Targeting Polo-like kinase 1 and TRAIL enhances apoptosis in non-small cell lung cancer

TRIAL-based combination therapies in cancers

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) shows promising therapeutic potential in cancer treatment as it is able to trigger extrinsic apoptotic pathways by binding to the cognate death receptor, causing broad-spectrum apoptosis in cancer cells with negligible toxicity to normal cells. However, the majority of cancers display resistance to TRAIL, limiting its clinical utility. Overcoming resistance to TRAIL therapies remains a challenge in the development of effective anti-cancer strategies. To address the limitations of TRAIL therapy, a viable alternative approach involves combining TRAIL with more potent drugs compared to monotherapy. This combination strategy aims to induce synergistic effects or sensitize drug-resistant cancer cells. This review provides an overview of relevant modalities of TRAIL combination therapy, highlighting different drug classes. The findings demonstrate that combining TRAIL with other agents can effectively counteract resistance observed with TRAIL therapies in cancer. These findings lay a foundation for future advancements in TRAIL-based therapies for treating various cancers.

PLK1 inhibition-based combination therapies for cancer management

Polo-like kinase I (PLK1), a cell cycle regulating kinase, has been shown to have oncogenic function in several cancers. Although PLK1 inhibitors, such as BI2536, BI6727 (volasertib) and NMS-1286937 (onvansertib) are generally well-tolerated with a favorable pharmacokinetic profile, clinical successes are limited due to partial responses in cancer patients, especially those in advanced stages. Recently, combination therapies targeting multiple pathways are being tested for cancer management. In this review, we first discuss structure and function of PLK1, role of PLK1 in cancers, PLK1 specific inhibitors, and advantages of using combination therapy versus monotherapy followed by a critical account on PLK1-based combination therapies in cancer treatments, especially highlighting recent advancements and challenges. PLK1 inhibitors in combination with chemotherapy drugs and targeted small molecules have shown superior effects against cancer both in vitro and in vivo. PLK1-based combination therapies have shown increased apoptosis, disrupted cell cycle, and potential to overcome resistance in cancer cells/tissues over monotherapies. Further, with successes in preclinical experiments, researchers are validating such approaches in clinical trials. Although PLK1-based combination therapies have achieved initial success in clinical studies, there are examples where they have failed to improve patient survival. Therefore, further research is needed to identify and validate novel biologically informed co-targets for PLK1-based combinatorial therapies. Employing a network-based analysis, we identified potential PLK1 co-targets that could be examined further. In addition, understanding the mechanisms of synergism between PLK1 inhibitors and other agents may lead to a better approach on which agents to pair with PLK1 inhibition for optimum cancer treatment.

Tumor-suppressive activity of sTRAIL on circulating CD44+ cells in patients with non-small cell lung cancer

Circulating CD44+ cells have been identified as a prognostic marker for patients with non-small cell lung cancer (NSCLC). Serum tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) is involved in the pathophysiology of many cancers. However, no previous studies have shown the roles of sTRAIL in circulating CD44+ cells in the blood of NSCLC patients. We detected circulating CD44+ cells and sTRAIL levels in blood samples from NSCLC patients using flow cytometry and an enzyme-linked immunosorbent assay (ELISA). Anti-tumor roles of TRAIL in CD44+ cells were confirmed using a CCK-8 assay and mouse models. A higher number of circulating CD44+ cells were identified in NSCLC patients compared with healthy control individuals. In addition, we confirmed the anti-tumor roles and mechanisms of TRAIL in CD44+ cells both in vitro and in vivo. Our results indicate that (1) there is a negative correlation between sTRAIL and circulating CD44+ cells in NSCLC patients and (2) CD44+ cells have cancer stem cell properties and are more sensitive than CD44- cells to TRAIL.

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.

Up-regulation of Polo-like Kinase 1 in nasopharyngeal carcinoma tissues: a comprehensive investigation based on RNA-sequencing, gene chips, and in-house tissue arrays

BACKGROUND

Nasopharyngeal carcinoma (NPC) is a highly invasive malignancy which has unique characteristics when found among individuals from certain ethnic or geographic populations. The role and molecular mechanism of Polo-like kinase 1 (PLK1) in NPC remain yet to be clarified. Hence, the aim of this study is to identify the clinical implications of PLK1 in NPC based on gene chip, tissue microarray, and other silico approaches.

METHODS

Relevant data related to PLK1 levels in NPC was screened for by searching in SRA, GEO, ArrayExpress, Oncomine and throughout the existing literature on this topic. The raw data about gene chips were normalized by using an RMA algorithm provided by "Limma" package. Furthermore, the "SVA" package of R software was used to remove the batch effect and data from the same platform were merged into one part. The differential expression levels of PLK1 between NPC and non-NPC tissues were extracted and analyzed with the Student's t-test. Meta-analyses were used to calculate the standard mean difference and sROC. Furthermore, in-house immunohistochemistry was performed with tissue microarrays. Weighted correlation network analysis was used to identify the PLK1-related genes. Several bioinformatic evaluations, including the Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, and protein-protein interactions, were also performed to assess the PLK1-related pathways.

RESULTS

The tissue microarray and gene chips indicated that the PLK1 levels clearly had an up-regulating trend as compared to the non-cancerous controls. These trends were observed in both the single study and the comprehensive meta-analysis. The area under the sROC curve in the NPC tissues was 0.87, with pooled sensitivity and specificity at 0.950 and 0.710, respectively, based on 393 NPC tissues and 83 non-cancerous controls. A total of 144 genes were identified as co-expressed genes of PLK1 in NPC and were mainly enriched in the "cell cycle" pathway. Among the genes related to the cell cycle, CDK1, CCNA2 and CCNB2 were all closely related to PLK1 expression level.

CONCLUSIONS

PLK1 may play a potential oncogenic role in the tumorigenesis and development of NPC. Since several PLK1 inhibitors have been developed, it is believed that the PLK1 inhibitors have great therapeutic potential in clinic applications for NPC patients.