Activities of adenosine deaminase, 5'-nucleotidase, guanase, and cytidine deaminase enzymes in cancerous and non-cancerous human breast tissues

Macrophage-Derived Adenosine Deaminase 2 Correlates with M2 Macrophage Phenotype in Triple Negative Breast Cancer

Several lines of evidence suggest that altered adenosine deaminase (ADA) activity, especially its ADA2 iso-enzyme, is associated with malignant breast cancer (BC) development. Triple-negative breast cancer (TNBC) is currently the most challenging BC subtype due to its metastatic potential and recurrence. Herein, we analyzed the sources of ADA iso-enzymes in TNBC by investigating the effects of cell-to-cell interactions between TNBC cells, macrophages, lymphocytes, and endothelial cells. We also examined the potential relationship between ADA activity and cancer progression in TNBC patients. In vitro analyses demonstrated that the interactions of immune and endothelial cells with MDA-MB-231 triple negative BC cells modulated their extracellular adenosine metabolism pattern. However, they caused an increase in the ADA1 activity, and did not alter ADA2 activity in cancer cells. In turn, the co-culture of MDA-MB-231 cells with THP-1 monocyte/macrophages, Jurkat cells, and human lung microvascular endothelial cells (HULEC) caused the increase in ADA2 activity on THP-1 cells and ADA1 activity on Jurkat cells and HULEC. Clinical sample analysis revealed that TNBC patients had higher plasma ADA2 activities and lower ADA1/ADA2 ratio at advanced stages of cancer development than in the initial stages, while patients with hormone receptor positive, HER2 negative (HR+HER2-), and triple positive (HR+HER2+) breast cancers at the same stages showed opposite trends. TNBC patients also demonstrated positive associations between plasma ADA2 activity and pro-tumor M2 macrophage markers, as well as between ADA1 activity and endothelial dysfunction or inflammatory parameters. The analysis of TNBC patients, at 6 and 12 months following cancer treatment, did not showed significant changes in plasma ADA activities and macrophage polarization markers, which may be the cause of their therapeutic failure. We conclude that alterations in both ADA iso-enzymes can play a role in breast cancer development and progression by the modulation of extracellular adenosine-dependent pathways. Additionally, the changes in ADA2 activity that may contribute to the differentiation of macrophages into unfavorable pro-tumor M2 phenotype deserve special attention in TNBC.

Ectophosphatase activity in the triple-negative breast cancer cell line MDA-MB-231

Breast cancer is one of the most common cancers in the female population worldwide, and its development is thought to be associated with genetic mutations that lead to uncontrolled and accelerated growth of breast cells. This abnormal behavior requires extra energy, and indeed, tumor cells display a rewired energy metabolism compared to normal breast cells. Inorganic phosphate (Pi) is a glycolytic substrate of glyceraldehyde-3-phosphate dehydrogenase and has an important role in cancer cell proliferation. For cells to obtain Pi, ectoenzymes in the plasma membrane with their catalytic site facing the extracellular environment can hydrolyze phosphorylated molecules, and this is an initial and possibly limiting step for the uptake of Pi by carriers that behave as adjuvants in the process of energy harvesting and thus partially contributes to tumor energy requirements. In this study, the activity of an ectophosphatase in MDA-MB-231 cells was biochemically characterized, and the results showed that the activity of this enzyme was higher in the acidic pH range and that the enzyme had a K_m  = 4.5 ± 0.5 mM para-nitrophenylphosphate and a V_max  = 2280 ± 158 nM × h^-1  × mg protein^-1 . In addition, classical acid phosphatase inhibitors, including sodium orthovanadate, decreased enzymatic activity. Sodium orthovanadate was able to inhibit ectophosphatase activity while also inhibiting cell proliferation, adhesion, and migration, which are important processes in tumor progression, especially in metastatic breast cancer MDA-MB-231 cells that have higher ectophosphatase activity than MCF-7 and MCF-10 breast cells.

Homopurine Alkaloids: A Brief Overview

The isolation, structure elucidation, synthesis, biological properties, and biosynthesis of the homopurine alkaloids are reviewed, with an emphasis on the “victim-guardian” relationships between co-occurring alkaloids.

Serum Adenosine Deaminase Levels and Human Papillomavirus as Prognostic and Predictive Factors for Laryngeal and Pharyngeal Carcinomas

Head and neck cancer is one of the most common cancers in the world, accounting for up to 30-40% malignancies in India. Research is always on the lookout for parameters that help in early diagnosis of such disease and to explore the possibility of discovering such parameters that would assist in management of the disease by its potential to predict and prognosticate the disease. To estimate serum ADA levels and to correlate with response to therapy and also to correlate between different clinical stages and serum ADA levels and to correlate HPV status to response to therapy. A prospective cohort study. 30 patients who were diagnosed with squamous cell carcinoma of the oropharynx, hypopharynx and larynx were considered in this study. The pre and post treatment values of serum ADA was estimated in these patients and the tumour was assessed for HPV status. The difference in the in the serum ADA levels before and after treatment was 9.982 which was statistically significant with a p value of < 0.001. HPV positive status and response to therapy in the form of recurrence shows a p value of 0.485 which is not statistically significant. Serum ADA level can be used as a parameter to assess the severity of the disease and the response to treatment in cases of carcinoma of the oropharynx, hypopharynx and larynx. HPV status of the disease has its limitation in prediction and prognosis of the disease.

Adenosine deaminase inhibition

Adenosine deaminase is a critical enzyme in purine metabolism that regulates intra and extracellular adenosine concentrations by converting it to inosine. Adenosine is an important purine that regulates numerous physiological functions by interacting with its receptors. Adenosine and consequently adenosine deaminase can have pro or anti-inflammatory effects on tissues depending on how much time has passed from the start of the injury. In addition, an increase in adenosine deaminase activity has been reported for various diseases and the significant effect of deaminase inhibition on the clinical course of different diseases has been reported. However, the use of inhibitors is limited to only a few medical indications. Data on the increase of adenosine deaminase activity in different diseases and the impact of its inhibition in various cases have been collected and are discussed in this review. Overall, the evidence shows that many studies have been done to introduce inhibitors, however, in vivo studies have been much less than in vitro, and often have not been expanded for clinical use.

CD73 a novel marker for the diagnosis of benign and malignant salivary gland tumors

Background

Ecto-5’-nucleotidase (CD73) plays an important role in the development of several types of cancer; however, its prognostic significance in salivary gland tumors remains unknown. The current study was conducted to investigate the expression of CD73 in such tumors.

Material and Methods

In this retrospective study, immunohistochemical expression of CD73 was evaluated in 25 pleomorphic adenomas, 20 mucoepidermoid carcinomas and 20 adenoid cystic carcinomas using the Envision technique. Labeling indices of CD73 expression were calculated and compared between lesions.

Results

Immunohistochemical analysis demonstrated that the CD73 expression was significantly higher in salivary gland tumors than in normal salivary gland tissue (p<0.001). CD73 expression was significantly higher in mucoepidermoid carcinoma and adenoid cystic carcinoma compared to pleomorphic adenoma p<0.001). In addition, the expression of CD73 was significantly higher in lymph node metastasizing cancers compared to non-metastasizing malignancies (P<0.001). In contrast, there was no significant association between CD73 expression and other clinicopathological variables such as age, gender, tumor size and distant metastasis (P>0.05).

