title: E2F-1 overexpression sensitizes colorectal cancer cells to camptothecin.
abstract: Topoisomerase I inhibitors have been shown to have clinical activity against human colorectal cancer. Previous studies showed that the cytotoxicity of camptothecin, a topoisomerase I inhibitor, occurs mainly in the S -phase of the cell cycle and is protectable by aphidicolin, an inhibitor of replicative DNA polymerase in some camptothecin-sensitive colorectal cells. Transcription factor E2F-1 regulates the G1/S transition, and recent studies have shown that E2F-1 potentiated the cytotoxicity of some cell-cycle-related drugs. Therefore, the present study was designed to investigate the effect of adenovirus-mediated E2F-1 gene transfer on chemosensitivity of colorectal cancer to camptothecin, in vitro and in vivo. Two human colorectal cancer cells, SW620 (mutant p53) and RKO (wild-type p53), were treated with camptothecin, alone or in combination with adenoviral vectors expressing beta-galactosidase (Ad-LacZ), or E2F-1 (Ad-E2F-1). E2F-1 overexpression was confirmed by Western blot analysis. Ad-E2F-1 gene transfer at low doses (less than the LD(20) dose) markedly increased the sensitivity of human colorectal cancer cells to camptothecin in vitro, which is because of induction of apoptosis. Aphidicolin did not have any protective effect on the Ad-E2F-1/camptothecin-mediated cytotoxicity. The level of topoisomerase I expression was not affected by combination treatment as well, suggesting that DNA replication and topoisomerase I activity may not account for the molecular mechanism of cell killing in response to Ad-E2F-1/camptothecin treatment. Fas and Fas ligand expression were not altered by treatment with camptothecin and/or Ad-E2F-1. Moreover, combination of camptothecin and Ad-E2F-1 has an additive antitumor effect in an in vivo nude mouse xenograft model. When combined with camptothecin, E2F-1 adenovirus therapy resulted in a 95.7% decrease in tumor size compared to control groups (P<.05). These results suggest a chemosensitization strategy that may have clinical utility in human colorectal cancer.
authors.affiliation: Department of Surgery, University of Louisville, James Graham Brown Cancer Center, KY 40202, USA.
authors.forename: Yan Bin
authors.initials: YB
authors.lastname: Dong
authors.forename: Hai Liang
authors.initials: HL
authors.lastname: Yang
authors.forename: Kelly M
authors.initials: KM
authors.lastname: McMasters
mesh_terms: D000256:Adenoviridae / Q000235:genetics*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000627:therapeutic use*; D016590:Aphidicolin / Q000627:therapeutic use; D017209:Apoptosis; D002166:Camptothecin / Q000627:therapeutic use*; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000473:pathology / Q000628:therapy*; D003131:Combined Modality Therapy; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D016158:Genes, p53; D015316:Genetic Therapy; D005822:Genetic Vectors; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D059004:Topoisomerase I Inhibitors; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C493754:E2f1 protein, mouse; D059004:Topoisomerase I Inhibitors; D014157:Transcription Factors; D016590:Aphidicolin; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin