Polo-like kinase isoform expression is a prognostic factor in ovarian carcinoma

Metformin synergizes with gilteritinib in treating FLT3-mutated leukemia via targeting PLK1 signaling

Fms-like tyrosine kinase 3 (FLT3) mutations, present in over 30% of acute myeloid leukemia (AML) cases and dominated by FLT3-internal tandem duplication (FLT3-ITD), are associated with poor outcomes in patients with AML. While tyrosine kinase inhibitors (TKIs; e.g., gilteritinib) are effective, they face challenges such as drug resistance, relapse, and high costs. Here, we report that metformin, a cheap, safe, and widely used anti-diabetic agent, exhibits a striking synergistic effect with gilteritinib in treating FLT3-ITD AML. Metformin significantly sensitizes FLT3-ITD AML cells (including TKI-resistant ones) to gilteritinib. Metformin plus gilteritinib (low dose) dramatically suppresses leukemia progression and prolongs survival in FLT3-ITD AML mouse models. Mechanistically, the combinational treatment cooperatively suppresses polo-like kinase 1 (PLK1) expression and phosphorylation of FLT3/STAT5/ERK/mTOR. Clinical analysis also shows improved survival rates in patients with FLT3-ITD AML taking metformin. Thus, the metformin/gilteritinib combination represents a promising and cost-effective treatment for patients with FLT3-mutated AML, particularly for those with low income/affordability.

PLK1 inhibition leads to mitotic arrest and triggers apoptosis in cholangiocarcinoma cells

Cholangiocarcinoma (CCA) is a lethal cancer originating from the epithelial cells within the bile duct and ranks as the second most prevalent form of liver cancer in Thailand. Polo-like kinase 1 (PLK1), a protein serine/threonine kinase, regulates a number of steps in cell mitosis and is upregulated in several types of cancer, including CCA. Our previous study identified PLK1 as a biomarker of the C1 subtype, correlating with poor prognosis in intrahepatic CCA. The present study aimed to examine the effect of PLK1 inhibition on CCA cells. Different CCA cell lines developed from Thai patients, HuCCA1, KKU055, KKU100 and KKU213A, were treated with two PLK1 inhibitors, BI2536 and BI6727, and were transfected with small interfering RNA, followed by analysis of cell proliferation, cell cycle distribution and cell apoptosis. It was discovered that BI2536 and BI6727 inhibited cell proliferation and caused G2/M-phase arrest in CCA cells. Furthermore, the number of total apoptotic cells was increased in PLK1 inhibitor-treated CCA cells. The expression levels of mitotic proteins, aurora kinase A, phosphorylated PLK1 (T210) and cyclin B1, were augmented in PLK1-inhibited CCA cells. Additionally, inhibition of PLK1 led to increased DNA damage, as determined by the upregulated levels of γH2AX and increased cleavage of poly (ADP-ribose) polymerase, an apoptotic marker. These results suggested that inhibiting PLK1 prolonged mitotic arrest and subsequently triggered cell apoptosis. Validation of the antiproliferative effects of PLK1 inhibition was accomplished through silencing of the PLK1 gene. In conclusion, targeting PLK1 provided promising results for further study as a potential candidate for targeted therapy in CCA.

MYC and HSF1 Cooperate to Drive PLK1 inhibitor Sensitivity in High Grade Serous Ovarian Cancer

Ovarian cancer is a deadly female cancer with high rates of recurrence. The primary treatment strategy for patients is platinum-based therapy regimens that almost universally develop resistance. Consequently, new therapeutic avenues are needed to overcome the plateau that current therapies have on patient outcomes. We describe a gene amplification involving both HSF1 and MYC, wherein these two genes on chromosome 8q are co-amplified in over 7% of human tumors that is enriched to over 30% of patients with ovarian cancer. We further found that HSF1 and MYC transcriptional activity is correlated in human tumors and ovarian cancer cell lines, suggesting they may cooperate in ovarian cancer cells. CUT&RUN for HSF1 and MYC in co-amplified ovarian cancer cells revealed that HSF1 and MYC have overlapping binding at a substantial number of locations throughout the genome where their binding peaks are near identical. Consistent with these data, a protein-protein interaction between HSF1 and MYC was detected in ovarian cancer cells, implying these two transcription factors have a molecular cooperation. Further supporting their cooperation, growth of HSF1-MYC co-amplified ovarian cancer cells were found to be dependent on both HSF1 and MYC. In an attempt to identify a therapeutic target that could take advantage of this dependency on both HSF1 and MYC, PLK1 was identified as being correlated with HSF1 and MYC in primary human tumor specimens, consistent with a previously established effect of PLK1 on HSF1 and MYC protein levels. Targeting PLK1 with the compound volasertib (BI-6727) revealed a greater than 200-fold increased potency of volasertib in HSF1-MYC co-amplified ovarian cancer cells compared to ovarian cancer cells wild-type HSF1 and MYC copy number, which extended to several growth assays, including spheroid growth. Volasertib, and other PLK1 inhibitors, have not shown great success in clinical trials and this study suggests that targeting PLK1 may be viable in a precision medicine approach using HSF1-MYC co-amplification as a biomarker for response.

Biomarkers of Alzheimer's Disease Associated with Programmed Cell Death Reveal Four Repurposed Drugs

Alzheimer's disease (AD) is a neurodegenerative disorder and the most common cause of dementia. Programmed cell death (PCD) is mainly characterized by unique morphological features and energy-dependent biochemical processes. The predominant pathway leading to cell death in AD has not been thoroughly analyzed, although there is evidence of neuron loss in AD and numerous pathways of PCD have been associated with this process. A better understanding of the systems biology underlying the relationship between AD and PCD could lead to the development of new therapeutic approaches. To this end, publicly available transcriptome data were examined using bioinformatic methods such as differential gene expression and weighted gene coexpression network analysis (WGCNA) to find PCD-related AD biomarkers. The diagnostic significance of these biomarkers was evaluated using a logistic regression-based predictive model. Using these biomarkers, a multifactorial regulatory network was developed. Last, a drug repositioning study was conducted to propose new drugs for the treatment of AD targeting PCD. The development of 3PM (predictive, preventive, and personalized) drugs for the treatment of AD would be enabled by additional research on the effects of these drugs on this disease.

PLK3 is linked with higher tumor stage and unfavorable prognosis in patients with colorectal cancer

Objective: This study intended to explore the relationship of PLK3 with prognosis in patients with colorectal cancer (CRC). Methods: PLK3 positivity was detected by immunohistochemistry in 160 patients with CRC receiving surgical resection. Results: The median tumor PLK3-positive rate was 26.5%. Tumor PLK3-positive rate was related to increased lymph node stage (p = 0.002) and tumor-node-metastasis stage (p < 0.001) of CRC. Tumor PLK3-positive rate ≥30% was related to shortened disease-free survival (p = 0.009) and overall survival (p = 0.003); tumor PLK3-positive rate ≥50% showed a stronger correlation with them (both p = 0.001), which was validated by multivariate Cox regression analyses (both p < 0.05). Conclusion: Tumor PLK3-positive rate ≥50% relates to increased tumor stage and unfavorable survival in patients with CRC.

PLK1 and FoxM1 expressions positively correlate in papillary thyroid carcinoma and their combined inhibition results in synergistic anti-tumor effects

Polo-like kinase 1 (PLK1; also known as serine/threonine-protein kinase PLK1) serves as a central player in cell proliferation, exerting critical regulatory roles in mitotic processes and cell survival. We conducted an analysis of PLK1 protein expression in a large cohort of samples from papillary thyroid carcinoma (PTC) patients and examined its functional significance in PTC cell lines, both in vitro and in vivo. PLK1 overexpression was noted in 54.2% of all PTC and was significantly associated with aggressive clinicopathological parameters; it was also found to be an independent prognostic marker for shorter recurrence-free survival. Given the significant association between PLK1 and forkhead box protein M1 (FoxM1), and their concomitant overexpression in a large proportion of PTC samples, we explored their correlation and their combined inhibitions in PTC in vitro and in vivo. Inhibition of PLK1 expression indeed suppressed cell proliferation, leading to cell cycle arrest and apoptosis in PTC cell lines. Significantly, the downregulation of PLK1 reduced the self-renewal capability of spheroids formed from PTC cells. Immunoprecipitation analysis shows that PLK1 binds to FoxM1 and vice versa in vitro. Mechanistically, PLK1 knockdown suppresses FoxM1 expression, whereas inhibition of FoxM1 does not affect PLK1 expression, which suggests that PLK1 acts through the FoxM1 pathway. The combined treatment of a PLK1 inhibitor (volasertib) and a FoxM1 inhibitor (thiostrepton) demonstrated a synergistic effect in reducing PTC cell growth in vitro and delaying tumor growth in vivo. This study highlights the important role of PLK1 in PTC tumorigenesis and prognosis. It also highlights the synergistic therapeutic potential of dual-targeting PLK1 and FoxM1 in PTC, unveiling a potential innovative therapeutic strategy for managing aggressive forms of PTC.

