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

Polo-like kinase 1 suppresses lung adenocarcinoma immunity through necroptosis

Polo-like kinase 1 (PLK1) plays a crucial role in cell mitosis and has been associated with necroptosis. However, the role of PLK1 and necroptosis in lung adenocarcinoma (LA) remains unclear. In this study, we analyzed The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression databases to evaluate the prognostic value and mechanistic role of PLK1 in LA. PLK1 was found to be highly expressed in LA and was positively associated with advanced disease staging and poor survival outcomes. Functional enrichment analysis showed that PLK1 was involved in cell mitosis, neurotransmitter transmission, and drug metabolism. Further analysis using single-sample gene set enrichment analysis and ESTIMATE algorithm revealed a correlation between PLK1 expression and immune infiltration in LA. Silencing of PLK1 using miRNA transfection in LA cells reduced cell proliferation and increased apoptosis, as well as upregulating the expression of necroptosis-related proteins, such as RIPK1, RIPK3, and MLKL. Additionally, nude mouse transplantation tumor experiments demonstrated that silencing PLK1 reduced the growth capacity of LA cells. These findings suggest that PLK1 plays a critical role in LA progression by regulating necroptosis and immune infiltration, and may serve as a potential therapeutic target for immunotherapy. Furthermore, PLK1 expression can be used as a prognostic biomarker for LA patients.

PAK2 is essential for chromosome alignment in metaphase I oocytes

As a highly conserved and ubiquitously expressed serine/threonine kinase, p21-activated kinase 2 (PAK2) participates in diverse biologic events. However, its roles in mouse oocyte meiotic maturation remain unclear. The present study revealed that mouse oocytes depleted of Pak2 were unable to completely progress through meiosis and that a majority were arrested at metaphase I. Pak2 depletion thus prompted MI arrest and induced meiotic chromosome alignment defects in mouse oocytes, in part due to a reduction in polo-like kinase (PLK1). We demonstrated that PAK2's interaction with PLK1 protected it from degradation by APC/C^Cdh1, and that it promoted meiotic progression and bipolar spindle formation. Our data collectively display critical functions for PAK2 in meiotic progression and chromosome alignment in mouse oocytes.

Development of a nanoparticle-based immunotherapy targeting PD-L1 and PLK1 for lung cancer treatment

Immune checkpoint inhibitors (ICIs) targeting PD-L1 and PD-1 have improved survival in a subset of patients with advanced non-small cell lung cancer (NSCLC). However, only a minority of NSCLC patients respond to ICIs, highlighting the need for superior immunotherapy. Herein, we report on a nanoparticle-based immunotherapy termed ARAC (Antigen Release Agent and Checkpoint Inhibitor) designed to enhance the efficacy of PD-L1 inhibitor. ARAC is a nanoparticle co-delivering PLK1 inhibitor (volasertib) and PD-L1 antibody. PLK1 is a key mitotic kinase that is overexpressed in various cancers including NSCLC and drives cancer growth. Inhibition of PLK1 selectively kills cancer cells and upregulates PD-L1 expression in surviving cancer cells thereby providing opportunity for ARAC targeted delivery in a feedforward manner. ARAC reduces effective doses of volasertib and PD-L1 antibody by 5-fold in a metastatic lung tumor model (LLC-JSP) and the effect is mainly mediated by CD8+ T cells. ARAC also shows efficacy in another lung tumor model (KLN-205), which does not respond to CTLA-4 and PD-1 inhibitor combination. This study highlights a rational combination strategy to augment existing therapies by utilizing our nanoparticle platform that can load multiple cargo types at once.

Only a minority of patients with non-small cell lung cancer (NSCLC) respond to immune checkpoint inhibitors. Here the authors design a nanosystem for the co-delivery of a PLK1 inhibitor and PD-L1 antibody, showing anti-tumor immune responses in preclinical lung cancer models.

