice in HCC patients.

Polo-like kinase-1 mediates hepatitis C virus-induced cell migration, a drug target for liver cancer

Polo-like kinase 1 (PLK1) is a regulator of cell mitosis and cytoskeletal dynamics. PLK1 overexpression in liver cancer is associated with tumour progression, metastasis, and vascular invasion. Hepatitis C virus (HCV) NS5A protein stimulates PLK1-mediated phosphorylation of host proteins, so we hypothesised that HCV-PLK1 interactions might be a mechanism for HCV-induced liver cancer. We used a HCV cell-culture model (Jc1) to investigate the effects of virus infection on the cytoskeleton. In HCV-infected cells, a novel posttranslational modification in β-actin was observed with phosphorylation at Ser239. Using in silico and in vitro approaches, we identified PLK1 as the mediating kinase. In functional experiments with a phosphomimetic mutant form of β-actin, Ser239 phosphorylation influences β-actin polymerization and distribution, resulting in increased cell motility. The changes were prevented by treating cells with the PLK1 inhibitor volasertib. In HCV-infected hepatocytes, increased cell motility contributes to cancer cell migration, invasion, and metastasis. PLK1 is an important mediator of these effects and early treatment with PLK1 inhibitors may prevent or reduce HCC progression, particularly in people with HCV-induced HCC.

The mitotic spindle-related seven-gene predicts the prognosis and immune microenvironment of lung adenocarcinoma

PURPOSE

Abnormalities in the mitotic spindle have been linked to a variety of cancers. Data on their role in the onset, progression, and treatment of lung adenocarcinoma (LUAD) need to be explored.

METHODS

The data were retrieved from The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and Molecular Signatures Database (MSigDB), for the training cohort, external validation cohort, and the hallmark mitotic spindle gene set, respectively. Mitotic spindle genes linked to LUAD prognosis were identified and intersected with differentially expressed up-regulated genes in the training cohort. Nomogram prediction models were built based on least absolute shrinkage and selection operator (LASSO) regression, univariate cox, and multivariate cox analyses. The seven-gene immunological score was examined, as well as the correlation of immune checkpoints. The DLGAP5 and KIF15 expression in BEAS-2B, A549, H1299, H1975, and PC-9 cell lines was validated with western blot (WB).

RESULTS

A total of 965 differentially expressed up-regulated genes in the training cohort intersected with 51 mitotic spindle genes associated with LUAD prognosis. Finally, the seven-gene risk score was determined and integrated with clinical characteristics to construct the nomogram model. Immune cell correlation analysis revealed a negative correlation between seven-gene expression with B cell, endothelial cell (excluding LMNB1), and T cell CD8 + (p < 0.05). However, the seven-gene expression was positively correlated with multiple immune checkpoints (p < 0.05). The expression of DLGAP5 and KIF15 were significantly higher in A549, H1299, H1975, and PC-9 cell lines than that in BEAS-2B cell line.

CONCLUSION

High expression of the seven genes is positively correlated with poor prognosis of LUAD, and these genes are promising as prospective immunotherapy targets.

The Role of APAL/ST8SIA6-AS1 lncRNA in PLK1 Activation and Mitotic Catastrophe of Tumor Cells

BACKGROUND

Tumor growth can be addicted to vital oncogenes, but whether long noncoding RNAs (lncRNAs) are essential to cancer survival is largely uncharacterized.

METHODS

We retrieved Gene Expression Omnibus datasets to identify lncRNA overexpression in 257 cancers vs 196 normal tissues and analyzed the association of ST8SIA6-AS1 (termed Aurora A/Polo-like-kinase 1 [PLK1]-associated lncRNA, APAL) with the clinical outcomes of multiple types of cancer from public RNA sequencing and microarray datasets as well as from in-house cancer cohorts. Loss- and gain-of-function experiments were performed to explore the role of APAL in cancers in vitro and in vivo. RNA pulldown and RNA immunoprecipitation were used to investigate APAL-interacting proteins. All statistical tests were two-sided.

