Polo-like kinase 1 as target for cancer therapy

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.

Mitotic kinases are emerging therapeutic targets against metastatic breast cancer

This review aims to outline mitotic kinase inhibitors' roles as potential therapeutic targets and assess their suitability as a stand-alone clinical therapy or in combination with standard treatments for advanced-stage solid tumors, including triple-negative breast cancer (TNBC). Breast cancer poses a significant global health risk, with TNBC standing out as the most aggressive subtype. Comprehending the role of mitosis is crucial for understanding how TNBC advances from a solid tumor to metastasis. Chemotherapy is the primary treatment used to treat TNBC. Some types of chemotherapeutic agents target cells in mitosis, thus highlighting the need to comprehend the molecular mechanisms governing mitosis in cancer. This understanding is essential for devising targeted therapies to disrupt these mitotic processes, prevent or treat metastasis, and improve patient outcomes. Mitotic kinases like Aurora kinase A, Aurora Kinase B, never in mitosis gene A-related kinase 2, Threonine-Tyrosine kinase, and Polo-kinase 1 significantly impact cell cycle progression by contributing to chromosome separation and centrosome homeostasis. When these kinases go awry, they can trigger chromosome instability, increase cell proliferation, and activate different molecular pathways that culminate in a transition from epithelial to mesenchymal cells. Ongoing clinical trials investigate various mitotic kinase inhibitors as potential biological treatments against advanced solid tumors. While clinical trials against mitotic kinases have shown some promise in the clinic, more investigation is necessary, since they induce severe adverse effects, particularly affecting the hematopoietic system.

Invasive FoxM1 phosphorylated by PLK1 induces the polarization of tumor-associated macrophages to promote immune escape and metastasis, amplified by IFITM1

BACKGROUND

Understanding the mechanism behind immune cell plasticity in cancer metastasis is crucial for identifying key regulators. Previously we found that mitotic factors regulate epithelial-mesenchymal transition, but how these factors convert to metastatic players in the tumor microenvironment (TME) is not fully understood.

METHODS

The clinical importance of mitotic factors was analyzed by heatmap analysis, a KM plot, and immunohistochemistry in lung adenocarcinoma (LUAD) patients. Immunoprecipitation, LC-MS/MS, kinase assay, and site-directed mutagenesis were performed for the interaction and phosphorylation. A tail-vein injection mouse model, Transwell-based 3D culture, microarray analysis, coculture with monocytes, and chromatin immunoprecipitation assays were used to elucidate the function of phosphorylated FoxM1 in metastasis of TME.

RESULTS

The phosphorylated FoxM1 at Ser25 by PLK1 acquires the reprogramming ability to stimulate the invasive traits in cancer and influence immune cell plasticity. This invasive form of p-FoxM1 upregulates the expression of IL1A/1B, VEGFA, and IL6 by direct activation, recruiting monocytes and promoting the polarization of M2d-like tumor-associated macrophages (TAMs). Upregulation of PD-L1 in LUAD having phosphomimetic FoxM1 facilitates immune evasion. In invasive LUAD with phosphomimetic FoxM1, IFITM1 is the most highly expressed through the activation of the STING-TBK1-IRF3 signaling, which enhances FoxM1-mediated signaling. Clinically, higher expression of FOXM1, PLK1, and IFITM1 is inversely correlated with the survival rate of advanced LUAD patients, providing a promising therapeutic strategy for the treatment of LUAD.

CONCLUSION

FoxM1-based therapy would be a potential therapeutic strategy for LUAD to reduce TAM polarization, immune escape, and metastasis, since FoxM1 functions as a genetic reprogramming factor reinforcing LUAD malignancy in the TME.

Establishment of a Necroptosis-Related Prognostic Signature to Reveal Immune Infiltration and Predict Drug Sensitivity in Hepatocellular Carcinoma

Background: Hepatocellular carcinoma (HCC) is a common type of primary liver cancer and has a poor prognosis. In recent times, necroptosis has been reported to be involved in the progression of multiple cancers. However, the role of necroptosis in HCC prognosis remains elusive.

Methods: The RNA-seq data and clinical information of HCC patients were downloaded from The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) databases. Differentially expressed genes (DEGs) and prognosis-related genes were explored, and the nonnegative matrix factorization (NMF) clustering algorithm was applied to divide HCC patients into different subtypes. Based on the prognosis-related DEGs, univariate Cox and LASSO Cox regression analyses were used to construct a necroptosis-related prognostic model. The relationship between the prognostic model and immune cell infiltration, tumor mutational burden (TMB), and drug response were explored.

Results: In this study, 13 prognosis-related DEGs were confirmed from 18 DEGs and 24 prognostic-related genes. Based on the prognosis-related DEGs, patients in the TCGA cohort were clustered into three subtypes by the NMF algorithm, and patients in C3 had better survival. A necroptosis-related prognostic model was established according to LASSO analysis, and HCC patients in TCGA and ICGC were divided into high- and low-risk groups. Kaplan–Meier (K–M) survival analysis revealed that patients in the high-risk group had a shorter survival time compared to those in the low-risk group. Using univariate and multivariate Cox analyses, the prognostic model was identified as an independent prognostic factor and had better survival predictive ability in HCC patients compared with other clinical biomarkers. Furthermore, the results revealed that the high-risk patients had higher stromal, immune, and ESTIMATE scores; higher TP53 mutation rate; higher TMB; and lower tumor purities compared to those in the low-risk group. In addition, there were significant differences in predicting the drug response between the high- and low-risk groups. The protein and mRNA levels of these prognostic genes were upregulated in HCC tissues compared to normal liver tissues.

Conclusion: We established a necroptosis-related prognostic signature that may provide guidance for individualized drug therapy in HCC patients; however, further experimentation is needed to validate our results.

Hypoxia-directed tumor targeting of CRISPR-Cas9 and HSV-TK suicide gene therapy using lipid nanoparticles

Hypoxia is a characteristic feature of solid tumors that contributes to tumor aggressiveness and is associated with resistance to cancer therapy. The hypoxia inducible factor-1 (HIF-1) transcription factor complex mediates hypoxia-specific gene expression by binding to hypoxia-responsive element (HRE) sequences within the promoter of target genes. HRE-driven expression of therapeutic cargo has been widely explored as a strategy to achieve cancer-specific gene expression. By utilizing this system, we achieve hypoxia-specific expression of two therapeutically relevant cargo elements: the herpes simplex virus thymidine kinase (HSV-tk) suicide gene and the CRISPR-Cas9 nuclease. Using an expression vector containing five copies of the HRE derived from the vascular endothelial growth factor gene, we are able to show high transgene expression in cells in a hypoxic environment, similar to levels achieved using the cytomegalovirus (CMV) and CBh promoters. Furthermore, we are able to deliver our therapeutic cargo to tumor cells with high efficiency using plasmid-packaged lipid nanoparticles (LNPs) to achieve specific killing of tumor cells in hypoxic conditions while maintaining tight regulation with no significant changes to cell viability in normoxia.

