Thymidine phosphorylase inhibits apoptosis induced by cisplatin

Investigation of novel bis-thiadiazole bearing schiff base derivatives as effective inhibitors of thymidine phosphorylase: Synthesis, in vitro bioactivity and molecular docking study

Thymidine phosphorylase (TP) is an angiogenic enzyme. It is crucial for the development, invasion and metastasis of tumors as well as angiogenesis. In our current research, we examine how structurally changing bis-thiadiazole bearing bis-schiff bases affects their ability to inhibit TP. Through the oxidative cyclization of pyridine-based bis-thiosemicarbazone with iodine, a series of fourteen analogs of bis-thiadiazole-based bis-imines with pyridine moiety were developed. Newly synthesized scaffolds were assessed in vitro for their thymidine phosphorylase inhibitory potential and showed moderate to good inhibition profile. Eleven scaffolds such as 4a-4d,4f-4 h and 4j-4 m were discovered to be more effective than standard drug at inhibiting the thymidine phosphorylase enzyme with IC50 values of 1.16 ± 1.20, 1.77 ± 1.10, 2.48 ± 1.30, 12.54 ± 1.60, 14.63 ± 1.70, 15.53 ± 1.80, 17.47 ± 1.70, 18.98 ± 1.70, 19.53 ± 1.50, 22.73 ± 2.40 and 24.87 ± 2.80 respectively, while remaining three analogs such as 4n, 4i and 4ewere found to be more potent, but they were less potent than the standard drug. All analogs underwent SAR studies based on the pattern of substitutions around the aryl part of the bis-thiadiazole skeleton. The most active analogs in the synthesized series were then molecular docking study performed to investigate their interactions of active part of enzyme. The results showed that remarkable interactions were exhibited by these analogs with the targeted enzymes active sites. Furthermore, to confirm the structure of synthesized analogs by employing spectroscopic tools such as HREI-MS and NMR.

Prognostic Impact of Dihydropyrimidine Dehydrogenase Germline Variants in Unresectable Non-Small Cell Lung Cancer Patients Treated with Platin-Based Chemotherapy

Platin-based chemotherapy is the standard treatment for patients with non-small cell lung cancer (NSCLC). However, resistance to this therapy is a major obstacle in successful treatment. In this study, we aimed to investigate the impact of several pharmacogenetic variants in patients with unresectable NSCLC treated with platin-based chemotherapy. Our results showed that DPYD variant carriers had significantly shorter progression-free survival and overall survival compared to DPYD wild-type patients, whereas DPD deficiency was not associated with a higher incidence of high-grade toxicity. For the first time, our study provides evidence that DPYD gene variants are associated with resistance to platin-based chemotherapy in NSCLC patients. Although further studies are needed to confirm these findings and explore the underlying mechanisms of this association, our results suggest that genetic testing of DPYD variants may be useful for identifying patients at a higher risk of platin-based chemotherapy resistance and might be helpful in guiding future personalized treatment strategies in NSCLC patients.

Heat shock protein 90 inhibitor 17-AAG down-regulates thymidine phosphorylase expression and potentiates the cytotoxic effect of tamoxifen and erlotinib in human lung squamous carcinoma cells

Elevated thymidine phosphorylase (TP) levels, a key enzyme in the pyrimidine nucleoside salvage pathway, in cancer cells, are related to a poor prognosis in a variety of cancers. Heat shock protein 90 (Hsp90) is a ubiquitous molecular chaperone that is involved in the stabilization and maturation of many oncogenic proteins. The aim of this study is to elucidate whether Hsp90 inhibitor 17-AAG could enhance tamoxifen- and erlotinib-induced cytotoxicity in nonsmall cell lung cancer (NSCLC) cells via modulating TP expression in two squamous NSCLC cell lines, H520 and H1703. We found that 17-AAG reduced TP expression via inactivating the MKK1/2-ERK1/2-mitogen-activated protein kinase (MAPK) pathway. TP knockdown with siRNA or ERK1/2 MAPK inactivation with the pharmacological inhibitor U0126 could enhance the cytotoxic and growth inhibitory effects of 17-AAG. In contrast, MKK1-CA or MKK2-CA (a constitutively active form of MKK1/2) vector-enforced expression could reduce the cytotoxic and cell growth inhibitory effects of 17-AAG. Furthermore, 17-AAG enhanced the cytotoxic and cell growth inhibitory effects of tamoxifen and erlotinib in NSCLC cells, which were associated with TP expression downregulation and MKK1/2-ERK1/2 signal inactivation. Taken together, Hsp90 inhibition downregulates TP, enhancing the tamoxifen- and erlotinib-induced cytotoxicity in H520 and H1703 cells.

Inhibition of thymidine phosphorylase expression by Hsp90 inhibitor potentiates the cytotoxic effect of salinomycin in human non-small-cell lung cancer cells

Salinomycin is a polyether ionophore antibiotic having anti-tumorigenic property in various types of cancer. Elevated thymidine phosphorylase (TP) levels, a key enzyme in the pyrimidine nucleoside salvage pathway, are associated with an aggressive disease phenotype and poor prognoses. Heat shock protein 90 (Hsp90) is a ubiquitous molecular chaperone that is responsible for the stabilization and maturation of many oncogenic proteins. In this study, we report whether Hsp90 inhibitor 17-AAG could enhance salinomycin-induced cytotoxicity in NSCLC cells through modulating TP expression in two non-small-cell lung cancer (NSCLC) cell lines, A549 and H1975. We found that salinomycin increased TP expression in a MKK3/6-p38 MAPK activation manner. Knockdown of TP using siRNA or inactivation of p38 MAPK by pharmacological inhibitor SB203580 enhanced the cytotoxic and growth inhibition effects of salinomycin. In contrast, enforced expression of MKK6E (a constitutively active form of MKK6) reduced the cytotoxicity and cell growth inhibition of salinomycin. Moreover, Hsp90 inhibitor 17-AAG enhanced cytotoxicity and cell growth inhibition of salinomycin in NSCLC cells, which were associated with down-regulation of TP expression and inactivation of p38 MAPK. Together, the Hsp90 inhibition induced TP down-regulation involved in enhancing the salinomycin-induced cytotoxicity in A549 and H1975 cells.

