Document Detail

Correlations between S and G2 arrest and the cytotoxicity of camptothecin in human colon carcinoma cells.
MedLine Citation:
PMID:  8813137     Owner:  NLM     Status:  MEDLINE    
Previous cell line comparisons indicated that neither S-phase fraction nor topoisomerase I (top1) levels are sufficient to predict camptothecin (CPT) cytotoxicity (F. Goldwasser el al., Cancer Res., 55: 2116-2121, 1995.). To identify new determinants for CPT activity, two mutant p53 human colon cancer cell lines, SW620 and KM12, that were previously reported to have similar top1 levels and differential sensitivity to CPT were studied. No difference in the kinetics of top1-mediated DNA single-strand breaks or DNA synthesis inhibition were observed after 1 h exposure to 1 microM CPT. Pulse-labeling alkaline elution showed deficiency of damaged replicon elongation in the more sensitive SW620 cells. Consistentiy, flow cytometry analyses showed that KM12 was arrested in G2, whereas SW620 cells were irreversibly blocked in S phase. Aphidicolin protection was minimal in KM12 and more pronounced in the more sensitive SW620 cells. Thus, CPT appears to have two cytotoxic mechanisms, one protectable by aphidicolin and present in SW620 and the other not protectable by aphidicolin and common to both cell lines. SW620 exhibited also a greater capacity to break through the G2 checkpoint after DNA damage. Consistently, SW620 cells failed to down-regulate cyclin B-cdc2 kinase activity, whereas KM12 cells down-regulated cyclin B/cdc2 kinase activity within 30 min to 20 % of control level after CPT treatment. Analysis of the 7 human colon carcinoma cell lines of the NCI Anticancer Drug Screen showed that defects in replicon elongation and G2 breakthrough capability correlate with sensitivity to CPT. Our results suggest that misrepair of damaged replicons and/or alterations in DNA damage checkpoints is critical to defining chemosensitivity to CPT-induced top1-cleavable complexes and that CPT appears to have two cytotoxic mechanisms, one protectable by aphidicolin, and the other not.
F Goldwasser; T Shimizu; J Jackman; Y Hoki; P M O'Connor; K W Kohn; Y Pommier
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Cancer research     Volume:  56     ISSN:  0008-5472     ISO Abbreviation:  Cancer Res.     Publication Date:  1996 Oct 
Date Detail:
Created Date:  1996-11-21     Completed Date:  1996-11-21     Revised Date:  2009-11-19    
Medline Journal Info:
Nlm Unique ID:  2984705R     Medline TA:  Cancer Res     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  4430-7     Citation Subset:  IM    
Laboratory of Molecular Pharmacology, Division of Basic Sciences, National Cancer Institute, NIH, Bethesda, Maryland 20892-4255, USA.
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MeSH Terms
Antineoplastic Agents, Phytogenic / pharmacology*
Aphidicolin / pharmacology
CDC2 Protein Kinase / metabolism
Camptothecin / pharmacology*
Carcinoma / pathology*
Colonic Neoplasms / pathology*
Cyclins / metabolism
DNA Damage
DNA Repair
DNA Replication / drug effects
DNA Topoisomerases, Type I / antagonists & inhibitors*
Enzyme Inhibitors / pharmacology*
G2 Phase / drug effects*
S Phase / drug effects*
Tumor Cells, Cultured
Reg. No./Substance:
0/Antineoplastic Agents, Phytogenic; 0/Cyclins; 0/Enzyme Inhibitors; 38966-21-1/Aphidicolin; 7689-03-4/Camptothecin; EC Protein Kinase; EC Topoisomerases, Type I

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