Establishment of a camptothecin analogue (CPT-11)-resistant cell line of human non-small cell lung cancer: characterization and mechanism of resistance.
Camptothecin-11 (CPT-11) is a new derivative of camptothecin, a plant alkaloid antitumor agent, and a good candidate for clinical trials because of higher antitumor activity, less toxicity, and high aqueous solubility. CPT-11 is known to be altered into an active form, SN-38, by esterase in in vivo. CPT-11-resistant cells (PC-7/CPT) established from a human non-small cell lung cancer cell (PC-7) by stepwise, continuous treatment with CPT-11 exhibit about a 10-fold increase in resistance to the drug. CPT-11-resistant cells show a moderate cross-resistance to camptothecin (x8.6) and SN-38 (x8.6), and weak cross-resistance to Adriamycin (x2.2) and 5-fluorouracil (x2.4). The comparative studies between the parent (PC-7) and resistant (PC-7/CPT) cell lines with respect to their growth characterization shows a longer cell doubling time (45.8 versus 35.5 h), a lower cloning efficiency (3.2 versus 7.1%), and a lower population of S-phase cells (26.4 versus 36.0%) in the CPT-11-resistant cells. This observation may partly explain the resistance to CPT-11, a drug whose activity is cell cycle specific. Accumulation of CPT-11 is nearly the same in both cell lines. However, the intracellular concentration of SN-38 formed in the parent cells was 2-fold greater than in the CPT-11-resistant cells. This alteration may affect to some extent to the resistance. As assayed by relaxation of supercoiled plasmid DNA, the total activity of DNA topoisomerase I from the CPT-11-resistant cells was shown to be reduced to one-fourth its level in sensitive cells. The reduced activity was caused by a reduction of amount of DNA topoisomerase I. Furthermore, the enzyme from the resistant cells was shown to be 5-fold more resistant to CPT-11 than the enzyme from the parent cells. Thus, decreased total activity of topoisomerase I may play an important role in cellular resistance to CPT-11, and it appears that this decreased activity is due to a resistant form of topoisomerase I in CPT-11 resistant cells.
Kanzawa
F
F
Pharmacology Division, National Cancer Center Research Institute, Tokyo, Japan.
Sugimoto
Y
Y
Minato
K
K
Kasahara
K
K
Bungo
M
M
Nakagawa
K
K
Fujiwara
Y
Y
Liu
L F
LF
Saijo
N
N
D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D002289:Carcinoma, Non-Small-Cell Lung / Q000201:enzymology / Q000473:pathology*; D002467:Cell Nucleus / Q000201:enzymology; D004264:DNA Topoisomerases, Type I / Q000032:analysis; D004351:Drug Resistance; D006801:Humans; D000077146:Irinotecan; D008175:Lung Neoplasms / Q000201:enzymology / Q000473:pathology*; D014407:Tumor Cells, Cultured
D000972:Antineoplastic Agents, Phytogenic; D000077146:Irinotecan; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin