Thymidine kinase 1 – A prognostic and diagnostic indicator in ALL and AML patients

Nanochannel-based biosensor for ultrasensitive and label-free detection of thymidine kinase activity

Thymidine Kinase 1 (TK1) is a pivotal enzyme in fundamental biochemistry and molecular diagnosis, but recognition and molecule detection is a challenging task. Here, we constructed a DNA-integrated hybrid nanochannel sensor for TK1 activity and inhibition assay. Single-stranded DNA containing thymidine was used as a substrate to functionalize the nanochannels, restricting the ion current through channels. With kinase, the thymidine at the termini of the substrate DNA is phosphorylated, elevating surface charge density and mitigating the pore-obstruction effect by increasing transmembrane ion current. The kinase-induced distinctness can be accurately monitored by this hybrid nanodevice, which benefits from its high sensitivity to the change of surface charge. The excellent analytical performance in both kinase enzyme activity and inhibition analysis resulted in efficient and selective evaluation in human serum. Furthermore, compared to current approaches, it greatly simplifies and offers a direct method of analysis, making it a promising sensor technology for cancer management as well as the activities of multiple types of nucleic acid kinases.

Increased levels of thymidine kinase 1 in malignant cell-derived extracellular vesicles

Extracellular vesicles (EVs), whose main subtypes are exosomes, microparticles, and apoptotic bodies, are secreted by all cells and harbor biomolecules such as DNA, RNA, and proteins. They function as intercellular messengers and, depending on their cargo, may have multiple roles in cancer development. Thymidine kinase 1 (TK1) is a cell cycle-dependent enzyme used as a biomarker for cell proliferation. TK1 is usually elevated in cancer patients' serum, making the enzyme a valuable tumor proliferation biomarker that strongly correlates with cancer stage and metastatic capabilities. Here, we investigated the presence of TK1 in EVs derived from three prostate cancer cell lines with various p53 mutation statuses (LNCaP, PC3, and DU145), EVs from the normal prostate epithelial cell line RWPE-1 and EVs isolated from human seminal fluid (prostasomes). We measured the TK1 activity by a real-time assay for these EVs. We demonstrated that the TK1 enzyme activity is higher in EVs derived from the malignant cell lines, with the highest activity from cells deriving from the most aggressive cancer, compared to the prostasomes and RWPE-1 EVs. The measurement of TK1 activity in EVs may be essential in future prostate cancer studies.

Enzymes as indispensable markers in disease diagnosis

Enzymes have been used for disease diagnosis for many decades; however, advancements in technology like ELISA and flow cytometry-based detection have significantly increased their use and have increased the sensitivity of detection. Technological advancements in recombinant enzyme production have increased enzymatic stability, and the use of colorimetric-based and florescence-based assays has led to their increased use as biomarkers for disease detection. Enzymes like acid phosphatase, cathepsin, lactate dehydrogenase, thymidine kinase and creatine kinase are indispensable markers for diagnosing cancer, cardiovascular diseases and others. This minireview summarizes various enzymes used in disease diagnosis, their metabolic role, market value and potential as disease markers across various metabolic and other disorders.

TK1 expression influences pathogenicity by cell cycle progression, cellular migration, and cellular survival in HCC 1806 breast cancer cells

Breast cancer is the most common cancer diagnosis worldwide accounting for 1 out of every 8 cancer diagnoses. The elevated expression of Thymidine Kinase 1 (TK1) is associated with more aggressive tumor grades, including breast cancer. Recent studies indicate that TK1 may be involved in cancer pathogenesis; however, its direct involvement in breast cancer has not been identified. Here, we evaluate potential pathogenic effects of elevated TK1 expression by comparing HCC 1806 to HCC 1806 TK1-knockdown cancer cells (L133). Transcriptomic profiles of HCC 1806 and L133 cells showed cell cycle progression, apoptosis, and invasion as potential pathogenic pathways affected by TK1 expression. Subsequent in-vitro studies confirmed differences between HCC 1806 and L133 cells in cell cycle phase progression, cell survival, and cell migration. Expression comparison of several factors involved in these pathogenic pathways between HCC 1806 and L133 cells identified p21 and AKT3 transcripts were significantly affected by TK1 expression. Creation of a protein-protein interaction map of TK1 and the pathogenic factors we evaluated predict that the majority of factors evaluated either directly or indirectly interact with TK1. Our findings argue that TK1 elevation directly increases HCC 1806 cell pathogenicity and is likely occurring by p21- and AKT3-mediated mechanisms to promote cell cycle arrest, cellular migration, and cellular survival.

Circulating Biomarkers Associated with the Diagnosis and Prognosis of B-Cell Progenitor Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is a hematological disease characterized by the dysfunction of the hematopoietic system that leads to arrest at a specific stage of stem cells development, suppressing the average production of cellular hematologic components. BCP-ALL is a neoplasm of the B-cell lineage progenitor. BCP-ALL is caused and perpetuated by several mechanisms that provide the disease with its tumor potential and genetic and cytological characteristics. These pathological features are used for diagnosis and the prognostication of BCP-ALL. However, most of these paraclinical tools can only be obtained by bone marrow aspiration, which, as it is an invasive study, can delay the diagnosis and follow-up of the disease, in addition to the anesthetic risk it entails for pediatric patients. For this reason, it is crucial to find noninvasive and accessible ways to supply information concerning diagnosis, prognosis, and the monitoring of the disease, such as circulating biomarkers. In oncology, a biomarker is any measurable indicator that demonstrates the presence of malignancy, tumoral behavior, prognosis, or responses to treatments. This review summarizes circulating molecules associated with BCP-ALL with potential diagnostic value, classificatory capacity during monitoring specific clinic features of the disease, and/or capacity to identify each BCP-ALL stage regarding its evolution and outcome of the patients with BCP-ALL. In the same way, we provide and classify biomarkers that may be used in further studies focused on clinical approaches or therapeutic target identification for BCP-ALL.