Conclusions

The findings suggest that CD73 can be an independent and useful biomarker for predicting the clinical behavior of salivary gland tumors.

Key words:Ecto-5’-nucleotidase, immunohistochemistry, salivary gland tumors.

Adenosine deaminase inhibition suppresses progression of 4T1 murine breast cancer by adenosine receptor-dependent mechanisms

The activity of a cell-surface ecto-adenosine deaminase (eADA) is markedly increased in the endothelial activation and vascular inflammation leading to decreased adenosine concentration and alterations in adenosine signalling. Depending on the specific pathway activated, extracellular purines mediate host cell response or regulate growth and cytotoxicity on tumour cells. The aim of this study was to test the effects of adenosine deaminase inhibition by 2'deoxycoformycin (dCF) on the breast cancer development. dCF treatment decreased a tumour growth and a final tumour mass in female BALB/c mice injected orthotopically with 4T1 cancer cells. dCF also counteracted cancer-induced endothelial dysfunction in orthotopic and intravenous 4T1 mouse breast cancer models. In turn, this low dCF dose had a minor effect on immune stimulation exerted by 4T1 cell implantation. In vitro studies revealed that dCF suppressed migration and invasion of 4T1 cells via A2a and A3 adenosine receptor activation as well as 4T1 cell adhesion and transmigration through the endothelial cell layer via A2a receptor stimulation. Similar effects of dCF were observed in human breast cancer cells. Moreover, dCF improved a barrier function of endothelial cells decreasing its permeability. This study highlights beneficial effects of adenosine deaminase inhibition on breast cancer development. The inhibition of adenosine deaminase activity by dCF reduced tumour size that was closely related to the decreased aggressiveness of tumour cells by adenosine receptor-dependent mechanisms and endothelial protection.

Role of adenosine signaling in the pathogenesis of head and neck cancer

The concentrations of adenosine may increase under ischemic conditions in the tumor microenvironment, and then it enters the systemic circulation. Adenosine controls cancer progression and responses to therapy by regulating angiogenesis, cell survival, apoptosis, cell proliferation, and metastases in tumors. Hence, adenosine metabolism, adenosine-generating enzymes, and adenosine signaling are potentially novel therapeutic targets in a wide range of pathological conditions, including cerebral and cardiac ischemic diseases, inflammatory disorders, immunomodulatory disorders, and, of special interest in this review, cancer. This review summarizes the role of adenosine in the pathogenesis of head and neck cancer for a better understanding of how this may be applied to treating this type of cancer.

Metabolic Hallmarks of Tumor and Immune Cells in the Tumor Microenvironment

Cytotoxic T lymphocytes and NK cells play an important role in eliminating malignant tumor cells and the number and activity of tumor-infiltrating T cells represent a good marker for tumor prognosis. Based on these findings, immunotherapy, e.g., checkpoint blockade, has received considerable attention during the last couple of years. However, for the majority of patients, immune control of their tumors is gray theory as malignant cells use effective mechanisms to outsmart the immune system. Increasing evidence suggests that changes in tumor metabolism not only ensure an effective energy supply and generation of building blocks for tumor growth but also contribute to inhibition of the antitumor response. Immunosuppression in the tumor microenvironment is often based on the mutual metabolic requirements of immune cells and tumor cells. Cytotoxic T and NK cell activation leads to an increased demand for glucose and amino acids, a well-known feature shown by tumor cells. These close metabolic interdependencies result in metabolic competition, limiting the proliferation, and effector functions of tumor-specific immune cells. Moreover, not only nutrient restriction but also tumor-driven shifts in metabolite abundance and accumulation of metabolic waste products (e.g., lactate) lead to local immunosuppression, thereby facilitating tumor progression and metastasis. In this review, we describe the metabolic interplay between immune cells and tumor cells and discuss tumor cell metabolism as a target structure for cancer therapy. Metabolic (re)education of tumor cells is not only an approach to kill tumor cells directly but could overcome metabolic immunosuppression in the tumor microenvironment and thereby facilitate immunotherapy.

Uncaria tomentosa extract alters the catabolism of adenine nucleotides and expression of ecto-5'-nucleotidase/CD73 and P2X7 and A1 receptors in the MDA-MB-231 cell line

ETHOPHARMACOLOGICAL RELEVANCE

Uncaria tomentosa (Willd.) DC. (Rubiaceae) (Ut), also known as cat's claw, is a woody liana widely spread throughout the Amazon rainforest of Central and South America, containing many chemical constituents such as oxindole alkaloids, which are responsible for various biological activities. Since ancient times, the indigenous people of Peru have used it as a bark infusion for the treatment of a wide range of health problems gastric ulcers, arthritis and rheumatism. Recently, Ut is distributed worldwide and used as an immunomodulatory and anti-inflammatory herbal remedy. Additionally, U. tomentosa also has antitumural activity. However, little is known about the action of U. tomentosa on the purinergic system mechanisms, which is involved in tumor progression.

AIM OF THE STUDY

Considering the pharmacological properties of U. tomentosa, we sought to evaluate the hydroalcoholic extract U tomentosa is able to influence the purinergic system in breast cancer cells, MDA-MB-231. Through the activity and expression of ectonucleotidases (NTPDase - CD39; Ecto-5'-nucleotidase - CD73) and purinergic repceptores (P2X7 and A1).

MATERIALS AND METHODS

A hydroalcoholic extract was prepared in two concentrations, 250 and 500μg/mL. (Ut250; Ut500). The effect of these concentrations on the activity and expression of ectonucleotidases, as well as on the density of purinergic receptors were investigated in MDA-MB-231 breast cancer cells. Cells were treated with the hydroalcoholic extract of Uncaria tomentosa and/or doxorubicin (Doxo 1μM; Ut250+Doxo; Ut500+Doxo) for 24h.

RESULTS

Although the results were not significant for the hydrolysis of the ATP, they presented an increase in the ADP hydrolysis in the Ut500+Doxo group when compared to the control group. Additionally, the activity of 5'-nucleotidase was inhibited in all groups when compared with the untreated group of cells. Inhibition of the enzyme was more evident in groups with U. tomentosa per se. The expression of CD39 was increased in the Ut250 and Ut250+Doxo groups when compared to the control group. No changes were found in the CD73 expression. Furthermore, a reduction in the density of the P2X7 receptor in all treated groups was detected. On the other hand, the density of the A1 receptor increased in all groups compared to the control group, with the exception of the Ut500+Doxo group.

CONCLUSION

Therefore, we conclude that hydroalcoholic extract of U. tomentosa may be responsible for the reduction of adenosine levels in the extracellular medium, which accelerates tumor progression. Interestingly, the dysregulation of A1 and P2X7 receptors in the MDA-MB-231 cells exacerbate the proliferation of this cells and U. tomentosa treatment may be stimulate the antitumor activity of adenosine A1 receptor and control the P2X7 effects. Our study demonstrates the significant participation of purinergic pathway in the regulation of MDA-MB-231 progression; additionally, U. tomentosa treatment alone or combined with chemotherapy may favor the action of doxorubicin.

