Deoxythymidine kinase in the staging of prostatic adenocarcinoma

Prediction of Overall Survival by Thymidine Kinase 1 Combined with Prostate-Specific Antigen in Men with Prostate Cancer

Thymidine kinase 1 (TK1) is an intracellular enzyme involved in DNA-precursor synthesis. Increased serum TK1 levels are used as a biomarker in various malignancies. We combined serum TK1 with PSA and evaluated its capacity to predict overall survival (OS) in 175 men with prostate cancer (PCa), detected by screening in 1988-1989 (n = 52) and during follow-up (median 22.6 years) (n = 123). TK1 was measured in frozen serum, age was stratified into four groups, and dates of PCa diagnosis and dates of death were obtained from Swedish population-based registries. The median concentration of TK1 and PSA was 0.25 and 3.8 ng/ml. TK1 was an independent variable of OS. In the multivariate analysis, PSA was not statistically significant in combination with age whereas the significance remained for TK1 + PSA. Measured once, TK1 + PSA predicted a difference of up to 10 years (depending on patient subgroup) in OS at a median of 9 years before PCa diagnosis. The TK1 concentration in 193 controls without malignancies did not differ from that of the PCa patients, hence TK1 was likely not released from incidental PCa. Thus, TK1 in the blood circulation may indicate the release of TK1 from sources other than cancers, nonetheless associated with OS.

The combination of AroCell TK 210 ELISA with Prostate Health Index or prostate-specific antigen density can improve the ability to differentiate prostate cancer from noncancerous conditions

BACKGROUND

Prostate-specific antigen (PSA) is an established tumour marker for prostate cancer (PCa). Serum thymidine kinase 1 is a possible new marker for the detection of PCa. The aim of the study was to investigate the diagnostic value of the AroCell TK 210 enzyme-linked immunosorbent assay (ELISA) together with free PSA, [-2]proPSA, and Prostate Health Index (PHI) in differentiating PCa from benign urological conditions.

METHODS

Serum samples from 140 patients with PSA values in the range between 2 and 10 µg/L were collected at the Ljubljana University Medical Centre and the Maribor University Medical Centre. Thymidine kinase (TK1) protein levels were determined using the AroCell TK 210 ELISA and PSA-related parameters analysed with commercial assays.

RESULTS

Serum TK1 protein, total and free PSA, proPSA, PSA density (PSAD), and PHI levels in patients with confirmed PCa were significantly higher than in patients with benign urological conditions (P < 0.05). Overall, the AroCell TK 210 ELISA results showed a significant correlation with PHI ( r = 0.25, P = 0.0031). Receiver-operating characteristic curve analyses were used to compare the area under the curve (AUC) of TK 210 ELISA, PHI, and PSA density. For PHI, the AUC was 0.73, comparable to those of TK 210 ELISA (0.67) and PSAD (0.66), with no significant differences in pairwise comparisons (PHI vs TK 210 ELISA P = 0.32, PHI vs PSAD P = 0.24, and TK 210 ELISA vs PSAD P = 0.95). The AUC for the combination of TK1 plus PSAD was significantly higher than those for the individual PSA-related biomarkers and marginally PHI, while the AUC for the combination of TK1 plus PHI was significantly higher than those for the individual PSA-related biomarkers except for PHI and marginally for PSAD. Total PSA concentration was the only marker, that was significantly higher in patients with an increasing Gleason grade.

CONCLUSIONS

These results suggest that TK1 protein determinations together with PHI or PSAD could be a valuable additional tool in PCa management.

Serum thymidine kinase 1 is associated with Gleason score of patients with prostate carcinoma

The aim of the present was to assess whether serum thymidine kinase 1 (STK1) concentration is a useful biomarker for the screening of benign prostatic hyperplasia (BPH) or prostate malignancy. Serum samples were collected from 123 patients with prostate carcinoma prior to surgery, biopsy or androgen deprivation therapy and at 3, 6 and 10 months following the procedure. A total of 205 patients with BPH and 266 healthy controls were also utilized. STK1 concentration and total prostate-specific antigen (PSA) were measured in patient serum by use of commercial assays. The pathological specimens (obtained from surgery or biopsy) were assessed according to Gleason scores (GS). STK1 concentration and total PSA were significantly higher in patients with prostate carcinoma compared with patients with BPH and healthy individuals. Furthermore, STK1 concentration was associated with Gleason score, while total PSA was not. However, no association was identified between STK1 concentration and total serum PSA. A receiver operating characteristic analysis was performed on STK1 concentrations among patients with prostate carcinoma. The results demonstrated that the sensitivity and specificity were high, with an area under the curve (AUC) of 0.97. Although the sensitivity and specificity of total PSA were also high, the AUC value was relatively low (0.74). The results indicated that STK1 concentration is a more reliable prognostic biomarker than total PSA in respect to the GS system. Additionally, since STK1 concentration is associated with Gleason score, the use of biopsies to determine Gleason score may be replaced to some extent by the STK1 concentration test, thus reducing the discomfort of patients from which biopsies are obtained.