S, M. Z, J. O, P. V, S. E. Analytical and clinical characterization of an optimized dual monoclonal sandwich ELISA for the quantification of thymidine kinase 1 (TK1) protein in human blood samples

Thymidine Kinase 1 (TK1) plays an important role in DNA precursor synthesis and serum TK1 activity has been used as a biomarker for prognosis and therapy monitoring of different malignancies. AroCell has developed a dual monoclonal antibody ELISA for determination of TK1 protein in clinical samples. The purpose of the study is to validate the ELISA analytically in relation to the gold standard, [3H]-deoxythymidine (dThd) phosphorylation assay for TK1 activity using sera from patients with different malignancies. The colorimetric TK 210 ELISA was validated analytically by assessment of precision, linearity, interfering substances, and stability. For the clinical validation, serum samples from patients with hematological malignancies (n = 100), breast cancer (n = 56), prostate cancer (n = 70) and blood donors (n = 159) were analyzed using TK 210 ELISA and TK1 activity by [3H]-deoxythymidine (dThd) phosphorylation assay. The sandwich TK 210 ELISA was highly specific for TK1 protein having a detection limit of 0.12 ng/mL, with a functional sensitivity of 0.25 ng/mL. Within-run CVs ranged from 5.5% to 10% and between-run CVs ranged from 5% to 15%. The ratio of observed to expected dilutional parallelism of 5 serum samples was in the range of 80-120%. Samples exhibited stability through four freeze/thaw cycles and 5 days at 4°C. Further, the ROC curve analysis showed that TK 210 ELISA and [3H]-dThd phosphorylation assay had similar sensitivity (62% vs 59%) in hematological malignancies. However, in the case of breast and prostate cancer sera, TK 210 ELISA had higher sensitivity (59% and 44%) compared to [3H]-dThd phosphorylation assay (47% and 25%) at a specificity of 98%. These data demonstrate that the dual monoclonal antibody based AroCell TK 210 ELISA is a robust, accurate and precise tool for measuring TK1 protein in different malignancies that can improve the clinical applications of TK1 as a biomarker in cancer management.

Comprehensive Analysis of a Ferroptosis Pattern and Associated Prognostic Signature in Acute Myeloid Leukemia

Ferroptosis is a widespread form of programmed cell death. The environment of cancer cells makes them vulnerable to ferroptosis, including AML cells, yet the specific association between ferroptosis and AML outcome is little known. In this study, we utilized ferroptosis-related genes to distinguish two subtypes in TCGA cohort, which were subsequently validated in independent AML cohorts. The subtypes were linked with tumor-related immunological abnormalities, mutation landscape and pathway dysregulation, and clinical outcome. Further, we developed a 13-gene prognostic model for AML from DEG analysis in the two subtypes. A risk score was calculated for each patient, and then the overall group was stratified into high- and low-risk groups; the higher risk score correlated with short survival. The model was validated in both independent AML cohorts and pan-cancer cohorts, which demonstrated robustness and extended the usage of the model. A nomogram was constructed that integrated risk score, FLT3-ITD, TP53, and RUNX1 mutations, and age. This model had the additional value of discriminating the sensitivity of several chemotherapeutic drugs and ferroptosis inducers in the two risk groups, which increased the translational value of this model as a potential tool in clinical management. Through integrated analysis of ferroptosis pattern and its related model, our work shed new light on the relationship between ferroptosis and AML, which may facilitate clinical application and therapeutics.

Re-Discovery of Pyrimidine Salvage as Target in Cancer Therapy

Nucleotides are synthesized through two distinct pathways: de novo synthesis and nucleoside salvage. Whereas the de novo pathway synthesizes nucleotides from amino acids and glucose, the salvage pathway recovers nucleosides or bases formed during DNA or RNA degradation. In contrast to high proliferating non-malignant cells, which are highly dependent on the de novo synthesis, cancer cells can switch to the nucleoside salvage pathways to maintain efficient DNA replication. Pyrimidine de novo synthesis remains the target of interest in cancer therapy and several inhibitors showed promising results in cancer cells and in vivo models. In the 1980s and 1990s, poor responses were however observed in clinical trials with several of the currently existing pyrimidine synthesis inhibitors. To overcome the observed limitations in clinical trials, targeting pyrimidine salvage alone or in combination with pyrimidine de novo inhibitors was suggested. Even though this approach showed initially promising results, it received fresh attention only recently. Here we discuss the re-discovery of targeting pyrimidine salvage pathways for DNA replication alone or in combination with inhibitors of pyrimidine de novo synthesis to overcome limitations of commonly used antimetabolites in various preclinical cancer models and clinical trials. We also highlight newly emerged targets in pyrimidine synthesis as well as pyrimidine salvage as a promising target in immunotherapy.

Spontaneous Partial Remission in a Child With B-Lineage Acute Lymphoblastic Leukemia and Chickenpox: A Role For Acyclovir?

