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Background: Thymidylate synthetase and thymidine kinase are key enzymes involved in de novo and salvage pathways for pyrimidine nucleotide synthesis, respectively., Materials and Methods: Weekly injections of 1,2-dimethyl-hydrazine induced high incidence of colorectal adenocarcinomas in rats., Results: An increased activity of thymidylate synthetase was found in the poorly differentiated adenocarcinomas of the chemically induced rat colorectal tumors. Six-week oral administration of 1-(2-tetrahydrofuryl)-5-fluorouracil in combination with uracil (UFT) reduced the total number of colorectal tumors, with the reduction of thymidylate synthetase activity in the poorly-differentiated type, though the mRNA expression of thymidylate synthetase and thymidine kinase differed little between the groups with or without UFT treatment., Conclusions: These results indicate that the long-term oral administration using UFT suppresses colorectal carcinogenesis and the growth of the poorly-differentiated type tumors.

Thymidylate synthetase (TS) and thymidine kinase (TK) are key enzymes in de novo and salvage pathways for pyrimidine nucleotide synthesis, respectively. A high incidence of colorectal adenocarcinomas with varied grades of cell differentiation can be induced by 1,2-dimethylhydrazine (DMH) in rats. The marked increases of TS and TK activities were found in the poorly and well-differentiated adenocarcinomas of the colon, respectively. Oral administration of 1-(2-tetrahydrofuryl)-5-fluorouracil in combination with uracil (UFT) markedly reduced the number and accumulated area of colonic carcinomas, and TS activity in the poorly differentiated adenocarcinomas. A potential balance between the de novo and the salvage pathways for pyrimidine nucleotide synthesis was suggested to be related with the histopathological grades of cell differentiation. Suppression of colonic TS activity by UFT administration reduced the colonic carcinogenesis and the potency of the poorly differentiated adenocarcinomas of the colon.

Thymidine kinase (TK) and thymidylate synthetase (TS) are known to catalyse the phosphorylation of thymidine for the salvage synthesis of dTMP and the methylation of dUMP for the de novo synthesis of dTMP, respectively. High TK and TS activities and the existence of TK isozymes have been observed in rapidly proliferating tissues. In this work I measured TK, TK-isozyme and TS activities, and DNA and RNA in human gastric cancer tissue. Tissue containing gastric cancer, (well differentiated adenocarcinoma (well: n = 29), poorly differentiated adenocarcinoma (por: n = 28)), and noninvolved paired normal gastric mucosa were obtained from fresh surgical specimens. Total TK and peak A TK activity of gastric cancer increased to 184% and 299% of activity of normal gastric mucosa. TK activity of "well" was higher than that of "por". On the other hand TS activity of gastric cancer increased to 122% of activity of normal gastric mucosa. TS activity of "por" was higher than that of "well". DNA and RNA content of gastric cancer increased to 294% and 228% than that of normal gastric mucosa. But difference wasn't observed between "well" and "por". These characteristics of gastric cancer suggest its susceptibility to control by inhibition of TK and TS.

Sho-Saiko-To (SST) is a modified Japanese traditional Chinese herbal medicine containing seven medical plants: Bupleuri radix, Pinelliae tuber, Suxtallariae radix, Zizyphi fructus, Ginseng radix, Glycyrrhizae radix, and Zingiberis recens rhizoma. This preparation has been used in the treatment of some inflammatory diseases of the respiratory system and chronic hepatitis. In the present study, the effects of SST were investigated on the activities of DNA-synthesizing enzymes in 1,2-dimethylhydrazine (DMH)-induced colonic carcinomas in rats. Six-week administration of SST prevented nearly 100% of the body weight loss and the final number of the colonic carcinomas compared to those in the rats treated with DMH alone, and suppressed the enhanced activities of thymidylate synthetase (TS) and thymidine kinase (TK) which were involved in the de novo and salvage pathways of pyrimidine synthesis, respectively, in DMH-induced colonic carcinomas. These results indicate that SST may show directly and/or indirectly inhibitory effects on the development of colonic carcinomas.

