CDK inhibitors upregulate BH3-only proteins to sensitize human myeloma cells to BH3 mimetic therapies.
BH3 mimetic drugs induce cell death by antagonizing the activity of antiapoptotic Bcl-2 family proteins. Cyclin-dependent kinase (CDK) inhibitors that function as transcriptional repressors downregulate the Bcl-2 family member Mcl-1 and increase the activity of selective BH3 mimetics that fail to target this protein. In this study, we determined whether CDK inhibitors potentiate the activity of pan-BH3 mimetics directly neutralizing Mcl-1. Specifically, we evaluated interactions between the prototypical pan-CDK inhibitor flavopiridol and the pan-BH3 mimetic obatoclax in multiple myeloma (MM) cells in which Mcl-1 is critical for survival. Coadministration of flavopiridol and obatoclax synergistically triggered apoptosis in both drug-naïve and drug-resistant MM cells. Mechanistic investigations revealed that flavopiridol inhibited Mcl-1 transcription but increased transcription of Bim and its binding to Bcl-2/Bcl-xL. Obatoclax prevented Mcl-1 recovery and caused release of Bim from Bcl-2/Bcl-xL and Mcl-1, accompanied by activation of Bax/Bak. Whether administered singly or in combination with obatoclax, flavopiridol also induced upregulation of multiple BH3-only proteins, including BimEL, BimL, Noxa, and Bik/NBK. Notably, short hairpin RNA knockdown of Bim or Noxa abrogated lethality triggered by the flavopiridol/obatoclax combination in vitro and in vivo. Together, our findings show that CDK inhibition potentiates pan-BH3 mimetic activity through a cooperative mechanism involving upregulation of BH3-only proteins with coordinate downregulation of their antiapoptotic counterparts. These findings have immediate implications for the clinical trial design of BH3 mimetic-based therapies that are presently being studied intensively for the treatment of diverse hematopoietic malignancies, including lethal multiple myeloma.
Division of Hematology/Oncology, Department of Medicine, Virginia Commonwealth University and the Massey Cancer Center, Institute of Molecular Medicine, Richmond, Virginia 23298, USA.
Shuang
S
Chen
Yun
Y
Dai
Xin-Yan
XY
Pei
Jennifer
J
Myers
Li
L
Wang
Lora B
LB
Kramer
Mandy
M
Garnett
Daniella M
DM
Schwartz
Florence
F
Su
Gary L
GL
Simmons
Justin D
JD
Richey
Dustin G
DG
Larsen
Paul
P
Dent
Robert Z
RZ
Orlowski
Steven
S
Grant
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D040761:Biomimetic Materials / Q000008:administration & dosage / Q000494:pharmacology; D045744:Cell Line, Tumor; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D004357:Drug Synergism; D005419:Flavonoids / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D007211:Indoles; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D016688:Mice, Inbred NOD; D008819:Mice, Nude; D016513:Mice, SCID; D008928:Mitochondria / Q000187:drug effects; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000201:enzymology; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010446:Peptide Fragments / Q000378:metabolism; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011758:Pyrroles / Q000008:administration & dosage / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays; D051020:bcl-X Protein / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; C474007:Bax protein (53-86); D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D005419:Flavonoids; D007211:Indoles; C579094:Mcl1 protein, mouse; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010446:Peptide Fragments; D010880:Piperidines; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011758:Pyrroles; D051020:bcl-X Protein; C077990:alvocidib; D018844:Cyclin-Dependent Kinases; C520962:obatoclax