A Review on Molecular Docking on HDAC Isoforms: Novel Tool for Designing Selective Inhibitors

Research into histone deacetylases (HDACs) has experienced a remarkable surge in recent years. These enzymes are key regulators of several fundamental biological processes, often associated with severe and potentially fatal diseases. Inhibition of their activity represents a promising therapeutic approach and a prospective strategy for the development of new therapeutic agents. A critical aspect of their inhibition is to achieve selectivity in terms of enzyme isoforms, which is essential to improve treatment efficacy while reducing undesirable pleiotropic effects. The development of computational chemistry tools, particularly molecular docking, is greatly enhancing the precision of designing molecules with inherent potential for specific activity. Therefore, it was considered necessary to review the molecular docking studies conducted on the major isozymes of the enzyme in order to identify the specific interactions associated with each selective HDAC inhibitor. In particular, the most critical isozymes of HDAC (1, 2, 3, 6, and 8) have been thoroughly investigated within the scope of this review.

Proteomic and Phosphoproteomic Reprogramming in Epithelial Ovarian Cancer Metastasis

Epithelial ovarian cancer (EOC) is a high-risk cancer presenting with heterogeneous tumors. The high incidence of EOC metastasis from primary tumors to nearby tissues and organs is a major driver of EOC lethality. We used cellular models of spheroid formation and readherence to investigate cellular signaling dynamics in each step toward EOC metastasis. In our system, adherent cells model primary tumors, spheroid formation represents the initiation of metastatic spread, and readherent spheroid cells represent secondary tumors. Proteomic and phosphoproteomic analyses show that spheroid cells are hypoxic and show markers for cell cycle arrest. Aurora kinase B abundance and downstream substrate phosphorylation are significantly reduced in spheroids and readherent cells, explaining their cell cycle arrest phenotype. The proteome of readherent cells is most similar to spheroids, yet greater changes in the phosphoproteome show that spheroid cells stimulate Rho-associated kinase 1 (ROCK1)-mediated signaling, which controls cytoskeletal organization. In spheroids, we found significant phosphorylation of ROCK1 substrates that were reduced in both adherent and readherent cells. Application of the ROCK1-specific inhibitor Y-27632 to spheroids increased the rate of readherence and altered spheroid density. The data suggest ROCK1 inhibition increases EOC metastatic potential. We identified novel pathways controlled by Aurora kinase B and ROCK1 as major drivers of metastatic behavior in EOC cells. Our data show that phosphoproteomic reprogramming precedes proteomic changes that characterize spheroid readherence in EOC metastasis.

CEBP-β and PLK1 as Potential Mediators of the Breast Cancer/Obesity Crosstalk: In Vitro and In Silico Analyses

Over the last two decades, obesity has reached pandemic proportions in several countries, and expanding evidence is showing its contribution to several types of malignancies, including breast cancer (BC). The conditioned medium (CM) from mature adipocytes contains a complex of secretes that may mimic the obesity condition in studies on BC cell lines conducted in vitro. Here, we report a transcriptomic analysis on MCF-7 BC cells exposed to adipocyte-derived CM and focus on the predictive functional relevance that CM-affected pathways/processes and related biomarkers (BMs) may have in BC response to obesity. CM was demonstrated to increase cell proliferation, motility and invasion as well as broadly alter the transcript profiles of MCF-7 cells by significantly modulating 364 genes. Bioinformatic functional analyses unraveled the presence of five highly relevant central hubs in the direct interaction networks (DIN), and Kaplan-Meier analysis sorted the CCAAT/enhancer binding protein beta (CEBP-β) and serine/threonine-protein kinase PLK1 (PLK1) as clinically significant biomarkers in BC. Indeed, CEBP-β and PLK1 negatively correlated with BC overall survival and were up-regulated by adipocyte-derived CM. In addition to their known involvement in cell proliferation and tumor progression, our work suggests them as a possible "deus ex machina" in BC response to fat tissue humoral products in obese women.

VIRMA Promotes Nasopharyngeal Carcinoma Tumorigenesis and Metastasis by Upregulation of E2F7 in an m6A-Dependent Manner

The N6-methyladenosine (m6A) modification possesses new and essential roles in tumor initiation and progression by regulating mRNA biology. However, the role of aberrant m6A regulation in nasopharyngeal carcinoma (NPC) remains unclear. Here, through comprehensive analyses of NPC cohorts from the GEO database and our internal cohort, we identified that VIRMA, an m6A writer, is significantly upregulated in NPC and plays an essential role in tumorigenesis and metastasis of NPC, both in vitro and in vivo. High VIRMA expression served as a prognostic biomarker and was associated with poor outcomes in patients with NPC. Mechanistically, VIRMA mediated the m6A methylation of E2F7 3'-UTR, then IGF2BP2 bound and maintained the stability of E2F7 mRNA. An integrative high-throughput sequencing approach revealed that E2F7 drives a unique transcriptome distinct from the classical E2F family in NPC, which functioned as an oncogenic transcriptional activator. E2F7 cooperated with CBFB-recruited RUNX1 in a non-canonical manner to transactivate ITGA2, ITGA5, and NTRK1, strengthening Akt signaling-induced tumor-promoting effect.

Resistance to BRAF Inhibitors: EZH2 and Its Downstream Targets as Potential Therapeutic Options in Melanoma

Activating BRAF mutations occurs in 50-60% of malignant melanomas. Although initially treatable, the development of resistance to BRAF-targeted therapies (BRAFi) is a major challenge and limits their efficacy. We have previously shown that the BRAF_V600E signaling pathway mediates the expression of EZH2, an epigenetic regulator related to melanoma progression and worse overall survival. Therefore, we wondered whether inhibition of EZH2 would be a way to overcome resistance to vemurafenib. We found that the addition of an EZH2 inhibitor to vemurafenib improved the response of melanoma cells resistant to BRAFi with regard to decreased viability, cell-cycle arrest and increased apoptosis. By next-generation sequencing, we revealed that the combined inhibition of BRAF and EZH2 dramatically suppresses pathways of mitosis and cell cycle. This effect was linked to the downregulation of Polo-kinase 1 (PLK1), a key regulator of cell cycle and proliferation. Subsequently, when we inhibited PLK1, we found decreased cell viability of melanoma cells resistant to BRAFi. When we inhibited both BRAF and PLK1, we achieved an improved response of BRAFi-resistant melanoma cells, which was comparable to the combined inhibition of BRAF and EZH2. These results thus reveal that targeting EZH2 or its downstream targets, such as PLK1, in combination with BRAF inhibitors are potential novel therapeutic options in melanomas with BRAF mutations.

Polo-like kinase 1 as a potential therapeutic target and prognostic factor for various human malignancies: A systematic review and meta-analysis

Objective

The overexpression of polo-like kinase 1 (PLK-1) has been found in a broad spectrum of human tumors, making it an attractive prognostic tumor biomarker. Nowadays, PLK-1 is considered a cancer therapeutic target with clinical therapeutic value. The aim of the present study was to systematically review the prognostic and therapeutic value of PLK-1 in different malignant neoplasms.

Methods

A systematic literature search of the Cochrane Library, PubMed, Web of Science, and China National Knowledge Internet (CNKI) databases was conducted between December 2018 and September 2022. In total, 41 published studies were screened, comprising 5,301 patients. We calculated the pooled odds ratios (ORs) and corresponding 95%CIs for the clinical parameters of patients included in these studies, as well as the pooled hazard ratios (HRs) and corresponding 95% CIs for 5-year overall survival (OS).

Results

Our analysis included 41 eligible studies, representing a total of 5,301 patients. The results showed that overexpression of PLK-1 was significantly associated with poor OS (HR, 1.57; 95% CI, 1.18–2.08) and inferior 5-year disease-free survival/relapse-free survival ((HR, 1.89; 95% CI, 1.47–2.44). The pooled analysis showed that PLK-1 overexpression was significantly associated with lymph node metastasis, histological grade, clinical stages (p &lt; 0.001 respectively), and tumor grade (p &lt; 0.001). In digestive system neoplasms, PLK-1 overexpression was significantly associated with histopathological classification, primary tumor grade, histological grade, and clinical stages (p = 0.002, p = 0.001, p &lt; 0.0001, respectively). In breast cancer, PLK-1 was significantly associated with 5-year overall survival, histological grade, and lymph node metastasis (p &lt; 0.001, p = 0.003, p &lt; 0.001, respectively). In the female reproductive system, PLK-1 was significantly associated with clinical stage (p = 0.011). In the respiratory system, PLK-1 was significantly associated with clinical stage (p = 0.021).

Conclusion

Our analysis indicates that high PLK-1 expression is associated with aggressiveness and poor prognosis in malignant neoplasms. Therefore, PLK-1 may be a clinically valuable target for cancer treatment.

Comprehensive analysis of PLKs expression and prognosis in breast cancer

OBJECTIVE

A thorough examination of PLKs in breast cancer, including their expression and prognosis.

METHODS

With the help of the Oncomine database, the transcript levels of PLKs in breast cancer were examined. The changes in PLKs expression with tumor stage and indeed the relationship between PLKs expression and stage of cancer in women with breast cancer were scrutinized by using the GEPIA database. Based on Kaplan-Meier plots, breast cancer patients were assessed for their prognosis. Breast cancer gene expression and mutations were analyzed within the cBioPortal database.

