Purification and tissue distribution of human thymidine phosphorylase; high expression in lymphocytes, reticulocytes and tumors

Metronomic capecitabine inhibits liver transplant rejection in rats by triggering recipients’ T cell ferroptosis

BACKGROUND

Capecitabine (CAP) is a classic antimetabolic drug and has shown potential antirejection effects after liver transplantation (LT) in clinical studies. Our previous study showed that metronomic CAP can cause the programmed death of T cells by inducing oxidative stress in healthy mice. Ferroptosis, a newly defined non-apoptotic cell death that occurs in response to iron overload and lethal levels of lipid peroxidation, is an important mechanism by which CAP induces cell death. Therefore, ferroptosis may also play an important role in CAP-induced T cell death and play an immunosuppressive role in acute rejection after trans-plantation.

AIM

To investigate the functions and underlying mechanisms of antirejection effects of metronomic CAP.

METHODS

A rat LT model of acute rejection was established, and the effect of metronomic CAP on splenic hematopoietic function and acute graft rejection was evaluated 7 d after LT. In vitro, primary CD3⁺ T cells were sorted from rat spleens and human peripheral blood, and co-cultured with or without 5-fluorouracil (5-FU) (active agent of CAP). The levels of ferroptosis-related proteins, ferrous ion concentration, and oxidative stress-related indicators were observed. The changes in mito-chondrial structure were observed using electron microscopy.

RESULTS

With no significant myelotoxicity, metronomic CAP alleviated graft injury (Banff score 9 vs 7.333, P < 0.001), prolonged the survival time of the recipient rats (11.5 d vs 16 d, P < 0.01), and reduced the infiltration rate of CD3⁺ T cells in peripheral blood (6.859 vs 3.735, P < 0.001), liver graft (7.459 vs 3.432, P < 0.001), and spleen (26.92 vs 12.9, P < 0.001), thereby inhibiting acute rejection after LT. In vitro, 5-FU, an end product of CAP metabolism, induced the degradation of the ferritin heavy chain by upregulating nuclear receptor coactivator 4, which caused the accumulation of ferrous ions. It also inhibited nuclear erythroid 2 p45-related factor 2, heme oxygenase-1, and glutathione peroxidase 4, eventually leading to oxidative damage and ferroptosis of T cells.

CONCLUSION

Metronomic CAP can suppress acute allograft rejection in rats by triggering CD3⁺ T cell ferroptosis, which makes it an effective immunosuppressive agent after LT.

Depletion of plasma thymidine results in growth retardation and mitochondrial myopathy in mice overexpressing human thymidine phosphorylase

Plasma thymidine levels in rodents are higher than in other mammals including humans, possibly due to a different pattern and lower level of thymidine phosphorylase expression. Here, we generated a novel knock-in (KI) mouse line with high systemic expression of human thymidine phosphorylase to investigate this difference in nucleotide metabolism in rodents. The KI mice showed growth retardation around weaning and died by 4 weeks of age with a decrease in plasma thymidine level compared with the litter-control WT mice. These phenotypes were completely or partially rescued by administration of the thymidine phosphorylase inhibitor 5-chloro-6-(2-iminopyrrolidin-1-yl) methyl-2,4(1H,3H)-pyrimidinedione hydrochloride or thymidine, respectively. Interestingly, when thymidine phosphorylase inhibitor administration was discontinued in adult animals, KI mice showed deteriorated grip strength and locomotor activity, decreased bodyweight, and subsequent hind-limb paralysis. Upon histological analyses, we observed axonal degeneration in the spinal cord, muscular atrophy with morphologically abnormal mitochondria in quadriceps, retinal degeneration, and abnormality in the exocrine pancreas. Moreover, we detected mitochondrial DNA depletion in multiple tissues of KI mice. These results indicate that the KI mouse represents a new animal model for mitochondrial diseases and should be applicable for the study of differences in nucleotide metabolism between humans and mice.

Capecitabine Can Induce T Cell Apoptosis: A Potential Immunosuppressive Agent With Anti-Cancer Effect

Capecitabine (CAP) is now widely used in the comprehensive treatment of digestive system tumors. Some clinical observations have shown that CAP may have immunosuppressive effects, but there is still a lack of clear experimental verification. In this study, different doses of CAP were administered to normal mice by gavage. Our results confirmed that CAP did not cause myelosuppression in bone marrow tissue; CAP selectively reduced the proportion of T cells and the concentration of related pro-inflammatory cytokines, while it increased the concentration of anti-inflammatory cytokines. Thymidylate phosphorylase (TP) is the key enzyme for the transformation of CAP in vivo; this study confirmed that T cells express TP, but the bone marrow tissue lacks TP expression, which explains the selectivity in pharmacodynamic effects of CAP. In addition, it was confirmed that CAP can induce T cell apoptosis in vivo and in vitro. In vitro experiments showed that CAP-induced T cell apoptosis was related to TP expression, endoplasmic reticulum stress (ERS) induction, reactive oxygen species (ROS) production, and mitochondria-mediated apoptosis activation. Therefore, this study confirmed that the differential expression of TP in cells and tissues explains why CAP avoids the toxic effects of myelosuppression while inducing T cell apoptosis to exert the immunosuppressive effect. Therefore, CAP may become an immunosuppressive agent with a simultaneous anti-cancer effect, which is worthy of further studies.

Therapy Prospects for Mitochondrial DNA Maintenance Disorders

Mitochondrial DNA depletion and multiple deletions syndromes (MDDS) constitute a group of mitochondrial diseases defined by dysfunctional mitochondrial DNA (mtDNA) replication and maintenance. As is the case for many other mitochondrial diseases, the options for the treatment of these disorders are rather limited today. Some aggressive treatments such as liver transplantation or allogeneic stem cell transplantation are among the few available options for patients with some forms of MDDS. However, in recent years, significant advances in our knowledge of the biochemical pathomechanisms accounting for dysfunctional mtDNA replication have been achieved, which has opened new prospects for the treatment of these often fatal diseases. Current strategies under investigation to treat MDDS range from small molecule substrate enhancement approaches to more complex treatments, such as lentiviral or adenoassociated vector-mediated gene therapy. Some of these experimental therapies have already reached the clinical phase with very promising results, however, they are hampered by the fact that these are all rare disorders and so the patient recruitment potential for clinical trials is very limited.

Pregnancy in MNGIE: a clinical and metabolic honeymoon

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an inherited disease caused by a deficiency in thymidine phosphorylase and characterized by elevated systemic deoxyribonucleotides and gastrointestinal (GI) and neurological manifestations. We report the clinical and biochemical manifestations that were evaluated in a single patient before, during, and after pregnancy, over a period of 7 years. GI symptoms significantly improved, and plasma deoxyribonucleotide concentrations decreased during pregnancy. Within days after delivery, the patient's digestive symptoms recurred, coinciding with a rapid increase in plasma deoxyribonucleotide concentrations. We hypothesize that the clinico-metabolic improvements could be attributed to the enzyme replacement action of the placental thymidine phosphorylase.