Targeting senescence as an anticancer therapy

Cellular senescence is a stress response elicited by different molecular insults. Senescence results in cell cycle exit and is characterised by multiple phenotypic changes such as the production of a bioactive secretome. Senescent cells accumulate during ageing and are present in cancerous and fibrotic lesions. Drugs that selectively kill senescent cells (senolytics) have shown great promise for the treatment of age-related diseases. Senescence plays paradoxical roles in cancer. Induction of senescence limits cancer progression and contributes to therapy success, but lingering senescent cells fuel progression, recurrence, and metastasis. In this review, we describe the intricate relation between senescence and cancer. Moreover, we enumerate how current anticancer therapies induce senescence in tumour cells and how senolytic agents could be deployed to complement anticancer therapies. "One-two punch" therapies aim to first induce senescence in the tumour followed by senolytic treatment to target newly exposed vulnerabilities in senescent tumour cells. "One-two punch" represents an emerging and promising new strategy in cancer treatment. Future challenges of "one-two punch" approaches include how to best monitor senescence in cancer patients to effectively survey their efficacy.

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.

Integrated genomics point to immune vulnerabilities in pleural mesothelioma

Pleural mesothelioma is an aggressive malignancy with limited effective therapies. In order to identify therapeutic targets, we integrated SNP genotyping, sequencing and transcriptomics from tumours and low-passage patient-derived cells. Previously unrecognised deletions of SUFU locus (10q24.32), observed in 21% of 118 tumours, resulted in disordered expression of transcripts from Hedgehog pathways and the T-cell synapse including VISTA. Co-deletion of Interferon Type I genes and CDKN2A was present in half of tumours and was a predictor of poor survival. We also found previously unrecognised deletions in RB1 in 26% of cases and show sub-micromolar responses to downstream PLK1, CHEK1 and Aurora Kinase inhibitors in primary mesothelioma cells. Defects in Hippo pathways that included RASSF7 amplification and NF2 or LATS1/2 mutations were present in 50% of tumours and were accompanied by micromolar responses to the YAP1 inhibitor Verteporfin. Our results suggest new therapeutic avenues in mesothelioma and indicate targets and biomarkers for immunotherapy.

Synergistic Therapy for Cervical Cancer by Codelivery of Cisplatin and JQ1 Inhibiting Plk1-Mutant Trp53 Axis

JQ1, a specific inhibitor of bromodomain-containing protein 4 (BRD4), could have great potential in the treatment of cervical cancer. However, its clinical application is limited by its short plasma half-life and limited antitumor efficacy. In this work, cisplatin (CDDP) was first utilized as the stabilizer and cooperator in the nanosystem (mPEG₁₁₃-b-P(Glu₁₀-co-Phe₁₀)-CDDP/JQ1, called PGP-CDDP/JQ1) to break through the efficiency limitation of JQ1. The PGP-CDDP/JQ1 had a combination index (CI) of 0.21, exerting a strong cytotoxic synergistic effect. In vivo experiments revealed that PGP-CDDP/JQ1 had a significantly higher tumor inhibition effect (tumor inhibition rate: 85% vs 14%) and plasma stability of JQ1 (area under the curve (AUC_0-∞): 335.97 vs 16.88 μg × h/mL) than free JQ1. The mechanism underling the synergism of JQ1 with CDDP in PGP-CDDP/JQ1 was uncovered to be inhibiting Plk1-mutant Trp53 axis. Thus, this study provides an optional method for improving the clinical application of JQ1 in cervical cancer.

