ATP depletion as a consequence of adenosine deaminase inhibition in man

Multiple Roles, Multiple Adaptors: Dynein During Cell Cycle

Dynein is an essential protein complex present in most eukaryotes that regulate biological processes ranging from ciliary beating, intracellular transport, to cell division. Elucidating the detailed mechanism of dynein function has been a challenging task owing to its large molecular weight and high complexity of the motor. With the advent of technologies in the last two decades, studies have uncovered a wealth of information about the structural, biochemical, and cell biological roles of this motor protein. Cytoplasmic dynein associates with dynactin through adaptor proteins to mediate retrograde transport of vesicles, mRNA, proteins, and organelles on the microtubule tracts. In a mitotic cell, dynein has multiple localizations, such as at the nuclear envelope, kinetochores, mitotic spindle and spindle poles, and cell cortex. In line with this, dynein regulates multiple events during the cell cycle, such as centrosome separation, nuclear envelope breakdown, spindle assembly checkpoint inactivation, chromosome segregation, and spindle positioning. Here, we provide an overview of dynein structure and function with focus on the roles played by this motor during different stages of the cell cycle. Further, we review in detail the role of dynactin and dynein adaptors that regulate both recruitment and activity of dynein during the cell cycle.

Extracellular guanosine regulates extracellular adenosine levels

The aim of this investigation was to test the hypothesis that extracellular guanosine regulates extracellular adenosine levels. Rat preglomerular vascular smooth muscle cells were incubated with adenosine, guanosine, or both. Guanosine (30 μmol/l) per se had little effect on extracellular adenosine levels. Extracellular adenosine levels 1 h after addition of adenosine (3 μmol/l) were 0.125 ± 0.020 μmol/l, indicating rapid disposition of extracellular adenosine. Extracellular adenosine levels 1 h after addition of adenosine (3 μmol/l) plus guanosine (30 μmol/l) were 1.173 ± 0.061 μmol/l, indicating slow disposition of extracellular adenosine. Cell injury increased extracellular levels of endogenous adenosine and guanosine, and the effects of cell injury on endogenous extracellular adenosine were modulated by altering the levels of endogenous extracellular guanosine with exogenous purine nucleoside phosphorylase (converts guanosine to guanine) or 8-aminoguanosine (inhibits purine nucleoside phosphorylase). Extracellular guanosine also slowed the disposition of extracellular adenosine in rat preglomerular vascular endothelial cells, mesangial cells, cardiac fibroblasts, and kidney epithelial cells and in human aortic and coronary artery vascular smooth muscle cells and coronary artery endothelial cells. The effects of guanosine on adenosine levels were not mimicked or attenuated by 5-iodotubericidin (adenosine kinase inhibitor), erythro-9-(2-hydroxy-3-nonyl)-adenine (adenosine deaminase inhibitor), 5-aminoimidazole-4-carboxamide (guanine deaminase inhibitor), aristeromycin (S-adenosylhomocysteine hydrolase inhibitor), low sodium (inhibits concentrative nucleoside transporters), S-(4-nitrobenzyl)-6-thioinosine [inhibits equilibrative nucleoside transporter (ENT) type 1], zidovudine (inhibits ENT type 2), or acadesine (known modulator of adenosine levels). Guanosine also increases extracellular inosine, uridine, thymidine, and cytidine, yet decreases extracellular uric acid. In conclusion, extracellular guanosine regulates extracellular adenosine levels.

Autoimmune dysregulation and purine metabolism in adenosine deaminase deficiency

Genetic defects in the adenosine deaminase (ADA) gene are among the most common causes for severe combined immunodeficiency (SCID). ADA-SCID patients suffer from lymphopenia, severely impaired cellular and humoral immunity, failure to thrive, and recurrent infections. Currently available therapeutic options for this otherwise fatal disorder include bone marrow transplantation (BMT), enzyme replacement therapy with bovine ADA (PEG-ADA), or hematopoietic stem cell gene therapy (HSC-GT). Although varying degrees of immune reconstitution can be achieved by these treatments, breakdown of tolerance is a major concern in ADA-SCID. Immune dysregulation such as autoimmune hypothyroidism, diabetes mellitus, hemolytic anemia, and immune thrombocytopenia are frequently observed in milder forms of the disease. However, several reports document similar complications also in patients on long-term PEG-ADA and after BMT or GT treatment. A skewed repertoire and decreased immune functions have been implicated in autoimmunity observed in certain B-cell and/or T-cell immunodeficiencies, but it remains unclear to what extent specific mechanisms of tolerance are affected in ADA deficiency. Herein we provide an overview about ADA-SCID and the autoimmune manifestations reported in these patients before and after treatment. We also assess the value of the ADA-deficient mouse model as a useful tool to study both immune and metabolic disease mechanisms. With focus on regulatory T- and B-cells we discuss the lymphocyte subpopulations particularly prone to contribute to the loss of self-tolerance and onset of autoimmunity in ADA deficiency. Moreover we address which aspects of immune dysregulation are specifically related to alterations in purine metabolism caused by the lack of ADA and the subsequent accumulation of metabolites with immunomodulatory properties.

The ADA*2 allele of the adenosine deaminase gene (20q13.11) and recurrent spontaneous abortions: an age-dependent association

OBJECTIVE

Adenosine deaminase acts on adenosine and deoxyadenosine metabolism and modulates the immune response. The adenosine deaminase G22A polymorphism (20q.11.33) influences the level of adenosine deaminase enzyme expression, which seems to play a key role in maintaining pregnancy. The adenosine deaminase 2 phenotype has been associated with a protective effect against recurrent spontaneous abortions in European Caucasian women. The aim of this study was to investigate whether the G22A polymorphism of the adenosine deaminase gene is associated with recurrent spontaneous abortions in Brazilian women.

METHODS

A total of 311 women were recruited to form two groups: G1, with a history of recurrent spontaneous abortions (N = 129), and G2, without a history of abortions (N = 182). Genomic DNA was extracted from peripheral blood with a commercial kit and PCR-RFLP analysis was used to identify the G22A genetic polymorphism. Fisher's exact test and odds ratio values were used to compare the proportions of adenosine deaminase genotypes and alleles between women with and without a history of recurrent spontaneous abortion (p<0.05). The differences between mean values for categorical data were calculated using unpaired t tests. The Hardy-Weinberg equilibrium was assessed with a chi-square test.

