title: A sensitive and kinetically defined radiochemical assay for canine and human serum thymidine kinase 1 (TK1) to monitor canine malignant lymphoma.
abstract: Thymidine kinase 1 (TK1) is a cell cycle regulated enzyme with maximum expression during the S phase. Serum TK1 (S-TK1) is a unique biomarker for cell proliferation. Here, an optimized [(3)H]-thymidine (dThd) phosphorylation assay is described, which is as sensitive as the commercially available TK-REA and TK-Liaison assays for measurement of S-TK1 activity in dogs and humans. Serum samples from dogs (35 healthy, 32 with lymphoma, 2 with leukemia, and 35 with solid tumors) and humans (18 healthy, 9 with chronic lymphocytic leukemia, 10 with myelodysplastic syndrome) were analyzed using the [(3)H]-dThd assay. Mean S-TK1 activities were 1.11 ± 0.46 pmol/min/mL in healthy dogs and 1.15 ± 0.32 pmol/min/mL in healthy humans. S-TK1 activities in dogs with hematological malignancies were 24.2 ± 47.9 pmol/min/mL, and the receiver operating characteristic curve showed an area under the curve of 0.88. With a cut-off value of 1.9 pmol/min/mL (mean value ± 2 SD), the sensitivity was 0.94 and the specificity was 0.68. Very similar results were obtained with human samples (healthy and lymphoma cases). S-TK1 activities measured during chemotherapy of six dogs with lymphoma were drastically reduced. In one case, S-TK1 activity increased prior to relapse. S-TK1 levels in dogs with solid tumors did not differ from the healthy group. S-TK1 activities correlated with those determined with the TK-REA and TK-Liaison assays (r=0.92 and r=0.96, respectively). In conclusion, this optimized [(3)H]-dThd assay is fast, sensitive and economical for measuring S-TK1 activity and should increase its clinical use as biomarker.
authors.affiliation: Department of Anatomy, Swedish University of Agricultural Sciences, BMC, P.O. Box 575, S-751 23 Uppsala, Sweden.
authors.forename: H
authors.initials: H
authors.lastname: Sharif
authors.forename: H
authors.initials: H
authors.lastname: von Euler
authors.forename: S
authors.initials: S
authors.lastname: Westberg
authors.forename: E
authors.initials: E
authors.lastname: He
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Eriksson
mesh_terms: D000818:Animals; D014408:Biomarkers, Tumor; D004283:Dog Diseases / Q000097:blood / Q000201:enzymology* / Q000378:metabolism; D004285:Dogs; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008223:Lymphoma / Q000097:blood / Q000378:metabolism / Q000662:veterinary*; D008297:Male; D000091402:Prohibitins; D011854:Radiochemistry / Q000379:methods*; D012680:Sensitivity and Specificity; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism*
chemical_list: D014408:Biomarkers, Tumor; C000717331:PHB2 protein, human; D000091402:Prohibitins; D013937:Thymidine Kinase; C092717:thymidine kinase 1