Applications of Human Peripheral Blood Lymphocytes in Genotoxicity and Cytotoxicity

A number of features make peripheral blood lymphocytes an excellent system for studying both genotoxicity and cytotoxicity in humans. They are an abundant and readily accessible source of somatic cells, mostly in a non-proliferative state, but able to be stimulated by mitogens to enter the cell cycle. The blastocyte transformation of lymphocytes is a useful model for investigating the mechanisms which regulate cell-cycle progression in mammalian cells. By stimulating lymphocytes in vitro, it is possible to detect the genetic damages they have sustained in vivo, which become manifest as chromosomal aberrations, sister-chromatid exchanges or gene mutations. The metabolic properties of lymphocytes have been extensively studied, especially with reference to their characteristic collection of enzymes involved in nucleotide turnover, which makes them exquisitely sensitive to changes in intracellular levels of DNA precursors. The data collected on the ability of lymphocytes to metabolise xenobiotics show a marked quantitative difference between resting and proliferating lymphocytes, and minor qualitative differences between lymphocytes and other cell types, e.g. hepatocytes. An indirect approach to detect the metabolism of genotoxic xenobiotics by lymphocytes is the analysis of DNA adducts in their chromatin after in vivo or in vitro exposure. Lymphocytes can be employed to identify the (cyto)genetic consequences of in vivo genotoxic exposure and inter-individual variation in sensitivity to genotoxic agents. The analysis of mutations at the hgprt locus in lymphocytes is a promising approach for the study of somatic-cell mutations in humans and of the possible mechanisms of in vivo selection against mutants.

In the field of cytotoxicity, the applications of lymphocytes are, as yet, still few: the main effect measured is the impairment of the proliferative response to mitogens. But lymphocytes can be employed as primary human cells to be treated in vitro with mutagenic or toxic chemicals in standard genotoxicity and cytotoxicity assays, and offer the advantage of avoiding the problems of inter-species extrapolation of results by testing in a human system. Moreover, the (geno)toxic effects detected in lymphocytes after treatments in vitro may give information on the spontaneous or environmentally-determined susceptibility of the individual donors to xenobiotics.

Mitochondrial Neurogastrointestinal Encephalomyopathy: Into the Fourth Decade, What We Have Learned So Far

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare metabolic autosomal recessive disease, caused by mutations in the nuclear gene TYMP which encodes the enzyme thymidine phosphorylase. The resulting enzyme deficiency leads to a systemic accumulation of the deoxyribonucleosides thymidine and deoxyuridine, and ultimately mitochondrial failure due to a progressive acquisition of secondary mitochondrial DNA (mtDNA) mutations and mtDNA depletion. Clinically, MNGIE is characterized by gastrointestinal and neurological manifestations, including cachexia, gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, ophthalmoplegia and ptosis. The disease is progressively degenerative and leads to death at an average age of 37.6 years. As with the vast majority of rare diseases, patients with MNGIE face a number of unmet needs related to diagnostic delays, a lack of approved therapies, and non-specific clinical management. We provide here a comprehensive collation of the available knowledge of MNGIE since the disease was first described 42 years ago. This review includes symptomatology, diagnostic procedures and hurdles, in vitro and in vivo disease models that have enhanced our understanding of the disease pathology, and finally experimental therapeutic approaches under development. The ultimate aim of this review is to increase clinical awareness of MNGIE, thereby reducing diagnostic delay and improving patient access to putative treatments under investigation.

Distinct substrate specificity and physicochemical characterization of native human hepatic thymidine phosphorylase

Thymidine phosphorylase (TP; EC 2.4.2.4) is involved regulation of intra- or extracellular thymidine concentration, angiogenesis, cancer chemotherapy, radiotherapy, as well as tumor imaging. Although the liver is main site of pyrimidine metabolism and contains high levels of TP, nonetheless, purification and characterization of human hepatic TP has not been accomplished. We here report the purification and characterization of native human hepatic TP. The enzyme was purified to apparent homogeneity by a procedure shorter and more efficient than previously reported methods. Human hepatic TP has an apparent Kthymidine of 285 ± 55 μM. Like the enzyme from other tissues, it is highly specific to 2'-deoxyribosides. However, in contrast to TP from other normal tissues, the hepatic enzyme is active in the phosphorolysis of 5'-deoxy-5-fluorouridine, and the riboside 5-fluorouridine. Furthermore, native hepatic TP exists in different aggregates of 50 kDa subunits, with unknown aggregation factor(s) while TP from extra tissues exists as a homodimer. Isoelectric point was determined as 4.3. A total of 65 residues in the N-terminal were sequenced. The sequence of these 65 amino acids in hepatic TP has 100% sequence and location homology to the deduced amino acid sequence of the platelet derived-endothelial cell growth factor (PD-ECGF) cDNA. However, and contrary to PD-ECGF, the N-terminal of hepatic TP is blocked. The block was neither N-formyl nor pyrrolidone carboxylic acid moieties. The differences in substrate specificities, existence in multimers, and weak interaction with hydroxyapatite resin strongly suggest that hepatic TP is distinct from the enzyme in normal extrahepatic tissues. These results may have important clinical implications when TP is involved in activation or deactivation of chemotherapeutic agents in different tissues.

Prediction of Differentiation Tendency Toward Hepatocytes from Gene Expression in Undifferentiated Human Pluripotent Stem Cells

Functional hepatocytes derived from human pluripotent stem cells (hPSCs) have potential as tools for predicting drug-induced hepatotoxicity in the early phases of drug development. However, the propensity of hPSC lines to differentiate into specific lineages is reported to differ. The ability to predict low propensity of hPSCs to differentiate into hepatocytes would facilitate the selection of useful hPSC clones and substantially accelerate development of hPSC-derived hepatocytes for pharmaceutical research. In this study, we compared the expression of genes associated with hepatic differentiation in five hPSC lines including human ES cell line, H9, which is known to differentiate into hepatocytes, and an hPSC line reported with a poor propensity for hepatic differentiation. Genes distinguishing between undifferentiated hPSCs, hPSC-derived hepatoblast-like differentiated cells, and primary human hepatocytes were drawn by two-way cluster analysis. The order of expression levels of genes in undifferentiated hPSCs was compared with that in hPSC-derived hepatoblast-like cells. Three genes were selected as predictors of low propensity for hepatic differentiation. Expression of these genes was investigated in 23 hPSC clones. Review of representative cells by induction of hepatic differentiation suggested that low prediction scores were linked with low hepatic differentiation. Thus, our model using gene expression ranking and bioinformatic analysis could reasonably predict poor differentiation propensity of hPSC lines.

Liver as a source for thymidine phosphorylase replacement in mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a rare autosomal recessive mitochondrial disease associated with mutations in the nuclear TYMP gene. As a result, the thymidine phosphorylase (TP) enzyme activity is markedly reduced leading to toxic accumulation of thymidine and therefore altered mitochondrial DNA. MNGIE is characterized by severe gastrointestinal dysmotility, neurological impairment, reduced life expectancy and poor quality of life. There are limited therapeutic options for MNGIE. In the attempt to restore TP activity, allogenic hematopoietic stem cell transplantation has been used as cellular source of TP. The results of this approach on ∼20 MNGIE patients showed gastrointestinal and neurological improvement, although the 5-year mortality rate is about 70%. In this study we tested whether the liver may serve as an alternative source of TP. We investigated 11 patients (7M; 35–55 years) who underwent hepatic resection for focal disorders. Margins of normal liver tissue were processed to identify, quantify and localize the TP protein by Western Blot, ELISA, and immunohistochemistry, and to evaluate TYMP mRNA expression by qPCR. Western Blot identified TP in liver with a TP/GAPDH ratio of 0.9±0.5. ELISA estimated TP content as 0.5±0.07 ng/μg of total protein. TP was identified in both nuclei and cytoplasm of hepatocytes and sinusoidal lining cells. Finally, TYMP mRNA was expressed in the liver. Overall, our study demonstrates that the liver is an important source of TP. Orthotopic liver transplantation may be considered as a therapeutic alternative for MNGIE patients.