RESULTS

Statistically significant differences were identified for the frequencies of adenosine deaminase genotypes and alleles between the G1 and G2 groups when adjusted for maternal age.

CONCLUSIONS

The results suggest that the adenosine deaminase *2 allele is associated with a low risk for recurrent spontaneous abortions, but this association is dependent on older age.

Purine nucleotides and their metabolites in erythrocytes of streptozotocin diabetic rats

OBJECTIVES

In the present study it was tried to obtain a complete overview of purine nucleotide metabolism in erythrocytes of streptozotocin (STZ) induced diabetes mellitus rats.

METHODS

Erythrocyte levels of the main nucleotides (ATP, ADP, AMP, GTP, GDP, GMP, IMP, NAD+, NADP+), nucleosides (Ado, Guo, Ino) and the base Hyp were measured using the HPLC method. The parameters that can be deduced from their concentrations: TAN, TGN and AEC, GEC expressed by the ratio of high/low energy nucleoside phosphates were calculated. The effects of streptozotocin-induced diabetes on the concentration and metabolism of rat erythrocyte purine and pyridine nucleotides and the activity of Na+, K+-ATPase as well as Ca2+-ATPase were investigated.

RESULTS

Increased dephosphorylation of adenine nucleotides (found as the increased concentration of Ado and Hyp and the decrease in AEC value) and the decrease in ATP and TAN and the changes in the concentrations of NAD+ and NADP+ suggest serious purine and pyridine metabolism disruptions in diabetic erythrocytes and decrease in ATPases activity.

CONCLUSION

The observations suggest that purine nucleotide degradation is markedly accelerated in erythrocytes of STZ diabetic rats.

A metabolic role for mitochondria in palmitate-induced cardiac myocyte apoptosis

After cardiac ischemia, long-chain fatty acids, such as palmitate, increase in plasma and heart. Palmitate has previously been shown to cause apoptosis in cardiac myocytes. Cultured neonatal rat cardiac myocytes were studied to assess mitochondrial alterations during apoptosis. Phosphatidylserine translocation and caspase 3-like activity confirmed the apoptotic action of palmitate. Cytosolic cytochrome c was detected at 8 h and plateaued at 12 h. The mitochondrial membrane potential (DeltaPsi) in tetramethylrhodamine ethyl ester-loaded cardiac myocytes decreased significantly in individual mitochondria by 8 h. This loss was heterogeneous, with a few energized mitochondria per myocyte remaining at 24 h. Total ATP levels remained high at 16 h. The DeltaPsi loss was delayed by cyclosporin A, a mitochondrial permeability transition inhibitor. Mitochondrial swelling accompanied changes in DeltaPsi. Carnitine palmitoyltransferase I activity fell at 16 h; this decline was accompanied by ceramide increases that paralleled decreased complex III activity. We conclude that carnitine palmitoyltransferase I inhibition, ceramide accumulation, and complex III inhibition are downstream events in cardiac apoptosis mediated by palmitate and occur independent of events leading to caspase 3-like activation.

Adenosine deaminase deficiency: genotype-phenotype correlations based on expressed activity of 29 mutant alleles

Adenosine deaminase (ADA) deficiency causes lymphopenia and immunodeficiency due to toxic effects of its substrates. Most patients are infants with severe combined immunodeficiency disease (SCID), but others are diagnosed later in childhood (delayed onset) or as adults (late onset); healthy individuals with "partial" ADA deficiency have been identified. More than 50 ADA mutations are known; most patients are heteroallelic, and most alleles are rare. To analyze the relationship of genotype to phenotype, we quantitated the expression of 29 amino acid sequence-altering alleles in the ADA-deleted Escherichia coli strain SO3834. Expressed ADA activity of wild-type and mutant alleles ranged over five orders of magnitude. The 26 disease-associated alleles expressed 0.001%-0.6% of wild-type activity, versus 5%-28% for 3 alleles from "partials." We related these data to the clinical phenotypes and erythrocyte deoxyadenosine nucleotide (dAXP) levels of 52 patients (49 immunodeficient and 3 with partial deficiency) who had 43 genotypes derived from 42 different mutations, including 28 of the expressed alleles. We reduced this complexity to 13 "genotype categories," ranked according to the potential of their constituent alleles to provide ADA activity. Of 31 SCID patients, 28 fell into 3 genotype categories that could express <=0.05% of wild-type ADA activity. Only 2 of 21 patients with delayed, late-onset, or partial phenotypes had one of these "severe" genotypes. Among 37 patients for whom pretreatment metabolic data were available, we found a strong inverse correlation between red-cell dAXP level and total ADA activity expressed by each patient's alleles in SO3834. Our system provides a quantitative framework and ranking system for relating genotype to phenotype.

Deoxyadenosine blockade of G0 to G1 transition in lymphocytes: possible involvement of protein kinases

Immunodeficiency in adenosine deaminase deficiency has been attributed to the lymphotoxicity of deoxyadenosine that accumulates to high levels in patients. To gain insight into the mechanism of deoxyadenosine toxicity, we investigated the dose-response and time course of its toxic effects on concanavalin A-stimulated mouse splenic lymphocytes by thymidine incorporation and flow cytometry. Deoxyadenosine at a level as low as 0.3 microM inhibited the progression of G0. In contrast, higher concentrations of the nucleoside, i.e., in the range of 1 to 3 microM, were needed to block transition of the stimulated lymphocytes from G0 to G1. The inhibition of their S entry and progression required even higher concentrations. Furthermore, staurosporine, a potent inhibitor of protein kinases, was found to potentiate the toxicity of deoxyadenosine in mitogen-stimulated lymphocytes. Calcium mobilization in mitogen-activated lymphocytes was inhibited by deoxyadenosine. Our data suggest that, while ribonucleotide reductase inhibition by dATP could explain the blockade of S entry and progression by deoxyadenosine in cycling lymphocytes or leukemic cells, more important effects of this compound on antigen-activated lymphocytes occur at the early G0 phase. A possible mechanism of deoxyadenosine lethality is its inhibition of protein phosphorylation.

