Binding of [3H]MSX-2 (3-(3-hydroxypropyl)-7-methyl-8-(m-methoxystyryl)-1-propargylxanthine) to rat striatal membranes--a new, selective antagonist radioligand for A(2A) adenosine receptors

The present study describes the preparation and binding properties of a new, potent, and selective A(2A) adenosine receptor (AR) antagonist radioligand, [3H]3-(3-hydroxypropyl)-7-methyl-8-(m-methoxystyryl)-1-propargy lxanth ine ([3H]MSX-2). [3H]MSX-2 binding to rat striatal membranes was saturable and reversible. Saturation experiments showed that [3H]MSX-2 labeled a single class of binding sites with high affinity (K(d)=8.0 nM) and limited capacity (B(max)=1.16 fmol.mg(-1) of protein). The presence of 100 microM GTP, or 10 mM magnesium chloride, respectively, had no effect on [3H]MSX-2 binding. AR agonists competed with the binding of 1 nM [3H]MSX-2 with the following order of potency: 5'-N-ethylcarboxamidoadenosine (NECA)>2-[4-(carboxyethyl)phenylethylamino]-5'-N-ethylcarboxami doaden osine (CGS-21680)>2-chloroadenosine (2-CADO)>N(6)-cyclopentyladenosine (CPA). AR antagonists showed the following order of potency: 8-(m-bromostyryl)-3, 7-dimethyl-1-propargylxanthine (BS-DMPX)>1, 3-dipropyl-8-cyclopentylxanthine (DPCPX)>(R)-5, 6-dimethyl-7-(1-phenylethyl)-2-(4-pyridyl)-7H-pyrrolo[2, 3-d]pyrimidine-4-amine (SH-128)>3,7-dimethyl-1-propargylxanthine (DMPX)>caffeine. The K(i) values for antagonists were in accordance with data from binding studies with the agonist radioligand [3H]CGS21680, while agonist affinities were 3-7-fold lower. [3H]MSX-2 is a highly selective A(2A) AR antagonist radioligand exhibiting a selectivity of at least two orders of magnitude versus all other AR subtypes. The new radioligand shows high specific radioactivity (85 Ci/mmol, 3150 GBq/mmol) and acceptable nonspecific binding at rat striatal membranes of 20-30%, at 1 nM.

Development of a 5-hydroxytryptamine(2A) receptor binding assay for high throughput screening using 96-well microfilter plates

A high throughput screening method for the analysis of 5-hydroxytryptamine(2A) (5-HT(2A)) receptor binding parameters has been developed, using 96-well filter plates of the Millipore MultiScreen system in combination with a MicroBeta PLUS microplate scintillation counter. MAFB filter plates (GF/B filter over a Durapore membrane) were used because of the lower nonspecific binding of the radioligand to GF/B filter material than to GF/C filters. Comparing different scintillation cocktails, highest counting efficiency and shortest equilibration time were detected with Betaplatescint, after drying the plates at 50 degrees C for 2 h. Measuring the plates without the plastic underdrain increased the counting efficiency by about 39% as compared with counting the plate with the underdrain intact. Presoaking the wells with 0.5% polyethyleneimine for 2 h reduced the nonspecific binding to the filter material by about 50%. A linear relationship of protein concentration and radioligand binding was established up to a protein concentration of 165 microg of protein/well. In the assays, 70 microg of protein/well was generally used, which has turned out to be favorable with respect to the number of counts obtained. When a higher concentration of protein was used, the period of time needed to aspirate the plate was too long because of obstruction of the filter material. Receptor-radioligand equilibration was reached after about 20 min at concentrations less than 0.05 nM [(3)H]ketanserin-HCl; at higher concentrations it was reached after about 10 min. Saturation analysis of [(3)H]ketanserin-HCl resulted in a mean B(max) of 393 fmol/mg protein and a K(D) of 2.0 nM using rat frontal cortex as a receptor source. Competition experiments with known 5-HT(2A) receptor ligands-DOB-HCl (K(i) = 59 nM), DOET-HCl (K(i) = 137 nM), DOM-HCl (K(i) = 533 nM), DMT (K(i) = 1,985 nM), and TMA-HCl (K(i) = 22,340 nM)-were in accordance with literature values.

