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

Developing Wound Dressings Using 2-deoxy-D-Ribose to Induce Angiogenesis as a Backdoor Route for Stimulating the Production of Vascular Endothelial Growth Factor

2-deoxy-D-Ribose (2dDR) was first identified in 1930 in the structure of DNA and discovered as a degradation product of it later when the enzyme thymidine phosphorylase breaks down thymidine into thymine. In 2017, our research group explored the development of wound dressings based on the delivery of this sugar to induce angiogenesis in chronic wounds. In this review, we will survey the small volume of conflicting literature on this and related sugars, some of which are reported to be anti-angiogenic. We review the evidence of 2dDR having the ability to stimulate a range of pro-angiogenic activities in vitro and in a chick pro-angiogenic bioassay and to stimulate new blood vessel formation and wound healing in normal and diabetic rat models. The biological actions of 2dDR were found to be 80 to 100% as effective as VEGF in addition to upregulating the production of VEGF. We then demonstrated the uptake and delivery of the sugar from a range of experimental and commercial dressings. In conclusion, its pro-angiogenic properties combined with its improved stability on storage compared to VEGF, its low cost, and ease of incorporation into a range of established wound dressings make 2dDR an attractive alternative to VEGF for wound dressing development.

Combined in silico and 19F NMR analysis of 5-fluorouracil metabolism in yeast at low ATP conditions

The cytotoxic effect of 5-fluorouracil (5-FU) on yeast cells is thought to be mainly via a misincorporation of fluoropyrimidines into both RNA and DNA, not only DNA damage via inhibition of thymidylate synthase (TYMS) by fluorodeoxyuridine monophosphate (FdUMP). However, some studies on Saccharomyces cerevisiae show a drastic decrease in ATP concentration under oxidative stress, together with a decrease in concentration of other tri- and diphosphates. This raises a question if hydrolysis of 5-fluoro-2-deoxyuridine diphosphate (FdUDP) under oxidative stress could not lead to the presence of FdUMP and the activation of so-called 'thymine-less death' route. We attempted to answer this question with in silico modeling of 5-FU metabolic pathways, based on new experimental results, where the stages of intracellular metabolism of 5-FU in Saccharomyces cerevisiae were tracked by a combination of 19F and 31P NMR spectroscopic study. We have identified 5-FU, its nucleosides and nucleotides, and subsequent di- and/or triphosphates. Additionally, another wide 19F signal, assigned to fluorinated unstructured short RNA, has been also identified in the spectra. The concentration of individual metabolites was found to vary substantially within hours, however, the initial steady-state was preserved only for an hour, until the ATP concentration dropped by a half, which was monitored independently via 31P NMR spectra. After that, the catabolic process leading from triphosphates through monophosphates and nucleosides back to 5-FU was observed. These results imply careful design and interpretation of studies in 5-FU metabolism in yeast.

Kinetics and mechanistic study of competitive inhibition of thymidine phosphorylase by 5-fluoruracil derivatives

In a previous investigation, cationic liposomes formulated with new 5-FU derivatives, differing for the length of the polyoxyethylenic spacer that links the N(3) position of 5-FU to an alkyl chain of 12 carbon atoms, showed a higher cytotoxicity compared to free 5-FU, the cytotoxic effect being directly related to the length of the spacer. To better understand the correlation of the spacer length with toxicity, we carried out initial rate studies to determine inhibition, equilibrium and kinetic constants (KI, KM, kcat), and get inside inhibition activity of the 5-FU derivatives and their mechanism of action, a crucial information to design structural variations for improving the anticancer activity. The experimental investigation was supported by docking simulations based on the X-ray structure of thymidine phosphorylase (TP) from Escherichia coli complexed with 3'-azido-2'-fluoro-dideoxyuridin. Theoretical and experimental results showed that all the derivatives exert the same inhibition activity of 5-FU either as monomer and when embedded in lipid bilayer.

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.

Gli3 regulation of myogenesis is necessary for ischemia-induced angiogenesis

RATIONALE

A better understanding of the mechanism underlying skeletal muscle repair is required to develop therapies that promote tissue regeneration in adults. Hedgehog signaling has been shown previously to be involved in myogenesis and angiogenesis: 2 crucial processes for muscle development and regeneration.

OBJECTIVE

The objective of this study was to identify the role of the hedgehog transcription factor Gli3 in the cross-talk between angiogenesis and myogenesis in adults.

METHODS AND RESULTS

Using conditional knockout mice, we found that Gli3 deficiency in endothelial cells did not affect ischemic muscle repair, whereas in myocytes, Gli3 deficiency resulted in severely delayed ischemia-induced myogenesis. Moreover, angiogenesis was also significantly impaired in HSA-Cre(ERT2); Gli3(Flox/Flox) mice, demonstrating that impaired myogenesis indirectly affects ischemia-induced angiogenesis. The role of Gli3 in myocytes was then further investigated. We found that Gli3 promotes myoblast differentiation through myogenic factor 5 regulation. In addition, we found that Gli3 regulates several proangiogenic factors, including thymidine phosphorylase and angiopoietin-1 both in vitro and in vivo, which indirectly promote endothelial cell proliferation and arteriole formation. In addition, we found that Gli3 is upregulated in proliferating myoblasts by the cell cycle-associated transcription factor E2F1.

CONCLUSIONS

This study shows for the first time that Gli3-regulated postnatal myogenesis is necessary for muscle repair-associated angiogenesis. Most importantly, it implies that myogenesis drives angiogenesis in the setting of skeletal muscle repair and identifies Gli3 as a potential target for regenerative medicine.

Characterization of pyrimidine nucleoside phosphorylase of Mycoplasma hyorhinis: implications for the clinical efficacy of nucleoside analogues

In the present paper we demonstrate that the cytostatic and antiviral activity of pyrimidine nucleoside analogues is markedly decreased by a Mycoplasma hyorhinis infection and show that the phosphorolytic activity of the mycoplasmas is responsible for this. Since mycoplasmas are (i) an important cause of secondary infections in immunocompromised (e.g. HIV infected) patients and (ii) known to preferentially colonize tumour tissue in cancer patients, catabolic mycoplasma enzymes may compromise efficient chemotherapy of virus infections and cancer. In the genome of M. hyorhinis, a TP (thymidine phosphorylase) gene has been annotated. This gene was cloned, expressed in Escherichia coli and kinetically characterized. Whereas the mycoplasma TP efficiently catalyses the phosphorolysis of thymidine (Km=473 μM) and deoxyuridine (Km=578 μM), it prefers uridine (Km=92 μM) as a substrate. Our kinetic data and sequence analysis revealed that the annotated M. hyorhinis TP belongs to the NP (nucleoside phosphorylase)-II class PyNPs (pyrimidine NPs), and is distinct from the NP-II class TP and NP-I class UPs (uridine phosphorylases). M. hyorhinis PyNP also markedly differs from TP and UP in its substrate specificity towards therapeutic nucleoside analogues and susceptibility to clinically relevant drugs. Several kinetic properties of mycoplasma PyNP were explained by in silico analyses.

