METABOLISM AND METABOLIC ACTIONS OF 6-METHYLPURINE AND 2-FLUOROADENINE IN HUMAN-CELLS

Activation of purine nucleoside analogs by Escherichia coli purine nuc leoside phosphorylase (PNP) is being evaluated as a suicide gene thera py strategy for the treatment of cancer. Because the mechanisms of act ion of two toxic purine bases, 6-methylpurine (MeP) and 2-fluoroadenin e (F-Ade), that are generated by this approach are poorly understood, mechanistic studies were initiated to learn how these compounds differ from agents that are being used currently. The concentration of F-Ade , MeP, or 5-fluorouracil required to inhibit CEM cell growth by 50% af ter a 4-hr incubation was 0.15, 9, or 120 mu M, respectively. F-Ade an d MeP were also toxic to quiescent MRC-5, CEM, and Balb 3T3 cells. Tre atment of CEM, MRC-5, or Balb 3T3 cells with either F-Ade or MeP resul ted in the inhibition of protein, RNA, and DNA syntheses. CEM cells co nverted F-Ade and MeP to F-ATP and MeP-ribonucleoside triphosphate (Me P-R-TP), respectively. The half-life for disappearance of HeP-ribonucl eosiJe triphosphate from CEM cells was approximately 48 hr, whereas th e half-lives of F-ATP and ATP were approximately 5 hr. Both MeP and F- Ade were incorporated into the RNA and DNA of CEM cells. These studies indicated that the mechanisms of action of F-Ade and MeP were quite d ifferent from those of other anticancer agents, and suggested that the generation of these agents in tumor cells by E. coli PNP could result in significant advantages over these generated by either herpes simpl ex virus thymidine kinase or E. coli cytosine deaminase. These advanta ges include a novel mechanism of action resulting in toxicity to non-p roliferating and proliferating tumor cells and the high potency of the se agents during short-term treatment. (C) 1998 Elsevier Science Inc.