Clinical presentations of infection by the human herpesvirus-7 (HHV-7)

Reports on the clinical picture of primary infection with the human herpesvirus-7 (HHV-7) are scarce. A heterogenous population of 478 patients (1 month-14 years) was examined for the presence of an acute HHV-7 infection. A variety of clinical pictures can be observed during primary infection with HHV-7, such as exanthema subitum and mononucleosis-like syndrome. The authors describe in two children, for the first time, the presentation of HHV-7-infection as an acute exacerbation or relapse of a patient's chronic disease. The hematological changes for the respective clinical presentations during HHV-7 infection are reported.

Water-soluble phosphate prodrugs of 1-propargyl-8-styrylxanthine derivatives, A(2A)-selective adenosine receptor antagonists

Water-soluble prodrugs of potent, A(2A)-selective adenosine receptor (AR) antagonists were prepared. 8-(m-Bromostyryl)-3, 7-dimethyl-1-propargylxanthine (BS-DMPX, 11) and the analogous 8-(m-methoxystyryl)xanthine derivative (MS-DMPX, 5b) were used as starting points. It was found that polar functional groups suitable for the attachment of a prodrug moiety were tolerated on the styryl ring and even better on the 3-substituent. 8-(m-Hydroxystyryl)-DMPX (7) and 3-(3-hydroxypropyl)-8-(m-methoxystyryl)-1-propargylxanthine (5e, MSX-2) were the most potent and A(2A)-selective compounds and were selected for prodrug formation. For the preparation of 5e a new ring-closure method was applied. Treatment of 6-amino-1-(3-hydroxypropyl)-5-(m-methoxycinnamoylamino)-3-propa rgylur acil with hexamethyldisilazane at high temperature resulted in higher yields of the target xanthine than the standard ring-closure procedure using sodium hydroxide. Phosphate prodrugs were prepared by classical phosphorylation using phosphorus oxychloride and alternatively by using a phosphoramidite method. Phosphates of the aliphatic alcohol 5e could be obtained by both methods in similar yields. The phenolic compound 7, however, could be phosphorylated only by using the phosphoramidite method. The disodium salts of the phosphate prodrugs exhibited high water solubility (8-(m-methoxystyryl)-7-methyl-3-[3-O-phosphatylpropyl]-1- propargylxan thine disodium salt, 9b: 17 mM, 9 mg/mL). Prodrug 9b was found to be stable in aqueous solution (pH 7) but readily cleaved by phosphatases to liberate 5e (MSX-2). Compound 5e showed high affinity for rat A(2A) AR (K(i) = 8 nM), human recombinant A(2A) AR (K(i) = 5 nM), and human native A(2A) AR (K(i) = 15 nM) and was highly selective versus rat A(1) AR (110-fold), human recombinant A(2A) AR (500-fold), human A(2B) AR (>2000-fold), and human A(3) AR (>2000-fold).

Relationships of cytokine (GM-CSF) serum concentration to blood cell count and the inflammatory parameters in children with malignant diseases

This study examined both the endogenous and exogenous (therapy-related) pharmacokinetics of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) in neutropenic children with solid and systemic malignancies. The daily endogenous GM-CSF serum concentration before application was 29 pg/mL. During the 10 days of examination, the concentration rose to an average value of 1351 pg/mL 8 h after application. A significant stimulation of the neutrophils, monocytes, and eosinophils in peripheral blood was documented. No significant correlation between the GM-CSF concentration and peripheral blood cell counts could be documented. Paraclinically, there was no evidence for functional disturbance of either the liver or the kidneys, i.e., under the cytokine therapy. The therapy was well tolerated by all the children involved in the study.

8-(Sulfostyryl)xanthines: water-soluble A2A-selective adenosine receptor antagonists

8-(Sulfostyryl)xanthine derivatives were synthesized as water-soluble A2A-selective adenosine receptor (AR) antagonists. meta- and para-sulfostyryl-DMPX (3,7-dimethyl-1-propargylxanthine) derivatives 11a and 11b exhibited high affinity to rat A2A-AR in submicromolar concentrations, and were 20- to 30-fold selective versus rat A1-AR. Styryl-DMPX derivatives were inactive at human A2B- and A3-AR. 1,3-Dipropyl-8-p-sulfostyrylxanthine (13) or only a 7-methyl derivative (14) showed similar (13) or higher (14) A2A affinity than 11a and 11b but showed no (13) or only a low degree (14) of selectivity versus A1-, A2B-, and A3-AR. The A2A-selective sulfostyryl-DMPX derivatives exhibit high water-solubility and may be useful research tools for in vivo studies.

