The human blood platelet: a cellular model to study the degradation of thymidine and its inhibition

Synthesis, Biological Evaluation and Molecular Docking Studies of Novel Series of Bis-1,2,4-Triazoles as Thymidine Phosphorylase Inhibitor

INTRODUCTION

Heterocyclic compounds have diverse biological activities and potential in drug development. This study aims to synthesize novel compounds with two 1,2,4-triazole cores and evaluate their biological properties, particularly their inhibitory activity against thymidine phosphorylase (TP), an enzyme involved in various physiological processes.

METHODS

The compounds were synthesized by reacting 5,5'-butane-bis-1,2,4-triazole derivatives with prenyl bromide. Characterization involved various techniques, including spectroscopy and elemental analysis. Antimicrobial potential was evaluated against bacteria and fungi, with comparative antibiotics as references. Inhibitory activity against TP was assessed, and molecular docking studies were conducted.

RESULTS

Six compounds were successfully synthesized and their structures confirmed. The synthesized triazole derivatives exhibited high biological activity, with compounds 2 and 6 showing the most promising TP inhibition. Molecular docking studies revealed interactions between compound 2 and TP, involving nine amino acids.

DISCUSSION

The synthesis of novel compounds with two 1,2,4-triazole cores contributes significantly to bis-triazole research. These compounds have potential as anti-tumor agents due to their inhibitory activity against TP, a crucial enzyme in tumor growth and metastasis. Comparative evaluation against antibiotics highlights their potency. Docking results provide insights into their interactions with TP, supporting their potential as potent TP inhibitors. Further research should focus on evaluating their efficacy in biological models, understanding their mechanisms of action, and optimizing their activities.

CONCLUSION

The synthesized compounds with two 1,2,4-triazole cores exhibit significant biological activity, including strong TP inhibition and broad-spectrum antimicrobial effects. These findings emphasize their potential as anti-tumor agents and the need for further exploration and optimization. Future research should focus on evaluating their efficacy in biological models, understanding their mechanisms of action, and developing more potent bis-triazole derivatives for drug discovery efforts. The combined results from assays and docking studies support the therapeutic potential of these compounds as anti-tumor agents.

2-Arylquinazolin-4(3H)-ones: A novel class of thymidine phosphorylase inhibitors

Thymidine phosphorylase (TP) over expression plays an important role in several pathological conditions, such as rheumatoid arthritis, chronic inflammatory diseases, psoriasis, and tumor angiogenesis. In this regard, a series of twenty-five 2-arylquinazolin-4(3H)-one derivatives 1-25 were evaluated for thymidine phosphorylase inhibitory activity. Six compounds 5, 6, 20, 2, 23, and 3 were found to be active against thymidine phosphorylase enzyme with IC50 values in the range of 42.9-294.6μM. 7-Deazaxanthine (IC50=41.0±1.63μM) was used as a standard inhibitor. Compound 5 showed a significant activity (IC50=42.9±1.0μM), comparable to the standard. The enzyme kinetic studies on the most active compounds 5, 6, and 20 were performed for the determination of their modes of inhibition, and dissociation constants Ki. All active compounds were found to be largely non-cytotoxic against the mouse fibroblast 3T3 cell line. This study identifies a novel class of thymidine phosphorylase inhibitors which may be further investigated as leads to develop therapeutic agents.

Relative mRNA expression of prostate-derived E-twenty-six factor and E-twenty-six variant 4 transcription factors, and of uridine phosphorylase-1 and thymidine phosphorylase enzymes, in benign and malignant prostatic tissue