Identification of Serum Biomarkers for Gastric Cancer Diagnosis Using a Human Proteome Microarray

We aimed to globally discover serum biomarkers for diagnosis of gastric cancer (GC). GC serum autoantibodies were discovered and validated using serum samples from independent patient cohorts encompassing 1,401 participants divided into three groups, i.e. healthy, GC patients, and GC-related disease group. To discover biomarkers for GC, the human proteome microarray was first applied to screen specific autoantibodies in a total of 87 serum samples from GC patients and healthy controls. Potential biomarkers were identified via a statistical analysis protocol. Targeted protein microarrays with only the potential biomarkers were constructed and used to validate the candidate biomarkers using 914 samples. To provide further validation, the abundance of autoantibodies specific to the biomarker candidates was analyzed using enzyme-linked immunosorbent assays. Receiver operating characteristic curves were generated to evaluate the diagnostic accuracy of the serum biomarkers. Finally, the efficacy of prognosis efficacy of the final four biomarkers was evaluated by analyzing the clinical records. The final panel of biomarkers consisting of COPS2, CTSF, NT5E, and TERF1 provides high diagnostic power, with 95% sensitivity and 92% specificity to differentiate GC patients from healthy individuals. Prognosis analysis showed that the panel could also serve as independent predictors of the overall GC patient survival. The panel of four serum biomarkers (COPS2, CTSF, NT5E, and TERF1) could serve as a noninvasive diagnostic index for GC, and the combination of them could potentially be used as a predictor of the overall GC survival rate.

Bioorthogonal labeling cell-surface proteins expressed in pancreatic cancer cells to identify potential diagnostic/therapeutic biomarkers

To develop new diagnostic and therapeutic tools to specifically target pancreatic tumors, it is necessary to identify cell-surface proteins that may serve as potential tumor-specific targets. In this study we used an azido-labeled bioorthogonal chemical reporter to metabolically label N-linked glycoproteins on the surface of pancreatic cancer cell lines to identify potential targets that may be exploited for detection and/or treatment of pancreatic cancer. Labeled glycoproteins were tagged with biotin using click chemistry, purified by streptavidin-coupled magnetic beads, separated by gel electrophoresis, and identified by liquid chromatography-tandem mass spectrometry (MS). MS/MS analysis of peptides from 3 cell lines revealed 954 unique proteins enriched in the azido sugar samples relative to control sugar samples. A comparison of the proteins identified in each sample indicated 20% of these proteins were present in 2 cell lines (193 of 954) and 17 of the proteins were found in all 3 cell lines. Five of the 17 proteins identified in all 3 cell lines have not been previously reported to be expressed in pancreatic cancer; thus indicating that novel cell-surface proteins can be revealed through glycoprotein profiling. Western analysis of one of these glycoproteins, ecto-5'-nucleotidase (NT5E), revealed it is expressed in 8 out of 8 pancreatic cancer cell lines examined. Further, immunohistochemical analysis of human pancreatic tissues indicates NT5E is significantly overexpressed in pancreatic tumors compared to normal pancreas. Thus, we have demonstrated that metabolic labeling with bioorthogonal chemical reporters can be used to selectively enrich and identify novel cell-surface glycoproteins expressed in pancreatic ductal adenocarcinomas.

Cell-death-associated molecular patterns as determinants of cancer immunogenicity

SIGNIFICANCE

Accumulating evidence indicates that the success of some anticancer treatments (select chemotherapies or radiotherapy or trastuzumab) could be related to the stimulation of an anticancer immune response through the induction of an immunogenic tumor cell death (ICD).

RECENT ADVANCES

Preclinical data revealed that dying tumor cells can emit a series of danger signals (so-called "cell-death-associated molecular patterns" (CDAMP)) that will dictate the recruitment and activation of specific inflammatory phagocytes. Hence, tumor cells succumbing to ICD are characterized by specific metabolic and molecular changes that will trigger a hierarchy of polarizing cytokine-producing cells, culminating in the recruitment and reactivation of antitumor interferon-γ-producing effector T cells which contribute to the success of cytotoxic treatments.

CRITICAL ISSUES

In this review, we summarize the molecular and cellular bases of this ICD, underscoring the crucial role of high mobility group box 1 protein (HMGB1) and adenosine tri-phosphate, both of which are released from dying tumor cells during ICD and are implicated in the chemotherapy-elicited anticancer immune response.

FUTURE DIRECTIONS

We discuss here how such CDAMP could serve as predictive biomarkers that could discriminate immunogenic from nonimmunogenic anti-cancer compounds, and, in case of deficiency, could be compensated by surrogate products to ameliorate the success rate of conventional anticancer treatment modalities.

Analogs of iso-azepinomycin as potential transition-state analog inhibitors of guanase: synthesis, biochemical screening, and structure-activity correlations of various selectively substituted imidazo[4,5-e][1,4]diazepines

Guanase is an important enzyme of the purine salvage pathway of nucleic acid metabolism and its inhibition has beneficial implications in viral, bacterial, and cancer therapy. The work described herein is based on a hypothesis that azepinomycin, a heterocyclic natural product and a purported transition state analog inhibitor of guanase, does not represent the true transition state of the enzyme-catalyzed reaction as closely as does iso-azepinomycin, wherein the 6-hydroxy group of azepinomycin has been translocated to the 5-position. Based on this hypothesis, and assuming that iso-azepinomycin would bind to guanase at the same active site as azepinomycin, several analogs of iso-azepinomycin were designed and successfully synthesized in order to gain a preliminary understanding of the hydrophobic and hydrophilic sites surrounding the guanase binding site of the ligand. Specifically, the analogs were designed to explore the hydrophobic pockets, if any, in the vicinity of N1, N3, and N4 nitrogen atoms as well as O(5) oxygen atom of iso-azepinomycin. Biochemical inhibition studies of these analogs were performed using a mammalian guanase. Our results indicate that (1) increasing the hydrophobicity near O(5) results in a negative effect, (2) translocating the hydrophobicity from N3 to N1 also results in decreased inhibition, (3) increasing the hydrophobicity near N3 or N4 produces significant enhancement of inhibition, (4) increasing the hydrophobicity at either N3 or N4 with a simultaneous increase in hydrophobicity at O(5) considerably diminishes any gain in inhibition made by solely enhancing hydrophobicity at N3 or N4, and (5) finally, increasing the hydrophilic character near N3 has also a deleterious effect on inhibition. The most potent compound in the series has a Ki value of 8.0±1.5μM against rabbit liver guanase.

Overexpression of CD73 in prostate cancer is associated with lymph node metastasis

Prostate cancer is the most common malignancy in men in Europe and North America. At present, it is becoming an increasingly common cancer in China. CD73 (ecto-5'-nucleotidase) is a glycosylphosphatidylinositol (GPI)-linked 70-kDa cell surface enzyme. It is also broadly expressed in many types of tissues. Recent studies have showed that CD73 is widely expressed on malignancies and is up-regulated in cancerous tissues. Consequently, we analyzed the expression of CD73 in prostate cancer tissue. The expression of the CD73 protein was evaluated by Immunohistochemistry staining in 116 tissue specimens. The expression was further examined by quantitative real-time PCR (qRT-PCR) and Western blot in the same set of patients. The intense cell membrane staining for the CD73 protein was observed. The expression of CD73 in lymph node non-metastasizing prostate cancer tissues can be seen at low levels, and is generally undetectable. RT-PCR and Western blot showed that the expression of CD73 in lymph node metastasizing prostate cancer was higher compared with non-metastasizing ones. These results suggest that CD73 could be considered as a relevant-specific target for molecular therapy of prostate cancer metastasis.