A novel PLK1 inhibitor onvansertib effectively sensitizes MYC-driven medulloblastoma to radiotherapy

BACKGROUND

Group 3 medulloblastoma (MB) is often accompanied by MYC amplification. PLK1 is an oncogenic kinase that controls cell cycle and proliferation and has been preclinically validated as a cancer therapeutic target. Onvansertib (PCM-075) is a novel, orally available PLK1 inhibitor, which shows tumor growth inhibition in various types of cancer. We aim to explore the effect of onvansertib on MYC-driven medulloblastoma as a monotherapy or in combination with radiation.

METHODS

Crisper-Cas9 screen was used to discover essential genes for MB tumor growth. Microarray and immunohistochemistry on pediatric patient samples were performed to examine the expression of PLK1. The effect of onvansertib in vitro was measure by cell viability, colony-forming assays, extreme limiting dilution assay, and RNA-Seq. ALDH activity, cell-cycle distribution, and apoptosis were analyzed by flow cytometry. DNA damage was assessed by immunofluorescence staining. Medulloblastoma xenografts were generated to explore the monotherapy or radio-sensitizing effect.

RESULTS

PLK1 is overexpressed in Group 3 MB. The IC50 concentrations of onvansertib in Group 3 MB cell lines were in a low nanomolar range. Onvansertib reduced colony formation, cell proliferation, stem cell renewal and induced G2/M arrest in vitro. Moreover, onvansertib in combination with radiation increased DNA damage and apoptosis compared with radiation treatment alone. The combination radiotherapy resulted in marked tumor regression in xenografts.

CONCLUSIONS

These findings demonstrate the efficacy of a novel PLK1 inhibitor onvansertib in vitro and in xenografts of Group 3 MB, which suggests onvansertib is an effective strategy as monotherapy or in combination with radiotherapy in MB.

Interleukin-17 contributes to Ross River virus-induced arthritis and myositis

Arthritogenic alphaviruses are mosquito-borne viruses that are a major cause of infectious arthropathies worldwide, and recent outbreaks of chikungunya virus and Ross River virus (RRV) infections highlight the need for robust intervention strategies. Alphaviral arthritis can persist for months after the initial acute disease, and is mediated by cellular immune responses. A common strategy to limit inflammation and pathology is to dampen the overwhelming inflammatory responses by modulating proinflammatory cytokine pathways. Here, we investigate the contribution of interleukin-17 (IL-17), a cytokine involved in arthropathies such as rheumatoid arthritis, in the development RRV-induced arthritis and myositis. IL-17 was quantified in serum from RRV-infected patients, and mice were infected with RRV and joints and muscle tissues collected to analyse cellular infiltrates, tissue mRNA, cytokine expression, and joint and muscle histopathology. IL-17 expression was increased in musculoskeletal tissues and serum of RRV-infected mice and humans, respectively. IL-17–producing T cells and neutrophils contributed to the cellular infiltrate in the joint and muscle tissue during acute RRV disease in mice. Blockade of IL-17A/F using a monoclonal antibody (mAb) reduced disease severity in RRV-infected mice and led to decreased proinflammatory proteins, cellular infiltration in synovial tissues and cartilage damage, without affecting viral titers in inflamed tissues. IL-17A/F blockade triggered a shift in transcriptional profile of both leukocyte infiltrates and musculoskeletal stromal cells by downregulating proinflammatory genes. This study highlights a previously uncharacterized role for an effector cytokine in alphaviral pathology and points towards potential therapeutic benefit in targeting IL-17 to treat patients presenting with RRV-induced arthropathy.

Some viruses transmitted by mosquitoes cause painful and debilitating arthritis, which manifests both as an acute form shortly following infection, and a chronic form long after the initial symptoms have subsided. These viruses, termed arboviruses, are difficult to control and there are currently no specific treatments to alleviate the pain and loss of mobility. Arthritis caused by arboviruses shares similarities with a non-infectious, autoimmune form of arthritis called rheumatoid arthritis (RA). In RA, an immune molecule termed interleukin-17, or IL-17, has been shown to drive arthritis and treatments that target or block IL-17 are being developed to treat RA. Here, we asked whether arthritis caused by an arbovirus, Ross River virus (RRV), was also associated with elevated IL-17 in humans and mice. Disease severity in mice was associated with high IL-17 expression in the feet and muscle, and blocking IL-17 using an anti-IL-17 monoclonal antibody ameliorated disease in mice infected with RRV. Our study provides new information on a molecule that is implicated in arthritic inflammation, and could be targeted to treat disease caused by arthritogenic arboviruses.

Tumor suppressor PLK2 may serve as a biomarker in triple-negative breast cancer for improved response to PLK1 therapeutics

Polo-like kinase (PLK) family members play important roles in cell cycle regulation. The founding member PLK1 is oncogenic and preclinically validated as a cancer therapeutic target. Paradoxically, frequent loss of chromosome 5q11-35 which includes PLK2 is observed in basal-like breast cancer. In this study, we found that PLK2 was tumor suppressive in breast cancer, preferentially in basal-like and triple-negative breast cancer (TNBC) subtypes. Knockdown of PLK1 rescued phenotypes induced by PLK2-loss both in vitro and in vivo. We also demonstrated that PLK2 directly interacted with PLK1 at prometaphase through the kinase but not the polo-box domains of PLK2, suggesting PLK2 functioned at least partially through the interaction with PLK1. Furthermore, an improved treatment response was seen in both Plk2-deleted/low mouse preclinical and PDX TNBC models using the PLK1 inhibitor volasertib alone or in combination with carboplatin. Re-expression of PLK2 in an inducible PLK2-null mouse model reduced the therapeutic efficacy of volasertib. In summary, this study delineates the effects of chromosome 5q loss in TNBC that includes PLK2, the relationship between PLK2 and PLK1, and how this may render PLK2-deleted/low tumors more sensitive to PLK1 inhibition in combination with chemotherapy.

The dysregulation of microarray gene expression in cervical cancer is associated with overexpression of a unique messenger RNA signature

Background and Objectives:

Human papillomavirus (HPV) is the fourth most common cause of cervical cancer (CC). The aim of the present study was to investigate gene expression levels of previously identified transcriptional signatures for malignant and non-malignant CC.

Materials and Methods:

To validate of previously analyzed microarray gene expression data, we selected two hub genes (CDK1 and PLK1) and four differentially expressed mRNAs that were common in pre-malignant-normal and malignant-pre-malignant networks (SMS, NNT, UHMK1 and DEPDC1). To this purpose, the study included women diagnosed histologically with malignant CC (n=15), pre-malignant (n=15), and normal subjects (n=15). The expression of six host genes and viral E6/E7 genes were measured by quantitative Real-Time PCR.