RESULTS

According to Oncomine data, PLK1 and PLK4 mRNA expression levels were dramatically elevated in breast cancer patients while PLK2 and PLK5P levels were significantly downregulated. PLK1 and PLK4 expression were discovered to be greater in breast cancer tissues than in healthy tissues following analysis of the GEPIA database (P < 0.05). High levels of PLK1 and PLK4 transcripts have been linked to poor relapse-free survival rates across all patients with breast cancer according to the Kaplan-Meier Plotter database. The high levels of PLK2, PLK3, and PLK5 were associated with a higher recurrence-free survival rate. In the cBioPortal database, PLK was altered in 9.6% of breast cancer samples. Genetic alterations occurred in 15.07% of clinically counted invasive breast cancers, with mutations in 4.11%, gene amplifications in 9.59%, and gene deletion mutations in 1.37%. Additionally, the KEGG database demonstrates that PLKs are crucial for the cell cycle. The findings imply that elevated PLK1 and PLK4 expression in tissues of breast cancer might contribute significantly to the carcinogenesis of breast cancer. Moreover, PLK1 and PLK4 are highly expressed in breast cancer, and their use as molecular markers to identify high-risk subsets from patients with breast cancer is potentially possible.

CONCLUSIONS

For the precise therapy of breast cancers, PLK1 and PLK4 are potential targets, while PLK2, PLK3, and PLK5 are brand-new biomarkers for predicting the prognosis of breast cancer.

Sequential Targeting of PLK1 and PARP1 Reverses the Resistance to PARP Inhibitors and Enhances Platin-Based Chemotherapy in BRCA-Deficient High-Grade Serous Ovarian Cancer with KRAS Amplification

Ovarian cancer (OC) accounts for approximately 4% of cancer deaths in women worldwide and is the deadliest gynecologic malignancy. High-grade serous ovarian cancer (HGSOC) is the most predominant ovarian cancer, in which BRCA1/2 gene mutation ranges from 3 to 27%. PARP inhibitors (PARPi) have shown promising results as a synthetically lethal therapeutic approach for BRCA mutant and recurrent OC in clinical use. However, emerging data indicate that BRCA-deficient cancers may be resistant to PARPi, and the mechanisms of this resistance remain elusive. We found that amplification of KRAS likely underlies PARPi resistance in BRCA2-deficient HGSOC. Our data suggest that PLK1 inhibition restores sensitivity to PARPi in HGSOC with KRAS amplification. The sequential combination of PLK1 inhibitor (PLK1i) and PARPi drastically reduces HGSOC cell survival and increases apoptosis. Furthermore, we were able to show that a sequential combination of PLK1i and PARPi enhanced the cellular apoptotic response to carboplatin-based chemotherapy in KRAS-amplified resistant HGSOC cells and 3D spheroids derived from recurrent ovarian cancer patients. Our results shed new light on the critical role of PLK1 in reversing PARPi resistance in KRAS-amplified HGSOC, and offer a new therapeutic strategy for this class of ovarian cancer patients where only limited options currently exist.

PLK3 amplification and tumor immune microenvironment of metastatic tumors are linked to adjuvant treatment outcomes in uterine serous cancer

Uterine serous carcinoma (USC), an aggressive variant of endometrial cancer representing approximately 10% of endometrial cancer diagnoses, accounts for ∼39% of endometrial cancer-related deaths. We examined the role of genomic alterations in advanced-stage USC associated with outcome using paired primary-metastatic tumors (n = 29) treated with adjuvant platinum and taxane chemotherapy. Comparative genomic analysis of paired primary-metastatic patient tumors included whole exome sequencing and targeted gene expression. Both PLK3 amplification and the tumor immune microenvironment (TIME) in metastatic tumors were linked to time-to-recurrence (TTR) risk without any such association observed with primary tumors. TP53 loss was significantly more frequent in metastatic tumors of platinum-resistant versus platinum-sensitive patients and was also associated with increased recurrence and mortality risk. Increased levels of chr1 breakpoints in USC metastatic versus primary tumors co-occur with PLK3 amplification. PLK3 and the TIME are potential targets for improving outcomes in USC adjuvant therapy.

WTAP-mediated m6A modification of lncRNA DIAPH1-AS1 enhances its stability to facilitate nasopharyngeal carcinoma growth and metastasis

As the most predominant RNA epigenetic regulation in eukaryotic cells, N⁶-methyladenosine (m⁶A) plays a critical role in human tumorigenesis and cancer progression. However, the biological function and molecular mechanism of m⁶A regulation in naso-pharyngeal carcinoma (NPC) remain elusive. Here, we showed that Wilms' tumor 1-associating protein (WTAP) expression was apparently upregulated in NPC, and increased WTAP was associated with poor prognosis. WTAP upregulated in NPC was fine-tuned by KAT3A-mediated H3K27 acetylation. Functionally, WTAP was required for the growth and metastasis of NPC. Mechanistically, lncRNA DIAPH1-AS1 was identified as a bona fide m⁶A target of WTAP. WTAP-mediated m⁶A modification of DIAPH1-AS1 enhanced its stability relying on the m⁶A reader IGF2BP2-dependent pathway. Furthermore, DIAPH1-AS1 acted as a molecular adaptor that promoted MTDH-LASP1 complex formation and upregulated LASP1 expression, ultimately facilitating NPC growth and metastasis. Thus, WTAP-mediated DIAPH1-AS1 m⁶A methylation is required for NPC tumorigenesis and metastasis.

Signatures of malignant cells and novel therapeutic targets revealed by single-cell sequencing in lung adenocarcinoma

Background

Single‐cell transcriptomics has been used to investigate various tumors to elucidate the molecular distinction of all cell type compositions of a complex mix.

Aims

This study aimed to investigate malignant‐cell‐specific genes to explore diagnostic and therapeutic biomarkers using single‐cell transcriptomic data of lung adenocarcinoma.

Materials & Methods

10X single‐cell RNA‐seq data of fourteen patients with lung adenocarcinoma were analyzed. Genes that expressed differentially and those with higher confidence to distinguish tumor cells from normal cells were picked out using the ROC curves. The LASSO regression method was used to select most markedly correlated genes to predict the malignancy of every single cell within a model. We also conducted further experiments to determine their roles in lung cancer in vitro.

Results

Twenty two thousand four hundred and ninety one tumor and 181 666 normal single cells were analyzed where 369 genes were found to be specifically expressed in single malignant cells. Seventy of them, encoding secreted or membrane‐bound proteins, showed involvement in cell‐to‐cell communications in tumor biology. KRT18 and the other six genes were identified as predictors to distinguish single malignant cells and were integrated to construct an accurate (96.1%) predicting model. Notably, IRX2, SPINK13, and CAPN8 outperformed the other four genes. Further experiments confirmed the upregulation of them in lung adenocarcinoma at both tissue and cell levels. Proliferative capacities of lung adenocarcinoma cells were attenuated by knocking‐down of either of them. However, targeting CAPN8, IRX2, or SPINK13 hardly exerted a cytotoxic effect on these cells.

Discussion

Apart from the current model, similar tools were still warranted using single‐cell RNA‐seq data of more types of tumors. The three genes identified as potential therapeutic targets in the present study still need to be validated in more in lung cancer.

Conclusion

Our model can aid the analyses of single‐cell sequencing data. CAPN8, IRX2, and SPINK13 may serve as novel targets of targeted and immune‐based therapies in lung adenocarcinoma.

Keep Calm and Carry on with Extra Centrosomes

Simple Summary

Precise chromosome segregation during mitosis is a vital event orchestrated by formation of bipolar spindle poles. Supernumerary centrosomes, caused by centrosome amplification, deteriorates mitotic processes, resulting in segregation defects leading to chromosomal instability (CIN). Centrosome amplification is frequently observed in various types of cancer and considered as a significant contributor to destabilization of chromosomes. This review provides a comprehensive overview of causes and consequences of centrosome amplification thoroughly describing molecular mechanisms.

Abstract

Aberrations in the centrosome number and structure can readily be detected at all stages of tumor progression and are considered hallmarks of cancer. Centrosome anomalies are closely linked to chromosome instability and, therefore, are proposed to be one of the driving events of tumor formation and progression. This concept, first posited by Boveri over 100 years ago, has been an area of interest to cancer researchers. We have now begun to understand the processes by which these numerical and structural anomalies may lead to cancer, and vice-versa: how key events that occur during carcinogenesis could lead to amplification of centrosomes. Despite the proliferative advantages that having extra centrosomes may confer, their presence can also lead to loss of essential genetic material as a result of segregational errors and cancer cells must deal with these deadly consequences. Here, we review recent advances in the current literature describing the mechanisms by which cancer cells amplify their centrosomes and the methods they employ to tolerate the presence of these anomalies, focusing particularly on centrosomal clustering.

