Cellular interactions of 5-fluorouracil and the camptothecin analogue CPT-11 (irinotecan) in a human colorectal carcinoma cell line

• Published in: Biochemical pharmacology 1998-03, Vol.55 (5), p.667-676
• Main Authors: Guichard, Sylvie, Hennebelle, Isabelle, Bugat, Roland, Canal, Pierre
• Format: Article
• Language: English
• Subjects: 5-fluorouracil; Antimetabolites, Antineoplastic - pharmacology; Antineoplastic agents; Antineoplastic Agents, Phytogenic - pharmacology; Biological and medical sciences; Camptothecin - analogs & derivatives; Camptothecin - pharmacology; Chemotherapy; Colorectal Neoplasms - metabolism; Colorectal Neoplasms - pathology; CPT-11; DNA, Neoplasm - drug effects; Enzyme Inhibitors - pharmacology; Fluorouracil - pharmacology; HT29 Cells; Humans; Irinotecan; Medical sciences; Pharmacology. Drug treatments; S Phase - drug effects; synergism, DNA-protein complexes; thymidylate synthase; Thymidylate Synthase - antagonists & inhibitors; topoisomerase I; Topoisomerase I Inhibitors
• ISSN: 0006-2952; 1873-2968
• DOI: 10.1016/S0006-2952(97)00541-8

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 · hr/10 6 cells, while it was 3875 ± 121 pmol · 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 · 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.