Demethoxycurcumin sensitizes the response of non-small cell lung cancer to cisplatin through downregulation of TP and ERCC1-related pathways

BACKGROUND

Excision repair cross-complementary 1 (ERCC1) overexpression in lung cancer cells is strongly correlated with its resistance to platinum-based chemotherapy. Overexpression of thymidine phosphorylase (TP) reverts platinum-induced cancer cell death.

PURPOSE

Curcumin has been reported to enhance antitumor properties through the suppression of TP and ERCC1 in non-small cell lung carcinoma cells (NSCLC). Nevertheless, whether two other curcuminoids, demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) from Curcuma longa demonstrate antitumor activity like that of curcumin remain unknown.

METHODS

MTT assay was conducted to determine the cell cytotoxicity. Western blotting was used to determine the protein expressions. Docking is the virtual screening of a database of compounds and predicting the strongest binders based on various scoring functions. BIOVIA Discovery Studio 4.5 (D.S. 4.5) were used for docking.

RESULTS

Firstly, when compared with curcumin and BDMC, DMC exhibited the most potent cytotoxic effect on NSCLC, most importantly, MRC-5, a lung fetal fibroblast, was insensitive to DMC (under 30 µM). Secondly, DMC alone significantly inhibited on-target cisplatin (CDDP) resistance protein, ERCC1, via PI3K-Akt-snail pathways, and TP protein expression in A549 cells. Thirdly, DMC treatment markedly increased post-target CDDP resistance pathway including Bax and cytochrome c. DMC significantly decreased Bcl-2 protein expressions. Finally, MTT assay indicated that DMC significantly increased CDDP-induced cytotoxicity and was confirmed with an increased Bax/Bcl-2 ratio, indicating upregulation of caspase-3.

CONCLUSIONS

We concluded that enhancement of the cytotoxicity to CDDP by coadminstration with DMC was mediated by down-regulation of the expression of TP and ERCC1, regulated by PI3K-Akt-Snail pathway inactivation.

Bevacizumab-enhanced antitumor effect of 5-fluorouracil via upregulation of thymidine phosphorylase through vascular endothelial growth factor A/vascular endothelial growth factor receptor 2-specificity protein 1 pathway

Bevacizumab (Bv) can be used synergistically with fluoropyrimidine-based chemotherapy to treat colorectal cancer. Whether and how it affects the delivery of fluoropyrimidine drugs is unknown. The present study aimed to explore the effect of Bv on the delivery of 5-fluorouracil (5-FU) to tumors and the underlying mechanism from metabolic perspective. Bv enhanced the anti-tumor effects of 5-FU in LoVo colon cancer xenograft mice and increased the 5-FU concentration in tumors without affecting hepatic 5-FU metabolism. Interestingly, Bv remarkably upregulated thymidine phosphorylase (TP) in tumors, which mediated the metabolic activation of 5-FU. Although TP is reported to promote angiogenesis and resistance, the combination of Bv and 5-FU resulted in anti-angiogenesis and vessel normalization in tumors, indicating that the elevated TP mainly contributed to the enhanced response to 5-FU. Bv also induced TP upregulation in LoVo cancer cells. Treatment with vascular endothelial growth factor receptor 2 (VEGFR2) antagonist apatinib and VEGFR2 silencing further confirmed TP upregulation. Bv and apatinib both enhanced the cytotoxicity of 5-FU in LoVo cells, but there was no synergism with adriamycin and paclitaxel. We further demonstrated that the effect of Bv was dependent on VEGFR2 blockade and specificity protein 1 activation via MDM2 inhibition. In summary, Bv enhanced the accumulation of 5-FU in tumors and the cytotoxicity of 5-FU via TP upregulation. We provide data to better understand how Bv synergizes with 5-FU from metabolic perspective, and it may give clues to the superiority of Bv in combination with fluoropyrimidine drugs compared to other chemotherapeutic drugs in colon cancer.

Thymidine phosphorylase: A potential new target for treating cardiovascular disease

We recently found that thymidine phosphorylase (TYMP), also known as platelet-derived endothelial cell growth factor, plays an important role in platelet activation in vitro and thrombosis in vivo by participating in multiple signaling pathways. Platelets are a major source of TYMP. Since platelet-mediated clot formation is a key event in several fatal diseases, such as myocardial infarction, stroke and pulmonary embolism, understanding TYMP in depth may lead to uncovering novel mechanisms in the development of cardiovascular diseases. Targeting TYMP may become a novel therapeutic for cardiovascular disorders. In this review article, we summarize the discovery of TYMP and the potential molecular mechanisms of TYMP involved in the development of various diseases, especially cardiovascular diseases. We also offer insights regarding future studies exploring the role of TYMP in the development of cardiovascular disease as well as in therapy.

Radiosensitization and downregulation of heterogeneous nuclear ribonucleoprotein K (hnRNP K) upon inhibition of mitogen/extracellular signal-regulated kinase (MEK) in malignant melanoma cells

Background

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is an important cofactor in the p53-mediated DNA damage response pathway upon ionizing radiation (IR) and exerts anti-apoptotic effects also independent of p53 pathway activation. Furthermore, hnRNP K is overexpressed in various neoplasms including malignant melanoma (MM). Here, we investigate the role of hnRNP K in the radioresistance of MM cells.