Folate-mediated targeted PLK1 inhibition therapy for ovarian cancer: A comparative study of molecular inhibitors and siRNA therapeutics

PLK1 is a promising target for clinical treatment of diverse malignancies including ovarian cancer (OC), in which PLK1 over-expression is often correlated with poor prognosis and short survival. PLK1 can be blocked with small molecular inhibitors like volasertib (Vol) or silenced with PLK1-specific siRNA (siPLK1), hence effectively suppressing tumor growth. Surprisingly, despite intensive work on molecular inhibitor and siRNA therapeutics, there is no direct comparison between them reported for targeted tumor therapy. Herein, we employing folate as a ligand and polymersomes as a nanovehicle performed a comparative study on Vol and siPLK1 in inhibiting OC in vitro and in vivo. Folate-targeted polymersomal Vol and siPLK1 (termed as FA-Ps-Vol and FA-Ps-siPLK1, respectively) were both nano-sized and stable, and displayed an optimal FA density of 20% for SKOV-3 cells. Notably, FA-Ps-Vol and FA-Ps-siPLK1 exhibited an IC₅₀ of 193 and 770 nM, respectively, to SKOV-3 cells, indicating a greater potency of Vol than siPLK1. The markedly increased uptake for FA-Ps-Vol and FA-Ps-siPLK1 compared with respective non-targeted controls by SKOV-3 tumor xenografts in mice confirmed that FA mediates strong OC-targeting in vivo. Intriguingly, FA-Ps-Vol while greatly lessening toxic effects of Vol potently repressed tumor growth with a remarkable tumor inhibition rate (TIR) of 97% at 20 mg (i.e. 32.4 µmol) Vol equiv./kg. FA-Ps-siPLK1 achieved effective tumor inhibition (TIR = ca. 87% or 90%) at 2 or 4 mg (i.e. 0.15 or 0.3 µmol) siPLK1 equiv./kg without causing adverse effects. This comparative study highlights that molecular inhibitor has the advantage of easy dose escalation and potent protein inhibition at the expense of certain adverse effects while siRNA therapeutics has low toxicity with moderate protein inhibition in vivo. STATEMENT OF SIGNIFICANCE: PLK1 is a promising target for the development of innovative and specific treatments against diverse malignancies. Interestingly, despite intensive work on molecular inhibitors and siRNA against PLK1, little work has been directed to compare their efficacy in targeted tumor therapy. Here, we employed folate as a ligand and polymersomes as a nanovehicle and have performed a comparative study on volasertib and siPLK1 in inhibiting ovarian cancer in vitro and in vivo. Our data show that the dose of volasertib can be easily escalated to induce prominent antitumor efficacy at the expense of certain adverse effects, while siPLK1 brings about moderate protein inhibition and antitumor therapy without causing toxicity at two-orders-of-magnitude lower dose.

A dimerization-dependent mechanism regulates enzymatic activation and nuclear entry of PLK1

Polo-like kinase 1 (PLK1) is a crucial regulator of cell cycle progression. It is established that the activation of PLK1 depends on the coordinated action of Aurora-A and Bora. Nevertheless, very little is known about the spatiotemporal regulation of PLK1 during G2, specifically, the mechanisms that keep cytoplasmic PLK1 inactive until shortly before mitosis onset. Here, we describe PLK1 dimerization as a new mechanism that controls PLK1 activation. During the early G2 phase, Bora supports transient PLK1 dimerization, thus fine-tuning the timely regulated activation of PLK1 and modulating its nuclear entry. At late G2, the phosphorylation of T210 by Aurora-A triggers dimer dissociation and generates active PLK1 monomers that support entry into mitosis. Interfering with this critical PLK1 dimer/monomer switch prevents the association of PLK1 with importins, limiting its nuclear shuttling, and causes nuclear PLK1 mislocalization during the G2-M transition. Our results suggest a novel conformational space for the design of a new generation of PLK1 inhibitors.

Polo-like kinase 1 (PLK1) signaling in cancer and beyond

PLK1 is an evolutionary conserved Ser/Thr kinase that is best known for its role in cell cycle regulation and is expressed predominantly during the G2/S and M phase of the cell cycle. PLK1-mediated phosphorylation of specific substrates controls cell entry into mitosis, centrosome maturation, spindle assembly, sister chromatid cohesion and cytokinesis. In addition, a growing body of evidence describes additional roles of PLK1 beyond the cell cycle, more specifically in the DNA damage response, autophagy, apoptosis and cytokine signaling. PLK1 has an indisputable role in cancer as it controls several key transcription factors and promotes cell proliferation, transformation and epithelial-to-mesenchymal transition. Furthermore, deregulation of PLK1 results in chromosome instability and aneuploidy. PLK1 is overexpressed in many cancers, which is associated with poor prognosis, making PLK1 an attractive target for cancer treatment. Additionally, PLK1 is involved in immune and neurological disorders including Graft versus Host Disease, Huntington's disease and Alzheimer's disease. Unfortunately, newly developed small compound PLK1 inhibitors have only had limited success so far, due to low therapeutic response rates and toxicity. In this review we will highlight the current knowledge about the established roles of PLK1 in mitosis regulation and beyond. In addition, we will discuss its tumor promoting but also tumor suppressing capacities, as well as the available PLK1 inhibitors, elaborating on their efficacy and limitations.

FOXM1: A Multifunctional Oncoprotein and Emerging Therapeutic Target in Ovarian Cancer

Forkhead box M1 (FOXM1) is a member of the conserved forkhead box (FOX) transcription factor family. Over the last two decades, FOXM1 has emerged as a multifunctional oncoprotein and a robust biomarker of poor prognosis in many human malignancies. In this review article, we address the current knowledge regarding the mechanisms of regulation and oncogenic functions of FOXM1, particularly in the context of ovarian cancer. FOXM1 and its associated oncogenic transcriptional signature are enriched in >85% of ovarian cancer cases and FOXM1 expression and activity can be enhanced by a plethora of genomic, transcriptional, post-transcriptional, and post-translational mechanisms. As a master transcriptional regulator, FOXM1 promotes critical oncogenic phenotypes in ovarian cancer, including: (1) cell proliferation, (2) invasion and metastasis, (3) chemotherapy resistance, (4) cancer stem cell (CSC) properties, (5) genomic instability, and (6) altered cellular metabolism. We additionally discuss the evidence for FOXM1 as a cancer biomarker, describe the rationale for FOXM1 as a cancer therapeutic target, and provide an overview of therapeutic strategies used to target FOXM1 for cancer treatment.

DNA polymerase β deficiency promotes the occurrence of esophageal precancerous lesions in mice

Esophageal mucosa undergoes mild, moderate, severe dysplasia, and other precancerous lesions and eventually develops into carcinoma in situ, and understanding the developmental progress of esophageal precancerous lesions is beneficial to prevent them from developing into cancer. DNA polymerase β (Polβ), a crucial enzyme of the base excision repair system, plays an important role in repairing damaged DNA and maintaining genomic stability. Abnormal expression or deletion mutation of Polβ is related to the occurrence of esophageal cancer, but the role of Polβ deficiency in the esophageal precancerous lesions is still unclear. Here, esophageal mucosa Polβ-knockout mice were used to explore the relationship of Polβ deficiency with esophageal precancerous lesions. First, we found the degree and number of esophageal precancerous lesions in Polβ-KO mice were more serious than those in Polβ-Loxp mice after N-nitrosomethylbenzylamine (NMBA) treatment. Whole exome sequencing revealed that deletion of Polβ increased the frequency of gene mutations. Gene expression prolife analysis showed that the expression of proteins correlated to cell proliferation and the cell cycle was elevated in Polβ-KO mice. We also found that deletion of Polβ promoted the proliferation and clone formation as well as accelerated cell cycle progression of human immortalized esophageal epithelial cell line SHEE treated with NMBA. Our findings indicate that Polβ knockout promotes the occurrence of esophageal precancerous lesions.

The Prognostic Relevance of the Proliferation Markers Ki-67 and Plk1 in Early-Stage Ovarian Cancer Patients With Serous, Low-Grade Carcinoma Based on mRNA and Protein Expression

Since type and duration of an appropriate adjuvant chemotherapy in early-stage ovarian cancer (OC) are still being debated, novel markers for a better stratification of these patients are of utmost importance for the design of an improved chemotherapeutical strategy. In contrast to numerous cancer studies on cellular proliferation based on the immunohistochemistry-driven evaluation of protein expression, we compared mRNA and protein expression of two independent markers of cellular proliferation, Ki-67 and Plk1, in a large cohort of 243 early-stage OC and their relationship with clinicopathological features and survival. Based on marker expression we demonstrate that early-stage OC patients (stages I/II, low-grade, serous) with high expression (Ki-67, Plk1) had a significantly shorter progression-free survival (PFS) and overall survival (OS) compared to patients with low expression (Ki-67, Plk1). Remarkably, based on mRNA expression this significant difference got lost in advanced stages (III/IV): At least for PFS, high levels of Ki-67 and Plk1 correlate with moderately better survival compared to patients with low expressing tumors. Our data suggest that in addition to Ki-67, Plk1 is a novel marker for the stratification of early-stage OC patients to maximize therapeutic efforts. Both, Ki-67 and Plk1, seem to be better suited in early-stages (I/II) as therapeutical targets compared to advanced-stages (III/IV) OC.

Bioinformatics analysis of gene expression profile of serous ovarian carcinomas to screen key genes and pathways

Background

Serous ovarian carcinomas (SCA) are the most common and most aggressive ovarian carcinoma subtype which etiology remains unclear. To investigate the prospective role of mRNAs in the tumorigenesis and progression of SCA, the aberrantly expressed mRNAs were calculated based on the NCBI-GEO RNA-seq data.

Results

Of 21,755 genes with 89 SCA and SBOT cases from 3 independent laboratories, 59 mRNAs were identified as differentially expressed genes (DEGs) (|log₂Fold Change| > 1.585, also |FoldChange| > 3 and adjusted P < 0.05) by DESeq R. There were 26 up-regulated DEGs and 33 down-regulated DEGs screened. The hierarchical clustering analysis, functional analysis and pathway enrichment analysis were performed on all DEGs and found that Polo-like kinase (PLK) signaling events are important. PPI network constructed with different filtration conditions screened out 4 common hub genes (KIF11, CDC20, PBK and TOP2A). Mutual exclusivity or co-occurrence analysis of 4 hub genes identified a tendency towards co-occurrence between KIF11 and CDC20 or TOP2A in SCA (p < 0.05). To analyze further the potential role of KIF11 in SCA, the co-expression profiles of KIF11 in SCA were identified and we found that CDC20 co-expressed with KIF11 also is DEG that we screened out before. To verify our previous results in this paper, we assessed the expression levels of 4 hub DEGs (all up-regulated) and 4 down-regulated DEGs in Oncomine database. And the results were consistent with previous conclusions obtained from GEO series. The survival curves showed that KIF11, CDC20 and TOP2A expression are significantly related to prognosis of SCA patients.

