Experimental modulation of PRPP availability for ribonucleotide synthesis from hypoxanthine in human skin fibroblast cultures

Adenosine metabolism in human skin fibroblasts

When normal fibroblasts were incubated in media containing various initial concentrations of [8-14C]adenosine, ranging from 0.25 to 400 microM, under conditions where product formation was linear, greater than 90% of the intracellular label was found in adenine nucleotides, largely in the form of ATP, less than 1% of the intracellular label appeared in the nucleic acids, the remaining intracellular label was found in adenosine, inosine, and hypoxanthine, and the media contained two labeled products, inosine and hypoxanthine. Production of labeled inosine and hypoxanthine from adenosine was considerably lower in adenosine deaminase (ADA)-deficient cells than in normal cells and virtually eliminated in normal cells by the presence of 1 microM deoxycoformycin (a potent ADA inhibitor), suggesting that labeled inosine and hypoxanthine production requires ADA activity. Initial rates of deamination (inosine and hypoxanthine formation) and phosphorylation (adenine nucleotide formation) were estimated by examining the metabolic fate of [8-14C]adenosine in hypoxanthine phosphoribosyltransferase-deficient cells, which cannot recycle hypoxanthine. The estimate of the initial rate of phosphorylation exceeded that of deamination only at the lowest adenosine concentration examined (0.25 microM). The ratio of deamination to phosphorylation rose from approximately 1 at 0.41 microM to approximately 15 at 400 microM extracellular adenosine.

Effect of L-glutamine antagonists on 5-phosphoribosyl 1-pyrophosphate levels in P388 leukemia and in murine colon adenocarcinomas in vivo

The intratumoral content of 5-phosphoribosyl 1-pyrophosphate (PRPP) and the activity of the enzymes anabolizing and catabolizing the sugar phosphate were determined following i.p. administration of an LD10 dose of an L-glutamine antagonist or saline to tumor-bearing animals. Elevation of PRPP pool size following administration of L-[alpha S,5S]-alpha-amino-3-chloro-4,5-dihydro-5-isopazoleacetic acid (NSC-163501) (AT-125) was maximal at 8 hr and returned to pretreatment levels by 24 hr. In P388 leukemia, dose for dose, at 4 hr, 6-diazo-5-oxo-L-norleucine (NSC-7365) (DON) was the most potent of the L-glutamine antagonists in elevating basal PRPP pool size (50% above control) followed by AT-125 and azaserine, 300 and 100% above control respectively. Moreover, such augmentation in PRPP pool size preferentially affected P388 tumor rather than the small intestine. Following i.p. administration of LD10 doses of AT-125, DON and azaserine, the specific activities of PRPP anabolizing and catabolizing enzymes were determined. A significant inhibition of PRPP amidotransferase was demonstrated with DON and AT-125 (P less than 0.05), and no inhibition with azaserine. A similar modulation of PRPP pool size demonstrated in vivo following administration of 250 mg/kg of ART-125 in mice bearing colonic adenocarcinoma lines. It was suggested that a significant increase of PRPP pool size might cause the possible synergism of a selected L-glutamine antagonist and 5-fluorouracil as reported after the appropriately scheduled administration of methotrexate and 5-fluorouracil.