Biomedical subjects

X D Ji

Publications and source records attributed to X D Ji.

At least 37 records · Page 2Linked to original sources

PubMed1996

Derivatives of the triazoloquinazoline adenosine antagonist (CGS15943) are selective for the human A3 receptor subtype.

The adenosine antagonist 9-chloro-2-(2-furanyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine (CGS15943) binds to human A3 receptors with high affinity (Ki = 14 nM), while it lacks affinity at rat A3 receptors. Acylated derivatives of the 5-amino group and other modifications were prepared in an effort to provide A3 subtype selectivity. Affinity was determined in radioligand binding assays at rat brain A1 and A2A receptors using [3H]-(R)-PIA ([3H]-(R)-N6-(phenylisopropyl)-adenosine) and [3H]CGS 21680 ([3H]-2-[[4-(2-carboxy ethyl)phenyl]ethylaminol]-5'-(N- ethyl- carbamoyl)adenosine), respectively. Affinity was determined at cloned human A3 receptors using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)-5'-(N-methylcarbamoyl)adenosine). A series of straight chain alkyl amides demonstrated that the optimal chain length occurs with the 5-N-propionyl derivative, 3, which had a Ki value of 7.7 nM at human A3 receptors, and was 40- and 14-fold selective vs rat A1 and A2A receptors, respectively. The 5-N-benzoyl derivative, 10, displayed Ki values of 680 and 273 nM at rat A1 and A2A receptors, respectively, and 3.0 nM at human A3 receptors. A 5-N-phenylacetyl derivative, 12, was 470-fold selective for human A3 vs rat A1 receptors with a Ki value of 0.65 nM. A conjugate of Boc-gamma-aminobutyric acid was also prepared but was nonselective. Conversion of the 5-amino group of CGS15943 to an oxo function resulted in lower affinity but 15-fold selectivity for human A3 receptors.

Adenosine↗

PubMed1996

Suppression of glioblastoma angiogenicity and tumorigenicity by inhibition of endogenous expression of vascular endothelial growth factor.

The development of new capillary networks from the normal microvasculature of the host appears to be required for growth of solid tumors. Tumor cells influence this process by producing both inhibitors and positive effectors of angiogenesis. Among the latter, the vascular endothelial growth factor (VEGF) has assumed prime candidacy as a major positive physiological effector. Here, we have directly tested this hypothesis in the brain tumor, glioblastoma multiforme, one of the most highly vascularized human cancers. We introduced an antisense VEGF expression construct into glioblastoma cells and found that (i) VEGF mRNA and protein levels were markedly reduced, (ii) the modified cells did not secrete sufficient factors so as to be chemoattractive for primary human microvascular endothelial cells, (iii) the modified cells were not able to sustain tumor growth in immunodeficient animals, and (iv) the density of in vivo blood vessel formation was reduced in direct relation to the reduction of VEGF secretion and tumor formation. Moreover, revertant cells that recovered the ability to secrete VEGF regained each of these tumorigenic properties. These results suggest that VEGF plays a major angiogenic role in glioblastoma.

Animals↗

PubMed1996

Synthesis and biological activities of flavonoid derivatives as A3 adenosine receptor antagonists.

