Thymidine kinase in epithelial ovarian cancer: relationship with the other pyrimidine pathway enzymes

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.

Clinical Significance of the TK1-Specific Activity in the Early Detection of Ovarian Cancer

INTRODUCTION

Ovarian cancer is the eighth most common cause of cancer death in women. One of the major concerns is almost two-thirds of cases are typically diagnosed in the late stage as the symptoms are unspecific in the early stage of ovarian cancer. It is known that the combination of TK1 protein with CA 125 or HE4 showed better performance than either of them alone. That is why, the aim of the study was to investigate whether the TK1-specific activity (TK1 SA) could function as a complement marker for early-stage diagnosis of ovarian cancer.

METHODS

The study included a set of 198 sera consisting of 134 patients with ovarian tumors (72 benign and 62 malignant) and 64 healthy age-matched controls. The TK1 SA was determined using TK1 activity by TK-Liaison and TK1 protein by AroCell TK 210 ELISA. Further, CA 125, HE4, as well as risk of ovarian malignancy algorithm index were also determined in the same set of clinical samples.

RESULTS

The TK1 SA was significantly different between healthy compared to ovarian cancer patients (p < 0.0001). Strikingly, TK1 SA has higher sensitivity (55%) compared to other biomarkers in the detection of benign ovarian tumors. Further, the highest sensitivity was achieved by the combination of TK1 SA with CA 125 and HE4 for the detection of benign tumors as well as malignant ovarian tumors (72.2% and 88.7%). In addition, TK1 SA could significantly differentiate FIGO stage I/II from stage III/IV malignancies (p = 0.026). Follow-up of patients after surgery and chemotherapy showed a significant difference compared to TK1 SA at the time of diagnosis.

CONCLUSIONS

These results indicate that TK1 SA is a promising blood-based biomarker that could complement CA 125 and HE4 for the detection of early stages of ovarian cancer.

La protein regulates protein expression by binding with the mRNAs of target genes and participates the pathological process of ovarian cancer

Research on the mechanism and new targets of ovarian cancer is of great significance to reduce the high mortality and drug resistance of ovarian cancer. Human La protein has been found to be highly expressed in a variety of malignant tumors and plays a role in tumorigenesis and development through its RNA-binding function. However, its role and mechanism in ovarian cancer are not completely clear. The present study showed that La protein was highly expressed in serum and tissues of patients with ovarian cancer by ELISA and immunohistochemistry, and the high expression of La protein was associated with the increased degree of malignancy and poor prognosis by searching the KM plotter database. Interference of the La gene resulted in a significant decrease in the proliferation, migration, and invasion of ovarian cancer cells with growth block in the G1 phase and increasing apoptosis. By RNA binding protein immunoprecipitation, transcriptome sequencing, and proteomics, 14 downstream target genes were screened. The La protein might affect the protein expression of these 14 genes by binding with the mRNAs. Therefore, it played a role in the pathological process of ovarian cancer.

A combined strategy of TK1, HE4 and CA125 shows better diagnostic performance than risk of ovarian malignancy algorithm (ROMA) in ovarian carcinoma

BACKGROUND

The dual marker algorithm Risk of Ovarian Malignancy Algorithm (ROMA) has been widely used in the clinic for the identification of equivocal pelvic masses in ovarian carcinoma. To obtain higher diagnostic efficiency, we created a new diagnostic index, Risk of Ovarian Malignancy Index (ROMI), by combing thymidine kinase 1 (TK1), HE4 and CA125.

METHODS

335 patients with pelvic masses on imaging and 46 healthy controls were enrolled. Serum TK1 was analyzed before further study. ROMI and ROMA were evaluated for diagnostic efficiency.

