Pyrimidine Nucleoside Phosphorylase Research Articles

Powerful methods to establish chromosomal markers in Lactococcus lactis: an analysis of pyrimidine salvage pathway mutants obtained by positive selections

Using different 5-fluoropyrimidine analogues, positive selection procedures for obtaining mutants blocked in pyrimidine and purine salvage genes of Lactococcus lactis were established. Strains lacking the following enzyme activities due to mutations in the corresponding genes were isolated: uracil phosphoribosyltransferase (upp), uridine/cytidine kinase (udk), pyrimidine nucleoside phosphorylase (pdp), cytidine/deoxycytidine deaminase (dd),thymidine kinase (tdk) and purine nucleoside phosphorylase (pup). Based on an analysis of the mutants obtained, the pathways by which L. lactis metabolizes uracil and the different pyrimidine nucleosides were verified. The substrate specificities of the different enzymes were determined. It was demonstrated that a single pyrimidine nucleoside phosphorylase accounts for the phosphorolytical cleavage of uridine, deoxyuridine and thymidine, and a single purine nucleoside phosphorylase has activity towards both the ribonucleoside and deoxyribonucleoside derivatives of adenine, guanine and hypoxanthine. No phosphorylase activity towards xanthosine appeared to be present. The selection procedures developed during this work may be employed in establishing markers on the chromosome of many related lactic acid bacteria.

Selective inhibition of spontaneous pulmonary metastasis of lewis lung carcinoma by 5′‐deoxy‐5‐fluorouridine

5'-deoxy-5-fluorouridine (5'-FUdR) is a cytostatic that is biotransformed to 5-fluorouracil (5-FUra) by pyrimidine nucleoside phosphorylase (PyNPase), the expression of which is up-regulated by tumor necrosis factor alpha (TNF alpha), interleukin-1 alpha (IL-1 alpha) and interferon gamma (IFN gamma). In Lewis lung carcinoma (LLC) cell cultures, these inflammatory cytokines up-regulated the expression of type-IV collagenase, metastatic factor, as well as PyNPase and consequently enhanced the antiproliferative activity of 5'-FUdR. However, the activity of 5-FUra was not enhanced. It appears that 5'-FUdR selectively kills highly metastatic cells which are exposed to these intrinsic cytokines in tumor tissues, because of their high PyNPase activity. In fact, 5'-FUdR inhibited the spontaneous metastasis of LLC from the s.c. inoculation site to the lung. When 5'-FUdR was given during the process of metastasis it greatly reduced the number of tumor nodules in the lung even at doses 46 times lower than those inhibiting the primary tumor growth. In addition, 5'-FUdR, but not 5-FUra, lowered type-IV collagenase levels in the tumors at the low dose showing only anti-metastatic activity. On the other hand, 5-FUra showed anti-metastatic activity at doses similar to or only several times lower than those inhibiting the primary tumor growth.

Interferon alpha and 5′-deoxy-5-fluorouridine in colon cancer: Effects as single agents and in combination on growth of xenograft tumours

Interferon-α (IFN-α) enhances the activity of the 5-fluorouracil (5-FU) prodrug 5′-deoxy-5-fluorouridine (5′dFUrd) in colorectal cancer cells in vitro by upregulating the enzyme pyrimidine nucleoside phosphorylase (PNPase), which is responsible for converting 5′-dFUrd to 5-FU. We examined whether such enhancement also occurs in vivo using human colorectal xenografts in nude mice. The Co-115 line has high basal levels of PNPase and the enzyme level was increased in tumours from mice treated for 3 weeks with 50 000 IU/day (5 days/week) of IFN-αA/D. The prodrug 5′-dFUrd (200 mg/day, 5 days/week) had a much greater antitumour activity than 5-FU had when it was used at an approximately equitoxic dose (20 mg/day, 5 days/week). However, because of the high activity of 5′/dFUrd as a single agent, no enhancement by IFN-αA/D was observed. Studies on xenografts of WiDr cells indicated that this line is much less sensitive to 5′-dFUrd. However, because of the high at doses of 75 Olio IU/day or 150 000 IU/day resulted in significant inhibition of WiDr tumour growth. Combination treatment with 75 mg/kg/day or 150 mg/kg/day of 5′-dFUrd resulted in enhanced antitumour activity, particularly at the higher dose of IFN-αA/D. Synergy of this drug combination was confirmed by isobologram analysis. Analysis of PNPase levels in WiDr tumours, excised from mice treated with IFN-αA/D, demonstrated that the enzyme activity was increased by IFN-α in a dose-dependent manner. Slight increases were also seen in normal liver and intestine from the same animals. Our results indicate that modulation of converting enzymes for anticancer prodrugs by cytokines could be a novel therapeutic strategy for combination therapy of colorectal cancer.

