Purine nucleoside phosphorylase, inhibition

Sircar J. C, Suto M. J, Scott M. E, Dong M. K, Gilbertsen R. B. Inhibitors of human purine nucleoside phosphorylase. Synthesis, purine nucleoside phosphorylase inhibition, and T-cell cytotoxicity of 2,5-diaminothiazolo[5,4-d]pyrimidin-7(6H)-one and 2,5-diaminothiazolo[4,5-d]pyrimidin-7(6H)-one. Two thioisosteres of 8-aminogua-nine, J. Med. Chem. 1986. p. 1804 -1806. DOI 10.1021/jm00159a045... 

Adenosine deaminase deficiency is associated with an immunodeficiency disease in which both thymus-derived lymphocytes (T cells) and bone marrow-derived lymphocytes (B cells) are sparse and dysfunctional. Purine nucleoside phosphorylase deficiency is associated with a severe deficiency of T cells but apparently normal B cell function. Immune dysfunctions appear to result from accumulation of dGTP and dATP, which inhibit ribonucleotide reductase and thereby deplete cells of DNA precursors. 

V. L. Schramm, Anopheles gambiae purine nucleoside phosphorylase Catalysis, structure, and inhibition, Biochemistry, 46 (2007) 12405—12415. 

The purine nucleoside phosphorylases (PNPs) are N-ribosyltransferases (Figure 7-7) where transition state analogue design on the basis of kinetic isotope effects analysis has had success. The inhibition of phosphorylation catalyzed by human... 

The enzyme, purine nucleoside phosphorylase (PNP), is directly involved with blood levels of T-cells. Low levels of this enzyme will inhibit T-ceU prohferation. Drugs that inhibit the enzyme can also be expected to act against proliferation of malignant T-cells. The PNP inhibitor forodesine (36) has shown early activity against T-cell mahgnancies. Treatment of the deazapurine (32) with lithium leads to derivative 33... 

Similarly a deficiency of Purine Nucleoside Phosphorylase causes accumulation of dGTP. In both cases Ribonucleotide Reductase is inhibited by accumulation of these nucleotides. 

To identify motifs that are effective for the inhibition of human purine nucleoside phosphorylase, Shibuya et al. have prepared numerous conforma-tionally restricted nucleotides (30) and (31) that act as multi-substrate analogue inhibitors for Preliminary results demonstrated that... 

In a commercially available assay, serum NTP catalyzes the hydrolysis of IMP to yield inosine, which is then converted to hypoxanthine by purine-nucleoside phosphorylase (EC 2.4.2.1). Hypoxanthine is oxidized to urate with xanthine oxidase (EC 1.2.3.2). Two moles of hydrogen peroxide are produced for each mole of hypoxanthine liberated and converted to uric acid. The formation rate of hydrogen peroxide is monitored by a spectrophotometer at 510nm by the oxidation of a chromogenic system. The effect of ALPs on IMP is inhibited by p-glycerophosphate. This material is substrate for ALP but not for NTP, and by forming substrate complexes with the former enzyme, it reduces the proportion of the total ALP activity that is directed to the hydrolysis of the NTP substrate, IMP. ... 

Reaction of formycin B (387) with diphenylsulfide and tributylphosphine took place regiospecifically with the primary hydroxyl group to yield the 5 -deoxy-5 -phenylmercaptoformycin B 478 (Scheme 130). This modified C-nucleoside (478) poorly inhibited purine nucleoside phosphorylase (93JMC1024). 

Tenofovir is not metabolized to a significant extent by CYPs and is not known to inhibit or induce these enzymes. However, tenofovir has been associated with a few potentially important pharmacokinetic drug interactions. A 300-mg dose of tenofovir increased the didanosine AUC by 44 to 60% probably as a consequence of inhibition of the enzyme purine nucleoside phosphorylase by both tenofovir and tenofovir monophosphate. These two drugs probably should not be used together, or if this is essential, the dose of didanosine should be reduced from 400 to 250 mg/day. 

Purine-9-ylalkyl derivatives (15) containing both the phosphonic and phosphinic substituent inhibit purine nucleoside phosphorylase. Compound 15 [R = NH2, R = OH, R r4 = h, = N, X = H, X = CH2)3] had K, = 0.0026 pmol (ref. 39). The phosphonate monoesters 16 (R = Me, R = o-, m- or P-NO2) inhibit the class A j5-lactamase, probably by phosphorylation of the active site of this enzyme" . When R = Ph they also inhibit class C j5-lactamase of Enterobacter cloacae P99 and may led to new antibiotics. They should be useful as active titrants of the enzyme ... 