Methods and results

Our results show cytoplasmic expression of hnRNP K in human MM surgical specimens, but not in benign nevi, and a quick dose- and time-dependent upregulation in response to IR accompanied by cytoplasmic redistribution of the protein in the IPC-298 cellular tumor model carrying an activating NRAS mutation (p.Q61L). SiRNA-based knockdown of hnRNP K induced a delayed decline in γH2AX/53BP1-positive DNA repair foci upon IR. Pharmacological interference with MAPK signaling abrogated ERK phosphorylation, diminished cellular hnRNP K levels, impaired γH2AX/53BP1-foci repair and proliferative capability and increased apoptosis comparable to the observed hnRNP K knockdown phenotype in IPC-298 cells.

Conclusion

Our results indicate that pharmacological interference with MAPK signaling increases vulnerability of NRAS-mutant malignant melanoma cells to ionizing radiation along with downregulation of endogenous hnRNP K and point towards a possible use for combined MEK inhibition and localized radiation therapy of MM in the NRAS-mutant setting where BRAF inhibitors offer no clinical benefit.

Thymidine Phosphorylase in Cancer; Enemy or Friend?

Thymidine phosphorylase (TP) is a nucleoside metabolism enzyme that plays an important role in the pyrimidine pathway.TP catalyzes the conversion of thymidine to thymine and 2-deoxy-α-D-ribose-1-phosphate (dRib-1-P). Although this reaction is reversible, the main metabolic function of TP is catabolic. TP is identical to the angiogenic factor platelet-derived endothelial-cell growth factor (PD-ECGF). TP is overexpressed in several human cancers in response to cellular stressful conditions like hypoxia, acidosis, chemotherapy and radiotherapy. TP has been shown to promote tumor angiogenesis, invasion, metastasis, evasion of the immune-response and resistance to apoptosis. Some of the biological effects of TP are dependent on its enzymatic activity, while others are mediated through cytokines like interleukin 10 (IL-10), basic fibroblast growth factor (bFGF) and tumour necrosis factor α (TNFα). Interestingly, TP also plays a role in cancer treatment through its role in the conversion of the oral fluoropyrimidine capecitabine into its active form 5-FU. TP is a predictive marker for fluoropyrimidine response. Given its various biological functions in cancer progression, TP is a promising target in cancer treatment. Further translational research is required in this area.

Synthesis and in vitro evaluation of 1,2,4-triazolo[1,5-a][1,3,5]triazine derivatives as thymidine phosphorylase inhibitors

In our lead finding program, a series of 1,2,4-triazolo[1,5-a][1,3,5]triazine derivatives were synthesized, and their in vitro thymidine phosphorylase inhibitory potential was explored. Among the different derivatives, compounds having keto group (C = O) at C7 and thioketo group (C = S) at C5 positions showed varying degrees of TP inhibitory activity comparable with positive control, 7-deazaxanthine (7-DX, 2) (IC50 value = 42.63 μm). Enzyme inhibition kinetics study suggested that compound IVn behaved as a mixed-type inhibitor of the enzyme with respect to thymidine (dThd) as a variable substrate. Compound IVn was also found to inhibit PMA-induced MMP-9 expression in MDA-MB-231 cells at sublethal concentrations. Computational docking study was performed to illustrate the enzyme inhibition kinetics and to explore the ligand-enzyme interactions.

A polymorphism in the TYMP gene is associated with the outcome of HLA-identical sibling allogeneic stem cell transplantation

Thymidine phosphorylase (TYMP), an enzyme involved in nucleotide synthesis, has been implicated in critical biological processes such as DNA replication, protection against mutations, and tissue repair. In this work, we retrospectively evaluated the influence of a polymorphism in the TYMP gene (rs112723255; G/A) upon the outcome of 448 patients subjected to allogeneic stem cell transplantation (allo-SCT) from an human leukocyte antigen (HLA)-identical sibling donor. The TYMP genotype of patients correlated with overall survival-carriers of the minor allele (A) being at an increased risk of dying after transplantation (hazard ratio, HR = 1.9; P = 0.004). This effect was mostly due to differences in transplant toxicity-related mortality (HR = 2.5; P = 0.029). In addition, the TYMP genotype of donors was associated with the risk of chronic graft-versus-host disease (GVHD)-carriers of the minor allele being at an increased risk of developing this complication ([HR] = 1.7; P = 0.039). The impact of such polymorphism on the risk of chronic GVHD is limited to patients transplanted in early stage disease (HR = 2.2; P = 0.019). The combination of a donor harboring the minor allele with a patient homozygous for the major allele was associated with the highest risk of chronic GVHD (HR = 2.8; P = 0.008). These findings provide the first evidence of the significant impact of the TYMP genotype upon the clinical outcome of patients treated with HLA-identical sibling allo-SCT.

Metformin induces cytotoxicity by down-regulating thymidine phosphorylase and excision repair cross-complementation 1 expression in non-small cell lung cancer cells

Metformin is an antidiabetic drug recently shown to inhibit cancer cell proliferation and growth, although the involved molecular mechanisms have not been elucidated. In many cancer cells, high expression of thymidine phosphorylase (TP) and Excision repair cross-complementation 1 (ERCC1) is associated with poor prognosis. We used A549 and H1975 human non-small cell lung cancer (NSCLC) cell lines to investigate the role of TP and ERCC1 expression in metformin-induced cytotoxicity. Metformin treatment decreased cellular TP and ERCC1 protein and mRNA levels by down-regulating phosphorylated MEK1/2-ERK1/2 protein levels in a dose- and time-dependent manner. The enforced expression of the constitutively active MEK1 (MEK1-CA) vectors significantly restored cellular TP and ERCC1 protein levels and cell viability. Specific inhibition of TP and ERCC1 expression by siRNA enhanced the metformin-induced cytotoxicity and growth inhibition. Arachidin-1, an antioxidant stilbenoid, further decreased TP and ERCC1 expression and augmented metformin's cytotoxic effect, which was abrogated in lung cancer cells transfected with MEK1/2-CA expression vector. In conclusion, metformin induces cytotoxicity by down-regulating TP and ERCC1 expression in NSCLC cells.

