Thymidine Phosphorylase Activity Research Articles

Tezacitabine enhances the DNA-directed effects of fluoropyrimidines in human colon cancer cells and tumor xenografts

Tezacitabine is a nucleoside analogue characterized by a dual mechanism of action. Following intracellular phosphorylation, the tezacitabine diphosphate irreversibly inhibits ribonucleotide reductase, while the tezacitabine triphosphate can be incorporated into DNA during replication or repair, resulting in DNA chain termination. In the present study we have investigated the effect of the combination of tezacitabine and 5-fluorouracil (5-FU) or 5-fluoro-2′-deoxyuridine (FUdR) on HCT 116 human colon carcinoma cells and xenografts. We used response surface analysis (RSA) and clonogenic assay to evaluate combination effects of tezacitabine and 5-FU. Tezacitabine is antagonistic when combined with 5-FU in the RSA assay and does not effect the clonogenicity of HCT 116 cells when compared with cells treated with 5-FU alone. However, when combined sequentially with FUdR, tezacitabine leads to potentiation of cell killing in the clonogenic assay, additivity in the RSA assay, and increased apoptosis when compared to FUdR alone, suggesting that cytotoxicity of fluoropyrimidines such as FUdR that have more DNA-directed effects can be potentiated by tezacitabine. We also report that oral administration of the fluoropyrimidine capecitabine, an oral prodrug of 5-FU, in combination with tezacitabine shows statistically significant additivity in the HCT 116 xenograft model. This interaction may be explained by the finding that tezacitabine elevates activity of thymidine phosphorylase (TP), the enzyme required for activation of the capecitabine prodrug in tumors. Our results provide evidence that tezacitabine enhances the DNA-directed effects of fluoropyrimidines in human colon cancer cells and may modulate the antitumor activity of fluoropyrimidines.

Allogeneic stem cell transplantation corrects biochemical derangements in MNGIE

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a multisystemic autosomal recessive disease due to primary thymidine phosphorylase (TP) deficiency. To restore TP activity, we performed reduced intensity allogeneic stem cell transplantations (alloSCTs) in two patients. In the first, alloSCT failed to engraft, but the second achieved mixed donor chimerism, which partially restored buffy coat TP activity and lowered plasma nucleosides. Thus, alloSCT can correct biochemical abnormalities in the blood of patients with MNGIE, but clinical efficacy remains unproven.

Synergistic cytotoxic interaction in hormone-refractory prostate cancer with the triple combination docetaxel–erlotinib and 5-fluoro-5′-deoxyuridine

The current reference treatment of hormone-refractory prostate cancer consists mainly of chemotherapy with docetaxel. To improve the management of advanced prostate cancer, one should examine the benefits of adding other agents to docetaxel. We examined the growth inhibitory effects of a triple combination, including the anti-epidermal growth factor receptor drug erlotinib, docetaxel and 5-fluoro-5'-deoxyuridine (the main intermediary metabolite of capecitabine), on the human prostate cancer cell lines PC3 and DU145, which are both devoid of androgen receptors. Marked synergistic cytotoxic effects were observed with the application of the double combination of erlotinib-5-fluoro-5'-deoxyuridine for both cell lines and to a lesser magnitude with the triple combination. For PC3 cells, all conditions resulted in synergistic interactions. The combination between erlotinib and docetaxel resulted in an approximately 50% reduction in thymidylate synthase activity (the molecular target of 5-fluorodeoxyuridine monophosphate, the active capecitabine anabolite) with an higher impact observed with DU145 cells than with PC3 cells. Neither erlotinib nor docetaxel alone displayed marked effects on thymidine phosphorylase activity (the enzyme that governs at the cellular level the final and crucial step in the activation cascade of capecitabine), in contrast to their combination that resulted in a strong increase in thymidine phosphorylase activity in PC3 cells. These data may serve as a rational basis for setting up clinical trials in advanced prostate cancer combining epidermal growth factor receptor-targeting agents like erlotinib together with docetaxel and capecitabine.

