Cancer Research VOLUME 29 OCTOBER 1969 NUMBER 10 [CANCER RESEARCH 29, 1749- 1754, October 1969] Influence of Ribose Donors on the Action of 5-Fluorouracil 1 David Kessel2 and Thomas C. Hall 2 Laboratories of Pharmacology, Children's Cancer Research Foundation, Departments of Pathology and Medicine, Harvard Medical School, Boston, Massachusetts 02115, and Department of Pharmacology, University of Rochester Medical Center, Rochester, New York, 14620 SUMMARY Although the most potent antimetabolite formed from 5-fluorouracil in vivo is a deoxyribonucleotide, evidence has accumulated which suggests an antineoplastic role for drug ribonucleotides. A study of the consequences of stimulating 5-fluorouracil metabolism along pathways leading to drug ribonucleotides was therefore made, using murine leukemias. Appropriate ribose donors, e.g., glucose and inosine, strongly enhanced the conversion of 5-fluorouracil to ribonucleotides, both in vitro and in vivo, but this had little effect on drug-promoted survival of tumor-bearing animals. INTRODUCTION The antineoplastic agent 5-fluorouracil (FU)rapidly pene- trates murine leukemia cells (11, 18, 22) and is subsequently converted to 5-fluorouridine-5"-monophosphate via uridine phosphorylase and uridine kinase (1, 6, 33), and via a pyrimidine-5"-pyrophosphorylase (20, 30). Di- and triphos- phates of 5-fluorouridine are also formed (3, 12). The drug is also converted, to a minor extent, to 5"-fluoro-2"-deoxyuridine (FUdRP) (3), but not to deoxynucleoside-5"-di- or- triphos- phates. All of these derivatives of 5-fluorouracil are potential antimetabolites. The most potent appears to be FUdRP, which strongly inhibits thymidylate synthetase (1,4, 12, 13), leading to interference with DNA synthesis, but incorporation of FU into RNA (3) and competition between FU and uracil for ISupported by contracts PH 43-66-541 and NIH 69-39 from Chemotherapy, National Cancer Institute, Nltt, and by Grant 04739 from the National Cancer Institute, NIH. 2present address, to which requests for reprints should be sent: Department of Pharmacology, University of Rochester Medical Center, Rochester, New York 14620. Received January 15, 1969; accepted June 3, 1969. enzymes involved in uracil metabolism (7, 32) are possible additional sites of drug action. Many cell lines exposed to the drug develop "resistance" to FU by deletion or impairment of cellular enzymes needed for FU conversion to ribotides (7, 20, 28, 29). Presumably FUdRP formation was affected as well. Inherent response to FU in different murine leukemias has been related to cell capacity for conversion of FU to ribotides (23). A number of reports have indicated that glucose, or other ribose donors, can enhance the rate of FU conversion to nucleotides and can potentiate the antimetabolic action of the drug in tumor cells (9, 26, 35). We have investigated the effects of glucose and of selected ribosides on FU anabolism and on the antitumor action of FU in several murine leukemias. The effect of ribose donors on the rate of FU transport was also measured. MATERIALS AND METHODS Labeled and Nonlabeled Compounds. FU-2J 4 C (12 mc/mmole) was purchased from Calbiochem. Nonlabeled FU was provided by Hoffman-LaRoche; inosine, deoxyinosine, and adenosine were purchased from Sigma Chemical Co.; N-tris(hydroxymethyl)-methyl-2-aminoethane sulfonic acid buffer was purchased from Calbiochem. Animal Tumors. These were provided by I. Wodinsky of the Arthur D. Little Corp., Cambridge, Massachusetts. The L1210/FU cell line was originally supplied by Dorris Hutchi- son, Sloan-Kettering laboratories, and was carried in BDFa mice with daily injections (15 mg/kg) of FU. The Flexner- Jobling tumor was carried in Charles River CD random-bred rats. Methods of propagation of other cell lines have been described (31). Isolation and Incubation of Cells. Ascitic tumor cells were isolated from tumor-bearing animals (31) and resuspended in a medium buffered with 75 mM N-tris(hydroxymethyl)- methyl-2-aminoethane sulfonic acid (8) at pH 7.3, and containing, at levels found in Ehrlich ascitic fluid (16), 71 mM OCTOBER 1969 1749 Research. on November 27, 2021. © 1969 American Association for Cancer cancerres.aacrjournals.org Downloaded from