Potential prognostic biomarker CD73 regulates epidermal growth factor receptor expression in human breast cancer

CD73, an ecto-enzyme overexpressed in breast-cancer cells, catalyzes the dephosphorylation of adenosine monophosphates into adenosine. Anti-CD73 slows breast cancer growth and its spread both in vivo and in vitro. In this study, we investigated the relation of CD73 to epidermal growth factor receptor (EGFR) expression using tissue array and breast cancer cell lines. We found that CD73 expression correlated positively to EGFR expression in vivo (n = 80, r = 0.425, P < 0.01) and in vitro. EGFR expression can be decreased by suppressing CD73 with an inhibitor or small shRNA, and this effect was reversed by adenosine and NECA (adenosine A2 receptor agonist), which suggested that adenosine is involved in EGFR expression regulated by CD73 (P < 0.01). We also showed that CD73 regulates EGFR phosphorylation by Src (P < 0.01). By transcription factor (TF) assay, CD73 was found to regulate some associated TFs activity such as PPARγ, which mediates EGFR expression, although whether PPARγ mediates the effect of CD73 on EGFR expression needs further study. The Kaplan-Meier recurrence-free survival curves for CD73 were also plotted in www.kmplot.com. The curves show that CD73 expression separates the cases into significantly different prognostic groups among the estrogen receptor-negative cancers (P < 0.01). Our results suggest that CD73 may be a potential prognostic biomarker associated with coexpression of EGFR in human breast cancer.

Ectonucleotide pyrophosphatase/phosphodiesterase (E-NPP) and adenosine deaminase (ADA) activities in prostate cancer patients: influence of Gleason score, treatment and bone metastasis

The relation between adenine nucleotides and cancer has already been described in literature. Considering that the enzymes ectonucleotide pyrophosphatase/phosphodiesterase (E-NPP) and adenosine deaminase (ADA) act together to control nucleotide levels, we aimed to investigate the role of these enzymes in prostate cancer (PCa). E-NPP and ADA activities were determined in serum and platelets of PCa patients and controls. We also verified the influence of the Gleason score, bone metastasis and treatment in the enzyme activities. Platelets and serum E-NPP activity increased, whereas ADA activity in serum decreased in PCa patients. In addition, Gleason score, metastasis and treatment influenced E-NPP and ADA activities. We may propose that E-NPP and ADA are involved in the development of PCa. Moreover, E-NPP and ADA activities are modified in PCa patients with distinct Gleason score, with bone metastasis, as well as in patients under treatment.

CD73 expression as a potential marker of good prognosis in breast carcinoma

Ecto-5'-nucleotidase (CD73) is a membrane-bound enzyme, which catalyzes the conversion of adenosine monophosphate to adenosine. CD73 has been postulated to play an important role in carcinogenesis, as adenosine promotes tumor progression and CD73-expressing cancer cell lines are more aggressive. However, other studies have shown that activated adenosine receptors may also inhibit cell proliferation. This study investigated the clinical significance of CD73 expression in breast cancer. The study group included 136 consecutive stage I-III breast cancer patients treated between 2001 and 2008 at 2 institutions. CD73 expression was examined by immunohistochemistry (IHC) on tissue microarrays, using antihuman mouse monoclonal antibody. Survival curves were generated by the Kaplan-Meier method and compared using the log-rank test. CD73 staining was expressed as the score calculated by multiplying the staining intensity (0=negative, 1=weak, 2=intermediate, 3=strong) and percentage of positive cells (0% to 100%). The median score among all samples was 100. Positive CD73 staining (defined as score equal or higher than 100) occurred in 74% of the cases. No correlation was found between CD73 expression and grading, tumor size, lymph node status, histologic type, estrogen receptor, or progesterone receptor status. Positive CD73 expression strongly correlated with longer disease-free survival (hazard ratio=0.26; 95% confidence interval, 0.1-0.66; P=0.0044) and overall survival (hazard ratio =0.24; 95% confidence interval, 0.07-0.85; P=0.027). Multivariate analysis for disease-free survival revealed correlation with tumor size and CD73 status. Elevated CD73 expression in breast cancer can predict a good prognosis. However, the actual role of CD73 in cancerogenesis remains unclear and requires further analysis.

A novel transition state analog inhibitor of guanase based on azepinomycin ring structure: Synthesis and biochemical assessment of enzyme inhibition

Synthesis and biochemical inhibition studies of a novel transition state analog inhibitor of guanase bearing the ring structure of azepinomycin have been reported. The compound was synthesized in five-steps from a known compound and biochemically screened against the rabbit liver guanase. The compound exhibited competitive inhibition profile with a K(i) of 16.7±0.5μM.

CD73 on tumor cells impairs antitumor T-cell responses: a novel mechanism of tumor-induced immune suppression

CD73, originally defined as a lymphocyte differentiation antigen, is thought to function as a cosignaling molecule on T lymphocytes and an adhesion molecule that is required for lymphocyte binding to endothelium. We show here that CD73 is widely expressed on many tumor cell lines and is upregulated in cancerous tissues. Because the ecto-5'-nucleotidase activity of CD73 catalyzes AMP breakdown to immunosuppressive adenosine, we hypothesized that CD73-generated adenosine prevents tumor destruction by inhibiting antitumor immunity. We confirmed this hypothesis by showing that combining tumor CD73 knockdown and tumor-specific T-cell transfer cured all tumor-bearing mice. In striking contrast, there was no therapeutic benefit of adoptive T-cell immunotherapy in mice bearing tumors without CD73 knockdown. Moreover, blockade of the A2A adenosine receptor with a selective antagonist also augmented the efficacy of adoptive T-cell therapy. These findings identify a potential mechanism for CD73-mediated tumor immune evasion and point to a novel cancer immunotherapy strategy by targeting the enzymatic activity of tumor CD73.

Diagnostic value of adenosine deaminase activity in benign and malignant breast tumors

BACKGROUND AND AIMS

The present study was carried out to evaluate the activity of adenosine deaminase (ADA) and its isoenzymes ADA1 and ADA2 activities as a diagnostic tool in patients with benign and malignant breast disease.

METHODS

Total ADA, ADA1, and ADA2 activities of serum and tumor were analyzed using 58 subjects including 20 patients with benign breast disease (BBD), 34 patients with primary breast cancer, and 20 patients as normal control subjects.

RESULTS

The mean values for total ADA and ADA2 activities in the serum and tumor of BBD were significantly higher than those of healthy controls (p <0.01). Furthermore, the mean values for total ADA and ADA2 activities of patients with breast cancer were significantly higher than those of the benign group (p <0.005) and healthy subjects (p <0.0001).

CONCLUSIONS

Based on the present results, it is concluded that the assessment of total ADA and ADA2 activities may be used as a reliable test for differential diagnosis of benign and malignant breast disease.

