Dual role of glutathione in modulating camptothecin activity: depletion potentiates activity, but conjugation enhances the stability of the topoisomerase I-DNA cleavage complex.
Depletion of glutathione (GSH) in MCF-7 and MDA-MB-231 cell lines by pretreatment with the GSH synthesis inhibitor buthionine sulfoximine potentiated the activity of 10,11-methylenedioxy-20(S)-camptothecin, SN-38 [7-ethyl-10-hydroxy-20(S)-camptothecin], topotecan, and 7-chloromethyl-10,11-methylenedioxy-20(S)-camptothecin (CMMDC). The greatest potentiation was observed with the alkylating camptothecin CMMDC. Buthionine sulfoximine pretreatment also increased the number of camptothecin-induced DNA-protein crosslinks, indicating that GSH affects the mechanism of action of camptothecin. We also report that GSH interacts with CMMDC to form a stable conjugate, 7-(glutathionylmethyl)-10,11-methylenedioxy-20(S)-camptothecin (GSMMDC), which is formed spontaneously in buffered solutions and in MCF-7 cells treated with CMMDC. GSMMDC was synthesized and found to be nearly as active as 10,11-methylenedioxy-20(S)-camptothecin in a topoisomerase (topo) I-mediated DNA nicking assay. The resulting topo I cleavage complexes were remarkably stable. In cell culture, GSMMDC displayed potent growth-inhibitory activity against U937 and P388 leukemia cell lines. GSMMDC was not active against a topo I-deficient P388 cell line, indicating that topo I is its cellular target. Peptide-truncated analogues of GSMMDC were prepared and evaluated. All three derivatives [7-(gamma-glutamylcysteinylmethyl)-10,11-methylenedioxy-20(S)-camptothecin, 7-(cysteinylglycylmethyl)-10,11-methylenedioxy-20(S)-camptothecin, and 7-(cysteinylmethyl)-10,11-methylenedioxy-20(S)-camptothecin] displayed topo I and cell growth-inhibitory activity. These results suggest that 7-peptidyl derivatives represent a new class of camptothecin analogues.
Gamcsik
M P
MP
Department of Medicine, Duke Comprehensive Cancer Center, Duke University Medical Center, Durham, North Carolina 27710, USA.
Kasibhatla
M S
MS
Adams
D J
DJ
Flowers
J L
JL
Colvin
O M
OM
Manikumar
G
G
Wani
M
M
Wall
M E
ME
Kohlhagen
G
G
Pommier
Y
Y
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology*; D002851:Chromatography, High Pressure Liquid; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000378:metabolism*; D004357:Drug Synergism; D005260:Female; D005978:Glutathione / Q000502:physiology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured / Q000187:drug effects* / Q000378:metabolism
D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; D019328:Buthionine Sulfoximine; D004264:DNA Topoisomerases, Type I; D005978:Glutathione; D002166:Camptothecin