Transition state analysis of thymidine hydrolysis by human thymidine phosphorylase

Human thymidine phosphorylase (hTP) is responsible for thymidine (dT) homeostasis, and its action promotes angiogenesis. In the absence of phosphate, hTP catalyzes a slow hydrolytic depyrimidination of dT yielding thymine and 2-deoxyribose (dRib). Its transition state was characterized using multiple kinetic isotope effect (KIE) measurements. Isotopically enriched thymidines were synthesized enzymatically from glucose or (deoxy)ribose, and intrinsic KIEs were used to interpret the transition state structure. KIEs from [1'-(14)C]-, [1-(15)N]-, [1'-(3)H]-, [2'R-(3)H]-, [2'S-(3)H]-, [4'-(3)H]-, and [5'-(3)H]dTs provided values of 1.033 ± 0.002, 1.004 ± 0.002, 1.325 ± 0.003, 1.101 ± 0.004, 1.087 ± 0.005, 1.040 ± 0.003, and 1.033 ± 0.003, respectively. Transition state analysis revealed a stepwise mechanism with a 2-deoxyribocation formed early and a higher energetic barrier for nucleophilic attack of a water molecule on the high energy intermediate. An equilibrium exists between the deoxyribocation and reactants prior to the irreversible nucleophilic attack by water. The results establish activation of the thymine leaving group without requirement for phosphate. A transition state constrained to match the intrinsic KIEs was found using density functional theory. An active site histidine (His116) is implicated as the catalytic base for activation of the water nucleophile at the rate-limiting transition state. The distance between the water nucleophile and the anomeric carbon (r(C-O)) is predicted to be 2.3 A at the transition state. The transition state model predicts that deoxyribose adopts a mild 3'-endo conformation during nucleophilic capture. These results differ from the concerted bimolecular mechanism reported for the arsenolytic reaction (Birck, M. R.; Schramm, V. L. J. Am. Chem. Soc. 2004, 126, 2447-2453).

Antiangiogenic and antitumor activity of 6-(2-aminoethyl)amino-5-chlorouracil, a novel small-molecule inhibitor of thymidine phosphorylase, in combination with the vascular endothelial growth factor-trap

PURPOSE

Tumors produce multiple proangiogenic factors, making it unlikely that agents targeting a single angiogenic pathway will be sufficient to treat the spectrum of tumors that occur clinically. Platelet-derived endothelial cell growth factor has angiogenic activity in vitro and in vivo and is overexpressed in most human cancers, where its expression has been correlated with increased microvessel density, more aggressive tumors, and poorer patient prognosis. Platelet-derived endothelial cell growth factor is identical to the enzyme thymidine phosphorylase (TP), and unlike other angiogenic factors, the proangiogenic actions of TP are dependent on its enzyme activity.

EXPERIMENTAL DESIGN

A potent and specific small-molecule inhibitor of the catalytic activity of TP, 6-(2-aminoethyl)amino-5-chlorouracil (AEAC), was tested for antiangiogenic and antitumor activity in human cancer xenografts in vivo.

RESULTS

Oral administration of AEAC caused 40% to 50% reductions in the growth of A549 non-small cell lung cancer and PANC-1 pancreatic cancer xenografts, but it was not active against a second pancreatic tumor, BxPC-3. AEAC reduced the microvessel density in the tumors, providing evidence for an antiangiogenic action. Equal or better activity was seen when the mice were treated with the vascular endothelial growth factor (VEGF)-Trap, a soluble VEGF decoy receptor, and the combination of AEAC and VEGF-Trap produced additive antitumor activity that was significantly greater than the VEGF-Trap alone. In the A549 tumors, the combination produced tumor regressions.

CONCLUSION

These studies show antitumor activity for a drug targeting TP and suggest that inhibitors of TP could be used to augment the clinical efficacy of drugs targeting the VEGF pathway.

Molecular profile of androgen-independent prostate cancer xenograft LuCaP 23.1

After castration or therapeutic hormone deprivation, most cancer of the prostate (CaP) cells develop androgen-independent (AI) growth. In this work, we studied the effect of androgen depletion (castration) on the growth of experimental model LuCaP 23.1 xenograft. A total of 101 nude mice were implanted and analysed for their growth profile before experimental period 1 (11 weeks) and after castration experimental period 2 (15 weeks). For specific periods, tumors were harvested and assessed for molecular marker expression specific for CaP. Taking into account tumor dynamic growth, prior to castration we found 37 fast growing (FG) tumors (948.9+/-76.9 mm3) and 63 slow growing (SG) tumors (229.6+/-18.4 mm3). Real-time quantitative RT-PCR showed that in comparison to SGs, FGs contained elevated expression of epidermal growth factor receptor type 1 (HER1), urokinase plasminogen activator (uPA), thymidine phosphorylase (TP) and thymidilate synthase (TS) mRNAs expression and low levels of 5alpha-reductase 2 (5alpha-R2) mRNA. After castration all FG tumors progressed rapidly (by 5 weeks) to AI growth (FG-P). In SG castrated tumors, 66% of tumors showed retarded progression (by 12 weeks) to AI (SG-P), whereas 34% responded to castration (SG-R). Molecular analysis demonstrated distinct molecular profiles integrating different pathways associated with AI progression. The progressive tumors FG-P, and some tumors of SG-P subgroup, presented significantly high levels of HER1, epidermal growth factor receptor type 2 (HER2), TS, uPA, TP, tumor necrosis factor superfamily member 6 (FAS) and peptidylglycine alpha-amidating mono-oxygenase (PAM) mRNA all of which correlated with androgen receptor (AR) mRNA. The second subgroup of SG-P tumors showed a high expression of the anti-apoptotic gene Bcl-2. A third subgroup of SG-P tumors showed significant expression of hypoxia-related genes such as adrenomedullin (AM) after castration. LuCaP 23.1 xenograft represent a useful dynamic model to study pre-clinically new therapeutic molecules and evaluate non-randomized therapeutics protocols combining different target inhibition specific to each AI pathways.

Interferons upregulate thymidine phosphorylase expression via JAK-STAT-dependent transcriptional activation and mRNA stabilization in human glioblastoma cells

Overexpression of the angiogenic enzyme thymidine phosphorylase (TP) in tumor cells and/or infiltrating macrophages correlates with increased microvessel density and poor prognosis in various tumor types including glioma. The present study examined how the TP gene expression is regulated by different types of interferons (IFNs) in human T98G and A172 glioblastoma cells. Both type I (alpha, beta) and type II (gamma) IFNs upregulated TP mRNA and protein expression while inhibiting cell proliferation. IFN-induced TP mRNA accumulation was not inhibited by the protein synthesis inhibitor cycloheximide, but was strongly blocked by the transcription inhibitor actinomycin D, as well as by transcription factor decoy oligodeoxynucleotides containing the putative IFN response element or the gamma-activated sequence in the TP promoter. The Janus kinase (JAK) inhibitor AG-490 blocked both IFN-induced STAT1 (signal transducers and activators of transcription 1) phosphorylation and TP expression. All IFNs increased the stability of TP mRNA as well. In addition, IFN-evoked TP enzyme activity enhanced the cytotoxicity of 5-fluorouracil (5-FU). These findings indicate that TP expression may be upregulated by IFNs via the JAK-STAT signaling pathway and both transcriptional and posttranscriptional mechanisms. Combined treatment with IFN and 5-fluorouracil may be a useful therapeutic strategy for malignant gliomas.