RESULTS

APAL is overexpressed in multiple human cancers associated with poor clinical outcome of patients. APAL knockdown causes mitotic catastrophe and massive apoptosis in human breast, lung, and pancreatic cancer cells. Overexpressing APAL accelerates cancer cell cycle progression, promotes proliferation, and inhibits chemotherapy-induced apoptosis. Mechanism studies show that APAL links up PLK1 and Aurora A to enhance Aurora A-mediated PLK1 phosphorylation. Notably, targeting APAL inhibits the growth of breast and lung cancer xenografts in vivo (MCF-7 xenografts: mean tumor weight, control = 0.18 g [SD = 0.03] vs APAL locked nucleic acids = 0.07 g [SD = 0.02], P < .001, n = 8 mice per group; A549 xenografts: mean tumor weight control = 0.36 g [SD = 0.10] vs APAL locked nucleic acids = 0.10 g [SD = 0.04], P < .001, n = 9 mice per group) and the survival of patient-derived breast cancer organoids in three-dimensional cultures.

CONCLUSIONS

Our data highlight the essential role of lncRNA in cancer cell survival and the potential of APAL as an attractive therapeutic target for a broad-spectrum of cancers.

miR-593-5p inhibit cell proliferation by targeting PLK1 in non small cell lung cancer cells

Worldwide, lung cancer has the highest rates of mortality and morbidity, with the majority of its pathology attributable to non-small cell lung cancer (NSCLC). MicroRNAs are pivotal in the occurrence and development of cancer. However, the role of miRNA-593-5p in the progression of NSCLC is not clear. In this study, we investigate, in vitro, whether miRNA-593-5p inhibits NSCLC cell proliferation. To clarify its specific mechanism of inhibition, we used bioinformatics to predict its target genes and identified PLK1. Luciferase reporter assay confirmed the binding of miR-593-5p to the PLK1 3'-UTR in a sequence-specific manner in NSCLC cells. Additionally, we also found through Western blot and quantitative RT-PCR that miR-593-5p down-regulates the expression of PLK1 protein. Finally, PLK1 overexpression was shown to disinhibit NSCLC cell proliferation. Taken together, this evidence suggests that miR-593-5p inhibits NSCLC cell proliferation by inhibiting PLK1 expression.

In vitro study of the Polo-like kinase 1 inhibitor volasertib in non-small-cell lung cancer reveals a role for the tumor suppressor p53

Polo-like kinase 1 (Plk1), a master regulator of mitosis and the DNA damage response, is considered to be an intriguing target in the research field of mitotic intervention. The observation that Plk1 is overexpressed in multiple human malignancies, including non-small-cell lung cancer (NSCLC), gave rise to the development of several small-molecule inhibitors. Volasertib, presently the most extensively studied Plk1 inhibitor, has been validated to efficiently reduce tumor growth in preclinical settings. Unfortunately, only modest antitumor activity against solid tumors was reported in clinical trials. This discrepancy prompted research into the identification of predictive biomarkers. In this study, we investigated the therapeutic effect of volasertib monotherapy (i.e., cytotoxicity, cell cycle distribution, apoptotic cell death, cellular senescence, and migration) in a panel of NSCLC cell lines differing in p53 status under both normal and reduced oxygen tension (<0.1% O2 ). A strong growth inhibitory effect was observed in p53 wild-type cells (A549 and A549-NTC), with IC50 values significantly lower than those in p53 knockdown/mutant cells (A549-920 and NCI-H1975) (P < 0.001). While mitotic arrest was significantly greater in cells with nonfunctional p53 (P < 0.005), apoptotic cell death (P < 0.026) and cellular senescence (P < 0.021) were predominantly induced in p53 wild-type cells. Overall, the therapeutic effect of volasertib was reduced under hypoxia (P < 0.050). Remarkably, volasertib inhibited cell migration in all cell lines tested (P < 0.040), with the exception of for the NCI-H1975 p53 mutant cell line. In conclusion, our results show an important difference in the therapeutic effect of Plk1 inhibition in NSCLC cells with versus without functional p53. Overall, the p53 wild-type cell lines were more sensitive to volasertib treatment, suggesting that p53 might be a predictive biomarker for Plk1 inhibition in NSCLC. Moreover, our results pave the way for new combination strategies with Plk1 inhibitors to enhance antitumor activity.

miR-129-3p controls centrosome number in metastatic prostate cancer cells by repressing CP110

