title: Inhibition of cyclin-dependent kinase 6 suppresses cell proliferation and enhances radiation sensitivity in medulloblastoma cells.
abstract: Medulloblastoma accounts for 20 % of all primary pediatric intracranial tumors. Current treatment cures 50-80 % of patients but is associated with significant long-term morbidity and thus new therapeutic targets are needed. One such target is cyclin-dependent kinase 6 (CDK6), a serine/threonine kinase that plays a vital role in cell cycle progression and differentiation. CDK6 is overexpressed in medulloblastoma patients and is associated with an adverse prognosis. To investigate the role of CDK6 in medulloblastoma, we assayed the effect of CDK6 inhibition on proliferation by depleting expression with RNA interference (RNAi) or by inhibiting kinase function with a small molecule inhibitor, PD0332991. Cell proliferation was assessed by colony focus assay or by the xCELLigence system. We then investigated the impact of CDK6 inhibition on differentiation of murine neural stem cells by immunofluorescence of relevant markers. Finally we evaluated the effects of PD0332991 treatment on medulloblastoma cell cycle and radiosensitivity using colony focus assays. Gene expression analysis revealed that CDK6 mRNA expression is higher than normal cerebellum in fifteen out of sixteen medulloblastoma patient samples. Inhibition of CDK6 by RNAi significantly decreased medulloblastoma cell proliferation and colony forming potential. Interestingly, CDK6 inhibition by RNAi increased differentiation in murine neural stem cells. PD0332991 treatment significantly decreased medulloblastoma cell proliferation and led to a G0/G1 cell cycle arrest. Furthermore, PD0332991 pretreatment sensitized medulloblastoma cells to ionizing radiation. Our findings suggest that targeting CDK6 with small molecule inhibitors may prove beneficial in the treatment of medulloblastoma, especially when combined with radiation.
authors.affiliation: Department of Pediatrics, Children's Hospital Colorado and University of Colorado Denver, Anschutz Medical Campus, Aurora, CO, USA. susan.whiteway@us.af.mil
authors.forename: Susan L
authors.initials: SL
authors.lastname: Whiteway
authors.forename: Peter S
authors.initials: PS
authors.lastname: Harris
authors.forename: Sujatha
authors.initials: S
authors.lastname: Venkataraman
authors.forename: Irina
authors.initials: I
authors.lastname: Alimova
authors.forename: Diane K
authors.initials: DK
authors.lastname: Birks
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Donson
authors.forename: Nicholas K
authors.initials: NK
authors.lastname: Foreman
authors.forename: Rajeev
authors.initials: R
authors.lastname: Vibhakar
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002528:Cerebellar Neoplasms / Q000473:pathology*; D002675:Child, Preschool; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D006801:Humans; D008297:Male; D008527:Medulloblastoma / Q000188:drug therapy / Q000473:pathology*; D051379:Mice; D058953:Neural Stem Cells / Q000187:drug effects / Q000502:physiology; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D034622:RNA Interference / Q000502:physiology; D011836:Radiation Tolerance / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D011839:Radiation, Ionizing; D014404:Tubulin / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D010879:Piperazines; D011725:Pyridines; C498585:TUBB3 protein, human; D014404:Tubulin; C495911:CDK6 protein, human; D051361:Cyclin-Dependent Kinase 6; C500026:palbociclib