Human deoxycytidine kinase as a deoxyribonucleoside phosphorylase

Human deoxycytidine kinase (dCK) is a key enzyme in the 5'-phosphorylation of purine and pyrimidine deoxynucleosides with deoxycytidine as the most efficient substrate. The ability of dCK to degrade 2'-deoxyribonucleosides to free nucleobases and 2-deoxy-alpha-d-ribofuranose-1-phosphate was demonstrated by 1H-31P correlation spectroscopy and by isotope enzyme kinetic methods. The reaction depended on inorganic phosphate, and dCK showed maximum cleavage activity between pH 7 and pH 8. In this pH range, [HPO4(2-)] is the dominant phosphate species, most likely being the phosphate donor. All natural deoxyribonucleosides could be cleaved and the Vmax of the phosphorylytic reaction compared to the kinase reaction was about 2-10%. The formation of free nucleobases occurred only with reduced dCK, because the reaction was highly dependent on the presence of reducing agents such as dithiotreitol. Thus, recombinant dCK can act as a phosphorylase, similar to the nucleoside phosphorylase family of enzymes. This catalytic activity is important for the design of in vitro experiments with dCK, such as crystallization and NMR spectroscopy.

Expression of the Angiogenic Factor Thymidine Phosphorylase in THP-1 Monocytes: Induction by Autocrine Tumor Necrosis Factor-α and Inhibition by Aspirin

The angiogenic factor thymidine phosphorylase (TP) is highly expressed in human monocytes and macrophages, and its expression has been linked to the pathology and progression of solid tumors, rheumatoid arthritis, and gastric ulcers. In this study, TP mRNA and enzyme activity were found to be up-regulated upon the induction of differentiation of the human monocyte cell line THP-1 by phorbol 12-myristate 13-acetate (PMA). TP expression in THP-1 cells was similarly increased by tumor necrosis factor-alpha (TNFalpha). Because monocytes and macrophages are a predominant source of TNFalpha, the up-regulation of TP upon THP-1 differentiation could have been caused by the autocrine production of TNFalpha. In support of this hypothesis, PMA increased TNFalpha mRNA levels; furthermore, the increase in TP expression with PMA treatment was partially blocked by a neutralizing antibody to TNFalpha, particularly at the earlier time points. This data also suggested there may be additional mechanisms regulating TP expression upon PMA treatment of the cells. The induction of TP by TNFalpha was mimicked by an antibody to the TNFalpha receptor R2 (TNF-R2; p75), but not by an antibody to TNF-R1 (p55), suggesting that the TNF-R2 plays a role in the regulation of TP expression. The PMA-induced increase in TP expression was blocked by aspirin but not by the related agent indomethacin, suggesting that aspirin's effect was not caused by the inhibition of cellular cyclooxygenases. An alternative mechanism by which aspirin inhibits gene expression is the modulation of the transcription factor NFkappaB, and the TNFalpha-induced increase in TP mRNA was blocked by a cell-permeable NFkappaB inhibitory peptide. Furthermore, TNFalpha increased and aspirin (but not indomethacin) decreased NFkappaB DNA-binding activity in THP-1 cells. In conclusion, the modulation of TP expression in monocytes by pro- and anti-inflammatory agents suggests that its angiogenic-related actions could contribute to the inflammatory response associated with a number of pathophysiological conditions.

Thymidine phosphorylase and 2-deoxyribose stimulate human endothelial cell migration by specific activation of the integrins alpha 5 beta 1 and alpha V beta 3

Thymidine phosphorylase is an angiogenic factor that is frequently overexpressed in solid tumors, in rheumatoid arthritis, and in response to inflammatory cytokines. Our previous studies showed that cells expressing thymidine phosphorylase stimulated endothelial cell migration in vitro. This was a consequence of the intracellular metabolism of thymidine by thymidine phosphorylase and subsequent extracellular release of 2-deoxyribose. The mechanisms by which 2-deoxyribose might mediate thymidine phosphorylase-induced cell migration in vitro, however, are obscure. Here we show that both thymidine phosphorylase and 2-deoxyribose stimulated the formation of focal adhesions and the tyrosine 397 phosphorylation of focal adhesion kinase in human umbilical vein endothelial cells. Although similar actions occurred upon treatment with the angiogenic factor vascular endothelial growth factor (VEGF), thymidine phosphorylase differed from VEGF in that its effect on endothelial cell migration was blocked by antibodies to either integrin alpha 5 beta 1 or alpha v beta 3, whereas VEGF-induced endothelial cell migration was only blocked by the alpha v beta 3 antibody. Further, thymidine phosphorylase and 2-deoxyribose, but not VEGF, increased the association of both focal adhesion kinase and the focal adhesion-associated protein vinculin with integrin alpha 5 beta 1 and, in intact cells, increased the co-localization of focal adhesion kinase with alpha 5 beta 1. Thymidine phosphorylase and 2-deoxyribose-induced focal adhesion kinase phosphorylation was blocked by the antibodies to alpha 5 beta 1 and alpha v beta 3, directly linking the migration and signaling components of thymidine phosphorylase and 2-deoxyribose action. Cell surface expression of alpha 5 beta 1 was also increased by thymidine phosphorylase and 2-deoxyribose. These experiments are the first to demonstrate a direct effect of thymidine phosphorylase and 2-deoxyribose on signaling pathways associated with endothelial cell migration.

The Sp1 transcription factor contributes to the tumor necrosis factor-induced expression of the angiogenic factor thymidine phosphorylase in human colon carcinoma cells

Thymidine phosphorylase (TP; also known as platelet-derived endothelial cell growth factor, PD-ECGF) is an angiogenic factor that is chemotactic for endothelial cells and has been found to induce neovascularization in vivo. TP is frequently overexpressed in human solid tumors, where its expression has been correlated with increased tumor microvessel density, invasion, and metastasis, and shorter patient survival. In this report, TP activity in the WiDr colon carcinoma cell line was found to be induced 100-fold by tumor necrosis factor (TNFalpha), a secretory product of activated macrophages that has indirect angiogenic activities. Increased TP activity was accompanied by increased TP mRNA levels and without an increase in mRNA stability. TNFalpha-induced TP mRNA levels were reduced by mithramycin, a DNA-binding transcription inhibitor specific for GC-rich sequences. Transcriptional regulation by TNFalpha was confirmed by transient transfection of WiDr with upstream TP sequences in a luciferase reporter construct. Deletion analysis of the reporter pinpointed two regions of the TP promoter with regulatory elements for both TNFalpha-inducible and basal expression, and they contained, respectively, three and one consensus binding sites for the Sp1-family of transcription factors. One additional region contributed only to basal TP expression, and it contained three Sp1 sites. TNFalpha-induced TP expression decreased when point mutations were made in three of the four Sp1 sites postulated to contribute to both basal and TNFalpha-inducible expression. Electrophoretic mobility shift assays further demonstrated binding of nuclear Sp1 to these three sites. Sp1-binding activity was also increased in cells treated with TNFalpha. These studies establish a role for Sp1 in the regulation of expression of the angiogenic factor TP in colon cancer WiDr cells.

Helicobacter pylori infection and expression of the angiogenic factor platelet-derived endothelial cell growth factor by pre-neoplastic gastric mucosal lesions and gastric carcinoma

BACKGROUND

Expression of the angiogenic factor platelet-derived endothelial cell growth factor is induced in some gastric carcinomas. Whether angiogenesis is induced early in the development of gastric pre-neoplastic lesions and whether Helicobacter pylori infection affects platelet-derived endothelial cell growth factor expression is not known.

AIM

To assess whether chronic gastritis, intestinal metaplasia, gastric dysplasia and gastric carcinomas express platelet-derived endothelial cell growth factor and whether Helicobacter pylori infection might affect the expression of platelet-derived endothelial cell growth factor in these lesions.

PATIENTS AND METHODS

Patients with gastric carcinomas, atrophic gastritis with associated intestinal metaplasia, dysplasia and controls without infection or carcinoma were studied.