Results:

The results showed higher expression of CDK1/PLK1 hub genes and SMS, NNT and UHMK1 genes in malignant CC group than non-malignant CC group and normal group. A positive correlation was observed between gene expression of viral E6/E7 oncogenes and UHMK1 gene.

Conclusion:

Dysregulation of several mRNA signatures are a common feature of CC and can be potentially used as diagnostic and prognostic biomarkers as well as can be applied to therapeutic targets for CC treatment.

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.

Targeted Polo-like Kinase Inhibition Combined With Aurora Kinase Inhibition in Pediatric Acute Leukemia Cells

BACKGROUND

Recent studies have shown that cell cycle events are tightly controlled by complex and shared activities of a select group of kinases. Among these, polo-like kinases (Plks) are regulatory mitotic proteins that are overexpressed in several types of cancer and are associated with poor prognosis.

MATERIALS AND METHODS

We have evaluated, in preclinical in vitro studies, the activity of a panel of Plk inhibitors against cell lines derived from refractory pediatric leukemia, as well as primary leukemia cells, in culture. Through in vitro growth inhibition studies, Western blot analysis for the expression and activation of key regulators of cell growth and survival and gene silencing studies, we specifically examined the ability of these agents to induce cytotoxicity through the activation of apoptosis and their capacity to interact and modulate the expression and phosphorylation of Aurora kinases.

RESULTS

Our findings show that the various Plk-1 inhibitors in development show potential utility for the treatment of pediatric leukemia and exhibit a wide range of phosphorylation and target modulatory capabilities. Finally, we provide evidence for a complex interregulatory relationship between Plk-1 and Aurora kinases enabling the identification of synergy and biologic correlates of drug combinations targeting the 2 distinct enzyme systems.

DISCUSSION

This information provide the rationale for the evaluation of Plk-1 as an effective target for therapeutics in refractory pediatric leukemia and indicate compensatory activities between Plk-1 and Aurora kinases, providing insight into some of the complex mechanisms involved in the process of cell division.

Molecular and enzoinformatics perspectives of targeting Polo-like kinase 1 in cancer therapy

Cancer is a disease that has been the focus of scientific research and discovery and continues to remain so. Polo-like kinases (PLKs) are basically serine/threonine kinase enzymes that control cell cycle from yeast to humans. PLK-1 stands for 'Polo-like kinase-1'. It is the most investigated protein among PLKs. It is crucial for intracellular processes, hence a 'hot' anticancer drug-target. Accelerating innovations in Enzoinformatics and associated molecular visualization tools have made it possible to literally perform a 'molecular level walk' traversing through and observing the minutest contours of the active site of relevant enzymes. PLK-1 as a protein consists of a kinase domain at the protein N-terminal and a Polo Box Domain (PBD) at the C-terminal connected by a short inter-domain linking region. PBD has two Polo-Boxes. PBD of PLK-1 gives the impression of "a small clamp sandwiched between two clips", where the two Polo Boxes are the 'clips' and the 'phosphopeptide' is the small 'clamp'. Broadly, two major sites of PLK-1 can be potential targets: one is the adenosine-5'-triphosphate (ATP)-binding site in the kinase domain and the other is PBD (more preferred due to specificity). Targeting PLK-1 RNA and the interaction of PLK-1 with a key binding partner can also be approached. However, the list of potent small molecule inhibitors targeting the PBD site of PLK-1 is still not long enough and needs due input from the scientific community. Recently, eminent scientists have proposed targeting the 'Y'-shaped pocket of PLK-1-PBD and encouraged design of ligands that should be able to concurrently bind to two or more modules of the 'Y' pocket. Hence, it is suggested that during molecular interaction analyses, particular focus should be kept on the moiety in each ligand/drug candidate which directly interacts with the amino acid residue(s) that belong(s) to one of the three binding modules which together create this Y-shaped cavity. This obviously includes (but it is not limited to) the 'shallow cleft'-forming residues i.e. Trp414, H538 and K540, as significance of these binding residues has been consistently highlighted by many studies. The present article attempts to give a concise yet critically updated overview of targeting PLK-1 for cancer therapy.

The methyltransferase SETD6 regulates Mitotic progression through PLK1 methylation

Lysine methylation, catalyzed by protein lysine methyltransferases (PKMTs), is a key player in regulating intracellular signaling pathways. However, the role of PKMTs and the methylation of nonhistone proteins during the cell cycle are largely unexplored. In a recent proteomic screen, we identified that the PKMT SETD6 methylates PLK1-a key regulator of mitosis and highly expressed in tumor cells. In this study, we provide evidence that SETD6 is involved in cell cycle regulation. SETD6-deficient cells were observed to progress faster through the different mitotic steps toward the cytokinesis stage. Mechanistically, we found that during mitosis SETD6 binds and methylates PLK1 on two lysine residues: K209 and K413. Lack of methylation of these two residues results in increased kinase activity of PLK1, leading to accelerated mitosis and faster cellular proliferation, similarly to SETD6-deficient cells. Taken together, our findings reveal a role for SETD6 in regulating mitotic progression, suggesting a pathway through which SETD6 methylation activity contributes to normal mitotic pace.

High LIN28A and PLK4 co‑expression is associated with poor prognosis in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is the most lethal gynecological malignancy. LIN28 homolog A (LIN28A) is a RNA‑binding protein, which serves a fundamental role in cell development and pluripotency. Polo‑like kinase 4 (PLK4) is a member of the polo‑like kinase family, which primarily takes part in the mitotic regulation. Overexpression of LIN28A has been demonstrated in ovarian cancer; however, the expression of PLK4 and the correlation between the expression of LIN28A and PLK4 in EOC has not been discussed. In the present study, the mRNA and protein levels of LIN28A and PLK4 were evaluated by reverse transcription‑quantitative polymerase chain reaction and immunohistochemistry in ovarian tissues of patients. Results demonstrated significantly increased expression in EOC compared with benign epithelial ovarian tumors. High expression of LIN28A and PLK4 was detected at the advanced pathological stage. Furthermore, PLK4 expression was positively correlated with LIN28A (r=0.555; P=0.039). The median survival analysis of patients with EOC with LIN28A and PLK4 double positive expression was 14 months, compared with 30 months in single positive and 60 months in double negative patients by Kaplan‑Meier analysis (P<0.05). The expressions of LIN28A and PLK4 was elevated in different EOC cell lines compared to with a normal ovarian cell line. The 293T cells transfected with LIN28A plus a PLK4 plasmid were the fastest‑growing group. These results suggest that co‑expression of LIN28A and PLK4 may be associated with poor prognosis of EOC and could serve as promising prognostic biomarkers and therapeutic targets in EOC. LIN28A and PLK4 may be used along with traditional morphological and clinical characteristics for predicting prognosis.

