title: Pharmaceutically inhibiting polo-like kinase 1 exerts a broad anti-tumour activity in retinoblastoma cell lines.
abstract: BACKGROUND
  Retinoblastoma is the most common malignant cancer of the eye in children. Although metastatic retinoblastoma is rare, cure rates for this advanced disease remain below 50%. High-level polo-like kinase 1 expression in retinoblastomas has previously been shown to be correlated with adverse outcome parameters. Polo-like kinase 1 is a serine/threonine kinase involved in cell cycle regulation at the G2/M transition. Polo-like kinase 1 inhibition has been demonstrated to have anti-tumour effects in preclinical models of several paediatric tumours. Here, we assessed its efficacy against retinoblastoma cell lines.
  
  
  METHODS
  Expression of polo-like kinase 1 was determined in a panel of retinoblastoma cell lines by polymerase chain reaction and western blot analysis. We analysed viability (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT assay), proliferation (5-bromo-2'-deoxyuridine enzyme-linked immunosorbent assay), cell cycle progression (propidium iodid staining) and apoptosis (cell death enzyme-linked immunosorbent assay) in three retinoblastoma cell lines after treatment with two adenosine triphosphate-competitive polo-like kinase 1 inhibitors, BI6727 or GSK461364. Activation of polo-like kinase 1 downstream signalling components including TP53 were assessed.
  
  
  RESULTS
  Treatment of retinoblastoma cells with either BI6727 or GSK461364 reduced cell viability and proliferative capacity and induced both cell cycle arrest and apoptosis. Polo-like kinase 1 inhibition also induced the p53 signalling pathway. Analysis of key players in cell cycle control revealed that low nanomolar concentrations of either polo-like kinase 1 inhibitor upregulated cyclin B1 and increased activated cyclin-dependent kinase 1 (phosphorylated at Y15) in retinoblastoma cell lines.
  
  
  CONCLUSIONS
  These preclinical data indicate that polo-like kinase 1 inhibitors could be useful as components in rationally designed chemotherapy protocols to treat patients with metastasized retinoblastoma in early phase clinical trials.
authors.affiliation: Department of Pediatric Oncology and Hematology, University Hospital Essen, Essen, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Schwermer
authors.affiliation: Department of Pediatric Oncology and Hematology, University Hospital Essen, Essen, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Dreesmann
authors.affiliation: Department of Pediatric Oncology and Hematology, Charité University Medicine Berlin, Berlin, Germany.
authors.forename: Angelika
authors.initials: A
authors.lastname: Eggert
authors.affiliation: Department of Pediatric Oncology and Hematology, University Hospital Essen, Essen, Germany.
authors.forename: Kristina
authors.initials: K
authors.lastname: Althoff
authors.affiliation: Institute of Human Genetics, University Hospital Essen, Essen, Germany.
authors.forename: Laura
authors.initials: L
authors.lastname: Steenpass
authors.affiliation: Department of Pediatric Oncology and Hematology, University Hospital Essen, Essen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Schramm
authors.affiliation: Department of Pediatric Oncology and Hematology, Charité University Medicine Berlin, Berlin, Germany.
authors.forename: Johannes H
authors.initials: JH
authors.lastname: Schulte
authors.affiliation: Department of Pediatric Oncology and Hematology, University Hospital Essen, Essen, Germany.|Eye Oncogenetics Research Group, Institute of Human Genetics, University Hospital Essen, Essen, Germany.|German Cancer Consortium (DKTK), Heidelberg, Germany.
authors.forename: Petra
authors.initials: P
authors.lastname: Temming
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001562:Benzimidazoles / Q000494:pharmacology; D015153:Blotting, Western; D016203:CDC2 Protein Kinase; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D056744:Cyclin B1 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006801:Humans; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D011621:Pteridines / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D019572:Retinal Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D012175:Retinoblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D013876:Thiophenes / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D000097869:Polo-Like Kinase 1
chemical_list: D000970:Antineoplastic Agents; D001562:Benzimidazoles; D016203:CDC2 Protein Kinase; D018797:Cell Cycle Proteins; D056744:Cyclin B1; D018844:Cyclin-Dependent Kinases; D004791:Enzyme Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D011621:Pteridines; D013876:Thiophenes; D000097869:Polo-Like Kinase 1; C541363:BI 6727; C534699:CCNB1 protein, human; C561573:GSK 461364; C528899:CDK1 protein, human
keywords: BI6727; GSK461364; metastasized retinoblastoma; polo like kinase 1; targeted therapy