Effect of 5-(phenylselenenyl)acyclouridine, an inhibitor of uridine phosphorylase, on plasma concentration of uridine released from 2′,3′,5′-tri-O-acetyluridine, a prodrug of uridine: relevance to uridine rescue in chemotherapy

Purpose: The purpose of this investigation was to study the effects of combining oral 5-(phenylselenenyl)acyclouridine (PSAU) with 2′,3′,5′-tri-O-acetyluridine (TAU) on the levels of plasma uridine in mice. PSAU is a new lipophilic and potent inhibitor of uridine phosphorylase (UrdPase, EC 2.4.2.3), the enzyme responsible for uridine catabolism. PSAU has 100% oral bioavailability and is a powerful enhancer of the bioavailability of oral uridine. TAU is a prodrug of uridine and a far superior source of uridine than uridine itself. Methods: Oral TAU was administered to mice alone or with PSAU. The plasma levels of uridine and its catabolites as well as PSAU were measured using HPLC and pharmacokinetic analysis was performed. Results: Oral administration of 2000 mg/kg TAU increased plasma uridine by over 250-fold with an area under the curve (AUC) of 754 μmol · h/l. Coadministration of PSAU at 30 and 120 mg/kg with TAU further improved the bioavailability of plasma uridine resulting from the administration of TAU alone by 1.7- and 3.9-fold, respectively, and reduced the C_max and AUC of plasma uracil. Conclusion: The exceptional effectiveness of PSAU plus TAU in elevating and sustaining a high plasma uridine concentration could be useful in the management of medical disorders that are remedied by administration of uridine, as well as the rescue or protection from host toxicities of various chemotherapeutic pyrimidine analogues. Received: 10 November 1999 / Accepted: 14 March 2000     

Intratumoral pyrimidine nucleoside phosphorylase (pynpase) activity predicts a selective effect of adjuvant 5’-deoxy-5-fluorouridine (5’ dfur) on breast cancer

BACKGROUND: Pyrimidine nucleoside phosphorylase (PyNPase) is the enzyme that converts 5'-deoxy-5-fluorouracil (5'DFUR) to 5-fluorouracil (5FU). Its activity in cancer tissue may correlate with the selective antitumor activity of 5'DFUR in breast cancer. METHODS: Two hundred and sixteen T2 breast cancer patients were treated consecutively with surgery followed by 5'DFUR (600 mg/body/day) + tamoxifen (20 mg/body/day) for 2 years. PyNPase activity in breast cancer tissue, determined by high-performance liquid chromatography, ranged from 4.2-626.0 micrograms FU/mg protein/hr (mean +/- SD, 203.5 +/- 122.4), and the examined patients were divided into two groups: group A (high PyNPase group), cases with the PyNPase activity equal to or more than the mean value of 203.5 micrograms FU/mg protein/hr, and group B (low PyNPase group), cases with activity less than the mean value. RESULTS: Although there was no difference in relapse-free survival (RFS) between groups A and B, among node-positive patients (n = 83) those in group A tended to have a longer RFS. When divided into subgroups according to estrogen receptor (ER) status, among node-positive and ER-positive tumors (n = 49), the RFS was significantly better in group A than in group B (p < 0.05). CONCLUSION: Intratumoral PyNPase activity might be of use as a predictor of the effect of adjuvant 5'DFUR on breast cancer.     

Comparative aspects of purine metabolism in some African trypanosomes

Some enzymes of purine salvage were detected in the cell-free preparations from bloodstream forms of African trypanosomes: Trypanosoma vivax; T. brucei and T. congolense. Extracts of trypanosomes cleave adenosine and inosine hydrolytically except in T. congolense where adenosine cleavage was mediated by a phosphorylase. All the trypanosomes apparently lacked adenosine deaminase. Adenine aminohydrolase was found only in T. vivax while adenosine monophosphate deaminase was detected in T. brucei and T. congolense. There was no detectable adenosine kinase activity in T. brucei. A pathway is proposed for the metabolism of purines in these trypanosomes.     

Role of growth hormone in regulation of polynucleotide-phosphorylase activity in rat liver

Hypophysectomy in rats is followed by a significant increase in polynucleotide-phosphorylase (PNPase) activity in ribosomal fractions of the liver. Injection of growth hormone into hypophysectomized animals leads to inhibition of PNPase activity. Within the dose range from 5 to 100 g the dose—effect curve is linear. The action of growth hormone is most marked 18h after a single injection.Laboratory of Enzymology, Academy of Medical Sciences of the USSR, and Laboratory of Biological Standardization of Hormones, Institute of Experimental Endocrinology and Hormone Chemistry, Academy of Medical Sciences of the USSR, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 2, pp. 162–163, February, 1980.     