RESULTS

The level of TK1 was elevated in malignant ovarian tumors compared to benign masses (p < 0.001) and healthy controls (p < 0.001). TK1 expression was positively correlated with stage, intrapelvic metastasis, lymphatic metastasis and distant metastasis (all p values < 0.001). The area under the receiver operating characteristic curve (AUC) of ROMI was higher than that of ROMA for both pre- and postmenopausal women. ROMI had better sensitivity, specificity, accuracy, and positive and negative predictive values than ROMA in diagnosis of all-stage or stage I + II ovarian carcinoma for both pre- and postmenopausal women.

CONCLUSIONS

TK1 is a potential biomarker in detection of ovarian carcinoma. ROMI shows better diagnostic performance than ROMA in distinguishing malignant ovarian tumors from benign masses.

5-Fluorouracil disrupts ovarian preantral follicles in young C57BL6J mice

PURPOSE

5-Fluorouracil (5-FU), an anti-cancer drug, has been used for hepatoblastoma (HB) chemotherapy in children, who may have impaired  ovarian follicle pool reserve with lasting effects to reproduction. Therefore, this study aimed to investigate 5-FU effects on survival, growth, and morphology of ovarian preantral follicles from C57BL6J young mice.

METHODS

Experiments were carried-out both in vivo and in vitro. Mice were treated with 5-FU injection (450 mg/kg i.p) or saline and sacrificed 3 days after to obtain ovaries for histology and molecular biology. Ovaries for in vitro studies were obtained from unchallenged mice and cultured under basic culture medium (BCM) or BCM plus 5-FU (9.2, 46.1, 92.2 mM). Preantral follicles were classified according to developmental stages, and as normal or degenerated. To assess cell viability, caspase-3 immunostaining was performed. Transcriptional levels for apoptosis (Bax, Bcl2, p53, Bax/Bcl2) and Wnt pathway genes (Wnt2 and Wnt4) were also analyzed. Ultrastructural analyses were carried-out on non-cultured ovaries. In addition, β-catenin immunofluorescence was assessed in mouse ovaries.

RESULTS

The percentage of all-types normal follicles was significantly lower after 5-FU challenge. A total loss of secondary normal follicles was found in the 5-FU group. The highest 5-FU concentrations reduced the percentage of cultured normal primordial follicles. Large vacuoles were seen in granulosa cells and ooplasm of preantral follicles by electron microscopy. A significantly higher gene expression for Bax and Bax/Bcl2 ratio was seen after 5-FU treatment. A marked reduction in β-catenin immunolabeling was seen in 5-FU-challenged preantral follicles. In the in vitro experiments, apoptotic and Wnt gene transcriptions were significantly altered.

CONCLUSION

Altogether, our findings suggest that 5-FU can deleteriously affect the ovarian follicle reserve by reducing preantral follicles survival.

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.

The role of thymidine kinase in cancer diseases

Thymidine kinase 1 (TK 1-fetal) is a cell cycle-dependent marker that increases dramatically during the S-phase of the cell cycle. In this review, the authors discuss serum levels of thymidine kinase in a variety of neoplasias. Determination of thymidine kinase helps to monitor the follow-up of solid tumours and haematological malignancies as well as indicating the efficacy of adjuvant and palliative chemotherapy. Elevated levels of thymidine kinase must always be interpreted together with a detailed knowledge of the patient's condition because nonspecific elevations of serum levels (inflammatory and autoimmune diseases) must be excluded.

Correlated tissue expression of genes of cytoplasmic and mitochondrial nucleotide metabolisms in normal tissues is disrupted in transformed tissues