The proliferation marker thymidine kinase 1 in clinical use

Tumor-related biomarkers are used for the diagnosis, prognosis and monitoring of treatments and follow-up of cancer patients, although only a few are fully accepted for the detection of invisible/visible tumors in health screening. Thymidine kinase 1 (TK1), a cell cycle-dependent and thus a proliferation-related marker, has been extensively studied during the last decades, using both biochemical and immunological techniques. Therefore, TK1 is an emerging potential proliferating biomarker in oncology that may be used for the prognosis and monitoring of tumor therapy, relapse and survival. In addition, TK1 concentration in serum (STK1p) is a useful biomarker in healthy screening for the detection of potential malignancy development as well as the identification of early-stage tumors, with a few false-positive cases (ROC value, 0.96; tumor proliferation sensitivity, 0.80; specificity, 0.99). In this review, we examine results regarding the expression of STK1p and TK1 in relation to cancer patients and STK1p in health screening published between 2000 and 2012. The use of tumor-related markers recommended by international cancer organizations is also discussed. This review provides valuable information for applications in tumor patients, in health screening and for cancer research.

Elevated serum thymidine kinase activity in canine splenic hemangiosarcoma*

Thymidine kinase 1 (TK1) is a soluble biomarker associated with DNA synthesis. This prospective study evaluated serum TK1 activity in dogs presenting with hemoabdomen and a splenic mass. An ELISA using azidothymidine as a substrate was used to evaluate TK1 activity. Sixty-two dogs with hemoabdomen and 15 normal controls were studied. Serum TK1 activity was significantly higher in dogs with hemangiosarcoma (HSA) than in normal dogs (mean ± SEM = 17.0 ± 5.0 and 2.01 ± 0.6, respectively), but not dogs with benign disease (mean ± SEM = 10.0 ± 3.3). Using a cut-off of 6.55 U/L, TK activity demonstrated a sensitivity of 0.52, specificity of 0.93, positive predictive value of 0.94 and negative predictive value of 0.48 for distinguishing HSA versus normal. When interval thresholds of <1.55 and >7.95 U/L were used together, diagnostic utility was increased. Serum TK1 evaluation may help to discriminate between benign disease and HSA in dogs with hemoabdomen and a splenic mass.

The proliferation marker thymidine kinase 1 level is high in normal kidney tubule cells compared to other normal and malignant renal cells

The activity of the proliferation related enzyme thymidine kinase 1 (TK1) was reported to be 3-fold higher in extracts from normal kidney tissue as compare to renal carcinoma extracts [3]. To verify these unexpected results, determinations of the protein levels of TK1 in normal kidney and in samples from different types of renal cell carcinoma (RCC) were done with immunohistochemistry and Western blot analysis. Two anti-TK1 peptide antibodies reacting with different TK1 epitops were used. TK1 levels were high in tubule cells as compared to glomerulus cells and connective tissue cells, while an intermediary TK1 was observed in renal cell carcinoma (RCC) cells. Western blot analysis demonstrated high levels of TK1 in extract from normal kidney, and lower levels of TK1 in the RCC extracts. The specificity of TK1 staining was demonstrated in competition experiments with excess TK1 antigen. The high TK1 levels in normal kidney tubule cells suggest that they are in a form of activated G1-state. The relatively low TK1 level in RCC, representing TK1 expression in S-phase cells, is in accordance with the low overall proliferation rate of these tumors. These results suggest that cell cycle regulation of TK1 in normal tubule cells differ from that in other type of normal and malignant renal cells.

Thymidine kinase: diagnostic and prognostic potential

Thymidine kinase is a cell cycle-dependent marker that can be detected in the serum of patients diagnosed with many different types of cancer. Serum levels of thymidine kinase have also been shown to reflect the progression of cancer as well as an indication of the efficacy of chemotherapeutic intervention. A new monoclonal antibody assay for thymidine kinase has been developed, which is capable of detecting thymidine kinase in both serum and tumor tissue. Thymidine kinase assay kits should be available at low cost and could serve as an effective low cost test for the detection and progression of many types of human cancer.