title: Pharmacologic inhibition of cyclin-dependent kinases 4 and 6 arrests the growth of glioblastoma multiforme intracranial xenografts.
abstract: Activation of cyclin-dependent kinases 4 and 6 (cdk4/6) occurs in the majority of glioblastoma multiforme (GBM) tumors, and represents a promising molecular target for the development of small molecule inhibitors. In the current study, we investigated the molecular determinants and in vivo response of diverse GBM cell lines and xenografts to PD-0332991, a cdk4/6-specific inhibitor. In vitro testing of PD-0332991 against a panel of GBM cell lines revealed a potent G(1) cell cycle arrest and induction of senescence in each of 16 retinoblastoma protein (Rb)-proficient cell lines regardless of other genetic lesions, whereas 5 cell lines with homozygous inactivation of Rb were completely resistant to treatment. Short hairpin RNA depletion of Rb expression conferred resistance of GBM cells to PD-0332991, further demonstrating a requirement of Rb for sensitivity to cdk4/6 inhibition. PD-0332991 was found to efficiently cross the blood-brain barrier and proved highly effective in suppressing the growth of intracranial GBM xenograft tumors, including those that had recurred after initial therapy with temozolomide. Remarkably, no mice receiving PD-0332991 died as a result of disease progression while on therapy. Additionally, the combination of PD-0332991 and radiation therapy resulted in significantly increased survival benefit compared with either therapy alone. In total, our results support clinical trial evaluation of PD-0332991 against newly diagnosed as well as recurrent GBM, and indicate that Rb status is the primary determinant of potential benefit from this therapy.
authors.affiliation: Department of Neurological Surgery, Helen Diller Comprehensive Cancer Center, University of California San Francisco, California 94143-0520, USA.
authors.forename: Karine
authors.initials: K
authors.lastname: Michaud
authors.forename: David A
authors.initials: DA
authors.lastname: Solomon
authors.forename: Eric
authors.initials: E
authors.lastname: Oermann
authors.forename: Jung-Sik
authors.initials: JS
authors.lastname: Kim
authors.forename: Wei-Zhu
authors.initials: WZ
authors.lastname: Zhong
authors.forename: Michael D
authors.initials: MD
authors.lastname: Prados
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ozawa
authors.forename: C David
authors.initials: CD
authors.lastname: James
authors.forename: Todd
authors.initials: T
authors.lastname: Waldman
mesh_terms: D000818:Animals; D001812:Blood-Brain Barrier; D001932:Brain Neoplasms / Q000188:drug therapy / Q000201:enzymology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism*; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism*; D005260:Female; D005909:Glioblastoma / Q000188:drug therapy / Q000201:enzymology*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D009368:Neoplasm Transplantation; D010879:Piperazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D016160:Retinoblastoma Protein / Q000737:chemistry
chemical_list: D010879:Piperazines; D011725:Pyridines; D016160:Retinoblastoma Protein; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; C500026:palbociclib