Abstract |
As a single agent, gemcitabine (2',2'-difluorodeoxycytidine) has shown minimal activity against gastrointestinal malignancies with only a modest improvement in survival in patients with pancreatic cancer. Recently, gemcitabine resistance has been associated with the up-regulation of mRNA and protein levels of the ribonucleotide reductase M2 subunit (RR-M2), a rate-limiting enzyme in DNA synthesis that is cell cycle regulated. In this study we show that flavopiridol, a cyclin-dependent kinase inhibitor, enhances the induction of apoptosis by gemcitabine in human pancreatic, gastric, and colon cancer cell lines. As determined by quantitative fluorescence microscopy, flavopiridol enhanced gemcitabine-induced apoptosis 10-15-fold in all of the cell lines tested in a sequence-dependent manner. This was confirmed by poly(ADP-ribose) polymerase cleavage and mitochondrial cytochrome c release. Colony formation assays confirmed the apoptotic rates, showing complete suppression of colony formation only after exposure to sequential treatment of G(24)-->F(24). This is associated with suppression of the RR-M2 protein. This appears to be related to down-regulation of E2F-1, a transcription factor that regulates RR-M2 transcription and hypophosphorylation of pRb. The proteasome inhibitor PS-341 could restore the protein levels of E2F-1 in G(24)-->F(24) treatment indicating that E2F-1 down-regulation is attributable to its increased degradation via ubiquitin- proteasome pathway. This also resulted in restoration of RR-M2 mRNA and protein. These results indicate that flavopiridol in gemcitabine-treated cells inhibits parts of the machinery necessary for the transcription induction of RR-M2. Thus, combining flavopiridol with gemcitabine may provide an important and novel new means of enhancing the efficacy of gemcitabine in the treatment of gastrointestinal cancers.
|
Authors | C P Jung, M V Motwani, G K Schwartz |
Journal | Clinical cancer research : an official journal of the American Association for Cancer Research
(Clin Cancer Res)
Vol. 7
Issue 8
Pg. 2527-36
(Aug 2001)
ISSN: 1078-0432 [Print] United States |
PMID | 11489836
(Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)
|
Chemical References |
- Antineoplastic Agents
- Cell Cycle Proteins
- Cyclin E
- Cytochrome c Group
- DNA-Binding Proteins
- E2F Transcription Factors
- E2F1 Transcription Factor
- E2F1 protein, human
- Enzyme Inhibitors
- Flavonoids
- Multienzyme Complexes
- Piperidines
- Protein Subunits
- RNA, Messenger
- Retinoblastoma Protein
- Transcription Factors
- Deoxycytidine
- Tritium
- Cyclin D1
- alvocidib
- Ribonucleotide Reductases
- Poly(ADP-ribose) Polymerases
- Cysteine Endopeptidases
- Proteasome Endopeptidase Complex
- Thymidine
- Gemcitabine
|
Topics |
- Antineoplastic Agents
(pharmacology)
- Apoptosis
(drug effects)
- Blotting, Western
- Cell Cycle Proteins
(drug effects, metabolism)
- Cyclin D1
(drug effects, metabolism)
- Cyclin E
(drug effects, metabolism)
- Cysteine Endopeptidases
(drug effects, metabolism)
- Cytochrome c Group
(drug effects, metabolism)
- DNA-Binding Proteins
- Deoxycytidine
(analogs & derivatives, pharmacology)
- Dose-Response Relationship, Drug
- Down-Regulation
- Drug Synergism
- E2F Transcription Factors
- E2F1 Transcription Factor
- Enzyme Inhibitors
(pharmacology)
- Flavonoids
(pharmacology)
- Gastrointestinal Neoplasms
(drug therapy, enzymology, pathology)
- Gene Expression Regulation, Enzymologic
(drug effects)
- Humans
- Mitochondria
(drug effects, metabolism)
- Multienzyme Complexes
(drug effects, metabolism)
- Phosphorylation
(drug effects)
- Piperidines
(pharmacology)
- Poly(ADP-ribose) Polymerases
(metabolism)
- Proteasome Endopeptidase Complex
- Protein Subunits
- RNA, Messenger
(drug effects, genetics, metabolism)
- Retinoblastoma Protein
(drug effects, metabolism)
- Ribonucleotide Reductases
(antagonists & inhibitors, genetics, metabolism)
- Thymidine
(metabolism)
- Transcription Factors
(drug effects, metabolism)
- Tritium
- Tumor Cells, Cultured
- Tumor Stem Cell Assay
- Gemcitabine
|