Motor effects induced by a blockade of adenosine A2A receptors in the caudate-putamen

Motor effects mediated through adenosine A2A receptors within the caudate-putamen were investigated in rats using bilateral microinfusions of MSX-3 (9 microg in 1 microl per side), a water-soluble phosphate prodrug of the selective A2A receptor antagonist MSX-2. Blockade of striatal A2A receptors produced a significant motor stimulation measured by an enhanced sniffing activity. Furthermore, catalepsy induced by systemic dopamine D1 (0.75 mg/kg SCH23390, i.p.) or dopamine D2 receptor blockade (1.5 mg/kg raclopride, i.p.) was potently reversed. These findings suggest that A2A receptors within the caudate-putamen are tonically activated by endogenous adenosine and that a striatal A2A receptor blockade produces motor stimulant effects, in particular in animals with dopamine hypofunction. The present results support the view that A2A receptor antagonists may be potentially useful therapeutics for the treatment of Parkinson's disease.

1-substituted 4-[chloropyrazolyl][1,2,4]triazolo[4,3-a]quinoxalines: synthesis and structure-activity relationships of a new class of benzodiazepine and adenosine receptor ligands

Starting from 3-(3-chloro-1H-pyrazol-5-yl)-1H-quinoxalin-2-one (2) a series of substituted [1,2,4]triazolo[4,3-a]quinoxalines (3a-f) was prepared via a multistep reaction sequence. Affinities of the novel derivatives 3a-f for benzodiazepine as well as for adenosine A1- and A2A-receptors of rat brain were determined by radioligand binding assays. 1-Methyl-4-(3-chloro-1H-pyrazol-5-yl) derivative 3a exhibited submicromolar affinity for the benzodiazepine binding site of GABAA receptors (Ki = 340 nM) and was less potent at A1-(Ki = 7.85 microM) and A2A-(Ki = 1.43 microM) adenosine receptors (AR). Derivatives with larger substituents in the 1-position showed reduced binding to benzodiazepine and A2A-AR, but increased A1-AR affinity, the 2-thienylmethyl derivative 3f being the most potent and selective A1-AR ligand of the present series (Ki = 200 nM).

Bioactive pyridoacridine alkaloids from the micronesian sponge Oceanapia sp

The Micronesian sponge Oceanapia sp. afforded three pyridoacridine alkaloids: the known compounds kuanoniamine C (1) and kuanoniamine D (2), as well as the new N-deacyl derivative (3) of the kuanoniamines. Compounds 1 and 2 exhibited insecticidal activity toward neonate larvae of the polyphagous pest insect Spodoptera littoralis (LC50 of 156 and 59 ppm, respectively), when incorporated into artificial diet. Both compounds also showed toxicity in the brine shrimp lethality test with a LC50 of 37 micrograms/mL (compound 1) and 19 micrograms/mL (compound 2), respectively. The N-deacyl derivative did not show any remarkable effect in both bioassays. Cytotoxcity of the alkaloids was studied in vitro, using two human cell lines. The new derivative (3) appeared to be active in the same range of concentrations as kuanoniamine C (1) and D (2). The IC50 of 3 was 1.2 micrograms/mL toward HeLa cells and 2.0 micrograms/mL toward MONO-MAC 6 cells. In receptor binding assays compound 2 showed affinity to A1- and A2A-adenosine receptors with Ki values of 2.94 and 13.7 microM, respectively. Compound 1 was less active than compound 2, whereas compound 3 showed no affinity toward adenosine receptors. In addition, compounds 1-3 exhibited moderate affinity to benzodiazepine binding sites of GABAA receptors.