The branched-chain compound 27 has been synthesized from 28 (available from D-mannose) by reductive amination then acid-catalysed hydrolysis. Compounds 27 thus prepared together with related compounds were tested for their inhibition against human blood purine nucleoside phosphorylase and a- and P-glucosidases. ... 

Further in vitro studies using a lung cancer cell line (A549) demonslrated that febuxostat (16 xM for 3h) completely inhibited xanthine oxidase activity without affecting the activities of adenosine deaminase, purine nucleoside phosphorylase, adenine phosphoribosyltransferase, hypoxanthine-guanine phosphoribosyltransferase, pyrimidine -nucleoside phosphorylase, or guanase. ... 

C11H13N3O5 267.241 Inhibits Pneumocystis carinii in vitro and in vivo. Purine nucleoside phosphorylase inhibitor. Antileishmanial and potential antileukaemic agent. Struct, originally assigned to Pyrrolosine, P-117. 

Adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiency have been recognized as the primary cause of an associated immune deficiency syndrome. A number of mechanisms have been proposed to explain the predominant effect of these enzyme deficiencies on the development and function of the lymphoid system. One of the mechanisms concerns the phosphorylation of accumulated metabolic compounds i.e. deoxyadenosine (dAdo) in case of ADA-deficiency and deoxyguanosine (dGuo) in case of PNP deficiency in the lymphoid cells and particularly in thymocytes (1). Indeed increased deoxyATP and deoxyGTP levels have been found in the lymphocytes of ADA- and PNP-deficient patients respectively (2,3). These triphosphates may inhibit the enzyme ribonucleotide reductase which leads to a depletion of deoxyCTP and interference with lymphocytic DNA-synthesis (1). 

IMP v/hich was always the main labeled compound present within erythrocytes). After the lag time, the rate of hypoxanthine release was about the same of that observed in the absence of formycin B (fig. 2). Since, at the concentration employed, formycin B is known to inhibit purine nucleoside phosphorylase in intact human erythrocytes, these results confirm that the cells sequentially degrade the intracellular IMP to inosine and hypoxanthine and suggest that the phosphory-lase-catalyzed formation of hypoxanthine from its nucleoside is not the rate limiting step in this catabolic path. 

The inhibitory effect of allopurinol on the first three steps of purine biosynthesis in Neurospora crassa cultures could be due 1. to the formation of allopurin-ol-l-ribonucleotide (by HGPRTase 1,19 nMol/mg protein/ hr in our Neurospora crassa cultures) 2. due to an oxipurinol-7-ribonucleotide effect, namely the formation of oxipurinol (by xanthine oxidase) and then oxipurinol-7-ribonucleotide (by OPRTase) and 3. by formation of allopurinol-1-ribotide through allopurin-ol-1-riboside (by a purine nucleoside phosphorylase) to allopurinol-1-ribonucleotide (by a nucleoside kinase). This latter pathway seems rather improbable because we could not demonstrate an effect on purine biosynthesis by direct addition of allopurinol-1-ribonucleoside to the incubation medium. Allopurinol-1-ribonucleotide inhibits significantly at higher concentrations. This is to explain if there is free access of the ribonucleotide form through the cell membrane (at least in these high concentrations) or if there is conversion to the ribonucleoside (which then enters the cell) by a nucleotidase located on the cell membrane. This latter mechanism however seems more improbable bcause there was no effect by allopurinol-1-ribonucleoside (which excludes the possibility for subsequent formation of allopurinol-1 -ribonucleotide by a nucleoside kinase, at least... 

Variation in Purine Synthesis. An important development in purine biochemistry came from studies on sulfonamide inhibition of bacteria. A compound was found to accumulate in cultures of E. colt incubated with sulfadiazine. This was identified as 4-aminoimidazole-5-car-boxamide. In the present concept, this compound represents a degradation product of the corresponding ribotide, but it can also be used as a purine precursor. The free imidazole reacts with ribose-l-phosphate in the presence of nucleoside phosphorylase to form a nucleoside which can be phosphorylated by a kinase. Thus, variations of the basic scheme can and do occur. 

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