2‐Deoxy‐L‐ribose inhibits the invasion of thymidine phosphorylase‐overexpressing tumors by suppressing matrix metalloproteinase‐9

Thymidine phosphorylase (TP), an enzyme involved in pyrimidine metabolism, is identical with an angiogenic factor, platelet-derived endothelial cell growth factor. 2-Deoxy-D-ribose (D-dRib), the degradation product of thymidine generated by TP activity, has been suggested to be a downstream mediator of TP function. 2-Deoxy-L-ribose (L-dRib), a stereoisomer of D-dRib, inhibited the promotion of angiogenesis, tumor growth and metastasis by TP. In our study, we have shown that nude mice inoculated with TP-overexpressing KB/TP cells had shorter survival times than those injected with control KB/CV cells. KB/TP tumors were also more highly invasive than KB/CV tumors in mice. The expression levels of matrix metalloproteinase (MMP)-9 in KB/TP tumors were significantly higher than those in KB/CV tumors. L-dRib and a TP inhibitior, TPI, extended the survival period of KB/TP tumor-bearing mice. L-dRib also reduced MMP-9 mRNA levels in KB/TP tumors. Furthermore, L-dRib suppressed the mRNA level of MMP-9 in cultured KB/TP cells, and the invasive activity of the cells. L-dRib may be useful for the suppression of invasion of TP-expressing tumor cells.

Capecitabine therapy in advanced gall bladder cancer: A phase II study

14153 Background: Thymidine phosphorylase (TP) activity is found at higher levels in gall bladder cancer (GBC) tissues than in adjacent healthy tissues. GBC is relatively sensitive to 5-FU. TP activated capecitabine (CAP) mimics the continuous infusion of 5-FU. In view of drug potentiality this present study was initiated. Our aim was to evaluate the therapeutic efficacy and safety of CAP in previously untreated GBC patients (Pts). Methods: It was an open-labelled, single-centred, non-randomised and prospective study. Outcome measures were response rate and type of response for efficacy measurement and safety was measured by adverse events & laboratory blood values (LBV). All LBV were within reference range at baseline. The patients had no prior chemo/ radio therapy or a family history of malignancy; adenocarcinoma (stage III–IV); age 40–70 yrs; male/female: 16/ 30; KPS ≥ 70%. 46 pts were treated with 306 cycles (min 3–max 12) of CAP at a dose of 2500 mg/day in two divided doses from day 1–14 followed by 1-week rest. Results: Median age was 50 yrs. Hand foot syndrome occurred in 17.39% pts, diarrhoea (grade 3 & 4) 21.75% and both 15.21%, all toxicities were manageable. Mean LBV before and after CAP therapy were hemoglobin: 11.38–0.35 g/dl (95% CI, 10.66–2.10); total count of WBC: 9,260–580/mm3 (95% CI, 8,680–9,840); platelet count: 251,000–2,000/mm3 (95% CI, 227,000–275,000) and serum bilirubin: 1.17–0.33 mg/dl (95% CI, 0.5–1.84). The LBV between baseline and after CAP therapy were not statistically significant. Partial response was found in 12 pts (26.08%), stable disease in 26 pts (56.21%), and progressive disease in 8 pts (17.39%). Mean KPS value after therapy was 76% (95% CI, 69–84). Conclusion: This clinical experience indicates that CAP is a convenient choice in phase II chemo naïve GBC pts not adversely affecting haematological values. No significant financial relationships to disclose.

Early results of a phase I clinical trial of capecitabine in combination with CPT-11 for metastatic breast cancer (MBC) pre-treated with anthracycline and taxane

10750 Background: Capecitabine (C) is administrated with other drugs to improve response rate of single agent and to extend time to progression for MBC expecting up-regulation of thymidine phosphorylase activity. Conversely, administration of CPT-11 (TOP) against MBC is less common while superiority of combination therapy C and TOP is established in metastatic setting of colorectal cancer. Therefore a phase I clinical trial was conducted to determine the recommended dose (RD) of TOP administrated with fixed dose of C (1,657 mg/m2/day) against MBC pre-treated with antracycline and taxane. Methods: Five dose level of CPT-11 (80, 90, 100,110 and 120 mg/m2) on Day 1 and 15 and C (1,657 mg/m2/day) on Day 1–21 were given every 28 days. A standard “3+3” design is used and dose limiting toxicity is defined in cycle 1. Results: To date, five patients were enrolled from October 2005 to January 2006 and 8 cycles were administrated without grade 3–4 toxicities as followed: 3 pts in Level I (TOP: 80 mg/m2), 2 pts in Level II (TOP: 90mg/m2). 5 pts have archived a response: PR in 1, SD in 2. Conclusions: Combination therapy C and TOP against MBC pre-treated antracycline and taxane is well-tolerated. Enrollment will continue until the RD is identified for further phase II clinical trial. No significant financial relationships to disclose.