Synthesis and structure-activity relationships of 3,7-dimethyl-1-propargylxanthine derivatives, A2A-selective adenosine receptor antagonists

A series of 8-substituted derivatives of 3,7-dimethyl-1-propargylxanthine (DMPX) was synthesized and investigated as A2A adenosine receptor antagonists. Different synthetic strategies for the preparation of DMPX derivatives and analogues were explored. A recently developed synthetic procedure starting from 3-propargyl-5,6-diaminouracil proved to be the method of choice for the preparation of this type of xanthine derivatives. The novel compounds were investigated in radioligand binding studies at the high-affinity adenosine receptor subtypes A1 and A2A and compared with standard A2A adenosine receptor antagonists. Structure-activity relationships were analyzed in detail. 8-Styryl-substituted DMPX derivatives were identified that exhibit high affinity and selectivity for A2A adenosine receptors, including 8-(m-chlorostyryl)-DMPX (CS-DMPX, Ki A2A = 13 nM, 100-fold selective), 8-(m-bromostyryl)-DMPX (BS-DMPX, Ki A2A = 8 nM, 146-fold selective), and 8-(3,4-dimethoxystyryl)-DMPX (Ki A2A = 15 nM, 167-fold selective). These and other novel compounds are superior to the standard A2A adenosine receptor antagonists KF17837 (4) and CSC (5) with respect to A2A affinity and/or selectivity.

Uridine nucleotide receptors and their ligands: structural, physiological, and pathophysiological aspects, with special emphasis on the nervous system

This review presents data on metabotropic uridine nucleotide receptor subtypes (P2UR) activated by UTP, sometimes also by UDP and/or ATP. Some chemical details of receptor subtypes and ligand interactions are described. Ligand-activated P2UR subtypes may couple to different second messengers, yet little is known about the nature of the coupling G-proteins. Data evaluating UTP as a physiological ligand include UTP origin, release and metabolism and illuminate especially roles for P2UR in the nervous system. No evidence shows UTP as a synaptic transmitter; sympathetic neurons may, however, carry P2UR allowing UTP-stimulation of norepinephrine release. UTP and derivatives act as therapeutic agents in several diseases involving mutated genes of transepithelial conductance regulators, including cystic fibrosis. This focuses interest to the synthesis of new compounds. Further, therapeutically used pyrimidine and pyrimidine analogues are suspected to have CNS-pathological effects. The presently scarce information in these areas strongly underlines the need for and importance of intense research on the suspected pyrimidine derivative triggered pathology as well as on the role of P2UR receptors in physiology and pathophysiology.

Aza-analogs of 8-styrylxanthines as A2A-adenosine receptor antagonists

In the present study we synthesized aza-analogs of 8-styrylxanthines, in which the ethenyl bridge is replaced by an imine, amide, or azo function, in order to investigate structure-activity relationships of the 8-substituent of A2A-selective xanthine derivatives. Thus, various 8-substituents were combined with theophylline or caffeine, respectively, and affinities of the novel compounds for adenosine A1- and A2a-receptors were determined and compared with those of analogous 8-styrylxanthine derivatives. 8-(Benzylideneamino)caffeine derivatives exhibited high affinity and selectivity for A2A-adenosine receptors, but were unstable in aqueous buffer solution at physiological pH values. 8-(Phenylazo)caffeine derivatives were less potent than corresponding 8-styrylcaffeine derivatives at adenosine receptors. The most potent azo compound of the present series was 8-(m-chlorophenylazo)caffeine (14b) exhibiting a Ki value of 400 nM at A2A-adenosine receptors and 20-fold selectivity versus A1-receptors. Due to the facile synthetic access to 8-(phenylazo)xanthine derivatives, which are obtained by coupling of 8-unsubstituted xanthines with phenyldiazonium salts, 14b may be an interesting new lead compound for the development of more potent and selective A2A-antagonists with azo structure.

Chiral pyrrolo[2,3-d]pyrimidine and pyrimido[4,5-b]indole derivatives: structure-activity relationships of potent, highly stereoselective A1-adenosine receptor antagonists