VPS33B modulates c-Myc/p53/miR-192-3p to target CCNB1 suppressing the growth of non-small cell lung cancer

VPS33B is reported to be a tumor suppressor in hepatocellular carcinoma, nasopharyngeal carcinoma, colon cancer, and lung adenocarcinoma. Here, we observed that reduced VPS33B protein level was an unfavorable factor that promoted the pathogenesis of non-small cell lung cancer (NSCLC) in clinical specimens. We achieved lentivirus-mediated stable overexpression of VPS33B in NSCLC cells. Increased VPS33B reduced cell cycle transition and cell proliferation of NSCLC cells in vivo and in vitro. Knocking down VPS33B restored cell growth. Mechanism analysis indicated that miR-192-3p was induced by VPS33B and acted as a tumor suppressor of cell growth in NSCLC. Further, c-Myc or p53 was identified as a transcription factor that bound to the miR-192-3p promoter and regulated its expression. miR-192-3p directly targeted cell cycle-promoted factor CCNB1 and suppressed NSCLC cell growth. VPS33B modulated c-Myc/p53/miR-192-3p signaling to target CCNB1 by reducing activation of the Ras/ERK pathway. Our study reveals a novel molecular basis for VPS33B as a tumor suppressor to participate in the pathogenesis of NSCLC.

Mitotic Poisons in Research and Medicine

Cancer is one of the greatest challenges of the modern medicine. Although much effort has been made in the development of novel cancer therapeutics, it still remains one of the most common causes of human death in the world, mainly in low and middle-income countries. According to the World Health Organization (WHO), cancer treatment services are not available in more then 70% of low-income countries (90% of high-income countries have them available), and also approximately 70% of cancer deaths are reported in low-income countries. Various approaches on how to combat cancer diseases have since been described, targeting cell division being among them. The so-called mitotic poisons are one of the cornerstones in cancer therapies. The idea that cancer cells usually divide almost uncontrolled and far more rapidly than normal cells have led us to think about such compounds that would take advantage of this difference and target the division of such cells. Many groups of such compounds with different modes of action have been reported so far. In this review article, the main approaches on how to target cancer cell mitosis are described, involving microtubule inhibition, targeting aurora and polo-like kinases and kinesins inhibition. The main representatives of all groups of compounds are discussed and attention has also been paid to the presence and future of the clinical use of these compounds as well as their novel derivatives, reviewing the finished and ongoing clinical trials.

Dual targeting of Polo-like kinase 1 and baculoviral inhibitor of apoptosis repeat-containing 5 in TP53-mutated hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC), often diagnosed at advanced stages without curative therapies, is the fifth most common malignant cancer and the second leading cause of cancer-related mortality. Polo-like kinase 1 (PLK1) is activated in the late G2 phase of the cell cycle and is required for entry to mitosis. Interestingly, PLK1 is overexpressed in many HCC patients and is highly associated with poor clinical outcome. Baculoviral inhibitor of apoptosis repeat-containing 5 (BIRC5) is also highly overexpressed in HCC and plays key roles in this malignancy.

AIM

To determine the expression patterns of PLK1 and BIRC5, as well as their correlation with p53 mutation status and patient clinical outcome.

METHODS

The expression patterns of PLK1 and BIRC5, and their correlation with p53 mutation status or patient clinical outcome were analyzed using a TCGA HCC dataset. Cell viability, cell apoptosis, and cell cycle arrest assays were conducted to investigate the efficacy of the PLK1 inhibitors volasertib and GSK461364 and the BIRC5 inhibitor YM155, alone or in combination. The in vivo efficacy of volasertib and YM155, alone or in combination, was assessed in p53-mutated Huh7-derived xenograft models in immune-deficient NSIG mice.

RESULTS

Our bioinformatics analysis using a TCGA HCC dataset revealed that PLK1 and BIRC5 were overexpressed in the same patient subset and their expression was highly correlated. The overexpression of both PLK1 and BIRC5 was more frequently detected in HCC with p53 mutations. High PLK1 or BIRC5 expression significantly correlated with poor clinical outcome. PLK1 inhibitors (volasertib and GSK461364) or a BIRC5 inhibitor (YM155) selectively targeted Huh7 cells with mutated p53, but not HepG2 cells with wild-type p53. The combination treatment of volasertib and YM155 synergistically inhibited the viability of Huh7 cells via apoptotic pathway. The efficacy of volasertib and YM155, alone or in combination, was validated in vivo in a Huh7-derived xenograft model.