Evolution of the arabinosides and the pharmacology of fludarabine

An understanding of the pharmacokinetics of a drug is essential to the optimal design of the dose and schedule of chemotherapy protocols. As an extension, knowledge of the mechanism of drug action is necessary to construct the optimal strategy for combination chemotherapy. Nucleoside antimetabolites such as arabinosylcytosine, arabinosyladenine, and fludarabine are prodrugs that must enter cells and be phosphorylated to the respective triphosphates before they can elicit biological activity. DNA synthesis is the major metabolic target for this class of compounds. Common to members of the arabinosyl nucleoside class is the finding in experimental systems of a relationship between incorporation of each drug into DNA and the loss of clonogenicity. Although additional inhibitory mechanisms have been identified, they all require formation of the respective triphosphate. Thus, knowledge of the pharmacokinetics of the triphosphates in target cells and an understanding of the mechanisms by which these active forms of arabinosyl nucleosides kill cells are indispensable to the rational design of treatment protocols. This article considers the clinical development of arabinosyl nucleosides with respect to investigations of their pharmacokinetics and mechanisms of action. An understanding of these elements of arabinosyl nucleoside metabolism should provide a rationale for combinations with other chemotherapeutic agents and anticancer modalities.

Activation of apoptosis in early mouse embryos by 2'-deoxyadenosine exposure

Adenosine deaminase (ADA) catalyzes the irreversible hydrolytic deamination of adenosine and deoxyadenosine to nontoxic derivatives. The importance of this reaction in the female reproductive tract of mice is suggested by pronounced utero-placental expression of ADA, and by embryolethality of the potent ADA-inhibitor deoxycoformycin (dCF) on day 7-8 of gestation. The present study investigated the effects of dCF, adenosine, and deoxyadenosine on the mouse neurula. Morphological cell death was monitored by the acridine orange reaction (AOR), and biochemical cell death by internucleosomal DNA cleavage (IDC). A strong AOR appeared in day 7-8 embryos between 3 and 4.5 hr post-exposure to dCF in utero; there was no apparent effect on day 6 or day 9 embryos. Most embryonic tissues were responsive, although the heart and extraembryonic membranes were resistant. Up to 75% of the embryonic chromatin was degraded in a regular pattern in concert with the AOR. Immediate activation of "whole-body" apoptosis was reproduced in short-term whole embryo culture with 0.1 mM deoxyadenosine in the presence of 0.01 mM dCF. This was not activated by exposure to dCF alone nor to adenosine; however, high concentrations of adenosine completely blocked the response to deoxyadenosine, whereas niacinamide inhibited the AOR without changing IDC. The cytotoxic effect of deoxyadenosine was correlated with an expansion of embryonic dATP pools determined by high-performance liquid chromatography analysis. The results suggest that deoxyadenosine is the embryotoxic metabolite which accumulates in the antimesometrium of pregnant mice treated with dCF. Exposure to this metabolic toxin activates apoptosis in day 7-8 embryos through an adenosine-sensitive, NAD-dependent mechanism.

Advances in therapy for hairy cell leukemia. A review

BACKGROUND

Hairy cell leukemia (HCL) is a chronic B-cell malignancy, typically seen in middle-aged men, characterized by pancytopenia, splenomegaly, immunologic abnormalities, and morphologically typical neoplastic mononuclear cells in the blood, bone marrow, liver, spleen, and other tissues. Diagnosis is confirmed by demonstration of hairy cells in biopsy specimens from the bone marrow or spleen or in peripheral blood. The natural history of this lymphoproliferative disorder varies. Patients may die early during the initial phase of therapy; others may require no therapy; and for some, splenectomy alone, without further treatment, may suffice for many years. Recently, the nucleosides pentostatin (2'-deoxycoformycin) (DCF) and 2'-chlorodeoxyadenosine (2-CdA) have been shown to produce greater numbers of durable complete remissions with curative potential in patients with HCL. The treatment options, with emphasis on major therapeutic advances with alpha-interferon, DCF, and 2-CdA, are reviewed in this article.

METHODS

Studies on HCL published from 1958 to 1992 were reviewed using the Cancerline and Medline retrieval systems and other bibliographies.

RESULTS

Management of HCL has changed in the last decade as a result of three new effective agents: alpha-interferon DCF, and 2-CdA. DCF has produced an overall response rate of 86% and a complete remission rate of 62%. 2-CdA has yielded an overall response rate of 95% and a complete remission rate of 82%. Alpha-interferon has given an overall response rate of 82% and a complete remission rate of 8%. Other agents with limited activities include chlorambucil, cyclophosphamide, cytarabine, vincristine, doxorubicin, and zorubicin hydrochloride. The effects of lithium carbonate, immunotherapy, splenic irradiation, androgens, and leukaphoresis are minimal and transient.

CONCLUSIONS

Modern management of HCL with 2-CdA and DCF is now potentially curative rather than palliative in some patients; however, the optimal therapeutic approach remains uncertain. Alpha-interferon has been approved by the Food and Drug Administration as the first-line drug therapy, followed by DCF in non-responding patients. 2-CdA remains an experimental therapy, but its higher response rate and ease of administration may make it the first-line treatment of choice. Additional research into the biology of HCL and further clinical trials are needed to determine the optimal treatment strategy for this disorder. Therefore, the best therapeutic approach at the current time is to include patients with HCL in ongoing clinical trials.

Characterization of adenosine deaminase (ADA)-negative B-lymphoblastoid cells cocultured with ADA-positive fibroblasts

A cell line, BAD05, derived from B lymphocytes of an adenosine deaminase (ADA; EC 3,5,4,4)-deficient patient could not proliferate in a serum-free medium containing 100 mumol/l deoxyadenosine. When BAD05 was cultured with ADA-positive fibroblasts, the proliferation of BAD05 was improved. BAD05 cell density increased when the initially mixed ratio of fibroblasts/BAD05 was 1/10 or higher, but decreased when the ratio was 1/20 or lower. Deoxyadenosine concentrations in the medium and ATP and deoxyATP (dATP) levels in the BAD05 were measured after 4 hours of coculture at initial BAD05 cell densities of 1 x 10(5) and 1 x 10(6) cells/ml. Deoxyadenosine concentrations in the medium decreased as the density of fibroblasts increased. The dATP level decreased as the mixed ratio rose. The ratio of fibroblasts/BAD05 rather than the cell density of fibroblasts had a larger effect on the dATP levels in BAD05. Under our experimental conditions, ADA-negative cells proliferated well when the ratio of ADA-positive cells/ADA-negative cells was over 1/10.

