Polo-like kinase 2 is a mediator of hedgehog survival signaling in cholangiocarcinoma

BI6727 and GSK461364A, potent PLK1 inhibitors induce G2/M arrest and apoptosis against cholangiocarcinoma cell lines

Polo-like kinase 1 (PLK1) is an essential mitotic checkpoint protein that plays a key role in cell cycle division. Overexpression of PLK1 has been associated with poor prognosis in various cancers. Cholangiocarcinoma (CCA) is a lethal bile duct cancer and the current treatments in inoperable patients have not been satisfactory. In order to develop novel targeted therapies, we investigated the efficacy of BI6727 (volasertib) and GSK461364A, polo-like kinase 1 (PLK1) inhibitors in KKU-100 and KKU-213A CCA cell lines. PLK1 expression was significantly up-regulated in CCA cases compared with normal tissues based on the results derived from GEPIA. Western blot results exhibited PLK1 protein expression in both CCA cell lines. Molecular dynamics simulations and free energy calculations based on MM/GBSA method revealed that BI6727-PLK1 and GSK461364A-PLK1 complexes were stable in an aqueous environment, and their complexation was mainly driven by Van der Waals interaction. BI6727 and GSK461364A clearly suppressed CCA cell proliferation and induced G2/M arrest, accompanied with upregulation of cyclin B1 and phosphorylated Histone H3 at Ser10 (pS10H3), specific markers of mitosis. Furthermore, both compounds triggered mitotic catastrophe followed by cell apoptosis via activation of PARP and Caspase 3, as well as downregulation of Mcl-1 anti-apoptotic protein in both CCA cell lines. In conclusion, pharmacologic PLK1 inhibition by BI6727 and GSK461364A blocked survival of CCA cells by several mechanisms. Our study provides evidence that BI6727 and GSK461364A could be alternative drugs and have potential implications at the clinical level for CCA therapy.

Polo-Like Kinase 2: From Principle to Practice

Polo-like kinase (PLK) 2 is an evolutionarily conserved serine/threonine kinase that shares the n-terminal kinase catalytic domain and the C-terminal Polo Box Domain (PBD) with other members of the PLKs family. In the last two decades, mounting studies have focused on this and tried to clarify its role in many aspects. PLK2 is essential for mitotic centriole replication and meiotic chromatin pairing, synapsis, and crossing-over in the cell cycle; Loss of PLK2 function results in cell cycle disorders and developmental retardation. PLK2 is also involved in regulating cell differentiation and maintaining neural homeostasis. In the process of various stimuli-induced stress, including oxidative and endoplasmic reticulum, PLK2 may promote survival or apoptosis depending on the intensity of stimulation and the degree of cell damage. However, the role of PLK2 in immunity to viral infection has been studied far less than that of other family members. Because PLK2 is extensively and deeply involved in normal physiological functions and pathophysiological mechanisms of cells, its role in diseases is increasingly being paid attention to. The effect of PLK2 in inhibiting hematological tumors and fibrotic diseases, as well as participating in neurodegenerative diseases, has been gradually recognized. However, the research results in solid organ tumors show contradictory results. In addition, preliminary studies using PLK2 as a disease predictor and therapeutic target have yielded some exciting and promising results. More research will help people better understand PLK2 from principle to practice.

PLK2 targets GSK3β to protect against cisplatin-induced acute kidney injury

Cisplatin-induced acute kidney injury (AKI), which is accompanied by a rapid decline in renal function and a high risk of death, is a complex critical illness with no effective or specific treatment. Polo-like kinase 2 (PLK2), a serine/threonine kinase, is involved in the progression of multiple diseases, including cancers, cardiac fibrosis, diabetic nephropathy, etc. Here, by integrating two Gene Expression Omnibus (GEO) datasets of cisplatin-induced AKI animal models, we identified PLK2 as a significantly up-regulated gene in AKI renal tissues, which was then verified in different AKI animal models and cell models. Suppressing PLK2 using siRNAs or inhibitors could enhance cisplatin-induced AKI by inducing severe apoptosis and oxidative stress damage, while enforced PLK2 expression could prevent renal dysfunction induced by cisplatin. We further discovered that PLK2 might phosphorylate glycogen synthase kinase 3β (GSK3β) in the pathogenesis of AKI. In conclusion, our results show that PLK2 play a protective role in cisplatin-induced AKI and may be a new protective target of cisplatin nephrotoxicity.

DNA Damage Response Inhibitors in Cholangiocarcinoma: Current Progress and Perspectives

Cholangiocarcinoma (CCA) is a poorly treatable type of cancer and its incidence is dramatically increasing. The lack of understanding of the biology of this tumor has slowed down the identification of novel targets and the development of effective treatments. Based on next generation sequencing profiling, alterations in DNA damage response (DDR)-related genes are paving the way for DDR-targeting strategies in CCA. Based on the notion of synthetic lethality, several DDR-inhibitors (DDRi) have been developed with the aim of accumulating enough DNA damage to induce cell death in tumor cells. Observing that DDRi alone could be insufficient for clinical use in CCA patients, the combination of DNA-damaging regimens with targeted approaches has started to be considered, as evidenced by many emerging clinical trials. Hence, novel therapeutic strategies combining DDRi with patient-specific targeted drugs could be the next level for treating cholangiocarcinoma.