Guanine deaminase functions as dihydropterin deaminase in the biosynthesis of aurodrosopterin, a minor red eye pigment of Drosophila

Dihydropterin deaminase, which catalyzes the conversion of 7,8-dihydropterin to 7,8-dihydrolumazine, was purified 5850-fold to apparent homogeneity from Drosophila melanogaster. Its molecular mass was estimated to be 48 kDa by gel filtration and SDS-PAGE, indicating that it is a monomer under native conditions. The pI value, temperature, and optimal pH of the enzyme were 5.5, 40 degrees C, and 7.5, respectively. Interestingly the enzyme had much higher activity for guanine than for 7,8-dihydropterin. The specificity constant (k(cat)/K(m)) for guanine (8.6 x 10(6) m(-1).s(-1)) was 860-fold higher than that for 7,8-dihydropterin (1.0 x 10(4) m(-1).s(-1)). The structural gene of the enzyme was identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis as CG18143, located at region 82A1 on chromosome 3R. The cloned and expressed CG18143 exhibited both 7,8-dihydropterin and guanine deaminase activities. Flies with mutations in CG18143, SUPor-P/Df(3R)A321R1 transheterozygotes, had severely decreased activities in both deaminases compared with the wild type. Among several red eye pigments, the level of aurodrosopterin was specifically decreased in the mutant, and the amount of xanthine and uric acid also decreased considerably to 76 and 59% of the amounts in the wild type, respectively. In conclusion, dihydropterin deaminase encoded by CG18143 plays a role in the biosynthesis of aurodrosopterin by providing one of its precursors, 7,8-dihydrolumazine, from 7,8-dihydropterin. Dihydropterin deaminase also functions as guanine deaminase, an important enzyme for purine metabolism.

Diminution in adenine nucleotide hydrolysis by platelets and serum from rats submitted to Walker 256 tumour

Extracellular adenine nucleotide hydrolysis in the circulation is mediated by the action of an NTPDase (CD39, apyrase) and of a 5'-nucleotidase (CD73), presenting as a final product, adenosine. Among other properties described for adenine nucleotides, an anti-cancer activity is suggested, since ATP is considered a cytotoxic molecule in several tumour cell systems. Conversely, some studies demonstrate that adenosine presents a tumour-promoting activity. In this study, we evaluated the pattern of adenine nucleotide hydrolysis by serum and platelets from rats submitted to the Walker 256 tumour model. Extracellular adenine nucleotide hydrolysis by blood serum and platelets obtained from rats at, 6, 10 and 15 days after the subcutaneous Walker 256 tumour inoculation, was evaluated. Our results demonstrate a significant reduction in ATP, ADP and AMP hydrolysis in blood serum at 6, 10 and 15 days after tumour induction. In platelets, a significant reduction in ATP and AMP hydrolysis was observed at 10 and 15 days after tumour induction, while an inhibition of ADP hydrolysis was observed at all times studied. Based on these results, it is possible to suggest a physiologic protection mechanism against the tumoral process in circulation. The inhibition in nucleotide hydrolysis observed probably maintains ATP levels elevated (cytotoxic compound) and, at the same time, reduces the adenosine production (tumour-promoting molecule) in the circulation.

Chapter 2: Ring-Expanded (‘Fat‘) Purines and their Nucleoside/Nucleotide Analogues as Broad-Spectrum Therapeutics

This chapter describes a family of ring-expanded purines, informally referred to as “fat” or f-purines, as well as their nucleoside/nucleotide analogues (RENs/RENTs) that have broad applications in chemistry, biology, and medicine. Although purine itself has never been found in nature, substituted purines, such as adenine and guanine, or their respective nucleoside derivatives, adenosine and guanosine, are the most ubiquitous class of nitrogen heterocycles and play crucial roles in wide variety of functions of living beings As nucleotides (AMP,GMP), they are the building blocks of nucleic acids (RNA/DNA). They serve as energy cofactors (ATP, GTP), as part of coenzymes (NAD/FAD) in oxidation-reduction reactions, as important second messengers in many intracellular signal transduction processes (cAMP/cGMP), or as direct neurotransmitters by binding to purinergic receptors (adenosine receptors). Therefore, it is not surprising that the analogues of purines have found utility both as chemotherapeutics (antiviral, antibiotic, and anticancer agents) and pharmacodynamic entities (the regulation of myocardial oxygen consumption and cardiac blood flow). While they can act as substrates or the inhibitors of the enzymes of purine metabolism to render their chemotherapeutic action, their ability to act as agonists or antagonists of A1/A2A receptors is the basis for the modulation of pharmacodynamic property.

Ecto-5'-nucleotidase promotes invasion, migration and adhesion of human breast cancer cells

PURPOSE

Associated with many molecules, metastasis includes cell adhesion to extracellular matrix, migration towards specific direction and invasion into local vessel of distant organs. The purpose of the present study was to evaluate the role of ecto-5'-nucleotidase (eN, ecto-5-NT, CD73) generated extracellular adenosine in biologically malignant behaviors of human breast cancer cell lines.

MATERIALS AND METHODS

Two human breast cancer cell lines, T-47D with lower expression of CD73 and MB-MDA-231 with higher expression of CD73, were used to investigate the functions of CD73. The effects of CD73 over-expression on invasion, migration and adhesion were observed in T-47D transfected with pcDNA-NT5E plasmid. The effects of specific CD73 inhibitor, alpha, ss-methylene ADP (APCP), were observed in MB-MDA-231 cells.

RESULTS

The results showed CD-73 overexpression increased invasion, migration and adhesion to ECM of the pcDNA-NT5E transfected T-47D cells compared to the saline and mock vector controls. The increased cell mobility of CD-73-overexpressed T-47D cells was blocked by APCP. Adenosine increased the mobility of wild type T-47D cells. APCP inhibited the mobility of the MB-MDA-231 cells.

CONCLUSION

Taken together, our results indicated that CD73 may facilitate the adhesion, migration and invasion of human breast cancer cells through its enzyme activity of generating adenosine. This study provided a possibly molecular mechanism of metastasis of breast carcinoma.

Catalytic mechanism of guanine deaminase: an ONIOM and molecular dynamics study

The catalytic mechanism of Bacillus subtilis guanine deaminase (bGD), a Zn metalloenzyme, has been investigated by a combination of quantum mechanical calculations using the multilayered ONIOM method and molecular dynamics simulations. In contrast to a previously proposed catalytic mechanism, which requires the bound guanine to assume a rare tautomeric state, the ONIOM calculations showed that the active-site residues of the enzyme do not affect the tautomeric state of guanine, and consequently the bound guanine is a tautomer that is the most abundant in aqueous solution. Two residues, Glutamate 55 and Aspartate 114, were found to play important roles in proton shuttling in the reaction. The proposed reaction path is initiated by proton transfer from a Zn-bound water to protonate Asp114. This process may be quite complex and rather dynamic in nature, as revealed by the molecular dynamics (MD) simulations, whereby another water may bridge the Zn-bound water and Asp114, which then is eliminated by positioning of guanine in the active site. The binding of guanine stabilizes protonated Asp114 by hydrogen bond formation. Asp114 can then transfer its proton to the N3 of the bound guanine, facilitating the nucleophilic attack on C2 of the guanine by the Zn-bound hydroxide to form a tetrahedral intermediate. This occurs with a rather low barrier. Glu55 then transfers a proton from the Zn-hydroxide to the amino group of the reaction intermediate and, at this point, the C2-N2 bond has lengthened by 0.2 A compared to guanine, making C2-N2 bond cleavage more facile. The C2-N2 bond breaks forming ammonia, with an energy barrier of approximately 8.8 kcal/mol. Ammonia leaves the active site, and xanthine is freed by the cleavage of the Zn-O2 bond, with a barrier approximately 8.4 kcal/mol. Along this reaction path, the highest barrier comes from C2-N2 bond cleavage, while the barrier from the cleavage of the Zn-O2 bond is slightly smaller. The Zn-O2 bond can be broken without the assistance of water during the release of xanthine.