Factors influencing the inhibition of repair of irradiation-induced DNA damage by 2'-deoxycoformycin and deoxyadenosine

Permeabilized L5178Y cells were used to investigate the mechanism underlying inhibition of the repair of irradiation-induced DNA strand breaks by 2'-deoxycoformycin combined with deoxyadenosine. Permeabilized cells repaired DNA strand breaks as effectively as did intact cells, and at deoxyadenosine concentrations that produced similar levels of deoxyadenosine triphosphate (dATP), repair of DNA strand breaks was inhibited by 2'-deoxycoformycin plus deoxyadenosine to a comparable extent in both types of cells. Accompanying the increase in intracellular dATP produced by 2'-deoxycoformycin combined with deoxyadenosine was a fall in levels of deoxythymidine triphosphate (dTTP), deoxyguanosine triphosphate (dGTP), and deoxycytidine triphosphate (dCTP). The addition of dTTP, dGTP, and dCTP reversed the inhibition of DNA repair by 2'-deoxycoformycin plus deoxyadenosine, although the level of dATP was not affected. Reducing the phosphorylation of deoxy-adenosine to dATP by the addition of adenosine prevented the decrease in levels of dTTP, dGTP, and dCTP and the inhibition of DNA repair by 2'-deoxycoformycin and deoxyadenosine. In contrast, increasing the intracellular levels of dATP by the addition of 2'-deoxycoformycin together with dATP, deoxyadenosine diphosphate (dADP), or deoxyadenosine monophosphate (dAMP) had no effect on the levels of the other deoxynucleotide triphosphates and did not inhibit DNA repair. Moreover, DNA repair was not inhibited by the breakdown products of deoxyadenosine, adenine, or deoxyribose. These results suggest that inhibition of the repair of irradiation-induced DNA strand breaks by 2'-deoxycoformycin combined with deoxyadenosine requires the phosphorylation of deoxyadenosine and involves alterations in the levels of deoxynucleotide triphosphates.

Effects of (R)-deoxycoformycin (pentostatin) on intrauterine nucleoside catabolism and embryo viability in the pregnant mouse

The viability of early mouse embryos is acutely sensitive to (R)-deoxycoformycin (pentostatin), a tight-binding inhibitor of adenosine deaminase (ADA). Previous studies have shown that a single 5-mg/kg dose on day 7 (plug = day 0) of gestation fully inhibits uteroplacental ADA activity within 0.5 h; causes massive cell death in the neural plate and primary mesenchyme by 6 h, major craniofacial anomalies by day 10, and resorption by day 12 (Knudsen et al., '89; Airhart et al., '91). The present study has examined further the developmental toxicity and early effects of this inhibitor on ADA metabolism. (R)-Deoxycoformycin was administered to pregnant CD-1 (ICR) mice as a single intraperitoneal dose of 0.5-10 mg/kg total body weight on days 6-11 of gestation. The major adverse effect, early resorption, was dose dependent and specific to day 7-8 exposure. Treatment with 5 mg/kg on day 7 resulted in 85% resorptions, 15% malformations, and a 24% reduction in mean fetal weight, whereas the same dose of (S)-deoxycoformycin had no effect. Levels of adenosine and 2'-deoxyadenosine, which are the endogenous substrates of ADA, were monitored in the embryo/decidual unit (E/D) by reversed-phase high-performance liquid chromatography (RP-HPLC). In response to the inhibitor, both nucleosides increased transiently in the antimesometrial compartment (antimesometrial decidua + embryo). Peak levels (Cmax) of adenosine and 2'-deoxyadenosine were dose dependent over the range tested (0.05-10 mg/kg). Exposure to 5 mg/kg on day 7 raised adenosine levels within 0.5 h to 42-fold over the basal level of 0.06 nmol/mg protein. There was an even stronger effect on 2'-deoxyadenosine levels, which were elevated 674-fold over the detection limit of 0.0005 nmol/mg protein. Direct exposure to the inhibitor in serum-free E/D culture produced similar results: 50 microM (R)-deoxycoformycin within 1 h raised adenosine levels 26-fold and 2'-deoxyadenosine levels 410-fold. In vivo studies also showed a general correlation between embryolethality and the length of adenine nucleoside pool expansion, apparent for exposure on day 7, 8, or 9 but not on day 6, suggesting that the embryo becomes sensitive to adenosine or 2'-deoxyadenosine once the neural plate has formed.

Studies on the energy metabolism of opossum (Didelphis virginiana) erythrocytes: V. Utilization of hypoxanthine for the synthesis of adenine and guanine nucleotides in vitro

High pressure liquid radiochromatography was used to test the ability of opossum erythrocytes to incorporate tracer amounts of [G-3H] hypoxanthine (Hy) into [3H] labelled triphosphates of adenine and guanine. In the presence of supraphysiologic (30 mM) phosphate which is optimal for PRPP synthesis, both ATP and GTP are extensively labelled. When physiologic (1 mM) medium phosphate is used, red cells incubated under an atmosphere of nitrogen accumulate [3H] ATP in a linear fashion suggesting ongoing PRPP synthesis in red cells whose hemoglobin is deoxygenated. In contrast, a lesser increase of labelled ATP is observed in cells incubated under oxygen, suggesting that conditions for purine nucleotide formation from ambient Hy are more favorable in the venous circulation.