A 2.5-year-old boy presented to his pediatrician with progressive pallor, asthenia, fever, splenomegaly, and hematomas. Leukemia was suspected, and a bone marrow aspirate confirmed acute lymphoblastic leukemia. Before chemotherapy induction, the child developed a vesicular rash and was diagnosed clinically with chickenpox. Acyclovir treatment was initiated immediately, whereas induction chemotherapy was postponed by 10 days. At the time of chickenpox resolution, a spontaneous partial recovery of his blood counts and a 50% decrease of blastic bone marrow infiltration were noted. After a brief nonsystematic review, we discuss the potential beneficial effect of acyclovir and chickenpox infection in children with leukemia.

Thymidine kinase 1 through the ages: a comprehensive review

Proliferation markers, such as proliferating cell nuclear antigen (PCNA), Ki-67, and thymidine kinase 1 (TK1), have potential as diagnostic tools and as prognostic factors in assessing cancer treatment and disease progression. TK1 is involved in cellular proliferation through the recovery of the nucleotide thymidine in the DNA salvage pathway. TK1 upregulation has been found to be an early event in cancer development. In addition, serum levels of TK1 have been shown to be tied to cancer stage, so that higher levels of TK1 indicate a more serious prognosis. As a result of these findings and others, TK1 is not only a potentially viable biomarker for cancer recurrence, treatment monitoring, and survival, but is potentially more advantageous than current biomarkers. Compared to other proliferation markers, TK1 levels during S phase more accurately determine the rate of DNA synthesis in actively dividing tumors. Several reviews of TK1 elaborate on various assays that have been developed to measure levels in the serum of cancer patients in clinical settings. In this review, we include a brief history of important TK1 discoveries and findings, a comprehensive overview of TK1 regulation at DNA to protein levels, and recent findings that indicate TK1’s potential role in cancer pathogenesis and its growing potential as a tumor biomarker and therapeutic target.

Novel monoclonal antibodies against thymidine kinase 1 and their potential use for the immunotargeting of lung, breast and colon cancer cells

BACKGROUND

Thymidine kinase 1 (TK1) is a pyrimidine salvage pathway enzyme that is up-regulated in malignant tissues and elevated in the serum of cancer patients. While TK1 has been well established as a tumor biomarker, little has been done to explore its potential as a tumor target. Recently, we reported the membrane expression of TK1 on malignant cells, but not on normal cells. This study explores the possible use of monoclonal antibodies for the targeting of membrane associated TK1 in lung, breast, colon and prostate cancer cells.

METHODS

We generated and evaluated a panel of monoclonal antibodies against six different epitopes exposed in the tetrameric form of TK1. Antibodies were developed with hybridoma technology and validated with Western blot, siRNA TK1 knockdown, enzyme-linked immunosorbent assay (ELISA) and flow cytometry. The therapeutic potential of the antibodies was evaluated in vitro in antibody-dependent cell-mediated-cytotoxicity (ADCC) experiments.

RESULTS

Binding of the antibodies to TK1 was confirmed by Western blot in purified recombinant protein, cancer serum, and cell lysate. After a TK1 knockdown was performed, a reduction of TK1 expression was observed with five antibodies. Using indirect ELISA, we identified 3B2E11, 9C10, 7H2, 3B4, 8G2 among the most sensitive antibodies (LOD = 10.73-66.9 pg/ml). Surface expression of TK1 on the membrane of various cancer cell lines was analyzed with flow cytometry. Antibodies 8G2, 3B4, 7HD and 5F7G11 detected TK1 on the membrane of various cancer cell lines, including lung, prostate, colon and breast. No significant binding was detected on normal lymphocytes. Increased cytolysis of lung (~ 70%. p = 0.0001), breast (~ 70%, p = 0.0461) and colon (~ 50% p = 0.0216) cancer cells by effector cells was observed when anti-TK1 antibodies were added during ADCC experiments.

CONCLUSIONS

The antibodies developed showed potential to be used to detect and target TK1 on the membrane of various tumor cells. The targeting of TK1 in malignant cells using monoclonal antibodies may be a feasible approach for the elimination of high TK1 expressing tumor cells.

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.

Doxorubicin effects on leukemia and breast cancer cells in culture on the TK1 protein levels using AroCell TK 210 ELISA: a tool for drug development

In this study changes in thymidine kinase 1 (TK1) levels after 24 hours of Doxorubicin (Dox) exposure of CEM and MDA MB-231 cells were determined using the commercially available AroCell TK 210 ELISA test. In cell extracts, TK1 levels increased twofold with 1 µM Dox in both cell lines, while the TK1 levels in the culture media increased with 5 and 10 µM of Dox only in case of CEM cells. In conclusion, this study reveals that the TK 210 ELISA can measure changes in intra- and extracellular TK1 levels apparently related to the mechanism of cytotoxicity of anti-cancer agents.

Membrane expression of thymidine kinase 1 and potential clinical relevance in lung, breast, and colorectal malignancies

Background

Lung, breast, and colorectal malignancies are the leading cause of cancer-related deaths in the world causing over 2.8 million cancer-related deaths yearly. Despite efforts to improve prevention methods, early detection, and treatments, survival rates for advanced stage lung, breast, and colon cancer remain low, indicating a critical need to identify cancer-specific biomarkers for early detection and treatment. Thymidine kinase 1 (TK1) is a nucleotide salvage pathway enzyme involved in cellular proliferation and considered an important tumor proliferation biomarker in the serum. In this study, we further characterized TK1’s potential as a tumor biomarker and immunotherapeutic target and clinical relevance.