Nucleotide metabolizing ecto-enzymes in Walker 256 tumor cells: molecular identification, kinetic characterization and biochemical properties

In this study we describe the molecular identification, kinetic characterization and biochemical properties of an E-NTPDase and an 5'-nucleotidase in Walker 256 cells. For the ATP, ADP and AMP hydrolysis there were optimum pH in the range 6.5-8.0, and absolute requirement for divalent cations (Mg(2+)>Ca(2+)). A significant inhibition of ATP and ADP hydrolysis was observed in the presence of high concentrations of sodium azide and 0.5 mM of Gadolinium chloride. These activities were insensitive to ATPase, adenylate kinase and alkaline phosphatase classical inhibitors. The K(m) values were 464.2+/-86.6 microM (mean+/-SEM, n=4), 137.0+/-31 microM (mean+/-SEM, n=5) and 44.8+/-10.2 microM (mean+/-SEM, n=4), and V(max) values were 655.0+/-94.6 (mean+/-SEM, n=4), 236.3+/-27.2 (mean+/-SEM, n=5) and 177.6+/-13.8 (mean+/-SEM, n=5) nmol of inorganic phosphate min(-1) mg of protein(-1) for ATP, ADP and AMP, respectively. Using RT-PCR analysis we identified the mRNA of two members of the ecto-nucleoside triphosphate diphosphohydrolase family (NTPDase 2 and 5) and a 5'-nucleotidase. The presence of NTPDases and 5'-nucleotidase enzymes in Walker 256 tumor cells may be important to regulate the ratio adenine nucleotides/adenine nucleoside extracellularly, therefore motivating tumor growth.

Design of inhibitors against guanase: Synthesis and biochemical evaluation of analogues of azepinomycin

As part of a program to design rational, mechanism-based inhibitors of guanase, we report here the synthesis and biochemical screening of two analogues of azepinomycin (1 and 2), a naturally occurring inhibitor of guanase, known to mimic the transition-state of the enzyme-catalyzed reaction. Our biochemical results show that compounds 1 and 2 are competitive inhibitors with K(i) of 2.01+/-0.16 x 10(-5) and 5.36+/-0.14 x 10(-5) M, respectively.

Anticancer effect of Kalpaamruthaa on mammary carcinoma in rats with reference to glycoprotein components, lysosomal and marker enzymes

A promising approach to reduce the occurrence of cancer is its treatment, specifically by chemical intervention through minor dietary constituents. Epidemiological studies suggest that specific pharmacologically active agents present in the diet might reduce cancer. A remarkable surge of interest in chemoprevention research has, thus, lead to the identification of many phytochemicals of dietary origin as effective potential chemotherapeutic agents. In the present investigation, attempt has been made to study the potency of Kalpaamruthaa (KA), a herbal preparation, against cancer. The changes in level of glycoprotein components, marker enzymes and lysosomal enzymes were carried out in 7,12-dimethylbenz(a)anthracene (DMBA) induced Sprague-Dawley rats. The changes in the body weights and volume were also determined. KA was administered at the dosage level of 100, 200, 300, 400 and 500 mg/kg body weight (BW) in olive oil orally for 14 d, after the induction period is completed (90 d). On administration of KA, the levels of the above enzymes and the changes in the body weights and volume were significantly normalized in a dose dependent manner. The present study shows that KA is effective at the dosage level of 300 mg/kg body weight in mammary carcinoma bearing rats.

Adenosine deaminase activity in the serum and malignant tumors of breast cancer: the assessment of isoenzyme ADA1 and ADA2 activities

OBJECTIVE

The potential relationship between adenosine deaminase activity and cancer progression was examined by investigating the activity of total ADA and its isoenzymes in serum and simultaneously in the cancerous tissue of each patient with breast cancer.

METHODS

Total ADA and its isoenzymes were measured using the Giusti method. ADA2 activity was measured in the presence of a specific ADA1 inhibitor, EHNA.

RESULTS

Our results indicated that ADA2 and total ADA activities were higher in serum and malignant tissues than those of corresponding controls (P < 0.05). Tumor ADA2 and total ADA activities were significantly (P < 0.05) correlated with lymph node involvement, histological grade and tumor size, whereas their levels in serum were significantly (P < 0.05) correlated with menopausal status and patient age.

CONCLUSION

Although serum and tumor total ADA activity and its ADA2 isoenzyme were both found to be increased, distinct correlation patterns were observed with some of the prognostic factors. It can be speculated that increased ADA and isoenzyme activities in serum originated from sources other than the breast tumors.

The 5'-nucleotidases as regulators of nucleotide and drug metabolism

The 5'-nucleotidases are a family of enzymes that catalyze the dephosphorylation of nucleoside monophosphates and regulate cellular nucleotide and nucleoside levels. While the nucleoside kinases responsible for the initial phosphorylation of salvaged nucleosides have been well studied, many of the catabolic nucleotidases have only recently been cloned and characterized. Aside from maintaining balanced ribo- and deoxyribonucleotide pools, substrate cycles that are formed with kinase and nucleotidase activities are also likely to regulate the activation of nucleoside analogues, a class of anticancer and antiviral agents that rely on the nucleoside kinases for phosphorylation to their active forms. Both clinical and in vitro studies suggest that an increase in nucleotidase activity can inhibit nucleoside analogue activation and result in drug resistance. The physiological role of the 5'-nucleotidases will be covered in this review, as will the evidence that these enzymes can mediate resistance to nucleoside analogues.

Effects of black grape extract on activities of DNA turn-over enzymes in cancerous and non cancerous human colon tissues

Effects of extract of dried whole black grape including seed on adenosine deaminase (ADA), 5' nucleotidase (5'NT) and xanthine oxidase (XO) enzymes were investigated in cancerous and non-cancerous human colon tissues. Enzyme activities were measured in 20 colon tissues, 10 from cancerous region and 10 from non cancerous region with and without pre incubation with black grape extract. ADA and 5'NT activities were found increased and that of the XO decreased in the cancerous tissues relative to non cancerous ones. After incubation period with black grape extract for 12 h, ADA and 5'NT activities were found to be significantly lowered but that of XO unchanged in both cancerous and non cancerous tissues. Results suggest that ADA and 5'NT activities increase but XO activity decreases in cancerous human colon tissues, which may provide advantage to the cancerous tissues in obtaining new nucleotides for rapid DNA synthesis through accelerated salvage pathway activity. Black grape extract makes significant inhibition on the ADA and 5'NT activities of cancerous and non cancerous colon tissues, thereby eliminating this advantage of cancer cells, which might be the basis for the beneficial effect of black grape in some kinds of human cancers.