Conclusions

From all the above results, we speculate that KIF11, CDC20 and TOP2A played an important role in SCA.

Identification of critical genes in gastric cancer to predict prognosis using bioinformatics analysis methods

Background

Ranking fourth in the world in tumor incidence and second in cancer-related death worldwide, gastric cancer (GC) is one of the major malignant tumors, and has a very complicated pathogenesis. In the present study, we aimed to identify new biomarkers to predict the survival rate of GC patients.

Methods

The differentially expressed genes (DEGs) between GC tissues and normal stomach tissues were obtained by using GEO2R, and overlapped DEGs were acquired with Venn diagrams. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were conducted with R software. Then, the protein-protein interaction (PPI) of these DEGs was visualized by Cytoscape. Gene Expression Profiling Interactive Analysis (GEPIA) was used to verify the expression differences of hub genes in gastric adenocarcinoma tissues and normal tissues. Overall survival (OS) of hub genes was calculated by Kaplan-Meier plotter.

Results

There were a total of 128 consistently expressed genes in the two datasets: 85 upregulated genes were enriched in extra-cellular matrix (ECM)-receptor interaction, protein digestion and absorption, focal adhesion, gastric acid secretion, mineral absorption, systemic lupus erythematosus, amoebiasis, and PI3K-Akt signaling pathway, and 43 downregulated genes were enriched in palate development, blood coagulation, positive regulation of transcription from RNA polymerase II promoter, axonogenesis, receptor internalization, negative regulation of transcription from RNA polymerase II promoter, and in no significant signaling pathways. From the PPI network analyzed by Molecular Complex Detection (MCODE) plug-in, all 27 upregulated genes were selected. Furthermore, to analyze the OS among these genes, Kaplan-Meier analysis was conducted, and 25 genes were associated with remarkably worse survival. For validation in GEPIA, 11 of 25 genes were discovered to be highly expressed in GC tissues compared to normal OS tissues. Furthermore, in the re-analysis of the Database for Annotation, Visualization and Integrated Discovery (DAVID), three genes [G2/miotic-specific cyclin B1 (CCNB1), polo-like kinases 1 (PLK1), and pituitary tumor-transforming gene-1 (PTTG1)] were markedly enriched in the cell cycle pathway, particulary the G1-G1/S phase.

Conclusions

Three remarkably upregulated DEGs with poor prognosis in GC were identified and may serve as new prognostic biomarkers and targets in GC therapy.

YLZ-F5, a novel polo-like kinase 4 inhibitor, inhibits human ovarian cancer cell growth by inducing apoptosis and mitotic defects

PURPOSE

Polo-like kinase 4 (PLK4), a member of the polo-like kinase family, plays several important roles in mitotic regulation, including centrosome duplication, spindle formation, and cytokinesis. PLK4 overexpression is frequently detected in many human cancers, including ovarian cancer, and the inhibition of PLK4 activity results in cancer cell mitotic arrest and apoptosis. Therefore, PLK4 might be a valid therapeutic target for antitumor therapy. In the present study, we aimed to determine if YLZ-F5, a potent small-molecule inhibitor of PLK4, inhibits ovarian cancer cell growth.

METHODS AND RESULTS

MTT assay showed that YLZ-F5 inhibited ovarian cancer cell proliferation in a concentration- and time-dependent manner. The results of colony formation assays were consistent with those of the MTT assay results. In addition, YLZ-F5 induced ovarian cancer cell apoptosis that was associated with activation of caspase-3/caspase-9. Moreover, YLZ-F5 caused aberrant in centriole duplication that was associated with the inhibition of PLK4 phosphorylation. Notably, we showed that YLZ-F5 promoted the accumulation of ovarian cancer cells with mitotic defects (> 4 N DNA content) in a concentration-dependent manner. Furthermore, YLZ-F5 markedly inhibited the migration of A2780 cells.

CONCLUSION

Taken together, these findings suggest that YLZ-F5 is a potential drug candidate for human ovarian cancer.

Polo-like kinase 1 as a promising diagnostic biomarker and potential therapeutic target for hepatocellular carcinoma

Hepatocellular carcinoma is a major cause of cancer mortality worldwide. The outcome of hepatocellular carcinoma depends mainly on its early diagnosis. To date, the performance of traditional biomarkers is unsatisfactory. Polo-like kinase 1 is a serine/threonine kinase that plays essential roles in cell cycle progression and deoxyribonucleic acid damage. Moreover, polo-like kinase 1 knockdown decreases the survival of hepatocellular carcinoma cells; therefore, polo-like kinase 1 is an attractive target for anticancer treatments. Nobiletin, a natural polymethoxy flavonoid, exhibits a potential antiproliferative effect against a wide variety of cancers. This study targets to identify a reliable diagnostic biomarker for hepatocellular carcinoma and provide a potential therapeutic target for its treatment. Polo-like kinase 1 levels were analyzed in 44 hepatocellular carcinoma patients, 33 non-hepatocellular carcinoma liver cirrhosis patients and 15 healthy controls using the enzyme-linked immunosorbent assay method. Receiver operating characteristics curve analysis was used to establish a predictive model for polo-like kinase 1 relative to α-fetoprotein in hepatocellular carcinoma diagnosis. Furthermore, in the in vitro study, gene expressions were assessed by quantitative polymerase chain reaction in two human hepatocellular carcinoma cell lines after treatment with doxorubicin and polo-like kinase 1 inhibitor volasertib (Vola) either alone or in combination with nobiletin. Cell viability was also determined using the crystal violet assay.: Serum polo-like kinase 1 levels in hepatocellular carcinoma patients were significantly higher than liver cirrhosis and control groups (p < 0.0001). Polo-like kinase 1 showed a reasonable sensitivity, specificity, positive predictive value, and negative predictive value in hepatocellular carcinoma diagnosis. Moreover, nobiletin improved inhibition of cell growth induced by Vola and doxorubicin. Regarding reverse transcription polymerase chain reaction results, nobiletin suppressed expressions of polo-like kinase 1 and proliferating cell nuclear antigen and elevated expressions of P53, poly (ADPribose) polymerase 1, and caspase-3. Nobiletin/doxorubicin and nobiletin/Vola showed a significant increase in caspase-3 activity indicating cell apoptosis. Polo-like kinase 1 may be a potential biomarker for hepatocellular carcinoma diagnosis and follow-up during treatment with chemotherapies. In addition, nobiletin synergistically potentiates the doxorubicin and Vola-mediated anticancer effect that may be attributed partly to suppression of polo-like kinase 1 and proliferating cell nuclear antigen expression and enhancement of chemotherapy-induced apoptosis.

Identification of PLK1 as a New Therapeutic Target in Mucinous Ovarian Carcinoma

Mucinous epithelial ovarian cancer (mEOC) is a rare subset of epithelial ovarian cancer. When diagnosed at a late stage, its prognosis is very poor, as it is quite chemo-resistant. To find new therapeutic options for mEOC, we performed high-throughput screening using a siRNA library directed against human protein kinases in a mEOC cell line, and polo-like kinase1 (PLK1) was identified as the kinase whose downregulation interfered with cell proliferation. Both PLK1 siRNA and two specific PLK1 inhibitors (onvansertib and volasertib) were able to inhibit cell growth, induce apoptosis and block cells in the G2/M phase of the cell cycle. We evaluated, in vitro, the combinations of PLK1 inhibitors and different chemotherapeutic drugs currently used in the treatment of mEOC, and we observed a synergistic effect of PLK1 inhibitors and antimitotic drugs. When translated into an in vivo xenograft model, the combination of onvansertib and paclitaxel resulted in stronger tumor regressions and in a longer mice survival than the single treatments. These effects were associated with a higher induction of mitotic block and induction of apoptosis, similarly to what was observed in vitro. These data suggest that the combination onvansertib/paclitaxel could represent a new active therapeutic option in mEOC.

Inhibition of PLK1 by capped-dose volasertib exerts substantial efficacy in MDS and sAML while sparing healthy haematopoiesis

INTRODUCTION

Targeting the cell cycle machinery represents a rational therapeutic approach in myelodysplastic syndromes (MDS) and secondary acute myeloid leukemia (sAML). Despite substantial response rates, clinical use of the PLK inhibitor volasertib has been hampered by elevated side effects such as neutropenia and infections.

OBJECTIVES

The primary objective was to analyse whether a reduced dose of volasertib was able to limit toxic effects on the healthy haematopoiesis while retaining its therapeutic effect.

METHODS

Bone marrow mononuclear cells (BMMNCs) of patients with MDS/sAML (n = 73) and healthy controls (n = 28) were treated with volasertib (1 μM to 1 nM) or vehicle control. Short-term viability analysis was performed by flow cytometry after 72 hours. For long-term viability analysis, colony-forming capacity was assessed after 14 days. Protein expression of RIPK3 and MCL-1 was quantified via flow cytometry.

