PLK1 as a potential prognostic marker of gastric cancer through MEK-ERK pathway on PDTX models

Telocinobufagin, a PLK1 suppressor that inhibits tumor growth and metastasis by modulating CDC25c and CTCF in HNSCC cells

BACKGROUND

The high metastasis and mortality rates of head and neck squamous cell carcinoma (HNSCC) urgently require new treatment targets and drugs. A steroidal component of ChanSu, telocinobufagin (TBG), was verified to have anti-cancer effects in various tumors, but its activity and mechanism in anti-HNSCC were still unknown.

PURPOSE

This study tried to demonstrate the anti-tumor effect of TBG on HNSCC and verify its potential mechanism.

METHODS

The effect of TBG on cell proliferation and metastasis were performed and the TBG changed genes were detected by RNA-seq analysis in HNSCC cells. The GSEA and PPI analysis were used to identify the pathways targeted for TBG-regulated genes. Meanwhile, the mechanism of TBG on anti-proliferative and anti-metastasis were investigated in vitro and in vivo.

RESULTS

The in vitro and in vivo experiments confirmed that TBG has favorable anti-tumor effects by induced G2/M phase arrest and suppressed metastasis in HNSCC cells. Further RNA-seq analysis demonstrated the genes regulated by TBG were enriched at the G2/M checkpoint and PLK1 signaling pathway. Then, the bioinformatic analysis of clinical data found that high expressed PLK1 were closely associated with poor overall survival in HNSCC patients. Furthermore, PLK1 directly and indirectly modulated G2/M phase and metastasis (by regulated CTCF) in HNSCC cells, simultaneously. TBG significantly inhibited the protein levels of PLK1 in both phosphorylated and non-phosphorylated forms and then, in one way, inactivated PLK1 failed to activate G2/M phase-related proteins (including CDK1, CDC25c, and cyclin B1). In another way, be inhibited PLK1 unable promote the nuclear translocation of CTCF and thus suppressed HNSC cell metastasis. In contrast, the anti-proliferative and anti-metastasis effects of TBG on HNSCC cell were vanished when cells high-expressed PLK1.

CONCLUSION

The present study verified that PLK1 mediated TBG induced anti-tumor effect by modulated G2/M phase and metastasis in HNSCC cells.

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.

Onvansertib inhibits the proliferation and improves the cisplatin-resistance of lung adenocarcinoma via β-catenin/c-Myc signaling pathway

Polo-like kinase 1 (PLK1) is a key regulator of cell division, and its abnormal expression is related to the progression and prognosis of cancers. However, the effect of PLK1 inhibitor onvansertib on the growth of lung adenocarcinoma (LUAD) has not been explored. In this study, we performed a series of bioinformatics and experimental analyses to comprehensively investigate the role of PLK1 in LUAD. We used CCK-8 assay and colony formation assay to evaluate the growth inhibitory ability of onvansertib. Furthermore, flow cytometry was applied to exploit the effects of onvansertib on cell cycle, apoptosis, and mitochondrial membrane potential. Moreover, the therapeutic potential of onvansertib was assessed in vivo by using xenograft tumor and patient-derived xenograft (PDX) models. We found that onvansertib significantly induced the apoptosis and inhibited the proliferation and migration of LUAD cells. Mechanistically, onvansertib arrested the cells at G2/M phase and enhanced the levels of reactive oxidative species in LUAD. Accordingly, onvansertib regulated the expression of glycolysis-related genes and improved the cisplatin resistance in LUAD. Notably, the protein levels of β-catenin and c-Myc were affected by onvansertib. Taken together, our findings provide insight into the function of onvansertib and shed light on the potential clinical application of onvansertib for the treatment of patients with LUAD.

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 < 0.001 respectively), and tumor grade (p < 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 < 0.0001, respectively). In breast cancer, PLK-1 was significantly associated with 5-year overall survival, histological grade, and lymph node metastasis (p < 0.001, p = 0.003, p < 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.