Thymidine Phosphorylase Gene Expression in Stage III Colorectal Cancer

BACKGROUND

The thymidine phosphorylase (TP) enzyme has several tumor-promoting functions. The aim of this study was to explore TP gene expression in relation to clinical and histopathological data obtained from patients with stage III colorectal cancer.

METHODS AND RESULTS

TP gene expression was analyzed by real-time quantitative PCR in tumor and mucosa samples from 254 patients. TP gene expression in tumors correlated with lymph node staging, with higher expression relating to a higher number of positive nodes and a worse N-stage. Higher TP expression was also associated with a worse histological tumor grade. Patients with rectal cancer had significantly higher TP expression in mucosa and tumors compared with patients having colon cancer.

CONCLUSION

Higher intratumoral TP expression appears to be related to a worse N stage, and thus, with a worse prognosis. TP gene expression measured in a preoperative biopsy could be of interest in preoperative staging.

Expression of thymidine phosphorylase in lymph nodes involved with mycosis fungoides and sézary syndrome

Thymidine phosphorylase may be overexpressed in both neoplastic cells and tumor stromal cells in a variety of malignancies. Our study explores thymidine phosphorylase expression in lymph nodes (LNs) from patients with mycosis fungoides (MF) or Sézary syndrome (SS). In MF/SS, the LNs may have a pathologic diagnosis of either dermatopathic lymphadenopathy (LN-DL) or involvement by MF/SS (LN-MF). We performed immunohistochemical staining on MF/SS lymph nodes using antibodies to thymidine phosphorylase, CD68, CD21, CD3, and CD4. In both LN-DL and benign nodes, thymidine phosphorylase staining was noted only in macrophages, dendritic cells, and endothelial cells. In LN-MF, thymidine phosphorylase expression was also noted in subsets of intermediate to large neoplastic T cells. Concurrent CD68, CD21, CD3, and CD4 staining supported the above observations. Similar results were noted in the skin and in LN-MF with large cell transformation. Other T-cell lymphomas were also examined (total 7 cases); only enteropathy-type T-cell lymphoma (1 case) showed TP positivity in neoplastic T lymphocytes. We demonstrated that thymidine phosphorylase staining is present in neoplastic T cells in mycosis fungoides. The exact mechanism needs further investigation.

Clinical and genetic spectrum of mitochondrial neurogastrointestinal encephalomyopathy

Mitochondrial neurogastrointestinal encephalomyopathy is a rare multisystemic autosomic recessive disorder characterized by: onset typically before the age of 30 years; ptosis; progressive external ophthalmoplegia; gastrointestinal dysmotility; cachexia; peripheral neuropathy; and leucoencephalopathy. The disease is caused by mutations in the TYMP gene encoding thymidine phosphorylasethymine phosphorylase. Anecdotal reports suggest that allogeneic haematopoetic stem cell transplantation may be beneficial for mitochondrial neurogastrointestinal encephalomyopathy, but is associated with a high mortality. After selecting patients who fulfilled the clinical criteria for mitochondrial neurogastrointestinal encephalomyopathy and had severe thymidine phosphorylase deficiency in the buffy coat (<10% of normal activity), we reviewed their medical records and laboratory studies. We identified 102 patients (50 females) with mitochondrial neurogastrointestinal encephalomyopathy and an average age of 32.4 years (range 11-59 years). We found 20 novel TYMP mutations. The average age-at-onset was 17.9 years (range 5 months to 35 years); however, the majority of patients reported the first symptoms before the age of 12 years. The patient distribution suggests a relatively high prevalence in Europeans, while the mutation distribution suggests founder effects for a few mutations, such as c.866A>G in Europe and c.518T>G in the Dominican Republic, that could guide genetic screening in each location. Although the sequence of clinical manifestations in the disease varied, half of the patients initially had gastrointestinal symptoms. We confirmed anecdotal reports of intra- and inter-familial clinical variability and absence of genotype-phenotype correlation in the disease, suggesting genetic modifiers, environmental factors or both contribute to disease manifestations. Acute medical events such as infections often provoked worsening of symptoms, suggesting that careful monitoring and early treatment of intercurrent illnesses may be beneficial. We observed endocrine/exocrine pancreatic insufficiency, which had not previously been reported. Kaplan-Meier analysis revealed significant mortality between the ages of 20 and 40 years due to infectious or metabolic complications. Despite increasing awareness of this illness, a high proportion of patients had been misdiagnosed. Early and accurate diagnosis of mitochondrial neurogastrointestinal encephalomyopathy, together with timely treatment of acute intercurrent illnesses, may retard disease progression and increase the number of patients eligible for allogeneic haematopoetic stem cell transplantation.

Maternal gene expression profiling during pregnancy and preeclampsia in human peripheral blood mononuclear cells

Preeclampsia is a major obstetrical complication affecting maternal and fetal health. While it is clear that there is a substantial placental contribution to preeclampsia pathogenesis, the maternal contribution is less well characterized. We therefore performed a genome-wide transcriptome analysis to explore disease-associated changes in maternal gene expression patterns in peripheral blood mononuclear cells (PBMCs).

METHODS

Preeclampsia was defined as gestational hypertension, proteinuria and hyperurecimia. Total RNA was isolated from PBMCs obtained from women with uncomplicated pregnancies (n = 5) and women with preeclamptic pregnancies (n = 5). Gene expression analysis was carried out using Agilent oligonucleotide microarrays. Biological pathway analysis was undertaken using Ingenuity Pathway Analysis software. Quantitative real-time PCR (QRTPCR) was performed to validate the gene expression changes of selected genes in normotensive and preeclamptic patients (n = 12 each).

RESULTS

We identified a total of 368 genes that were differentially expressed in women with preeclampsia compared to normal controls with false discovery rate (FDR) controlled at 10%. In follow up experiments we further analyzed the expression levels of a number of genes that were identified as altered by the microarray data including survivin (BIRC5), caveolin (CAV1), GATA binding protein-1 (GATA1), signal tranducer and activator of transcription 1 (STAT1), E2F transcription factor-1 (E2F1), fibronectin-1 (FN1), interleukin-4 (IL-4), matrix metalloprotease-9 (MMP-9) and WAP four disulfide domain protein (WFDC-1) by QRTPCR. Additionally we performed immuno blot analysis and zymography to verify some of these candidate genes at the protein level. Computational analysis of gene function identified an anti-proliferative and altered immune function cellular phenotype in severe preeclamptic samples.

CONCLUSIONS

We have characterized the genome-wide mRNA expression changes associated with preeclampsia-specific genes in circulating maternal blood cells at the time of delivery. In addition to providing information relating to the biological basis of the preeclampsia phenotype, our data provide a number of potential biomarkers for use in the further characterization of this disease.

A second MNGIE patient without typical mitochondrial skeletal muscle involvement

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease caused by mutations in the gene encoding thymidine phosphorylase (TYMP). Clinically, MNGIE is characterized by gastrointestinal dysmotility, cachexia, ptosis, ophthalmoparesis, peripheral neuropathy and leukoencephalopathy. Most MNGIE patients have signs of mitochondrial dysfunction in skeletal muscle at morphological and enzyme level, as well as mitochondrial DNA depletion, multiple deletions and point mutations. A case without mitochondrial skeletal muscle involvement and with a TYMP splice-acceptor site mutation (c. 215-1 G>C) has been reported. Here, we describe an Italian patient with the same mutation and without mitochondrial skeletal muscle involvement, suggesting a possible genotype-phenotype correlation.