Pyrimidine nucleoside phosphorylase activity and 5-fluorouracil concentration in tissue from breast cancer patients after administration of 5′-deoxy-5-fluorouridine

To better understand the mechanism of action of the chemotherapeutic agent 5′-deoxy-5-fluorouridine (5′-DFUR), we attempted to establish histopathologically whether a correlation exists between pyrimidine nucleoside phosphorylase (PyNPase) activity, 5-fluorouracil (5-FU) concentration in breast tissue, and the antitumor effects of 5′-DFUR. Ninety-nine patients with breast cancer received oral 5′-DFUR for 1 week preoperatively at daily doses of 600 mg (group A), 800 mg (group B), and 1200 mg (group C). PyNPase activity and 5-FU concentration were measured in tumors, neighboring normal breast tissue, and axillary lymph nodes with or without metastases. PyNPase activity was higher in breast cancer tissue, involved lymph nodes, and normal lymph nodes than in normal breast tissue. 5-FU concentrations were also higher in tumor tissue than in normal mammary gland tissue in all three groups. In the lymph nodes, 5-FU concentrations were higher in patients with metastases than in those without metastases. Of the 89 evaluated patients, 12 (13.5%) showed histologic improvement. PyNPase activity was higher and 5-FU concentrations were lower in the improved patients than in those who showed little or no improvement. Although these findings were not statistically significant, they suggest that the level of PyNPase activity may be directly related to the antitumor effect of 5′-DFUR.

Circadian rhythm of orotate phosphoribosyltransferase, pyrimidine nucleoside phosphorylases and dihydrouracil dehydrogenase in mouse liver: Possible relevance to chemotherapy with 5-fluoropyrimidines

In female mice (30–35 g) maintained in standardized conditions of 12 hr light (0600–1800 hr) alternating with 12 hr darkness (1800–0600 hr), food and water ad lib., there was a 24-hr cycle change (P < 0.0001, Cosinor analysis) in the activity of hepatic orotate phosphoribosyltransferase (OPRTase; EC 2.4.2.10), uridine phosphorylase (UrdPase; EC 2.4.2.3), and dihydrouracil dehydrogenase (DHUDase; 1.3.1.2) but not thymidine phosphorylase (EC 2.4.2.4). The peaks of both OPRTase and UrdPase activities occurred in the activity span at around 18 and 15 hours after light onset (HALO) and the trough at 6 and 3 HALO, respectively, when samples were taken every 4 hr. Conversely, the peak of DHUDase occurred in the rest span at around 3 HALO and the trough at 15 HALO. The maximal enzyme activities (3146 ± 172, 561 ± 25, and 6.7 ± 0.7 pmol/min/mg protein) was 210, 400 and 560% higher than the minimal activities (1507 ± 172, 139 ± 25, and 1.2 ± 0.7 pmol/min/mg protein), for OPRTase UrdPase, and DHUDase, respectively. A circadian rhythm was also observed when the light-dark cycle was shifted (reverse cycle) so that the lights went on at 2200 hr and off at 1000 hr. Under the reverse cycle condition there was a corresponding shift in UrdPase and DHUDase activities with a period of 1 hr difference in the time of maximum and minimum enzyme activities. OPRTase, on the other hand, showed little change after 4 weeks of adaptation under the reverse light cycle. The circadian rhythm of these key enzymes of pyrimidine metabolism, the interrelationship of their activities, and their role in the regulation of uridine bioavailability could be of particular significance in modulating the therapeutic regimens with 5-fluorinated pyrimidines.

Differential effects of acyclothymidine, a potent pyrimidine nucleoside phosphorylase inhibitor, on the pharmacokinetics of doxifluridine in rabbits via oral administration.