New Cell Cycle Inhibitors Target Aneuploidy in Cancer Therapy

Aneuploidy is a hallmark of cancer. Defects in chromosome segregation result in aneuploidy. Multiple pathways are engaged in this process, including errors in kinetochore-microtubule attachments, supernumerary centrosomes, spindle assembly checkpoint (SAC) defects, and chromosome cohesion defects. Although aneuploidy provides an adaptation and proliferative advantage in affected cells, excessive aneuploidy beyond a critical level can be lethal to cancer cells. Given this, enhanced chromosome missegregation is hypothesized to limit survival of aneuploid cancer cells, especially when compared to diploid cells. Based on this concept, proteins and pathways engaged in chromosome segregation are being exploited as candidate therapeutic targets for aneuploid cancers. Agents that induce chromosome missegregation and aneuploidy now exist, including SAC inhibitors, those that alter centrosome fidelity and others that are under active study in preclinical and clinical contexts. This review explores the therapeutic potentials of such new agents, including the benefits of combining them with other antineoplastic agents.

Engineering Human Epidermal Growth Receptor 2-Targeting Hepatitis B Virus Core Nanoparticles for siRNA Delivery in Vitro and in Vivo

Hepatitis B virus core (HBc) particles acquire the capacity to disassemble and reassemble in a controlled manner, allowing entrapment and delivery of drugs and macromolecules to cells. HBc particles are made of 180-240 copies of 21 kDa protein monomers, assembled into 30-34 nm diameter icosahedral particles. In this study, we aimed at formulating HBc particles for the delivery of siRNA for gene silencing in vitro and in vivo. We have previously reported recombinant HBc particles expressing Z_HER2 affibodies, specifically targeting human epidermal growth receptor 2 (HER2)-expressing cancer cells (Z_HER2-ΔHBc). siRNA was encapsulated within the Z_HER2-ΔHBc particles following disassembly and reassembly. The Z_HER2-ΔHBc-siRNA hybrids were able to secure the encapsulated siRNA from serum and nucleases in vitro. Enhanced siRNA uptake in HER2-expressing cancer cells treated with Z_HER2-ΔHBc-siRNA hybrids was observed compared to the nontargeted HBc-siRNA hybrids in a time- and dose-dependent manner. A successful in vitro polo-like kinase 1 (PLK1) gene knockdown was demonstrated in cancer cells treated with Z_HER2-ΔHBc-siPLK1 hybrids, to levels comparable to commercial transfecting reagents. Interestingly, Z_HER2-ΔHBc particles exhibit intrinsic capability of reducing the solid tumor mass, independent of siPLK1 therapy, in an intraperitoneal tumor model following intraperitoneal injection.

Targeting Polo-like Kinase 1 by a Novel Pyrrole-Imidazole Polyamide-Hoechst Conjugate Suppresses Tumor Growth In Vivo

The serine/threonine kinase Polo-like kinase 1 (Plk1) plays a pivotal role in cell proliferation and has been validated as a promising anticancer drug target. However, very limited success has been achieved in clinical applications using existing Plk1 inhibitors, due to lack of sufficient specificity toward Plk1. To develop a novel Plk1 inhibitor with high selectivity and efficacy, we designed and synthesized a pyrrole-imidazole polyamide-Hoechst conjugate, PIP3, targeted to specific DNA sequence in the PLK1 promoter. PIP3 could specifically inhibit the cell cycle-regulated Plk1 expression and consequently retard tumor cell growth. Cancer cells treated with PIP3 exhibited severe mitotic defects and increased apoptosis, whereas normal cells were not affected by PIP3 treatment. Furthermore, subcutaneous injection of PIP3 into mice bearing human cancer xenografts induced significant tumor growth suppression with low host toxicity. Therefore, PIP3 exhibits the potential as an effective agent for targeted cancer therapy. Mol Cancer Ther; 17(5); 988-1002. ©2018 AACR.

BI2536, a potent and selective inhibitor of polo-like kinase 1, in combination with cisplatin exerts synergistic effects on gastric cancer cells

BI2536 is a highly selective and potent inhibitor of polo-like kinase 1 (PLK1). In this study, we aimed to determine whether BI2536 and cisplatin can synergistically inhibit the malignant behavior of gastric cancer cells. For this purpose, the expression of PLK1 in gastric cancer cells was determined. The effects of BI2536, cisplatin, and the combination of BI2536 and cisplatin on gastric cancer cell viability, invasion, cell cycle arrest and apoptosis were assessed. Furthermore, the expression of cell cycle-regulated proteins was examined. Moreover, the differentially expressed proteins between the SGC-7901 and SGC-7901/DDP (cisplatin-resistant) cells, and the enriched signaling pathways were analyzed by protein pathway array following treatment with BI2536 (IC50) for 48 h. Our results revealed that PLK1 was upregulated in the SGC-7901/DDP (cisplatin-resistant) gastric cancer cells compared with the SGC-7901 cells. BI2536 enhanced the inhibitory effect of cisplatin on SGC-7901 cell viability and invasion. BI2536 induced G2/M arrest in SGC-7901 and SGC-7901/DDP cells. BI2536 promoted cisplatin-induced gastric cancer SGC-7901/DDP cell apoptosis. It also induced the differential expression of 68 proteins between the SGC-7901 and SGC-7901/DDP cells, and these differentially expressed proteins were involved in a number of cellular functions and signaling pathways, such as cell death, cell development, tumorigenesis, the cell cycle, DNA duplication/recombination/repair, cellular movement, and the Wnt/β-catenin and mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK)/ribosomal S6 kinase 1 (RSK1) signaling pathways. On the whole, our findings suggest that BI2536 and cisplatin synergistically inhibit the malignant behavior of SGC-7901/DDP (cisplatin‑resistant) gastric cancer cells.

Kinase-targeted cancer therapies: progress, challenges and future directions

The human genome encodes 538 protein kinases that transfer a γ-phosphate group from ATP to serine, threonine, or tyrosine residues. Many of these kinases are associated with human cancer initiation and progression. The recent development of small-molecule kinase inhibitors for the treatment of diverse types of cancer has proven successful in clinical therapy. Significantly, protein kinases are the second most targeted group of drug targets, after the G-protein-coupled receptors. Since the development of the first protein kinase inhibitor, in the early 1980s, 37 kinase inhibitors have received FDA approval for treatment of malignancies such as breast and lung cancer. Furthermore, about 150 kinase-targeted drugs are in clinical phase trials, and many kinase-specific inhibitors are in the preclinical stage of drug development. Nevertheless, many factors confound the clinical efficacy of these molecules. Specific tumor genetics, tumor microenvironment, drug resistance, and pharmacogenomics determine how useful a compound will be in the treatment of a given cancer. This review provides an overview of kinase-targeted drug discovery and development in relation to oncology and highlights the challenges and future potential for kinase-targeted cancer therapies.