Prostate cancer is the most frequent urological tumor, and the second most common cancer diagnosed in men. Incidence and mortality are variable and appear to depend on behavioral factors and genetic predisposition. The prostate-derived E-twenty-six factor (PDEF) and E-twenty-six variant 4 (ETV4) transcription factors, and the thymidine phosphorylase (TP) and uridine phosphorylase-1 (UP-1) enzymes, are reported to be components of the pathways leading to tumorigenesis and/or metastasis in a number of tumors. The present study aimed to analyze the mRNA expression levels of these proteins in prostatic cancerous and benign tissue, and their association with clinical and pathological variables. Using quantitative reverse transcription polymerase chain reaction, the mRNA expression levels of PDEF, ETV4, TP and UP-1 were studied in 52 tissue samples (31 of benign prostatic hyperplasia and 21 of prostate adenocarcinomas) obtained from patients treated by transurethral resection of the prostate or by radical prostatectomy. Relative expression was assessed using the ∆-CT method. Data was analyzed using Spearman's tests for correlation. P<0.05 was considered to indicate a statistically significant difference. The results revealed that PDEF, ETV4, UP-1 and TP were expressed in 85.7, 90.5, 95.2 and 100% of the prostate cancer samples, and in 90.3, 96.8, 90.3 and 96.8% of the benign samples, respectively. PDEF and ETV4 exhibited a significantly higher relative expression level in the tumor samples compared with their benign counterparts. The relative expression of TP and UP-1 did not differ significantly between benign and cancerous prostate tissues. The relative expression of TP was moderately and significantly correlated with the expression of ETV4 in the benign tissues. The relative expression of UP-1 was significantly lower in T3 compared with T1 and T2 cancers. These findings indicate that PDEF, ETV4, TP and UP-1 are typically expressed in benign and malignant prostatic tissues. Further studies are necessary to define the role of these proteins as therapeutic targets in prostate cancer.

Xanthine oxidase-activated prodrugs of thymidine phosphorylase inhibitors

Thymidine phosphorylase (TP) is over-expressed in various tumour types and plays an important role in tumour angiogenesis, growth, invasion and metastasis. The enzymatic activity of TP is required for the angiogenic effect of TP, therefore, inhibitors of TP are of significant interest in cancer chemotherapy. A series of xanthine oxidase (XO) activated prodrugs of known inhibitors of TP have been designed and synthesized with the ultimate intent of improving tumour selectivity and pharmacokinetic characteristics. These prodrugs were not inhibitors of TP, but were selectively oxidized by XO at C-2 and/or C-4 of the uracil ring moiety to generate the desired TP inhibitor. Molecular modelling of both the TP inhibitors and XO-activated prodrugs rationalized their binding in the active site of the human TP crystal structure.

Synthesis and evaluation of 6-methylene-bridged uracil derivatives. Part 1: Discovery of novel orally active inhibitors of human thymidine phosphorylase

A series of novel 6-methylene-bridged uracil derivatives have been prepared as inhibitors of human thymidine phosphorylase (TP). To enhance the in vivo antitumor activity of fluorinated pyrimidine 2'-deoxyribonucleosides such as 2'-deoxy-5-(trifluoromethyl)uridine (F(3)dThd), a potent TP inhibitor preventing their degradation to an inactive compound, has become a target of medicinal chemistry. We present here the synthesis and evaluation of novel human TP inhibitors. Introduction of an N-substituted aminomethyl side chain at the 6-position of 5-chlorouracil has improved water solubility and enhanced inhibitory activity compared with the known TP inhibitor, 6-amino-5-chlorouracil. Compound 42 was reasonably well absorbed in mice after oral administration. When combined with F(3)dThd, compound 42 exerted its TP inhibitory potency by increasing the maximum plasma concentrations of the former as evidenced in experiments with monkeys. Positive changes in pharmacokinetic profile were accompanied by the enhanced in vivo antitumor activity of this combination when compared to F(3)dThd alone, in mice bearing human tumor xenografts. Both biochemical and pharmacological effects appeared to fit the concept as anticipated.