RESULTS

Platelet-derived endothelial cell growth factor was detected by immunohistochemistry in 9 out 19 gastric carcinomas (45%). Only focal immunostaining was detected in intestinal metaplasia adjacent to dysplasia and in dysplastic cells. Of the tumours, 90% contained platelet-derived endothelial cell growth factor-positive interstitial cells. A significant correlation was found between active Helicobacter pylori infection and a larger number of platelet-derived endothelial cell growth factor-positive interstitial cells in areas of intestinal metaplasia (p<0.05).

CONCLUSION

Helicobacter pylori infection does not influence the expression of platelet-derived endothelial cell growth factor, once gastric cancer has developed. However, Helicobacter pylori infection may increase the extension of expression of platelet-derived endothelial cell growth factor by infiltrating interstitial cells in premalignant lesions, such as intestinal metaplasia, which may help create a favourable environment for tumour development. This may possibly be due to non-specific increase in recruitment of inflammatory cells caused by Helicobacter pylori infection. Further studies, with a larger number of samples, are now needed in order to confirm this finding.

Synthesis and enzymatic evaluation of pyridinium-substituted uracil derivatives as novel inhibitors of thymidine phosphorylase

A series of water soluble N(1)- and C(6)-substituted uracil pyridinium compounds were prepared as potential inhibitors of thymidine phosphorylase (TP). The C(6)-uracil substituted derivatives were the most active. 1-[(5-Chloro-2,4-dihydroxypyrimidin-6-yl)methyl]pyridinium chloride, was identified as the best inhibitor being 5-fold more potent than the known inhibitor, 6-amino-5-bromouracil.

Novel 6-substituted uracil analogs as inhibitors of the angiogenic actions of thymidine phosphorylase

Thymidine phosphorylase (TP) catalyzes the reversible phosphorolysis of thymidine and other pyrimidine 2'-deoxyribonucleosides. In addition, TP has been shown to possess angiogenic activity in a number of in vitro and in vivo assays, and its angiogenic activity has been linked to its catalytic activity. A series of 5- and 6-substituted uracil derivatives were synthesized and evaluated for their abilities to inhibit TP activity. Among the most active compounds was a 6-amino-substituted uracil analog, 6-(2-aminoethyl)amino-5-chlorouracil (AEAC), which was a competitive inhibitor with a K(i) of 165 nM. The inhibitory activity of AEAC was selective for TP, as it did not inhibit purine nucleoside phosphorylase or uridine phosphorylase at concentrations up to 1 mM. Human recombinant TP induced human umbilical vein endothelial cell (HUVEC) migration in a modified Boyden chamber assay in vitro, and this action could be abrogated by the TP inhibitors. The actions of the inhibitors were specific for TP, as they had no effect on the chemotactic actions of vascular endothelial growth factor (VEGF). HUVEC migration was also induced when TP-transfected human colon and breast carcinoma cells were co-cultured in the Boyden chamber assay in place of the purified angiogenic factors, and a TP inhibitor blocked the tumor cell-mediated migration almost completely. These studies suggest that inhibitors of TP may be useful in pathological conditions that are dependent upon TP-driven angiogenesis.

Thymidine phosphorylase expression correlates with tumor differentiation and Bcl-2 in invasive breast cancer

BACKGROUND

Angiogenesis plays an important role in the growth and metastasis of solid tumors. Several angiogenic factors have been identified, and thymidine phosphorylase (TP) is thought to be one such factor. To date, little information is available on the relationship between TP and other clinicopathological variables.

METHODS

Formalin-fixed, paraffin-embedded materials from 116 primary breast carcinomas were used. The expression of TP, estrogen receptor, Bcl-2, Bax, p53, c-erbB-2 and MIB-1 was examined by immunohistochemical methods.

RESULTS

Nuclear and/or cytoplasmic TP expression was observed in the neoplastic cells, and accentuation of TP was often present at the infiltrating tumor edge and intraductal spread region. Tumor cell TP expression was significantly inversely correlated with histological grade (p< 0.05) and positively correlated with Bcl-2 expression, but no association with other tumor variables was found.

CONCLUSIONS

TP is associated with Bcl-2 expression and tumor differentiation in breast cancer. TP may be a new prognostic parameter for breast cancer.

Kinetic analysis of novel multisubstrate analogue inhibitors of thymidine phosphorylase

A kinetic analysis was performed for the novel 1-(8-phosphonooctyl)-6-amino-5-bromouracil and 1-(8-phosphonooctyl)-7-deazaxanthine inhibitors of Escherichia coli thymidine (dThd) phosphorylase (TPase). The structure of the compounds was rationally designed based on the available crystal structure coordinates of bacterial TPase. These inhibitors reversibly inhibited TPase. Kinetic analysis revealed that the compounds inhibited TPase in a purely competitive or mixed fashion not only when dThd, but also when inorganic phosphate (Pi), was used as the variable substrate. In contrast, the free bases 6-amino-5-bromouracil and 7-deazaxanthine behaved as non-competitive inhibitors of the enzyme in the presence of variable Pi concentrations while being competitive or mixed with respect to thymine as the natural substrate. Our kinetic data thus revealed that the novel 1-(8-phosphonooctyl)pyrimidine/purine derivatives are able to function as multisubstrate inhibitors of TPase, interfering at two different sites (dThd(Thy)- and phosphate-binding site) of the enzyme. To our knowledge, the described compounds represent the first type of such multisubstrate analogue inhibitors of TPase; they should be considered as lead compounds for the development of mechanistically novel type of TPase inhibitors.

Epidermal and fibroblast growth factors enhance fibrovascular integration of porous polyethylene implants

PURPOSE

Porous implants used in functional and aesthetic reconstruction of the orbit, face, and cranium are less likely to develop complications after they become biointegrated. We investigated whether the administration of exogenous growth factors could increase the rate of implant integration.

METHODS

High-density porous polyethylene cubes were placed in dorsal paraspinal muscles of rabbits, and daily transcutaneous injections of saline, epidermal growth factor, or basic fibroblast growth factor were administered directly over the cubes for 10 days. At serial time points up to 10 weeks, cubes were explanted and the fibroblasts present at the center of the cubes were counted.

RESULTS

Injections of epidermal growth factor and basic fibroblast growth factor increased the rate at which fibroblasts accumulated in porous polyethylene implants and decreased the time required to achieve a maximal rate of cellular accumulation within the cubes. At 4 weeks, when all cell populations had attained a linear rate of accumulation, cubes previously injected with saline, epidermal growth factor, or basic fibroblast growth factor contained an average of 10, 40, and 80 cells per 0.0156 mm2, at their centers, respectively.

CONCLUSIONS

Enhancement of the rate of biointegration of porous polyethylene cubes in rabbits is achievable by repeated, transcutaneous administration of exogenous growth factors.

Novel nonsubstrate inhibitors of human thymidine phosphorylase, a potential target for tumor-dependent angiogenesis

Thymidine phosphorylase/platelet-derived endothelial cell growth factor (TP/PD-ECGF) is an enzyme involved in thymidine metabolism and homeostasis, and its catalytic activity appears to play an important role in angiogenesis. Here we describe the cloning and expression of a His-tagged human TP/PD-ECGF and its assay with uracil and thymine analogues. We present the design, synthesis, and biological evaluation of novel 6-(phenylalkylamino)uracil derivatives which, at micromolar concentrations, inhibit both catabolic and anabolic reactions of human TP in vitro. These base analogues are not converted by the enzyme into the nucleoside form, thus representing pure nonsubstrate inhibitors of the enzyme.