Differential deoxyadenosine toxicity to immature rabbit cartilage in vitro. A model for the chondro-osseous dysplasia of adenosine deaminase deficiency

Deoxyadenosine metabolism was investigated in rabbit growth plate and articular cartilage to elucidate the biochemical basis for the chondro-osseous dysplasia observed in adenosine deaminase (ADA) deficiency. Models of ADA deficiency, the combination of deoxy-adenosine and either of 2 ADA inhibitors, were selectively toxic to immature cartilage, supporting the hypothesis that the chondro-osseous dysplasia of ADA deficiency is the consequence of the enzyme deficiency. Depletion of ATP may play a role in the altered chondrocyte viability and function observed in this model.

Inability of poly-ADP-ribosylation inhibitors to protect peripheral blood lymphocytes from the toxic effects of ADA inhibition

We have evaluated the effectiveness of two inhibitors of poly-ADP-ribosylation, nicotinamide and 3-aminobenzamide as rescue agents in resting and PHA-stimulated lymphocytes damaged by the combination of deoxycoformycin (dCF) plus deoxyadenosine (dAdo). Incubation with dCF (10(-5)M) and dAdo (10(-4)M) for 18 hours, inhibited protein and RNA synthesis in unstimulated lymphocytes and impaired the ability of the cells to respond to PHA stimulation or to give rise to T-cell colonies in methyl-cellulose. Predominantly dead cells using trypan blue exclusion were observed at day 4, in both unstimulated and PHA-stimulated lymphocytes, whether or not the drugs were removed at 18 hours. The number of viable cells at day 4 increased from 13.7% to 41.1% with the addition of 5 mM nicotinamide, and to 28.8% with 5 mM 3-aminobenzamide added with dCF and dAdo. Although nicotinamide was able to prevent a fall in NAD concentration for 24h (but not for 48h) and to reduce the fall of cell ATP concentration, the inhibition by dCF and dAdo of protein synthesis, RNA synthesis, ability of cells to form colonies or to respond to PHA was not reversed. We conclude that inhibition of NAD utilisation by inhibiting ADP-ribosylation with nicotinamide or 3-aminobenzamide does not protect cells in vitro from deoxyadenosine toxicity with ADA inhibition and is not likely to give significant clinical benefit in ADA deficiency.

Treatment of cutaneous T cell lymphoma with 2'-deoxycoformycin (pentostatin)

2'-Deoxycoformycin, a potent inhibitor of adenosine deaminase, was administered to three patients with cutaneous T cell lymphoma refractory to multiple treatment modalities. Patient 1, who received 5 mg/m2/day for 3 days at 35- to 71-day intervals, has achieved a complete remission greater than 16 months in duration. Patient 2 had progressive disease despite two courses of 2'-deoxycoformycin at a dose of 5 mg/m2/day for 3 days at 28-day intervals. The third patient, who was treated with 4 mg/m2 2'-deoxycoformycin weekly to biweekly, had an initial response, but the disease progressed after eight treatments. Only one patient had any side effects: Patient 1 developed reversible episcleritis, mild elevation of liver enzymes, and persistent nausea and vomiting. In red blood cells of all patients, there was near complete inhibition of adenosine deaminase (91% to 96%) and S-adenosylhomocysteine hydrolase (89% to 95%) activities with treatment. In peripheral blood lymphocytes, adenosine deaminase was inhibited by 85% to 98% and S-adenosylhomocysteine hydrolase by 51% to 88%. The deoxyadenosine triphosphate level, reflected by the total cellular adenine deoxyribonucleotide measurement in erythrocytes, was noted to be modestly elevated during treatment, with the highest level in the patient who demonstrated the only complete response and the only toxic effects. Low-dose 2'-deoxycoformycin appears to be safe but may be an insufficiently intensive regimen to treat refractory cutaneous T cell lymphoma. With proper biochemical monitoring, higher doses may be both safe and more effective.

Synergistic effect of 3'-deoxyadenosine N1-oxide and adenosine deaminase inhibitors on growth of Ehrlich ascites tumor cells in vivo

The simultaneous administration of 3'-deoxyadenosine N1-oxide (3'-dANO) and the adenosine deaminase inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) or 2'-deoxycoformycin (2'-dCF) to mice bearing Ehrlich ascites tumor cells resistant to 3'-dANO resulted in 80%-90% inhibition of tumor growth in vivo. 3'-dANO and 2'-dCF increased the survival time of tumor-bearing mice by a factor of 2. In vitro studies showed that the 3'-dANO resistant Ehrlich cells initiate the metabolism of 3'-dANO by a reduction to 3'-deoxyadenosine, which is converted primarily to 3'-deoxyinosine by adenosine deaminase and, to a small extent, phosphorylated to the cell toxic agent 3'-dATP. By the addition of EHNA or 2'-dCF it was possible to block the formation of 3'-deoxyinosine, resulting in a profound stimulation in the accumulation of 3'-dATP. The development of resistance to 3'-dANO was studied in cell cultures and found to be accompanied by changes in the enzyme activities of the reductase, the adenosine kinase, and the adenosine deaminase.

Substrate inhibition of adenosine phosphorylation in adenosine deaminase deficiency and adenosine-mediated inhibition of PP-ribose-P dependent nucleotide synthesis in hypoxanthine phosphoribosyltransferase deficient erythrocytes

The metabolism of adenosine and its effects on phosphoribosylpyrophosphate, PP-ribose-P, dependent nucleotide synthesis were studied using erythrocytes from patients with adenosine deaminase and hypoxanthine phosphoribosyltransferase deficiency as models. The phosphorylation of adenosine was progressively inhibited by concentrations of adenosine greater than 1 mumol L-1 for control and ADA deficient erythrocytes. There was essentially no initial rate of phosphorylation at 30 mumol L-1 adenosine. Adenosine, 1 mumol L-1, also caused a 60% reduction in PP-ribose-P concentration in ADA deficient erythrocytes. For HPRT deficient erythrocytes in which ADA activity was blocked by coformycin, 10 mumol L-1 inosine stimulated PP-ribose-P dependent nucleotide synthesis from adenine, whereas, 10 mumol L-1 adenosine inhibited nucleotide synthesis. These observations suggest that adenosine phosphorylation and PP-ribose-P dependent nucleotide synthesis are inhibited under conditions in which adenosine accumulates, such as in hereditary or pharmacologically induced ADA deficiency.