A series of 33 novel, mostly chiral pyrrolo[2,3-d]pyrimidine and pyrimido[4,5-b]indole derivatives has been synthesized and investigated in radioligand binding assays at the high-affinity adenosine receptor (AR) subtypes A1 and A2a. The compounds can be envisaged as adenine and hypoxanthine analogs lacking the nitrogen in the 7-position (7-deazaadenines and 7-deazahypoxanthines). 7-Deazaadenines were much more potent than 7-deazahypoxanthines at AR with A1AR affinities in the low-nanomolar range, extraordinarily high selectivity for the rat brain A1AR versus the A2aAR (several thousandfold), and high stereoselectivity (up to 96-fold). Pyrimido[4,5-b]indoles were more potent A1AR antagonists compared to pyrrolo[2,3-d]pyrimidines. Compound 34a (APEPI) is one of the most potent and most selective nonxanthine A1AR antagonists known to date (Ki = 2.8 nM, > 2000-fold A1-selective). A new class of very potent A1AR antagonists has been identified, namely, 2-phenyl-7-deazaadenines bearing a substituent at the exocyclic amino group (N4-substituted pyrrolo[2,3-d]pyrimidines). (R)-N- (1-Phenylethyl)-4-amino-5,6-dimethyl-2-phenyl-7H-pyrrolo[2,3-d]pyrimidin e (DPEAP, 17a) showed a Ki value of 6.7 nM at A1AR and > 4000-fold A1 selectivity. Different binding modes are postulated for the N4-substituted 4-aminopyrrolo[2,3-d]pyrimidines (e.g., 17a) and the 7-substituted derivatives (e.g., 1a), based on a comparison of steric, electronic, and hydrophobic properties of the two classes of compounds. Water solubility and lipophilicity have been determined for selected compounds. 4-Amino-5,6-dimethyl-2-(3-chlorophenyl)-7H-pyrrolo[2,3-d]pyrimidine (4a) showed the highest water solubility/A1AR affinity ratio of 368 in the present series, over 2000-fold A1 selectivity, and 64-fold stereoselectivity (R > S). Therefore, 4a should be an interesting compound for in vivo evaluation.

Tricyclic theophylline derivatives with high water-solubility: structure-activity relationships at adenosine receptors, phosphodiesterases, and benzodiazepine binding sites

A series of tricyclic, highly water-soluble theophylline derivatives (pyrimido[2,1-f]-theophyllines) containing a basic side chain was investigated in rat brain A1- and A2 adenosine receptor binding assays, phosphodiesterase assays, and benzodiazepine binding studies. Among the new compounds adenosine receptor antagonists with affinities in the same range as the parent compound theophylline were identified. In addition, some compounds were selective for the A1 adenosine receptor subtype. The compounds generally exhibited lower inhibitory activity at brain phosphodiesterases than the parent theophylline. Two compounds were found to show an about 10-fold affinity for benzodiazepine binding sites compared with caffeine and theophylline.

Amino-substituted 1,8-naphthyridines and pyrido[2,3-d]pyrimidines: new compounds with affinity for A1- and A2-adenosine receptors

Two novel classes of adenosine receptor (AR) antagonists, 4-amino-1,8-naphthyridines and 5-aminopyrido[2,3-d]pyrimidines, have been identified and investigated in radioligand binding assays. The compounds exhibit affinities for A1 and A2a AR of rat brain in the micromolar range. 1,8-Naphthyridines are non-selective, or somewhat selective for either A1- or A2 AR. Pyrido[2,3-d]pyrimidines are several-fold selective for A1 AR, the most potent and selective compound being 5-n-butylamino-1,3-dimethyl-1,2,3,4-tetrahydropyrido-[2,3-d]pyr imi dine-2,4-dione (12) with a Ki value of 1.8 microM at A1 AR and greater than 10-fold A1-selectivity.

Immobilization, a risk factor for urinary tract stones in children. A case report

Immobilization causes bone dissolution leading to hypercalcemia and hypercalciuria in children. We report the case of a 10-year-old boy who developed 2 stones in the pelvis off his left healthy kidney after only 8 days of immobilization. He was on bedrest after pyeloplasty done for a ureteropelvic junction obstruction on the right side. Compared to references in literature our patient showed stone formation very early during the course of immobilization. Temporary hypercalciuria and stone formation are well documented because of underlying kidney disease. The risk factors of immobilization-induced hypercalciuria and hypercalcemia are discussed together with possible treatment and prophylaxis of this pathology.

