Pyrimidine 5'-nucleotidase activities detected in real samples by means of micellar electrokinetic chromatography

Targeting Metabolism of Extracellular Nucleotides via Inhibition of Ectonucleotidases CD73 and CD39

In the tumor microenvironment, unusually high concentrations of extracellular adenosine promote tumor proliferation through various immunosuppressive mechanisms. Blocking adenosine production by inhibiting nucleotide-metabolizing enzymes, such as ectonucleotidases CD73 and CD39, represents a promising therapeutic strategy that may synergize with other immuno-oncology mechanisms and chemotherapies. Emerging small-molecule ectonucleotidase inhibitors have recently entered clinical trials. This Perspective will outline challenges, strategies, and recent advancements in targeting this class with small-molecule inhibitors, including AB680, the first small-molecule CD73 inhibitor to enter clinical development. Specific case studies, including structure-based drug design and lead optimization, will be outlined. Preclinical data on these molecules and their ability to enhance antitumor immunity will be discussed.

A new simple approach for the determination of pyrimidine 5'-nucleotidase activity in human erythrocytes using an ELISA reader

INTRODUCTION

Pyrimidine 5' nucleotidase type I (P5'N-1) deficiency is the most frequent abnormality of cell nucleotide metabolism causing hereditary non spherocytic hemolytic anemia (HNSHA). The aim of this study was to develop a simple method of determination of P5'N-1 activity in human erythrocytes using an ELISA reader

METHODS

Determination of P5'N-1 activity is based on the liberation of inorganic phosphorus (Pi) after incubation with uridine monophosphate/cytidine monophosphate. Inorganic phosphorus (Pi), a product of the enzymatic reaction is directly quantitated from its ultraviolet absorbance. Purine/Pyrimidine nucleotides ratio (OD 260: OD 280) was also measured

RESULTS

P5'N-1 deficient patients showed reduction in P5'N-1 activity (Mean ± SD; 4.06 ± 0.66 using an ELISA reader & 6.25 ± 1.37 using a spectrophotometer) as compared to the normal control group (ELISA reader: 13.24 ± 3.42 & Spectrophotometer: 18.25 ± 3.20). Heterozygotes showed intermediate activity (ELISA reader: 6.06 ± 0.48 & Spectrophotometer: 8.06 ± 1.28), however they would have been missed on screening using the Purine/Pyrimidine nucleotides ratio

CONCLUSION

Determination of P5'N-1 activity by using an ELISA reader is a new, simple, less time consuming and reliable method. It also avoids the use of radioactive material or HPLC which is a significant advantage.

Hereditary erythrocyte pyrimidine 5'-nucleotidase deficiency: a biochemical, genetic and clinical overview

Pyrimidine 5' -nucleotidase (P5'N-1) deficiency is the third most common enzyme abnormality after glucose 6-phosphate dehydrogenase and pyruvate kinase causing hereditary non-spherocytic hemolytic anemia. The disease is transmitted as an autosomal recessive trait. The degree of hemolysis is generally mild-to moderate. The hallmark of this enzyme deficiency is the presence of pronounced basophylic stippling in red blood cell peripheral blood smear together with accumulation of pyrimidine nucleotides within erythrocytes. No correlation has been found between residual activity and degree of hemolysis. The structural human gene for P5'N-1 is now available and fifteen different mutations had been identified so far. More recently, a functional analysis of P5'N-1 mutants had been performed providing a rationale for the pathological effects of the mutations. All mutations investigated affect amino acid residues unambiguously essential for the catalytic efficiency and/or protein stability, suggesting drastic reduction of the enzyme activity in red blood cells of patients affected by the disorder. Nevertheless, some patients exhibit high residual P5'N-1 activity, suggesting that P5'N-1 deficiency is compensate by other nucleotidases and/or alternative pathways in nucleotide metabolism. No specific therapy for P5'N-1 deficiency is now available.

Development and validation of a capillary electrophoresis method for the characterization of herpes simplex virus type 1 (HSV-1) thymidine kinase substrates and inhibitors

A fast, convenient capillary electrophoresis (CE) method was developed for monitoring the enzymatic reaction of herpes simplex virus type 1 thymidine kinase (HSV-1 TK). The reaction was performed in a test tube followed by quantitative analysis of the products. The optimized CE conditions were as follows: polyacrylamide-coated capillary (20 cm effective length x 50 microm), electrokinetic injection for 30s, 50 mM phosphate buffer at pH 6.5, constant current of -60 microA, UV detection at 210 nm, UMP or cAMP were used as internal standards. Phosphorylated products eluted within less than 7 min. The limits of detection were 0.36 microM for dTMP and 0.86 microM for GMP. The method was used to study enzyme kinetics, and to investigate alternative substrates and inhibitors.

Hereditary pyrimidine 5'-nucleotidase deficiency: from genetics to clinical manifestations

Hereditary pyrimidine 5'-nucleotidase (P5'N) deficiency is the most frequent abnormality of the red cell nucleotide metabolism causing hereditary non-spherocytic haemolytic anaemia. The disorder is usually characterised by mild-to-moderate haemolytic anaemia associated with the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. The precise mechanisms leading to the destruction of P5'N deficient red cells are still unclear. The pyrimidine 5'-nucleotidase type-I (P5'N-1) gene is localised on 7p15-p14 and the cDNA has been cloned and sequenced; 20 mutations have been identified so far in 30 unrelated families, most of them at the homozygous level. Recently, the comparison of recombinant mutants of human P5'N-1 with the wild-type enzyme has enabled the effects of amino acid replacements on the enzyme molecular properties to be determined and help to correlate genotype to clinical phenotype.

Determination of enzymatic activity by capillary electrophoresis

Enzymes are biological catalysts that play an important role in biochemical reactions necessary for normal growth, maturation and reproduction through whole live world. Their accurate quantitation in biological samples is important in many fields of biochemistry, not only in routine biochemistry and in fundamental research, but also in clinical and pharmacological research and diagnosis. Since the direct measurement of enzymes by masses is impossible, they must be quantified by their catalytic activities. Many different methods have been applied for this purpose so far. Although photometric methods are undoubtedly the most frequently used, separation methods will further gain their position in this field. The article reviews different possibilities for the assay of enzymatic activity by means of capillary electrophoresis (CE). Both the off-line and on-line enzyme assays based on CE are discussed.