PD-L1 promotes myofibroblastic activation of hepatic stellate cells by distinct mechanisms selective for TGF-β receptor I versus II

Intrahepatic cholangiocarcinoma (ICC) contains abundant myofibroblasts derived from hepatic stellate cells (HSCs) through an activation process mediated by TGF-β. To determine the role of programmed death-ligand 1 (PD-L1) in myofibroblastic activation of HSCs, we disrupted PD-L1 of HSCs by shRNA or anti-PD-L1 antibody. We find that PD-L1, produced by HSCs, is required for HSC activation by stabilizing TGF-β receptors I (TβRI) and II (TβRII). While the extracellular domain of PD-L1 (amino acids 19-238) targets TβRII protein to the plasma membrane and protects it from lysosomal degradation, a C-terminal 260-RLRKGR-265 motif on PD-L1 protects TβRI mRNA from degradation by the RNA exosome complex. PD-L1 is required for HSC expression of tumor-promoting factors, and targeting HSC PD-L1 by shRNA or Cre/loxP recombination suppresses HSC activation and ICC growth in mice. Thus, myofibroblast PD-L1 can modulate the tumor microenvironment and tumor growth by a mechanism independent of immune suppression.

The Role of the Hedgehog Pathway in Cholangiocarcinoma

Simple Summary

Cholangiocarcinoma (CCA) is one of the most refractory malignancies with a high mortality rate. Among all the pathways involved in CCA development, emerging evidence highlights Hedgehog (HH) signaling as a substantial player in CCA-genesis and development. The pro-tumoral function of HH provides potential therapeutic implications, and recently the use of HH inhibitors has paved the way for clinical application in various solid tumors. Targeting HH members, namely Hedgehog ligands, SMO transmembrane protein and GLI transcription factors may thus confer therapeutic options for the improvement of CCA treatment outcome.

Abstract

Cholangiocarcinoma (CCA) is a poorly treatable type of cancer and, along with hepatocellular carcinoma (HCC), is the predominant type of primitive liver cancer in adults. The lack of understanding of CCA biology has slowed down the identification of novel targets and the development of effective treatments. While tumors share some general characteristics, detailed knowledge of specific features is essential for the development of effectively tailored therapeutic approaches. The Hedgehog (HH) signaling cascade regulates stemness biology, embryonal development, tissue homeostasis, and cell proliferation and differentiation. Its aberrant activation has been associated with a variety of solid and hematological human malignancies. Several HH-inhibiting compounds have been indeed developed as potential anticancer agents in different types of tumors, with Smoothened and GLI inhibitors showing the most promising results. Beside its well-established function in other tumors, findings regarding the HH signaling in CCA are still controversial. Here we will give an overview of the most important clinical and molecular features of cholangiocarcinoma, and we will discuss the available evidence of the crosstalk between the HH signaling pathway and the cholangiocarcinoma cell biology.

Identification and assessment of PLK1/2/3/4 in lung adenocarcinoma and lung squamous cell carcinoma: Evidence from methylation profile

Lung cancer is a very aggressive cancer characterized with molecular heterogeneities in different subtypes, including lung adenocarcinoma and lung squamous cell carcinoma. However, few related molecular signatures have been established for the treatment of lung cancer subtypes. Polo-like kinase (PLK) family is a crucial regulator during cell division. Aberrant genetic and epigenetic alteration of PLK members plays a controversial role among different cancers. In this study, we performed an analysis of transcriptional and protein expression to identify overexpressed PLK1/4 and under-expressed PLK2/3 in lung cancer subtypes. We then analysed biological function of PLKs and related genes. Besides, we estimated a correlation of PLKs with patient's genders and TP53 mutation in lung cancer. Higher PLK1/4 expression was significantly associated with male patient and TP53 mutant status, separately. Moreover, we carried out a methylation profile analysis including methylation level, DNA methyltransferases correlation and survival analysis of global methylation. Global methylation survival analysis showed that prognostic value of PLK1/2/4 methylation remained the same significant trend between two lung cancer subtypes, whereas prognostic value of PLK3 methylation lacked consistency. Taken together, these results provided instructive insights into a comprehensive evaluation for advanced therapeutic strategy based on epigenetic evidences.

PLK2 protects retinal ganglion cells from oxidative stress by potentiating Nrf2 signaling via GSK-3β

Oxidative stress of retinal ganglion cells (RGCs) has been established as a main contributor to retinal degeneration in the pathogenesis of glaucoma. Polo-like kinase 2 (PLK2) has recently been reported to be a potent antioxidant protein that enhances cell survival in response to oxidative stress. To date, the involvement of PLK2 in RGC-associated oxidative stress is undermined. In the present work, we evaluated whether PLK2 regulates oxidative stress evoked by hydrogen peroxide (H₂ O₂ ) in RGCs. PLK2 expression was induced by H₂ O₂ stimulation in RGCs. Upregulation of PLK2 had a profoundly cytoprotective effect on H₂ O₂ -stimulated RGCs by attenuating cellular apoptosis and reactive oxygen species (ROS) level. Further data revealed that upregulation of PLK2 strikingly enhanced the activation of Nrf2 signaling. Moreover, PLK2 overexpression promoted glycogen synthase kinase (GSK)-3β phosphorylation, whereas PLK2 knockdown reduced the levels of GSK-3β phosphorylation. Notably, GSK-3β inhibition using a chemical inhibitor markedly abrogated the suppressive effects of PLK2 knockdown on Nrf2 activation. Repression of Nrf2 blocked the PLK2 overexpression-induced protective effects in H₂ O₂ -stimulated RGCs. Overall, this study elucidates that upregulation of PLK2 protects RGCs against H₂ O₂ -induced oxidative stress injury by upregulating Nrf2 activation via modulation of GSK-3β phosphorylation. These findings underline the pivotal role of PLK2 in mediating oxidative stress-evoked retinal degeneration in the pathogenesis of glaucoma.