Expression of platelet-derived endothelial cell growth factor/thymidine phosphorylase in human gallbladder lesions

The aim of this study was to investigate the expression of platelet-derived endothelial growth factor (PD-ECGF) in human gallbladder carcinomas to elucidate its role in angiogenesis and tumour progression. To this end, 56 archival surgical specimens of gallbladder lesions were examined for PD-ECGF/thymidine phosphorylase (TP) expression by immunohistochemistry and the PD-ECGF/TP protein level was assessed in five fresh specimens of gallbladder carcinoma by enzyme-linked immunosorbent assay (ELISA). Hyperplastic epithelial cells and adenoma cells showed no or faint staining with PD-ECGF/TP. Out of 43 gallbladder carcinomas, 27 (63%) showed moderate to strong immunoreactivity in the cytoplasm and nuclei of the tumour cells. PD-ECGF/TP immunoreactivity in stromal infiltrating cells was detected in 43% (3/7) hyperplasias, 17% (1/6) adenomas and 86% (37/43) carcinomas. PD-ECGF/TP protein levels in carcinoma tissues were higher than those in corresponding normal mucosa. PD-ECGF/TP expression did not correlate with angiogenesis, but significantly correlated with depth of invasion, lymph node metastasis, and tumour stage. These results overall suggest that PD-ECGF/TP produced by both cancer cells and infiltrating cells is associated with tumour progression in human gallbladder carcinoma.

Thymidine phosphorylase: its role in sensitivity and resistance to anticancer drugs

Thymidine phosphorylase (TP) is an angiogenic enzyme present in normal tissues. Increased levels are found in many tumors, in stromal cells, tumor cells or both. High tumor TP levels may confer a poor prognosis. Cytokines (including interferons), tissue hypoxia and low pH increase TP levels. The influence of tumor TP on fluoropyrimidine toxicity is variable, but capecitabine is a prodrug of fluorouracil that requires activation by TP and hence may have a higher therapeutic index than other fluoropyrimidines. Folate-based thymidylate synthase inhibitors may also be more effective in tumors with a high TP because of increased degradation of endogenous thymidine. Copyright 1999 Harcourt Publishers Ltd.

Induction and Suppression of Endothelial Cell Apoptosis by Sphingolipids: A Possible In Vitro Model for Cell-Cell Interactions Between Platelets and Endothelial Cells

Because sphingosine (Sph) is actively incorporated into platelets and rapidly converted to sphingosine 1-phosphate (Sph-1-P), which is then released extracellularly, it is important to study the effects of Sph and Sph-1-P on endothelial cells from the viewpoint of platelet-endothelial cell interaction. In this study, we found that Sph, as well as ceramide, induces apoptosis in human umbilical vein endothelial cells (HUVECs). In contrast, Sph-1-P acts as a HUVEC survival factor; this bioactive lipid was shown to protect HUVECs from apoptosis induced by the withdrawal of growth factors and to stimulate HUVEC DNA synthesis. In metabolic studies, [3H]Sph, incorporated into HUVECs, was converted to [3H]Cer and further to [3H]sphingomyelin in a time-dependent manner, whereas [3H]Sph-1-P formation from [3H]Sph was weak and transient. These findings in HUVECs are very different from those of platelets, which possess a highly active Sph kinase but lack Sph-1-P lyase. As a result, platelets abundantly store Sph-1-P, whereas HUVECs contain much less Sph-1-P. Finally, HUVECs, in contrast to platelets, failed to release Sph-1-P extracellularly, indicating that HUVECs themselves are not able to supply the survival factor Sph-1-P, but receive it from activated platelets. Our results suggest that platelets may maintain the integrity of endothelial cells by incorporating Sph and releasing Sph-1-P.

Induction and Suppression of Endothelial Cell Apoptosis by Sphingolipids: A Possible In Vitro Model for Cell-Cell Interactions Between Platelets and Endothelial Cells

Because sphingosine (Sph) is actively incorporated into platelets and rapidly converted to sphingosine 1-phosphate (Sph-1-P), which is then released extracellularly, it is important to study the effects of Sph and Sph-1-P on endothelial cells from the viewpoint of platelet-endothelial cell interaction. In this study, we found that Sph, as well as ceramide, induces apoptosis in human umbilical vein endothelial cells (HUVECs). In contrast, Sph-1-P acts as a HUVEC survival factor; this bioactive lipid was shown to protect HUVECs from apoptosis induced by the withdrawal of growth factors and to stimulate HUVEC DNA synthesis. In metabolic studies, [3H]Sph, incorporated into HUVECs, was converted to [3H]Cer and further to [3H]sphingomyelin in a time-dependent manner, whereas [3H]Sph-1-P formation from [3H]Sph was weak and transient. These findings in HUVECs are very different from those of platelets, which possess a highly active Sph kinase but lack Sph-1-P lyase. As a result, platelets abundantly store Sph-1-P, whereas HUVECs contain much less Sph-1-P. Finally, HUVECs, in contrast to platelets, failed to release Sph-1-P extracellularly, indicating that HUVECs themselves are not able to supply the survival factor Sph-1-P, but receive it from activated platelets. Our results suggest that platelets may maintain the integrity of endothelial cells by incorporating Sph and releasing Sph-1-P.

Angiogenesis and expression of thymidine phosphorylase by inflammatory and carcinoma cells in ductal carcinoma in situ of the breast

Angiogenesis is essential for tumour growth and important in metastasis and for prognosis in invasive carcinoma of the breast. Two patterns of increased vascularity have been shown in mammary ductal carcinoma in situ (DCIS): a cuff of vessels close to the involved ducts, and vessels in the interductal stroma. Inflammation may potentially promote angiogenesis by release of angiogenic factors and digestive enzymes. A correlation has previously been found between the intensity of perivascular inflammation and stromal vascularity in DCIS, but no strong relationship has been observed between inflammation and angiogenesis in invasive carcinoma. Tumour angiogenesis is regulated by a number of angiogenic factors, including thymidine phosphorylase (platelet-derived endothelial cell growth factor), which is expressed at high levels in macrophages. Using immunohistochemical methods, thymidine phosphorylase expression and vascularity have been studied in DCIS (n = 34) and invasive carcinoma (n = 32). Stromal vascularity in DCIS was associated with thymidine phosphorylase expression in the perivascular inflammatory cells and in the cytoplasm of carcinoma cells. In invasive carcinoma, no relationship was found between vascularity and thymidine phosphorylase expression in either the carcinoma or the inflammatory cells. This study suggests that thymidine phosphorylase expression in both inflammatory and carcinoma cells may contribute to one of the patterns of vascularity in DCIS, but not in invasive disease.