RESULTS

Reduced dose levels of volasertib retained high cell death-inducing efficacy in primary human stem and progenitor cells of MDS/sAML patients without affecting healthy haematopoiesis in vitro. Interestingly, volasertib reduced colony-forming capacity and cell survival independent of clinical stage or mutational status.

CONCLUSIONS

Volasertib offers a promising therapeutic approach in patients with adverse prognostic profile. RIPK3 and MCL-1 might be potential biomarkers for sensitivity to volasertib treatment.

Evaluation of core serous epithelial ovarian cancer genes as potential prognostic markers and indicators of the underlying molecular mechanisms using an integrated bioinformatics analysis

Ovarian cancer is a major cause of mortality in women. However, the molecular events underlying the pathogenesis of the disease are yet to be fully elucidated. In the present study, an integrated bioinformatics analysis was performed to identify core genes involved in serous epithelial ovarian cancer. A total of three expression datasets were downloaded from the Gene Expression Omnibus database, and included 46 serous epithelial ovarian cancer and 30 ovarian surface epithelium samples. The three datasets were merged, and batch normalization was performed. The normalized merged data were subsequently analyzed for differentially expressed genes (DEGs). In total, 2,212 DEGs were identified, including 1,300 upregulated and 912 downregulated genes. Gene Ontology analysis revealed that these DEGs were primarily involved in ‘regulation of cell cycle’, ‘mitosis’, ‘DNA packaging’ and ‘nucleosome assembly’. The main cellular components included ‘extracellular region part’, ‘chromosome’, ‘extracellular matrix’ and ‘condensed chromosome kinetochore’, whereas the molecular functions included ‘Calcium ion binding’, ‘polysaccharide binding’, ‘enzyme inhibitor activity’, ‘growth factor activity’, ‘cyclin-dependent protein kinase regulator activity’, ‘microtubule motor activity’ and ‘Wnt receptor activity’. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that these DEGs were predominantly involved in ‘Wnt signaling pathway’, ‘pathways in cancer’, ‘PI3K-Akt signaling pathway’, ‘cell cycle’, ‘ECM-receptor interaction’, ‘p53 signaling pathway’ and ‘focal adhesion’. The 20 most significant DEGs were identified from the protein-protein interaction network, and Oncomine analysis of these core genes revealed that 13 were upregulated and two were downregulated in serous epithelial ovarian cancer. Survival analysis revealed that cyclin B1, polo like kinase 1, G protein subunit γ transducin 1 and G protein subunit γ 12 are key molecules that may be involved in the prognosis of serous epithelial ovarian cancer. These core genes may provide novel treatment targets, although their roles in the carcinogenesis and prognosis of serous epithelial ovarian cancer require further study.

The role of polo-like kinase 3 in the response of BRAF-mutant cells to targeted anticancer therapies

The activation of oncogenic mitogen-activated protein kinase cascade via mutations in BRAF is often observed in human melanomas. Targeted inhibitors of BRAF (BRAFi), alone or as a part of a combination therapy, offer a significant benefit to such patients. Unfortunately, some cases are initially nonresponsive to these drugs, while others become refractory in the course of treatment, underscoring the need to understand and mitigate the underlying resistance mechanisms. We report that interference with polo-like kinase 3 (PLK3) reduces the tolerance of BRAF-mutant melanoma cells to BRAFi, while increased PLK3 expression has the opposite effect. Accordingly, PLK3 expression correlates with tolerance to BRAFi in a panel of BRAF-mutant cell lines and is elevated in a subset of recurring BRAFi-resistant melanomas. In PLK3-expressing cells, R406, a kinase inhibitor whose targets include PLK3, recapitulates the sensitizing effects of genetic PLK3 inhibitors. The findings support a role for PLK3 as a predictor of BRAFi efficacy and suggest suppression of PLK3 as a way to improve the efficacy of targeted therapy.

Therapeutic potential of PLK1 inhibition in triple-negative breast cancer

Triple negative breast cancer (TNBC) is responsible for significant number of breast cancer-associated deaths because of lacking of successful molecular-targeted therapy. To explore a therapeutic target for TNBC, we performed a siRNA-mediated knockdown screening and identified Polo-like kinase 1 (PLK1) as a potential therapeutic target for TNBC. Knockdown of PLK1 as well as a small compound inhibitor for PLK1, BI-2536, induced G2/M arrest and created polyploid cell population, shown by increased DNA content and nuclear size. Inhibition of PLK1 eventually triggered apoptosis in multiple TNBC cell lines. In addition, we confirmed that PLK1 was significantly overexpressed in the tissues from TNBC patients compared with the tissues of normal mammary glands and benign breast tumors. Our data indicated that PLK1 plays a pivotal role in the regulation of mitosis of TNBC cells. Although future in vivo studies are warranted, targeting PLK1 by a selective inhibitor such as BI-2536 can be an attractive molecular-targeted therapy for TNBC.

Association of Polo-Like Kinase 3 and PhosphoT273 Caspase 8 Levels With Disease-Related Outcomes Among Cervical Squamous Cell Carcinoma Patients Treated With Chemoradiation and Brachytherapy

Introduction: Definitive chemoradiation (CRT) followed by high-dose-rate (HDR) brachytherapy (BT) represents state-of-the-art treatment for locally-advanced cervical cancer. Despite use of this treatment paradigm, disease-related outcomes have stagnated in recent years, indicating the need for biomarker development and improved patient stratification. Here, we report the association of Polo-like kinase (PLK) 3 expression and Caspase 8 T273 phosphorylation levels with survival among patients with cervical squamous cell carcinoma (CSCC) treated with CRT plus BT.

Methods: We identified 74 patients with FIGO Stage Ib to IVb cervix squamous cell carcinoma. Baseline immunohistochemical scoring of PLK3 and pT273 Caspase 8 levels was performed on pre-treatment samples. Correlation was then assessed between marker expression and clinical endpoints, including cumulative incidences of local and distant failure, cancer-specific survival (CSS) and overall survival (OS). Data were then validated using The Cancer Genome Atlas (TCGA) dataset.

Results: PLK3 expression levels were associated with pT273 Caspase 8 levels (p = 0.009), as well as N stage (p = 0.046), M stage (p = 0.026), and FIGO stage (p = 0.001). By the same token, pT273 Caspase 8 levels were associated with T stage (p = 0.031). Increased PLK3 levels corresponded to a lower risk of distant relapse (p = 0.009), improved CSS (p = 0.001), and OS (p = 0.003). Phospho T273 Caspase 8 similarly corresponded to decreased risk of distant failure (p = 0.021), and increased CSS (p < 0.001) and OS (p < 0.001) and remained a significant predictor for OS on multivariate analysis. TCGA data confirmed the association of low PLK3 expression with resistance to radiotherapy and BT (p < 0.05), as well as increased propensity for metastasis (p = 0.019). Finally, a combined PLK3 and pT273 Caspase 8 score predicted for decreased distant relapse (p = 0.005), and both improved CSS (p < 0.001) and OS (p < 0.001); this combined score independently predicted distant failure (p = 0.041) and CSS (p = 0.003) on multivariate analyses.

Conclusion: Increased pre-treatment tumor levels of PLK3 and pT273 Caspase 8 correspond to improved disease-related outcomes among cervical cancer patients treated with CRT plus BT, representing a potential biomarker in this context.

Blocking Mitotic Exit of Ovarian Cancer Cells by Pharmaceutical Inhibition of the Anaphase-Promoting Complex Reduces Chromosomal Instability

Paclitaxel is a frontline drug for the treatment of epithelial ovarian cancer (EOC). However, following paclitaxel-platinum based chemotherapy, tumor recurrence occurs in most ovarian cancer patients. Chromosomal instability (CIN) is a hallmark of cancer and represents genetic variation fueling tumor adaptation to cytotoxic effects of anticancer drugs. In this study, our Kaplan-Meier analysis including 263 ovarian cancer patients (stages I/II) revealed that high Polo-like kinase (PLK) 1 expression correlates with bad prognosis. To evaluate the role of PLK1 as potential cancer target within a combinatorial trial, we induced strong mitotic arrest in ovarian cancer cell lines by synergistically co-targeting microtubules (paclitaxel) and PLK1 (BI6727) followed by pharmaceutical inhibition of the Anaphase-Promoting Complex (APC/C) using proTAME. In short- and long-term experiments, this triple treatment strongly activated apoptosis in cell lines and primary ovarian cells derived from cancer patients. Mechanistically, BI6727/paclitaxel/proTAME stabilize Cyclin B1 and trigger mitotic arrest, which initiates mitochondrial apoptosis by inactivation of antiapoptotic BCL-2 family proteins, followed by activation of caspase-dependent effector pathways. This triple treatment prevented endoreduplication and reduced CIN, two mechanisms that are associated with aggressive tumors and the acquisition of drug resistance. This "two-punch strategy" (strong mitotic arrest followed by blocking mitotic exit) has important implications for developing paclitaxel-based combinatorial treatments in ovarian cancer.

The Mitotic Cancer Target Polo-Like Kinase 1: Oncogene or Tumor Suppressor?

The master mitotic regulator, Polo-like kinase 1 (Plk1), is an essential gene for the correct execution of cell division. Plk1 has strong clinical relevance, as it is considered a bona fide cancer target, it is found overexpressed in a large collection of different cancer types and this tumoral overexpression often correlates with poor patient prognosis. All these data led the scientific community to historically consider Plk1 as an oncogene. Although there is a collection of scientific reports showing how Plk1 can contribute to tumor progression, recent data from different laboratories using mouse models, show that Plk1 can surprisingly play as a tumor suppressor. Therefore, the fact that Plk1 is an oncogene is now under debate. This review summarizes the proposed mechanisms by which Plk1 can play as an oncogene or as a tumor suppressor, and extrapolates this information to clinical features.