Enzyme activities controlling adenosine levels in normal and neoplastic tissues

Adenosine is known to be associated with effects such as inhibition of immune response, coronary vasodilation, stimulation of angiogenesis, and inhibition of inflammatory reactions. Some authors suggest that adenosine may also have similar functions in tumor tissues. Tissue levels of adenosine are under close regulation by different enzymes acting at different levels. Adenosine is produced from AMP by the action of 5'-nucleotidase (5'-NT) and is converted back into AMP by adenosine kinase (AK) or into inosine by adenosine deaminase (ADA). Inosine is converted into purine catabolites by purine nucleoside phosphorylase (PNP), whereas AMP is converted into ADP and ATP by adenylate kinase (MK). The aim of this study was to analyze the activities of the above enzymes in fragments of neoplastic and apparently normal mucosa, obtained less than 5 cm and at least 10 cm from tumors, in 40 patients with colorectal cancer. The results showed much higher activities of ADA, AK, 5'-NT, and PNP in tumor tissue than in neighboring mucosa (p > 0.01 for ADA, AK, and PNP; p > 0.05 for 5'-NT), suggesting that the activities of purine metabolizing enzymes increase to cope with accelerated purine metabolism in cancerous tissue. The simultaneous increase in ADA and 5'-NT activities might be a physiological attempt by cancer cells to provide more substrate to accelerate salvage pathway activity.

Role of estrogen receptor in the regulation of ecto-5'-nucleotidase and adenosine in breast cancer

PURPOSE

The purpose is to understand the expression of ecto-5'-nucleotidase (eN), an adenosine producing enzyme with potential roles in angiogenesis, growth, and immunosuppression, in estrogen receptor (ER)-negative and -positive breast cancer.

EXPERIMENTAL DESIGN

We investigated the regulation of eN expression at the mRNA and protein levels by alpha in a panel of breast cancer cell lines that differ in ER status and invasive and metastatic potential. We also determined rates of adenosine formation in cells with high and low eN expression and in ER+ cells treated with estradiol.

RESULTS

ER-negative cells express high eN protein and mRNA levels and produce up to 104-fold more adenosine from AMP and ATP. Estradiol and antiestrogen treatments confirm that eN mRNA and protein expression and adenosine generation are negatively regulated through the ER. Endogenous expression of eN in ER- cells transfected with ERalpha and phorbol ester-induced eN expression in ER+ cells was strongly suppressed by estradiol, suggesting a dominant function of ER. Finally, an examination of 18 clinical breast cancer samples that were analyzed for both ER status and eN expression by Martin et al. (Cancer Res., 60: 2232-2238, 2000) revealed a significant inverse correlation between ER and eN status.

CONCLUSIONS

Our results show for the first time that eN is negatively regulated by ERalpha in dominant fashion and suggests that eN expression and its generation of adenosine may relate to breast cancer progression. Additionally, increased expression of eN in a subset of ER-negative cells may serve as a novel marker for a subset of more aggressive breast carcinoma.

Estimation of guanine deaminase using guanosine as a "prosubstrate"

Plasma guanine deaminase (guanase; GD) is well established as an indicator of hepatocellular disease, recently being applied in the detection of hepatitis C in donor blood and in the diagnosis of hepatoma. No totally efficient, simple method for the estimation of plasma GD activity is routine since both guanine and 8-azaguanine, the substrates of the enzyme, are scarcely soluble in water. This difficulty in preparing stable substrates of sufficient concentration has resulted in methods that are both troublesome and inaccurate. Here we describe the development of new colorimetric and high-performance liquid chromatography (HPLC) methods utilizing guanosine as a "prosubstrate." After an initial breakdown of the guanosine to guanine using purine nucleoside phosphorylase, the ammonia formed as a result of the breakdown of the guanine by GD was estimated colorimetrically by the Berthelot reaction. As an alternative or a complementary assay, the xanthine also formed was measured using an isocratic HPLC method. These methods are suitable for routine assays for measuring plasma GD over a wide range of activities.

Crystal Structure of Bacillus subtilis Guanine Deaminase

Guanine deaminase, a key enzyme in the nucleotide metabolism, catalyzes the hydrolytic deamination of guanine into xanthine. The crystal structure of the 156-residue guanine deaminase from Bacillus subtilis has been solved at 1.17-A resolution. Unexpectedly, the C-terminal segment is swapped to form an intersubunit active site and an intertwined dimer with an extensive interface of 3900 A(2) per monomer. The essential zinc ion is ligated by a water molecule together with His(53), Cys(83), and Cys(86). A transition state analog was modeled into the active site cavity based on the tightly bound imidazole and water molecules, allowing identification of the conserved deamination mechanism and specific substrate recognition by Asp(114) and Tyr(156'). The closed conformation also reveals that substrate binding seals the active site entrance, which is controlled by the C-terminal tail. Therefore, the domain swapping has not only facilitated the dimerization but has also ensured specific substrate recognition. Finally, a detailed structural comparison of the cytidine deaminase superfamily illustrates the functional versatility of the divergent active sites found in the guanine, cytosine, and cytidine deaminases and suggests putative specific substrate-interacting residues for other members such as dCMP deaminases.

Wnt and beta-catenin signaling target the expression of ecto-5'-nucleotidase and increase extracellular adenosine generation

Solid tumors, which routinely experience necrosis and ischemia, release and degrade adenine nucleotides. This process may lead, depending on the expression of enzymes that regulate adenosine, to the generation of extracellular adenosine. Since genes encoding ecto-5'-nucleotidase (eN) and adenosine deaminase (ADA) contain TCF/LEF consensus binding sites, we asked whether Wnt/beta-catenin signaling, a pathway that is deregulated in several human tumors, targets the expression of these genes and thus influence extracellular adenosine generation. Our results show that beta-catenin strongly increased the activity of the 969-bp promoter of eN and this increase depended on the presence of TCF-1 transcription factor. Reciprocally, the eN promoter activity was decreased by co-transfection of APC, a beta-catenin antagonist. The expression of endogenous eN mRNA was increased either in Cos-7 cells transfected with a mutated beta-catenin and TCF-1 or in Rat-1 cells transformed by the Wnt-1 oncogene. In Rat-1 cells, expression of Wnt-1 correlated with increased eN protein levels and enzymatic activity and a concomitant decrease of adenosine deaminase mRNA and enzymatic activity. This expression profile is accompanied by a threefold increase in the generation of extracellular adenosine. Our study demonstrates a link between the Wnt signaling and the regulation of two enzymes that control the metabolism of adenosine.

Altered extracellular ATP, ADP and AMP catabolism in glioma cell lines

In order to characterize the enzymes involved in the purine nucleotide catabolism as indicators of invasiveness and aggressiveness of malignant gliomas, the degradation of extracellular nucleotides by five different glioma cell lines was investigated and compared with primary astrocytes. Rapid hydrolysis of extracellular ATP and ADP by astrocytes was observed, whereas all glioma cell lines examined presented low rates of ATP hydrolysis. In contrast, ecto-5'-nucleotidase activity was increased in glioma cell lines when compared to astrocytes. Considering that ATP is recognized as a mitogenic factor that induces proliferation in human glioma cells, the substantial decrease in ATP and ADP hydrolysis observed in gliomas leads us to suggest that alterations in the ecto-nucleotidases pathway may represent an important mechanism associated with malignant transformation of glioma cell lines.