Determination of Thymidine Phosphorylase Activity in Human Blood Cells and Fibroblasts by a Nonradiochemical Assay Using Reversed-Phase High-Performance Liquid Chromatography

In this study, we demonstrated that the highest activity of thymidine phosphorylase (TP) was found in peripheral blood mononuclear (PBM) cells followed by that of thrombocytes and granulocytes whereas no activity of TP could be detected in erythrocytes. The activity of TP in leukocytes proved to be intermediate compared to the TP activity observed in PBM cells and granulocytes. The activity of TP also was readily detectable in human fibroblasts.

An evaluation of thymidine phosphorylase as a means of preventing thymidine rescue from the thymidylate synthase inhibitor raltitrexed

The antitumour effect of thymidylate synthase inhibitors such as raltitrexed (RTX) may be reversed by salvage of thymidine (Thd). Since thymidine phosphorylase (TP) depletes Thd, the potential for tumour-selective depletion of Thd using antibody-mediated delivery of TP to tumours was investigated. In vitro studies demonstrated that 25 x 10(-3) units/ml TP depleted extracellular Thd (3 microM) and restored sensitivity to the growth inhibitory effects of RTX in Lovo and HT29 cell lines. Thymidine concentrations in xenograft tumours were inversely proportional to the activity of TP in the tumour, and the presence of a subcutaneous Lovo xenograft reduced plasma Thd concentrations from 0.92 +/- 0.07 to 0.37 +/- 0.04 microM. Intravenous administration of native TP enzyme depleted plasma Thd to 5 nM, but following rapid elimination of TP, plasma Thd returned to pretreatment values. There was no effect on tumour TP or Thd. Conjugation of TP to the A5B7 F(ab)2 antibody fragment, which targets carcinoembryonic antigen (CEA) expressed on colorectal cell-lines such as Lovo, did result in selective accumulation of TP in the tumour. However, there was no tumour-selective depletion of Thd and there did not appear to be any potential benefit of combining antibody-targeted TP with RTX.

Relationship between p53 status and 5-fluorouracil sensitivity in 3 cell lines

Mouse lymphoma L5178Ytk +/− (MOLY) cells and human lymphoblastoid TK6 and WTK-1 cells are widely used to detect mutagens in vitro. MOLY and WTK-1 cells have a p53 mutation, while TK6 cells, which were derived from the same parental line as WTK-1 cells, do not. In this study, we tested the clastogen 5-fluorouracil (5-FU) in the Tk assay and the in vitro micronucleus (MN) assay in MOLY, TK6, and WTK-1 cells to clarify whether differential responses were related to p53 gene status. We also determined the effect of 5-FU on the frequency of apoptotic cells and on cell cycle distribution in each cell line. Furthermore, we measured the activity of the 5-FU metabolizing enzymes (thymidylate synthetase (TS), dihydrouracil dehydrogenase (DPD), orotate phosphoribosyl transferase (OPRT), and thymidine phosphorylase (TP)) in each cell line. We treated MOLY cells with 1.0–8.0 μg/mL 5-FU for 3 h and TK6 and WTK-1 cells with 1.56–25 and 3.13–50 μg/mL, respectively, for 4 h. In MOLY cells, the mutation frequency (MF) and MN frequency increased. In WTK-1 cells, the MN frequency but not the MF increased. In TK6 cells, neither the MF nor the MN frequency increased. Furthermore, the IC 50 of 5-FU was lower in MOLY cells than in the human cells. The response to 5-FU treatment differed in other ways as well. At the same level of cytotoxicity, the frequency of apoptotic cell was highest in TK6 cells. The cell cycle was delayed just after treatment in MOLY cells while the delay appeared 24 h later in TK6 and WTK-1 cells. Nothing in our analysis, however, revealed marked differences between the cell lines that could account for the severe cytotoxic and mutagenic responses that 5-FU elicited only in MOLY cells. 5-FU is phosphorylated by OPRT and TP and detoxified by DPD. MOLY cells have higher OPRT activity and markedly lower DPD and TP activity than TK6 and WTK-1 cells. The content of TS, however, the target enzyme of 5-FU, was similar in all cell lines, suggesting that 5-FU was more readily phosphorylated and less readily detoxified in MOLY cells than in TK6 and WTK-1 cells. MOLY cells were more sensitive to 5-FU than WTK-1 cells even though both have a mutated p53 gene, suggesting that the different responses to 5-FU were due to differences in 5-FU metabolism rather than the p53 status.

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.