Modelling the Functions of Polo-Like Kinases in Mice and Their Applications as Cancer Targets with a Special Focus on Ovarian Cancer

Polo-like kinases (PLKs) belong to a five-membered family of highly conserved serine/threonine kinases (PLK1-5) that play differentiated and essential roles as key mitotic kinases and cell cycle regulators and with this in proliferation and cellular growth. Besides, evidence is accumulating for complex and vital non-mitotic functions of PLKs. Dysregulation of PLKs is widely associated with tumorigenesis and by this, PLKs have gained increasing significance as attractive targets in cancer with diagnostic, prognostic and therapeutic potential. PLK1 has proved to have strong clinical relevance as it was found to be over-expressed in different cancer types and linked to poor patient prognosis. Targeting the diverse functions of PLKs (tumor suppressor, oncogenic) are currently at the center of numerous investigations in particular with the inhibition of PLK1 and PLK4, respectively in multiple cancer trials. Functions of PLKs and the effects of their inhibition have been extensively studied in cancer cell culture models but information is rare on how these drugs affect benign tissues and organs. As a step further towards clinical application as cancer targets, mouse models therefore play a central role. Modelling PLK function in animal models, e.g., by gene disruption or by treatment with small molecule PLK inhibitors offers promising possibilities to unveil the biological significance of PLKs in cancer maintenance and progression and give important information on PLKs' applicability as cancer targets. In this review we aim at summarizing the approaches of modelling PLK function in mice so far with a special glimpse on the significance of PLKs in ovarian cancer and of orthotopic cancer models used in this fatal malignancy.

Cholangiocarcinoma: shedding light on the most promising drugs in clinical development

Introduction: Cholangiocarcinoma (CCA) is a diverse group of fatal malignancies arising from the biliary tract. Surgical resection with negative margin offers the only potentially curative option. The majority of patients present at locally advanced or metastatic stages, when surgical resection is not feasible, highlighting the significance of systemic therapy. Given the limited effectiveness of traditional chemotherapy regimens in CCA, many investigators have focused on developing novel molecular therapies targeting key aberrant signaling pathways.Areas covered: We present the main genomic aberrations known to play a key role in cholangiocarcinogenesis and discuss promising targeted therapies in clinical development.In October of 2020, a review of the English literature was performed utilizing PubMed and Web of Science databases for the keywords of 'cholangiocarcinoma', 'biliary tract cancer', and 'targeted therapy'.Expert opinion: Unfortunately, despite encouraging results in preclinical studies, the outcome of clinical trials with established targeted therapies like anti-EGFR medications have been discouraging. Currently, agents targeting FGFR2 fusion and IDH1/2 mutations hold great promise for improving the management of CCA. Future studies focused on enhancing our understanding of key aberrant signaling pathways of cholangiocarcinogenesis and the design of homogeneous and biomarker-driven cohorts are key elements of establishing precision medicine in CCA.

Targeted therapies for extrahepatic cholangiocarcinoma: preclinical and clinical development and prospects for the clinic

Introduction: Until recently, cholangiocarcinoma (CCA) was a largely overlooked disease, and among CCAs, extrahepatic CCA (eCCA) was even more neglected. Despite the growing impact of molecularly targeted therapies and immunotherapy, prognosis of eCCA is dismal. Therefore, unraveling the complex molecular landscape of eCCA has become an urgent need. Deep phenotyping studies have revealed that eCCA is a heterogeneous tumor, harboring specific alterations categorizable into four classes, 'Mesenchymal', 'Proliferation', 'Immune', 'Metabolic'. Molecular alterations convey the activation of several pro-oncogenic pathways, where either actionable drivers or outcome predictors can be identified.Areas covered: We offer insights on perturbed pathways, molecular profiling, and actionable targets in eCCA and present a perspective on the potential stepping-stones to future progress. A systematic literature search in PubMed/ClinicalTrials.gov websites was performed by authors from different disciplines according to their specific topic knowledge to identify the newest and most relevant advances in precision medicine of eCCA.Expert opinion: eCCA is a distinct entity with unique features in terms of molecular classes, oncogenic drivers, and tumor microenvironment. Since more prevalent mutations are currently undruggable, and immunotherapy can be offered only to a minority of patients, international collaborations are instrumental to improve the understanding of the molecular underpins of this disease.

Knocking down of Polo-like kinase 2 inhibits cell proliferation and induced cell apoptosis in human glioma cells

AIMS

Polo-like kinase 2 (PLK2) belongs to a family of serine/threonine kinases, and it is involved in tumorigenesis. The present study aimed to explore the potential clinical significance of PLK2 in the development of gliomas.

MAIN METHODS

Immunohistochemistry (IHC) was performed to detect the expression of PLK2 in glioma tissues. Cell proliferation and apoptosis were determined by Cell Counting Kit 8 (CCK8) and flow cytometry analysis, respectively.

KEY FINDINGS

PLK2 expression gradually increased with the degree of glioma malignancy. High PLK2 expression was associated with a poor prognosis in glioma. Short hairpin RNAs targeting PLK2 (shPLK2) inhibited the viability and induced apoptosis of glioma cells, both in vitro and in vivo. Ring finger protein 180 (RNF180), an E3 ubiquitin ligase, interacted with PLK2 and induced the ubiquitination of PLK2. Overexpression of PLK2 in glioma cells significantly inhibited RNF180 upregulation-induced cell apoptosis. The expression level of RNF180 gradually decreased with the degree of glioma malignancy.