Methods

We assessed TK1 surface localization by flow cytometry and confocal microscopy in lung (NCI-H460, A549), breast (MDA-MB-231, MCF7), and colorectal (HT-29, SW620) cancer cell lines. We also isolated cell surface proteins from HT-29 cells and performed a western blot confirming the presence of TK1 on cell membrane protein fractions. To evaluate TK1’s clinical relevance, we compared TK1 expression levels in normal and malignant tissue through flow cytometry and immunohistochemistry. We also analyzed RNA-Seq data from The Cancer Genome Atlas (TCGA) to assess differential expression of the TK1 gene in lung, breast, and colorectal cancer patients.

Results

We found significant expression of TK1 on the surface of NCI-H460, A549, MDA-MB-231, MCF7, and HT-29 cell lines and a strong association between TK1’s localization with the membrane through confocal microscopy and Western blot. We found negligible TK1 surface expression in normal healthy tissue and significantly higher TK1 expression in malignant tissues. Patient data from TCGA revealed that the TK1 gene expression is upregulated in cancer patients compared to normal healthy patients.

Conclusions

Our results show that TK1 localizes on the surface of lung, breast, and colorectal cell lines and is upregulated in malignant tissues and patients compared to healthy tissues and patients. We conclude that TK1 is a potential clinical biomarker for the treatment of lung, breast, and colorectal cancer.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0633-9) contains supplementary material, which is available to authorized users.

Thymidine kinase 1 as a tumor biomarker: technical advances offer new potential to an old biomarker

Thymidine kinase 1 (TK1) is a key enzyme in DNA precursor synthesis. It is upregulated during the S phase of the cell cycle and its presence in cells is an indicator of active cell proliferation. In studies since the 1980s, TK1 has been shown as a clinically valuable biomarker for the management of hematological malignancies. However, TK1 activity assays may underestimate serum TK1 in subjects with solid tumors limiting its sensitivity. The development of TK1 immunoassays has made the assay of TK1 more widely available and increased its applicability to solid tumor diseases. This paper will review TK1 as a tumor biomarker with emphasis on recent studies and technologies plus highlight its potential in drug discovery and as a therapeutic target.

A review of HPRT and its emerging role in cancer

Hypoxanthine guanine phosphoribosyltransferase (HPRT) is a common salvage housekeeping gene with a historically important role in cancer as a mutational biomarker. As an established and well-known human reporter gene for the evaluation of mutational frequency corresponding to cancer development, HPRT is most commonly used to evaluate cancer risk within individuals and determine potential carcinogens. In addition to its use as a reporter gene, HPRT also has important functionality in the body in relation to purine regulation as demonstrated by Lesch-Nyhan patients whose lack of functional HPRT leads to significant purine overproduction and further neural complications. This regulatory role, in addition to an established connection between other salvage enzymes and cancer development, points to HPRT as an emerging influence in cancer. Recent work has shown that not only is the enzyme upregulated within malignant tumors, it also has significant surface localization within some cancer cells. With this is mind, HPRT has the potential to become a significant biomarker not only for the characterization of cancer, but also for its potential treatment.

Early assessment of response to induction therapy in acute myeloid leukemia using 18F-FLT PET/CT

Background

We evaluated the suitability of ¹⁸F-fluorodeoxythymidine (¹⁸F-FLT) positron emission tomography (PET)/computed tomography (CT) for assessment of the early response to induction therapy and its value for predicting clinical outcome in patients with acute myeloid leukemia (AML). Adult patients who had histologically confirmed AML and received induction therapy were enrolled. All patients underwent ¹⁸F-FLT PET/CT after completion of induction. PET/CT images were visually and quantitatively assessed. Cases with intensely increased bone marrow uptake in more than one third of the long bones and throughout the central skeleton were interpreted as PET-positive for resistant disease (RD). PET results were compared to the clinical response and outcome.

Results

In visual PET analysis of 10 eligible patients (7 male, 3 female; median age 58 years), 5 patients were interpreted as being PET-positive and 5 as PET-negative. Standardized uptake values were significantly different between PET-positive and PET-negative groups. Eight of 10 patients achieved clinical complete remission (CR)/CR with incomplete blood count recovery (CRi). Five CR/CRi patients had PET-negative findings, but 3 CR patients had PET-positive findings. Both of the RD patients had PET-positive findings. During follow-up, 2 CR patients with PET-positive findings relapsed, or were strongly suspected of relapse, 4 months after consolidation.

Conclusion

¹⁸F-FLT PET/CT after induction therapy showed good sensitivity and negative-predictive value for evaluating RD in patients with AML. This preliminary study suggests that ¹⁸F-FLT PET/CT may be valuable as a noninvasive tool for early assessment of the response to treatment and may provide prognostic value for survival in patients with AML.

Biomarker analysis and clinical relevance of TK1 on the cell membrane of Burkitt's lymphoma and acute lymphoblastic leukemia

TK1 is an enzyme involved in DNA synthesis and repair. TK1 is usually found elevated in cancer patients’ serum, which makes it a useful tumor proliferation biomarker that strongly correlates with cancer stage, metastatic capabilities, and recurrence risk. In this study, we show that TK1 is upregulated and localizes on the plasma membrane of Burkitt’s lymphoma, acute promyelocytic leukemia, T cell leukemia, and acute lymphoblastic leukemia (ALL). Using flow cytometry, we confirmed that TK1 localizes on the surface of Raji, HL60, and Jurkat cell lines and on ALL clinical samples. Using fluorescent microscopy, we found a strong association of TK1 with the plasma membrane in Raji, HL60, and Jurkat cell lines. These findings were also confirmed by scanning electron microscopy. Our study also shows that this phenomenon does not occur on normal resting or proliferating lymphocytes. In addition, we show that membrane TK1 is found in all oligomeric forms ranging from monomer to tetramer and exhibits enzymatic activity. These findings suggest TK1 as a possible target for immunotherapy with the potential to be utilized in the treatment of hematological cancers.