Cells maintain dual metabolic pathways to provide substrates for the replication of mitochondrial and nuclear DNA. These pathways involve two separate sets of genes in the nuclear DNA, with one set encoding proteins targeted to the mitochondrion. However, the cytoplasmic and mitochondrial metabolisms are capable of communication through the transport of deoxyribonucleosides and deoxyribonucleotides between the two subcellular compartments. Cytoplasmic and mitochondrial deoxyribonucleoside triphosphate concentrations are strongly correlated in normal cells but not in transformed cells. We were therefore interested in comparing the interactions in normal and transformed tissues between the corresponding cytoplasmic and mitochondrial metabolisms that produce deoxyribonucleoside triphosphates. We conducted an analysis of gene expression data in normal and transformed human tissues obtained from the UniGene database for a selected set of genes for proteins involved in nucleoside salvage in either the cytoplasm or mitochondria. We also included ribonucleotide reductase in our analysis due to its importance in generating deoxyribonucleoside triphosphates. This analysis revealed a large number of highly significant positive correlations between the tissue expression profiles of the genes of the mitochondrial and cytoplasmic pathways in normal tissues, indicating that in normal tissues, the two metabolisms coordinately generate deoxyribonucleoside triphosphates. In transformed tissues, this correlation structure was disrupted. Multiple correlations involving the mitochondrial nucleoside kinase gene DGUOK were statistically significantly different between normal and transformed tissues, suggesting that control of DGUOK expression relative to other cytoplasmic genes is important in transformed tissues.

Combining small interfering RNAs targeting thymidylate synthase and thymidine kinase 1 or 2 sensitizes human tumor cells to 5-fluorodeoxyuridine and pemetrexed

Thymidylate synthase (TS) is the only de novo source of thymidylate (dTMP) for DNA synthesis and repair. Drugs targeting TS protein are a mainstay in cancer treatment, but off-target effects and toxicity limit their use. Cytosolic thymidine kinase (TK1) and mitochondrial thymidine kinase (TK2) contribute to an alternative dTMP-producing pathway, by salvaging thymidine from the tumor milieu, and may modulate resistance to TS-targeting drugs. Combined down-regulation of these enzymes is an attractive strategy to enhance cancer therapy. We have shown previously that antisense-targeting TS enhanced tumor cell sensitivity to TS-targeting drugs in vitro and in vivo. Because both TS and TKs contribute to increased cellular dTMP, we hypothesized that TKs mediate resistance to the capacity of TS small interfering RNA (siRNA) to sensitize tumor cells to TS-targeting anticancer drugs. We assessed the effects of targeting TK1 or TK2 with siRNA alone and in combination with siRNA targeting TS and/or TS-protein targeting drugs on tumor cell proliferation. Down-regulation of TK with siRNA enhanced the capacity of TS siRNA to sensitize tumor cells to traditional TS protein-targeting drugs [5-fluorodeoxyuridine (5FUdR) and pemetrexed]. The sensitization was greater than that observed in response to any siRNA used alone and was specific to drugs targeting TS. Up-regulation of TK1 in response to combined 5FUdR and TS siRNA suggests that TK knockdown may be therapeutically useful in combination with these agents. TKs may be useful targets for cancer therapy when combined with molecules targeting TS mRNA and TS protein.

Identification of common microRNA-mRNA regulatory biomodules in human epithelial cancers

The complex regulatory network between microRNAs and gene expression remains unclear domain of active research. We proposed to address in part this complex regulation with a novel approach for the genome-wide identification of biomodules derived from paired microRNA and mRNA profiles, which could reveal correlations associated with a complex network of de-regulation in human cancer. Two published expression datasets for 68 samples with 11 distinct types of epithelial cancers and 21 samples of normal tissues were used, containing microRNA expression (Lu et al. Nature Letters 2005) and gene expression (Ramaswarmy et al. PNAS 2001) profiles, respectively. As results, the microRNA expression used jointly with mRNA expression can provide better classifiers of epithelial cancers against normal epithelial tissue than either dataset alone (p=1×10(-10), F-Test). We identified a combination of six microRNA-mRNA biomodules that optimally classified epithelial cancers from normal epithelial tissue (total accuracy = 93.3%; 95% confidence intervals: 86% - 97%), using penalized logistic regression (PLR) algorithm and three-fold cross-validation. Three of these biomodules are individually sufficient to cluster epithelial cancers from normal tissue using mutual information distance. The biomodules contain 10 distinct microRNAs and 98 distinct genes, including well known tumor markers such as miR-15a, miR-30e, IRAK1, TGFBR2, DUSP16, CDC25B and PDCD2. In addition, there is a significant enrichment (Fisher's exact test p=3×10(-10)) between putative microRNA-target gene pairs reported in five microRNA target databases and the inversely correlated micro-RNA-mRNA pairs in the biomodules. Further, microRNAs and genes in the biomodules were found in abstracts mentioning epithelial cancers (Fisher Exact Test, unadjusted p<0.05). Taken together, these results strongly suggest that the discovered microRNA-mRNA biomodules correspond to regulatory mechanisms common to human epithelial cancer samples. In conclusion, we developed and evaluated a novel comprehensive method to systematically identify, on a genome scale, microRNA-mRNA expression biomodules common to distinct cancers of the same tissue. These biomodules also comprise novel microRNA and genes as well as an imputed regulatory network, which may accelerate the work of cancer biologists as large regulatory maps of cancers can be drawn efficiently for hypothesis generation.