Mitochondrial Neurogastrointestinal Encephalomyopathy: Evidence of Mitochondrial DNA Depletion in the Small Intestine

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease clinically defined by gastrointestinal dysmotility, cachexia, ptosis, ophthalmoparesis, peripheral neuropathy, white-matter changes in brain magnetic resonance imaging, and mitochondrial abnormalities. Loss-of-function mutations in thymidine phosphorylase gene induce pathologic accumulations of thymidine and deoxyuridine that in turn cause mitochondrial DNA (mtDNA) defects (depletion, multiple deletions, and point mutations). Our study is aimed to define the molecular basis of gastrointestinal dysmotility in a case of MNGIE. By using laser capture microdissection techniques, we correlated histologic features with mtDNA abnormalities in different tissue components of the gastrointestinal wall in a MNGIE patient and ten controls. The patient's small intestine showed marked atrophy and mitochondrial proliferation of the external layer of muscularis propria. Genetic analysis revealed selective depletion of mtDNA in the small intestine compared with esophagus, stomach, and colon, and microdissection analysis revealed that mtDNA depletion was confined to the external layer of muscularis propria. Multiple deletions were detected in the upper esophagus and skeletal muscle. Site-specific somatic point mutations were detected only at low abundance both in the muscle and nervous tissue of the gastrointestinal tract. Analysis of the gastrointestinal tract from 10 controls revealed a non-homogeneous distribution of mtDNA content; the small intestine had the lowest levels of mtDNA. Atrophy, mitochondrial proliferation, and mtDNA depletion in the external layer of muscularis propria of small intestine indicate that visceral myopathy is responsible for gastrointestinal dysmotility in this MNGIE patient.

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 48 h after exposure to AZT (20, 100 or 300 μM). 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.

Influence of α‐tumor necrosis factor and β‐interleukin‐1 on production of angiogenetic factors and thymidine phosphorylase activity in immortalized human decidual fibroblasts in vitro

The aim of the present study was to investigate regulatory mechanisms of angiogenesis in the decidua using immortalized human decidual fibroblasts. A sample of decidual fibroblasts was taken from a woman in early pregnancy. A cell line, DE-1, was established by infecting the decidual fibroblasts with the simian virus 40 large T antigen. Using this cell line, the ability to produce vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), beta-transforming growth factor (TGF-beta), and thymidine phosphorylase (TP) activity was investigated using immunohistochemistry, and the influences of beta-interleukin-1 (IL-1beta) and alpha-tumor necrosis factor (TNF-alpha) on these angiogenetic factors was investigated using enzyme-linked immunosorbent assays. Furthermore, the effects of TNF-alpha on proliferative capacity and apoptosis induction in DE-1 were studied. It was demonstrated that DE-1 produced all of these angiogenetic factors. The production of VEGF, bFGF and TGF-beta respectively was enhanced by both IL-1beta and TNF-alpha. TP activity was increased by TNF-alpha, but no increase was observed as a result of IL-1beta. It was shown that TNF-alpha suppressed the proliferation of DE-1 cells and significantly increased the percentage of apoptotic cells. It is suggested that IL-1beta and TNF-alpha stimulate decidual fibroblasts to up-regulate angiogenesis in the human decidua.

Thymidine Phosphorylase Gene Mutation is not a Primary Cause of Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE)

The authors identified a patient with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), who completely fulfilled the clinical criteria with low thymidine phosphorylase (TP) activity. However, the same homozygotic S471L TP gene mutation was also found in her unaffected mother, but with normal TP activity. To elucidate the pathogenesis of MNGIE, we performed the analysis below. We analyzed the TP gene mutation in the proband and 145 unrelated individuals by direct sequence and restriction fragment length polymorphism (RFLP). TP activity was determined by the spectrophotometric method for each TP S471L genotype. Among 145 normal persons, the S471L homozygote mutants were identified in 2.76% and their enzyme activity was normal. TP gene mutation is not a primary cause of MNGIE, but with a mitochondrial deletion mutation, a single nucleotide polymorphism (SNP) of the TP gene may be crucial in the pathogenesis of MNGIE.