A clinical evaluation of the TK 210 ELISA in sera from breast cancer patients demonstrates high sensitivity and specificity in all stages of disease

Thymidine kinase (TK1) is an enzyme involved in DNA synthesis that leaks into the blood as a result of high cell turnover, particularly in the case of cancer. Serum TK1 activity has been used for prognosis and monitoring of leukemia and lymphoma patients for many years. Here, we describe the first clinical results with the newly developed TK 210 ELISA from AroCell AB. Sera from 124 breast cancer patients with known TNM classification along with sera from 53 healthy females were analyzed by TK 210 ELISA for TK1 protein and TK1 activity levels by the ³[H]-deoxythymidine (dThd) phosphorylation assay. The limit of detection for the TK 210 ELISA was 0.17 ng/ml, and 60 % of the sera from female blood donors were below this value. The median TK1 levels found in sera from breast cancer patients with T1 to T4 stage disease were 0.31, 0.46, 0.47, and 0.55 ng/ml, and these levels significantly differed from healthy controls. The median values of the biomarker CA 15-3 were also increased in patient sera from T1 to T4 patients (16, 34, 36, 40 U/ml, respectively). TK 210 ELISA showed significantly higher sensitivity for the T1 and T2 breast cancer patients compared to the TK activity assay. The combination of the TK1 ELISA and CA 15-3 biomarkers demonstrated a significant increase in sensitivity up to 15 % compared to each marker alone. This evaluation of the TK 210 ELISA strongly suggests that it can provide independent and complementary information for patients with breast cancer.

Thymidine Kinase: A Biomarker for Recently Diagnosed Acute Leukemia in Pediatric Patients According to the Cell Line Involved

BACKGROUND AND AIMS

Acute leukemia (AL) is a heterogeneous group of diseases characterized by a disorganized clone proliferation of hematopoietic cells. Thymidine kinase (TK) is a cell enzyme involved in DNA synthesis and is considered a cellular proliferation marker in some solid tumors.

METHODS

A cross-sectional prospective and comparative study was performed in the Federico Gomez Children's Hospital in Mexico (HIMFG, in Spanish) in 125 samples of patients of the HIMFG with AL and 138 samples of children without leukemia. Serum TK levels were determined for both groups.

RESULTS

Of the children with AL, 90 presented B-cell acute lymphoblastic leukemia (B-ALL); 13, T-cell acute lymphoblastic leukemia (T-ALL); and 22, acute myeloid leukemia (AML). A median (m) TK level of 23.7 IU (IQR 17-35.7) was observed in the group without AL and 91 IU (IQR 98-392) in the AL group. This difference was statistically significant (p <0.0001). When analyzing TK levels according to the type of leukemia, the m was as follows: 68 IU (IQR 35-118) for B-ALL, 470 IU (IQR 88-750) for AML, and 1678 IU (IQR 288-2108) for T- ALL.

CONCLUSION

TK is an enzyme showing heterogeneous levels in B-ALL although it is significantly increased in 90% of patients with T-ALL and AML.

Expression of cell cycle-regulated genes and prostate cancer prognosis in a population-based cohort

BACKGROUND

Prostate cancer (PCa) is clinically and biologically heterogeneous, making it difficult to predict at detection whether it will take an indolent or aggressive disease course. Cell cycle-regulated genes may be more highly expressed in actively dividing cells, with transcript levels reflecting tumor growth rate. Here, we evaluated expression of cell cycle genes in relation to PCa outcomes in a population-based cohort.

METHODS

Gene expression data were generated from tumor tissues obtained at radical prostatectomy for 383 population-based patients (12.3-years average follow-up). The overall mean and individual transcript levels of 30 selected cell cycle genes was compared between patients with no evidence of recurrence (73%) and those who recurred (27%) or died (7%) from PCa.

RESULTS

The multivariate adjusted hazard ratio (HR) for a change from the 25th to 75th percentile of mean gene expression level (range 8.02-10.05) was 1.25 (95%CI 0.96-1.63; P = 0.10) for PCa recurrence risk, and did not vary substantially by Gleason score, TMPRSS2-ERG fusion status, or family history of PCa. For lethal PCa, the HR for a change (25th to 75th percentile) in mean gene expression level was 2.04 (95%CI 1.26-3.31; P = 0.004), adjusted for clinicopathological variables. The ROC curve for mean gene expression level alone (AUC = 0.740) did not perform as well as clinicopathological variables alone (AUC = 0.803) for predicting lethal PCa, and the addition of mean gene expression to clinicopathological variables did not substantially improve prediction (AUC = 0.827; P = 0.18). Higher TK1 expression was strongly associated with both recurrent (P = 6.7 × 10(-5)) and lethal (P = 6.4 × 10(-6)) PCa.

CONCLUSIONS

Mean expression level for 30 selected cell cycle-regulated genes was unrelated to recurrence risk, but was associated with a twofold increase in risk of lethal PCa. However, gene expression had less discriminatory accuracy than clinical variables alone for predicting lethal events. Transcript levels for several genes in the panel were significantly overexpressed in lethal versus non-recurrent PCa.

Muscle-invasive bladder cancer is characterized by overexpression of thymidine kinase 1

OBJECTIVE

Thymidine kinases have an important role in the synthesis of DNA and exhibit high activity in rapidly proliferating cells. Thymidine kinase 1 (TK1) activity has been shown to be increased in various cancer types and proposed as a prognostic parameter. Aim of the present study was to investigate TK1 in muscle-invasive urothelial carcinoma (UC).

