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

Biochem Pharmacol. 1998 Mar 1;55(5):667-76. 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 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antimetabolites, Antineoplastic / pharmacology*
  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Camptothecin / analogs & derivatives*
  • Camptothecin / pharmacology
  • Colorectal Neoplasms / metabolism
  • Colorectal Neoplasms / pathology*
  • DNA, Neoplasm / drug effects
  • Enzyme Inhibitors / pharmacology
  • Fluorouracil / pharmacology*
  • HT29 Cells
  • Humans
  • Irinotecan
  • S Phase / drug effects
  • Thymidylate Synthase / antagonists & inhibitors
  • Topoisomerase I Inhibitors


  • Antimetabolites, Antineoplastic
  • Antineoplastic Agents, Phytogenic
  • DNA, Neoplasm
  • Enzyme Inhibitors
  • Topoisomerase I Inhibitors
  • Irinotecan
  • Thymidylate Synthase
  • Fluorouracil
  • Camptothecin