SIGNIFICANCE

Knocking down of PLK2 may suppress the glioma development through cancer cell proliferation inhibition and cell apoptosis promotion. Furthermore, RNF180 may mediate the ubiquitination of PLK2. The present findings may help improve the clinical management of glioma in the future.

Emerging pathways for precision medicine in management of cholangiocarcinoma

Cholangiocarcinoma (CCA) is the second most common biliary tract malignancy with a dismal prognosis. Surgical resection with a negative microscopic margin offers the only hope for long-term survival. However, the majority of patients present with advanced disease not amenable to curative resection, mainly due to late presentation and aggressive nature of the disease. Unfortunately, due to the heterogeneous nature of CCA as well as limitations of available chemotherapy medications, traditional chemotherapy regimens offer limited survival benefit. Recent advances in genomic studies and next-generation sequencing techniques have assisted in better understanding of cholangiocarcinogenesis and identification of potential aberrant signaling pathways. Targeting the specific genomic abnormalities via novel molecular therapies has opened a new avenue in management of CCA with encouraging results in preclinical studies and early clinical trials. In this review, we present emerging therapies for precision medicine in CCA.

CDK7 inhibitor THZ1 inhibits MCL1 synthesis and drives cholangiocarcinoma apoptosis in combination with BCL2/BCL-XL inhibitor ABT-263

Cholangiocarcinoma (CCA) is a fatal disease without effective targeted therapy. We screened a small-molecule library of 116 inhibitors targeting different targets of the cell cycle and discovered several kinases, including Cyclin-dependent kinase 7 (CDK7) as vulnerabilities in CCA. Analysis of multiple CCA data sets demonstrated that CDK7 was overexpressed in CCA tissues. Further studies demonstrated that CDK7 inhibitor THZ1 inhibited cell viability and induced apoptosis in CCA cells. We also showed that THZ1 inhibited CCA cell growth in a xenograft model. RNA-sequencing followed by Gene ontology analysis showed a striking impact of THZ1 on DNA-templated transcriptional programs. THZ1 downregulated CDK7-mediated phosphorylation of RNA polymerase II, indicative of transcriptional inhibition. A number of oncogenic transcription factors and survival proteins, like MCL1, FOSL1, and RUNX1, were repressed by THZ1. MCL1, one of the antiapoptotic BCL2 family members, was significantly inhibited upon THZ1 treatment. Accordingly, combining THZ1 with a BCL2/BCL-XL inhibitor ABT-263 synergized in impairing cell growth and driving apoptosis. Our results demonstrate CDK7 as a potential target in treating CCA. Combinations of CDK7 inhibition and BCL2/BCL-XL inhibition may offer a novel therapeutic strategy for CCA.

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 (Plk1), a master regulator of mitosis and the DNA damage response, is considered to be an intriguing target in the research field of mitotic intervention. The observation that Plk1 is overexpressed in multiple human malignancies, including non-small-cell lung cancer (NSCLC), gave rise to the development of several small-molecule inhibitors. Volasertib, presently the most extensively studied Plk1 inhibitor, has been validated to efficiently reduce tumor growth in preclinical settings. Unfortunately, only modest antitumor activity against solid tumors was reported in clinical trials. This discrepancy prompted research into the identification of predictive biomarkers. In this study, we investigated the therapeutic effect of volasertib monotherapy (i.e., cytotoxicity, cell cycle distribution, apoptotic cell death, cellular senescence, and migration) in a panel of NSCLC cell lines differing in p53 status under both normal and reduced oxygen tension (<0.1% O2 ). A strong growth inhibitory effect was observed in p53 wild-type cells (A549 and A549-NTC), with IC50 values significantly lower than those in p53 knockdown/mutant cells (A549-920 and NCI-H1975) (P < 0.001). While mitotic arrest was significantly greater in cells with nonfunctional p53 (P < 0.005), apoptotic cell death (P < 0.026) and cellular senescence (P < 0.021) were predominantly induced in p53 wild-type cells. Overall, the therapeutic effect of volasertib was reduced under hypoxia (P < 0.050). Remarkably, volasertib inhibited cell migration in all cell lines tested (P < 0.040), with the exception of for the NCI-H1975 p53 mutant cell line. In conclusion, our results show an important difference in the therapeutic effect of Plk1 inhibition in NSCLC cells with versus without functional p53. Overall, the p53 wild-type cell lines were more sensitive to volasertib treatment, suggesting that p53 might be a predictive biomarker for Plk1 inhibition in NSCLC. Moreover, our results pave the way for new combination strategies with Plk1 inhibitors to enhance antitumor activity.

Animal models of cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive biliary tract malignancy with a poor overall prognosis. There is a critical need to develop effective targeted therapies for the treatment of this lethal disease. In an effort to address this challenge, preclinical in vivo studies have become paramount in understanding CCA carcinogenesis, progression, and therapy. Various CCA animal models exist including carcinogen-based models in which animals develop CCA after exposure to a carcinogen, genetically engineered mouse models in which genetic changes are induced in mice leading to CCA, murine syngeneic orthotopic models, as well as xenograft tumors derived from xenotransplantation of CCA cells, organoids, and patient-derived tissue. Each type has distinct advantages as well as shortcomings. In the ideal animal model of CCA, the tumor arises from the biliary tract in an immunocompetent host with a species-matched tumor microenvironment. Such a model would also be time-efficient, recapitulate the genetic and histopathological features of human CCA, and predict therapeutic response in humans. Recently developed biliary tract transduction and orthotopic syngeneic transplant mouse models encompass several of these elements. Herein, we review the different animal models of CCA, their advantages and deficiencies, as well as features which mimic human CCA.