The role of thymidine phosphorylase and uridine phosphorylase in (fluoro)pyrimidine metabolism in peripheral blood mononuclear cells

Thymidine phosphorylase (TP) and uridine phosphorylase (UP) catalyze the (in)activation of several fluoropyrimidines, depending on their catalytic activity and substrate specificity. Blood cells are the first compartment exposed to most anticancer agents. The role of white blood cells in causing toxic side effects and catalyzing drug metabolism is generally underestimated. Therefore we determined the contribution of the white blood cell compartment to drug metabolism, and we investigated the activity and substrate specificity of TP and UP for the (fluoro)pyrimidines thymidine (dThd), uridine (Urd), 5′-deoxy-5-fluorouridine (5′dFUrd) and 5-fluorouracil (5FU) in peripheral blood mononuclear cells (PBMC) and undifferentiated monocytes and differentiated monocytes: macrophages and dendritic cells. PBMC had an IC 50 of 742 μM exposed to 5′dFUrd, increasing to >2000 μM when both TP and UP activities were inhibited. Total phosphorolytic activity was higher with dThd than with Urd, 5′dFUrd or 5FU. Using a specific TP inhibitor (TPI) and UP inhibitor (BAU) we concluded that dThd and Urd were preferentially converted by TP and UP, respectively, while 5′dFUrd and 5FU were mainly converted by TP (about 80%) into 5FU and FUrd, respectively. 5FU was effectively incorporated into RNA. dThd conversion into thymine was highest in dendritic cells (52.6 nmol thymine/h/10 6 cells), followed by macrophages (two-fold) and undifferentiated monocytes (eight-fold). TPI prevented dThd conversion almost completely. In conclusion, PBMC were relatively insensitive to 5′dFUrd, and the natural substrates dThd and Urd were preferentially converted by TP and UP, respectively. TP and UP were both responsible for converting 5′dFUrd/5FU into 5FU/FUrd, respectively.

Late‐onset MNGIE due to partial loss of thymidine phosphorylase activity

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the gene encoding thymidine phosphorylase (TP). All MNGIE patients have had severe loss of TP function and prominent plasma accumulations of the TP substrates thymidine (dThd) and deoxyuridine (dUrd). Here, we report for the first time to our knowledge three MNGIE patients with later onset, milder phenotype, and less severe TP dysfunction, compared with typical MNGIE patients. This report demonstrates a direct relationship between the biochemical defects and clinical phenotypes in MNGIE and supports the notion that reduction of dThd and dUrd accumulation or TP replacement could be useful therapy for MNGIE.

The activities of thymidine phosphorylase and dihydropyrimidine dehydrogenase in colorectal cancer depend on where the sample is taken

The significance of tumor tissue thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) levels, as well as the TP/DPD ratio have recently been reported as prognostic factors and for custom-made chemotherapy. However, there have been no distinct studies on actual tumor sampling methods. For 16 patients who had undergone resection of advanced colorectal cancer, we: i) measured TP and DPD levels in different portions of the tumor using enzyme-linked immunosorbent assay (ELISA); ii) categorized the tumor into an edge, center, and base area, and histo-pathologically calculated the ratio of cancer cell/cancer cell + stromal cell; and iii) examined the correlation between cancer and stromal cell TP expression and TP value. Variation within the same tumor was seen in each activity level and TP/DPD ratio. The ratio of cancer cell in the edge area was high, with the ratio of stromal cell in the center and base areas increasing in that order. A correlation was seen between TP expression and TP levels, and TP expression was evident in the stromal cells. It is therefore recommended to sample the edge area for tumor TP levels.

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

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

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.

Prognostic significance of the thymidine phosphorylase/dihydropyrimidine dehydrogenase ratio in invasive cervical cancer

Objective: In this study, we measured both thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD) levels, and then determined the TP/DPD ratios, in a number of invasive cervical cancers. Our aim was to investigate the association between these values and the clinicopathological features of invasive cervical cancer, including patient prognosis. Study design: Using enzyme-linked immunosorbent assays, the TP and DPD activities were quantitatively measured in 51 patients with cervical cancer who had also undergone a radical hysterectomy. Results: The TP, DPD and TP/DPD values in squamous cell carcinoma (SCC) were found to be significantly higher than the levels in non-SCC. Furthermore, in a SCC subgroup, the TP/DPD levels were significantly higher in cases where parametrial invasion was evident, and in a non-SCC subgroup, these levels were also significantly higher in cases with deep stromal invasion, lymph-vascular space invasion, large tumor size and parametrial invasion. The disease-free survival rate is shown to be significantly higher in patients with low TP/DPD levels indicating that this ratio may be associated with both the progression and recurrence of invasive cervical cancer. Conclusion: TP/DPD ratios may be associated with both the progression and recurrence of invasive cervical cancer.