A broad screening of phytochemicals has demonstrated that certain flavone and flavonol derivatives have a relatively high affinity at A3 adenosine receptors, with Ki values of > or = 1 microM (Ji et al. J. Med. Chem. 1996, 39, 781-788). We have further modified the flavone structure to achieve a degree of selectivity for cloned human brain A3 receptors, determined in competitive binding assays versus [125I]AB-MECA[N6-(4-amino-3-iodobenzyl)adenosine-5'-(N-methylur onamide)]. Affinity was determined in radioligand binding assays at rat brain A1 and A2a receptors using [3H]-N6-PIA ([3H]-(R)-N6-phenylisopropyladenosine) and [3H]CGS21680 [[3H]-2-[[4-(2-carboxyethyl)phenyl]ethylamino]-5'-(N-ethylcarbamoyl++ +)adenosine], respectively. The triethyl and tripropyl ether derivatives of the flavonol galangin, 4, had Ki values of 0.3 - 0.4 microM at human A3 receptors. The presence of a 5-hydroxyl group increased selectivity of flavonols for human A3 receptors. The 2',3,4',7-tetraethyl ether derivative of the flavonol morin, 7, displayed a Ki value of 4.8 microM at human A3 receptors and was inactive at rat A1/A2a receptors. 3,6-Dichloro-2'-(isopropyloxy)-4'-methylflavone, 11e, was both potent and highly selective (approximately 200-fold) for human A3 receptors (Ki = 0.56 microM). Among dihydroflavonol analogues, the 2-styryl instead of the 2-aryl substituent, in 15, afforded selectivity for human A3 vs rat A1 or A2A receptors. The 2-styryl-6-propoxy derivative, 20, of the furanochromone visnagin was 30-fold selective for human A3 receptors vs either rat A1 or A2A receptors. Several of the more potent derivatives effectively antagonized the effects of an agonist in a functional A3 receptor assay, i.e. inhibition of adenylyl cyclase in CHO cells expressing cloned rat A3 receptors. In conclusion, these series of flavonoids provide leads for the development of novel potent and subtype selective A3 antagonists.

Animals↗

PubMed1996

Novel N6-(substituted-phenylcarbamoyl)adenosine-5'-uronamides as potent agonists for A3 adenosine receptors.

A series of adenosine-5'-uronamide derivatives bearing N6-phenylurea groups have been synthesized and tested for their affinity at A1 and A2A adenosine receptors in rat brain membranes and at cloned rat A3 receptors from stably transfected CHO cells. Some N6-arylcarbamoyl derivatives, N6-((2-chlorophenyl)carbamoyl)-, N6-((3-chlorophenyl)carbamoyl)-, and N6-((4-methoxyphenyl)carbamoyl)adenosine-5'-ethyluronamide (4l-n), were found to have affinity at A3 receptors in the low nanomolar range (Ki values < 10 nM). In CHO cells stably transfected with the rat A3 receptor, compound 4n was found to be a full agonist in inhibiting adenylate cyclase activity. The present study represents the first example of N6-acyl-substituted adenosine analogs having high affinity at adenosine receptors and, in particular, at the A3 receptor subtype.

Adenylyl Cyclases↗

PubMed1996

Interactions of flavonoids and other phytochemicals with adenosine receptors.

Flavone derivatives and other phytochemicals were found to bind to three subtypes of adenosine receptors in the micromolar range. Affinity was determined in radioligand binding assays at rat brain A1 and A2A receptors using [3H]-N6-PIA ([3H]-(R)-N6-phenylisopropyladenosine) and [3H]CGS21680 ([3H]-2-[[4-(2-carboxyethyl)phenyl]ethylamino]-5'- (N-ethylcarbamoyl)adenosine), respectively. Affinity was determined at cloned human and rat brain A3 receptors using [125I]-AB-MECA [N6-(4-amino-3-iodobenzyl)adenosine-5'-(N-methyluronamide)]. A structure-activity analysis indicated that the hydroxyl groups of naturally occurring flavones are not essential for affinity at adenosine receptors. Galangin, 14, displayed Ki values of 1 microM at both rat A1 and A2A receptors and 3 microM at human A3 receptors. Methylation but not acetylation of the hydroxyl groups of galangin enhanced A3 affinity. Pentamethylmorin, 20, appeared to bind with 14-17-fold selectivity for human A3 receptors vs rat A1 and A2A receptors, with a Ki value of 2.65 microM. Two flavone derivatives (14 and 15) showed 14-fold greater affinity at human vs rat A3 receptors. Reduction of the 2,3-olefinic bond, as in (+/-)-dihydroquercetin, or glycosidation, as in robinin, greatly diminished affinity. An isoflavone, genistein, also bound only very weakly at A3 receptors. alpha-Naphthoflavone had greater receptor affinity (0.79 microM at A1 receptors) than the beta-isomer. Other natural products of plant origin, including oxogalanthine lactam, hematoxylin, and arborinine were found to bind to A1 adenosine receptors with Ki values of 3-13 microM. These findings indicate that the flavones, flavonols, flavanones, and other phytochemicals may provide leads for the development of novel adenosine antagonists. The unexpected finding of considerable affinity of flavones at both rat and human A3 receptors may explain some of the previously observed biological effects of these compounds.