Platelet-derived endothelial cell growth factor thymidine phosphorylase in tumour growth and response to therapy

Angiogenesis plays an important role in the growth and metastasis of solid tumours. Platelet-derived endothelial cell growth factor (PD-ECGF) is known to be chemotactic for endothelial cells in vitro and angiogenic in vivo. It is also known as gliostatin, a factor promoting neuronal survival, and thymidine phosphorylase (dThdPase), which catalyses the reversible phosphorylation of thymidine to thymine and 2-deoxyribose-1-phosphate. This enzymatic activity is critical for angiogenic activity. PD-ECGF protein is highly expressed in tumours compared with most normal tissues and has been correlated with tumour growth, invasion and metastasis in clinical studies. In addition, dThdPase activity (by inference PD-ECGF) has been found to be a major determinant of the toxicity of 5-fluorouracil and its prodrugs, which are extensively studied clinically as anti-cancer agents. This review attempts to summarize recent gains in understanding the nature, location and action of PD-ECGF and its specific relevance to tumour biology.

Thymidine phosphorylase is angiogenic and promotes tumor growth

Platelet-derived endothelial cell growth factor was previously identified as the sole angiogenic activity present in platelets; it is now known to be thymidine phosphorylase (TP). The effect of TP on [methyl-3H]thymidine uptake does not arise from de novo DNA synthesis and the molecule is not a growth factor. Despite this, TP is strongly angiogenic in a rat sponge and freeze-injured skin graft model. Neutralizing antibodies and site-directed mutagenesis confirmed that the enzyme activity of TP is a condition for its angiogenic activity. The level of TP was found to be elevated in human breast tumors compared to normal breast tissue (P < 0.001). Overexpression of TP in MCF-7 breast carcinoma cells had no effect on growth in vitro but markedly enhanced tumor growth in vivo. These data and the correlation of expression in tumors with malignancy identify TP as a target for antitumor strategies.

Controlling the vasculature: angiogenesis, anti-angiogenesis and vascular targeting of gene therapy

Angiogenesis is the development of new blood vessels from an existing vascular bed. Normal vascular proliferation occurs only during embryonic development, the female reproductive cycle and wound repair. By contrast, many pathological conditions (for example, cancer, atherosclerosis and diabetic retinopathy), are characterized by persistent, unregulated angiogenesis. Conversely, inadequate angiogenesis can lead to failure of ulcers to heal and myocardial infarction. Control of vascular development could permit new therapeutic approaches to these disorders. For example, several anti-angiogenic drugs are currently undergoing clinical trials for the treatment of cancer, whereas enhancement of angiogenesis by exogenous growth factors can prevent or limit the damage in chronic wounds and duodenal ulcers. Here Tai-Ping Fan, Rhys Jaggar and Roy Bicknell highlight recent achievements and discuss the prospects of receptor antagonists, enzyme inhibitors, tumour suppressor genes and vascular targeted approaches, especially that of gene therapy, in the future development of angiotherapy.

Thymidine phosphorylase activity of platelet-derived endothelial cell growth factor is responsible for endothelial cell mitogenicity

Recombinant human platelet-derived endothelial cell growth factor, expressed in the yeast Saccharomyces cerevisiae was purified to greater than 98% purity by anion-exchange and hydroxyapatite chromatography. It was shown to possess thymidine phosphorolytic activity in vitro (pH optimum, pH 5.3; Km, 0.11 mM; Vmax, 12.5 mmol min-1 mg-1; turnover number, 9.4 s-1). Covalent modification simultaneously inhibited the enzymatic and mitogenic properties of the protein, while interaction with a cell-surface receptor was not required to stimulate mitogenesis. Purified Escherichia coli thymidine phosphorylase was also mitogenic toward endothelial cells. It is proposed that platelet-derived endothelial cell growth factor is human thymidine phosphorylase which promotes endothelial cell proliferation by reducing thymidine levels that would otherwise be inhibitory to endothelial cell growth.