Colorectal cancer cells require glycogen synthase kinase-3β for sustaining mitosis via translocated promoter region (TPR)-dynein interaction

Glycogen synthase kinase (GSK) 3β, which mediates fundamental cellular signaling pathways, has emerged as a potential therapeutic target for many types of cancer including colorectal cancer (CRC). During mitosis, GSK3β localizes in mitotic spindles and centrosomes, however its function is largely unknown. We previously demonstrated that translocated promoter region (TPR, a nuclear pore component) and dynein (a molecular motor) cooperatively contribute to mitotic spindle formation. Such knowledge encouraged us to investigate putative functional interactions among GSK3β, TPR, and dynein in the mitotic machinery of CRC cells. Here, we show that inhibition of GSK3β attenuated proliferation, induced cell cycle arrest at G2/M phase, and increased apoptosis of CRC cells. Morphologically, GSK3β inhibition disrupted chromosome segregation, mitotic spindle assembly, and centrosome maturation during mitosis, ultimately resulting in mitotic cell death. These changes in CRC cells were associated with decreased expression of TPR and dynein, as well as disruption of their functional colocalization with GSK3β in mitotic spindles and centrosomes. Clinically, we showed that TPR expression was increased in CRC databases and primary tumors of CRC patients. Furthermore, TPR expression in SW480 cells xenografted into mice was reduced following treatment with GSK3β inhibitors. Together, these results indicate that GSK3β sustains steady mitotic processes for proliferation of CRC cells via interaction with TPR and dynein, thereby suggesting that the therapeutic effect of GSK3β inhibition depends on induction of mitotic catastrophe in CRC cells.

PLK1 protects against sepsis-induced intestinal barrier dysfunction

Sepsis and sepsis-associated intestinal barrier dysfunction are common in intensive care units, with high mortality. The aim of this study is to investigate whether Polo-like kinase 1 (PLK1) ameliorates sepsis-induced intestinal barrier dysfunction in the intestinal epithelium. The mouse intestinal barrier was disrupted after Lipopolysaccharide (LPS) injection due to intestinal epithelial cell apoptosis and proliferation inhibition, accompanied by decreased PLK1. In HT-29 intestinal epithelial cells, LPS stimulation induced cell apoptosis and inhibited cell proliferation. Overexpression of PLK1 partly rescued the apoptosis and proliferation inhibition in HT29 cells caused by LPS. Finally, LPS stimulation promoted the reduction of PLK1, resulting in apoptosis and proliferation inhibition in intestinal epithelial cells, disrupting the intestinal epithelial barrier. These findings indicate that PLK1 might be a potential therapeutic target for the treatment of sepsis-induced intestinal barrier dysfunction.

Bowhead: Bayesian modelling of cell velocity during concerted cell migration

Cell migration is a central biological process that requires fine coordination of molecular events in time and space. A deregulation of the migratory phenotype is also associated with pathological conditions including cancer where cell motility has a causal role in tumor spreading and metastasis formation. Thus cell migration is of critical and strategic importance across the complex disease spectrum as well as for the basic understanding of cell phenotype. Experimental studies of the migration of cells in monolayers are often conducted with 'wound healing' assays. Analysis of these assays has traditionally relied on how the wound area changes over time. However this method does not take into account the shape of the wound. Given the many options for creating a wound healing assay and the fact that wound shape invariably changes as cells migrate this is a significant flaw. Here we present a novel software package for analyzing concerted cell velocity in wound healing assays. Our method encompasses a wound detection algorithm based on cell confluency thresholding and employs a Bayesian approach in order to estimate concerted cell velocity with an associated likelihood. We have applied this method to study the effect of siRNA knockdown on the migration of a breast cancer cell line and demonstrate that cell velocity can track wound healing independently of wound shape and provides a more robust quantification with significantly higher signal to noise ratios than conventional analyses of wound area. The software presented here will enable other researchers in any field of cell biology to quantitatively analyze and track live cell migratory processes and is therefore expected to have a significant impact on the study of cell migration, including cancer relevant processes. Installation instructions, documentation and source code can be found at http://bowhead.lindinglab.science licensed under GPLv3.

Improved therapy for neuroblastoma using a combination approach: superior efficacy with vismodegib and topotecan

Aberrant activation/expression of pathways/molecules including NF-kB, mTOR, hedgehog and polo-like-kinase-1 (PLK1) are correlated with poor-prognosis neuroblastoma. Therefore, to identify a most efficacious treatment for neuroblastoma, we investigated the efficacy of NF-kB/mTOR dual-inhibitor 13-197, hedgehog inhibitor vismodegib and PLK1 inhibitor BI2536 alone or combined with topotecan against high-risk neuroblastoma. The in vitro efficacy of the inhibitors alone or combined with topotecan on cell growth/apoptosis and molecular mechanism(s) were investigated. Results showed that as single agents 13-197, BI2536 and vismodegib significantly decreased neuroblastoma cell growth and induced apoptosis by targeting associated pathways/molecules. In combination with topotecan, 13-197 did not show significant additive/synergistic effects against neuroblastoma. However, BI2536 or vismodegib further significantly decreased neuroblastoma cell growth/survival. These results clearly showed that vismodegib combination with topotecan was synergistic and more efficacious compared with BI2536 in combination. Together, in vitro data demonstrated that vismodegib was most efficacious in potentiating topotecan-induced antineuroblastoma effects. Therefore, we tested the combined efficacy of vismodegib and topotecan against neuroblastoma in vivo using NSG mice. This resulted in significantly (p<0.001) reduced tumor growth and increased survival of mice. Together, the combination of vismodegib and topotecan showed a significant enhanced antineuroblastoma efficacy by targeting associated pathways/molecules which warrants further preclinical evaluation for translation to the clinic.

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.

FoxM1: Repurposing an oncogene as a biomarker

The past few decades have witnessed a tremendous progress in understanding the biology of cancer, which has led to more comprehensive approaches for global gene expression profiling and genome-wide analysis. This has helped to determine more sophisticated prognostic and predictive signature markers for the prompt diagnosis and precise screening of cancer patients. In the search for novel biomarkers, there has been increased interest in FoxM1, an extensively studied transcription factor that encompasses most of the hallmarks of malignancy. Considering the attractive potential of this multifarious oncogene, FoxM1 has emerged as an important molecule implicated in initiation, development and progression of cancer. Bolstered with the skill to maneuver the proliferation signals, FoxM1 bestows resistance to contemporary anti-cancer therapy as well. This review sheds light on the large body of literature that has accumulated in recent years that implies that FoxM1 neoplastic functions can be used as a novel predictive, prognostic and therapeutic marker for different cancers. This assessment also highlights the key features of FoxM1 that can be effectively harnessed to establish FoxM1 as a strong biomarker in diagnosis and treatment of cancer.

