Flavopiridol increases sensitization to gemcitabine in human gastrointestinal cancer cell lines and correlates with down-regulation of ribonucleotide reductase M2 subunit Journal Article
| Authors: | Jung, C. P.; Motwani, M. V.; Schwartz, G. K. |
| Article Title: | Flavopiridol increases sensitization to gemcitabine in human gastrointestinal cancer cell lines and correlates with down-regulation of ribonucleotide reductase M2 subunit |
| 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 G24→F24. 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 G24→F24 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. |
| Keywords: | cancer survival; protein phosphorylation; human cell; dna-binding proteins; antineoplastic agents; gemcitabine; pancreas cancer; dna synthesis; cell cycle proteins; apoptosis; proteasome endopeptidase complex; transcription initiation; down-regulation; cancer cell culture; dose-response relationship, drug; tumor cells, cultured; phosphorylation; transcription factors; digestive system cancer; drug synergism; gastrointestinal neoplasms; blotting, western; dna; enzyme regulation; enzyme inhibitors; rna, messenger; colon cancer; stomach cancer; flavonoids; flavopiridol; piperidines; protein subunits; cyclin d1; multienzyme complexes; deoxycytidine; enzyme subunit; retinoblastoma protein; mitochondria; nicotinamide adenine dinucleotide adenosine diphosphate ribosyltransferase; concentration response; cyclin e; thymidine; tritium; gene expression regulation, enzymologic; cytochrome c; poly(adp-ribose) polymerases; ribonucleotide reductase; colony formation; e2f1 transcription factor; cysteine endopeptidases; tumor stem cell assay; e2f transcription factors; humans; human; priority journal; article; ribonucleotide reductases; cytochrome c group |
| Journal Title: | Clinical Cancer Research |
| Volume: | 7 |
| Issue: | 8 |
| ISSN: | 1078-0432 |
| Publisher: | American Association for Cancer Research |
| Date Published: | 2001-08-01 |
| Start Page: | 2527 |
| End Page: | 2536 |
| Language: | English |
| PUBMED: | 11489836 |
| PROVIDER: | scopus |
| DOI/URL: | |
| Notes: | Export Date: 21 May 2015 -- Source: Scopus |
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