Methotrexate decreases thymidine kinase activity

• Published in: Biochemical and biophysical research communications Vol. 187; no. 1; pp. 522 - 528
• Main Authors: Abonyi, Margit, Prajda, Noemi, Hata, Yuki, Nakamura, Hiroyuki, Weber, George
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 31.08.1992; Elsevier
• Subjects: Animals; Antineoplastic agents; Biological and medical sciences; Bone Marrow - drug effects; Bone Marrow - enzymology; Bone Marrow Cells; Cell Count; Cycloheximide - pharmacology; Dactinomycin - pharmacology; General aspects; Kinetics; Liver - drug effects; Liver - enzymology; Liver Neoplasms, Experimental - enzymology; Male; Medical sciences; Methotrexate - administration & dosage; Methotrexate - pharmacology; Neoplasm Transplantation; Pharmacology. Drug treatments; Rats; Rats, Inbred Strains; Thymidine Kinase - antagonists & inhibitors; Thymidine Kinase - metabolism; MTX; IC 50; TdR; DH; t 1/2; s.c; GPRT; i.p; AZT; dTMP; APRT; Antineoplastic agent; Thymidine kinase; Rat; Enzyme; Rodentia; Time response relation; Dose activity relation; Antifolate; Vertebrata; Mammalia; Enzymatic activity; Animal; Mechanism of action
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/S0006-291X(05)81525-6

MTX eytotoxicity is not fully explained by its well-known inhibition of dihydrofolate reductase activity which leads to a decrease in the dTMP synthase reaction, since TdR kinase which converts TdR to dTMP could readily circumvent MTX action through this salvage activity. TdR kinase is of particular significance, since in various types of carcinoma cells its activity is orders of magnitude higher than that of dTMP synthase. To throw light on this problem, we tested the hypothesis that the impact of MTX treatment might in fact involve an inhibition or decrease in TdR kinase activity. Injection in rat of MTX (i.p.) decreased TdR kinase activity in a time- and dose-dependent fashion in liver (t 1/2 = 46 h; IC 50 = 95 mg/kg), bone marrow (t 1/2 = 10 h; IC 50 = 5 mg/kg) and rapidly growing transplantable hepatoma 3924A (t 1/2 = 56 h; IC 50 = 5 mg/kg). Injection in rat of cycloheximide (15 mg/kg, i.p.), an inhibitor of protein biosynthesis, rapidly decreased TdR kinase activity in the hepatoma (t 1/2 = 3.6 h); activities of other purine and pyrimidine synthetic enzymes, dTMP synthase, IMP dehydrogenase, GMP reductase and GMP synthase, declined at a markedly slower rate (t 1/2 = 11, 11.6, 12 and 22 h, respectively). MTX, by curtailing purine and pyrimidine biosynthesis, limits production of TdR kinase which is more sensitive to unopposed protein degradation than other enzymes of nucleic acid biosynthesis. TdR kinase is a newly discovered target of MTX treatment.