A Critical Review on the Effect of Docosahexaenoic Acid (DHA) on Cancer Cell Cycle Progression

Globally, there were 14.1 million new cancer diagnoses and 8.2 million cancer deaths in 2012. For many cancers, conventional therapies are limited in their successes and an improved understanding of disease progression is needed in conjunction with exploration of alternative therapies. The long chain polyunsaturated fatty acid, docosahexaenoic acid (DHA), has been shown to enhance many cellular responses that reduce cancer cell viability and decrease proliferation both in vitro and in vivo. A small number of studies suggest that DHA improves chemotherapy outcomes in cancer patients. It is readily incorporated into cancer cell membranes and, as a result there has been considerable research regarding cell membrane initiated events. For example, DHA has been shown to mediate the induction of apoptosis/reduction of proliferation in vitro and in vivo. However, there is limited research into the effect of DHA on cell cycle regulation in cancer cells and the mechanism(s) by which DHA acts are not fully understood. The purpose of the current review is to provide a critical examination of the literature investigating the ability of DHA to stall progression during different cell cycle phases in cancer cells, as well as the consequences that these changes may have on tumour growth, independently and in conjunction with chemotherapy.

The therapeutic potential of cell cycle targeting in multiple myeloma

Proper cell cycle progression through the interphase and mitosis is regulated by coordinated activation of important cell cycle proteins (including cyclin-dependent kinases and mitotic kinases) and several checkpoint pathways. Aberrant activity of these cell cycle proteins and checkpoint pathways results in deregulation of cell cycle progression, which is one of the key hallmarks of cancer. Consequently, intensive research on targeting these cell cycle regulatory proteins identified several candidate small molecule inhibitors that are able to induce cell cycle arrest and even apoptosis in cancer cells. Importantly, several of these cell cycle regulatory proteins have also been proposed as therapeutic targets in the plasma cell malignancy multiple myeloma (MM). Despite the enormous progress in the treatment of MM the past 5 years, MM still remains most often incurable due to the development of drug resistance. Deregulated expression of the cyclins D is observed in virtually all myeloma patients, emphasizing the potential therapeutic interest of cyclin-dependent kinase inhibitors in MM. Furthermore, other targets have also been identified in MM, such as microtubules, kinesin motor proteins, aurora kinases, polo-like kinases and the anaphase promoting complex/cyclosome. This review will provide an overview of the cell cycle proteins and checkpoint pathways deregulated in MM and discuss the therapeutic potential of targeting proteins or protein complexes involved in cell cycle control in MM.

Targeted Treatment of Metastatic Breast Cancer by PLK1 siRNA Delivered by an Antioxidant Nanoparticle Platform

Metastatic breast cancer is developed in about 20% to 30% of newly diagnosed patients with early-stage breast cancer despite treatments. Herein, we report a novel nanoparticle platform with intrinsic antimetastatic properties for the targeted delivery of Polo-like kinase 1 siRNA (siPLK1). We first evaluated it in a triple-negative breast cancer (TNBC) model, which shows high metastatic potential. PLK1 was identified as the top therapeutic target for TNBC cells and tumor-initiating cells in a kinome-wide screen. The platform consists of a 50-nm mesoporous silica nanoparticle (MSNP) core coated layer-by-layer with bioreducible cross-linked PEI and PEG polymers, conjugated with an antibody for selective uptake into cancer cells. siRNA is loaded last and fully protected under the PEG layer from blood enzymatic degradation. The material has net neutral charge and low nonspecific cytotoxicity. We have also shown for the first time that the MSNP itself inhibited cancer migration and invasion in TNBC cells owing to its ROS- and NOX4-modulating properties. In vivo, siPLK1 nanoconstructs (six doses of 0.5 mg/kg) knocked down about 80% of human PLK1 mRNA expression in metastatic breast cancer cells residing in mouse lungs and reduced tumor incidence and burden in lungs and other organs of an experimental metastasis mouse model. Long-term treatment significantly delayed the onset of death in mice and improved the overall survival. The platform capable of simultaneously inhibiting the proliferative and metastatic hallmarks of cancer progression is unique and has great therapeutic potential to also target other metastatic cancers beyond TNBC. Mol Cancer Ther; 16(4); 763-72. ©2017 AACR.

PLK1, A Potential Target for Cancer Therapy

Polo-like kinase 1 (PLK1) plays an important role in the initiation, maintenance, and completion of mitosis. Dysfunction of PLK1 may promote cancerous transformation and drive its progression. PLK1 overexpression has been found in a variety of human cancers and was associated with poor prognoses in cancers. Many studies have showed that inhibition of PLK1 could lead to death of cancer cells by interfering with multiple stages of mitosis. Thus, PLK1 is expected to be a potential target for cancer therapy. In this article, we examined PLK1’s structural characteristics, its regulatory roles in cell mitosis, PLK1 expression, and its association with survival prognoses of cancer patients in a wide variety of cancer types, PLK1 interaction networks, and PLK1 inhibitors under investigation. Finally, we discussed the key issues in the development of PLK1-targeted cancer therapy.

Maintaining Genome Stability in Defiance of Mitotic DNA Damage

The implementation of decisions affecting cell viability and proliferation is based on prompt detection of the issue to be addressed, formulation and transmission of a correct set of instructions and fidelity in the execution of orders. While the first and the last are purely mechanical processes relying on the faithful functioning of single proteins or macromolecular complexes (sensors and effectors), information is the real cue, with signal amplitude, duration, and frequency ultimately determining the type of response. The cellular response to DNA damage is no exception to the rule. In this review article we focus on DNA damage responses in G2 and Mitosis. First, we set the stage describing mitosis and the machineries in charge of assembling the apparatus responsible for chromosome alignment and segregation as well as the inputs that control its function (checkpoints). Next, we examine the type of issues that a cell approaching mitosis might face, presenting the impact of post-translational modifications (PTMs) on the correct and timely functioning of pathways correcting errors or damage before chromosome segregation. We conclude this essay with a perspective on the current status of mitotic signaling pathway inhibitors and their potential use in cancer therapy.

