Inactivation of p53 increases the cytotoxicity of camptothecin in human colon HCT116 and breast MCF-7 cancer cells.
Camptothecin (CPT) derivatives are topoisomerase I (top1) inhibitors recently introduced as clinical agents. To explore the role of p53 in CPT-induced cytotoxicity, we examined CPT effects in two isogenic pairs of human cancer cell lines, MCF-7 breast carcinoma and HCT116 colon carcinoma cells, in which p53 function had been disrupted by transfection with the human papillomavirus type-16 E6 gene. Clonogenic survival assays showed that both MCF-7/E6 and HCT116/E6 cells were more sensitive to CPT. No differences in top1 protein levels and activity analyzed by a novel in vitro oligonucleotide assay were observed in the E6 transfectants. Also, CPT showed comparable top1 cleavable complex formation in vivo, as determined by DNA single-strand breaks and DNA protein cross-links. These results suggest that p53 can protect against CPT-induced cytotoxicity and that this protection is mediated downstream of CPT-induced DNA damage. Flow cytometry analyses showed that CPT can induce G1 arrest in cells with normal p53. This G1 arrest was markedly reduced in the p53-deficient cells. These results demonstrate a critical role of p53 as a G1 checkpoint regulator after CPT-induced DNA damage and suggest a rationale for the selectivity of CPT toward tumors with p53 mutations.
Gupta
M
M
Laboratory of Molecular Pharmacology, Division of Basic Sciences, National Cancer Institute, NIH, Bethesda, Maryland 20892-4255, USA.
Fan
S
S
Zhan
Q
Q
Kohn
K W
KW
O'Connor
P M
PM
Pommier
Y
Y
D000230:Adenocarcinoma / Q000473:pathology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology*; D002166:Camptothecin / Q000494:pharmacology*; D003110:Colonic Neoplasms / Q000473:pathology*; D004249:DNA Damage; D053938:DNA Fragmentation; D004273:DNA, Neoplasm / Q000032:analysis; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004967:Estrogens; D005260:Female; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects; D016158:Genes, p53; D006801:Humans; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D009376:Neoplasms, Hormone-Dependent / Q000473:pathology*; D015739:Nocodazole / Q000494:pharmacology; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012097:Repressor Proteins; D059004:Topoisomerase I Inhibitors; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014410:Tumor Stem Cell Assay; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors*
D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; C068651:E6 protein, Human papillomavirus type 16; D004791:Enzyme Inhibitors; D004967:Estrogens; D009363:Neoplasm Proteins; D009856:Oncogene Proteins, Viral; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53; D015739:Nocodazole; D002166:Camptothecin