Activation of Phosphorylase by Anoxia and Dinitrophenol in Rabbit Colon Smooth Muscle: Relation to Release of Calcium from Mitochondria

Abstract: The effect of anoxia or 2,4-dinitrophenol (DNP) on the phosphorylase a activity and the calcium content in subcellular fractions from rabbit colon smooth muscle was studied. Anoxia for 15 min. as well as DNP (6.6 × 10^?5 M) for 5 min. increased the phosphorylase a activity. The calcium content in the mitochondrial subfraction, prepared from the anoxic- or DNP-treated intact muscle and determined by atomic absorption spectroscopy, was reduced. The calcium content in the nuclear and the microsomal fractions was not changed in preparations with a normal Ca-content. When the muscle was incubated for 60 min. in a Ca²⁺-free medium containing 2.0 mM EGTA, the calcium content in the mitochondrial fraction was reduced to 38 % of the control. This calcium level was still further reduced and the phosphorylase a activity was increased by DNP in this “Ca-poor” muscle. In these preparations the Ca-content of the microsomal + supernatant fraction increased. Only when the muscle was incubated, initially, in an anoxic medium containing 0.1 mM Ca²⁺ for 120 min. and, subsequently, in an oxygenated medium containing 0.1 mM Ca²⁺ for 20 min., DNP failed to activate phosphorylase and to decrease the calcium content in the mitochondrial fraction. These results indicate that mitochondrial Ca²⁺ release is one of the regulatory factors of the anoxic-induced glycogenolysis.     

中国与北欧乳癌组织TP、TS、DPD mRNA表达比较

目的:检测北欧和中国人乳癌患者TP、TS、DPD mRNA水平的差异。方法:应用定量RT-PCR法检测北欧乳癌患者中3种指标的表达,用半定量RT-PCR法检测中国乳癌患者中3种指标的表达。结果:仅中国标本TP mRNA水平显示肿瘤组织(0.44±0.23)高于正常组织(0.15±0.16),TP mRNA高表达率中国患者(56.67%)高于北欧患者(34.12%),60岁以下患者这种差异消失。TS、DPD mRNA高表达率在二地区无差异。结论:北欧和中国乳癌患者之间TP、TS、DPD mRNA表达无明显种族差异。     

甲硫腺苷磷酸化酶基因在非小细胞肺癌中的转录表达及临床意义

目的 探讨甲硫腺苷磷酸化酶(MTAP)基因在非小细胞肺癌中的转录表达变化情况及其临床意义。方法 采用逆转录聚合酶链反应(RT-PCR)方法检测了15例新鲜肺癌标本及相应癌旁组织中MTAP mRNA的表达情况。同时运用Western印迹法检测了MTAP蛋白质的表达情况。结果 MTAP在73．30%,(11／15)的肿瘤标本中不表达或转录水平降低,而MTAP在癌旁对照组织中的表达率却高达93．3％(14／15);对于11例RT-PCR分析认定低表达或不表达的样本,再通过Western印迹方法进一步验证,发现与RT-PCR结果一致。另外,MTAP在肺腺癌和鳞癌中低表达现象差异无显著意义,但在中／低分化肺癌中的低表达与高分化癌相比增高,差异有显著意义。结论 MTAP基因低表达或丢失可能与肺癌的恶性程度密切相关。     

Thymidine phosphorylase expression is preserved after radiotherapy in patients with cervical squamous cell carcinoma

Purpose The aim of this study was to investigate the changes in two of the enzymes involved in fluorouracil metabolism, thymidine phosphorylase (TP) and dihydropyrimidine dehydrogenase (DPD), in uterine cervical squamous cell cancer tissue after radiotherapy.Subjects and methods Cervical tissue from 27 patients diagnosed with stage IIIB or IV uterine cervical squamous cell cancer was compared with normal cervical tissue from 33 patients with benign gynecologic diseases. Expression of TP and DPD in the cervical tissues was measured using enzyme-linked immunosorbent assays. TP and DPD expression before and after irradiation with 10 and 20 Gy was measured in 9 of the 27 patients with cervical cancer.Results Before irradiation, DPD expression in cancer tissue did not differ from that in normal tissue. TP expression and the TP/DPD ratio were significantly higher in cancer tissue than in normal tissue (P<0.00001). TP and DPD expression and the TP/DPD ratio were not significantly changed by irradiation with 10 and 20 Gy. TP expression and the TP/DPD ratio after irradiation with 10 and 20 Gy were significantly higher than in normal tissue.Conclusion The increased TP expression and the elevated TP/DPD ratio following irradiation with up to 20 Gy may offer an increased clinical advantage to chemoradiotherapy with capecitabine or doxyfluridine over radiotherapy alone.     

Mode of action of neuropeptides from the adipokinetic hormone family

Neuropeptides of the adipokinetic hormone (AKH) family regulate inter alia mobilisation of various substrates from stores in the fat body of insects during episodes of flight. How is this achieved? In insects which exclusively oxidise carbohydrates for flight (cockroaches), or which oxidise carbohydrates in conjunction with lipids (locusts) or proline (a number of beetles), the endogenous AKHs bind to a G(q)-protein-coupled receptor, activate a phospholipase C and the resulting inositol trisphosphate releases Ca(2+) from internal stores. In addition, influx of extracellular Ca(2+) is increased and, via a kinase cascade, glycogen phosphorylase is activated, glucose-1-phosphate produced, and transformed to trehalose, which is released into the haemolymph. In locusts, additionally, adenylate cyclase is activated and cyclic AMP is synthesised. In insects which use lipids for sustained flight (locust, tobacco hornworm moth) or proline for flight (certain beetles), adenylate cyclase is activated after the AKHs bind to their respective G(s)-protein-coupled receptor. The resulting cyclic AMP, together with the messengers intra- and extracellular Ca(2+), activate a triacylglycerol lipase, which results in the production of 1,2 diacylglycerols (in locusts, moths) or (hypothetically) free fatty acids (fruit beetle).