Acyclothymidine (AcyT, 5-methyl-1-(2'-hydroxyethoxymethyl)uracil), a potent inhibitor of pyrimidine nucleoside phosphorylase (PyNPase), was co-administered with 5'-deoxy-5-fluorouridine (5'-DFUR), a PyNPase activating prodrug of 5-fluorouracil (5-FU), to rabbits. The absorption and pharmacokinetic parameters of 5'-DFUR and its active metabolite 5-FU, after administration of 5'-DFUR in combination with AcyT, were evaluated in the animals. Animals were given an oral or intravenous administration of 5'-DFUR (50 mg/kg) in combination with an equimolar dose of AcyT (40 mg/kg). The half-lives (t1/2) of 5'-DFUR and 5-FU in plasma were 16.8 and 11.5 min, respectively. AUC (area under the plasma concentration-time curve) of 5'-DFUR and 5-FU following the oral administration of 5'-DFUR (50 mg/kg) was 1710 and 24.3 micrograms.min/ml, respectively. After the oral co-administration of 5'-DFUR and AcyT (at a molar ratio of 1:1), the AUC values for 5'-DFUR and 5-FU increased to 2680 and to 121.1 micrograms.min/ml, respectively. However, this combination had little effect on the t1/2 of 5'-DFUR.

Cellular metabolism of (−) enantiomeric 2′-deoxy-3′-thiacytidine

The metabolism of (−) enantiomeric 2'-deoxy-3'-thiacytidine (3TC) was examined in human immunodeficiency virus type 1 (HIV-1)-infected and mock-infected human cells. 3TC 5'-triphosphate levels accumulated comparably in HIV-1-infected and mock-infected phytohaemagglutinin-stimulated peripheral blood lymphocytes (PBL) and reached 40% or more of total intracellular 3TC metabolites after 4 hr. The rate of decay of 3TC triphosphate in HIV-1-infected and mock-infected PBL measured as a half-life ( T 1 2 ) ranged from 10.5 to 15.5 hr. 3TC did not significantly affect metabolism of deoxynucleotides in the U937 cell line, and was shown to be resistant to the action of human platelet pyrimidine nucleoside phosphorylase.

Stimulation of 5-fluorouracil metabolic activation by interferon-α in human colon carcinoma cells

Interferon-α (IFNα) increases the cytotoxicity of 5-fluorouracil (FUra) in vitro , and the combination has clinical efficacy against advanced colorectal cancer. IFNα treatment of HT-29 colon carcinoma cells induced a greater than two-fold increase in the intracellular levels of the active metabolite of FUra, FdUMP. Using cell extracts from HT-29 cells and FUra as substrate, IFNα produced a 1.9- and 8.7-fold increase, respectively, in the activities of uridine phosphorylase and pyrimidine nucleoside phosphorylase (PyNP). Furthermore, the effect was selective for the conversion of FUra to FdUMP, as IFNα did not increase the cellular levels of FUTP, nor did it change the extent of incorporation of FUra into RNA (or DNA). IFNα also had no effect on thymidine kinase activity, the second step in the activation of FUra. Hence the effect of IFNα on PyNP activity is likely a critical biochemical event that modulates the cytotoxicity of FUra.

Enzymatic Synthesis of 5-Methyluridine from Adenosine and Thymine with High Efficiency.

5-Methyluridine (5MU) was synthesized efficiently from adenosine, thymine, and phosphate by a combination of adenosine deaminase (ADA), purine nucleoside phosphorylase (PUNP), pyrimidine nucleoside phosphorylase (PYNP), and xanthine oxidase (XOD). Adenosine was converted into inosine first by ADA. 5MU and hypoxanthine were synthesized from inosine and thymine by PUNP and PYNP. The hypoxanthine formed was converted into urate via xanthine by XOD. After inosine was completely consumed, an equilibrium state, in which 5MU, thymine, ribose-1-phosphate, and phosphate were involved, was achieved. At the equilibrium state, the maximum yield of 5MU was obtained. The yield of 5MU was 74%, when the initial concentrations of adenosine, thymine, and phosphate were 5 mM each. On the other hand, in the absence of ADA or XOD the yield of 5MU was 1.8%. Several kinds of nucleosides were also synthesized with high yield by the same method.

Mechanism and site dependency of intestinal mucosal transport and metabolism of thymidine analogues.

