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Doctoral thesis, 2012

Molecular properties of serum thymidine kinase 1 and use of the canine enzyme in disease monitoring

Sharif, Hanan


Thymidine kinase 1 (ATP: thymidine 5'-phosphotransferase, EC, TK1) catalyzes the transfer of the gamma phosphate group from a phosphate donor to the 5´- hydroxyl group of thymidine to form thymidine monophosphate, which is converted to thymidine triphosphate and then utilized in DNA synthesis. TK1 activity markedly increases in G1 and S phase of the cell cycle and is found mainly in dividing cells, but also in an extracellular form in the blood. Increased serum TK1 levels are considered as a sensitive and useful marker for cell proliferation and detection of malignancy in clinical medicine. The aim of this study was to investigate the molecular characteristics of canine thymidine kinase 1 and utilize several anti-TK1 antibodies to a better understanding its role in disease prognostics, risk assessment, and monitoring of cancer development. Study I was undertaken to clarify the structure of recombinant, cellular and serum TK1 in order to improve the usefulness of serum TK1 (STK1) as a proliferation biomarker in neoplastic diseases. Several forms of STK1 were observed with different enzymatic activities. The active form of STK1 was found mainly as an oligomer. Dimer and tetramer forms of STK1 were also seen in serum by immunoaffinity method, but they were enzymatically less active. Study II described a sensitive method using a [3H]-deoxythymidine phosphorylation assay to measure STK1 activity in dogs and humans with hematologic malignancies and dogs with solid tumors. The results revealed that the dThd phosphorylation assay was suitable for measurement of TK1 in hematologic malignancy (lymphoma and leukemia) and provided valuable information regarding the disease recurrence. Significant correlation was observed between the [3H]-dThd assay and the TK1 activity assays, TK-REA and TK Liaison. However, STK1 activity levels in dogs with solid tumors were very low. Therefore, another method to determine the levels of TK1 in serum based on immunoaffinity techniques was performed in study III. The concentration of STK1 protein in dogs with solid tumors was much higher than expected from the activity. Thus, methods to determine STK1 protein are more sensitive than activity tests in solid tumors. Study IV revealed that serum TK1 activity was elevated in 41% of bitches with pyometra, and thus TK1 determinations may be clinically valuable also in some non-neoplastic diseases.


blood biomarkers; thymidine kinase; cell proliferation biomarker; canine pyometra; radio-enzymatic assay; solid tumor; hematologic malignancy

Published in

Acta Universitatis Agriculturae Sueciae
2012, number: 2012:51
ISBN: 978-91-576-7698-6
Publisher: Dept. of Anatomy, Physiology and Biochemistry, Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Anatomy, Physiology and Biochemistry (AFB)

Associated SLU-program

Future Animal Health and Welfare (until Jan 2017)

UKÄ Subject classification

Medical Bioscience

URI (permanent link to this page)