The centrosome plays a key role in cancer invasion and metastasis. However, it is unclear how abnormal centrosome numbers are regulated when prostate cancer (PCa) cells become metastatic. CP110 was previously described for its contribution of centrosome amplification (CA) and early development of aggressive cell behaviour. However its regulation in metastatic cells remains unclear. Here we identified miR-129-3p as a novel metastatic microRNA. CP110 was identified as its target protein. In PCa cells that have metastatic capacity, CP110 expression was repressed by miR-129-3p. High miR-129-3p expression levels increased cell invasion, while increasing CP110 levels decreased cell invasion. Overexpression of CP110 in metastatic PCa cells resulted in a decrease in the number of metastasis. In tissues of PCa patients, low CP110 and high miR-129-3p expression levels correlated with metastasis, but not with the expression of genes related to EMT. Furthermore, overexpression of CP110 in metastatic PCa cells resulted in excessive-CA (E-CA), and a change in F-actin distribution which is in agreement with their reduced metastatic capacity. Our data demonstrate that miR-129-3p functions as a CA gatekeeper in metastatic PCa cells by maintaining pro-metastatic centrosome amplification (CA) and preventing anti-metastatic E-CA.

Spotlight on Volasertib: Preclinical and Clinical Evaluation of a Promising Plk1 Inhibitor

Considering the important side effects of conventional microtubule targeting agents, more and more research focuses on regulatory proteins for the development of mitosis-specific agents. Polo-like kinase 1 (Plk1), a master regulator of several cell cycle events, has arisen as an intriguing target in this research field. The observed overexpression of Plk1 in a broad range of human malignancies has given rise to the development of several potent and specific small molecule inhibitors targeting the kinase. In this review, we focus on volasertib (BI6727), the lead agent in category of Plk1 inhibitors at the moment. Numerous preclinical experiments have demonstrated that BI6727 is highly active across a variety of carcinoma cell lines, and the inhibitor has been reported to induce tumor regression in several xenograft models. Moreover, volasertib has shown clinical efficacy in multiple tumor types. As a result, Food and Drug Administration (FDA) has recently awarded volasertib the Breakthrough Therapy status after significant benefit was observed in acute myeloid leukemia (AML) patients treated with the Plk1 inhibitor. Here, we discuss both preclinical and clinical data available for volasertib administered as monotherapy or in combination with other anticancer therapies in a broad range of tumor types.

Volasertib for the treatment of acute myeloid leukemia: a review of preclinical and clinical development

Volasertib is a potent inhibitor of Polo-like kinase (PLK) 1 and to lesser extent also PLK2 and PLK3. PLKs are key regulators of the cell cycle and volasertib blocks cells in G2-M phase of the cell cycle. The compound has been evaluated in Phase I and II studies in acute myeloid leukemia and solid tumors. Side effects are mainly hematological. In acute myeloid leukemia (AML), a randomized Phase II study has been conducted in elderly patients unfit for intensive chemotherapy. Patients have been randomized to a combination of volarsetib and low-dose cytarabine versus low-dose cytarabine alone. Preliminary results show significantly higher rates of complete remission and of complete remission with incomplete hematological recovery in the combination versus the monotherapy arm, with 31% and 13%, respectively. Longer event-free survival was observed with the combination with 5.6 versus 2.3 months, respectively (p = 0.0237). These encouraging data supported the initiation of an international Phase III trial, which currently underway, to confirm these results. Volasertib has not yet been approved for regular clinical use.

Efficacy and mechanism of action of volasertib, a potent and selective inhibitor of Polo-like kinases, in preclinical models of acute myeloid leukemia

Polo-like kinase 1 (Plk1), a member of the Polo-like kinase family of serine/threonine kinases, is a key regulator of multiple steps in mitosis. Here we report on the pharmacological profile of volasertib, a potent and selective Plk inhibitor, in multiple preclinical models of acute myeloid leukemia (AML) including established cell lines, bone marrow samples from AML patients in short-term culture, and subcutaneous as well as disseminated in vivo models in immune-deficient mice. Our results indicate that volasertib is highly efficacious as a single agent and in combination with established and emerging AML drugs, including the antimetabolite cytarabine, hypomethylating agents (decitabine, azacitidine), and quizartinib, a signal transduction inhibitor targeting FLT3. Collectively, these preclinical data support the use of volasertib as a new therapeutic approach for the treatment of AML patients, and provide a foundation for combination approaches that may further improve and prolong clinical responses.