The dual role of thymidine phosphorylase in cancer development and chemotherapy

Thymidine phosphorylase (TP), also known as "platelet-derived endothelial cell growth factor" (PD-ECGF), is an enzyme, which is upregulated in a wide variety of solid tumors including breast and colorectal cancers. TP promotes tumor growth and metastasis by preventing apoptosis and inducing angiogenesis. Elevated levels of TP are associated with tumor aggressiveness and poor prognosis. Therefore, TP inhibitors are synthesized in an attempt to prevent tumor angiogenesis and metastasis. TP is also indispensable for the activation of the extensively used 5-fluorouracil prodrug capecitabine, which is clinically used for the treatment of colon and breast cancer. Clinical trials that combine capecitabine with TP-inducing therapies (such as taxanes or radiotherapy) suggest that increasing TP expression is an adequate strategy to enhance the antitumoral efficacy of capecitabine. Thus, TP plays a dual role in cancer development and therapy: on the one hand, TP inhibitors can abrogate the tumorigenic and metastatic properties of TP; on the other, TP activity is necessary for the activation of several chemotherapeutic drugs. This duality illustrates the complexity of the role of TP in tumor progression and in the clinical response to fluoropyrimidine-based chemotherapy.

Micro-vessel density and the expression of vascular endothelial growth factor (VEGF) and platelet-derived endothelial cell growth factor (PdEGF) in classical Hodgkin lymphoma (HL)

There is little information to date regarding the role of angiogenesis in Hodgkin lymphoma (HL). The present study examines micro-vessel density and the expression of vascular endothelial growth factor (VEGF) and platelet-derived endothelial growth factor (PdEGF) in lymph node biopsies of patients with HL at presentation and relapse. Using immunohistochemistry, the degree of new blood vessel formation and the expression of VEGF and PdEGF was assessed in Hodgkin-rich tissue. The micro-vessel density (MVD) increased with disease progression in seven out of 11 cases. Expression of VEGF was observed in endothelial cells (EC) of some micro-vessels and also in follicular dendritic cells. The Hodgkin/Reed-Sternberg (H-RS) cells as well as the inflammatory lymphocytes were negative for VEGF. Cytoplasmic or cytoplasmic and nuclear expression of PdEGF by the H-RS cells was observed in five of the 11 presentation cases. The expression of PdEGF increased with disease progression in seven cases. In conclusion, Hodgkin tissue shows prominent vascularization. The increased MVD and PdEGF expression with disease progression merits further investigation.

The cytosol activity of thymidine phosphorylase in endometrial cancer

BACKGROUND

Thymidine phosphorylase (TP) is identical with platelet-derived endothelial cell growth factor (PD-ECGF) which promotes angiogenesis. The aim of this study was to evaluate the cytosol activity of TP in tumor samples from patients with endometrial cancer.

METHODS

The activity of TP was measured by the spectrophotometric method in the cytosol of endometrial tumor samples from 43 patients. Moreover, the expression of platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP) protein and microvessel density (MD) were examined in the same endometrial tumor samples by immunohistochemical staining. Normal endometrium from 16 women, treated surgically due to nononcological reasons served as a control.A relationship between the cytosol TP activity, PD-ECGF/TP protein expression, MD and clinicopathologic features was investigated.

RESULTS

A significantly higher the cytosol TP activity, PD-ECGF/TP protein expression and MD was stated in malignant tumor samples when compared to the control (samples of normal endometrium). A positive statistically significant correlation between the cytosol enzyme activity and PD-ECGF/TP protein expression and MD was found, but weaker from the remaining ones between PD-ECGF/TP protein expression and MD was observed.Besides no correlation between the cytosol TP activity, PD-ECGF/TP protein expression as well as MD and grading or histopatological type of endometrial cancer was stated.

CONCLUSION

The cytosol TP activity in endometrial cancer is significantly higher than in normal endometrium, with no relation as to the stage and grade of tumors, but correlates with the PD-ECGF/TP protein expression and MD may therefore be associated with favorable prognosis in patients treated with chemo- or radiotherapy after surgery.

In vitro evaluation of cancer-specific NF-kappaB-CEA enhancer-promoter system for 5-fluorouracil prodrug gene therapy in colon cancer cell lines

Nuclear factor-kappa B (NF-κB) is a transcription factor with high transcriptional activity in cancer cells. In this study, we developed a novel enhancer–promoter system, κB4-CEA205, in which the basal carcinoembryonic antigen (CEA) promoter sequence (CEA205) was placed downstream of the four tandem-linked NF-κB DNA-binding sites (κB4). In combination with a κB4 enhancer, the transcriptional activity of the CEA promoter was significantly enhanced (three- to eight-fold) in cancer cell lines but not in normal cells. In cancer cell lines, the transcriptional activity of κB4-CEA205 was comparable with that of the SV40 promoter. We also constructed vectors in which the thymidine phosphorylase (TP) cDNA was under the control of CEA205, κB4, κB4-CEA205 and CMV promoters, respectively. TP protein and enzyme activity were detected at comparable levels in κB4-CEA205- and CMV-driven TP cDNA-transfected cancer cell lines (H630 and RKO). The κB4-TP and CEA205-TP-transfected cell lines, respectively, only demonstrated negligible and low levels of TP protein and enzyme activity. Both CMV- and κB4-CEA205-driven TP cDNA transiently transfected cells were 8- to 10-fold sensitised to 5-fluorouracil (5-FU) prodrug, 5′-deoxy-5-fluorouradine (5′-DFUR), in contrast to only 1.5- to 2-fold sensitised by the κB4- and CEA205-driven TP cDNA-transfected cells. The bystander killing effect of CMV- and κB4-CEA205-driven TP cDNA-transfected cells was comparable. This is the first report that indicates that the NF-κB DNA-binding site could be used as a novel cancer-specific enhancer to improve cancer-specific promoter activity in gene-directed enzyme prodrug therapy.

Thymidine and deoxyuridine accumulate in tissues of patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE)

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease due to ECGF1 gene mutations causing thymidine phosphorylase (TP) deficiency. Analysis of post-mortem samples of five MNGIE patients and two controls, revealed TP activity in all control tissues, but not in MNGIE samples. Converse to TP activity, thymidine and deoxyuridine were absent in control samples, but present in all tissues of MNGIE patients. Concentrations of both nucleosides in the tissues were generally higher than those observed in plasma of MNGIE patients. Our observations indicate that in the absence of TP activity, tissues accumulate nucleosides, which are excreted into plasma.

Expression of thymidine phosphorylase in peripheral blood cells of breast cancer patients is not increased by paclitaxel

Background

A synergistic cytotoxic effect has been hypothesized for taxanes and capecitabine, a prodrug of 5-fluorouracil. Based on preclinical studies, this synergism has been attributed to an up-regulation of the enzyme thymidine phosphorylase (TP). Beside tumour tissue, TP is highly expressed in white blood cells, possibly causing increased hematotoxicity, when taxanes are combined with capecitabine. So far, this hypothesis has not been investigated in humans.

Methods

A total of 128 consecutive blood samples were collected from eight patients with advanced breast cancer receiving paclitaxel weekly at a dose of 80 mg/m². To assess the expression of TP in blood cells, samples were collected prior to first therapy, at the end of infusion, and up to 15 days thereafter. This procedure was repeated during the sixth application of paclitaxel. After isolation of the peripheral mononuclear blood cells, the expression of TP was assessed by ELISA. In parallel, paclitaxel level in plasma was evaluated at three selected time points as pharmacokinetic control parameter.