Animals↗

PubMed1995

Structure-activity relationships of 9-alkyladenine and ribose-modified adenosine derivatives at rat A3 adenosine receptors.

9-Alkyladenine derivatives and ribose-modified N6-benzyladenosine derivatives were synthesized in an effort to identify selective ligands for the rat A3 adenosine receptor and leads for the development of antagonists. The derivatives contained structural features previously determined to be important for A3 selectivity in adenosine derivatives, such as an N6-(3-iodobenzyl) moiety, and were further substituted at the 2-position with halo, amino, or thio groups. Affinity was determined in radioligand binding assays at rat brain A3 receptors stably expressed in Chinese hamster ovary (CHO) cells, using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)adenosine-5'-(N-methyluronamide)), and at rat brain A1 and A2a receptors using [3H]-N6-PIA ((R)-N6-phenylisopropyladenosine) and [3H]CGS 21680 (2-[[[4-(2-carboxyethyl)-phenyl]ethyl]amino]-5'- (N-ethylcarbamoyl)adenosine), respectively. A series of N6-(3-iodobenzyl) 2-amino derivatives indicated that a small 2-alkylamino group, e.g., methylamino, was favored at A3 receptors. N6-(3-Iodobenzyl)-9-methyl-2-(methylthio)adenine was 61-fold more potent than the corresponding 2-methoxy ether at A3 receptors and of comparable affinity at A1 and A2a receptors, resulting in a 3-6-fold selectivity for A3 receptors. A pair of chiral N6-(3-iodobenzyl) 9-(2,3-dihydroxypropyl) derivatives showed stereoselectivity, with the R-enantiomer favored at A3 receptors by 5.7-fold. 2-Chloro-9-(beta-D-erythrofuranosyl)-N6-(3-iodobenzyl)adenine had a Ki value at A3 receptors of 0.28 microM. 2-Chloro-9-[2-amino-2,3-dideoxy-beta-D-5-(methylcarbamoyl)- arabinofuranosyl]-N6-(3-iodobenzyl)adenine was moderately selective for A1 and A3 vs A2a receptors. A 3'-deoxy analogue of a highly A3-selective adenosine derivative retained selectivity in binding and was a full agonist in the inhibition of adenylyl cyclase mediated via cloned rat A3 receptors expressed in CHO cells. The 3'-OH and 4'-CH2OH groups of adenosine are not required for activation at A3 receptors. A number of 2',3'-dideoxyadenosines and 9-acyclic-substituted adenines appear to inhibit adenylyl cyclase at the allosteric "P" site.

Adenine↗

PubMed1995

Search for new purine- and ribose-modified adenosine analogues as selective agonists and antagonists at adenosine receptors.