Fucoxanthin enhances cisplatin-induced cytotoxicity via NFκB-mediated pathway and downregulates DNA repair gene expression in human hepatoma HepG2 cells

Cisplain, a platinum-containing anticancer drug, has been shown to enhance DNA repair and to inhibit cell apoptosis, leading to drug resistance. Thus, the combination of anticancer drugs with nutritional factors is a potential strategy for improving the efficacy of cisplatin chemotherapy. In this study, we investigated the anti-proliferative effects of a combination of fucoxanthin, the major non-provitamin A carotenoid found in Undaria Pinnatifida, and cisplatin in human hepatoma HepG2 cells. We found that fucoxanthin (1–10 μΜ) pretreatment for 24 h followed by cisplatin (10 μΜ) for 24 h significantly decreased cell proliferation, as compared with cisplatin treatment alone. Mechanistically, we showed that fucoxanthin attenuated cisplatin-induced NFκB expression and enhanced the NFκB-regulated Bax/Bcl-2 mRNA ratio. Cisplatin alone induced mRNA expression of excision repair cross complementation 1 (ERCC1) and thymidine phosphorylase (TP) through phosphorylation of ERK, p38 and PI3K/AKT pathways. However, fucoxanthin pretreatment significantly attenuated cisplatin-induced ERCC1 and TP mRNA expression, leading to improvement of chemotherapeutic efficacy of cisplatin. The results suggest that a combined treatment with fucoxanthin and cisplatin could lead to a potentially important new therapeutic strategy against human hepatoma cells.

Synergistic effect of curcumin and cisplatin via down-regulation of thymidine phosphorylase and excision repair cross-complementary 1 (ERCC1)

Curcumin (diferuloylmethane), a phenolic compound obtained from the rhizome of Curcuma longa, is known to have antiproliferative and antitumor properties. Thymidine phosphorylase (TP), an enzyme of the pyrimidine salvage pathway, is considered an attractive therapeutic target, and its expression could suppress cancer cell death induced by DNA damage agents. Excision repair cross-complementary 1 (ERCC1) is a protein involved the process of nucleotide excision repair. The ERCC1 gene is expressed at high levels in cancers and has been associated with resistance to platinum-based chemotherapy. In this study, the effects of curcumin on TP and ERCC1 expression induced by cisplatin in non-small-cell lung cancer (NSCLC) cell lines was investigated. Exposure of the NSCLC cells to various concentrations of curcumin (5-40 μM) down-regulates the mRNA and protein levels of TP and ERCC1 through destabilization of the mRNA and proteins via a mechanism involving inactivation of MKK1/2-extracellular signal-regulated kinase (ERK1/2). Depletion of endogenous TP or ERCC1 expression by transfection with specific small interfering RNAs significantly decreases cell viability in curcumin-exposed NSCLC cells. Curcumin enhances the sensitivity of cisplatin treatment for NSCLC through inactivation of ERK1/2 and by decreasing the TP and ERCC1 protein levels. Enhancement of ERK1/2 signaling by constitutively active MKK1/2 causes an increase in TP and ERCC1 protein levels and promotes cell viability after cotreatment with curcumin and cisplatin. Enhancement of the cytotoxicity to cisplatin by administration of curcumin is mediated by down-regulation of the expression levels of TP and ERCC1 and by inactivation of ERK1/2.

Up-regulation of extracellular signal-regulated kinase 1/2-dependent thymidylate synthase and thymidine phosphorylase contributes to cisplatin resistance in human non-small-cell lung cancer cells

Chemotherapy for advanced human non-small-cell lung cancer (NSCLC) includes platinum-containing compound such as cisplatin in combination with a second- or third-generation cytotoxic agent. 5-Fluorouracil (5-FU) belongs to antimetabolite chemotherapeutics, and its mechanism of cytotoxicity is involved in the inhibition of thymidylate synthase (TS). TS and thymidine phosphorylase (TP) are key enzymes of the pyrimidine salvage pathway. In this study, we have examined the molecular mechanism of TS and TP in regulating drug sensitivity to cisplatin in NSCLC cell lines. Cisplatin could increase the phosphorylation of mitogen-activated protein kinase kinase 1/2 (MKK1/2)-extracellular signal-regulated kinase 1/2 (ERK1/2) and the protein levels of TS and TP through enhancing the protein stability in A549 and H1975 cells. Blocking ERK1/2 activation by MKK1/2 inhibitor [U0126; 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene)] decreased TS and TP protein levels in both cell lines treated with cisplatin. Depletion of endogenous TS or TP expression by specific small interfering RNA transfection significantly increased cisplatin-induced cell death and growth inhibition. Combined treatment with 5-FU could decrease cisplatin-induced ERK1/2 activation and the induction of TS and TP, which subsequently resulted in synergistic cytotoxic effects. Enforced expression of constitutive active MKK1/2 vectors rescued the protein levels of phospho-ERK1/2, TS, and TP, and the cell viability that were decreased by cisplatin and 5-FU combination. In contrast, U0126 enhanced drug sensitivity to cisplatin and/or 5-FU in lung cancer cells. In conclusion, the up-regulation of ERK1/2-dependent TS and TP can protect human lung cancer cells from cisplatin-induced cytotoxicity.