Augmented expression of Polo-like kinase 1 is a strong predictor of shorter cancer-specific overall survival in early stage breast cancer at 15-year follow-up

Polo-like kinase 1 (PLK1) is a serine-threonine kinase that plays a crucial role in the regulation of cell division. In addition, it acts as a modulator of the DNA damage response and as a novel factor in the maintenance of genome stability during DNA replication. The present study aimed to reveal the associations between PLK1 expression and clinicopathological features of patients with breast cancer (BC), particularly patient survival at 5-, 10- and 15-year follow-up. PLK1 expression was evaluated immunohistochemically in routine diagnostic tissue specimens from 83 patients treated radically for stage II BC. Kaplan-Meier analysis revealed a correlation between PLK1 overexpression and long-term survival. High PLK1 immunoreactivity was associated with shorter cancer-specific overall survival (CSOS) and disease-free survival (P=0.00001 and 0.00013, respectively). Multivariate analysis confirmed the negative prognostic significance of PLK1 overexpression for CSOS in all 83 patients (P=0.00030). Furthermore, analogous correlations were observed in both subgroups with and without nodal metastases (P=0.01400 and 0.01200, respectively). The present results indicate that PLK1 expression has a prognostic role in early BC. Immunohistochemical assessment of PLK1 reactivity may potentially become a qualifier for inclusion of PLK1 inhibitor therapy.

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

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

ER maleate is a novel anticancer agent in oral cancer: implications for cancer therapy

ER maleate [10-(3-Aminopropyl)-3, 4-dimethyl-9(10H)-acridinone maleate] identified in a kinome screen was investigated as a novel anticancer agent for oral squamous cell carcinoma (OSCC). Our aim was to demonstrate its anticancer effects, identify putative molecular targets and determine their clinical relevance and investigate its chemosensitization potential for platinum drugs to aid in OSCC management. Biologic effects of ER maleate were determined using oral cancer cell lines in vitro and oral tumor xenografts in vivo. mRNA profiling, real time PCR and western blot revealed ER maleate modulated the expression of polo-like kinase 1 (PLK1) and spleen tyrosine kinase (Syk). Their clinical significance was determined in oral SCC patients by immunohistochemistry and correlated with prognosis by Kaplan-Meier survival and multivariate Cox regression analyses. ER maleate induced cell apoptosis, inhibited proliferation, colony formation, migration and invasion in oral cancer cells. Imagestream analysis revealed cell cycle arrest in G2/M phase and increased polyploidy, unravelling deregulation of cell division and cell death. Mechanistically, ER maleate decreased expression of PLK1 and Syk, induced cleavage of PARP, caspase9 and caspase3, and increased chemosensitivity to carboplatin; significantly suppressed tumor growth and increased antitumor activity of carboplatin in tumor xenografts. ER maleate treated tumor xenografts showed reduced PLK1 and Syk expression. Clinical investigations revealed overexpression of PLK1 and Syk in oral SCC patients that correlated with disease prognosis. Our in vitro and in vivo findings provide a strong rationale for pre-clinical efficacy of ER maleate as a novel anticancer agent and chemosensitizer of platinum drugs for OSCC.

Targeting Mitosis in Cancer: Emerging Strategies

The cell cycle is an evolutionarily conserved process necessary for mammalian cell growth and development. Because cell-cycle aberrations are a hallmark of cancer, this process has been the target of anti-cancer therapeutics for decades. However, despite numerous clinical trials, cell-cycle-targeting agents have generally failed in the clinic. This review briefly examines past cell-cycle-targeted therapeutics and outlines how experience with these agents has provided valuable insight to refine and improve anti-mitotic strategies. An overview of emerging anti-mitotic approaches with promising pre-clinical results is provided, and the concept of exploiting the genomic instability of tumor cells through therapeutic inhibition of mitotic checkpoints is discussed. We believe this strategy has a high likelihood of success given its potential to enhance therapeutic index by targeting tumor-specific vulnerabilities. This reasoning stimulated our development of novel inhibitors targeting the critical regulators of genomic stability and the mitotic checkpoint: AURKA, PLK4, and Mps1/TTK.

Polo-like kinase inhibitors in hematologic malignancies

Polo-like kinases (Plk) are key regulators of the cell cycle and multiple aspects of mitosis. Two agents that inhibit the Plk signaling pathway have shown promising activity in patients with hematologic malignancies and are currently in phase III trials. Volasertib is a Plk inhibitor under evaluation combined with low-dose cytarabine in older patients with acute myeloid leukemia (AML) ineligible for intensive induction therapy. Rigosertib, a dual inhibitor of the Plk and phosphatidylinositol 3-kinase pathways, is under investigation in patients with myelodysplastic syndrome (MDS) who have failed azacitidine or decitabine treatment. The prognosis for patients with AML, who are ineligible for intensive induction therapy, and for those with MDS refractory/relapsed after a hypomethylating agent, remains poor. Novel approaches, such as Plk inhibitors, are urgently needed for these patients. Here, we provide a comprehensive overview of the current state of development of Plk inhibitors for the treatment of hematologic malignancies.

Volasertib Versus Chemotherapy in Platinum-Resistant or -Refractory Ovarian Cancer: A Randomized Phase II Groupe des Investigateurs Nationaux pour l'Etude des Cancers de l'Ovaire Study

PURPOSE

Volasertib is a potent and selective cell-cycle kinase inhibitor that induces mitotic arrest and apoptosis by targeting Polo-like kinase. This phase II trial evaluated volasertib or single-agent chemotherapy in patients with platinum-resistant or -refractory ovarian cancer who experienced failure after treatment with two or three therapy lines.

PATIENTS AND METHODS

Patients were randomly assigned to receive either volasertib 300 mg by intravenous infusion every 3 weeks or an investigator's choice of single-agent, nonplatinum, cytotoxic chemotherapy. The primary end point was 24-week disease control rate. Secondary end points included best overall response, progression-free survival (PFS), safety, quality of life, and exploratory biomarker analyses.

RESULTS

Of the 109 patients receiving treatment, 54 received volasertib and 55 received chemotherapy; demographics were well balanced. The 24-week disease control rates for volasertib and chemotherapy were 30.6% (95% CI, 18.0% to 43.2%) and 43.1% (95% CI, 29.6% to 56.7%), respectively, with partial responses in seven (13.0%) and eight (14.5%) patients, respectively. Median PFS was 13.1 weeks and 20.6 weeks for volasertib and chemotherapy (hazard ratio, 1.01; 95% CI, 0.66 to 1.53). Six patients (11%) receiving volasertib achieved PFS fore more than 1 year, whereas no patient receiving chemotherapy achieved PFS greater than 1 year. No relationship between the expression of the biomarkers tested and their response was determined. Patients treated with volasertib experienced more grade 3 and 4 drug-related hematologic adverse events (AEs) and fewer nonhematologic AEs than did patients receiving chemotherapy. Discontinuation resulting from AEs occurred in seven (13.0%) and 15 (27.3%) patients in the volasertib and chemotherapy arms, respectively. Both arms showed similar effects on quality of life.

CONCLUSION

Single-agent volasertib showed antitumor activity in patients with ovarian cancer. AEs in patients receiving volasertib were mainly hematologic and manageable.