Results

Paclitaxel concentrations at the end of infusion did not change significantly from week 1 to week 6. The expression of TP in peripheral mononuclear blood cells decreased significantly after infusion below pretherapeutic values (p = 0.023; n = 8). After the nadir on day 3, the expression of TP increased moderately returning to baseline levels within one week. The overall picture in week 6 was similar to week 1. Using a trend analysis, neither a short-term nor a long-term induction of TP was observed.

Conclusion

TP in peripheral mononuclear blood cells was hardly regulated under therapy with paclitaxel. Therefore, no increased haematotoxicity due to TP upregulation is expected from the combination of taxanes and capecitabine.

Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE): Biochemical Features and Therapeutic Approaches

Over the last 15 years, important research has expanded our knowledge of the clinical, molecular genetic, and biochemical features of mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). The characterization of mitochondrial involvement in this disorder and the seminal determination of its genetic cause, have opened new possibilities for more detailed and deeper studies on the pathomechanisms in this progressive and fatal disease. It has been established that MNGIE is caused by mutations in the gene encoding thymidine phosphorylase (TP), which lead to absolute or nearly complete loss of its catalytic activity, producing systemic accumulations of its substrates, thymidine (dThd) and deoxyuridine (dUrd). Findings obtained from in vitro and in vivo studies indicate that the biochemical imbalances specifically impair mitochondrial DNA (mtDNA) replication, repair, or both leading to mitochondrial dysfunction. We have proposed that therapy for MNGIE should be aimed at reducing the concentrations of these toxic nucleosides to normal or nearly normal levels. The first treatment, allogeneic stem-cell transplantation (alloSCT) reported in 2006, produced a nearly full biochemical correction of the dThd and dUrd imbalances in blood. Clinical follow-up of this and other patients receiving alloSCT is necessary to determine whether this and other therapies based on a permanent restoration of TP will be effective treatment for MNGIE.

Design and synthesis of novel 5,6-disubstituted uracil derivatives as potent inhibitors of thymidine phosphorylase

We report on a series of novel 5,6-disubstituted uracils with significant inhibitory activity against human and Escherichia coli thymidine phosphorylases. Bis-uracil conjugates were identified as the most potent inhibitors of TPs in this study.

No relationship between thymidine phosphorylase (TP, PD-ECGF) expression and hypoxia in carcinoma of the cervix

The expression of hypoxia-regulated genes promotes an aggressive tumour phenotype and is associated with an adverse cancer treatment outcome. Thymidine phosphorylase (TP) levels increase under hypoxia, but the protein has not been studied in association with hypoxia in human tumours. An investigation was made, therefore, of the relationship of tumour TP with hypoxia, the expression of other hypoxia-associated markers and clinical outcome. This retrospective study was carried out in patients with locally advanced cervical carcinoma who underwent radiotherapy. Protein expression was evaluated with immunohistochemistry. Hypoxia was measured using microelectrodes and the level of pimonidazole binding. There was no relationship of TP expression with tumour pO₂ (r=−0.091, P=0.59, n=87) or pimonidazole binding (r=0.13, P=0.45, n=38). There was no relationship between TP and HIF-1α, but there was a weak borderline significant relationship with HIF-2α expression. There were weak but significant correlations of TP with the expression of VEGF, CA IX and Glut-1. In 119 patients, the presence of TP expression predicted for disease-specific (P=0.032) and metastasis-free (P=0.050) survival. The results suggest that TP is not a surrogate marker of hypoxia, but is linked to the expression of hypoxia-associated genes and has weak prognostic power.

Induction of thymidine phosphorylase expression by AZT contributes to enhancement of 5'-DFUR cytotoxicity

Thymidine phosphorylase (TP) regulates intracellular thymidine metabolism and can enhance the anti-tumor effectiveness of 5'-deoxy-5-fluorouridine (5'-DFUR) by conversion of the pro-drug 5'-DFUR to 5-fluorouracil (5-FU) in tumor tissues. 5'-DFUR is an effective anti-tumor drug in cells expressing high levels of TP. 3'-Azido 3'-deoxythymidine (AZT) is a thymidine analog that has been proven useful in the treatment of acquired immunodefiency syndrome (AIDS). In this study, we found that AZT induces TP expression and enhances the sensitivity of human myeloid leukemia U937 cells to 5'-DFUR. Both the protein level and the activity of TP in U937 cells were elevated for 48h after exposure to AZT (20, 100 or 300muM). AZT enhanced TP promoter activity in a dose-dependent manner. AZT also increased TP mRNA levels in U937 cells as assayed by Real-time reverse-transcription PCR. AZT enhanced the cytotoxic effect of 5'-DFUR on U937 cells. A TP inhibitor, TPI, abrogated the cytotoxic activity of 5'-DFUR, and attenuated the combined cytotoxicity of AZT and 5'-DFUR. These results suggest that AZT enhances the cytotoxic effect of 5'-DFUR on U937 cells by upregulating TP activity in addition to its inhibition of thymidine kinase (TK) activity and reduction of intracellular dTTP pools.

Thymidine phosphorylase mutations cause instability of mitochondrial DNA

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder characterized by ptosis and progressive external ophthalmoplegia, peripheral neuropathy, severe gastrointestinal dysmotility, cachexia and leukoencephalopathy. Muscle biopsies of MNGIE patients have revealed morphologically abnormal mitochondria and defects of respiratory chain enzymes. In addition, patients harbor depletion, multiple deletions, and point mutations of mitochondrial DNA (mtDNA). This disorder is caused by loss-of-function mutations in the gene encoding thymidine phosphorylase (TP) a cytosolic enzyme. In MNGIE patients, TP activity is very low or absent resulting in dramatically elevated levels of plasma thymidine and deoxyuridine. We have hypothesized that the increased levels of thymidine and deoxyuridine cause mitochondrial nucleotide pool imbalances that, in turn, generate mtDNA alterations.

Upregulation of thymidine phosphorylase in chronic glomerulonephritis and its role in tubulointerstitial injury

Chronic tubulointerstitial injury (CTI), commonly a sequel to chronic glomerulonephritis (CGN), is associated with the proliferation of new blood vessels. Angiogenesis is an essential process in chronic inflammation, and is controlled by a number of angiogenic factors including thymidine phosphorylase (TP). Knowledge of TP in renal disease is still rudimentary, and its role in CGN has not been explored. We analyzed the expression of TP by RTPCR, immunohistology and in situ hybridization in 20 human kidneys with CGN. To evaluate the degree of angiogenesis, we counted the microvessel density (MVD). MVD was significantly higher in all categories of CGN, between 19.7 +/- 7.7 and 58.9 +/- 7.5, compared to control value, 12.7 +/- 5.0 (p < 0.05). MVD was increased in areas of abundant mononuclear cell infiltration with minimal interstitial fibrosis, and decreased or absent in areas of marked fibrosis. There was a significant correlation between MVD and interstitial fibrosis (p < 0.0001). TP mRNA was upregulated for all categories of CGN. TP was strongly expressed by mononuclear inflammatory cells and in most atrophic tubules. Each MVD and interstitial volume was significantly correlated with both the number of TP+ mononuclear cells and TP+ tubular cells, respectively (p < 0.0001). We have demonstrated an upregulation of TP and increase in MVD in areas of CTI in a variety of CGN. The up-regulation of TP may contribute to angiogenesis, which may play a critical role in the progression of interstitial fibrosis in CGN.