Serum thymidine kinase activity as a useful marker for bovine leukosis

Serum thymidine kinase (TK) activity has recently been evaluated as a serum marker for human and canine hematopoietic neoplasms. The purpose of the current study was to establish the significance of serum TK activity in the diagnosis of bovine leukosis. The discrimination value for TK activity was set at 5.4 U/l based on the receiver operating characteristic curve. In the group of clinically healthy cows, only 2 out of 83 cows (2.4%) had serum TK activity above the discrimination value. In contrast, 19 out of 20 cows (95.0%) with bovine leukosis showed serum TK activity above the discrimination value, although only 7 of 79 (8.9%) cows diagnosed with diseases other than bovine leukosis showed elevated serum TK activity. Thymidine kinase activities of all Bovine leukemia virus-positive cows with or without lymphocytosis were below the discrimination value. Sensitivity and specificity of measuring serum TK activity as a diagnostic tool for bovine leukosis was 95.0% and 95.9%, respectively. Results indicate that serum TK activity may be a marker for bovine leukosis.

Iodine alters gene expression in the MCF7 breast cancer cell line: evidence for an anti-estrogen effect of iodine

The protective effects of iodine on breast cancer have been postulated from epidemiologic evidence and described in animal models. The molecular mechanisms responsible have not been identified but laboratory evidence suggests that iodine may inhibit cancer promotion through modulation of the estrogen pathway. To elucidate the role of iodine in breast cancer, the effect of Lugol's iodine solution (5% I(2), 10% KI) on gene expression was analyzed in the estrogen responsive MCF-7 breast cancer cell line. Microarray analysis identified 29 genes that were up-regulated and 14 genes that were down-regulated in response to iodine/iodide treatment. The altered genes included several involved in hormone metabolism as well as genes involved in the regulation of cell cycle progression, growth and differentiation. Quantitative RT-PCR confirmed the array data demonstrating that iodine/iodide treatment increased the mRNA levels of several genes involved in estrogen metabolism (CYP1A1, CYP1B1, and AKR1C1) while decreasing the levels of the estrogen responsive genes TFF1 and WISP2. This report presents the results of the first gene array profiling of the response of a breast cancer cell line to iodine treatment. In addition to elucidating our understanding of the effects of iodine/iodide on breast cancer, this work suggests that iodine/iodide may be useful as an adjuvant therapy in the pharmacologic manipulation of the estrogen pathway in women with breast cancer.