Polo-like kinase 3 is associated with poor prognosis and regulates proliferation and metastasis in prostate cancer

Background

Biological mechanism of prostate cancer (PCa) recurrence and progress is complex but many of the key elements are not fully understood. Polo-like kinases (Plks) represent a family of highly conserved serine–threonine kinases that play essential roles in cell cycle progression. Plk3 plays contradictory roles in different cancers. However, the roles of Plk3 in PCa remain largely unexplored.

Methods

Kaplan–Meier analysis and Cox regression analysis were performed to evaluate the relationship between Plk3 and prognosis of patients with PCa. Gene set enrichment analysis (GSEA) was conducted to evaluate proliferation and metastasis gene sets using The Cancer Genome Atlas Dataset. MTS assay, clone formation assay, cell migration, and wound healing assay were carried out to investigate biological functions of Plk3.

Results

We found that high Plk3 expression was closely correlated with poor prognosis. GSEA revealed that Plk3 was involved in proliferation and metastasis. Loss-of-function assays demonstrated that Plk3 promoted proliferation and metastasis in PCa cells in vitro.

Conclusion

We discovered that Plk3 plays a critical role in PCa, indicating that it may be a potential prognostic marker and help predict the progression, especially recurrence of PCa.

Impact of iASPP on chemoresistance through PLK1 and autophagy in ovarian clear cell carcinoma

Ovarian clear cell carcinoma (OCCC) is a type of epithelial ovarian cancer that is strongly associated with endometriosis, resistance against conventional chemotherapy and thus poorer prognosis. The expression of inhibitory member of the ASPP family proteins (iASPP) and Polo-like kinase (PLK)1 were significantly higher in OCCC compared to benign cystadenomas and endometriosis. Both protein expressions were found to correlate with chemoresistance in patients with OCCC while high iASPP expression alone was significantly associated with a poor patient survival. The growth of OCCC cell lines, OVTOKO and KK, were inhibited after iASPP silencing. Such effect was related to senescence triggering as evidenced by increased SA-β-Gal staining and p21WAF1/Cip1 expression. Moreover, knockdown of iASPP induced PLK1 downregulation, whereas either genes' silencing sensitized the cells in response to cisplatin treatment. More prominent apoptosis was induced by cisplatin in OCCC cells after the knockdown of either iASPP or PLK1 as evidenced by the formation of more cleaved caspase 3. Heightened chemosensitivity to cisplatin after iASPP knockdown was further demonstrated in in vivo xenograft model. Additionally, both iASPP and PLK1 were shown to regulate autophagic flux as the induction of LC3B-II and LC3 puncta were much less in OCCC cells with either knockdown. Importantly, inhibition of autophagy also enhanced chemosensitivity to cisplatin in OCCC cells. These findings strongly imply that iASPP and PLK1 affect the chemoresistance of OCCC via the regulation of autophagy and apoptosis. Both iASPP and PLK1 can be potential therapeutic targets for treating OCCC in combination with conventional chemotherapy.

MECHANISMS OF ENDOCRINOLOGY: Cell cycle regulation in adrenocortical carcinoma

Adrenocortical carcinomas (ACCs) are rather rare endocrine tumors that often have a poor prognosis. The reduced survival rate associated with these tumors is due to their aggressive biological behavior, combined with the scarcity of effective treatment options that are currently available. The recent identification of the genomic alterations present in ACC have provided further molecular mechanisms to develop consistent strategies for the diagnosis, prevention of progression and treatment of advanced ACCs. Taken together, molecular and genomic advances could be leading the way to develop personalized medicine in ACCs similarly to similar developments in lung or breast cancers. In this review, we focused our attention to systematically compile and summarize the alterations in the cell cycle regulation that were described so far in ACC as they are known to play a crucial role in cell differentiation and growth. We have divided the analysis according to the major transition phases of the cell cycle, G1 to S and G2 to M. We have analyzed the most extensively studied checkpoints: the p53/Rb1 pathway, CDC2/cyclin B and topoisomerases (TOPs). We reached the conclusion that the most important alterations having a potential application in clinical practice are the ones related to p53/Rb1 and TOP 2. We also present a brief description of on-going clinical trials based on molecular alterations in ACC. The drugs have targeted the insulin-like growth factor receptor 1, TOP 2, polo-like kinase1, cyclin-dependent kinase inhibitors, p53 reactivation and CDC25.

Synthetic lethality in CCNE1-amplified high grade serous ovarian cancer through combined inhibition of Polo-like kinase 1 and microtubule dynamics

The taxanes are effective microtubule-stabilizing chemotherapy drugs that inhibit mitosis, induce apoptosis, and produce regression in a fraction of cancers that arise at many sites including the ovary. Novel therapeutic targets that augment taxane effects are needed to improve clinical chemotherapy response in CCNE1-amplified high grade serous ovarian cancer (HGSOC) cells. In this study, we conducted an siRNA-based kinome screen to identify modulators of mitotic progression in CCNE1-amplified HGSOC cells that may influence clinical paclitaxel response. PLK1 is overexpressed in many types of cancer, which correlates with poor prognosis. Here, we identified a novel synthetic lethal interaction of the clinical PLK1 inhibitor BI6727 and the microtubule-targeting drug paclitaxel in HGSOC cell lines with CCNE1-amplification and elucidated the underlying molecular mechanisms of this synergism. BI6727 synergistically induces apoptosis together with paclitaxel in different cell lines including a patient-derived primary ovarian cancer culture. Moreover, the inhibition of PLK1 reduced the paclitaxel-induced neurotoxicity in a neurite outgrowth assay. Mechanistically, the combinatorial treatment with BI6727/paclitaxel triggers mitotic arrest, which initiates mitochondrial apoptosis by inactivation of anti-apoptotic BCL-2 family proteins, followed by significant loss of the mitochondrial membrane potential and activation of caspase-dependent effector pathways. This conclusion is supported by data showing that BI6727/paclitaxel-co-treatment stabilizes FBW7, a component of SCF-type ubiquitin ligases that bind and regulate key modulators of cell division and growth including MCL-1 and Cyclin E. This identification of a novel synthetic lethality of PLK1 inhibitors and a microtubule-stabilizing drug has important implications for developing PLK1 inhibitor-based combination treatments in CCNE1-amplified HGSOC cells.

Combination of PI3K/Akt Pathway Inhibition and Plk1 Depletion Can Enhance Chemosensitivity to Gemcitabine in Pancreatic Carcinoma

The prognosis of pancreatic cancer (PC) remains pessimistic because of the difficulty in early diagnosis as well as the little advance in chemotherapy. Although being the first-line chemotherapy drug for PC at present, gemcitabine still has some disadvantages, such as low drug sensitivity and significant side effects. Thus, how to further improve the sensitivity of PC cells to gemcitabine is still a difficult subject in the field of pancreatic cancer-treatment. Polo-like kinase 1 (Plk1) is closely related to poor outcome in many malignant tumors and its high expression is linked to chemoresistance in PC. As a downstream gene activated by PI3K/Akt signal pathway, we assumed that the targeted depletion of Plk1 could contribute to the chemosensitization induced by synergistic drug interaction of PI3K inhibitor LY294002 together with gemcitabine. To analyze effect of Plk1 in chemotherapy, we constructed two recombinant adenoviral vectors which carry enhanced green fluorescent protein (rAd-EGFP) and Plk1-shRNA (rAd-shPlk1), respectively. Both inhibition of PI3K/Akt signal pathway through PI3K inhibitor LY294002 and targeted depletion of Plk1 via recombinant adenoviral shRNA can cause chemosensitization, and the targeted depletion of Plk1 can enhance the chemosensitization of LY294002. Thus, the gene therapy like targeted depletion of Plk1 may create new perspectives for chemosensitization of PC.

Plk2 Loss Commonly Occurs in Colorectal Carcinomas but not Adenomas: Relationship to mTOR Signaling

Plk2 is a target of p53. Our previous studies demonstrated that with wild-type p53, Plk2 impacts mTOR signaling in the same manner as TSC1, and Plk2-deficient tumors grew larger than control. Other investigators have demonstrated that Plk2 phosphorylates mutant p53 in a positive feedback loop. We investigated Plk2’s tumor suppressor functions in relationship to mTOR signaling. Archival specimens from 12 colorectal adenocarcinomas were stained for markers including Plk2, phosphorylated mTOR (serine 2448) and ribosomal S6 (Serine 235/236). We show that Plk2 is expressed in normal colon, with a punctate staining pattern in supranuclear cytoplasm. In colorectal adenocarcinoma, Plk2 demonstrates complete or partial loss of expression. Strong expression of phosphorylated mTOR is observed in the invasive front. Phosphorylated S6 expression partially correlates with phosphorylated mTOR expression but appears more diffuse in some cases. p53 and Ki67 expression is diffuse, in the subset of cases examined. In order to determine whether Plk2 is lost prior to the development of invasive cancer, 8 colon polyps from 6 patients were evaluated for Plk2 expression. All polyps are positive for Plk2. A Cancer Genome Atlas search identified Plk2 mutations to be infrequent in colorectal adenocarcinomas. Neither Plk2 methylation (in the gene body) nor copy number variations correlated with changes in mRNA expression levels. Loss of Plk2 expression along with accentuated expression of phosphorylated mTOR and phosphorylated S6 at the invasive front in some colorectal carcinomas is consistent with previous findings that an interaction between Plk2 and TSC1 / mTOR signaling molecules plays a role in tumor suppression. Plk2 protein expression is lost at the same stage in colorectal carcinogenesis as p53. The p53 dependence of Plk2 loss and tumor suppressor function in relationship to mTOR signaling may have therapeutic implications.