Increased muscle nucleoside levels associated with a novel frameshift mutation in the thymidine phosphorylase gene in a Spanish patient with MNGIE

We studied a patient with the cardinal features of mitochondrial gastrointestinal encephalomyopathy (MNGIE). Two of his siblings showed a similar clinical picture. Muscle histochemistry displayed ragged red fibres (RRF) which were COX negative and biochemistry revealed combined defects of complexes III and IV of the mitochondrial respiratory chain. Southern-blot analysis showed multiple mtDNA deletions. Molecular analysis of the ECGF1 gene revealed the presence of a homozygous deletion of 20 base pairs in exon 10, c.1460_1479delGACGGCCCCGCGCTCAGCGG, resulting in a frameshift and synthesis of a protein larger than the wild-type. Thymidine and deoxyuridine accumulation was detected in muscle, indicating loss-of-function of thymidine phosphorylase (TP).

Prognostic value of thymidine phosphorylase activity in liver tissue adjacent to hepatocellular carcinoma

BACKGROUND

Measurement of thymidine phosphorylase (TP) activity in normal liver tissue adjacent to hepatocellular carcinoma (HCC) may predict multicentric recurrence a long time after an operation. The authors investigated this activity in 92 patients with HCC who had a single HCC equal to or less than 5 cm.

METHODS

Fresh samples (tumors with adjacent normal tissues) were collected from 92 patients with HCC who underwent curative hepatic resection. The levels of TP activity in nonfixed, fresh, and frozen HCC specimens with adjacent noncancerous liver tissue were biochemically measured by using an enzyme-linked immunosorbent assay method.

RESULTS

Patients who had a high TP level in normal liver tissue had significantly earlier recurrence (median disease-free survival, 819 days; 95% confidence interval [95% CI], 478-1044 days) compared with patients who had a low TP level (median disease-free survival, 1376 days; lower limit of 95% CI, 921 days; P = 0.0171). Multivariate analysis showed that patients who had a low TP level in adjacent liver tissue had a 0.387-fold higher risk of postoperative recurrence compared with patients who had a high TP level (P = 0.0067).

CONCLUSION

TP activity in normal liver tissue adjacent to HCC is related to tumor occurrence and may predict postoperative tumor recurrence.

Bioactivation of capecitabine in human liver: involvement of the cytosolic enzyme on 5'-deoxy-5-fluorocytidine formation

Capecitabine, an anticancer prodrug, is thought to be biotransformed into active 5-fluorouracil (5-FU) by three enzymes. After oral administration, capecitabine is first metabolized to 5'-deoxy-5-fluorocytidine (5'-DFCR) by carboxylesterase (CES), then 5'-DFCR is converted to 5'-deoxy-5-fluorouridine (5'-DFUR) by cytidine deaminase. 5'-DFUR is activated to 5-FU by thymidine phosphorylase. Although high activities of drug metabolizing enzymes are expressed in human liver, the involvement of the liver in capecitabine metabolism is not fully understood. In this study, the metabolism of capecitabine in human liver was investigated in vitro. 5'-DFCR, 5'-DFUR, and 5-FU formation from capecitabine were investigated in human liver S9, microsomes, and cytosol in the presence of the inhibitor of dihydropyrimidine dehydrogenase, 5-chloro-2,4-dihydroxypyridine. 5'-DFCR, 5'-DFUR, and 5-FU were formed from capecitabine in cytosol and in the combination of microsomes and cytosol. Only 5'-DFCR formation was detected in microsomes. The apparent K(m) and V(max) values of 5-FU formation catalyzed by cytosol alone and in combination with microsomes were 8.1 mM and 106.5 pmol/min/mg protein, and 4.0 mM and 64.0 pmol/min/mg protein, respectively. The interindividual variability in 5'-DFCR formation in microsomes and cytosol among 14 human liver samples was 8.3- and 12.3-fold, respectively. Capecitabine seems to be metabolized to 5-FU in human liver. 5'-DFCR formation was exhibited in cytosol with large interindividual variability, although CES is located in microsomes in human liver. In the present study, it has been clarified that the cytosolic enzyme would be important in 5'-DFCR formation, as is CES.

Localization of thymidine phosphorylase in advanced gastric and colorectal cancer

Thymidine phosphorylase (TP) is known to be more concentrated in human cancer tissues than in adjacent normal tissue based on findings using enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry. However, the ultrastructural localization of TP in cancer tissues has not previously been demonstrated. We investigated the localization of TP in gastric cancer and colorectal cancer tissue by ELISA, immunohistochemistry, and immunoelectron microscopy. Between April 1997 and May 2000, we obtained surgically resected specimens from 42, 46, and 36 cases of advanced gastric, colon, and rectal cancer, respectively. ELISA demonstrated that the TP level was higher in cancer tissues than in adjacent normal tissue. Immunohistochemically, cancer cells were positive for the enzyme in some cases. However, in a number of cases immunopositive inflammatory cells were also present in cancerous tissues. At the electron microscope level, TP was diffusely distributed in the cytoplasm of cancer cells and in the mitochondria of the neutrophil in gastric cancer tissue. In rectal cancer tissues, cytoplasmic granules in macrophages in cancer tissues were immunoreactive for the TP. These findings suggest that TP is produced by macrophages and exists in neutrophils and cancer cells.

Comparative Antitumor Activity of 5-Fluorouracil and 5’-Deoxy-5-Fluorouridine in Combination with Interferon-α in Renal Cell Carcinoma Cell Lines

OBJECTIVES

Although interferon-alpha (IFNalpha) and interleukin-2 are used in the treatment of advanced renal cell carcinoma (RCC), the rate of efficacy is about 15% and not satisfactory. Therefore, a more effective treatment is being investigated. In this study, we examined the combined effects of IFNalpha and 5-fluorouracil (5-FU) as well as 5-deoxy-5-fluorouridine (5'-DFUR), a produrg of 5-FU, in vitro.

MATERIALS AND METHODS

Four RCC cell lines (OCUU1, OCUU3, OCUU4, OCUU5) were established at our laboratory from RCC patients. OS-RC-2, RCC10RGB, TUHR14TKB, TUHR4TKB, A498 and Caki-1 were obtained from a commercial source. The sensitivity of the 10 RCC cell lines to 5-FU and 5'-DFUR was evaluated using MTT assay. The IC50 value for the cytostatics was expressed as the concentration at which growth was inhibited by 50% as compared with the control value. Thymidine phosphorylase (TP), the enzyme that converts 5'-DFUR into 5-FU and 5-FU into FdUMP, was estimated by ELISA.

RESULTS

When the 10 RCC cell lines were divided into the low TP expression group and high TP expression group at 2.0 U/ml protein, TP expression was not enhanced by IFNalpha in all 4 cell lines in the low TP expression group. Antitumor effects were not enhanced by IFNalpha in 3 out of 4 cell lines for 5-FU and in all 4 cell lines for 5'-DFUR. On the other hand, in the high TP expression group, TP expression was enhanced by IFNalpha in 5 out of 6 cell lines, and antitumor effects were enhanced by IFNalpha in 5 out of 6 cell lines for 5-FU and in all 6 cell lines for 5'-DFUR. In addition, there was a significant correlation between TP expression and sensitivity to 5-FU and 5'-DFUR in all RCC cell lines.

CONCLUSIONS

These results suggested that TP may be useful as a predictive factor in combination therapy with IFNalpha and 5-FU or 5'-DFUR, which may be a promising treatment for advanced RCC.