Genetic and biochemical modulation of 5-fluorouracil through the overexpression of thymidine kinase: an in-vitro study

The pro-drug 5-fluorouracil (5-FU) exerts its anti-proliferative action after conversion into cytotoxic metabolites. We previously demonstrated that the anti-cancer action of 5-FU could be enhanced by boosting thymidine phosphorylase (TP) activity in cancer cells, the first step of the DNA pathway, that yields the critical anti-thymidylate synthase (TS) fluorodeoxyuridine monophosphate (FdUMP) metabolite. In the present study, we further studied to what extent 5-FU activity could be optimized by overexpressing cancer cell thymidine kinase (TK), the second step of the DNA pathway, for which controversial data have been published so far. Additionally, screening of biochemical modulators likely to contribute to 5-FU activation was also carried out. TK-overexpressing colorectal cells were obtained after designing vectors harboring viral and human cDNA, and performing stable transfection in the human HT29 cell line. Anti-proliferative assays were subsequently performed so as to evaluate change in cell sensitivity to 5-FU, and metabolism monitoring was carried out to follow drug activation and FdUMP formation after cellular uptake. Finally, TS inhibition was assessed as a pharmacological endpoint. Results showed that overexpression of TK led to a marked desensitization of our model. A negative correlation (r = 0.87) was found between the level of TK activity and 5-FU anti-proliferative action - the higher the activity, the lower the sensitivity. Of the various drugs screened as putative modulators, only those involved in TP activity proved to enhance 5-FU efficacy via optimized FdUMP formation. Conversely, genetically increasing TK activity did not modify 5-FU activation pathway nor subsequent TS inhibition in our model. Therefore, our results indicate that TK is not a limiting step in the production of anti-TS FdUMP and that tumor cells overexpressing TK are likely to resist 5-FU-based chemotherapies.

Kinase-mediated trapping of bi-functional conjugates of paclitaxel or vinblastine with thymidine in cancer cells

In the present work, we explore the possibility of introducing selectivity to existing chemotherapeutics via the design of non-pro-drug, bi-functional molecules comprising a microtubule-binding agent and a substrate for a disease-associated kinase. The design, synthesis, and in vitro biological evaluation of paclitaxel-thymidine and vinblastine-thymidine bi-functional conjugates are reported here. This work provides the first account of 'kinase-mediated trapping' of cancer therapeutics.

Thymidylate synthase and dihydropyrimidine dehydrogenase gene expression in breast cancer predicts 5-FU sensitivity by a histocultural drug sensitivity test

Thymidylate synthase (TS), Dihydropyrimidine dehydrogenase (DPD) and Thymidine Phosphorylase (TP) gene expressions are reported to be predictive markers for 5-fluorouracil (5-FU) sensitivity in gastrointestinal cancer. However, in breast cancer, it is still controversial whether those molecular markers predict 5-FU sensitivity or not. One possible reason for the difficulty may be the histological heterogeneity in breast cancer specimens. In this study, TS, DPD and TP mRNA expression in 40 breast cancer tumors were semi-quantified separately in cancer cells (Ca), cancerous stroma (Str) and normal glands (Nor) using laser capture microdissection and real time RT-PCR (LCM+RT-PCR). The histoculture drug response assay (HDRA) for 5-FU sensitivity was performed for 22 tumors. TS and TP mRNA expressions were higher in Ca than Str, although DPD gene expression was lower in Ca than Str. The group of high TS and high DPD gene expression in Ca was resistant to 5-FU, and the group of low TS and low DPD gene expression in Ca was sensitive to 5-FU (P=0.048 chi-square test). TS and DPD mRNA expressions measured using LCM+RT-PCR might be useful predictive markers for 5-FU sensitivity in human breast cancer.

Increased expression of mRNA specific for thymidine kinase, deoxycytidine kinase or thymidine phosphorylase in human papillary thyroid carcinoma

The aim of the present study was to estimate the expression of mRNA, specific for thymidine kinase 1 (TK1), deoxycytidine kinase (dCK), and thymidine phosphorylase (dThdPase), i.e. enzymes involved in pyrimidine and purine metabolism in human papillary thyroid carcinoma (PTC) tissue. Additionally, the expression of dCK was estimated, in medullary thyroid carcinoma (MTC). For control, the RNA expression levels for all the enzymes were measured in macroscopically unchanged thyroid tissue. Reverse transcriptase-polymerase chain reaction (RT-PCR) and densitometry were employed for mRNA expression measurements, with the beta-actin gene as a control housekeeping gene. The levels of mRNA expression for TK1, dCK and dThdPase in human PTC, as well as mRNA expression for dCK in MTC, were significantly higher than mRNA expressions for those enzymes found in macroscopically unchanged thyroid tissue. It is concluded that an increased expression of mRNA, specific for TK1, dCK and dThdPase, may be involved in carcinogenic processes in the human thyroid.