In silico identification of putative bifunctional Plk1 inhibitors by integrative virtual screening and structural dynamics approach

Polo like kinase (Plk1) is a master regulator of cell cycle and considered as next generation antimitotic target in human. As Plk1 predominantly expresses in the dividing cells with a much higher expression in cancerous cells, it serves as a discriminative target for cancer therapeutics. Here we implied a novel and promising integrative strategy to identify "bifunctional" Plk1 inhibitors that compete simultaneously with ATP and substrate for their binding sites. We integrated structure-based virtual screening (SBVS) and molecular dynamics simulations with emphasis on unique structural properties of Plk1. Through screening of 20,000 compounds, nearly ~2000 hits were enriched and subjected to SBVS against ATP and substrate binding sites of Plk1. Subsequently, on the basis of their binding abilities to Plk1 kinase and polo box domains, filtration of candidate hits resulted in the isolation of 26 compounds. By exclusion of close analogs or isomers, 10 unique compounds were selected for detailed study. A representative compound was subjected to molecular dynamics simulation assay to have deep structural insights and to gauge critical structural crunch for inhibitor binding against kinase and polo box domains. Our integrative approach may complement high-throughput screening and identify bifunctional Plk1 inhibitors that may contribute in selective targeting of Plk1 to elicit desired biological process.

Human ATP-Binding Cassette Transporter ABCB1 Confers Resistance to Volasertib (BI 6727), a Selective Inhibitor of Polo-like Kinase 1

The overexpression of the serine/threonine specific polo-like kinase 1 (Plk1) is associated with poor prognosis in many types of cancer. Consequently, Plk1 has emerged as a valid therapeutic target for anticancer drug design. Volasertib is a potent inhibitor of Plk1 that inhibits the proliferation of multiple human cancer cell lines by promoting cell cycle arrest at nanomolar concentrations. However, the risk of developing drug resistance, which is often associated with the overexpression of the ATP-binding cassette (ABC) transporter ABCB1 (P-glycoprotein), can present a therapeutic challenge for volasertib and many other therapeutic drugs. Although volasertib is highly effective against the proliferation of numerous cancer cell lines, we found that the overexpression of ABCB1 in cancer cells leads to cellular resistance to volasertib and reduces the level of volasertib-stimulated G2/M cell cycle arrest and subsequent onset of apoptosis. Furthermore, we demonstrate that volasertib competitively inhibits the function of ABCB1 and stimulates the basal ATPase activity of ABCB1 in a concentration-dependent manner, which is consistent with substrate transport by ABCB1. More importantly, we discovered that the coadministration of an inhibitor or drug substrate of ABCB1 restored the anticancer activity of volasertib in ABCB1-overexpressing cancer cells. In conclusion, the results of our study reveal that ABCB1 negatively affects the efficacy of volasertib and supports its combination with a modulator of ABCB1 to improve clinical responses.

Large-scale RNA-Seq Transcriptome Analysis of 4043 Cancers and 548 Normal Tissue Controls across 12 TCGA Cancer Types

The Cancer Genome Atlas (TCGA) has accrued RNA-Seq-based transcriptome data for more than 4000 cancer tissue samples across 12 cancer types, translating these data into biological insights remains a major challenge. We analyzed and compared the transcriptomes of 4043 cancer and 548 normal tissue samples from 21 TCGA cancer types, and created a comprehensive catalog of gene expression alterations for each cancer type. By clustering genes into co-regulated gene sets, we identified seven cross-cancer gene signatures altered across a diverse panel of primary human cancer samples. A 14-gene signature extracted from these seven cross-cancer gene signatures precisely differentiated between cancerous and normal samples, the predictive accuracy of leave-one-out cross-validation (LOOCV) were 92.04%, 96.23%, 91.76%, 90.05%, 88.17%, 94.29%, and 99.10% for BLCA, BRCA, COAD, HNSC, LIHC, LUAD, and LUSC, respectively. A lung cancer-specific gene signature, containing SFTPA1 and SFTPA2 genes, accurately distinguished lung cancer from other cancer samples, the predictive accuracy of LOOCV for TCGA and GSE5364 data were 95.68% and 100%, respectively. These gene signatures provide rich insights into the transcriptional programs that trigger tumorigenesis and metastasis, and many genes in the signature gene panels may be of significant value to the diagnosis and treatment of cancer.

Volasertib for AML: clinical use and patient consideration

Acute myeloid leukemia (AML) is a disease diagnosed mostly in patients >65 years of age. Despite its heterogeneous nature, the different types of AMLs are still managed by standard induction chemotherapy for those who can tolerate it in the beginning. For the elderly and infirm patients, however, this approach leads to unacceptably high induction mortality rate. This article reviews past and current efforts searching for low-intensiveness treatments for the elderly and infirm patients who cannot tolerate the standard induction regimen. Volasertib, currently in Phase III clinical trials in combination with cytarabine, is reviewed as a promising agent for this patient population with AML, from the viewpoints of potential compliance and efficacy.

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

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

Therapeutic opportunities within the DNA damage response

The DNA damage response (DDR) is essential for maintaining the genomic integrity of the cell, and its disruption is one of the hallmarks of cancer. Classically, defects in the DDR have been exploited therapeutically in the treatment of cancer with radiation therapies or genotoxic chemotherapies. More recently, protein components of the DDR systems have been identified as promising avenues for targeted cancer therapeutics. Here, we present an in-depth analysis of the function, role in cancer and therapeutic potential of 450 expert-curated human DDR genes. We discuss the DDR drugs that have been approved by the US Food and Drug Administration (FDA) or that are under clinical investigation. We examine large-scale genomic and expression data for 15 cancers to identify deregulated components of the DDR, and we apply systematic computational analysis to identify DDR proteins that are amenable to modulation by small molecules, highlighting potential novel therapeutic targets.

BI 6727 and GSK461364 suppress growth and radiosensitize osteosarcoma cells, but show limited cytotoxic effects when combined with conventional treatments

Polo-like kinase 1 (PLK1), a key regulator of mitosis, is often overexpressed in childhood cancers and is associated with poor prognosis. Previous reports have shown that inhibition of PLK1 might serve as a promising anticancer treatment for osteosarcoma. In this study, we tested the second-generation PLK1 inhibitors BI 6727 and GSK461364 in HOS and MG-63 cell lines, both as a single agent and in combination with methotrexate, cisplatin, vinblastine, doxorubicin, or ionizing radiation. Both PLK1 inhibitors worked equally in terms of cell growth arrest, apoptosis induction, and radiosensitization. Combining BI 6727 or GSK461364 with conventional treatments, however, showed trivial synergistic antitumor effects in vitro. Our results reinforce the potential use of PLK1 inhibitors for a pharmacologic intervention in osteosarcoma, although their applicability in polychemotherapeutic regimens deserves further investigation.