Role of canonical Hedgehog signaling pathway in liver

Hedgehog (Hh) signaling pathway plays an important role in embryonic development. It becomes reactivated in many types of acute and chronic liver injuries. Hh signaling is required for liver regeneration, regulates capillarisation, controls the fates of hepatic stellate cells, promotes liver fibrosis and liver cancers. In this review, we summarize the current knowledge of the role of canonical Hh signaling pathway in adult liver. This help to understand the pathogenesis of liver diseases and find out the new effective targeted therapeutic strategies for liver diseases treatments.

Emerging molecular therapeutic targets for cholangiocarcinoma

Cholangiocarcinomas (CCAs) are diverse epithelial tumors arising from the liver or large bile ducts with features of cholangiocyte differentiation. CCAs are classified anatomically into intrahepatic (iCCA), perihilar (pCCA), and distal CCA (dCCA). Each subtype has distinct risk factors, molecular pathogenesis, therapeutic options, and prognosis. CCA is an aggressive malignancy with a poor overall prognosis and median survival of less than 2years in patients with advanced disease. Potentially curative surgical treatment options are limited to the subset of patients with early-stage disease. Presently, the available systemic medical therapies for advanced or metastatic CCA have limited therapeutic efficacy. Molecular alterations define the differences in biological behavior of each CCA subtype. Recent comprehensive genetic analysis has better characterized the genomic and transcriptomic landscape of each CCA subtype. Promising candidates for targeted, personalized therapy have emerged, including potential driver fibroblast growth factor receptor (FGFR) gene fusions and somatic mutations in isocitrate dehydrogenase (IDH)1/2 in iCCA, protein kinase cAMP-activated catalytic subunit alpha (PRKACA) or beta (PRKACB) gene fusions in pCCA, and ELF3 mutations in dCCA/ampullary carcinoma. A precision genomic medicine approach is dependent on an enhanced understanding of driver mutations in each subtype and stratification of patients according to their genetic drivers. We review the current genomic landscape of CCA, the potentially actionable molecular aberrations in each CCA subtype, and the role of immunotherapy in CCA.

New Horizons for Precision Medicine in Biliary Tract Cancers

Biliary tract cancers (BTC), including cholangiocarcinoma and gallbladder cancer, are poor-prognosis and low-incidence cancers, although the incidence of intrahepatic cholangiocarcinoma is rising. A minority of patients present with resectable disease but relapse rates are high; benefit from adjuvant capecitabine chemotherapy has been demonstrated. Cisplatin/gemcitabine combination chemotherapy has emerged as the reference first-line treatment regimen; there is no standard second-line therapy. Selected patients may be suitable for liver-directed therapy (e.g., radioembolization or external beam radiation), pending confirmation of benefit in randomized studies. Initial trials targeting the epithelial growth factor receptor and angiogenesis pathways have failed to deliver new treatments. Emerging data from next-generation sequencing analyses have identified actionable mutations (e.g., FGFR fusion rearrangements and IDH1 and IDH2 mutations), with several targeted drugs entering clinical development with encouraging results. The role of systemic therapies, including targeted therapies and immunotherapy for BTC, is rapidly evolving and is the subject of this review.Significance: The authors address genetic drivers and molecular biology from a translational perspective, in an intent to offer a clear view of the recent past, present, and future of BTC. The review describes a state-of-the-art update of the current status and future directions of research and therapy in advanced BTC. Cancer Discov; 7(9); 943-62. ©2017 AACR.

New Horizons for Precision Medicine in Biliary Tract Cancers

Biliary tract cancers (BTC), including cholangiocarcinoma and gallbladder cancer, are poor-prognosis and low-incidence cancers, although the incidence of intrahepatic cholangiocarcinoma is rising. A minority of patients present with resectable disease but relapse rates are high; benefit from adjuvant capecitabine chemotherapy has been demonstrated. Cisplatin/gemcitabine combination chemotherapy has emerged as the reference first-line treatment regimen; there is no standard second-line therapy. Selected patients may be suitable for liver-directed therapy (e.g., radioembolization or external beam radiation), pending confirmation of benefit in randomized studies. Initial trials targeting the epithelial growth factor receptor and angiogenesis pathways have failed to deliver new treatments. Emerging data from next-generation sequencing analyses have identified actionable mutations (e.g., FGFR fusion rearrangements and IDH1 and IDH2 mutations), with several targeted drugs entering clinical development with encouraging results. The role of systemic therapies, including targeted therapies and immunotherapy for BTC, is rapidly evolving and is the subject of this review.Significance: The authors address genetic drivers and molecular biology from a translational perspective, in an intent to offer a clear view of the recent past, present, and future of BTC. The review describes a state-of-the-art update of the current status and future directions of research and therapy in advanced BTC. Cancer Discov; 7(9); 943-62. ©2017 AACR.