Synthesis and structure-activity relationships of deazaxanthines: analogs of potent A1- and A2-adenosine receptor antagonists

A set of 22 9-deazaxanthines (pyrrolo[3,2-d]pyrimidine-2,4-diones) and three 7-deazaxanthines (pyrrolo[2,3-d]pyrimidine-2,4-diones) with various substituents in the 1-, 3-, 7- or 9-, and 8-positions was synthesized and investigated in A1 and A2a adenosine receptor binding assays at rat brain cortical membranes and rat brain striatal membranes, respectively. 9-Deazaxanthines showed structure-activity relationships that were similar to those of xanthines. They were about equipotent to the corresponding xanthines at A2a adenosine receptors. 9-Deazaxanthines were generally at least 2-3-fold more potent than xanthines at A1 receptors and therefore exhibited higher A1 selectivities compared to the xanthines. 1,3-Dimethyl-8-(2-naphthyl)-9- deazaxanthine (19e) showed high affinity (Ki = 26 nM) and selectivity for A1 adenosine receptors. A hydroxyl function at N7 of 9-deazaxanthines was unfavorable for A1 and A2a receptor binding. 7-Deazaxanthines were considerably less potent compared to xanthines and to 9-deazaxanthines at both receptor subtypes.

Stimulation of calcium release by caffeine analogs in pheochromocytoma cells

Caffeine (EC50 approximately 20 mM) causes a maximal 400% increase in intracellular calcium ion concentration ([Ca2+]i) in pheochromocytoma PC12 cells. A range of caffeine analogs in which methyl groups at the 1, 3, and 7 positions were replaced with relatively nonpolar (ethyl, allyl, propyl, propargyl) or polar (CH2COOH, CH2CH2OH, CH2CN, CH2OCH3) substituents were tested at a 10 mM concentration. Many analogs were as efficacious or only somewhat less efficacious than 10 mM caffeine. Certain analogs with polar substituents had no effect. Disubstituted xanthines were less efficacious (theophylline, paraxanthine) than caffeine or were ineffective (theobromine). 1-Propyl-3,7-dimethylxanthine (EC50 4 mM) and 1-propargyl-3,7-dimethylxanthine (EC50 5 mM) were several-fold more potent than caffeine in causing elevation of [Ca2+]i and the latter was at least as efficacious.

Synthesis of paraxanthine analogs (1,7-disubstituted xanthines) and other xanthines unsubstituted at the 3-position: structure-activity relationships at adenosine receptors

Synthetic procedures for the preparation of various 3-unsubstituted xanthines, including paraxanthine analogs (1,7-disubstituted xanthines) and 1,8-disubstituted xanthines, were developed. Silylation of 1-substituted xanthines followed by alkylation at the 7-position provides a facile route to paraxanthine analogs. Regioselective alkylation of tris(trimethylsilyl)-6-aminouracil provides 3-substituted 6-aminouracils, which are converted to 1,8-disubstituted xanthines by standard procedures. The ring closure of 3-substituted 5-cyclopentanecarboxamido- and 5-(benzoylamino)-6-aminouracils requires drastic reaction conditions. Affinity for brain A1 and A2 adenosine receptors was determined in binding assays for these and other xanthines with substituents in 1-, 3-, 7-, 8-, and 9-positions. Substitution at the 1-position was necessary for high affinity at adenosine receptors. 1,3-Disubstituted xanthines generally had higher affinity than 1,7-disubstituted xanthines. 1,8-Disubstituted xanthines had high affinity for adenosine receptors; some were highly selective for A1 receptors.

Adenosine receptors and their modulators

The identification and characterization of adenosine receptors and the development of potent, receptor subtype-selective agonists and antagonists has been an active area of research for the past 20 years. Major recent advances in the field have been the cloning of several adenosine receptor subtypes of different species, including the discovery of a new subtype, designated A3, the discovery and development of new agonists and antagonists, particularly those with selectivity for the A2a adenosine receptor, the characterization of signal transduction pathways, and the development of agents which act indirectly on the adenosine receptor system. The present article focusses on aspects of pharmaceutical/medicinal chemistry related to adenosine receptors.