Proteomic profile regulated by the anticancer peptide CIGB-300 in non-small cell lung cancer (NSCLC) cells

CIGB-300 is a proapoptotic peptide-based drug that abrogates the CK2-mediated phosphorylation. This peptide has antineoplastic effect on lung cancer cells in vitro and in vivo. To understand the mechanisms involved on such anticancer activity, the NCI-H125 cell line proteomic profile after short-term incubation (45 min) with CIGB-300 was investigated. As determined by 2-DE or 2D-LC-MS/MS, 137 proteins changed their abundances more than 2-fold in response to the CIGB-300 treatment. The expression levels of proteins related to ribosome biogenesis, metastasis, cell survival and proliferation, apoptosis, and drug resistance were significantly modulated by the presence of CIGB-300. The protein translation process was the most affected (23% of the identified proteins). From the proteome analysis of the NCI-H125 cell line, novel potentialities for CIGB-300 as anticancer agent were evidenced.

Effects of interferon-alpha on thymidine phosphorylase expression and apoptosis in human hepatocellular carcinoma SMMC-7721 cells

AIM: To investigate the effects of interferon-alpha (IFN-α) on thymidine phosphorylase (TP) expression and apoptosis in human hepatocellular carcinoma SMMC-7721 cells.

METHODS: The expression of TP mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR). The expression of TP protein was evaluated by immunocytochemistry. The percentage of apoptotic cells was measured by flow cytometry.

RESULTS: IFN-α upregulated the expression of TP mRNA in a dose-dependent manner in SMMC-7721 cells. IFN-α at a dose of 5000 or 10 000 kU/L induced a 3-fold upregulation of TP mRNA compared to non-treated cells (P < 0.05). Compared with non-treated cells, the intensity of TP staining and the number of TP-positive cells significantly increased in IFN-α treated cells (5000 or 10 000 kU/L). However, no significant difference was found in the percentage of apoptotic cells between IFN-α (10 000 kU/L)-treated cells and non-treated cells (6.42% ± 3.66% vs 7.19% ± 2.76%, P > 0.05).

CONCLUSION: IFN-α at appropriate doses may upregulate the expression of TP mRNA and protein and antagonize TP-induced inhibition of apoptosis in human hepatocellular carcinoma cells.

Enhanced platelet responsiveness due to chilling and its relation to CD40 ligand level and platelet-leukocyte aggregate formation

To investigate platelet responsiveness during cold storage of whole blood, we examined platelet aggregation, expression of CD40 ligand (CD40L) on platelets, the plasma levels of soluble form of CD40L (sCD40L) as well as platelet-leukocyte aggregates. Flow cytometry analysis was performed to investigate platelet-leukocyte aggregate formation using antibodies against CD42b and CD45 and platelet activation using antibodies against P-selectin and PAC-1. Blood samples were collected from healthy volunteers, patients with cardiovascular diseases, or both. In the healthy volunteers' blood samples stored at 4 degrees C for 6 h, platelet aggregation in response to 1 micromol/l ADP was enhanced, and released levels of soluble form of P-selectin and thromboxane B2 in response to 1 micromol/l ADP markedly increased. In the samples stored at 4 degrees C for 6 h but not stimulated by any agonists, CD40L expression on the platelets was increased, and plasma levels of sCD40L were also elevated. Under the same condition, the increase in simultaneous expression of CD45 and CD42b was observed. In patients with cardiovascular diseases, the platelet aggregability, coexpression of P-selectin and PAC-1, expression of CD40L on platelets and both CD45-bound and CD42b-bound subsets were all comparable to those of healthy volunteers' samples stored at 4 degrees C for 6 h. Plasma levels of sCD40L in patients were higher than those in healthy volunteers' control. Taken together, storage of whole blood at 4 degrees C for 6 h caused platelet activation comparable to that of patients with cardiovascular diseases, and enhanced platelet activity in such patients may be involved in increased risk for thromboembolic events.

The dual role of thymidine phosphorylase in cancer development and chemotherapy

Thymidine phosphorylase (TP), also known as "platelet-derived endothelial cell growth factor" (PD-ECGF), is an enzyme, which is upregulated in a wide variety of solid tumors including breast and colorectal cancers. TP promotes tumor growth and metastasis by preventing apoptosis and inducing angiogenesis. Elevated levels of TP are associated with tumor aggressiveness and poor prognosis. Therefore, TP inhibitors are synthesized in an attempt to prevent tumor angiogenesis and metastasis. TP is also indispensable for the activation of the extensively used 5-fluorouracil prodrug capecitabine, which is clinically used for the treatment of colon and breast cancer. Clinical trials that combine capecitabine with TP-inducing therapies (such as taxanes or radiotherapy) suggest that increasing TP expression is an adequate strategy to enhance the antitumoral efficacy of capecitabine. Thus, TP plays a dual role in cancer development and therapy: on the one hand, TP inhibitors can abrogate the tumorigenic and metastatic properties of TP; on the other, TP activity is necessary for the activation of several chemotherapeutic drugs. This duality illustrates the complexity of the role of TP in tumor progression and in the clinical response to fluoropyrimidine-based chemotherapy.