Pharmacokinetic modeling of species-dependent enhanced bioavailability of trifluorothymidine by thymidine phosphorylase inhibitor

TAS-102, a new oral drug, is composed of an antitumor drug, alpha,alpha,alpha-trifluorothymidine (FTD), and its metabolic inhibitor, 5-chloro-6-(2-iminopyrrolidine-1-yl)methyl-2,4(1H,3H)-pyrimidinedione hydrochloride (TPI). It has been reported that the oral administration of TAS-102 increases the AUC of FTD in rodents and monkeys in different manners. In this study, a pharmacokinetic model was developed, in an attempt to evaluate the bioavailability of FTD in these animals after the co-administration of TPI. Since TPI inhibits FTD metabolism competitively, a time-dependent as well as concentration-dependent model for the hepatic intrinsic clearance of FTD was developed including the time courses of both FTD and TPI. Based on this modeling, we were able to quantitatively explain the TPI dose-dependent enhancement of AUC of FTD in monkeys, while little increase was observed in rats. These results are consistent to observations that thymidine phosphorylase (TPase) is predominantly expressed in monkeys; while uridine phosphorylase (UPase) is superior to TPase in rats. Since TPase is also predominantly expressed in humans, the pharmacokinetic model developed in this study can be used to explain the bioavailability of TAS-102 in humans.

The role of thymidine phosphorylase, an angiogenic enzyme, in tumor progression

Thymidine phosphorylase (TP), an enzyme involved in pyrimidine metabolism, is identical with an angiogenic factor, platelet-derived endothelial cell growth factor (PD-ECGF). TP is overexpressed in various tumors and plays an important role in angiogenesis, tumor growth, invasion and metastasis. The enzymatic activity of TP is required for the angiogenic effect of TP. A novel, specific TP inhibitor, TPI, inhibits angiogenesis induced by overexpression of TP in KB/TP cells (human KB epidermoid carcinoma cells transfected with TP cDNA), as well as the growth and metastasis of KB/TP cells in vivo. 2-deoxy-D-ribose, the degradation product of thymidine generated by TP activity, has both angiogenic and chemotactic activity. Both 2-deoxy-D-ribose and TP inhibit a hypoxia-induced apoptotic pathway. These findings suggest that 2-deoxy-D-ribose is a downstream mediator of TP function. 2-deoxy-L-ribose, a stereoisomer of 2-deoxy-D-ribose, inhibits the promotion of angiogenesis, tumor growth and metastasis by TP. Although the mechanism of the action of 2-deoxy-D-ribose is still unknown, 2-deoxy-L-ribose may inhibit the physiological activities of 2-deoxy-D-ribose, and consequently those of TP. Inhibition of TP activity and function appears to be a promising approach for the chemotherapy of various tumors.

Enzyme-catalyzed activation of anticancer prodrugs

The rationale fo the development of prodrugs relies upon delivery of higher concentrations of a drug to target cells compared to administration of the drug itself. In the last decades, numerous prodrugs that are enzymatically activated into anti-cancer agents have been developed. This review describes the most important enzymes involved in prodrug activation notably with respect to tissue distribution, up-regulation in tumor cells and turnover rates. The following endogenous enzymes are discussed: aldehyde oxidase, amino acid oxidase, cytochrome P450 reductase, DT-diaphorase, cytochrome P450, tyrosinase, thymidylate synthase, thymidine phosphorylase, glutathione S-transferase, deoxycytidine kinase, carboxylesterase, alkaline phosphatase, beta-glucuronidase and cysteine conjugate beta-lyase. In relation to each of these enzymes, several prodrugs are discussed regarding organ- or tumor-selective activation of clinically relevant prodrugs of 5-fluorouracil, axazaphosphorines (cyclophosphamide, ifosfamide, and trofosfamide), paclitaxel, etoposide, anthracyclines (doxorubicin, daunorubicin, epirubicin), mercaptopurine, thioguanine, cisplatin, melphalan, and other important prodrugs such as menadione, mitomycin C, tirapazamine, 5-(aziridin-1-yl)-2,4-dinitrobenzamide, ganciclovir, irinotecan, dacarbazine, and amifostine. In addition to endogenous enzymes, a number of nonendogenous enzymes, used in antibody-, gene-, and virus-directed enzyme prodrug therapies, are described. It is concluded that the development of prodrugs has been relatively successful; however, all prodrugs lack a complete selectivity. Therefore, more work is needed to explore the differences between tumor and nontumor cells and to develop optimal substrates in terms of substrate affinity and enzyme turnover rates fo prodrug-activating enzymes resulting in more rapid and selective cleavage of the prodrug inside the tumor cells.

The activity of thymidine phosphorylase as a new ovarian tumor marker

OBJECTIVE

The aim of this study was to evaluate the thymidine phosphorylase (TP) activity of tumor cells and serum as a marker in patients with ovarian cancer.

METHODS

The activity of TP was measured by the spectrophotometric method in the cytosol of ovarian tumor tissues from 47 patients after surgery, and in the presurgery serum from the same patients. Ten women with normal ovaries, treated surgically due to nononcological reasons served as a control. Microvessel density (MD) was evaluated in tumor using immunohistochemical methods. A relationship between TP activity and MD and clinicopathologic features was investigated.

RESULTS

A significantly higher TP activity was stated both in malignant tumor and serum specimens from ovarian cancer patients when compared to the control. A positive correlation between the enzyme activity in the serum and neoplasmatic tissue was found. Neoangiogenesis is higher in ovarian cancer when compared to the group of borderline malignancy tumors but a reverse correlation between MD and TP activity in malignant tumors was observed. TP activity is significantly higher in more advanced neoplasmatic disease (FIGO III and IV) although no correlation between TP activity and grading or histopathological type of ovarian tumor was observed.

CONCLUSION

Thymidine phosphorylase activity might be useful in diagnostic characterization of ovarian cancer.

Platelet-derived endothelial cell growth factor expression is an independent prognostic factor in colorectal cancer patients after curative surgery

AIMS

Platelet-derived endothelial cell growth factor (PD-ECGF) is an angiogenic factor that undergoes increased expression in colorectal carcinomas, but its prognostic value is a topic of debate. The aim of this study is to clarify the prognostic value of PD-ECGF expression in colorectal carcinomas.

METHODS

PD-ECGF expression was measured by enzyme-linked immunosorbent assay in frozen materials from 134 colorectal cancer patients who had received curative resections. Patients were divided into high expression and low expression groups based upon selected cut-off value. Correlations among PD-ECGF expression, clinicopathologic features, and disease-free interval were studied by univariate and multivariate analysis. To evaluate the origin of PD-ECGF, serial sections of the 134 tumours were stained for PD-ECGF and CD68.

RESULTS

PD-ECGF expression in the normal mucosa was 34.4+/-15.5 (Units/mg protein) and the cut-off value was 65.4 (mean+2SD). There were no significant correlations between clinicopathological features and PD-ECGF expression. The disease-free interval for the high PD-ECGF expression group was significantly longer than that of the low expression group (P=0.05). A multivariate Cox's regression analysis revealed that high PD-ECGF expression is an independent factor for better outcome. In immunohistochemical study, almost all tumour cells were negative for PD-ECGF, but stromal macrophages were predominantly positive for PD-ECGF.

CONCLUSIONS

The PD-ECGF expression originated from stromal macrophages was a predictor for favorable outcome after curative resections for colorectal cancer.

Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE): A Disease of Two Genomes

BACKGROUND

Mitochondrial encephalomyopathies are clinically and genetically heterogeneous because mitochondria are the products of 2 genomes: mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). Among the mendelian-inherited mitochondrial diseases are defects of intergenomic communication, disorders due to nDNA mutations that cause depletion and multiple deletions of mtDNA.