Activities of adenosine deaminase and 5'-nucleotidase in cancerous and noncancerous human colorectal tissues

In order to characterize human colorectal cancer, much attention has been paid to enzyme studies. However, little is known about the correlation between the levels of key enzymes of purine nucleotide pathway and some clinical and biological indicators of tumor invasiveness and aggressiveness. Adenosine deaminase (ADA) and 5'-nucleotidase (5'-NT) were measured in cancerous and cancer-free adjacent large bowel tissues from 38 patients with colorectal carcinoma. We have analyzed the relationship between the enzyme levels and some clinical and pathological parameters. The enzymes' activities were markedly higher in primary tumors than in corresponding normal mucosae. The ADA level in tumor tissue was significantly correlated with lymph node metastasis, histologic type, tumor location, and patient's age, whereas the 5'-NT level showed a significant correlation with tumor grade and tumor location. ADA activity in tumor tissues was significantly higher in patients whose clinical course remained stable than in those with recurrent diseases. The purine metabolism and salvage pathway activity of purine nucleotides are accelerated in the cancerous human colorectal tissue. Although our findings suggest that these enzymes' activities are most likely related to the same histomorphological architecture of the tumor, the authors believe that long-term follow-up studies are needed to evaluate the prognostic value of purine enzymes for colorectal cancer.

Tumor-promoting functions of adenosine

Tumor growth is a multifactorial process that, in addition to mutations leading to dysregulated expression of oncogenes and tumor suppressive genes, requires specific conditions that provide a supportive physiological environment at the primary and metastatic sites of the disease. Adenosine is one of the factors potentially contributing to tumor growth that thus far has not received adequate attention, despite evidence for a broad range of cytoprotective, growth-promoting, and immunosuppressive activities. Adenosine accumulates in solid tumors at high concentrations, and has been shown to stimulate tumor growth and angiogenesis and to inhibit cytokine synthesis, adhesion of immune cells to the endothelial wall, and the function of T-cells, macrophages, and natural killer cells. However, the mechanisms whereby adenosine accumulates in cancer and the specific effects that result from this accumulation are not well understood. This article surveys the available evidence that supports an important role of adenosine in cancer.

VEGF and VEGF type C play an important role in angiogenesis and lymphangiogenesis in human malignant mesothelioma tumours

The vascular endothelial growth factor (VEGF) family is a novel regulator of endothelial cell proliferation. We assessed the mRNA expression of VEGF, VEGF type C (VEGF-C) and their receptors together with the microvessel density (VD) and microlymphatic vessel density (LVD) in pursuit of their connection and prognostic value in malignant pleural mesothelioma (MPM). We used four human MPM cell lines, 54 MPM tumours and five normal pleural tissues. Expression levels for receptors and ligands were assessed by semiquantitative reverse transcriptase polymerase chain reaction analysis. Microvessels were highlighted by immunohistochemical staining for factor VIII. The discrimination of lymphatics was performed by enzyme-histochemistry for 5'-nucleotidase after adequate inhibition of non-specific activity. The expression levels of VEGF, VEGF-C and VEGFRs were high in all MPM cell lines. The percentages of tumours with higher expression compared to the mean values of normal pleural tissues were 31.5% (17/54) for VEGF, 66.7% (36/54) for VEGF-C, 20.4% (11/54) for fms-like tyrosine kinase (flt)-1, 42.6% (23/54) for kinase insert domain-containing recepter (KDR) and 59.3% (32/54) for flt-4. Significant positive correlations were found between VEGF-C and flt-4, VEGF and KDR, VEGF and flt-1 in tumour tissues. The association between LVD and VEGF-C expression level was especially strong (P< 0.0001, r= 0.63). There were also significant correlations between LVD and flt-4, and VD and VEGF. No correlation, however, was found between LVD and nodal metastasis. VD was a negative prognostic indicator in this study. The associations between VEGFNEGF-C and vessel density suggest that these factors play an important role in angiogenesis and lymphangiogenesis in this tumour, and assessment of vascularity may be a useful prognostic indicator for MPM patients.

Tissue-specific regulation of the ecto-5'-nucleotidase promoter. Role of the camp response element site in mediating repression by the upstream regulatory region

We have isolated the 5' region of the ecto-5'-nucleotidase (low K(m) 5'-NT) gene and established that a 969-base pair (bp) fragment confers cell-specific expression of a CAT reporter gene that correlates with the expression of endogenous ecto-5'-NT mRNA and enzymatic activity. A 768-bp upstream negative regulatory region has been identified that conferred lymphocyte-specific negative regulation in a heterologous system with a 244-bp deoxycytidine kinase core promoter. DNase I footprinting identified several protected areas including Sp1, Sp1/AP-2, and cAMP response element (CRE) binding sites within the 201-bp core promoter region and Sp1, NRE-2a, TCF-1/LEF-1, and Sp1/NF-AT binding sites in the upstream regulatory region. Whereas the CRE site was essential in mediating the negative activity of the upstream regulatory region in Jurkat but not in HeLa cells, mutation of the Sp1/AP-2 site decreased promoter activity in both cell lines. Electrophoretic mobility shift assay analysis of proteins binding to the CRE site identified both ATF-1 and ATF-2 in Jurkat cells. Finally, phorbol 12-myristate 13-acetate increased the activity of both the core and the 969-bp promoter fragments, and this increase was abrogated by mutations at the CRE site. In summary, we have identified a tissue-specific regulatory region 5' of the ecto-5'-NT core promoter that requires the presence of a functional CRE site within the basal promoter for its suppressive activity.

Activities of DNA turnover and free radical metabolizing enzymes in cancerous human prostate tissue

Activities of adenosine deaminase (ADA), 5'nucleotidase (5'NT), xanthine oxidase (XO), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) and levels of thiobarbituric acid reagent substances (TBARS) were measured in 10 cancerous and 10 noncancerous human prostate tissues. Decreased activities of DNA turnover enzymes (ADA and 5'NT), increased activities of GSH-Px and CAT, and unchanged activities of SOD and XO were observed in cancerous prostate tissues compared with those of noncancerous ones. TBARS levels were found to be higher in cancerous tissues than noncancerous ones. In correlation analysis, mostly positive correlations were established between enzyme activities of the cancerous tissues, whereas no meaningful correlations were found between enzyme activities of the noncancerous tissues except for a positive correlation between XO and SOD. The results indicate that the activities of DNA turnover enzymes were reduced, which was possibly an attempt to lower the rate of purine catabolism, and the activities of GSH-Px and CAT enzymes were increased, probably in response to increased free radical stress occurring in cancerous prostate tissues. Increased concentrations of TBARS suggested oxidant stress and thus accelerated peroxidative reactions in the cancerous tissues, even though antioxidant defense mechanisms were activated. These findings suggest that enzymatic antioxidant systems of cancerous prostate tissues cannot sufficiently eliminate oxidant factors and prevent cellular peroxidative reactions occurring during the carcinogenic process.

Activity of the enzymes participating in purine metabolism of cancerous and noncancerous human kidney tissues

In this study, activity of some of the key enzymes participating in purine metabolism was measured in cancerous and noncancerous human kidney tissues from 18 patients with renal cell carcinoma. Twelve cancerous tissues were at stage T1-T2 and 6 tissues were at stage T3-T4. Adenosine deaminase (ADA) and guanase (GUA) activity was increased and xanthine oxidase (XO) activity decreased in cancerous tissues compared to noncancerous ones. No difference was, however, found between 5'-Nucleotidase (5'-NT) activity of the tissues. There were also no statistically meaningful differences between the enzyme activities of the cancerous tissues at stage T1-2 and T3-4. Results suggest that the changes observed in the activity of the enzymes participating in purine metabolism result from accelerated DNA turnover in the cancerous tissues and cells, and these changes might provide selective advantage, possibly by causing acceleration of salvage pathway activity, to the cancer cells to grow and develop more rapidly.