Enzymatic markers of neoplastic transformation and regulation of purine and pyrimidine metabolism.

Abstract Enzymes that were identified as transformation-linked in the spectrum of hepatomas of different growth rates in the rat were used as markers of malignancy for liver tumors in rat and in man. The applicability of the enzymatic pattern was examined in kidney tumors of the rat, in lymphomas of the mouse and in hypernephroma-type kidney tumors in human. The impact of altered gene expression, as manifested in the enzymic imbalance, was further investigated by determining the concentration and behavior of purine and pyrimidine ribonucleotides in normal and neoplastic liver. The activity of transformation-linked enzymes was also studied in different organs of the rat and mouse to elucidate whether the activity might prove to be a predictor of the changes in activity observed in the different neoplasms. 1. 1.|In the hepatoma spectrum AMP deaminase and CTP synthetase activities were increased in all examined tumors and the rise correlated positively with the growth rate of the neoplasms. 2. 2.|A comparison of the in vivo concentrations (0-min sample) of ribonucleotides revealed that the level of adenine nucleotides was lower in rapidly-growing hepatoma 3924-A than in normal control liver. A further outstanding difference in ribonucleotide levels is the 5-fold increase in CTP content along with an overall elevation of the concentration of cytidine nucleotides. This biochemical imbalance in the hepatoma is attributed, in part at least, to the increased activity of UDP kinase and CTP synthetase in these tumors. 3. 3.|When ischemia was imposed, in normal liver there was a breakdown of the adenine, uridine, guanine and cytidine nucleotide triphosphates and a concurrent rise in the nucleoside monophosphate contents. It was particularly striking that the level of IMP increased 75-fold in 10-min ischemia. In contrast, no change was observed on ischemia in the hepatoma. When the hepatoma was injected with iodoacetamide and then subjected to ischemia the nucleoside triphosphates decreased as in the normal liver. 4. 4.|In measuring the activities of key carbohydrate, pentose phosphate, purine and pyrimidine enzymes we observed that frequently the high activity observed in the rat thymus was a predictor that the enzyme activity would be markedly increased in the rapidly growiing tumor. This relationship did not hoold without exception and did not apply to the mouse. 5. 5.|The integrated pattern of enzymatic alternations observed in rat, mouse and human neoplasms is specific to cancer cells, as no similar enzyme activity pattern was observed in the various normal organs and tissues examined in rat, mouse and human. 6. 6.|The present work demonstrates the applicability of the molecular correlation concept and much of the altered biochemical pattern discovered in the rat hepatoma spectrum to other tumors in rat, to lymphomas in mice and to primary kidney tumor in humans. Thus, increased activities of pyruvate kinase, glutamine PRPP amidotransferase, IMP dehydrogenase, AMP deaminase, adenylosuccinase and UDP kinase and decreased activity of xanthine oxidase were markers of malignancy in the three mouse tumors tested, plasma cell myeloma, Mecca lymphosarcoma and P1534 lymphocytic leukemia. In 15 cases of human hypernephromas, hexokinase and pyruvate kinase activities increased whereas those of glucose 6-phosphatase and fructose 1,6-diphosphatase decreased. Activities of glucose 6-phosphate dehydrogenase and glutamine PRPP amidotransferase increased, whereas that of xanthine oxidase decreased. IMP dehydrogenase, adenylosuccinase and AMP deaminase activities were elevated. Thus, these enzymes could be used in the biochemical diagnosis of human primary kidney tumors of the hypernephroma type. The biochemical imblance is similar to that observed in transplanted hepatomas and kidney tumors in the rat. 7. 7.|The applicability of the enzymatic imbalance observed in rodents to human tissue underlines the importance of such enzymatic markers in neoplastic transformation and these enzymes should be targets in the design of selective chemotherapy of neoplastic diseases.