The binding affinities at rat A1, A2a, and A3 adenosine receptors of a wide range of derivatives of adenosine have been determined. Sites of modification include the purine moiety (1-, 3-, and 7-deaza; halo, alkyne, and amino substitutions at the 2- and 8-positions; and N6-CH2-ring, -hydrazino, and -hydroxylamino) and the ribose moiety (2'-, 3'-, and 5'-deoxy; 2'- and 3'- O-methyl; 2'-deoxy 2'-fluoro; 6'-thio; 5'-uronamide; carbocyclic; 4'- or 3'-methyl; and inversion of configuration). (-)- and (+)-5'-Noraristeromycin were 48- and 21-fold selective, respectively, for A2a vs A1 receptors. 2-Chloro-6'-thioadenosine displayed a Ki value of 20 nM at A2a receptors (15-fold selective vs A1). 2-Chloroadenin-9-yl(beta-L-2'-deoxy-6'- thiolyxofuranoside) displayed a Ki value of 8 microM at A1 receptors and appeared to be an antagonist, on the basis of the absence of a GTP-induced shift in binding vs a radiolabeled antagonist (8-cyclopentyl-1,3-dipropyl-xanthine). 2-Chloro-2'-deoxyadenosine and 2-chloroadenin-9-yl(beta-D-6'-thioarabinoside) were putative partial agonists at A1 receptors, with Ki values of 7.4 and 5.4 microM, respectively. The A2a selective agonist 2-(1-hexynyl)-5'-(N-ethylcarbamoyl)adenosine displayed a Ki value of 26 nM at A3 receptors. The 4'-methyl substitution of adenosine was poorly tolerated, yet when combined with other favorable modifications, potency was restored. Thus, N6-benzyl-4'-methyladenosine-5'-(N-methyluronamide) displayed a Ki value of 604 nM at A3 receptors and was 103- and 88-fold selective vs A1 and A2a receptors, respectively. This compound was a full agonist in the A3-mediated inhibition of adenylate cyclase in transfected CHO cells. The carbocyclic analogue of N6-(3-iodobenzyl)adenosine-5'-(N-methyluronamide) was 2-fold selective for A3 vs A1 receptors and was nearly inactive at A2a receptors.

Adenosine↗

PubMed1994

Selective ligands for rat A3 adenosine receptors: structure-activity relationships of 1,3-dialkylxanthine 7-riboside derivatives.

1,3-Dibutylxanthine 7-riboside has been found to be a partial agonist at A3 adenosine receptors (van Galen et al. Mol. Pharmacol. 1994, 45, 1101-1111). 1,3-Dialkylxanthine 7-riboside analogues modified at the 1-, 3-, and 8-purine positions and at the ribose 5'-position were synthesized. The nucleoside analogues were examined for affinity in radioligand binding assays at rat brain A3 adenosine receptors stably expressed in CHO cells, using the radioligand [[125I]-4-amino-3-iodobenzyl]adenosine-5'-N-methyluronamide (AB-MECA). Affinity was assayed at rat brain A1 and A2a receptors using [3H]PIA and [3H]CGS 21680, respectively. The affinity of xanthine 7-ribosides at A3 receptors depended on the 1,3-dialkyl substituents in the order: Pent > or = Bu >> Hx > Pr approximately Me. 1,3-Dipentylxanthine 7-riboside was slightly selective for A3 receptors (2-fold vs A1 and 10-fold vs A2a). 8-Methoxy substitution was tolerated at A3 receptors. 2-Thio vs 2-oxo substitution increased potency at all three subtypes and slightly increased A3 vs A1 selectivity. The 5'-uronamide modification, which was previously found to enhance A3 selectivity in N6-benzyladenosine derivatives, was also incorporated into the xanthine 7-ribosides, with similar results. The affinity of 1,3-dialkylxanthine 7-riboside 5'-uronamides at A3 receptors depended on the N-alkyluronamide substituent in the order: MeNH > EtNH >> NH2 >> Me2N. Affinity of the 5'-uronamides at A3 receptors was dependent on the 1,3-dialkyl substitution in the order: Bu > Pent > Hex. 1,3-Dibutylxanthine 7-riboside 5'-N-methylcarboxamide, with a Ki value of 229 nM at A3 receptors, was 160-fold selective for rat A3 vs A1 receptors and > 400-fold selective vs A2a receptors. This derivative acted as a full agonist in the A3 receptor-mediated inhibition of adenylate cyclase.

Animals↗

PubMed1994

2-Substitution of N6-benzyladenosine-5'-uronamides enhances selectivity for A3 adenosine receptors.