REVIEW SUMMARY

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder of intergenomic communication and is defined clinically by 1) severe gastrointestinal dysmotility; 2) cachexia; 3) ptosis, ophthalmoparesis, or both; 4) peripheral neuropathy; and 5) leukoencephalopathy. Skeletal muscle biopsies of patients have revealed abnormalities of mtDNA and mitochondrial respiratory chain enzymes. The disease is caused by mutations in the thymidine phosphorylase (TP) gene. TP protein catalyzes phosphorolysis of thymidine to thymine and deoxyribose 1-phosphate. In MNGIE patients, TP enzyme activity is reduced drastically, and plasma thymidine and deoxyuridine are elevated dramatically. We have hypothesized that alterations of nucleoside metabolism cause an imbalanced mitochondrial nucleotide pool that leads to depletion and deletions of mtDNA.

CONCLUSIONS

MNGIE is a recognizable clinical syndrome caused by mutations in TP. The diagnosis can be confirmed by measuring TP activity in buffy coat or plasma levels of thymidine and deoxyuridine. Reduction of circulating thymidine and deoxyuridine in MNGIE patients may be therapeutic.

Role of thymidine phosphorylase on invasiveness and metastasis in lung adenocarcinoma

Thymidine phosphorylase (TP) is expressed at higher levels in a variety of human cancers than in adjacent normal tissue. It is reported that the higher expression is associated with an increase of intratumoral microvessel density and a poor prognosis. We investigated the role of TP in human non small cell lung cancers (NSCLCs). The concentrations of TP in the tumors and the adjacent normal tissue from surgically resected specimens of 54 cases of NSCLCs were measured by using an enzyme-linked immunosorbent assay. Tumor specimens were also examined immunohistochemically. TP concentrations in the tumors were 169 +/- 18 units/mg protein (mean +/- SD), whereas those in normal tissue were 43 +/- 4 units/mg protein (mean +/- SD), consistent with TP staining patterns. There was no correlation between TP expression and microvessel density. Among clinicopathologic factors examined, the concentrations of TP but not TP immunoreactivity correlated with tumor differentiation in lung adenocarcinoma. Although a specific TP inhibitor (TPI) and overexpression of TP did not affect the growth of A549 lung adenocarcinoma cells, Matrigel invasion assay showed that A549 transfected with TP had higher invasive potential than mock transfectant, and such enhanced invasive activity was markedly diminished by treatment with TPI. Furthermore, administration of TPI suppressed lung metastasis of TP-overexpressing A549 cells in nude mice. These results demonstrate that TP may play an important role in tumor differentiation, invasiveness and metastasis in lung adenocarcinoma, and suggest that TP could be a novel target for treatment of TP-overexpressing lung adenocarcinoma.

Alteration of nucleotide metabolism: a new mechanism for mitochondrial disorders

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease caused by loss-of-function mutations in the gene encoding thymidine phosphorylase (TP). TP deficiency alters the metabolism of the nucleosides thymidine and deoxyuridine, which, in turn, produces abnormalities of mitochondrial DNA (mtDNA) including depletion, deletions, and point mutations. MNGIE is the best characterized of the expanding number of mitochondrial disorders caused by alterations in the metabolism of nucleosides/nucleotides. Because mitochondria contain their own machinery for nucleoside and nucleotide metabolism and have physically separate nucleotide pools, it is not surprising that disorders of these pathways cause human diseases. Other diseases in this group include mtDNA depletion syndromes caused by mutations on the nuclear genes encoding the mitochondrial thymidine kinase and deoxyguanosine kinase; autosomal dominant progressive external ophthalmoplegia with multiple deletions of mtDNA due to mutations in the genes encoding the muscle-isoform of mitochondrial ADP/ATP translocator; and mitochondrial DNA depletion due to toxicities of nucleoside analogues. Mutations in the deoxynucleotide carrier, a transporter of deoxynucleoside diphosphates, have been identified as a cause of congenital microcephaly. However, alterations of mtDNA have not yet been established in this disorder. Future studies are likely to reveal additional diseases and provide further insight into this new subject.

Significance of thymidine phosphorylase in HCC with chronic liver disease for long-term postoperative recurrence

BACKGROUND AND OBJECTIVES

Little is known about the significance of thymidine phosphorylase (TP) levels in HCC. The authors investigated the TP activity of HCC and adjacent normal liver tissue in 70 HCC patients, and the prognostic significance of the TP levels.

METHODS

We obtained fresh samples (tumors with adjacent normal tissues) from 70 patients with HCC who have undergone curative hepatic resection. The levels of TP activity in unfixed, fresh, frozen HCC tissue, together with adjacent normal liver tissue specimens, were determined by the enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

The mean TP activity in HCC was approximately 1.5-fold higher than that in adjacent liver tissues (P = 0.0013). Disease-free survival rates for patients with low and high TP levels in HCC were not significantly different. Although disease-free survival rates for low and high TP levels in adjacent normal liver tissue were also not significantly different, disease-free survival for patients with low and high TP levels in adjacent normal liver tissue, excluding cases of postoperative recurrence within 700 days of hepatectomy, showed a significant difference (P = 0.0494). The group with high TP activity in adjacent liver tissue showed more frequent postoperative recurrence in the long-term than that with low TP activity.

CONCLUSIONS

Measurement of TP activity of adjacent normal liver tissue to HCC may allow us to predict metachronous long-term postoperative recurrence.

Effects of various steroids on platelet-derived endothelial cell growth factor (PD-ECGF) and its mRNA expression in uterine endometrial cancer cells

Progestins diminish the estrogen-induced angiogenic potential related to basic fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) in uterine endometrial cancer cells. This led us to study the effect of various steroids on the expression of platelet-derived endothelial cell growth factor (PD-ECGF) as the other pertinent angiogenic factor in well-differentiated uterine endometrial cancer cell line Ishikawa. In Ishikawa cells, estradiol induced the expression of PD-ECGF and its mRNA. The estrogen-induced expression was increased approximately two-fold by progesterone and by its metabolite, 17alpha-hydroxyprogesterone, but not by medroxyprogesterone acetate (MPA). Therefore, progesterone and 17alpha-hydroxyprogesterone as endogenous steroids might induce PD-ECGF-related angiogenic potential in uterine endometrial cancer cells, but not MPA as a synthetic steroid. In conclusion, the failure of PD-ECGF induction by MPA might be the great merit of anti-angiogenic treatment with MPA for uterine endometrial cancers.

Mitochondrial neurogastrointestinal encephalomyopathy and thymidine metabolism: results and hypotheses

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease with mitochondrial DNA (mtDNA) alterations and is caused by mutations in the nuclear gene encoding thymidine phosphorylase (TP). The cardinal clinical manifestations are ptosis, ophthalmoparesis, gastrointestinal dysmotility, cachexia, peripheral neuropathy, and leukoencephalopathy. Skeletal muscle shows mitochondrial abnormalities, including ragged-red fibers and cytochrome c oxidase deficiency, together with mtDNA depletion, multiple deletions or both. In MNGIE patients, TP mutations cause a loss-of-function of the cytosolic enzyme, TP. As a direct consequence of the TP defect, thymidine metabolism is altered. High blood levels of this nucleoside are likely to lead to mtDNA defects even in cells that do not express TP, such as skeletal muscle. We hypothesize that high concentrations of thymidine affect dNTP (deoxyribonucleoside triphosphate) metabolism in mitochondria more than in cytosol or nuclei, because mitochondrial dNTPs depend mainly on the thymidine salvage pathway, whereas nuclear dNTPs depend mostly on de novo pathway. The imbalance in the mitochondrial dNTP homeostasis affects mtDNA replication, leading to mitochondrial dysfunction.