This study has been undertaken to investigate the mechanisms of intestinal mucosal transport and metabolism of thymidine analogues and to identify any optimal site(s) of the rat intestine particularly involved in the absorption of thymidine analogues. The intestinal absorption of 3'-azido-3'-deoxythymidine (AZT) was studied at three initial concentrations in four segments of the rat intestine using an in situ recirculating perfusion technique. Disappearance of AZT followed first-order kinetics throughout the gastrointestinal (GI) tract at all tested concentrations. The apparent first-order rate constants were found to be relatively invariant over a broad range of concentrations from 0.01 to 1.0 mM. Corrected for the length of each segment, the apparent permeability (Papp) of AZT was 3.01 +/- 0.32 x 10(-5) cm/sec (mean +/- SE) in the duodenum, 2.06 +/- 0.24 x 10(-5) cm/sec in the upper jejunum, 0.76 +/- 0.13 x 10(-5) cm/sec in the combined lower jejunum and ileum, and 0.32 +/- 0.10 x 10(-5) cm/sec in the colon, which indicated that intrinsic absorptivity was greater in the upper GI tract than in the lower portions possibly due to the differences in surface area for absorption. No AZT metabolite appeared in any part of the GI tract. On the other hand, thymidine and other analogues, i.e., 5-iodo-2'-deoxyuridine and 2'-deoxyuridine, were rapidly metabolized into nucleobase and sugar in the upper GI tract, whereas in the colon no metabolite appeared. A free 3'-OH group appears to be necessary for the metabolism (catabolism) of thymidine analogues in the rat intestine mainly by pyrimidine nucleoside phosphorylase.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain parenchymal metabolism of 5-iodo-2'-deoxyuridine and 5'-ester prodrugs.

In an attempt to generate derivatives of 5-iodo-2'-deoxyuridine (IDU) with enhanced blood-brain barrier (BBB) permeability, a series of 5' ester prodrugs of IDU was synthesized and their metabolism studied in rat brain homogenate and its different subcellular fractions. The rate of hydrolysis was dependent on the steric and polar nature of the ester substituent. Ester hydrolyzing activities were associated primarily with the cytosolic fraction and were due mainly to the presence of cholinesterases as confirmed by inhibition experiments performed with different esterase inhibitors. The metabolism of IDU to 5-iodouracil (5-IU) by the cytosolic fraction, in the presence and absence of specific pyrimidine nucleoside phosphorylase inhibitors, also suggests that there are two specific enzyme systems catalyzing two different metabolic processes. IDU 5'-esters competitively inhibit the metabolism of IDU and the inhibitory effect depends on the affinity of a particular ester toward the enzyme and also on the rate by which the ester itself undergoes hydrolysis. In the absence of any 5'-ester, 95% IDU was metabolized within 6 hr. However, in the presence of an eightfold molar excess of butyryl-IDU, the hydrolysis of IDU was completely inhibited over a 6-hr time period.

A comparison of 5-fluorouracil metabolism in human colorectal cancer and colon mucosa

The metabolism of 5-fluorouracil (5-FU) was studied in biopsy specimens of primary colorectal cancer and healthy colonic mucosa obtained from previously untreated patients immediately after surgical removal. The conversion of 5-FU to anabolites was measured under saturating substrate (5-FU) and cosubstrate concentrations. For all enzymes, the activity was about threefold higher in tumor tissue compared with healthy mucosa of the same patient. The activity of pyrimidine nucleoside phosphorylase with deoxyribose-1-phosphate (dRib-1-P) was about tenfold higher (about 130 and 1200 nmol/hr/mg protein in tumors) than with ribose-1-phosphate (Rib-1-P), both in tumor and mucosa. Synthesis of the active nucleotides (5-fluoro-uridine-5'-monophosphate [FUMP] and 5-fluoro-2'-deoxyuridine-5'-monophosphate [FdUMP]) was studied by adding physiologic concentrations of adenosine triphosphate (ATP) to the reaction mixture; the rate of FdUMP synthesis was 50% of that of FUMP (about 4 and 7 nmol/hr/mg protein in tumors). Direct synthesis of FUMP from 5-FU in the presence of 5-phosphoribosyl-1-pyrophosphate (PRPP) was about 2 nmol/hr/mg protein. With the natural substrate for this reaction, orotic acid, the activity was about 14-fold higher. To obtain insight into the recruitment of precursors for these cosubstrates, the authors also tested the enzyme activity of pyrimidine nucleoside phosphorylase with inosine and ribose-5-phosphate (Rib-5-P, as precursors for Rib-1-P) and deoxyinosine (as a precursor for dRib-1-P); enzyme activities were approximately 7%, 7%, and 3%, respectively, of that with the normal substrates, both in tumors and mucosa. However, when ATP and Rib-5-P were combined, the synthesis of FUMP was about 70% of that with PRPP, but only in tumors. In normal tissues no activity was detectable. These data suggest a preference of colon tumor over colon mucosa for the conversion of 5-FU to active nucleotides by a direct pathway; a selective antitumor effect of 5-FU may be related to this difference.