Flexible heteroarotinoid (Flex-Het) SHetA2 inhibits angiogenesis in vitro and in vivo

Flexible heteroarotinoids (Flex-Hets) compounds regulate growth, differentiation and apoptosis in cancer cells. The hypothesis of this study was that the lead Flex-Het, SHetA2, inhibits angiogenesis by blocking cytokine release from cancer cells. SHetA2 altered secretion of thrombospondin-4 (TSP-4), vascular endothelial growth factor A (VEGF) and fibroblast growth factor (bFGF) proteins from normal and cancerous ovarian and renal cultures. Thymidine phosphorylase (TP) expression was inhibited in cancer, but not normal cultures. Endothelial tube formation was stimulated by conditioned media from cancer but not normal cultures, and SHetA2 reduced secretion of this angiogenic activity. SHetA2 directly inhibited endothelial cell tube formation and proliferation through G1 cell cycle arrest, but not apoptosis. Recombinant TP reversed SHetA2 anti-angiogenic activity. SHetA2 inhibition of in vivo angiogenesis was observed in Caki-1 renal cancer xenografts. In conclusion, SHetA2 inhibits angiogenesis through alteration of angiogenic factor secretion by cancer cells and through direct effects on endothelial cells.

2-deoxy-d-ribose induces apoptosis by inhibiting the synthesis and increasing the efflux of glutathione

Oxidative stress is caused by imbalance between the production of reactive oxygen species (ROS) and biological system ability to readily detoxify the reactive intermediates or repair the resulting damage. 2-deoxy-D-ribose (dRib) is known to induce apoptosis by provoking an oxidative stress by depleting glutathione (GSH). In this paper, we elucidate the mechanisms underlying GSH depletion in response to dRib treatment. We demonstrated that the observed GSH depletion is not only due to inhibition of synthesis, by inhibiting gamma-glutamyl-cysteine synthetase, but also due to its increased efflux, by the activity of multidrug resistance associated proteins transporters. We conclude that dRib interferes with GSH homeostasis and that likely cellular oxidative stress is a consequence of GSH depletion. Various GSH fates, such as direct oxidation, lack of synthesis or of storage, characterize different kinds of oxidative stress. In the light of our observations we conclude that dRib does not induce GSH oxidation but interferes with GSH synthesis and storage. Lack of GSH allows accumulation of ROS and cells, disarmed against oxidative insults, undergo apoptosis.

The angiogenic factor thymidine phosphorylase up-regulates the cell adhesion molecule P-selectin in human vascular endothelial cells and is associated with P-selectin expression in breast cancers

Thymidine phosphorylase (TP) is an angiogenic enzyme, catalysing the reversible phosphorylation of thymidine to thymine and 2-deoxyribose. TP is up-regulated in neoplasia, being associated with advanced tumour stage, microvessel density and prognosis in several tumour types. Although TP is a non-mitogenic migratory factor for endothelium, the mechanism by which TP mediates these effects is still unclear. We compared the gene expression profile of endothelial cells grown in vitro in the presence or absence of TP by cDNA microarray analysis. To determine the time-course of TP angiogenic induction, endothelial cells were stimulated with TP (10 ng/ml) for 5 and 18 h. Gene expression levels of Tie2, angiopoietin (Ang)1 and Ang2, measured by RNase protection assay (RPA), showed maximal alteration at 18 h. cDNA from human umbilical vein endothelial cells (HUVEC) grown for 18 h in the presence or absence of TP (10 ng/ml) was hybridized to a human cDNA cytokine array representing 375 angiogenic genes. Significantly altered expression occurred in 89 human angiogenic genes (72 genes were up-regulated and 17 down-regulated). Changes in five genes relevant to vascular remodelling biology (Tie2, nNos, P-selectin, ephrin-B1 and TP) were validated in triplicate experiments by real-time RT-PCR. But only P-selectin gene expression remained significant. Correlation between P-selectin and TP was assessed by immunohistochemistry on 161 human breast cancers, using human tissue microarray. Tumour cell TP correlated with tumour cell P-selectin but not with endothelial cell P-selectin. These data show that TP stimulates changes in mRNA expression maximally after 18 h culture in vitro. It confirms a role for TP in vascular remodelling involving several classes of genes, including the cell adhesion molecule, P-selectin. Although confirmation of the role of TP-mediated cell adhesion molecule (CAM) induction is required; however, this pathway may provide an attractive therapeutic target, since it is likely to affect several important tumour processes, including angiogenesis and metastasis.

5′-O-Tritylated Nucleoside Derivatives: Inhibition of Thymidine Phosphorylase and Angiogenesis

Thymidine phosphorylase (TPase) is one of the key enzymes involved in the pyrimidine nucleoside salvage pathway. However, TPase also stimulates angiogenesis, and its expression correlates well with microvessel density and metastasis in a variety of human tumors. We have shown recently that 5'-O-trityl-inosine (KIN59) allosterically inhibits TPase enzymatic activity. KIN59 also inhibits TPase-induced angiogenesis in the chick chorioallantoic membrane (CAM) assay. The trityl group was found to be instrumental to preserve both the anti-TPase and antiangiogenic effect. We have now synthesized a variety of novel 5'-O-trityl nucleoside derivatives. Enzyme activity studies showed that the anti-TPase activity is significantly improved by replacement of the hypoxanthine base by thymine [3.5-fold; i.e., 5'-O-tritylthymidine (KIN6)] and the introduction of chloride on the trityl group [7-fold; i.e., 5'-O-(4-chlorotrityl)-inosine (TP136)], whereas removal of 2'-hydroxyl in the ribose did not significantly alter the anti-TPase activity. Enzyme kinetic studies also demonstrated that 1-(5'-O-trityl-beta-d-ribofuranosyl)-thymine (TP124), like KIN59, inhibits TPase in a noncompetitive fashion both with respect to phosphate and thymidine. Most KIN59 analogs markedly inhibited TPase-induced angiogenesis in the CAM assay. In vitro studies showed that the antiangiogenic effect of these compounds is not attributed to endothelial cell toxicity. For several compounds, there was no stringent correlation between their anti-TPase and antiangiogenic activity, indicating that these compounds may also act on other angiogenesis mediators. The antiangiogenic 5'-O-trityl nucleoside analogs also caused degradation of pre-existing, immature vessels at the site of drug exposure. Thus, 5'-O-trityl nucleoside derivatives combine antiangiogenic and vascular-targeting activities, which opens perspectives for their potential use as anticancer agents.