METHODS

Corresponding UC and benign samples from paraffin embedded tissue of 111 patients treated with cystectomy for invasive UC from 1996 to 2006 were immunohistochemically (IHC) assessed for TK1. IHC expression patterns were evaluated in a semiquantitative fashion by 2 independent reviewers. Localization of staining was categorized into pure nuclear and additional cytoplasmic localization. Uni- and multivariate analyses were performed to assess differential expression in normal and UC tissue and to evaluate the diagnostic and predictive capability of TK1 by correlation to clinical data. To correlate TK1 expression with molecular subtypes of UC, analysis of TK1 RNA expression levels of the Cancer Genome Atlas UC cohort was performed.

RESULTS

TK1 was significantly overexpressed in invasive UC, compared to benign urothelium (P<0.0001), and cytoplasmic expression was more often found in cancer tissue than in benign tissue (P = 0.0001). No correlations of TK1 protein expression patterns to standard histopathological determinants were detected. In univariate analysis, TK1 nuclear and cytoplasmic expression was associated with improved cancer-specific survival (P = 0.0119). However, only metastasis status and histologic grade were identified as independent predictors of cancer-specific survival in multivariate analysis. TK1 expression was merely found in the basal layers of benign urothelium. RNA overexpression of TK1 could be correlated to the biologically more aggressive basal UC subtype.

CONCLUSIONS

TK1 expression is significantly different in invasive UC and benign urothelium, which underlines its potential as a diagnostic marker. Although TK1 is considered to be a marker of proliferation, and TK1 RNA overexpression is associated with an aggressive UC subtype, its capability as a predictive IHC biomarker for invasive UC remains limited.

Clinical significance of thymidine kinase in Egyptian children with acute lymphoblastic leukemia

BACKGROUND

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy, representing one-third of pediatric cancers. Thymidine kinase-1 (TK-1) is expressed in proliferating cells so elevated TK-1 indicates active tumor growth.

OBJECTIVE

To study the clinical significance of TK-1 in children with ALL.

PATIENTS AND METHODS

This study was carried out on 40 children with newly diagnosed ALL who were admitted to Oncology Unit, Pediatric department, Tanta University (26 males and 14 females) with their ages ranged from 4 to 10 years and 30 healthy children of matched age and sex as a control group. For all patients the following were done: Complete blood picture, bone marrow examination, immunophenotyping and TK-1 serum levels.

RESULTS

Mean TK-1 level was significantly higher in patients at diagnosis than controls and significantly higher in patients with unfavorable outcome than patients with favorable outcome. Mean TK-1 level was significantly higher in patients in relapse than patients in remission and controls. No significant differences in mean TK-1 level between patients in remission and controls. There were statistically significant differences in disease free survival and overall survival between patients with favorable and unfavorable outcome.

CONCLUSION

From this study we concluded that TK is a helpful marker in diagnosis and follow-up of patients with ALL.

RECOMMENDATIONS

Thymidine kinase-1 should be routinely assessed at diagnosis and during follow-up in ALL patients for better diagnostic and prognostic assessment and should be taken in consideration in designing future therapeutic strategies based on patients-specific risk factors.

Microchip immunoaffinity electrophoresis of antibody-thymidine kinase 1 complex

Thymidine kinase 1 (TK1) is an important cancer biomarker whose serum levels are elevated in early cancer development. We developed a microchip electrophoresis immunoaffinity assay to measure recombinant purified TK1 (pTK1) using an antibody (Ab) that binds to human TK1. We fabricated PMMA microfluidic devices to test the feasibility of detecting Ab-pTK1 immune complexes as a step toward TK1 analysis in clinical serum samples. We were able to separate immune complexes from unbound Abs using 0.5× PBS (pH 7.4) containing 0.01% Tween-20, with 1% w/v methylcellulose that acts as a dynamic surface coating and sieving matrix. Separation of the Ab and Ab-pTK1 complex was observed within a 5 mm effective separation length. This method of detecting pTK1 is easy to perform, requires only a 10 μL sample volume, and takes just 1 min for separation.

Breast and prostate cancer patients differ significantly in their serum Thymidine kinase 1 (TK1) specific activities compared with those hematological malignancies and blood donors: implications of using serum TK1 as a biomarker

Background

Thymidine kinase 1 (TK1) is a cellular enzyme involved in DNA precursor synthesis, and its activity has been used as a proliferation marker for monitoring malignant diseases. Here, for the first time, we evaluated both TK1 activity and protein levels in sera from patients with different malignancies.

Methods

Serum samples from patients with myelodysplastic syndrome (MDS, n = 22), breast cancer (n = 42), prostate cancer (n = 47) and blood donors (n = 30) were analyzed for TK1 protein and activity levels, using a serum TK1 (STK1) protein assay based on antibodies and an activity assay that measured [³H]-deoxythymidine (dThd) phosphorylation. The molecular forms of TK1 in sera from some of these patients were analyzed using size-exclusion chromatography.

Results

Mean STK1 activities in sera from MDS, breast and prostate cancer were 11 ± 17.5, 6.7 ± 19 and 1.8 ± 1.4 pmol/min/mL, differing significantly from blood donors (mean ± standard deviation (SD) = 1.1 ± 0.9 pmol/min/mL). Serum TK1 protein (25 kDa polypeptide) levels were also significantly higher in MDS, breast, prostate cancer compared to blood donors (mean ± SD = 19 ± 9, 22 ± 11, 20 ± 12, and 5 ± 3.5 ng/mL, respectively). The STK1 specific activities of sera from patients with MDS and blood donors were significantly higher when compared with activities in sera from breast and prostate cancer patients. Size-exclusion analysis of sera from breast and prostate cancer showed that the detected active TK1 was primarily a high molecular weight complex, similar to the forms found in sera from MDS patients and blood donors. However, Western blotting demonstrated high TK1 25 kDa protein levels in fractions lacking TK1 activity in sera from cases with breast and prostate cancer.