Emerging concepts in biliary repair and fibrosis

Chronic diseases of the biliary tree (cholangiopathies) represent one of the major unmet needs in clinical hepatology and a significant knowledge gap in liver pathophysiology. The common theme in cholangiopathies is that the target of the disease is the biliary tree. After damage to the biliary epithelium, inflammatory changes stimulate a reparative response with proliferation of cholangiocytes and restoration of the biliary architecture, owing to the reactivation of a variety of morphogenetic signals. Chronic damage and inflammation will ultimately result in pathological repair with generation of biliary fibrosis and clinical progression of the disease. The hallmark of pathological biliary repair is the appearance of reactive ductular cells, a population of cholangiocyte-like epithelial cells of unclear and likely mixed origin that are able to orchestrate a complex process that involves a number of different cell types, under joint control of inflammatory and morphogenetic signals. Several questions remain open concerning the histogenesis of reactive ductular cells, their role in liver repair, their mechanism of activation, and the signals exchanged with the other cellular elements cooperating in the reparative process. This review contributes to the current debate by highlighting a number of new concepts derived from the study of the pathophysiology of chronic cholangiopathies, such as congenital hepatic fibrosis, biliary atresia, and Alagille syndrome.

Bcl-2 degradation is an additional pro-apoptotic effect of polo-like kinase inhibition in cholangiocarcinoma cells

AIM

To examine the influence on apoptotic mechanisms following inhibition of polo-like kinases as therapeutically approach for cholangiocellular cancer treatment.

METHODS

As most cholangiocarcinomas are chemotherapy-resistant due to mechanisms preventing tumor cell death, we investigated the effect of Cisplatin on cholangiocellular carcinoma (CCA) cell lines KMCH-1 and Mz-Ch-1. Polo-like kinases (PLK) are important regulators of the cell cycle and their inhibition is discussed as a potential therapy while PLK inhibition can regulate apoptotic mediators. Here, cells were treated with PLK inhibitor BI6727 (Volasertib), Cisplatin, and in combination of both compounds. Cell viability was assessed by MTT; apoptosis was measured by DAPI staining and caspase-3/-7 assay. Western blot and qRT-PCR were used to measure expression levels of apoptosis-related molecules Bax and Bcl-2.

RESULTS

The cell viability in the CCA cell lines KMCH-1 and Mz-Ch-1 was reduced in all treatment conditions compared to vehicle-treated cells. Co-treatment with BI6727 and cisplatin could even enhance the cytotoxic effect of cisplatin single treatment. Thus, co-treatment of cisplatin with BI6727 could slightly enhance the cytotoxic effect of the cisplatin in both cell lines whereas there was evidence of increased apoptosis induction solely in Mz-Ch-1 as compared to KMCH-1. Moreover, PLK inhibition decreases protein levels of Bcl-2; an effect that can be reversed by the proteasomal degradation inhibitor MG-132. In contrast, protein levels of Bax were not found to be altered by PLK inhibition. These findings indicate that cytotoxic effects of Cisplatin in Mz-Ch-1 cells can be enhanced by cotreatment with BI6727.

CONCLUSION

In conclusion, BI6727 treatment can sensitize CCA cells to cisplatin-induced apoptosis with proteasomal Bcl-2 degradation as an additional pro-apoptotic effect.

Autocrine and Paracrine Mechanisms Promoting Chemoresistance in Cholangiocarcinoma

Resistance to conventional chemotherapeutic agents, a typical feature of cholangiocarcinoma, prevents the efficacy of the therapeutic arsenal usually used to combat malignancy in humans. Mechanisms of chemoresistance by neoplastic cholangiocytes include evasion of drug-induced apoptosis mediated by autocrine and paracrine cues released in the tumor microenvironment. Here, recent evidence regarding molecular mechanisms of chemoresistance is reviewed, as well as associations between well-developed chemoresistance and activation of the cancer stem cell compartment. It is concluded that improved understanding of the complex interplay between apoptosis signaling and the promotion of cell survival represent potentially productive areas for active investigation, with the ultimate aim of encouraging future studies to unveil new, effective strategies able to overcome current limitations on treatment.

MicroRNA-146a Induces Lineage-Negative Bone Marrow Cell Apoptosis and Senescence by Targeting Polo-Like Kinase 2 Expression

OBJECTIVE

Lineage-negative bone marrow cells (lin- BMCs) are enriched in endothelial progenitor cells and mediate vascular repair. Aging-associated senescence and apoptosis result in reduced number and functionality of lin- BMCs, impairing their prorepair capacity. The molecular mechanisms underlying lin- BMC senescence and apoptosis are poorly understood. MicroRNAs (miRNAs) regulate many important biological processes. The identification of miRNA-mRNA networks that modulate the health and functionality of lin- BMCs is a critical step in understanding the process of vascular repair. The aim of this study was to characterize the role of the miR-146a-Polo-like kinase 2 (Plk2) network in regulating lin- BMC senescence, apoptosis, and their angiogenic capability.

APPROACH AND RESULTS

Transcriptome analysis in lin- BMCs isolated from young and aged wild-type and ApoE^-/- (apolipoprotein E) mice showed a significant age-associated increase in miR-146a expression. In silico analysis, expression study and Luciferase reporter assay established Plk2 as a direct target of miR-146a. miR-146a overexpression in young lin- BMCs inhibited Plk2 expression, resulting in increased senescence and apoptosis, via p16Ink4a/p19Arf and p53, respectively, as well as impaired angiogenic capacity in vitro and in vivo. Conversely, suppression of miR-146a in aged lin- BMCs increased Plk2 expression and rejuvenated lin- BMCs, resulting in decreased senescence and apoptosis, leading to improved angiogenesis.