Phase I dose escalation study of NMS-1286937, an orally available Polo-Like Kinase 1 inhibitor, in patients with advanced or metastatic solid tumors

Background Pharmacological inhibition of polo-like kinase 1 (PLK1) represents a new approach for the treatment of solid tumors. This study was aimed at determining the first cycle dose-limiting toxicities (DLTs) and related maximum tolerated dose (MTD) of NMS-1286937, a selective ATP-competitive PLK1-specific inhibitor. Secondary objectives included evaluation of its safety and pharmacokinetic (PK) profile in plasma, its antitumor activity, and its ability to modulate intracellular targets in biopsied tissue. Methods This was a Phase I, open-label, dose-escalation trial in patients with advanced/metastatic solid tumors. A treatment cycle comprised 5 days of oral administration followed by 16 days of rest, for a total of 21 days (3-week cycle). Results Nineteen of 21 enrolled patients with confirmed metastatic disease received study medication. No DLTs occurred at the first 3 dose levels (6, 12, and 24 mg/m2/day). At the subsequent dose level (48 mg/m2/day), 2 of 3 patients developed DLTs. An intermediate level of 36 mg/m2/day was therefore investigated. Four patients were treated and two DLTs were observed. After further cohort expansion, the MTD and recommended phase II dose (RP2D) were determined to be 24 mg/m2/day. Disease stabilization, observed in several patients, was the best treatment response observed. Hematological toxicity (mostly thrombocytopenia and neutropenia) was the major DLT. Systemic exposure to NMS-1286937 increased with dose and was comparable between two cycles of treatment following oral administration of the drug. Conclusions This study successfully identified the MTD and DLTs for NMS-1286937 and characterized its safety profile.

Polo-like kinase 3 and phosphoT273 caspase-8 are associated with improved local tumor control and survival in patients with anal carcinoma treated with concomitant chemoradiotherapy

We have recently shown that caspase-8 is a new substrate of Polo-like kinase 3 (Plk3) that phosphorylates the protein on residue T273 thereby promoting its pro-apoptotic function. In the present study we aimed to investigate the clinical relevance of Plk3 expression and phosphorylation of caspase-8 at T273 in patients with anal squamous cell carcinoma (SSC) treated with 5-fluorouracil and mitomycin C-based chemoradiotherapy (CRT). Immunohistochemical detection of the markers was performed in pretreatment biopsy specimens of 95 patients and was correlated with clinical/histopathologic characteristics including HPV-16 virus load/p16^INK4a expression and cumulative incidence of local and distant failure, cancer specific survival (CSS), and overall survival (OS). We observed significant positive correlations between Plk3 expression, pT273 caspase-8 signal, and levels of HPV-16 virus DNA load/p16^INK4a detection. Patients with high scores of Plk3 and pT273 caspase-8 showed increased local control (p = 0.011; p = 0.001), increased CSS (p = 0.011; p = 0.013) and OS (p = 0.024; p = 0.001), while the levels of pT273 caspase-8 were significantly associated (p = 0.033) with distant metastases. In multivariate analyses Plk3 expression remained significant for local failure (p = 0.018), CSS (p = 0.016) and OS (p = 0.023). Moreover, a combined HPV16 DNA load and Plk3 or pT273 caspase-8 variable revealed a significant correlation to decreased local failure (p = 0.001; p = 0.009), increased CSS (p = 0.016; p = 0.023) and OS (p = 0.003; p = 0.003). In conclusion these data indicate that elevated levels of Plk3 and pT273 caspase-8 are correlated with favorable clinical outcome in patients with anal SCC treated with concomitant CRT.

TPX2 promotes cell proliferation and migration via PLK1 in OC

BACKGROUND

Targeting protein for Xenopus kinesin-like protein 2 (TPX2) is a microtubule-associated proteinrequired for mitosis and spindle assembly. It has been revealed that TPX2 is overexpressedin various human cancers and promotes cancer progression.

METHODS

The expression of TPX2 was examined in ovarian cancer (OC) tissues and by Western blotting, quantitative real-time reverse transcription PCR (qRT-PCR) and immunohistochemistry. The effects of TPX2 on proliferation and migration of two OC cell lines SKOV3and RMG1 were analyzed using the methylthiazol tetrazolium (MTT) assay, flow cytometry and transwell assay. The mechanisms underlying the effects of TPX2 on OC cells were explored by qRT-PCR and Western blot.

RESULTS

In this study, we found that TPX2 was upregulated in OC tissues. We observed knockdown of TPX2 inhibited the expression of Polo-like kinase 1 (PLK1), which has an important role in the regulation of M phase of the cell cycle, and the activity of Cdc2, induced cell arrested at the G2/M phase and decreased proliferation. Moreover, our data revealed that the levels of PLK1, β-catenin, MMP7 and MMP9 were inhibited following TPX2 knockdown, leading to decrease of cell migration. Finally, we showed that the restoration of PLK1 expression attenuated the anti-proliferation and anti-migration effects of TPX2 knockdown in OC cells.

CONCLUSIONS

TPX2 promotes the proliferation and migration of human OC cells by regulating PLK1 expression.

The Emerging Role of Polo-Like Kinase 1 in Epithelial-Mesenchymal Transition and Tumor Metastasis

Polo-like kinase 1 (PLK1) is a serine/threonine kinase that plays a key role in the regulation of the cell cycle. PLK1 is overexpressed in a variety of human tumors, and its expression level often correlates with increased cellular proliferation and poor prognosis in cancer patients. It has been suggested that PLK1 controls cancer development through multiple mechanisms that include canonical regulation of mitosis and cytokinesis, modulation of DNA replication, and cell survival. However, emerging evidence suggests novel and previously unanticipated roles for PLK1 during tumor development. In this review, we will summarize the recent advancements in our understanding of the oncogenic functions of PLK1, with a focus on its role in epithelial-mesenchymal transition and tumor invasion. We will further discuss the therapeutic potential of these functions.

The clinical and prognostic value of polo-like kinase 1 in lung squamous cell carcinoma patients: immunohistochemical analysis

Polo-like kinase 1 (PLK1) has been suggested to serve as an oncogene in most human cancers. The aim of our study is to present more evidence about the clinical and prognostic value of PLK1 in lung squamous cell carcinoma patients. The status of PLK1 was observed in lung adenocarcinoma, lung squamous cell carcinoma, and normal lung tissues through analyzing microarray dataset (GEO accession numbers: GSE1213 and GSE 3627). PLK1 mRNA and protein expressions were detected in lung squamous cell carcinoma and normal lung tissues by using quantitative real-time PCR (qRT-PCR) and immunohistochemistry. In our results, the levels of PLK1 in lung squamous cell carcinoma tissues were higher than that in lung adenocarcinoma tissues. Compared with paired adjacent normal lung tissues, the PLK1 expression was increased in lung squamous cell carcinoma tissues. Furthermore, high expression of PLK1 protein was correlated with differentiated degree, clinical stage, tumor size, lymph node metastasis, and distant metastasis. The univariate and multivariate analyses showed PLK1 protein high expression was an unfavorable prognostic biomarker for lung squamous cell carcinoma patients. In conclusion, high expression of PLK1 is associated with the aggressive progression and poor prognosis in lung squamous cell carcinoma patients.

Mutual regulation between Polo-like kinase 3 and SIAH2 E3 ubiquitin ligase defines a regulatory network that fine-tunes the cellular response to hypoxia and nickel

Elevated cellular response to hypoxia, which contributes to cell transformation and tumor progression, is a prominent feature of malignant cells in solid tumors. Polo-like kinase 3 (Plk3) is a serine/threonine protein kinase known to inhibit the cellular response to hypoxia and tumorigenesis. Nickel compounds are well-established human carcinogens that induce tumorigenesis partly through their hypoxia-mimicking effects. Despite previous research efforts, the role of Plk3 in the hypoxic response induced by hypoxia or nickel is not completely understood. Here, we show that NiCl₂ (Ni(II)) or hypoxia reduces the protein level and shortens the half-life of cytoplasmic Plk3 in a ubiquitin-proteasome-dependent manner. We identify SIAH2, a RING finger E3 ubiquitin ligase associated with the cellular hypoxic response, to be the ubiquitin E3 ligase that mediates the degradation of Plk3. We show that SIAH2 binds to Plk3 and mediates its ubiquitination primarily through its polo-box domain. We report that USP28, a deubiquitinase known to be inhibitable by Ni(II) or hypoxia, may also contribute to the suppression of the Plk3 protein by Ni(II). We also show that Plk3 in turn suppresses the SIAH2 protein level in a kinase activity-dependent manner. Our study revealed an interesting mutual regulation between Plk3 and SIAH2 and uncovered a regulatory network that functions to fine-tune the cellular hypoxic response. We propose that suppression of Plk3 expression contributes to carcinogenesis and tumor progression induced by nickel compounds.