Adenosine kinase deficiency in tritiated deoxyadenosine-resistant mouse S49 lymphoma cell lines

Mutant sublines were derived of S49 mouse T-lymphoma cells that were resistant to tritiated deoxyadenosine. Twenty-five isolates that were selected in 1 microCi/ml of the nucleoside were cross-resistant to 6-thioguanine, were sensitive to HAT (hypoxanthine, aminopterin, and thymidine), and contained less than 1% of hypoxanthine phosphoribosyltransferase activity in wild-type cells. One of the mutant clones, S49-dA2, was further subjected to selection in a medium containing 2 microCi/ml tritiated deoxyadenosine and 1 microgram/ml deoxycoformycin, an inhibitor of adenosine deaminase. All resistant subclones were cross-resistant to tubercidin, 6-methylmercaptopurine riboside, and arabinosyladenine. One of the subclones, S49-12, was completely devoid of adenosine kinase and was partially deficient in deoxyadenosine kinase. This subclone, however, contained wild-type levels of deoxycytidine kinase. DEAE chromatography of the wild-type cell extracts revealed two deoxyadenosine phosphorylating activities, one of which coeluted with adenosine kinase and was the enzyme missing in S49-12. The other species phosphorylated both deoxyadenosine and deoxycytidine, of which deoxycytidine was the preferred substrate.

Biochemical consequences of 2'-deoxycoformycin treatment in a patient with T-cell lymphoma. Some unusual findings

The nucleotide content of the various blood cells and the urinary excretion of purine and pyrimidine metabolites were studied in a patient with a T-cell lymphoma (early T-cell phenotype) before and during treatment with deoxycoformycin (dCF; given intravenously [iv] during 3 days, biweekly). During and after the administration of dCF, high amounts of dATP were found in the lymphoid cells and the erythrocytes (maximally, 480 pmol/10(6) lymphocytes and 5.5 nmol/10(6) erythrocytes), but not in the polymorphonuclear leukocytes. The amount of dATP in the erythrocytes, however, was significantly lower than described in the literature. During each administration of dCF, the number of blast cells in the peripheral blood rose initially, followed by a rapid decrease. After three courses, a hematologic remission was achieved and maintained for 6 weeks; then an autologous bone-marrow transplantation was performed. During the first dCF course a large amount of deoxyadenosine was found in the urine. During the second course, this excretion was much lower, but still higher than in healthy individuals. In the patient described, dCF showed a highly specific toxicity for the immature T-lymphoblast; hardly any changes were seen in the numbers of the other hematopoietic cells, both in the blood and in the bone marrow.

Treatment of adenosine deaminase deficiency with polyethylene glycol-modified adenosine deaminase

We treated two children who had adenosine deaminase deficiency and severe combined immunodeficiency disease by injecting bovine adenosine deaminase modified by conjugation with polyethylene glycol. The modified enzyme was rapidly absorbed after intramuscular injection and had a half-life in plasma of 48 to 72 hours. Weekly doses of approximately 15 U per kilogram of body weight maintained plasma adenosine deaminase activity at two to three times the level of erythrocyte adenosine deaminase activity in normal subjects. The principal biochemical consequences of adenosine deaminase deficiency were almost completely reversed. In erythrocytes, adenosine nucleotides increased and deoxyadenosine nucleotides decreased to less than 0.5 percent of total adenine nucleotides. The activity of S-adenosylhomocysteine hydrolase, which is inactivated by deoxyadenosine, increased to normal in red cells and nucleated marrow cells. Neither toxic effects nor hypersensitivity reactions were observed. In vitro tests of the cellular immune function of each patient showed marked improvement, along with an increase in circulating T lymphocytes. Clinical improvement was indicated by absence of infection and resumption of weight gain. We conclude that from the standpoints of efficacy, convenience, and safety, polyethylene glycol-modified adenosine deaminase is preferable to red-cell transfusion as a treatment for adenosine deaminase deficiency. Patients with other inherited metabolic diseases in which accumulated metabolites equilibrate with plasma could benefit from treatment with the appropriate polyethylene glycol-modified enzyme.

Hairy cell leukemia

Hairy cell leukemia is a chronic lymphoproliferative disorder that has been recognized as a separate clinical pathologic entity for the last 25 years. After a decade of discussions about the origin of the neoplastic cell, it has now been well established that hairy cells represent a certain, rather mature stage of B-cell differentiation. Evidence for this has been derived from studies using immunophenotyping with monoclonal and polyclonal antibodies, cytochemistry, and immunoglobulin gene rearrangement. For many years, splenectomy was the only therapy of proven value in hairy cell leukemia. For patients who showed insufficient response to the operation, chemotherapy with low-dose alkylating agents was moderately successful, whereas polychemotherapy often resulted in excessive toxicity. More recently, therapy with alpha-interferon has been shown to be very promising, whereas deoxycoformicin may be an attractive alternative. These new advances in immunology and therapy are reviewed.

The treatment of hairy-cell leukaemia with 2'-deoxycoformycin

Eight patients with hairy-cell leukaemia (HCL) complicated by pancytopenia were treated with low dose regimens of the adenosine deaminase (ADA) inhibitor 2'-deoxycoformycin (DCF). All patients had significant haematological and clinical improvement. One patient who had been splenectomized and five patients with mild to moderate splenomegaly achieved normal blood counts within 2 months, which have been maintained for up to 18 months. Complete remissions occurred in two patients and four patients had 50-95% marrow clearance of hairy cells. The initial DCF treatments produced a 1-3 g/dl fall in the haemoglobin levels and one patient had a temporary reduction in granulocyte and platelet counts. Five patients had nausea/vomiting, and/or lethargy following DCF, but there was no correlation between the plasma levels of deoxyadenosine and adenosine and the incidence or severity of these side effects. An increased incidence of infection and drug hypersensitivity may reflect the effects of DCF on the immune system. Low dose DCF is a highly effective agent in HCL.