The kinase PLK1 promotes the development of <i>Kras</i>/<i>Tp53</i>-mutant lung adenocarcinoma through transcriptional activation of the receptor RET

Increased abundance of polo-like kinase 1 (PLK1) is observed in various tumor types, particularly in lung adenocarcinoma (LUAD). Here, we found that PLK1 accelerated the progression of LUAD through a mechanism that was independent of its role in mediating mitotic cell division. Analysis of human tumor databases revealed that increased PLK1 abundance in LUAD correlated with mutations in KRAS and p53, with tumor stage, and with reduced survival in patients. In a mouse model of KRAS^G12D-driven, p53-deficient LUAD, PLK1 overexpression increased tumor burden, decreased tumor cell differentiation, and reduced animal survival. PLK1 overexpression in cultured cells and mice indirectly increased the expression of the gene encoding the receptor tyrosine kinase RET by phosphorylating the transcription factor TTF-1. Signaling by RET and mutant KRAS in these tumors converged to activate the mitogen-activated protein kinase (MAPK) pathway. Pharmacological inhibition of the MAPK pathway kinase MEK combined with inhibition of either RET or PLK1 markedly suppressed tumor growth. Our findings show that PLK1 can amplify MAPK signaling and reveal a potential target for stemming progression in lung cancers with high PLK1 abundance.

ARV-825 Demonstrates Antitumor Activity in Gastric Cancer via MYC-Targets and G2M-Checkpoint Signaling Pathways

Objective

Suppression of bromodomain and extra terminal (BET) proteins has a bright prospect to treat MYC-driven tumors. Bromodomain containing 4 (BRD4) is one of the BET proteins. ARV-825, consisting of a BRD4 inhibitor conjugated with a cereblon ligand using proteolysis-targeting chimera (PROTAC) technology, was proven to decrease the tumor growth effectively and continuously. Nevertheless, the efficacy and mechanisms of ARV-825 in gastric cancer are still poorly understood.

Methods

Cell counting kit 8 assay, lentivirus infection, Western blotting analysis, Annexin V/propidium iodide (PI) staining, RNA sequencing, a xenograft model, and immunohistochemistry were used to assess the efficacy of ARV-825 in cell level and animal model.

Results

The messenger RNA (mRNA) expression of BRD4 in gastric cancer raised significantly than those in normal tissues, which suggested poor outcome of patients with gastric cancer. ARV-825 displayed higher anticancer efficiency in gastric cancer cells than OTX015 and JQ1. ARV-825 could inhibit cell growth, inducing cell cycle block and apoptosis in vitro. ARV-825 induced degradation of BRD4, BRD2, BRD3, c-MYC, and polo-like kinase 1 (PLK1) proteins in four gastric cancer cell lines. In addition, cleavage of caspase 3 and poly-ADP-ribose polymerase (PARP) was elevated. Knockdown or overexpression CRBN could increase or decrease, respectively, the ARV-825 IC50 of gastric cancer cells. ARV-825 reduced MYC and PLK1 expression in gastric cancer cells. ARV-825 treatment significantly reduced tumor growth without toxic side effects and downregulated the expression of BRD4 in vivo.

Conclusions

High mRNA expression of BRD4 in gastric cancer indicated poor prognosis. ARV-825, a BRD4 inhibitor, could effectively suppress the growth and elevate the apoptosis of gastric cancer cells via transcription downregulation of c-MYC and PLK1. These results implied that ARV-825 could be a good therapeutic strategy to treat gastric cancer.

Current research developments of patient-derived tumour xenograft models (Review)

Patient-derived tumor xenograft (PDTX) models are established by transferring patient tumors into immunodeficient mice. In these murine models, the characteristics of the primary tumor are retained, including the microenvironment of tumor cell growth and histopathology. Due to this, it has become the most reliable in vivo human cancer model. However, the success rates differ by type of tumor, site of transplantation and tumor aggressiveness. Subcutaneous transplantation is a standard method for PDTX, and subrenal capsule transplantation improves the engraftment rate. Recently, PDTX models are frequently used in the fields of precision medicine, predictive biomarkers, evaluation of drug efficacy and preclinical research on tumor immunotherapeutic drugs. The aim of the present article was to review the establishment, clinical applications and limitations of the PDTX model in tumor research.

