Mechanism of cross-resistance to a camptothecin analogue (CPT-11) in a human ovarian cancer cell line selected by cisplatin.
We established a cisplatin-resistant human ovarian cancer cell line (HAC2/0.1) from the parent cell line (HAC2/P) by continuous exposure of HAC2/P to 0.1 microgram of cisplatin/ml. Drug sensitivity determined by colony assay revealed that HAC2/0.1 was 2.4 times as resistant to cisplatin as the parental cell line. HAC2/0.1 was 12.1 and 2.0 times as resistant to (4s)-4,11-diethyl-4-hydroxy-9-[(4-piperidinopiperidino)-carbony loxy]dione hydrochloride trithydrate (CPT-11) and 7-ethyl-10-hydroxy-CPT (SN-38; an active metabolite of CPT-11), respectively, than HAC2/P. We studied the mechanism of cross-resistance to CPT-11 in HAC2/0.1. The glutathione (GSH) content was higher in HAC2/0.1 than in HAC2/P. The activity of DNA topoisomerase I and the accumulation of CPT-11 and SN-38 were also the same. On the other hand, the conversion of CPT-11 to SN-38 in HAC2/0.1 was about 3-fold less than in HAC2/P. Treatment of the parent and resistant cell lines with buthionine sulfoxamine (BSO) decreased the GSH content of both cell lines and decreased the 50% inhibitory concentrations of all the tested drugs for HAC2/0.1. The accumulation of CPT-11 in HAC2/0.1 but not in HAC2/P was increased by BSO treatment. On the other hand, in HAC2/P the 50% inhibitory concentrations of SN-38 and CPT-11 were not influenced by BSO treatment. The 50% inhibitory concentration of CPT-11 for HAC2/0.1 was not reduced by BSO treatment to the level for HAC2/P, even though the GSH content had been reduced more than in HAC2/P. These results show that there is no clear relationship between GSH and resistance to CPT-11. The decreased conversion of CPT-11 to SN-38 is considered to be the main cause of resistance to CPT-11 in this cell line.
Department of Obstetrics and Gynecology, Tokyo Jikei University School of Medicine, Minato-ku, Japan.
S
S
Niimi
K
K
Nakagawa
Y
Y
Sugimoto
K
K
Nishio
Y
Y
Fujiwara
S
S
Yokoyama
Y
Y
Terashima
N
N
Saijo
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000633:toxicity; D002945:Cisplatin / Q000633:toxicity*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004351:Drug Resistance; D005260:Female; D015870:Gene Expression; D016259:Genes, myc; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D000077146:Irinotecan; D008562:Membrane Glycoproteins / Q000235:genetics; D010051:Ovarian Neoplasms / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D014407:Tumor Cells, Cultured / Q000187:drug effects*
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D000077146:Irinotecan; D005982:Glutathione Transferase; D004264:DNA Topoisomerases, Type I; D005978:Glutathione; D002945:Cisplatin; D002166:Camptothecin