Metabolism of pyrimidine analogues and their nucleosides

The pyrimidine antimetabolite drugs consist of base and nucleoside analogues of the naturally occurring pyrimidines uracil, thymine and cytosine. As is typical of antimetabolites, these drugs have a strong structural similarity to endogenous nucleic acid precursors. The structural differences are usually substitutions at one of the carbons in the pyrimidine ring itself or substitutions at on of the hydrogens attached to the ring of the pyrimidine or sugar (ribose or deoxyribose). Despite the differences noted above, these analogues, can still be taken up into cells and then metabolized via anabolic or catabolic pathways used by endogenous pyrimidines. Cytotoxicity results when the antimetabolite either is incorporated in place of the naturally occurring pyrimidine metabolite into a key molecule (such as RNA or DNA) or competes with the naturally occurring pyrimidine metabolite for a critical enzyme. There are four pyrimidine antimetabolites that are currently used extensively in clinical oncology. These include the fluoropyrimidines fluorouracil and fluorodeoxyuridine, and the cytosine analogues, cytosine arabinoside and azacytidine.

The significance of 3H-thymidine degradation in cell culture experiments with special reference to rheumatoid arthritis

The degradation of 3H-thymidine under various cell culture conditions was analysed. It was found that a half of 3H-thymidine was degraded to 3H-thymine during 24 hours in PHA stimulation of blood lymphocytes. A control culture in which PHA was not added also caused 3H-thymidine degradation. 3H-thymidine degradation was prevented by adding 5-nitrouracil to the incubation medium at a concentration of 0.577 mg/ml. At the same time 5-NU increased 3H-thymidine incorporation into lymphocytes by 47%. 5-NU also eliminated the inhibitory effect of rheumatoid arthritis synovial tissue eluate on PHA stimulation. In addition 5-NU and nonradioactive thymine increased the 3H-thymidine labelling index of fresh rheumatoid arthritis synovial membrane biopsies, and also more of the isotope was accumulated in the individual cells of the membrane. These studies demonstrate that 3H-thymidine degradation is an important phenomenon in cell cultures and that it can be prevented effectively by using 5-nitrouracil with 3H-thymidine.

The role of blood platelets in nucleoside metabolism: regulation of megakaryocyte development and platelet production

In higher vertebrates, different types of blood cells develop from common precursors. Mammals are unique in possessing two types of blood cells--erythrocytes and platelets--which lack nuclei. Although platelets display consistent and easily-recognisable morphological and ultrastructural characteristics and show extreme metabolic and functional versatility, they are not true cells, being produced by fragmentation of giant polyploid precursors called megakaryocytes. At present, the physiological mechanisms which regulate megakaryocyte development and platelet production are not well understood. Platelets are actively involved in metabolism of purine derivatives and a significant platelet role in pyrimidine metabolism has also been demonstrated (see previous papers). Here an attempt is made to integrate information about platelet involvement in nucleic acid precursor metabolism with current concepts of haematopoiesis, particularly megakaryocyte development and platelet production. It is concluded (i) that megakaryocytic cells are immediate descendents of haematopoietic stem cells which have become polyploid as a result of genetic damage or metabolic imbalances, (ii) megakaryocytes and platelets are the ultimate regulators of stem cell development because they control the availability of thymidine and (iii) that the production of megakaryocytes and platelets is a physiological safety mechanism which prevents fixation of genetic damage and protects other cells from potentially cytotoxic and genotoxic stimuli.

In vitro and in vivo studies of a promising antileukemic thymidine analogue, 5-hydroxymethyl-2' deoxyuridine

The toxicity and metabolism of a thymidine analogue, 5-hydroxymethyl-2'-deoxyuridine (5HmdUrd) were studied with human leukemia cells (HL-60) and with human platelets. 3 X 10(-5) M 5HmdUrd caused a 50% inhibition in the proliferation of HL-60 cells. The compound was hydrolyzed to 5-hydroxymethyluracil (5HmUra) by the enzyme thymidine phosphorylase (EC 2.4.2.4) present in leukemia cells; this catabolic product was non-toxic. The catabolism of 5HmdUrd by human platelet thymidine phosphorylase could be inhibited by 6-aminothymine. The toxicity of 5HmdUrd was effectively reversed by deoxycytidine and 5HmdUrd increased the incorporation of deoxycytidine into dCTP and DNA several fold. The two latter phenomena are explicable in terms of a feedback action to ribonucleotide reductase, resulting in deoxycytidylate starvation, which is a known effect of excess thymidine. We report here also our preliminary observations that 5HmdUrd is active against mouse leukemia in vivo.