CONCLUSIONS

(1) miR-146a regulates lin- BMC senescence and apoptosis by suppressing Plk2 expression that, in turn, activates p16Ink4a/p19Arf and p53 and (2) modulation of miR-146a or its target Plk2 may represent a potential therapeutic intervention to improve lin- BMC-mediated angiogenesis and vascular repair.

Cell death mechanisms in human chronic liver diseases: a far cry from clinical applicability

The liver is constantly exposed to a host of injurious stimuli. This results in hepatocellular death mainly by apoptosis and necrosis, but also due to autophagy, necroptosis, pyroptosis and in some cases by an intricately balanced combination thereof. Overwhelming and continuous cell death in the liver leads to inflammation, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Although data from various disease models may suggest a specific (predominant) cell death mode for different aetiologies, the clinical reality is not as clear cut. Reliable and non-invasive cell death markers are not available in general practice and assessment of cell death mode to absolute certainty from liver biopsies does not seem feasible, yet. Various aetiologies probably induce different predominant cell death modes within the liver, although the death modes involved may change during disease progression. Moreover, current methods applicable in patients are limited to surrogate markers for apoptosis (M30), and possibly for pyroptosis (IL-1 family) and necro(pto)sis (HMGB1). Although markers for some death modes are not available at all (autophagy), others may not be specific for a cell death mode or might not always definitely indicate dying cells. Physicians need to take care in asserting the presence of cell death. Still the serum-derived markers are valuable tools to assess severity of chronic liver diseases. This review gives a short overview of known hepatocellular cell death modes in various aetiologies of chronic liver disease. Also the limitations of current knowledge in human settings and utilization of surrogate markers for disease assessment are summarized.

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.

Expert consensus document: Cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA)

Cholangiocarcinoma (CCA) is a heterogeneous group of malignancies with features of biliary tract differentiation. CCA is the second most common primary liver tumour and the incidence is increasing worldwide. CCA has high mortality owing to its aggressiveness, late diagnosis and refractory nature. In May 2015, the "European Network for the Study of Cholangiocarcinoma" (ENS-CCA: www.enscca.org or www.cholangiocarcinoma.eu) was created to promote and boost international research collaboration on the study of CCA at basic, translational and clinical level. In this Consensus Statement, we aim to provide valuable information on classifications, pathological features, risk factors, cells of origin, genetic and epigenetic modifications and current therapies available for this cancer. Moreover, future directions on basic and clinical investigations and plans for the ENS-CCA are highlighted.

Polo-like kinase 3 is associated with improved overall survival in cholangiocarcinoma

BACKGROUND & AIMS

Cholangiocarcinomas (CCA) paradoxically express the death ligand TRAIL and thus, are dependent on effective survival signals to circumvent apoptosis. Hedgehog signalling exerts major survival signals in CCA by regulating serine/threonine kinase polo-like kinase (PLK)2. We here aimed to examine the role of PLK1/2/3 expression for CCA tumour biology.

METHODS

We employed CCA samples from 73 patients and human HUCCT-1/Mz-CHA1/KMCH-1 CCA cells. Immunohistochemistry for PLK1/2/3 was performed using tissue microarrays from representative tumour areas.

RESULTS

PLK1/2/3-immunoreactive cancer cells were present in most of the CCA samples. However, only PLK1 and especially PLK3 were expressed in higher amounts within CCA cells as compared to normal liver. Given that fibroblast growth factor (FGF) can induce PLK3 expression and also is present in CCA, we examined the effect of FGF on PLK3 in vitro. Indeed, rhFGF rapidly increased PLK3 mRNA expression all three CCA cell lines giving an explanation for the abundant PLK3 presence in the tissue samples. Clinicopathologically, PLK3 expression was associated with decreased tumour cell migration and lymph/blood vessel infiltration whereas higher levels of PLK1 were correlated with larger tumour sizes. Moreover, strong PLK3 expression was associated with prolonged overall survival.

CONCLUSIONS

The results suggest that PLK3 predominantly is expressed in CCA cells and that high PLK3 expression correlates with prolonged overall survival. These observations might have implications for prognosis prediction of human CCA as well as the potential therapeutic use of polo-like kinase inhibitors (i.e., PLK1/2 specifity).

Impact of microenvironment and stem-like plasticity in cholangiocarcinoma: molecular networks and biological concepts

Clinical complexity, anatomic diversity and molecular heterogeneity of cholangiocarcinoma (CCA) represent a major challenge in the assessment of effective targeted therapies. Molecular and cellular mechanisms underlying the diversity of CCA growth patterns remain a key issue of clinical concern. Crucial questions comprise the nature of the CCA-origin, the initial target for cellular transformation as well as the relationship with the cancer stem cells (CSC) concept. Additionally, since CCA often develops in the context of an inflammatory milieu (cirrhosis and cholangitis), the stromal compartment or tumour microenvironment (TME) likely promotes initiation and progression of this malignancy, contributing to its heterogeneity. This review will emphasize the dynamic interplay between stem-like intrinsic and TME-extrinsic pathways, which may represent novel options for multi-targeted therapies in CCA.

