Novel camptothecin analogues that circumvent ABCG2-associated drug resistance in human tumor cells.
Irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxycamptothecin; CPT-11) is a widely used potent antitumor drug that inhibits mammalian DNA topoisomerase I (Topo I); however, overexpression of ABCG2 (BCRP/MXR/ABCP) can confer cancer cell resistance to SN-38, the active form of CPT-11. We have recently demonstrated that plasma membrane vesicles prepared from ABCG2-overexpressing PC-6/SN2-5H cells transported SN-38 and its glucuronide conjugate in an ATP-dependent manner (Nakatomi et al., Biochem Biophys Res Commun 2001;288:827-32). In the present study, we have characterized a total of 14 new camptothecin (CPT) analogues with respect to both the inhibition of Topo I and the substrate specificity of ABCG2. All of the tested CPT analogues, which have different substitutions at positions 10 and 11, strongly inhibited the Topo I activity in a cell-free system, as did SN-38. Their antitumor activities in the SN-38-resistant PC-6/SN2-5H2 cell line greatly varied, however, being correlated with intracellular accumulation levels. We have examined ATP-dependent transport of those CPT analogues by using plasma membrane vesicles prepared from both PC-6/SN2-5H2 cells and ABCG2-transfected HEK-293 cells. Based on the substrate specificity of ABCG2 thus evaluated, it is strongly suggested that CPT analogues with high polarity are good substrates for ABCG2 and are therefore effectively extruded from cancer cells. In this context, to circumvent ABCG2-associated drug resistance, low-polarity CPT analogues are considered to be potent lead compounds. The present study provides a practical approach to discover new CPT-based drugs for the chemotherapy of drug-resistant human cancer.
Yoshikawa
Megumi
M
Department of Drug Metabolism and Disposition, Meiji Pharmaceutical University, Noshio 2-522-1, Kiyose, Tokyo 204-8588, Japan.
Ikegami
Yoji
Y
Hayasaka
Shinya
S
Ishii
Kazuyuki
K
Ito
Akiko
A
Sano
Kazumi
K
Suzuki
Toshihiro
T
Togawa
Tadayasu
T
Yoshida
Hisahiro
H
Soda
Hiroshi
H
Oka
Mikio
M
Kohno
Shigeru
S
Sawada
Seigo
S
Ishikawa
Toshihisa
T
Tanabe
Shinzo
S
D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000970:Antineoplastic Agents / Q000633:toxicity; D001692:Biological Transport; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000633:toxicity*; D018288:Carcinoma, Small Cell; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D003001:Cloning, Molecular; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D006801:Humans; D008175:Lung Neoplasms; D009363:Neoplasm Proteins / Q000235:genetics*; D011994:Recombinant Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship
C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D000970:Antineoplastic Agents; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate; D002166:Camptothecin