Pyrimidine nucleoside phosphorylase assay by automated high-performance liquid chromatography

A new assay for pyrimidine nucleoside phosphorylase is reported. This method utilizes an isocratic reversed-phase high-performance liquid chromatographic system for separation of nucleosides and bases. Product detection is accompanied by ultraviolet monitoring and radioactive flow detection. Use of an automated sample injector allows for the analysis of a series of samples, with data recorded onto a microprocessor-based cassette recorder. Data can then be downloaded into computer memory. The velocity of uridine phosphorylase (E.C. 2.4.2.3) was a linear function of enzyme concentration. The Michaelis constant for uridine at pH 8.0 was found to be in close agreement with the value obtained by a thin-layer chromatographic assay method.

Regeneration of the antiviral drug (E)-5-(2-bromovinyl)-2'-deoxyuridine in vivo

The highly potent and selective antiherpes drug BVdUrd [(E)-5-(2-bromovinyl)-2'-deoxyuridine] is cleared within 2-3 hours from the bloodstream upon intraperitoneal administration to rats. It is degraded to BVUra [(E)-5-(2-bromovinyl)uracil] and this inactive metabolite is cleared very slowly from the bloodstream so that 24 hours after the administration of BVdUrd, BVUra is still detectable in the plasma. This contrasts with several other 5-substituted uracils, i.e. 5-fluorouracil, 5-iodouracil, 5-trifluorothymine and thymine itself, which are, like their 2'-deoxyuridine counterparts FdUrd, IdUrd, F3dThd and dThd, cleared from the plasma within 2-3 hours. The injection of dThd or any of the other 5-substituted 2'-deoxyuridines at 3 hours after the injection of BVdUrd, that is at a time when BVdUrd has disappeared completely from the circulation, results in the re-apparition of BVdUrd in the plasma. Apparently, BVdUrd is regenerated from BVUra following the reaction catalyzed by pyrimidine nucleoside phosphorylases : BVUra + dThd----BVdUrd + Thy. BVdUrd can even be generated de novo if dThd (or FdUrd, IdUrd or F3dThd) are administered 3 hours after a preceding injection of BVUra. These findings represent a unique example of the (re)generation of an active drug from its inactive metabolite in vivo.

Phosphorolysis of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and other 5-substituted-2'-deoxyuridines by purified human thymidine phosphorylase and intact blood platelets

Various 5-substituted-2'-deoxyuridines (dUrd), including 5-ethyl,5-propyl-, 5-trifluoromethyl-, 5-hydroxymethyl-, 5-formyl-, 5-vinyl-, (E)-5-(2-chlorovinyl)-, (E)-5-(2-bromovinyl)-, 5-fluoro-, 5-chloro-, 5-bromo-, 5-iodo-, 5-cyano-, 5-thiocyano-, 5-nitro- and 5-amino-dUrd, were shown to be effective substrates for the thymidine (dThd) phosphorylase isolated from human blood platelets. Some of dUrd analogs, i.e. the highly potent and selective antiherpes agent (E)-5-(2-bromovinyl)-dUrd, were degraded more rapidly than the natural substrates, dUrd and dThd. All dUrd analogs were also readily catabolised by intact human blood platelets. The potent inhibitors of thymidine phosphorylase, 6-amino-thymine and 6-amino-5-bromo-uracil, strongly inhibited the phosphorolysis of (E)-5-(2-bromovinyl)-dUrd by both purified enzyme and intact platelets.