Polo like kinase 1 expression in cervical cancer tissues generated from multiple detection methods

Background

Existing studies of PLK1 in cervical cancer had several flaws. The methods adopted by those studies of detecting PLK1 expression in cervical cancer were single and there lacks comprehensive evaluation of the clinico-pathological significance of PLK1 in cervical cancer.

Methods

A total of 303 cervical tissue samples were collected for in-house tissue microarrays. Immunohistochemistry was performed for evaluating PLK1 expression between cervical cancer (including cervical squamous cell carcinoma (CESC) and cervical adenocarcinoma) and non-cancer samples. The Expression Atlas database was searched for querying PLK1 expression in different cervical cancer cell lines and different tissues in the context of pan-cancer. Standard mean difference (SMD) was calculated and the summarized receiver's operating characteristics (SROC) curves were plotted for integrated tissue microarrays, exterior high-throughput microarrays and RNA sequencing data as further verification. The effect of PLK1 expression on the overall survival, disease-free survival and event-free survival of cervical cancer patients was analyzed through Kaplan Meier survival curves for cervical cancer patients from RNA-seq and GSE44001 datasets. The gene mutation and alteration status of PLK1 in cervical cancer was inspected in COSMIC and cBioPortal databases. Functional enrichment analysis was performed for genes correlated with PLK1 from aggregated RNA-seq and microarrays.

Results

A total of 963 cervical cancer samples and 178 non-cancer samples were collected from in-house tissue microarrays and exterior microarrays and RNA-seq datasets. The combined expression analysis supported overexpression of PLK1 in CESC, cervical adenocarcinoma and all types of cervical cancer (SMD = 1.59, 95%CI [0.56-2.63]; SMD = 2.99, 95%CI [0.75-5.24]; SMD = 1.57, 95% CI [0.85-2.29]) and the significant power of PLK1 expression in distinguishing CESC or all types of cervical cancer samples from non-cancer samples (AUC = 0.94, AUC = 0.92). Kaplan-Meier survival curves showed that the event-free survival rate of cervical cancer patients with higher expression of PLK1 was shorter than that of patients with lower PLK1 (HR = 2.020, P = 0.0197). Genetic alteration of PLK1 including missense mutation and mRNA low occurred in 6% of cervical cancer samples profiled in mRNA expression. Genes positively or negatively correlated with PLK1 were mainly assembled in pathways such as DNA replication, cell cycle, mismatch repair, Ras signaling pathway, melanoma, EGFR tyrosine kinase inhibitor resistance and homologous recombination (P < 0.05).

Conclusions

Here, we provided sufficient evidence of PLK1 overexpression in cervical cancer. The overexpression of PLK1 in cervical cancer and the contributory effect of it on clinical progression indicated the hopeful prospect of PLK1 as a biomarker for cervical cancer.

Long non‑coding RNA ZEB2‑AS1 affects cell proliferation and apoptosis via the miR‑122‑5p/PLK1 axis in acute myeloid leukemia