Thymidine phosphorylase activity and prodrug effects in a three-dimensional model of angiogenesis: implications for the treatment of ovarian cancer

Platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP) is associated with angiogenesis and the progression of human ovarian cancer. The enzyme converts thymidine to thymine and 2'-deoxyribose-1-phosphate and can also metabolize the prodrug 5'-deoxy-5-fluorouridine (Furtulon) to 5-fluorouracil and 5'-deoxy-D-ribose-1-phosphate. The aim of this study was to obtain information about the activities of Furtulon in an established three-dimensional model of angiogenesis. The plan was to study partial and complete effects of Furtulon (in the absence and presence of PD-ECGF/TP or ovarian cancer cyst fluids) on the formation and destruction of microvessels from cultured segments of rat aorta in serum-free media. The endpoint was the number and form of microvessels compared with controls after 4, 7, 11, and 14 (and sometimes 17) days in culture. Furtulon (10 micromol/L) gradually reduced the size and number of microvessels over 17 days of culture (100 micromol/L significantly reduced the number by day 4). PD-ECGF/TP (10 ng/ml) and ovarian cancer cyst fluids (2% in medium, v/v) stimulated the production of microvessels. The culture of explants with Furtulon and PD-ECGF/TP or ovarian cancer cyst fluids (from day 1 or day 11 of culture) enhanced the vasoclastic activity of the drug. The effect of Furtulon at the highest dose (1000 micromol/L) or at a lower dose (100 micromol/L) in the presence of ovarian cancer cyst fluid was not reversible after culture day 11.

Expression of platelet-derived endothelial cell growth factor (PD-ECGF) and its mRNA in uterine endometrial cancers

To determine the potential of growth, invasion and metastasis of uterine endometrial cancer cells associated with neovascularization, the expressions of platelet-derived endothelial cell growth factor (PD-ECGF) and its mRNA in uterine endometrial cancers and in normal uterine endometria as controls were determined and the relationship between their expressions and histological grades, grades of myometrial invasion and clinical stages of uterine endometrial cancers was analyzed. The levels of PD-ECGF were significantly higher in uterine endometrial cancers of well-differentiated grade (G1) with invasion to < or =1/2 myometrium (B) and of stage 1 than in those of moderately and poorly differentiated grades (G2 and G3, respectively) limited to endometrium (A) and with invasion to >1/2 myometrium (C) and of stages II and III/IV and in normal uterine endometria. There was no significant difference in the levels between uterine endometrial cancers of G2 and G3, A and C, or stages II and III/IV and normal uterine endometria. Therefore, the active availability of PD-ECGF might contribute to the acceleration of angiogenic activity in the early process of invasion of well-differentiated uterine endometrial cancers.

Significance of angiogenesis in cancer therapy

BACKGROUND

For most solid tumours, surgery remains the most effective primary treatment. Despite apparently curative resection, significant numbers of patients develop secondary disease due to growth of undetected micrometastases. The ability of a tumour to metastasize is related to the degree of angiogenesis it induces. In addition, micrometastases rely on new vessel formation to provide the nutrients necessary for growth. A better understanding of how tumours acquire their blood supply may lead to more effective adjuvant therapies and improve survival following surgery.

METHODS

A systematic review of the literature on angiogenesis between 1971 and 1997 was performed using the Medline database to ascertain current thinking on angiogenesis and its relevance in oncological surgery.

RESULTS

Angiogenesis is a physiological process subject to autocrine and paracrine regulation which has the potential to become abnormal and play a part in a number of pathological states, including cancer. Increased angiogenic stimuli in the perioperative period, associated with concomitant reduction in tumour-derived antiangiogenic factors following resection of a primary tumour, result in a permissive environment which allows micrometastases to grow.

CONCLUSION

Recognition of the role of angiogenesis in metastatic tumour growth represents a significant development in our understanding of tumour biology. The development of antiangiogenic agents offers new promise in the treatment of malignancy. Such agents may prevent or control the development and growth of primary and metastatic tumours.

Stromal angiogenesis in human glioma: a role of platelet-derived endothelial cell growth factor

BACKGROUND

Although several tumor angiogenic factors have been identified previously and characterized, it is not yet fully clear how tumor angiogenic factors induce endothelial cell transformation and proliferation. Platelet-derived endothelial cell growth factor (PD-ECGF) has been recently discovered to be an endothelial cell growth factor initially purified from human platelets. However, there has been no previous report describing the significance of PD-ECGF in the growth of brain tumors by angiogenic stimulation. We report the immunohistochemical localization of PD-ECGF in human gliomas and meningiomas, and discuss whether PD-ECGF could play a role in the modulation of stromal angiogenesis in human glioblastoma multiforme.

METHODS

Twenty-eight cases of glioma (11 glioblastomas and 17 astrocytomas) derived from the neuroectoderm in embryogenesis and 12 meningiomas from the mesoderm were investigated by both immunohistochemical localization of the PD-ECGF and a semiquantitative assay to determine the degree of stromal angiogenesis.

RESULTS

Numerous PD-ECGF positive cells were observed within and around the blood vessels of glioblastoma multiforme, especially on the borders of tumor tissue. The PD-ECGF positive cells were negative for anti-von Willebrand factor (vWF) and antiglial fibrillary acidic protein (GFAP) antibodies and were positive for antimacrophage (HAM-56). The expression of PD-ECGF by macrophages closely correlated with the degree of stromal vascularity in glioblastoma multiforme; no such correlation was found in either astrocytoma or meningioma. Proliferating cell nuclear antigen (PCNA) was found to be positive in some endothelial cells of stromal vessels in glioblastoma multiforme. These findings suggest that PD-ECGF expressed by macrophages plays an important role in the growth of glioblastoma multiforme with stromal angiogenesis.

Platelet-derived endothelial cell growth factor/thymidine phosphorylase immunohistochemical expression in lymphoid tissue and lymphoid malignancies

The catabolic enzyme thymidine phosphorylase (TP) plays a crucial role in nucleic acid metabolism by regulating the availability of thymidine. Platelet-derived endothelial cell growth factor (PD-ECGF) is an angiogenic factor that was recently shown to be TP. The angiogenic properties of PD-ECGF/TP are attributable to a reduction of thymidine levels that results in a promotion of endothelial cell proliferation. Early studies showed a higher concentration of TP in macrophages than in parenchymal cells and in neoplastic than in nonneoplastic tissues. We examined the immunohistochemical expression of PD-ECGF/TP in reactive lymphoid tissues (lymph node and tonsil), as well as in a series of 20 cases of Hodgkin's disease and 31 cases of non-Hodgkin's lymphomas. Macrophages, sinus lining cells, and cells with dendritic morphology, of both follicular dendritic and interdigitating reticular cell type, presented a prominent nuclear and cytoplasmic positivity in reactive lymphoid tissue and in malignant lymphomas. Small lymphocytes and the neoplastic population were always negative, whereas endothelial staining was variable and showed no correlation to the type or grade of the lymphomas. In Hodgkin's disease (with the exception of the nodular lymphocyte predominance type) and some cases of high-grade non-Hodgkin's lymphomas, the positive dendritic cells formed a dense meshwork closely surrounding the neoplastic population. Our results suggest that the reported upregulation of PD-ECGF/TP activity in lymphoid malignancies is attributable to the nonneoplastic population, especially to cells of dendritic morphology.

Tumor cell motility and metastasis : Autocrine motility factor as an example of ecto/exoenzyme cytokines

Cellular locomotion plays a critical role in such normal processes as embryonic development, tissue segregation, as well as the infiltration of fibroblasts and vascular cells during wound repair and the inflammatory responses of the adult immune system. During tumor invasion and metastasis the processes of cell migration achieve dire significance. Disruption of normal homeostatic mechanisms to benefit the survival of the individual tumor cell is a common theme discovered during the characterization of factors once thought to be tumor-specific. One such molecule, tumor cell autocrine motility factor, was so described and has only recently been identified as a normal protein involved in intracellular glycolysis as well as implicated as an extracellular effector of normal cell functions including survival of certain populations of neurons. This molecule represents a member of the newly emerging family of intracellular enzymes whose disparate functions as extracellular mediators of cellular responses defines a new class of ecto/exoenzymes which play a role in normal cellular processes and are inappropriately utilized by tumor cells to elicit new survival strategies.