CONCLUSION

PLK1 and BIRC5 are highly co-expressed in p53-mutated HCC and inhibition of both PLK1 and BIRC5 synergistically compromises the viability of p53-mutated HCC cells in vitro and in vivo.

Cancer Stem Cells-Origins and Biomarkers: Perspectives for Targeted Personalized Therapies

The use of biomarkers in diagnosis, therapy and prognosis has gained increasing interest over the last decades. In particular, the analysis of biomarkers in cancer patients within the pre- and post-therapeutic period is required to identify several types of cells, which carry a risk for a disease progression and subsequent post-therapeutic relapse. Cancer stem cells (CSCs) are a subpopulation of tumor cells that can drive tumor initiation and can cause relapses. At the time point of tumor initiation, CSCs originate from either differentiated cells or adult tissue resident stem cells. Due to their importance, several biomarkers that characterize CSCs have been identified and correlated to diagnosis, therapy and prognosis. However, CSCs have been shown to display a high plasticity, which changes their phenotypic and functional appearance. Such changes are induced by chemo- and radiotherapeutics as well as senescent tumor cells, which cause alterations in the tumor microenvironment. Induction of senescence causes tumor shrinkage by modulating an anti-tumorigenic environment in which tumor cells undergo growth arrest and immune cells are attracted. Besides these positive effects after therapy, senescence can also have negative effects displayed post-therapeutically. These unfavorable effects can directly promote cancer stemness by increasing CSC plasticity phenotypes, by activating stemness pathways in non-CSCs, as well as by promoting senescence escape and subsequent activation of stemness pathways. At the end, all these effects can lead to tumor relapse and metastasis. This review provides an overview of the most frequently used CSC markers and their implementation as biomarkers by focussing on deadliest solid (lung, stomach, liver, breast and colorectal cancers) and hematological (acute myeloid leukemia, chronic myeloid leukemia) cancers. Furthermore, it gives examples on how the CSC markers might be influenced by therapeutics, such as chemo- and radiotherapy, and the tumor microenvironment. It points out, that it is crucial to identify and monitor residual CSCs, senescent tumor cells, and the pro-tumorigenic senescence-associated secretory phenotype in a therapy follow-up using specific biomarkers. As a future perspective, a targeted immune-mediated strategy using chimeric antigen receptor based approaches for the removal of remaining chemotherapy-resistant cells as well as CSCs in a personalized therapeutic approach are discussed.

Radiosensitization of Non-Small Cell Lung Cancer Cells by the Plk1 Inhibitor Volasertib Is Dependent on the p53 Status

Polo-like kinase 1 (Plk1), a master regulator of mitotic cell division, is highly expressed in non-small cell lung cancer (NSCLC) making it an interesting drug target. We examined the in vitro therapeutic effects of volasertib, a Plk1 inhibitor, in combination with irradiation in a panel of NSCLC cell lines with different p53 backgrounds. Pretreatment with volasertib efficiently sensitized p53 wild type cells to irradiation. Flow cytometric analysis revealed that significantly more cells were arrested in the G₂/M phase of the cell cycle after the combination therapy compared to either treatment alone (p < 0.005). No significant synergistic induction of apoptotic cell death was observed, but, importantly, significantly more senescent cells were detected when cells were pretreated with volasertib before irradiation compared to both monotherapies alone (p < 0.001), especially in cells with functional p53. Consequently, while most cells with functional p53 showed permanent growth arrest, more p53 knockdown/mutant cells could re-enter the cell cycle, resulting in colony formation and cell survival. Our findings assign functional p53 as a determining factor for the observed radiosensitizing effect of volasertib in combination with radiotherapy for the treatment of NSCLC.