Adenosine derivatives bearing an N6-(3-iodobenzyl) group, reported to enhance the affinity of adenosine-5'-uronamide analogues as agonists at A3 adenosine receptors (J. Med. Chem. 1994, 37, 636-646), were synthesized starting from methyl beta-D-ribofuranoside in 10 steps. Binding affinities at A1 and A2a receptors in rat brain membranes and at cloned rat A3 receptors from stably transfected CHO cells were compared. N6-(3-Iodobenzyl)adenosine was 2-fold selective for A3 vs A1 or A2a receptors; thus it is the first monosubstituted adenosine analogue having any A3 selectivity. The effects of 2-substitution in combination with modifications at the N6- and 5'-positions were explored. 2-Chloro-N6-(3-iodobenzyl)adenosine had a Ki value of 1.4 nM and moderate selectivity for A3 receptors. 2-Chloro-N6-(3-iodobenzyl)adenosine- 5'-N-methyluronamide, which displayed a Ki value of 0.33 nM, was selective for A3 vs A1 and A2a receptors by 2500- and 1400-fold, respectively. It was 46,000-fold selective for A3 receptors vs the Na(+)-independent adenosine transporter, as indicated in displacement of [3H]N6-(4- nitrobenzyl)-thioinosine binding in rat brain membranes. In a functional assay in CHO cells, it inhibited adenylate cyclase via rat A3 receptors with an IC50 of 67 nM. 2-(Methylthio)-N6-(3-iodobenzyl)-adenosine-5'-N-methyluronamide and 2-(methylamino)-N6-(3-iodobenzyl)adenosine-5'-N-methyluronamide were less potent, but nearly as selective for A3 receptors. Thus, 2-substitution (both small and sterically bulky) is well-tolerated at A3 receptors, and its A3 affinity-enhancing effects are additive with effects of uronamides at the 5'-position and a 3-iodobenzyl group at the N6-position.

Adenosine↗

PubMed1994

Structure-activity relationships of 1,3-dialkylxanthine derivatives at rat A3 adenosine receptors.

1,3-Dialkylxanthine analogues containing carboxylic acid and other charged groups on 8-position substituents were synthesized. These derivatives were examined for affinity in radioligand binding assays at rat brain A3 adenosine receptors stably expressed in CHO cells using the new radioligand [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)adenosine-5'-N-methyluronamide), and at rat brain A1 and A2a receptors using [3H]PIA and [3H]CGS 21680, respectively. A synthetic strategy for introducing multiple carboxylate groups at the 8-position using iminodiacetic acid derivatives was explored. The presence of a sulfonate, a carboxylate, or multiple carboxylate groups did not result in a significant enhancement of affinity at rat A3 receptors, although as previously observed an anionic group tended to diminish potency at A1 and A2a receptors. The rat A3 receptor affinity was not highly dependent on the distance of a carboxylate group from the xanthine pharmacophore. 2-Thio vs 2-oxo substitution favored A3 potency, and 8-alkyl vs 8-aryl substitution favored A3 selectivity, although few derivatives were truly selective for rat A3 receptors. 1,3-Dimethyl-8-(3-carboxypropyl)-2-thioxanthine was 7-fold selective for A3 vs A2a receptors. 1,3,7-Trimethyl-8-(trans-2-carboxyvinyl)xanthine was somewhat selective for A3 vs A1 receptors. For 8-arylxanthines affinity at A3 receptors was enhanced by 1,3-dialkyl substituents, in the order dibutyl > dipropyl > diallyl.

Adenosine↗

PubMed1994

A selective agonist affinity label for A3 adenosine receptors.