Up-regulation of thymidine phosphorylase expression is associated with a discrete pattern of angiogenesis in ductal carcinomas in situ of the breast

Angiogenesis is essential for tumour growth and metastasis. Although vascular density as a measure of angiogenesis is an important prognostic factor in invasive breast carcinoma, the mechanism of a switch to an angiogenic phenotype in ductal in situ breast carcinomas (DCIS) has yet to be identified. Nevertheless, two distinct vascular patterns have been reported in DCIS: a diffuse increase of stromal vascularity and a dense rim of microvessels close to the basement membrane of involved ducts. This suggests that tumour angiogenesis in invasive breast cancer arises from two different angiogenic pathways. Platelet-derived endothelial cell growth factor, now known to be thymidine phosphorylase (TP), is a candidate for initiating one of these pathways, since it is important in remodelling the existing vasculature through its chemotactic non-mitogenic properties and is expressed early in breast cancer development. The expression of TP was therefore examined in 75 formalin-fixed, paraffin-embedded specimens of DCIS by immunohistochemistry, using the monoclonal antibody PGF44c to detect TP. The results were correlated with blood vessel staining by polyclonal antibodies to von Willebrand factor (Factor VIII-related antigen, FVIIIrAg) and other clinicopathological variables. TP expression was nuclear and/or cytoplasmic and was observed in all subtypes of DCIS. High TP expression was demonstrated in 36 per cent (27/75) of tumours. This was not limited to the neoplastic cells, but was also present in stroma, endothelium, and tumour-associated macrophages. There was no correlation between high TP and DCIS subtype (P > 0.05). There was a significant correlation between TP expression and the presence of a dense vascular rim (P = 0.042; chi 2 = 4.1), but not with an increase in stromal vascularity (P = 0.800; chi 2 = 0.1). There was no significant correlation between tumour TP expression and relapse-free survival (P = 0.662; chi 2 = 0.2). These findings suggest that remodelling of the pre-existing vascular network induced by TP is important in generating a dense rim of microvessels around DCIS.

Angiogenesis as a biologic and prognostic indicator in human breast carcinoma

In this review we describe angiogenesis pathways involved in the development of breast carcinoma. Different assessment techniques for angiogenesis and their optimisation are discussed. Angiogenesis is an important factor for prognosis and will be increasingly important in therapeutic decisions.

Enhancement of drug sensitivity and a bystander effect in PC-9 cells transfected with a platelet-derived endothelial cell growth factor thymidine phosphorylase cDNA

5'-Deoxy-5-fluorouridine (5'-DFUR) and 1-(tetrahydro-2-furyl)-5-fluorouracil (tegafur), prodrugs of 5-fluorouracil (5-FU), are anticancer agents activated by thymidine phosphorylase (dThdPase). As it is well known that the levels of dThdPase are higher in tumours than in normal tissue, it should be advantageous to use such pyrimidine antimetabolites for the selective inhibition of tumour growth. However, tumours are not necessarily sensitive to 5'-DFUR and tegafur because their levels of dThdPase vary. In this study, we examined whether transfection of tumour cells with a human platelet-derived endothelial cell growth factor (PD-ECGF) complementary DNA (cDNA) expressing dThdPase would sensitize the cells to the cytotoxic effects of pyrimidine antimetabolites in vitro. A cDNA encoding PD-ECGF was transfected into PC-9 cells (human lung adenocarcinoma). The transfected cells, PC9-DPE2, had a more than 50 times higher activity of dThdPase than the parental PC-9 cells or control PC-9 cells transfected with the pcDNA3 vector alone (PC9-D1). They were more sensitive than parental PC-9 or PC9-D1 cells not only to 5'-DFUR and tegafur but also to 5-FU. In addition, we demonstrated that PC9-DPE2 cells are able to potentiate the cytotoxic effects of 5'-DFUR towards co-cultured parental PC-9 cells. This "bystander effect' did not require cell-cell contact. These results suggest that transfection of PD-ECGF (dThdPase) genes may be useful as a gene therapy strategy for cancer treatment.

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.

Tumor angiogenesis and expression of thymidine phosphorylase/platelet derived endothelial cell growth factor in human gastric carcinoma

To investigate the relationship between tumor angiogenesis and the expression of platelet-derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/dThdPase) and between patients' survival and the expression of PD-ECGF/ dThdPase in human gastric carcinoma tissues, we performed immunohistochemical studies with anti-PD-ECGF/dThdPase and anti-CD34 monoclonal antibodies. Out of 154 gastric carcinoma tissue samples, 61 (40%) were evaluated as PD-ECGF/ dThdPase-positive. The expression of PD-ECGF/dThdPase was significantly associated with the intratumoral microvessel counts (P < 0.0001) and the incidence of hematogenous metastasis (P < 0.05). Intratumoral vessel counts were significantly correlated with overall survival of 154 patients (P < 0.000001). Cox proportional hazards model showed that tumor vasculature was an independent and strong prognostic variable. However, the prevalence of the expression of PD-ECGF did not associate the overall survival. We suggest that expression of PD-ECGF/dThdPase plays a role in the promotion of angiogenesis in human gastric carcinomas, without any definite influence on patient's survival.

Thymidine phosphorylase expression in Kaposi sarcoma

AIMS

To examine the immunohistochemical distribution of thymidine phosphorylase (TP) in all clinicopathological subtypes of Kaposi sarcoma.

METHODS

Thirty two biopsy specimens of Kaposi sarcoma (29 patients) were studied. Six of these patients represented classic, six endemic, eight HIV associated, seven post-immunosuppression/transplant related, and two unclassified variants of Kaposi sarcoma. The average age was 49 years (range 22-83 years) and the male: female ratio 24:5. Four samples of angiosarcoma and one of spindle cell haemangio-endothelioma were stained in parallel. All specimens were fixed in formalin, embedded in paraffin wax and processed routinely. Immunohistochemistry was carried out using an antibody directed against CD31 (JC70) and the monoclonal antibody P-GF.44C against TP.

RESULTS

All biopsy specimens showed immunoexpression for TP. The spindle cell component stained more strongly than newly formed endothelium lined vessels and normal, resident vessels at a distance from the lesions.

CONCLUSIONS

The strong immunoexpression of TP suggests up-regulation of TP and a role for TP in angiogensis in Kaposi sarcoma. The mechanism for the up-regulation of TP remains unknown, but viral infections may trigger it. The differential staining of the various cell components of Kaposi sarcoma also suggest that TP either plays a role in the differentiation and maturation of Kaposi sarcoma or is a reflection of such changes.

The angiogenic factor platelet-derived endothelial cell growth factor/thymidine phosphorylase is up-regulated in breast cancer epithelium and endothelium

Tumour angiogenesis is a complex multistep process regulated by a number of angiogenic factors. One such factor, platelet-derived endothelial cell growth factor has recently been shown to be thymidine phosphorylase (TP). TP catalyses the reversible phosphorylation of thymidine to deoxyribose-1-phosphate and thymine. Although known to be generally elevated in tumours, the expression of this enzyme in breast carcinomas is unknown. Therefore, we used ribonuclease protection assays and immunohistochemistry to examine the expression of TP in 240 primary breast carcinomas. Nuclear and/or cytoplasmic TP expression was observed in the neoplastic tumour epithelium in 53% of tumours. Immunoreactivity was also often present in the stromal, inflammatory and endothelial cell elements. Although endothelial cell staining was usually focal, immunoreactivity was observed in 61% of tumours and was prominent at the tumour periphery, an area where tumour angiogenesis is most active. Tumour cell TP expression was significantly inversely correlated with grade (P = 0.05) and size (P = 0.003) but no association was observed with other tumour variables. These findings suggest that TP is important for remodelling the existing vasculature early in tumour development, consistent with its chemotactic non-mitogenic properties, and that additional angiogenic factors are more important for other angiogenic processes like endothelial cell proliferation. Relapse-free survival was higher in node-positive patients with elevated TP (P = 0.05) but not in other patient groups. This might be due to the potentiation of chemotherapeutic agents like methotrexate by TP. Therefore, this enzyme might be a prediction marker for response to chemotherapy.