Regulation of deoxyadenosine and nucleoside analog phosphorylation by human placental adenosine kinase

The enzymes responsible for phosphorylation of adenosine and nucleoside analogs are important in the pathogenesis of adenosine deaminase deficiency and for the activation of specific anticancer and antiviral drugs. We examined the role of adenosine kinase in catalyzing these reactions using an enzyme purified 4000-fold (2.1 umol/min/mg) from human placenta. The Km values of adenosine and ATP are 135 uM and 4 uM, respectively. Adenosine kinase phosphorylates adenine arabinoside with an apparent Km value of 1 mM using adenosine kinase assay conditions. The Km values for 6-methylmercaptopurine riboside and 5-iodotubercidin, substrates for adenosine kinase, are estimated to be 4.5 uM and 2.6 nM, respectively. These data indicate that dadenosine phosphorylation by adenosine kinase is primarily regulated by its Km, and the concentrations of Mg2+, ADP and AMP. The high Km values for phosphorylation of dadenosine and adenine arabinoside suggest that adenosine kinase may be less likely to phosphorylate these nucleosides in vivo than other enzymes with lower Km values. Adenosine kinase appears to be important for adenosine analog phosphorylation where the Michaelis constant is in the low micromolar range.

Differential metabolism of deoxyribonucleosides by leukaemic T cells of immature and mature phenotype

Experimental evidence has indicated that T lymphoblasts are more sensitive to deoxynucleoside toxicity than are B lymphoblasts. These data have led to the use of purine enzyme inhibitors as selective chemotherapeutic drugs in the treatment of T cell malignancies ranging from T cell acute lymphoblastic leukaemia to cutaneous T cell lymphomas. We have compared the toxicities of 2'-deoxyadenosine, 2'-deoxyguanosine, and thymidine for T cell lines derived from patients with T cell acute lymphoblastic leukaemia with those for mature T cell lines derived from patients with cutaneous T cell leukaemia/lymphoma. We have found that both deoxynucleosides are far less toxic to the mature T cell lies than to T lymphoblasts and that the mature cells accumulate much lower amounts of dATP and dGTP when exposed to deoxyadenosine and deoxyguanosine, respectively. Similar studies performed on peripheral blood cells from patients with T cell leukaemias of mature phenotype and on peripheral blood T cells demonstrate similar low amounts of deoxynucleotide accumulation. Measurements of the activities of several purine metabolizing enzymes that participate in deoxynucleoside phosphorylation or degradation do not reveal differences which would explain the toxicity of deoxynucleosides for immature, as compared to mature, T cells. We conclude that deoxynucleoside metabolism in leukaemic T cells varies with their degree of differentiation. These observations may be relevant to the design of chemotherapeutic regimes for T cell malignancies.

Concentrative transport of purine nucleosides in brush border vesicles of the rat kidney

Nephrotoxicity has been reported in humans and in animals during treatment with nucleosides. We described recently a Na+ gradient-dependent concentrative transport of adenosine in brush border vesicles isolated from the cortex of the rat kidney. The results of the present study suggest that that transport is shared by other purine nucleosides. The transport of adenosine is inhibited by several purines at micromolar concentrations. The transports of deoxyadenosine, of inosine and of guanosine are concentrative in the presence of a Na+ gradient and they are inhibited by adenosine. We conclude that there exists a concentrative system for reabsorption of various purine nucleosides in the proximal tubule. The transport of nucleosides is non-concentrative in all other cell types studied so far. The concentrative capacity of the transport of nucleosides in the kidney might explain the particular sensitivity of that organ during treatment with nucleosides.

An approach to a selection system for adenosine-deaminase-positive (ADA+) cells and detection of rat ADA+ "revertants"

We have substituted deoxyadenosine or adenosine for hypoxanthine in the standard HAT selection system in an attempt to select for ADA-normal (ADA+) cells. ADA- human lymphoid line cells could not utilize deoxyadenosine as an alternative to hypoxanthine as a purine source (DAT) and failed to grow but were only somewhat inhibited in growth when adenosine was substituted for hypoxanthine (AAT). In contrast, ADA+ cells utilized adenosine or deoxyadenosine as efficiently as hypoxanthine as a purine source. Growth in DAT, but not in HAT, of an artificial mixture of one ADA+ human lymphoid cells in 1,000 ADA- cells resulted in enrichment of ADA+ cells to 25-86% of total cells. When we grew a rat ADA- cell line in two variations of the DAT system, we detected at least three electrophoretically different ADA+ patterns, one of which corresponded to normal rat ADA. These could represent "revertants."

Immunodeficiencies associated with errors in purine metabolism

The genetic deficiencies of adenosine deaminase and purine nucleoside phosphorylase lead to blocks in the purine pathway. The intracellular accumulation of deoxynucleosides and deoxynucleotides is toxic to both dividing and nondividing lymphocytes via multiple mechanisms. T-lymphocytes are uniquely sensitive to purine-mediated cytotoxicity because of a functional imbalance of phosphorylating and dephosphorylating enzymatic activities. These inborn errors or purine metabolism are rare disorders. The study of these conditions, however, has uncovered unique enzymatic properties of lymphocytes and lymphocyte subclasses. A better understanding of the mechanisms of lymphocytotoxicity in these two purine enzyme defects may lead to better modes of therapeutic manipulation of the immune system.

Effects of deoxycoformycin in mice. III. A murine model reproducing multi-system pathology of human adenosine deaminase deficiency

Adult AKR/J mice were treated with 10 micrograms/g or 100 micrograms/g 2'-deoxycoformycin, an adenosine deaminase inhibitor with chemotherapeutic potential. The thymus and adrenal glands were decreased in weight more than any other organ. Histologic and cytofluorographic analyses indicated preferential depletion of peanut-agglutinin-positive, cortical thymocytes, as well as acute, dose-dependent damage to the adrenal cortex and medulla. The effect of 2'-deoxycoformycin on the thymus was proven to be independent of the adrenal glands by use of adrenalectomized mice. Dose-dependent liver necrosis, hemolysis, and leukemoid reactivity were observed. These findings illustrate a differential sensitivity of thymocyte subpopulations and suggest, in addition, preferential sensitivity of certain nonlymphoid tissues to 2'-deoxycoformycin administered in vivo.

