Dual targeting of the cyclin/Rb/E2F and mitochondrial pathways in mantle cell lymphoma with the translation inhibitor silvestrol.
OBJECTIVE
During cell-cycle progression, D-cyclins activate cyclin-dependent kinases (CDKs) 4/6 to inactivate Rb, permitting E2F1-mediated S-phase gene transcription. This critical pathway is typically deregulated in cancer, and novel inhibitory strategies would be effective in a variety of tumors. The protein synthesis inhibitor silvestrol has potent activity in B-cell leukemias via the mitochondrial pathway of apoptosis, and also reduces cyclin D1 expression in breast cancer and lymphoma cell lines. We hypothesized that this dual activity of silvestrol would make it especially effective in malignancies driven by aberrant cyclin D1 expression.


METHODS
Mantle cell lymphoma (MCL), characterized by elevated cyclin D1, was used as a model to test this approach. The cyclin D/Rb/E2F1 pathway was investigated in vitro using MCL cell lines and primary tumor cells. Silvestrol was also evaluated in vivo using an aggressive model of MCL.


RESULTS
Silvestrol showed low nanomolar potency both in MCL cell lines and primary MCL tumor cells. D-cyclins were depleted with just 10 nmol/L silvestrol at 16 hours, with subsequent reductions of phosphorylated Rb, E2F1 protein, and E2F1 target transcription. As showed in other leukemias, silvestrol caused Mcl-1 depletion followed by mitochondrial depolarization and caspase-dependent apoptosis, effects not related to inhibition of CDK4/6. Silvestrol significantly (P < 0.0001) prolonged survival in a MCL xenograft model without detectable toxicity.


CONCLUSIONS
These data indicate that silvestrol effectively targets the cyclin/CDK/Rb pathway, and additionally induces cytotoxicity via intrinsic apoptosis. This dual activity may be an effective therapeutic strategy in MCL and other malignancies.
Department of Internal Medicine, College of Medicine, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA.
Lapo
L
Alinari
Courtney J
CJ
Prince
Ryan B
RB
Edwards
William H
WH
Towns
Rajeswaran
R
Mani
Amy
A
Lehman
Xiaoli
X
Zhang
David
D
Jarjoura
Li
L
Pan
A Douglas
AD
Kinghorn
Michael R
MR
Grever
Robert A
RA
Baiocchi
David M
DM
Lucas
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D020522:Lymphoma, Mantle-Cell / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000628:therapy; D053858:Metabolic Networks and Pathways; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014183:Transplantation, Heterologous; D014315:Triterpenes / Q000494:pharmacology*; D001572:Benzofurans
D019938:Cyclin D1; D050687:E2F1 Transcription Factor; D016160:Retinoblastoma Protein; D014315:Triterpenes; C489897:silvestrol; D001572:Benzofurans