title: Cellular interactions of 5-fluorouracil and the camptothecin analogue CPT-11 (irinotecan) in a human colorectal carcinoma cell line.
abstract: CPT-11 (irinotecan) is a DNA topoisomerase I inhibitor active against metastatic colorectal carcinoma. We investigated, in a human colon carcinoma cell line, HT-29, the effects of CPT-11 and 5-fluorouracil (5FU) combinations. A strong synergism between CPT-11 and 5FU was observed after sequential exposure and only additivity or antagonism after simultaneous exposure. When cells were first exposed to 5FU, the product of cellular CPT-11 concentrations versus time (CxT) was 6895 +/- 1020 pmol x hr/10(6) cells, while it was 3875 +/- 121 pmol x hr/10(6) cells with CPT-11 alone (p < 0.01). The same phenomenon was observed with SN-38: 148.2 +/- 49.5 versus 83.4 +/- 23.6 pmol x hr/10(6) cells (p < 0.05). Consequently, the formation of protein-DNA complexes was 1.4 times greater with 5FU pretreatment than with CPT-11 alone (p = 0.03). Moreover, the incorporation of 5FU derivatives into DNA was multiplied by a factor of 1.5 24 hr after CPT-11 exposure. When cells were first incubated with CPT-11, the decrease in thymidylate synthase (TS) activity was identical to that obtained after 5FU exposure (1.09 to 0.023 pmol/min/mg protein), but this decrease persisted for 24 hr (0.014 pmol/min/mg protein) (p = 0.035). At the same time, a 1.8-fold increase in the incorporation of 5FU derivatives into DNA and a 2-fold increase in DNA-protein complex formation were evidenced. With the two sequential associations, we observed a persistent S-phase arrest, as compared with CPT-11 alone. These results suggest that CPT-11 and 5FU combinations are of clinical interest, and mechanisms of interaction between the two drugs seem to be multifactorial.
authors.affiliation: Groupe de Pharmacologie Clinique et Expérimentale, Institut Claudius Regaud, Toulouse, France.
authors.forename: S
authors.initials: S
authors.lastname: Guichard
authors.forename: I
authors.initials: I
authors.lastname: Hennebelle
authors.forename: R
authors.initials: R
authors.lastname: Bugat
authors.forename: P
authors.initials: P
authors.lastname: Canal
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D002166:Camptothecin / Q000031:analogs & derivatives* / Q000494:pharmacology; D015179:Colorectal Neoplasms / Q000378:metabolism / Q000473:pathology*; D004273:DNA, Neoplasm / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005472:Fluorouracil / Q000494:pharmacology*; D019073:HT29 Cells; D006801:Humans; D000077146:Irinotecan; D016196:S Phase / Q000187:drug effects; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors; D059004:Topoisomerase I Inhibitors
chemical_list: D000964:Antimetabolites, Antineoplastic; D000972:Antineoplastic Agents, Phytogenic; D004273:DNA, Neoplasm; D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D000077146:Irinotecan; D013940:Thymidylate Synthase; D005472:Fluorouracil; D002166:Camptothecin