Abstract
BackgroundThymidine kinase 1 (TK1) is a deoxyribonucleic acid (DNA) precursor enzyme and a proliferation biomarker used for prognosis and treatment monitoring of breast cancer in humans. The aim was to determine if serum thymidine kinase 1 (sTK1) activity and sTK1 protein levels in dogs with mammary tumors could be useful in veterinary medicine.ResultsSerum samples from 20 healthy dogs and 27 dogs with mammary tumors were analyzed for sTK1 activity, using an [3H]-deoxythymidine (dThd) phosphorylation assay, and for sTK1 protein levels by immune affinity/Western blot assay. The molecular forms of sTK1 in acute lymphocytic leukemia (ALL), canine mammary tumor (CMT), and healthy sera were determined by size exclusion chromatography.Mean sTK1 activities in CMT were 1.0 ± 0.36 pmol/min/mL, differing significantly from healthy dogs (mean ± SD = 0.73 ± 0.26 pmol/min/mL). Serum TK1 protein (26 kDa polypeptide) levels were also significantly higher in CMTs compared to healthy dogs (mean ± SD = 28.5 ± 11.4, and 8.5 ± 4 ng/mL, respectively). Cellular TK1 isolated from ALL tumor cells was predominantly a dimer, while the serum TK1 activity eluted as a high molecular weight (MW) oligomer. In analyses of CMT tissue extracts, TK1 activity eluted in two peaks, a minor peak with a high MW oligomer and a major tetramer peak. Western blot analysis of chromatographic fractions showed that cellular TK1 protein in both ALL and CMT dogs, and to some extent serum TK1 from ALL dogs, correlated with activity profiles, but a large fraction of inactive TK1 protein was detected in CMT.ConclusionsSerum TK1 protein and activity levels were significantly higher in CMT than in healthy dogs. Size exclusion chromatography demonstrated major differences in the molecular forms of sTK1 in ALL, healthy, and CMT dogs, with a large fraction of inactive TK1 protein in CMT. Our results showed that the sTK1 protein assay can differentiate benign tumors (early stage tumors) from healthy more efficiently than sTK1 activity assay. This preliminary data supports that sTK1 protein assay is clinically useful. Further studies are needed to evaluate the diagnostic or prognostic role of serum TK1 protein in CMTs.
Highlights
Thymidine kinase 1 (TK1) is a deoxyribonucleic acid (DNA) precursor enzyme and a proliferation biomarker used for prognosis and treatment monitoring of breast cancer in humans
Serum thymidine kinase 1 activity and protein levels in canine mammary tumor Sera from 20 healthy dogs and 27 CMT dogs were analyzed for serum thymidine kinase 1 (sTK1) activity and sTK1 protein, as described in the Materials and Methods section
High sTK1 protein levels were found in the mammary tumor sera (Figure 2B) and the sTK1 protein concentration ranged from 9 ng/mL to 54 ng/mL
Summary
Thymidine kinase 1 (TK1) is a deoxyribonucleic acid (DNA) precursor enzyme and a proliferation biomarker used for prognosis and treatment monitoring of breast cancer in humans. The aim was to determine if serum thymidine kinase 1 (sTK1) activity and sTK1 protein levels in dogs with mammary tumors could be useful in veterinary medicine. Development of canine mammary tumors (CMTs) is influenced by age, hormone and genetic predispositions. A recent study has shown that variations in the BRCA1 and BRCA2 genes are associated with CMT in ESSs [9] and these genes are responsible for early onset of breast cancer in women. Inherited mutations in BRCA1 or BRCA2 increase the risk of breast cancer in women by around 56–84% [10,11]. BRCA1-associated breast cancers often occur in younger women, and these tumors are high grade and lack estrogen receptors (ERs), and are often triple-negative and, as such, harder to treat [16]. Comparative breast cancer studies are likely to greatly benefit both human and veterinary medicine
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