Autoinhibition and relief mechanism for Polo-like kinase 4

Polo-like kinase 4 (Plk4) is a master regulator of centriole duplication, and its hyperactivity induces centriole amplification. Homodimeric Plk4 has been shown to be ubiquitinated as a result of autophosphorylation, thus promoting its own degradation and preventing centriole amplification. Unlike other Plks, Plk4 contains three rather than two Polo box domains, and the function of its third Polo box (PB3) is unclear. Here, we performed a functional analysis of Plk4's structural domains. Like other Plks, Plk4 possesses a previously unidentified autoinhibitory mechanism mediated by a linker (L1) near the kinase domain. Thus, autoinhibition is a conserved feature of Plks. In the case of Plk4, autoinhibition is relieved after homodimerization and is accomplished by PB3 and by autophosphorylation of L1. In contrast, autophosphorylation of the second linker promotes separation of the Plk4 homodimer. Therefore, autoinhibition delays the multiple consequences of activation until Plk4 dimerizes. These findings reveal a complex mechanism of Plk4 regulation and activation which govern the process of centriole duplication.

PLK1-inhibition can cause radiosensitization or radioresistance dependent on the treatment schedule

BACKGROUND AND PURPOSE

PLK1-inhibitors are emerging as new potential anticancer agents. It is therefore important to explore the combined effects of PLK1-inhibitors with conventional therapies. Based on the functional roles of PLK1 in both mitosis and the G2 checkpoint, we hypothesized that the treatment schedule might influence the combined effects of PLK1-inhibiton and radiation.

MATERIALS AND METHODS

Human osteosarcoma U2OS and colorectal cancer HT29 and SW620 cells were treated with the PLK1-inhibitor BI2536 before or after X-ray irradiation (0-6 Gy). Clonogenic assays, flow cytometry, immunofluorescence and mCherry-53BP1 time-lapse imaging were used to assay cell survival, cell cycle progression and DNA damage repair.

RESULTS

Treatment with the PLK1-inhibitor for 24h before radiation caused cells to accumulate in G2/M and resulted in increased radiosensitivity. In contrast, the cytotoxic effects of the two treatments were less-than-additive when cells were treated with the PLK1-inhibitor for 24h after radiation. This resistance was associated with a prolonged G2 checkpoint causing enhanced repair of the radiation-induced damage and decreased BI2536-mediated mitotic damage.

CONCLUSIONS

PLK1-inhibitors need to be administrated several hours before radiation to achieve radiosensitization. If PLK1-inhibitors are given after radiation, cell killing is reduced due to the prolonged G2 checkpoint.

The σ2 receptor: a novel protein for the imaging and treatment of cancer

The σ2 receptor is an important target for the development of molecular probes in oncology because of its 10-fold higher density in proliferating tumor cells compared with that in quiescent tumor cells and because of the observation that σ2 receptor agonists are able to kill tumor cells via apoptotic and nonapoptotic mechanisms. Although recent evidence indicates that the σ2 receptor binding site is localized within the progesterone receptor membrane component 1 (PGRMC1), most information regarding this protein has been obtained using either radiolabeled or fluorescent receptor-based probes and from biochemical analysis of the effect of σ2 selective ligands on cells grown in culture. This article reviews the development of σ2 receptor ligands and presents an overview of how they have been used in vitro and in vivo to increase our understanding of the role of the σ2 receptor in cancer and proliferation.

Gravin is a transitory effector of polo-like kinase 1 during cell division

The mitogenic and second-messenger signals that promote cell proliferation often proceed through multienzyme complexes. The kinase-anchoring protein Gravin integrates cAMP and calcium/phospholipid signals at the plasma membrane by sequestering protein kinases A and C with G protein-coupled receptors. In this report we define a role for Gravin as a temporal organizer of phosphorylation-dependent protein-protein interactions during mitosis. Mass spectrometry, molecular, and cellular approaches show that CDK1/Cyclin B1 phosphorylates Gravin on threonine 766 to prime the recruitment of the polo-like kinase Plk1 at defined phases of mitosis. Fluorescent live-cell imaging reveals that cells depleted of Gravin exhibit mitotic defects that include protracted prometaphase and misalignment of chromosomes. Moreover, a Gravin T766A phosphosite mutant that is unable to interact with Plk1 negatively impacts cell proliferation. In situ detection of phospho-T766 Gravin in biopsy sections of human glioblastomas suggests that this phosphorylation event might identify malignant neoplasms.