Effects of Orally Administered 5-Fluorouracil and Its Derivative 5′-Deoxy-5-fluorouridine on 7,12-Dimethylbenz[β]Anthracene-Induced Breast Carcinomas in Rats

Antitumour activity of 20 mg/kg 5-fluorouracil (5-FU) and 100 or 200 mg/kg 5'-deoxy-5-fluorouridine (5'-DFUR) was assessed by tumour regression, light and electron microscopic changes, and immunohistochemical variations in broxuridine labelling in 7,12-dimethyl-benz[a]anthracene- (DMBA-) induced breast carcinomas in rats. The relative regression of tumours was significantly (P less than 0.05) greater in animals receiving 5-FU or 5'-DFUR than in control animals. Light microscopic changes became apparent after 3 or 4 days' treatment and were more evident after 4-21 days. Electron microscopic degeneration of tumours was observed after 1 day. The broxuridine labelling index decreased significantly (P less than 0.05) in rats receiving 5-FU and especially in those receiving 5'-DFUR. Concentrations of 5-FU in DMBA-induced breast carcinomas were significantly (P less than 0.05) higher in rats treated with 5'-DFUR than in those treated with 5-FU, and the histological degeneration was significantly (P less than 0.05) more advanced in 5'-DFUR- than in 5-FU-treated animals, possibly due to the higher pyrimidine nucleoside phosphorylase activity in the former treatment group.

Effects of Xanthine Oxidase on Synthesis of 5-Methyluridine by the Ribosyl Transfer Reaction

In the presence of xanthine oxidase, 5-methyluridine was synthesized from inosine and thymine by the ribosyl transfer reaction using purine nucleoside phosphorylase and pyrimidine nucleoside phosphorylase. The hypoxanthine formed was converted into urate via xanthine by xanthine oxidase. After inosine was completely consumed, an equilibrium state, in which 5-methyluridine, thymine, ribose-1-phosphate, and phosphate were involved, was achieved. At the equilibrium state, maximum yield of 5-methyluridine was obtained. The equilibrium constant of the reaction (K = [thymine] [ribose-1-phosphate]/[5-methyluridine] [phosphate]) was 0.062. Based on the equilibrium constant, the yield of 5-methyluridine depended on a ratio of initial concentrations of inosine and phosphate, on condition that the initial concentrations of inosine and thymine were the same. The yields of 5-methyluridine in the presence and absence of xanthine oxidase were 76 and 33%, respectively, when the initial concentrations of inosine, thymine, and phosphate were 5 mm each.

Production of 5-methyluridine by immobilized thermostable purine nucleoside phosphorylase and pyrimidine nucleoside phosphorylase from Bacillus stearothermophilus JTS 859

5-Methyluridine was produced continuously from thymine and inosine by immobilized enzymes, which consisted of thermostable purine nucleoside phosphorylase and thermostable pyrimidine nucleoside phosphorylase obtained from Bacillus stearothermophilus JTS 859. The process was carried out in a column reactor at 60° C for 17 d without any bacterial contamination under non-aseptical conditions. Half-lives of the activity of the immobilized enzymes were 47 d and 4.5 d at 60° C and 70° C, respectively, although half-life of the crude enzyme was only 14 h at 70° C.

The Effects of Organic Solvent on the Ribosyl Transfer Reaction by Thermostable Purine Nucleoside Phosphorylase and Pyrimidine Nucleoside Phosphorylase from Bacillus stearothermophilus JTS 859

The effects of organic solvents on the reaction rate and equilibrium of the ribosyl transfer reaction catalyzed by thermostable purine nucleoside phosphorylase and pyrimidine nucleoside phosphorylase from Bacillus stearothermophilus JTS 859 were examined at 60°C. The reaction rate in the presence of 10% acetone was 1.6 times higher than that of the control. Acetone was the best organic solvent among those tested for accelerating the reaction rate without denaturing the enzymes. On the other hand, the reaction rate in the presence of 5% ethyl acetate was 1.5 times higher than that of the control. However the enzymes were denatured completely after 1 h incubation. Consequently, the acceleration was not attributed to the stabilization of the enzymes. The equilibrium constants of the reaction were not influenced by the presence of acetone, methyl or ethyl alcohols.

Effects of xanthine oxidase on synthesis of 5-methyluridine by the ribosyl transfer reaction.

