Thymidine kinase 1 (TK), which is involved in the synthesis of
DNA precursors, is only expressed in S-G2 cells. Serum TK levels correlate to the proliferative activity of
tumor disease. Determinations of TK levels have so far relied on radio
enzyme assay (REA) and experimental ELISA methods, which have limited the clinical use of this
biomarker, although recent studies in dogs with
malignant lymphoma (ML) demonstrate its wide potential. A non-radiometric method based on a competitive immunoassay with specific anti-3'-azido-deoxythymidine monophosphate (
AZTMP)
antibodies has been further developed into the fully automated Liaison TK assay (DiaSorin). Sera from healthy dogs (
n=30), and dogs with
leukemia (LEUK) (n=35), ML (n=84), non-hematological
tumors (n=50), and inflammatory disease (n=14) were tested using both methods.
Lymphoma and LEUK samples were available before and during
chemotherapy. The coefficients of variation for the Liaison TK assay in this study were 6.3 and 3.4% (low/high TK, respectively), and the correlation between TK REA (X) and the Liaison TK assay (Y) was y=0.9203x+1.3854 (R2=0.9501). The TK1 levels measured during
chemotherapy gave very clear differences between dogs
in complete remission and dogs out of remission. A Tukey-Kramer analysis showed that all LEUKs and MLs out of remission differed significantly from the other groups. The Liaison TK assay showed high precision, high sensitivity and a good correlation to the TK REA. The Liaison TK assay provides valuable clinical information in the treatment and management of canine LEUK and ML, with a potential to be further validated in human trials.