Metastatic gastric cancer - focus on targeted therapies

Gastric cancer (GC) is currently the second leading cause of cancer death worldwide; unfortunately, most patients will present with locally advanced or metastatic disease. Despite recent progress in diagnosis, surgery, chemotherapy, and radiotherapy, prognosis remains poor. A better understanding of GC biology and signaling pathways is expected to improve GC therapy, and the integration of targeted therapies has recently become possible and appears to be promising. This article focuses on anti-Her-2 therapy, specifically trastuzumab, as well as other epidermal growth factor receptor antagonists such as cetuximab, panitumub, matuzumab, nimotzumab, gefitinib, and erlotinib. Additionally, drugs that target angiogenesis pathways are also under investigation, particulary bevacizumab, ramucirumab, sorafenib, sunitinib, and cediranib. Other targeted agents in preclinical or early clinical development include mTOR inhibitors, anti c-MET, polo-like kinase 1 inhibitors, anti-insulin-like growth factor, anti-heat shock proteins, and small molecules targeting Hedgehog signaling.

NMS-P937, an orally available, specific small-molecule polo-like kinase 1 inhibitor with antitumor activity in solid and hematologic malignancies

Polo-like kinase 1 (PLK1) is a serine/threonine protein kinase considered to be the master player of cell-cycle regulation during mitosis. It is indeed involved in centrosome maturation, bipolar spindle formation, chromosome separation, and cytokinesis. PLK1 is overexpressed in a variety of human tumors and its overexpression often correlates with poor prognosis. Although five different PLKs are described in humans, depletion or inhibition of kinase activity of PLK1 is sufficient to induce cell-cycle arrest and apoptosis in cancer cell lines and in xenograft tumor models. NMS-P937 is a novel, orally available PLK1-specific inhibitor. The compound shows high potency in proliferation assays having low nanomolar activity on a large number of cell lines, both from solid and hematologic tumors. NMS-P937 potently causes a mitotic cell-cycle arrest followed by apoptosis in cancer cell lines and inhibits xenograft tumor growth with clear PLK1-related mechanism of action at well-tolerated doses in mice after oral administration. In addition, NMS-P937 shows potential for combination in clinical settings with approved cytotoxic drugs, causing tumor regression in HT29 human colon adenocarcinoma xenografts upon combination with irinotecan and prolonged survival of animals in a disseminated model of acute myelogenous leukemia in combination with cytarabine. NMS-P937, with its favorable pharmacologic parameters, good oral bioavailability in rodent and nonrodent species, and proven antitumor activity in different preclinical models using a variety of dosing regimens, potentially provides a high degree of flexibility in dosing schedules and warrants investigation in clinical settings.

Identification of novel, potent and selective inhibitors of Polo-like kinase 1

A series of pyrimidodiazepines was identified as potent Polo-like kinase 1 (PLK1) inhibitors. The synthesis and SAR are discussed. The lead compound 7 (RO3280) has potent inhibitory activity against PLK1, good selectivity against other kinases, and excellent in vitro cellular potency. It showed strong antitumor activity in xenograft mouse models.

Discovery of a potent and orally bioavailable benzolactam-derived inhibitor of Polo-like kinase 1 (MLN0905)

This article describes the discovery of a series of potent inhibitors of Polo-like kinase 1 (PLK1). Optimization of this benzolactam-derived chemical series produced an orally bioavailable inhibitor of PLK1 (12c, MLN0905). In vivo pharmacokinetic-pharmacodynamic experiments demonstrated prolonged mitotic arrest after oral administration of 12c to tumor bearing nude mice. A subsequent efficacy study in nude mice achieved tumor growth inhibition or regression in a human colon tumor (HT29) xenograft model.