Schedule-dependent cytotoxicity of 5-fluorouracil and irinotecan in a colon cancer cell line.
BACKGROUND
Our aim was to clarify the significance of widely accepted irinotecan (CPT-11)/5-fluorouracil (5-FU) combinations in colon cancer by investigating their sequential effect.


METHODS
The sequential effect of CPT-11/5-FU in two colon cancer cell lines, LoVo and SW480, was evaluated by WST-8 colorimetric assay. The cell cycle distributions of each drug were analyzed by flow cytometry, and then the chemoresistant mechanisms and expression of a drug transporter (MDR1), the bcl-2 apoptotic pathway, metabolizing enzymes [carboxylesterase (CE), dihydropyrimidine dehydrogenase], and target enzymes (topoisomerase I, thymidine synthase) associated with sequence-dependent cytotoxicity were examined.


RESULTS
The cytotoxicity of 5-FU (10, 100, 1000 microM) followed by CPT-11 (1 microM) was significantly greater than that of CPT-11 (1 microM) followed by 5-FU (10, 100, 1000 microM) (P < 0.05). Reverse transcription-polymerase chain reaction analysis revealed that exposure to 5-FU downregulated both MDR1 and bcl-2 mRNA and simultaneously upregulated CE2 mRNA expression, suggesting enhancement of subsequent CPT-11 cytotoxicity.


CONCLUSIONS
The cytotoxic effects of the CPT-11/5-FU combinations were shown to be schedule-dependent in human colon cancer cells. The findings suggest that 5-FU followed by CPT-11 administration might be the optimal sequence for CPT-11/5-FU treatment of advanced colon cancer.
Inoue
Yasuhiro
Y
Department of Gastrointestinal and Pediatric Surgery, Division of Reparative Medicine, Institute of Life Sciences, Mie University Graduate School of Medicine, 2-174 Edobashi, Tsu 514-8507, Japan.
Miki
Chikao
C
Watanabe
Hideki
H
Hiro
Junichiro
J
Toiyama
Yuji
Y
Ojima
Eiki
E
Yanagi
Hidenori
H
Kusunoki
Masato
M
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000964:Antimetabolites, Antineoplastic / Q000008:administration & dosage / Q000009:adverse effects; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000009:adverse effects; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage* / Q000009:adverse effects; D002166:Camptothecin / Q000008:administration & dosage / Q000009:adverse effects / Q000031:analogs & derivatives*; D003110:Colonic Neoplasms / Q000188:drug therapy*; D004334:Drug Administration Schedule; D005434:Flow Cytometry; D005472:Fluorouracil / Q000008:administration & dosage* / Q000009:adverse effects; D006801:Humans; D000077146:Irinotecan; D014407:Tumor Cells, Cultured
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000964:Antimetabolites, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D000077146:Irinotecan; D005472:Fluorouracil; D002166:Camptothecin