Thymidine phosphorylase mediates the sensitivity of human colon carcinoma cells to 5-fluorouracil

Interferon-alpha (IFN alpha) potentiates the antitumor activity of 5-fluorouracil (FUra) in colon cancer in vitro, in vivo, and clinically. A likely mechanism for this action is the induction by IFN alpha of thymidine phosphorylase (TP), the first enzyme in one pathway for the metabolic activation of FUra to fluorodeoxyribonucleotides. To test this hypothesis, an expression vector containing the TP cDNA was transfected into HT-29 human colon carcinoma cells. Five stable transfectants were selected and analyzed. All showed increased sensitivity to FUra cytotoxicity, ranging from a 2-fold to a 19-fold decrease in the IC50 for FUra, compared to wild-type cells. Levels of TP mRNA, protein, and enzyme activity were elevated in the transfectants, and there was a significant correlation between the relative increase in sensitivity to FUra and both the increase in both TP mRNA levels and TP activity. Transfected cells exhibited increased formation of FdUMP, but not the ribonucleotides FUDP and FUTP, from FUra when compared to wild-type cells. The changes in TP activity, FdUMP formation, and FUra sensitivity in the transfected cells were comparable with those seen after treatment of wild-type cells with IFN alpha. These studies provide direct evidence for the role of TP in mediating the sensitivity of colon carcinoma cells to FUra, and further support the importance of the induction of TP in the biomodulating action of IFN alpha on FUra chemosensitivity.

Tumour vasculature--a potential therapeutic target

The tumour vasculature is vital for the establishment, growth and metastasis of solid tumours. Its physiological properties limit the effectiveness of conventional anti-cancer strategies. Therapeutic approaches directed at the tumour vasculature are reviewed, suggesting the potential of anti-angiogenesis and the targeting of vascular proliferation antigens as cancer treatments.

Neurons of the peripheral nervous system express thymidine phosphorylase

Platelet-derived endothelial cell growth factor (PD-ECGF) is an angiogenic factor which recently has been shown to be identical to thymidine phosphorylase. We describe here, high levels of expression of PD-ECGF/thymidine phosphorylase in neurons of the peripheral nervous system (PNS) but very little in the central nervous system (CNS). Monoclonal and polyclonal antibodies were used for the staining of sections of dorsal root ganglia, sympathetic cervical ganglia and the enteric plexus as well as the brain and spinal cord. In addition, in situ hybridisation confirmed the results of immunohistochemistry. The possible role of thymidine phosphorylase in the PNS is discussed.

Platelet-derived endothelial cell growth factor/thymidine phosphorylase expression in normal tissues: an immunohistochemical study

Angiogenesis is the formation of new blood vessels from the existing vascular bed. It is a complex multi-step process controlled by a number of angiogenic factors. One such factor is platelet-derived endothelial cell growth factor (PD-ECGF), recently shown to be thymidine phosphorylase (TP), which is angiogenic in several in vivo assays and tumour systems. PD-ECGF/TP catalyses the reversible phosphorylation of thymidine to deoxyribose-1-phosphate and thymine. Since PD-ECGF/TP has an important role in cellular metabolism and in angiogenesis and its expression has been only partially characterized, we raised a monoclonal antibody against recombinant PD-ECGF/TP and used an immunohistochemical approach to examine the expression of PD-ECGF/TP in a comprehensive range of normal human tissues. The clone P-GF44.C, which recognizes recombinant PD-ECGF/TP and cell lysates transfected with a plasmid expressing PD-ECGF/TP cDNA on Western blotting, was selected for its ability to stain routinely processed tissue. Staining was observed in both the cytoplasm and/or the nucleus. Immunoreactivity was strongly expressed by macrophages, stromal cells, glial cells, and some epithelia. Gastrointestinal epithelium, smooth muscle, adrenal, lung, and testis were negative. Although endothelial cell expression was observed, there was no correlation with sites of new vessel growth. This pattern of expression suggests tight PD-ECGF/TP regulation and that cellular thymidine pools may serve to control its different functions. Thus, in the nucleus it might modulate the pool for DNA synthesis, whilst in the cytoplasm it could control other effects through different enzyme systems. The high expression present in macrophages and skin might be important for total body thymidine homeostasis.

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.

The isolation and long-term culture of normal human endometrial epithelium and stroma. Expression of mRNAs for angiogenic polypeptides basally and on oestrogen and progesterone challenges

A highly reproducible and technically straightforward technique for the isolation and long-term culture of normal human endometrial epithelial cells is described. The essential conditions for long-term culture are that the cells be seeded onto a gelatin matrix and that ‘endothelial cell growth supplement’ be present in the culture medium. Normal endometrial epithelial cells express cytokeratins and oestrogen receptors. They may be passaged five to six times without change in properties. Growth of normal endometrial epithelial cells was stimulated by 17-beta-oestradiol and epidermal growth factor. Expression of the mRNA coding for seven polypeptide angiogenic factors, by normal endometrial epithelial, stromal and three endometrial carcinoma lines, was examined. The endometrial epithelial and stromal cells express mRNA for the polypeptide angiogenic factors, basic fibroblast growth factor, vascular endothelial cell growth factor, transforming growth factor-beta 1 and pleiotrophin, as well as the cytokine midkine. Expression of the mRNA for both vascular endothelial growth factor and midkine by normal endometrial epithelial cells showed a 2-fold increase on treatment with a physiological dose of 17-beta-oestradiol (10(−10) M) while, in contrast, the mRNA of transforming growth factor-beta 1 decreased 4-fold on treatment with 17-beta-oestradiol (10(−10) M) and was abolished by exposure to progesterone (5 × 10(−9) M). Expression of the mRNAs for angiogenic polypeptides by the endometrial carcinoma lines was more restricted.

Aberrant production of gliostatin/platelet-derived endothelial cell growth factor in rheumatoid synovium

OBJECTIVE

To purify a protein inhibitor from rheumatoid arthritis (RA) synovial fluids which suppresses the apparent incorporation of 3H-thymidine into fibroblasts and synovial cells, and to define its biochemical features that have clinical relevance to the pathogenesis of RA.

METHODS

Several standard chromatographic techniques were employed for the purification of the protein. Immunochemical methods with monoclonal antibody were used to quantify and visualize the protein in sera, synovial fluids, and tissues from RA patients.

RESULTS

The chemical properties of purified inhibitor from RA synovial fluids confirmed its identity as gliostatin/platelet-derived endothelial cell growth factor (PD-ECGF), a potent angiogenic factor. The gliostatin/PD-ECGF level in synovial fluid and serum was higher in RA patients than in osteoarthritis controls.

CONCLUSION

These findings strongly suggest that gliostatin/PD-ECGF might play an important role in the aberrant neovascularization of rheumatoid synovium.