Mechanism of deoxyadenosine and 2-chlorodeoxyadenosine toxicity to nondividing human lymphocytes

Deoxyadenosine has been implicated as the toxic metabolite causing profound lymphopenia in immunodeficient children with a genetic deficiency of adenosine deaminase (ADA), and in adults treated with the potent ADA inhibitor deoxycoformycin. However, the biochemical basis for deoxyadenosine toxicity toward lymphocytes remains controversial. The present experiments have examined in detail the sequential metabolic changes induced in nondividing human peripheral blood lymphocytes by incubation with deoxyadenosine plus deoxycoformycin, or with 2-chlorodeoxyadenosine (CdA), an ADA resistant deoxyadenosine congener with anti-leukemic and immunosuppressive properties. The lymphotoxic effect of deoxyadenosine and CdA required their phosphorylation, and was inhibited by deoxycytidine. As early as 4 h after exposure to the deoxynucleosides, strand breaks in lymphocyte DNA began to accumulate, and RNA synthesis decreased. These changes were followed by a significant fall in intracellular NAD levels at 8 h, a drop in ATP pools at 24 h, and cell death by 48 h. Incubation of the lymphocytes with 5 mM nicotinamide, a NAD precursor and an inhibitor of poly(ADP-ribose) synthetase, prevented NAD depletion. The nicotinamide treatment also rendered the lymphocytes highly resistant to deoxyadenosine and CdA toxicity, without altering dATP formation or the accumulation of DNA strand breaks. The poly(ADP-ribose) synthetase inhibitor 3-aminobenzamide exerted a similar although less potent effect. These results suggest that NAD depletion, probably triggered by poly(ADP-ribose) formation, is the principle cause of death in normal resting human lymphocytes exposed to deoxyadenosine plus deoxycoformycin, or to CdA.

Morphological changes in leukemic lymphoblasts and normal lymphocytes treated with deoxyadenosine plus deoxycoformycin

It remains unclear how lympholysis occurs in children with an inherited deficiency of adenosine deaminase (ADA) and in leukemic patients undergoing treatment with an inhibitor of ADA, deoxycoformycin. Adenosine deaminase deficiency with subsequent lympholysis can be simulated in vitro by treatment of lymphoid cells with deoxyadenosine plus deoxycoformycin. We found that such in vitro treatment caused fragmentation of the nucleus, disintegration of nuclear chromatin, and the formation of cytoplasmic blebs in T-lymphoblast lines, but not in B-lymphoblast lines. For all but one of the cell lines tested, the extent of morphological changes paralleled the sensitivity to growth inhibition by deoxyadenosine plus deoxycoformycin. Similar morphological changes were observed in normal peripheral blood lymphocytes treated with deoxyadenosine plus deoxycoformycin. These morphological changes were energy-dependent processes. They were preceded by inhibition of DNA synthesis and deoxyadenosine triphosphate (dATP) accumulation, but followed by depletion of adenosine triphosphate (ATP) and cell lysis. These changes may represent an intermediate step between metabolic alterations and lympholysis.

Effects of pentostatin (2'deoxycoformycin), an inhibitor of adenosine deaminase, on type II collagen-induced arthritis in rats

Pentostatin (2'-deoxycoformycin), a potent inhibitor of adenosine deaminase, was administered therapeutically to rats with type II collagen-induced arthritis and the effects on hindpaw swelling, serum haptoglobin concentration, and anticollagen antibody titer determined. Daily intraperitoneal administration of pentostatin at 10.0 or 1.0 mg/kg/day for three weeks produced significant enhancement of hind-paw swelling and elevation of serum haptoglobin. Continuous subcutaneous infusion of pentostatin at 1.0 or 0.1 mg/kg/day had the same effects. None of the dosing regimens had any effect on anticollagen antibody titer.

Antileukemic and immunosuppressive activity of 2-chloro-2'-deoxyadenosine

The adenosine deaminase-resistant purine deoxynucleoside 2-chloro-2'-deoxyadenosine (CdA) is markedly toxic in vitro to nondividing and proliferating normal human lymphocytes and to many leukemia cell specimens. The CdA is also effective against mouse L1210 leukemia in vivo. The present investigations have examined the pharmacology, chemotherapeutic activity, and toxicity of CdA in nine patients with advanced hematologic malignancies refractory to conventional therapy. When administered by continuous intravenous infusion, the deoxyadenosine analog was well tolerated. As monitored by radioimmunoassay, plasma CdA levels rose gradually during the infusions. The CdA was not deaminated significantly. In all patients with leukemia, the CdA lowered the blast count by at least 50%. In one patient with a T-cell leukemia-lymphoma, and in another patient with chronic myelogenous leukemia in blast crisis, the CdA infusion eliminated all detectable blasts from the blood and bone marrow. In a patient with a diffuse lymphoma complicated by severe autoimmune hemolytic anemia, CdA treatment quickly terminated the hemolytic process. Bone marrow suppression represented the dose-limiting toxicity, and was related to plasma CdA levels, cumulative drug dosage, and the rapid release of CdA that accompanied tumor cell lysis.

The biochemical and clinical consequences of 2'-deoxycoformycin in T cell chronic lymphocytic leukaemia

The mechanisms for cell toxicity with adenosine deaminase inhibition by 2'-deoxycoformycin (dCF) in non replicating lymphoid cells include S-adenosylhomocysteine (SAH) hydrolase inactivation and reduction of cellular ATP content. These postulates were explored in a patient with T-CLL receiving dCF with a resultant fall in peripheral blood lymphocytes from 740 X 10(9)/1 to 90 X 10(9)/1 over 15 d. In red cells there was complete inhibition of adenosine deaminase and SAH hydrolase activities, progressive deoxyadenosine triphosphate (dATP) accumulation and ATP depletion but no significant alteration in adenosine monophosphate (AMP) deaminase activity or distribution in purine intermediates from radioactive adenosine. In T-CLL lymphocytes, there was incomplete lymphoid SAH hydrolase inactivation, reduced AMP deaminase activity and progressive dATP accumulation. The limited decrease in lymphocyte ATP content was related more to dCF administration than dATP accumulation, nor accompanied by significant changes in the distribution of purine intermediates from adenosine. These findings suggest that ATP depletion with dCF therapy does not reflect AMP deaminase activity modulation nor is of critical importance for cell toxicity. The exact role for elevated cellular dATP content and SAH hydrolase inactivation in this toxicity remains to be established.