The changes of gene expression profiles in hydatidiform mole and choriocarcinoma with hyperplasia of trophoblasts

The purpose of this study is to investigate changes of gene expression profiles in hydatidiform moles (HM) and choriocarcinoma and to explore causes of trophoblastic hyperplasia. Using cDNA microarray, 4,096 genes were analyzed in two pairs of the tissues of HM versus normal villi and in two pairs of normal primary culture trophoblasts versus JAR cell line of choriocarcinoma. The expressions of two genes in normal villi and HM, as well as in JAR and JEG-3, were examined with the help of immunohistochemistry, immunoblot, and reverse transcriptase-polymerase chain reaction in order to confirm the findings of cDNA microarray. Twenty-four genes were upregulated and 65 genes were downregulated in all HM. Four hundred thirty-three genes were upregulated and 380 genes were downregulated in JAR. Forty-six genes were upregulated in both HM and choriocarcinoma, whereas 13 genes were downregulated. Genes associated with the inhibition of cell proliferation were significantly downregulated, whereas genes associated with cell proliferation, malignant transformation, metastasis, and drug resistance were upregulated. Thymidine kinase-1 (TK-1) and small subunit ribonucleotide reductase (RRM-2) were overexpressed in HM, JAR, and JEG-3. The expressions of TK-1 and RRM-2 in moles were positively correlated with proliferative index of trophoblasts. Our results suggest that altered expression of genes exist in HM and choriocarcinoma. Trophoblastic hyperplasia may be involved in the overexpression of DNA synthetic enzymes.

Synthesis of [18F]Xeloda as a novel potential PET radiotracer for imaging enzymes in cancers

Xeloda (Capecitabine), a prodrug of antitumor agent 5-fluorouracil, is the first and only oral fluoropyrimidine to be approved for use as second-line therapy in metastatic breast cancer, colorectal cancer, and other solid malignancies. Fluorine-18 labeled Xeloda may serve as a novel radiotracer for positron emission tomography (PET) to image enzymes such as thymidine phosphorylase and uridine phosphorylase in cancers. The precursor 2',3'-di-O-acetyl-5'-deoxy-5-nitro-N(4)-(pentyloxycarbonyl)cytidine (11) was synthesized from D-ribose and cytosine in 8 steps with approximately 18% overall chemical yield. The reference standard 5'-deoxy-5-fluoro-N(4)-(pentyloxycarbonyl)cytidine (Xeloda; 1) was synthesized from D-ribose and 5-fluorocytosine in eight steps with approximately 28% overall chemical yield. The target radiotracer 5'-deoxy-5-[(18)F]fluoro-N(4)-(pentyloxycarbonyl)cytidine ([(18)F]Xeloda; [(18)F]1) was prepared by nucleophilic substitution of the nitro-precursor with K(18)F/Kryptofix 2.2.2 followed by a quick deprotection reaction and purification with the HPLC method in 20-30% radiochemical yields.

Sensitive nonradiometric method for determining thymidine kinase 1 activity

BACKGROUND

Thymidine kinase 1 (TK1) is a cytoplasmic enzyme, produced only in the S-phase of proliferating cells, that has potential as a tumor marker. Specific determination of TK1 in serum is difficult, in part because of differences in the physical properties of serum TK1 compared with cytoplasmic TK1.