Identification of the angiogenic endothelial-cell growth factor-1/thymidine phosphorylase as a potential target for immunotherapy of cancer

Characterization of the antigens recognized by tumor-reactive T cells isolated from patients successfully treated with allogeneic HLA-matched hematopoietic stem cell transplantation (SCT) can lead to the identification of clinically relevant target molecules. We isolated tumor-reactive cytotoxic CD8(+) T-cell (CTL) clones from a patient successfully treated with donor lymphocyte infusion for relapsed multiple myeloma after allogeneic HLA-matched SCT. Using cDNA expression cloning, the target molecule of an HLA-B7-restricted CTL clone was identified. The CTL clone recognized a minor histocompatibility antigen produced by a single nucleotide polymorphism (SNP) in the angiogenic endothelial-cell growth factor-1 (ECGF1) gene also known as thymidine phosphorylase. The SNP leads to an Arg-to-His substitution in an alternatively translated peptide that is recognized by the CTL. The ECGF1 gene is predominantly expressed in hematopoietic cells, although low expression can also be detected in other tissues. The patient from whom this CTL clone was isolated had mild graft-versus-host disease despite high numbers of circulating ECGF-1-specific T cells as detected by tetramer staining. Because solid tumors expressing ECGF-1 could also be lysed by the CTL, ECGF-1 is an interesting target for immunotherapy of both hematologic and solid tumors.

Protection against DNA damage-induced apoptosis by the angiogenic factor thymidine phosphorylase

Thymidine phosphorylase (TP) is involved both in pyrimidine nucleoside metabolism and in angiogenesis. TP also conferred the resistance to hypoxia-induced apoptosis of the cancer cells. In U937 cells, DNA damage-inducing agents significantly enhanced the expression of TP. Cell lines stably transfected with TP cDNA were more resistant to the DNA damage-inducing agents than the mock-transfected cells and showed augmented activity of Akt. The cytoprotective function of TP against DNA damage was independent of its enzymatic activity. The resistance to apoptosis was partially abrogated by treatment with the phosphatidyl inositol 3-kinase (PI3K) inhibitors, suggesting that the cytoprotective function of TP is mediated, at least in part, by regulation of the PI3K/Akt pathway. These findings indicate that TP expression in increased by various stress including DNA damage and that TP molecules confer resistance to DNA damage-induced apoptosis in cancer cells.

Thymidine phosphorylase suppresses apoptosis induced by microtubule-interfering agents

We investigated the ability of thymidine phosphorylase (TP) to confer cancer cells resistance to MIA (microtubule-interfering agents)-induced apoptosis. Jurkat cells were stably transfected with TP cDNA (Jurkat/TP) and the sensitivity to MIAs were examined. Jurkat/TP cells were more resistant to apoptosis induced by nocodazole, vincristine, vinblastine, paclitaxel and 2-methoxyestradiol than mock-transfected Jurkat/CV cells. TP enzymatic activity was not required for this effect of TP. Jurkat/TP cells showed weak phosphorylation of Bcl-2, and kinase inhibitors staurosporine and genistein attenuated not only MIA-induced Bcl-2 phosphorylation but also cytotoxicity of MIA in Jurkat/CV, but not in Jurkat/TP. MIAs diminished expression of FasL in Jurkat/TP but not in Jurkat/CV, and neutralization of FasL by anti-FasL antibody considerably attenuated the cytotoxic effect of the MIAs in Jurkat/CV, but the effect of the antibody was marginal in Jurkat/TP cells. Our study provides further evidence that TP functions in conferring resistance on cancer cells to the stress induced by MIAs. In addition, we show that TP-induced inhibition of Bcl-2 phosphorylation and suppression of FasL may contribute to the protective function of TP in cancer cells.

Thymidine phosphorylase (platelet-derived endothelial-cell growth factor) in cancer biology and treatment

Thymidine phosphorylase (TP) is often induced in the tumour microenvironment by physiological and chemical stress. Its induction protects cells from apoptosis and helps cell survival by stimulating nucleoside metabolism and angiogenesis. Chemotherapy often upregulates TP, which acts in cell rescue; this result indicates that TP is a crucial therapeutic target. Clinical trials for metastatic diseases have shown that TP-targeting chemotherapy with fluorouracil derivatives greatly improves the effectiveness of conventional chemotherapy for not only response but also prognosis. This new idea, the improvement of TP-inducible therapy with TP-targeting therapy, should be further investigated for early disease states, and inhibitors of TP warrant extensive investigation.

Increased blood-brain barrier permeability with thymidine phosphorylase deficiency

Mitochondrial neurogastrointestinal encephalomyopathy is an autosomal recessive multisystemic disorder caused by thymidine phosphorylase deficiency. Whereas the pathomechanism of the secondary mitochondrial dysfunction has been extensively studied, that of the leukoencephalopathy has not been elucidated. We hypothesized that the white matter hyperintensities on T2-weighted magnetic resonance images reflect disturbance of blood-brain barrier function. Albumin immunohistochemistry disclosed quantitative (p < 0.01) and qualitative differences between the mitochondrial neurogastrointestinal encephalomyopathy and control brains, indicating that loss of thymidine phosphorylase function impairs the integrity of the blood-brain barrier.