A newly synthesized, chemically reactive adenosine derivative, N6-(3-isothiocyanatobenzyl)adenosine-5'-N-methyluronamide, was found to bind selectively to A3 receptors. Ki values for this isothiocyanate derivative in competition binding at rat brain A1, A2a, and A3 receptors were 145, 272 and 10.0 nM, respectively. A preincubation with this derivative resulted in irreversible inhibition of radioligand binding at rat A3 receptors in membranes of transfected CHO cells or RBL-2H3 mast cells, but not at rat A1 or A2a receptors. The loss of binding sites for 0.1 nM [125I]N6-(4-aminobenzyl)adenosine-5'-N-methyluronamide, a high affinity A3 receptor radioligand, in transfected CHO cell membranes was concentration-dependent with an IC50 of 50 nM. No change was observed in the Kd value of the remaining A3 receptor sites. The inhibition was also insensitive to theophylline (1 mM), consistent with the pharmacology of rat A3 receptors. Structurally similar adenosine analogues lacking the chemically reactive isothiocyanate group failed to irreversibly inhibit A3-binding.

Adenosine↗

PubMed1994

A mutant epidermal growth factor receptor common in human glioma confers enhanced tumorigenicity.

The development and neoplastic progression of human astrocytic tumors appears to result through an accumulation of genetic alterations occurring in a relatively defined order. One such alteration is amplification of the epidermal growth factor receptor (EGFR) gene. This episomal amplification occurs in 40-50% of glioblastomas, which also normally express endogenous receptors. Moreover, a significant fraction of amplified genes are rearranged to specifically eliminate a DNA fragment containing exons 2-7 of the gene, resulting in an in-frame deletion of 801 bp of the coding sequence of the extracellular domain. Here we used retroviral transfer of such a mutant receptor (de 2-7 EGFR) into glioblastoma cells expressing normal endogenous receptors to test whether the mutant receptor was able to augment their growth and malignancy. Western blotting analysis showed that these cells expressed endogenous EGFR of 170 kDa as well as the exogenous de 2-7 EGFR of 140-155 kDa. Although holo-EGFRs were phosphorylated on tyrosine residues only after exposure of the cells to ligand, de 2-7 EGFRs were constitutively phosphorylated. In tissue culture neither addition of EGF nor expression of the mutant EGFR affected the rate of cell growth. However, when cells expressing mutant EGFR were implanted into nude mice subcutaneously or intracerebrally, tumorigenic capacity was greatly enhanced. These results suggest that a tumor-specific alteration of the EGFR plays a significant role in tumor progression perhaps by influencing interactions of tumor cells with their microenvironment in ways not easily assayed in vitro.

Animals↗

PubMed1994

Chronic administration of selective adenosine A1 receptor agonist or antagonist in cerebral ischemia.

The effect of chronic administration of selective adenosine A1 receptor agonists and antagonists on the outcome of cerebral ischemia is entirely unknown. Therefore, we have investigated the impact of such regimens on the hippocampal adenosine A1 receptor density, and on the recovery from 10 min forebrain ischemia in gerbils. While acutely administered N6-cyclopentyladenosine (CPA) given at 0.02 mg/kg resulted only in a significant reduction of mortality, at 1 mg/kg it improved both survival and neuronal preservation in the hippocampal CA1 region. Acute treatment with 1,3-dipropyl-8-cyclopentylxanthine (CPX) significantly worsened the outcome and enhanced neuronal destruction. The effects of chronic administration of these drugs (15 days followed by 1 drug-free day) were opposite. Thus, although chronic CPA at 0.02 mg/kg did not have any effect at all, at 1 mg/kg both survival and neuronal preservation were significantly poorer than in controls, while chronic CPX resulted in a significant improvement of both measures. These results were not accompanied by adenosine A1 receptor up- or downregulation. Our study indicates that highly selective adenosine analogues may have therapeutic potential in treatment of cerebral ischemia/stroke and possibly other neurodegenerative disorders as well.

Adenosine↗

PubMed1994

Structure-activity relationships of N6-benzyladenosine-5'-uronamides as A3-selective adenosine agonists.