METHODS

The first step in the new assay was phosphorylation of 3'-azido-2',3'-deoxythymidine (AZT) to AZT 5'-monophosphate (AZTMP) by TK1 present in patient material. The AZTMP formed was measured in a competitive immunoassay with specific anti-AZTMP antibodies and AZTMP-labeled peroxidase. Results were compared with those of a TK radioenzyme assay (REA) for 78 samples from patients suffering from hematologic diseases.

RESULTS

The detection limit was 78 microIU/L, and within-run CVs <20% were seen for samples with TK1 down to 130 microIU/L. Cross-determination of the mitochondrial isoenzyme TK2 activity was <0.1%. Between-assay imprecision (CV) was 3.5-7.4%, and the within-assay imprecision was 4.1-9.1%. In studies of recovery and linearity on dilution, measured values ranged from 84% to 115% of expected at concentrations of 0.26-10.4 mIU/L. Results of the new assay (mIU/L) = 0.109 x TK REA (U/L) + 0.092. Heterophilic antibodies did not interfere in the assay. The upper 95th percentile, in 100 healthy individuals, was 0.94 mIU/L, and the median value was 0.43 mIU/L.

CONCLUSION

The TK1 enzyme-labeled immunoassay uses a stable substrate, is precise, appears to be accurate, and is resistant to interferences. It may provide a practical tool in the management of hematologic malignancies.

Dihydropyrimidine dehydrogenase in normal and malignant endometrium: relationship with cell proliferation and thymidine phosphorylase

Dihydropyrimidine dehydrogenase (DPD) is a pyrimidine salvage enzyme responsible for degradation of thymine, which is produced from thymidine by thymidine phosphorylase (TP). Our purpose was to determine the relationship between DPD, cell proliferation and TP expression in human endometrium. We examined DPD gene expression using reverse transcription-polymerase chain reaction, DPD protein levels using enzyme-linked immunosorbent assay, and DPD protein localization using immunohistochemistry in 58 normal endometria and 28 endometrial cancers. DPD gene expression was then related to the proliferating cell nuclear antigen index and to TP gene expression. DPD gene expression, which was correlated with DPD protein level, was relatively stable throughout various menstrual phases but was significantly elevated in postmenopausal status. It was significantly lower in endometrial cancer than in normal endometrium. Localization analysis revealed that DPD protein was located primarily in epithelial cells, but was also present in stromal cells. DPD gene expression correlated inversely with the PCNA index. TP gene expression pattern contrasted with that of DPD in postmenopausal and malignant endometrium. A high ratio of TP to DPD gene expression was significantly more frequent in endometrial cancer than in normal endometrium in any menstrual phase. DPD may act cooperatively with TP to affect cell function by maintaining the pyrimidine nucleotide pool balance in normal and malignant endometrium.

Impaired adrenocorticotropic hormone response to bacterial endotoxin in mice deficient in prostaglandin E receptor EP1 and EP3 subtypes

Sickness evokes various neural responses, one of which is activation of the hypothalamo-pituitary-adrenal (HPA) axis. This response can be induced experimentally by injection of bacterial lipopolysaccharide (LPS) or inflammatory cytokines such as IL-1. Although prostaglandins (PGs) long have been implicated in LPS-induced HPA axis activation, the mechanism downstream of PGs remained unsettled. By using mice lacking each of the four PGE receptors (EP1-EP4) and an EP1-selective antagonist, ONO-8713, we showed that both EP1 and EP3 are required for adrenocorticotropic hormone release in response to LPS. Analysis of c-Fos expression as a marker for neuronal activity indicated that both EP1 and EP3 contribute to activation of neurons in the paraventricular nucleus of the hypothalamus (PVN). This analysis also revealed that EP1, but not EP3, is involved in LPS-induced activation of the central nucleus of the amygdala. EP1 immunostaining in the PVN revealed its localization at synapses on corticotropin-releasing hormone-containing neurons. These findings suggest that EP1- and EP3-mediated neuronal pathways converge at corticotropin-releasing hormone-containing neurons in the PVN to induce HPA axis activation upon sickness.