Acute myeloid leukemia (AML) is a highly heterogeneous disease featured by the clonal accumulation of immature myeloid cells. Zinc finger E‑box binding homeobox 2 (ZEB2)‑antisense RNA 1 (AS1) has been verified to participate in the progression of several types of cancer, including AML. However, the potential mechanisms of ZEB2‑AS1 in AML have not yet been fully elucidated. The present study aimed to elucidate the role and regulatory mechanisms of ZEB2‑AS1 in AML. The expression of ZEB2‑AS1, microRNA‑122‑5p (miRNA/miR‑122‑5p) and polo‑like kinase 1 (PLK1) was detected by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) in AML tissues or cells. Cell proliferation and apoptosis were examined by methyl thiazolyl tetrazolium (MTT) assay and apoptosis assay, respectively. The protein levels were examined by western blot analysis. The targeted sequence between miR‑122‑5p and ZEB2‑AS1 or PLK1 was predicted using an online database and verified by dual‑luciferase reporter assay. A mouse tumor xenograft model was established to confirm the effects of ZEB2‑AS1 on tumor growth in vivo. The results revealed that the expression levels of ZEB2‑AS1 and PLK1 were upregulated, while those of miR‑122‑5p were downregulated in AML tissues and cells. The knockdown of ZEB2‑AS1 inhibited proliferation and induced apoptosis in vitro, and inhibited tumor growth in vivo. By experimental verification, ZEB2‑AS1 was found to negatively regulate miR‑122‑5p expression and PLK1 was found to be a target gene of miR‑122‑5p. Furthermore, ZEB2‑AS1 was verified to regulate the expression of PLK1 by sponging miR‑122‑5p in AML cells. On the whole, the findings of the present study demonstrate that ZEB2‑AS1 promotes cell proliferation and inhibits apoptosis, at least partly by targeting PLK1 mediated by miR‑122‑5p in AML cells.

Identification of hub genes and discovery of promising compounds in gastric cancer based on bioinformatics analysis

Aim: To explore the mechanism of gastric carcinogenesis by mining potential hub genes and to search for promising small-molecular compounds for gastric cancer (GC). Materials & methods: The microarray datasets were downloaded from Gene Expression Omnibus database and the genes and compounds were analyzed by bioinformatics-related tools and software. Results: Six hub genes (MKI67, PLK1, COL1A1, TPX2, COL1A2 and SPP1) related to the prognosis of GC were confirmed to be upregulated in GC and their high expression was correlated with poor overall survival rate in GC patients. In addition, eight candidate compounds with potential anti-GC activity were identified, among which resveratrol was closely correlated with six hub genes. Conclusion: Six hub genes identified in the present study may contribute to a more comprehensive understanding of the mechanism of gastric carcinogenesis and the predicted potential of resveratrol may provide valuable clues for the future development of targeted anti-GC inhibitors.

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.

RO3280: A Novel PLK1 Inhibitor, Suppressed the Proliferation of MCF-7 Breast Cancer Cells Through the Induction of Cell Cycle Arrest at G2/M Point

BACKGROUND

As a member of serine/threonine-protein kinase, Polo.like kinase 1 (PLK1) plays crucial roles during mitosis and also contributes to DNA damage response and repair. PLK1 is aberrantly expressed in many types of tumor cells and increased levels of PLK1 are closely related to tumorigenesis and poor clinical outcomes. Therefore, PLK1 is accepted as one of the potential targets for the discovery of novel anticancer agents. The objective of this study was to assess the cytotoxic effects of a novel PLK1 inhibitor, RO3280, against MCF-7, human breast cancer cells; HepG2, human hepatocellular carcinoma cells; and PC3, human prostate cancer cells, as well as non-cancerous L929 fibroblast cells.

METHODS

Antiproliferative activity of RO3280 was examined using the XTT assay. Flow cytometry assay was performed to evaluate cell cycle distribution, apoptosis, multicaspase activity, mitochondrial membrane potential, and DNA damage response. Apoptosis with fluorescence imaging studies was also examined.

RESULTS

According to the results of XTT assay, although RO3280 displayed potent cytotoxicity in all treated cancer cells, the most sensitive cell line was identified as MCF-7 cells that were selected for further studies. The compound induced a cell cycle arrest in MCF-7 cells at G2/M phase and significantly induced apoptosis, multicaspase activity, DNA damage response, and decreased mitochondrial membrane potential of MCF-7 cells.

CONCLUSION

Overall, RO3280 induces anticancer effects promoted mainly by DNA damage, cell cycle arrest, and apoptosis in breast cancer cells. Further studies are needed to assess its usability as an anticancer agent with specific cancer types.