Activated hedgehog pathway is a potential target for pharmacological intervention in biliary tract cancer

Hedgehog (Hh) signalling contributes to carcinogenesis and represents a valid druggable target in human cancers, possibly also in biliary tract cancer (BTC). We analysed the expression of Hh components in BTC using eight heterogeneously differentiated cell lines, xenograft tumours and a human tissue microarray. The dose-, time- and cell line-dependent effects of two Hh inhibitors (cyclopamine and Gant-61) were analysed in vitro for survival, apoptosis, cell cycle distribution and possible synergism with conventional chemotherapeutic agents. In human BTC samples, the sonic Hh ligand and the Gli1 transcription factor showed increased expression in tumours compared to normal adjacent tissue and were significantly associated with high tumour grade and positive lymph node status. In BTC cell lines, we could confirm the Hh component expression at varying extent within the employed cell lines in vitro and in vivo indicating non-canonical signalling. Both Hh inhibitors showed dose-dependent cytotoxicity above 5 µM with a stronger effect for Gant-61 inducing apoptosis whereas cyclopamine rather inhibited proliferation. Cytotoxicity was associated with low cytokeratin expression and higher mesenchymal marker expression such as vimentin. Additionally, drug combinations of Gant-61 with conventional chemotherapy (cisplatin) exerted synergistic effects. In conclusion, Hh pathway is significantly activated in human BTC tissue compared to normal adjacent tissue. The current data demonstrate for the first time an effective anticancer activity of especially Gant-61 in BTC and suggest second generation Hh pathway inhibitors as a potential novel treatment strategy in BTC.

Identification of the PLK2-dependent phosphopeptidome by quantitative proteomics [corrected]

Polo-like kinase 2 (PLK2) has been recently recognized as the major enzyme responsible for phosphorylation of α-synuclein at S129 in vitro and in vivo, suggesting that this kinase may play a key role in the pathogenesis of Parkinson's disease and other synucleinopathies. Moreover PLK2 seems to be implicated in cell division, oncogenesis, and synaptic regulation of the brain. However little is known about the phosphoproteome generated by PLK2 and, consequently the overall impact of PLK2 on cellular signaling. To fill this gap we exploited an approach based on in vitro kinase assay and quantitative phosphoproteomics. A proteome-derived peptide library obtained by digestion of undifferentiated human neuroblastoma cell line was exhaustively dephosphorylated by lambda phosphatase followed by incubation with or without PLK2 recombinant kinase. Stable isotope labeling based quantitative phosphoproteomics was applied to identify the phosphosites generated by PLK2. A total of 98 unique PLK2-dependent phosphosites from 89 proteins were identified by LC-MS/MS. Analysis of the primary structure of the identified phosphosites allowed the detailed definition of the kinase specificity and the compilation of a list of potential PLK2 targets among those retrieved in PhosphositePlus, a curated database of in cell/vivo phosphorylation sites.

Molecular pathogenesis of intrahepatic cholangiocarcinoma

Cholangiocarcinoma (CCA) is an orphan cancer of the hepatobiliary tract, the incidence of which has increased in the past decade. The molecular pathogenesis of this treatment-refractory disease is poorly understood. Desmoplasia is a key causal feature of CCA; however, a majority of tumors develop with no apparent etiological background. The impact of the stromal compartment on tumor progression as well as resistance to therapy is in vogue, and the epithelial-stromal crosstalk may present a target for novel treatment strategies. As such, the complexity of tumor cellularity and the molecular mechanisms underlying the diversity of growth patterns of this malignancy remain a clinical concern. It is crucial to advance our present understanding of the molecular pathogenesis of CCA to improve current clinical strategies and patient outcome. This will facilitate the delineation of patient subsets and individualization for precision therapies. Many questions persevere as to the evolutionary process and cellular origin of the initial transforming event, the context of intratumoral plasticity and the causal driver action. Next-generation sequencing has begun to underline the persistent alterations, which may be the trigger of acquired drug resistance, and the cause of metastasis and disease recurrence. A complex issue that remains is to account for the heterogeneous pool of "backseat" aberrations, which in chromosomal proximity to the causative variant are likely to influence, for example, drug response. This review explores the recent advances in defining the molecular pathways implicated in the development of this devastating disease and, which present putative clinical strategies.

A perspective on molecular therapy in cholangiocarcinoma: present status and future directions

Cholangiocarcinoma (CCA) is an orphan cancer with limited understanding of its genetic and genomic pathogenesis. Typically, it is highly treatment-refractory and patient outcome is dismal. Currently, there are no approved therapeutics for CCA and surgical resection remains the only option with curative intent. Clinical trials are currently being performed in a mixed cohort of biliary tract cancers that includes intrahepatic CCA, extrahepatic/perihilar CCA, distal extrahepatic CCA, gallbladder carcinoma and, in rare cases, even pancreatic cancers. Today, clinical trials fail primarily because they are underpowered mixed cohorts and designed without intent to enrich for markers to optimize success for targeted therapy. This review aims to emphasize current clinical attempts for targeted therapy of CCA, as well as highlight promising new candidate pathways revealed by translational genomics.

Liver renewal: detecting misrepair and optimizing regeneration

Cirrhosis and liver cancer, the main causes of liver-related morbidity and mortality, result from defective repair of liver injury. This article summarizes rapidly evolving knowledge about liver myofibroblasts and progenitors, the 2 key cell types that interact to orchestrate effective repair, because deregulation of these cells is likely to be central to the pathogenesis of both cirrhosis and liver cancer. We focus on cirrhosis pathogenesis because cirrhosis is the main risk factor for primary liver cancer. Emerging evidence suggests that the defective repair process has certain characteristics that might be exploited for biomarker development. Recent findings in preclinical models also indicate that the newly identified cellular and molecular targets are amenable to therapeutic manipulation. Thus, recent advances in our understanding about key cell types and fundamental mechanisms that regulate liver regeneration have opened new avenues to improve the outcomes of liver injury.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT01899859.