Adenosine analogues modified at the 5'-position as uronamides and/or as N6-benzyl derivatives were synthesized. These derivatives were examined for affinity in radioligand binding assays at the newly discovered rat brain A3 adenosine receptor and at rat brain A1 and A2a receptors. 5'-Uronamide substituents favored A3 selectivity in the order N-methyl > N-ethyl approximately unsubstituted carboxamide > N-cyclopropyl. 5'-(N-Methylcarboxamido)-N6-benzyladenosine was 37-56-fold more selective for A3 receptors. Potency at A3 receptors was enhanced upon substitution of the benzyl substituent with nitro and other groups. 5'-N-Methyluronamides and N6-(3-substituted-benzyl)adenosines are optimal for potency and selectivity at A3 receptors. A series of 3-(halobenzyl)-5'-N-ethyluronamide derivatives showed the order of potency at A1 and A2a receptors of I approximately Br > Cl > F. At A3 receptors the 3-F derivative was weaker than the other halo derivatives. 5'-N-Methyl-N6-(3-iodobenzyl)adenosine displayed a Ki value of 1.1 nM at A3 receptors and selectivity versus A1 and A2a receptors of 50-fold. A series of methoxybenzyl derivatives showed that a 4-methoxy group best favored A3 selectivity. A 4-sulfobenzyl derivative was a specific ligand at A3 receptors of moderate potency. An aryl amino derivative was prepared as a probe for radioiodination and receptor cross-linking.

Adenosine↗

PubMed1994

Chronic adenosine A1 receptor agonist and antagonist: effect on receptor density and N-methyl-D-aspartate induced seizures in mice.

The effect of chronic administration of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) and the adenosine A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX) on N-methyl-D-aspartate (NMDA)-evoked seizures was studied in C57BL/6 mice (20/group). Animals were injected i.p. for 9 days with either 1.0 mg/kg CPA or 1.0 mg/kg CPX followed by 2 injection-free days (the washout period) and subsequent administration of a single dose of 60 mg/kg NMDA. As in our previous study, this dose of NMDA caused clonic/tonic seizures resulting in high (60%) mortality within 3 h after injection of the drug. Despite insignificant changes in seizure latency, chronic pretreatment with CPA increased the incidence of clonic/tonic episodes and end-point mortality. Conversely; chronic exposure to CPX completely eliminated clonic/tonic episodes, significantly increased average survival time, and reduced end-point mortality (P < 0.05). The results indicate that chronic treatment with adenosine A1 receptor antagonist may protect against NMDA-evoked seizures to the same degree as previously observed following a single, acute exposure to CPA. Since the density of adenosine receptor binding sites was unchanged after chronic treatment with either CPX or CPA, it is likely that the mechanism behind the observed protection may rest at the level of second messenger systems coupled to adenosine A1 receptors.

Adenosine↗

PubMed1994

Adenosine receptor prodrugs: synthesis and biological activity of derivatives of potent, A1-selective agonists.

5'-Ester derivatives of the potent adenosine agonists N6-[4-[[[[4-[[[(2-acetylaminoethyl)amino]carbonyl]methyl] anilino]carbonyl]methyl]phenyl]adenosine (N-AcADAC; 1) and N6-cyclopentyladenosine (CPA; 2) were prepared as prodrugs. Both alkyl esters or carbonates (designed to enter the brain by virtue of increased lipophilicity) and 1,4-dihydro-1-methyl-3-[(pyridinylcarbonyl)oxy]esters designed to concentrate in the brain by virtue of a redox delivery system were synthesized. In the 5'-blocked form, the adenosine agonists displayed highly diminished affinity for rat brain A1-adenosine receptors in binding assays. The dihydropyridine prodrug 29 was active in an assay of locomotor depression in mice, in which adenosine agonists are highly depressant. The behavior depression was not reversible by peripheral administration of a non-central nervous system active adenosine antagonist. In an assay of the peripheral action of adenosine (i.e., the inhibition of lipolysis in rats), the parent compounds were highly potent and the dihydropyridine prodrug was much less potent.