Conclusions

These results demonstrate that there are differences in the specific activities and the subunit compositions of STK1 in hematological malignancies compared with breast and prostate cancer. This fact has several important implications for the use of STK1 as a tumor biomarker. One is that STK1 protein assays may differentiate early-stage tumor development in breast and prostate cancer more effectively than STK1 activity assays.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1073-8) contains supplementary material, which is available to authorized users.

Properties of cellular and serum forms of thymidine kinase 1 (TK1) in dogs with acute lymphocytic leukemia (ALL) and canine mammary tumors (CMTs): implications for TK1 as a proliferation biomarker

BACKGROUND

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.

RESULTS

Serum samples from 20 healthy dogs and 27 dogs with mammary tumors were analyzed for sTK1 activity, using an [(3)H]-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.

CONCLUSIONS

Serum 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.

High levels of inactive thymidine kinase 1 polypeptide detected in sera from dogs with solid tumours by immunoaffinity methods: implications for in vitro diagnostics

Determination of serum thymidine kinase 1 (STK1) activity has been used as a proliferation marker for neoplastic diseases in both human and veterinary medicine. The purpose of this study was to determine STK1 activity and enzyme levels in different dog tumours. Serum samples from three dogs with leukaemia, five with lymphoma, 21 with solid tumours and 18 healthy dogs were analyzed for STK1 activity, using an optimized [(3)H]-deoxythymidine (dThd) phosphorylation assay, and for STK1 protein levels using an immunoaffinity/western blot assay. STK1 activity in dogs with haematological tumours was significantly higher than in the solid tumour and healthy dog groups (mean ± standard deviation [SD] = 65 ± 79, 1.1 ± 0.5, and 1.0 ± 0.4 pmol/min/mL, respectively). Serum samples were analyzed after immunoaffinity isolation by western blot and the TK1 26 kDa band intensities quantified revealing that concentrations were significantly higher in dogs with haematological tumours and solid tumours compared to healthy dogs (mean ± SD=33 ± 12, 30 ± 13, and 10 ± 5 ng/mL, respectively). Pre-incubation with the reducing agent dithioerythritol (DTE) showed a decrease in STK1 activity and protein levels in most samples, but an increase of about 20% in sera from healthy dogs and from those with haematological malignancies. Compared to animals with solid tumours, the specific STK1 activity (nmol [(3)H]-deoxythymidine monophosphate (dTMP)/min/mg of TK1 protein of 26 kDa) was 30-fold higher in haematological malignancies and 2.5-fold higher in healthy dogs, respectively. The results demonstrate that there is a large fraction of inactive TK1 protein, particularly in sera from dogs with solid tumours. The findings are important in the use of STK1 as a biomarker.

Thymidine kinase 1 as a diagnostic tumor marker is of moderate value in cancer patients: A meta-analysis

Thymidine kinase 1 (TK1) is an enzyme involved in nucleic acid synthesis and is therefore considered to be an important tumor proliferation marker. The aim of the present study was to determine the diagnostic role of TK1 measurement in cancer. An extensive electronic search was performed in PubMed, EMBASE and the Cochrane Library using the keywords 'thymidine kinase 1' and 'tumor' and synonyms. This study was conducted as part of a project to establish evidence-based guidelines for the diagnosis and treatment of cancer. A total of 453 abstracts were screened, after which the full text of 40 studies were selected for further investigation, including screening of the references cited by studies in the original search. Fifteen studies were enrolled following full-text evaluation. The areas under the receiver operating characteristic curves for the radioenzymatic assay (REA), the chemiluminescence immunoassay (CLIA) and the total were 0.88, 0.75 and 0.8, respectively. These results were all between <0.9 and >0.7, which suggested a moderate diagnostic efficacy. The positive likelihood ratio of the CLIA method was the highest (10.229), which demonstrated that CLIA exhibited a satisfactory specificity in tumor diagnosis. However, TK1 as a single diagnostic tumor marker was not of significant value and the combination of more tumor markers in the diagnosis of tumors may be preferable.

Elevated thymidine kinase 1 in serum following neoadjuvant chemotherapy predicts poor outcome for patients with locally advanced breast cancer

Patients with locally advanced breast cancer (LABC) commonly have an unfavorable prognosis. A molecular predictor for the identification of at-risk patients is urgently required. Thymidine kinase 1 in serum (S-TK1) is an enzyme involved in the synthesis of DNA precursors. In studies using immunohistochemistry, it was reported to be a more useful proliferation marker than Ki-67 in breast, lung and colorectal carcinoma. In the present study, we extended the research of prior breast carcinoma studies by postulating that in patients with LABC, overexpression of S-TK1 following neoadjuvant chemotherapy predicts cancer outcome. An experimental design consisting of 48 patients with LABC was prospectively constructed and analyzed. All patients received neoadjuvant chemotherapy and definitive surgical therapy. Study homogeneity was maintained by standardized treatment, surveillance and compliance protocols. The S-TK1 concentration was detected using the anti-TK1 chicken IgY antibody, using a dot-blot immuno-assay. After a median follow-up of 30 months, the results indicated a statistically significant trend (unadjusted). Patients with high S-TK1 overexpression had a significantly higher incidence of recurrence (P=0.006) and cancer death (P= 0.0128) than those with low S-TK1 overexpression. A multivariate analysis provided identical results. The hazards ratio for developing recurrence in patients with higher S-TK1 expression was 6-7 times higher than the hazards ratio in patients with lower expression. In conclusion, our results indicate that a high S-TK1 concentration in sera from LABC patients receiving neoadjuvant chemotherapy is predictive of cancer outcome.