It has been known that a high incidence of adenocarcinoma in distal colon can be induced by s.c. injection of 1, 2-dimethylhydrazine (DMH) into rats at weekly intervals. We investigated effects of radiofrequency hyperthermia (RF-HT) in combination with anti-cancer drug UFT (a combination of tegafur and uracil) on activities of DNA-synthesizing enzymes, using colon carcinomas induced by DMH treatment in rats. 1) Thymidylate synthetase (TS), DNA-synthesizing enzyme in de novo pathway of pyrimidine metabolism, increased to approximately 7-fold that of normal control colon in DMH-induced colon carcinomas in activity, but was markedly reduced to 48% of that in the carcinomas by administration of UFT. 2) Thymidine kinase (TK) in salvage pathway increased to approximately 8-fold that of the control in the carcinomas in activity, but was markedly reduced to 25% of that in the carcinomas by RF-HT treatment. 3) The TK-isozyme, that was thought to be a fetal type in the intracellularly cytoplasmic fraction and closely involved in rapid DNA replication, increased to approximately 24-fold that of the control in the carcinomas in activity, but was reduced to the nearly same level as that of the control by RF-HT treatment. This isozyme was labile in thermostability and easy to be inactivated in low pH. 4) The activities of TS and TK in the carcinomas were extremely suppressed by UFT administration in combination with RF-HT treatment. These results indicate that hyperthermochemotherapy with UFT may serve as an available treatment for colon carcinomas.

Carcinoma of the colon was induced in rats by injection of a carcinogen 1,2-dimethylhydrazine (DMH), and thymidylate synthetase (TS) and thymidine kinase (TK) activities, which catalyze the biosynthesis of dTMP by the de novo pathway and the salvage pathway of pyrimidine synthesis, respectively, were measured in normal control colon, DMH-treated normal colon, and DMH-induced colon carcinoma with or without administration of two doses of an anti-cancer drug UFT (a combination of tegafur and uracil). TS and TK activities were both increased after treatment with DMH, markedly in colon carcinoma tissue, and to a lesser degree in normal-appearing colon tissue. This phenomenon is well explained by the hypothesis that biochemical alterations of DNA-synthesizing enzyme activities occur as a preliminary step prior to the development of overt cancerous transformation. A low dose of UFT inhibited TS activity but enhanced TK activity, therefore, the salvage pathway may compensate for the reduced level of the de novo synthesis. On the other hand, a large dose of UFT reduced both TS and TK activities, perhaps due to cytotoxic effects of UFT incorporation into RNA.

Thymidylate synthetase (TS) and thymidine kinase (TK) are known to catalyse the methylation of dUMP for the de novo synthesis of dTMP and the phosphorylation of thymidine for the salvage synthesis of dTMP in the pyrimidine pathway, respectively. High TS and TK activities have been observed in rapidly proliferating tissues such as foetal tissue, regenerating liver and carcinomas. TS and TK activities were measured in histologically normal colon mucosa and colorectal carcinomas with or without neo-adjuvant chemotherapy of an antitumor drug UFT (a combination of tegafur and uracil) in humans. In colorectal carcinomas, 5-FU and uracil levels were increased to 2.6- and 3.2-fold, respectively, those in normal colon mucosa by neo-adjuvant chemotherapy of UFT. In colorectal carcinomas, TS and TK activities were both increased to approximately 2- and 3-fold, respectively, those in normal colon mucosa without UFT treatment. In normal colon mucosa and colorectal carcinomas with neo-adjuvant chemotherapy of UFT, TS activities were reduced to approximately 50% and 40%, respectively, those without UFT treatment. These results indicate that neo-adjuvant chemotherapy with UFT may prevent dissemination of cancer cells during operation, and local recurrence and distant metastasis after operation, inhibiting DNA synthesis via the de novo pathway of pyrimidine synthesis in carcinomas.