Adenosine↗

PubMed1993

Solubilized rabbit striatal A2a-adenosine receptors: stability and antagonist binding.

The A2a-adenosine binding subunit from rabbit striatal membranes was solubilized using 1% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and was characterized using the antagonist radioligand [3H]8-[4-[[[[2-aminoethyl)amino]carbonyl]methyl]oxy] phenyl]-1,3-dipropylxanthine (XAC). The solubilized receptor was very stable, with 55% of the specific [3H]XAC binding remaining after storage for 15 days at 4 degrees C. The dissociation constant (Kd) for binding of [3H]XAC to solubilized A2 receptors was determined in saturation studies to be 4.0 nM, with a Bmax of 600 fmol/mg protein. Xanthine inhibitors displaced the specific binding of the adenosine antagonist [3H]XAC (in the presence of 50 nM 8-cyclopentyl-1,3-dipropylxanthine) at 25 degrees C, with Ki values consonant with the expected affinities at A2a receptors. Binding of [3H]XAC (1 nM) or the adenosine agonist [3H]2-(carboxyethylphenylethylamino)adenosine-5'-N-ethyl carboxamide (5 nM) to A2a receptors was diminished in the presence of 0.1 M Na+ in both membranes and solubilized preparations. Agonist binding was increased (by 280% for membranes and 180% for solubilized receptors), and antagonist binding was decreased in the presence of 10 mM Mg2+. Displacement of [3H]XAC by the agonist (R)-N6-phenylisopropyladenosine was biphasic, corresponding to high (IC50 = 188 nM, RH = 30%) and low (IC50 = 9730 nM, RL = 70%) affinity sites. Preincubation with 100 microM GTP (10 mM Mg2+) converted the high affinity binding to low affinity, suggesting that receptor and G-protein are dissociated by the guanine nucleotide. The solubilized receptor was more easily inactivated by exposure to the reducing agent dithiothreitol (IC50 = 3 mM) than in membranes (IC50 = 220 mM), suggesting increased accessibility of structurally essential disulfide bridges.

Animals↗

PubMed1992

Synthesis and biological activity of N6-(p-sulfophenyl)alkyl and N6-sulfoalkyl derivatives of adenosine: water-soluble and peripherally selective adenosine agonists.

A series of N6-(p-sulfophenyl)alkyl and N6-sulfoalkyl derivatives of adenosine was synthesized, revealing that N6-(p-sulfophenyl)adenosine (10b) is a moderately potent (Ki vs [3H]PIA in rat cortical membranes was 74nM) and A1-selective (120-fold) adenosine agonist, of exceptional aqueous solubility of > 1.5 g/mL (approximately 3 M). Compound 10b was very potent in inhibiting synaptic potentials in gerbil hippocampal slices with an IC50 of 63 nM. At a dose of 0.1 mg/kg ip in rats, 10b inhibited lipolysis (a peripheral A1 effect) by 85% after 1 h. This in vivo effect was reversed using the peripherally selective A1-antagonist 1,3-dipropyl-8-[p-(carboxyethynyl)phenyl]xanthine (BW1433). The same dose of 10b in NIH Swiss mice (ip) was nearly inactive in locomotor depression, an effect that has been shown to be centrally mediated when elicited by lower doses of other potent adenosine agonists, such as N6-cyclohexyladenosine (CHA) (Nikodijevic et al. FEBS Lett. 1990, 261, 67). HPLC studies of biodistribution of a closely related and less potent homologue, N6-[4-(p-sulfophenyl)butyl]adenosine indicated that a 25 mg/kg ip dose in mice resulted in a plasma concentration after 30 min of 0.46 micrograms/mL and no detectable drug in the brain (detection limit < 0.1% of plasma level). Although 10b at doses > 0.1 mg/kg in mice depressed locomotor activity, this depression was unlike the effects of CHA and was reversible by BW1433. These data suggest that 10b is a potent adenosine agonist in vivo and shows poor CNS penetration.

Adenosine↗