Comparative aspects of the proliferation marker thymidine kinase 1 in human and canine tumour diseases

As cell proliferation is one of the hallmarks of cancer, various types of proliferation markers are used as important tools in diagnosis, prognosis, treatment decision-making and follow-up in clinical oncology. The S phase-specific protein thymidine kinase 1 (TK1) can be used in immunohistochemistry for RNA/protein expression in tissue specimens and for activity or protein/peptide levels in serum from patients. TK1 has been used mainly in haematologic malignancies in humans, but also found beneficial in canine malignancies. As the protein sequence homology is high between humans and dogs, findings in canine models will have a high comparative value in further human research as well. In the present review, we will focus on the recent results concerning TK1's S phase-correlated expression, increased serum levels of TK1 in patients with malignancies and the relevance for veterinary and comparative oncology. Finally, the benefit of recently developed specific anti-TK1 antibodies suitable for immunologic assay is discussed.

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 1 expression defines an activated G1 state of the cell cycle as revealed with site-specific antibodies and ArrayScan assays

Thymidine kinase 1 (TK1) is a DNA salvage enzyme involved in the synthesis of thymidine triphosphate needed during S phase. Although TK1 has been utilized as a cell proliferation marker for many years no well-characterized antibodies are available. The preparation and properties of two types of poly- and monoclonal anti-TK1 peptide antibodies are described and they are used to determine the levels of TK1 in intact cells. Expression of TK1, c-fos, cyclin B1, Ki67, phosphorylated histone H3, phosphorylated ribosomal protein S6, as well as bromodeoxyuridine (BrdU) incorporation in human normal dermal fibroblast cultures were studied with high-content ArrayScan fluorescence microscopy. The levels of TK1 increased 6-7h after serum re-addition to starved cells as they passed through G1, S and G2/M phases, which was earlier than the increase in Ki67 protein levels and before BrdU incorporation was detected. Thus, a population of activated G1 cells with high TK1 and low Ki67 expression could be identified and their role in cell proliferation can now be clarified.

Elevated levels of thymidine kinase 1 peptide in serum from patients with breast cancer

OBJECTIVES

Thymidine kinase (TK) has an important role in DNA synthesis and is thus related to cell proliferation and turn-over. Traditionally, TK has been measured by enzymatic activity or radioimmunoassays. These assays are difficult to adapt to random access instruments. The aim of this study was to evaluate a new immunological sandwich assay for detection of TK peptides in serum from breast cancer patients.

MATERIAL AND METHODS

Serum samples were collected from patients with breast cancer and stored frozen at -70 degrees C. The samples were collected after surgery, after metastatic tumor recurrence and after chemotherapy due to tumour recurrence. Patients' serum samples were analysed by the TK enzyme-linked immunosorbent assay (ELISA).

RESULTS

In receiver operating characteristics (ROC) analyses of TK1 for diagnosis of breast cancer, the area under the curve (AUC) collected four weeks after surgery was 0.56 (95% CI 0.47-0.65), for samples collected postsurgically after tumour recurrence 0.73 (95% CI 0.65-0.80), and after chemotherapy 0.64 (95% CI 0.56-0.72).

CONCLUSIONS

This study indicates that the tumour proliferation marker TK has a potential as a serum marker in breast cancer. Further studies are warranted to verify this observation.

First demonstration of leukemia imaging with the proliferation marker 18F-fluorodeoxythymidine

Acute myeloid leukemia (AML) is a neoplasm of hematopoietic stem cells with partial or complete loss of the ability to differentiate but with preserved proliferation capacity. The aim of our study was to evaluate if the in vivo proliferation marker 3'-deoxy-3'-18F-fluorothymidine (FLT) is suitable for visualizing leukemia manifestation sites and if 18F-FLT is a surrogate marker for disease activity.

METHODS

In this pilot study, 10 patients with AML underwent pretherapeutic imaging with 18F-FLT PET or 18F-FLT PET/CT. The biodistribution of 18F-FLT was assessed 60 min after intravenous injection of the radiotracer. Standardized uptake values were calculated for reference segments of bone marrow, spleen, and normal organs. 18F-FLT PET in 10 patients with benign pulmonary nodules and the absence of malignant or inflammatory disease served as controls.

RESULTS

Retention of 18F-FLT was observed predominantly in bone marrow and spleen and was significantly higher in AML patients than in controls (mean 18F-FLT SUV in bone marrow, 11.5 and 6.6, P < 0.05; mean 18F-FLT SUV in spleen, 6.1 and 1.8, P < 0.05). Outside bone marrow, focal 18F-FLT uptake showed extramedullary manifestation sites of leukemia in 4 patients (meningeal disease, pericardial, abdominal, testicular, and lymph node), proven by other diagnostic procedures.

CONCLUSION

This pilot study indicated that PET using 18F-FLT is able to visualize extramedullary manifestation sites of AML and reflects disease activity. Because 18F-FLT uptake in bone marrow is caused by a combination of both neoplastic and normal hematopoietic cells, the correlation of 18F-FLT uptake in bone marrow and leukemic blast infiltration did not reach statistical significance.