In the presence of xanthine oxidase, 5-methyluridine was synthesized from inosine and thymine by the ribosyl transfer reaction using purine nucleoside phosphorylase and pyrimidine nucleoside phosphorylase. The hypoxanthine formed was converted into urate via xanthine by xanthine oxidase. After inosine was completely consumed, an equilibrium state, in which 5-methyluridine, thymine, ribose-1-phosphate, and phosphate were involved, was achieved. At the equilibrium state, maximum yield of 5-methyluridine was obtained. The equilibrium constant of the reaction (K = [thymine] [ribose-1-phosphate]/[5-methyluridine] [phosphate]) was 0.062. Based on the equilibrium constant, the yield of 5-methyluridine depended on a ratio of initial concentrations of inosine and phosphate, on condition that the initial concentrations of inosine and thymine were the same. The yields of 5-methyluridine in the presence and absence of xanthine oxidase were 76 and 33%, respectively, when the initial concentrations of inosine, thymine,...

Cis-trans-isomerization of [E]-5-(2-bromovinyl)-2,2'-anhydrouridine in vivo in rats.

1. [E]-5-(2-bromovinyl)-2,2'-anhydrouridine [( E]BVANUR) has considerable antiviral activity against herpes simplex virus type 1 (HSV-1). 2. [E]BVANUR is not a substrate of pyrimidine nucleoside phosphorylases, but it is an inhibitor of uridine phosphorylase (Ki = 450 nM). 3. [E]BVANUR (trans-isomer, parent compound) undergoes isomerization to [Z]BVANUR (cis-isomer), the only metabolite in rat, which was identified by h.p.l.c., mass spectra and n.m.r. spectroscopy. 4. Absorption of the drug from the gastrointestinal tract after oral administration is minimal. Absorption of [E]BVANUR from the abdominal cavity after i.p. administration was slow.

Comparative Antitumor Activity and Intestinal Toxicity of 5′‐Deoxy‐5‐fluorouridine and Its Prodrug Trimethoxybenzoyl‐5′‐deoxy‐5‐fluorocytidine

N4‐Trimethoxybenzoyl‐5′‐deoxy‐5‐fluorocytidine (Ro 09–1390), a prodrug of the cytostatic 5′‐deoxy‐5‐fluorouridine (5′‐DFUR), was synthesized with the aim of reducing of the dose‐limiting toxicity of 5′‐DFUR, which is diarrhea. In mice bearing Lewis lung carcinoma, 5′‐DFUR given po produced a substantial amount of 5‐fluorouracil (5‐FU) in the intestinal tract as well as in tumors, where the enzyme pyrimidine nucleoside phosphorylase, essential for conversion of 5′‐DFUR to 5‐FU, is predominantly located. With the oral administration of Ro 09–1390 only a small amount of 5‐FU was formed in the intestine; however, the administration of Ro 09–1390 and 5′‐DFUR at the same dose produced similar amounts of 5‐FU in tumor tissues. These differences in metabolism were reflected in their toxicity and antitumor efficacy. The administration of 5′‐DFUR resulted in damage to the intestinal mucosal membrane and diarrhea in normal mice, whereas Ro 09–1390 was much less toxic to the intestinal tract. As regards antitumor activity, Ro 09–1390 and 5′‐DFUR at equivalent doses inhibited the growth of Lewis lung carcinoma to similar extents. Since Ro 09–1390 was much less toxic to the intestinal tract than 5′‐DFUR, mice bearing Lewis lung carcinoma could be given Ro 09–1390 daily over a longer period and at a higher dose, resulting in a longer survival time.

Effect of (E)-5-(2-bromovinyl)-2′-deoxyuridine on life-span and 5-fluorouracil metabolism in mice with hepatic metastases

5-Fluorouracil (5FU) is rapidly metabolised in the liver by dihydrouracil dehydrogenase. Bromovinyluracil is formed in the liver from ( E)-5-(2-bromovinyl)-2′-deoxyuridine (BVDU) by pyrimidine nucleoside phosphorylase and is a potent inhibitor of dihydrouracil dehydrogenase. The co-administration of 5FU (intravenously) and BVDU (orally) was investigated in normal BDF 1 mice and in those bearing liver metastases of Lewis lung carcinoma. 5FU alone rapidly disappeared from plasma and liver within 60 min of dosing. Administered with BVDU, 5FU persisted in plasma and liver for 60–180 min. The combination also significantly enhanced the life-span of tumour-bearing mice. 5FU plus BVDU may have therapeutic potential in the treatment of primary and secondary liver tumours.