The role of thymidine phosphorylase, an angiogenic enzyme, in tumor progression

Thymidine phosphorylase (TP), an enzyme involved in pyrimidine metabolism, is identical with an angiogenic factor, platelet-derived endothelial cell growth factor (PD-ECGF). TP is overexpressed in various tumors and plays an important role in angiogenesis, tumor growth, invasion and metastasis. The enzymatic activity of TP is required for the angiogenic effect of TP. A novel, specific TP inhibitor, TPI, inhibits angiogenesis induced by overexpression of TP in KB/TP cells (human KB epidermoid carcinoma cells transfected with TP cDNA), as well as the growth and metastasis of KB/TP cells in vivo. 2-deoxy-D-ribose, the degradation product of thymidine generated by TP activity, has both angiogenic and chemotactic activity. Both 2-deoxy-D-ribose and TP inhibit a hypoxia-induced apoptotic pathway. These findings suggest that 2-deoxy-D-ribose is a downstream mediator of TP function. 2-deoxy-L-ribose, a stereoisomer of 2-deoxy-D-ribose, inhibits the promotion of angiogenesis, tumor growth and metastasis by TP. Although the mechanism of the action of 2-deoxy-D-ribose is still unknown, 2-deoxy-L-ribose may inhibit the physiological activities of 2-deoxy-D-ribose, and consequently those of TP. Inhibition of TP activity and function appears to be a promising approach for the chemotherapy of various tumors.

Modulation of thymidine phosphorylase by neoadjuvant chemotherapy in primary breast cancer

The combination effect of docetaxel and capecitabine on tumour response rate and survival was demonstrated recently in metastatic breast cancer patients. This combination was based on an experimental hypothesis that taxane can increase tumour sensitivity to the effect of capecitabine through the upregulation of thymidine phosphorylase (TP), which is responsible for the metabolism of 5-fluorouracil (5-FU) and its derivatives, including capecitabine. To examine the alteration in TP expression before and after neoadjuvant chemotherapy, 92 patients with primary breast cancer (T2-4N0-1M0) were enrolled in this study; 14 were treated with adriamycin and cyclophosphamide (AC) or epirubicin and cyclophosphamide (EC); 58 with 5-FU, adriamycin, and cyclophosphamide (FAC) or 5-FU, epirubicin, and cyclophosphamide (FEC); and 20 with FEC followed by docetaxel/taxotere (TXT-containing regimen). Thymidine phosphorylase upregulation was seen in 54.4% and 32.6% of patients in tumour cells and stromal cells, respectively. Increases in TP expression were found only in the AC/EC and TXT-containing regimen groups. In conclusion, it was strongly suggested that unlike 5-FU-containing regimens, the taxane and AC combination therapies upregulate TP expression in primary breast cancer. Thymidine phosphorylase upregulation by several anticancer drugs implies the importance of individualised strategies for sensitisation of tumour tissues to 5-FU and its derivatives.

The nucleoside derivative 5'-O-trityl-inosine (KIN59) suppresses thymidine phosphorylase-triggered angiogenesis via a noncompetitive mechanism of action

Thymidine phosphorylase (TPase) catalyzes the reversible phosphorolysis of pyrimidine deoxynucleosides to 2-deoxy-d-ribose-1-phosphate and their respective pyrimidine bases. The enzymatic activity of TPase was found to be essential for its angiogenesis-stimulating properties. All of the previously described TPase inhibitors are either pyrimidine analogues that interact with the nucleoside-binding site of the enzyme or modified purine derivatives that mimic the pyrimidine structure and either compete with thymidine or act as a multisubstrate (competitive) inhibitor. We now describe the inhibitory activity of the purine riboside derivative KIN59 (5'-O-tritylinosine) against human and bacterial recombinant TPase and TPase-induced angiogenesis. In contrast to previously described TPase inhibitors, KIN59 does not compete with the pyrimidine nucleoside or the phosphate-binding site of the enzyme but noncompetitively inhibits TPase when thymidine or phosphate is used as the variable substrate. In addition, KIN59 was far more active than other TPase inhibitors, previously tested by us, against TPase-induced angiogenesis in the chorioallantoic membrane assay. The observed anti-angiogenic effect of KIN59 was not accompanied by inflammation or any visible toxicity. Inosine did not inhibit the enzymatic or angiogenic activity of the enzyme, indicating that the 5'-O-trityl group in KIN59 is essential for the observed effects. In contrast with current concepts, our data indicate that the angiogenic activity of TPase is not solely directed through its functional nucleoside and phosphate-binding sites. Other regulatory (allosteric) site(s) in TPase may play an important role in the mechanism of TPase-triggered angiogenesis stimulation and apoptosis inhibition. Identification of these site(s) is important to obtain a better insight into the molecular role of TPase in the progression of cancer and angiogenic diseases.

Intracellular renin and the nature of intracrine enzymes

Recently, the binding of renin and prorenin to cellular receptors with the subsequent generation of second messengers and the production of physiological effects has been demonstrated. In addition, the internalization of prorenin by target cells has been associated with increased cellular synthesis of angiotensin and cardiac pathology. Also, a renin transcript lacking the sequences encoding a secretory signal has been reported, and this transcript appears to produce a renin that acts in the cell that synthesized it. Some years ago, we coined the term intracrine for a peptide hormone or factor that acts in the intracellular space either after internalization or retention in its cell of synthesis. Thus defined, a wide variety of peptides display intracrine functionality, including hormones, growth factors, transcription factors, and enzymes. For example, considerable evidence indicates that angiotensin II is an intracrine. Also, general principles of intracrine functionality have been developed. Thus, recent evidence demonstrates that the prorenin/renin molecule is an intracrine enzyme. Here, the actions of intracrine enzymes (angiogenin, phosphoglucose isomerase, phospholipase A2, granzyme A and B, thioredoxin, platelet-derived endothelial growth factor, and serine protease inhibitors) are reviewed. The relation of prorenin/renin to other intracrine enzymes, and to intracrines in general, is discussed.