title: A novel therapeutic combination using PD 0332991 and bortezomib: study in the 5T33MM myeloma model.
abstract: Multiple myeloma (MM) remains incurable partly because no effective cell cycle-based therapy has been available to both control tumor cell proliferation and synergize with cytotoxic killing. PD 0332991 is an orally active small molecule that potently and specifically inhibits Cdk4 and Cdk6. It has been shown to induce rapid G(1) cell cycle arrest in primary human myeloma cells and suppress tumor growth in xenograft models. To improve therapeutic targeting of myeloma progression, we combined tumor suppression by PD 0332991 with cytotoxic killing by bortezomib, a proteasome inhibitor widely used in myeloma treatment, in the immunocompetent 5T33MM myeloma model. We show that 5T33MM tumor cells proliferate aggressively in vivo due to expression of cyclin D2, elevation of Cdk4, and impaired p27(Kip1) expression, despite inhibition of Cdk4/6 by p18(INK4c) and the maintenance of a normal plasma cell transcription program. PD 0332991 potently inhibits Cdk4/6-specific phosphorylation of Rb and cell cycle progression through G(1) in aggressively proliferating primary 5T33MM cells, in vivo and ex vivo. This leads to tumor suppression and a significant improvement in survival. Moreover, induction of G(1) arrest by PD 0332991 sensitizes 5T33MM tumor cells to killing by bortezomib. Inhibition of Cdk4/6 by PD 0332991, therefore, effectively controls myeloma tumor expansion and sensitizes tumor cells to bortezomib killing in the presence of an intact immune system, thereby representing a novel and promising cell cycle-based combination therapy.
authors.affiliation: Vrije Universiteit Brussels, Laarbeeklaan 103, Brussels, Belgium.
authors.forename: Eline
authors.initials: E
authors.lastname: Menu
authors.forename: Josefina
authors.initials: J
authors.lastname: Garcia
authors.forename: Xiangao
authors.initials: X
authors.lastname: Huang
authors.forename: Maurizio
authors.initials: M
authors.lastname: Di Liberto
authors.forename: Peter L
authors.initials: PL
authors.lastname: Toogood
authors.forename: Isan
authors.initials: I
authors.lastname: Chen
authors.forename: Karin
authors.initials: K
authors.lastname: Vanderkerken
authors.forename: Selina
authors.initials: S
authors.lastname: Chen-Kiang
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis; D001897:Boronic Acids / Q000008:administration & dosage*; D000069286:Bortezomib; D002453:Cell Cycle; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D051361:Cyclin-Dependent Kinase 6 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000008:administration & dosage; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009101:Multiple Myeloma / Q000188:drug therapy*; D009368:Neoplasm Transplantation; D010879:Piperazines / Q000008:administration & dosage*; D011719:Pyrazines / Q000008:administration & dosage*; D011725:Pyridines / Q000008:administration & dosage*
chemical_list: D001897:Boronic Acids; D004791:Enzyme Inhibitors; D010879:Piperazines; D011719:Pyrazines; D011725:Pyridines; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000069286:Bortezomib; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; C500026:palbociclib