Methylxanthines block antigen-induced responses in RBL-2H3 cells independently of adenosine receptors or cyclic AMP: evidence for inhibition of antigen binding to IgE

Activation of a novel adenosine receptor in a rat tumor mast cell line (RBL-2H3 cells) elicits a transient generation of inositol 1,4,5-trisphosphate and an equally transient increase in the level of free cytosol Ca++: Such responses promote little exocytosis, but markedly enhance the secretory response to antigen. A variety of xanthine adenosine receptor antagonists did not suppress the responses to the adenosine analog 5-N-ethylcarboxamidoadenosine. However, 3-isobutyl-1-methylxanthine (IBMX) and certain related xanthines inhibited antigen (dinitrophenylated bovine serum albumin, DNP-BSA)-induced generation of inositol phosphates, the increase in level of free cytosolic Ca++ and exocytosis in RBL-2H3 cells that were primed with a monoclonal DNP-specific immunoglobulin E (from hybridoma H1 DNP-epsilon-26.82). The same compounds inhibited the binding of antigen to cell attached DNP-specific IgE in a highly selective manner. Incorporation of an aromatic or cycloalkyl group in the 8-position of IBMX or theophylline, for example, resulted in compounds that were more potent inhibitors than the parent compounds. Conversely, substituents in the 7- or 9-position of IBMX resulted in inactive compounds. 1,3-Diethylxanthine and 1,3-dipropylxanthine had no activity, suggesting that substituents as large as ethyl or propyl are not tolerated at the 1-position. Inhibition by IBMX was not observed when cells were activated by nonimmunological stimulants or when cells were primed with certain other monoclonal preparations of DNP-specific IgE and stimulated by DNP-BSA.(ABSTRACT TRUNCATED AT 250 WORDS)

Caffeine analogs: structure-activity relationships at adenosine receptors

Caffeine and analogs that contain ethyl, propyl, allyl, propargyl and other substituents in place of methyl at 1-, 3- and 7-positions were antagonists at the two major classes (A1 and A2) of adenosine receptors. Potency at both receptors increased as methyls were replaced with larger substituents. Certain analogs with only one of the three methyl groups of caffeine replaced by larger substituents were somewhat selective for A2 receptors. None of the analogs were particularly selective for A1 receptors. The presence of polar entities in the substituent at the 1- or 7-position was poorly tolerated at adenosine receptors. Activity of caffeine analogs at A1 and A2 adenosine receptors in a variety of systems and cell types is presented and summarized.

7-Deaza-2-phenyladenines: structure-activity relationships of potent A1 selective adenosine receptor antagonists

A series of derivatives of 7-deazapurines with varying substituents in the 2-, 6-, and 9-position was synthesized in an attempt to improve the adenosine receptor affinity and A1 or A2 selectivity. The adenosine receptor affinities were assessed by measuring the inhibition of [3H]-(R)-N6-(phenylisopropyl) adenosine (R-PIA) binding to rat brain A1 and inhibition of [3H]-5'-(N-ethylcarboxamido)adenosine (NECA) binding to rat striatum A2 adenosine receptors. A selected set of compounds representing the main structural variations was further examined in adenosine receptor coupled adenylate cyclase assays. All tested compounds antagonized the inhibition of adenylate cyclase elicited by interaction of R-PIA with A1 receptors in rat fat cell membranes and the activation of adenylate cyclase elicited by interaction of NECA with A2 receptors of pheochromocytoma PC12 cell membranes. The results indicate that 7-deazahypoxanthines have a potential for A2 selectivity, while all 7-deazaadenines are A1 selective. Introduction of a phenyl residue in the 2-position of 7-deazaadenines increases A1 activity tremendously. 2-(p-Chlorophenyl)-7,8-dimethyl-9-phenyl-7-deazaadenine (29) is potent and specific for the A1 receptors of rat brain (Ki = 122 nM), having no affinity for the A2 receptors of rat striatum. The compound has low activity at the A2 receptors of rat PC12 cell membranes where it appears to act as a noncompetitive inhibitor. A 1-phenylethyl substituent at the 9-position was found to be superior to a phenyl residue in terms of A1 affinity. The most potent A1 antagonist in the present series is the highly A1 selective (790-fold) (R)-7,8-dimethyl-2-phenyl-9-(1-phenylethyl)-7-deazaadenine (31, Ki = 4.7 nM), which is 30-35 times more potent at A1 receptors than its S enantiomer. The solubility of six of the potent 7-deaza-2-phenyladenines was determined by means of an A1 binding assay. Chloro substitution of the 2-phenyl ring appeared to improve the solubility as well as the solubility over A1 affinity ratio of 9-phenyl- and 9-(1-phenylethyl)-substituted 7-deazadenines.