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Biomedical subjects

X D Ji

Publications and source records attributed to X D Ji.

At least 19 recordsLinked to original sources
PubMed2001

Growth suppression of intracranial xenografted glioblastomas overexpressing mutant epidermal growth factor receptors by systemic administration of monoclonal antibody (mAb) 806, a novel monoclonal antibody directed to the receptor.

A mutant epidermal growth factor receptor (variously called DeltaEGFR, de2-7 EGFR, or EGFRvIII) containing a deletion of 267 amino acids of the extracellular domain is frequently highly expressed in human malignant gliomas and has been reported for cancers of the lung, breast, and prostate. We tested the efficacy of a novel monoclonal anti-DeltaEGFR antibody, mAb 806, on the growth of intracranial xenografted gliomas in nude mice. Systemic treatment with mAb 806 significantly reduced the volume of tumors and increased the survival of mice bearing xenografts of U87 MG.DeltaEGFR, LN-Z308.DeltaEGFR, or A1207.DeltaEGFR gliomas, each of which expresses high levels of DeltaEGFR. In contrast, mAb 806 treatment was ineffective with mice bearing the parental U87 MG tumors, which expressed low levels of endogenous wild-type EGFR, or U87 MG.DK tumors, which expressed high levels of kinase-deficient DeltaEGFR. A slight increase of survival of mice xenografted with a wild-type EGFR-overexpressing U87 MG glioma (U87 MG.wtEGFR) was effected by mAb 806 concordant with its weak cross-reactivity with such cells. Treatment of U87 MG.DeltaEGFR tumors in mice with mAb 806 caused decreases in both tumor growth and angiogenesis, as well as increased apoptosis. Mechanistically, in vivo mAb 806 treatment resulted in reduced phosphorylation of the constitutively active DeltaEGFR and caused down-regulated expression of the apoptotic protector, Bcl-XL. These data provide preclinical evidence that mAb 806 treatment may be a useful biotherapeutic agent for those aggressive gliomas that express DeltaEGFR.

Animals↗
PubMed2001

Ring-Constrained (N)-methanocarba nucleosides as adenosine receptor agonists: independent 5'-uronamide and 2'-deoxy modifications.

Novel methanocarba adenosine analogues, having the pseudo-ribose northern (N) conformation preferred at adenosine receptors (ARs), were synthesized and tested in binding assays. The 5'-uronamide modification preserved [N6-(3-iodobenzyl)] or enhanced (N6-methyl) affinity at A3ARs, while the 2'-deoxy modification reduced affinity and efficacy in a functional assay.

Adenine↗
PubMed2000

A peptide derived from the non-receptor-binding region of urokinase plasminogen activator inhibits glioblastoma growth and angiogenesis in vivo in combination with cisplatin.

The urokinase plasminogen activator system is involved in angiogenesis and tumor growth of malignant gliomas, which are highly neovascularized and so may be amenable to antiangiogenic therapy. In this paper, we describe the activity of A6, an octamer capped peptide derived from the non-receptor-binding region of urokinase plasminogen activator. A6 inhibited human microvascular endothelial cell migration but had no effect on the proliferation of human microvascular endothelial cells or U87MG glioma cells in vitro. In contrast, A6 or cisplatin (CDDP) alone suppressed subcutaneous tumor growth in vivo by 48% and 53%, respectively, and, more strikingly, the combination of A6 plus CDDP inhibited tumor growth by 92%. Such combination treatment also greatly reduced the volume of intracranial tumor xenografts and increased survival of tumor-bearing animals when compared with CDDP or A6 alone. Tumors from the combination treatment group had significantly reduced neovascularization, suggesting a mechanism involving A6-mediated inhibition of endothelial cell motility, thereby eliciting vascular sensitivity to CDDP-mediated toxicity. These data suggest that the combination of an angiogenesis inhibitor that targets endothelial cells with a cytotoxic agent may be a useful therapeutic approach.

Animals↗
PubMed2000

The utilization of a unified pharmacophore query in the discovery of new antagonists of the adenosine receptor family.

Pharmacophore queries from previously known potent selective A3 antagonists were generated by Chem-X. These queries were used to search a pharmacophore database of diverse compounds (CNS-Set). In vitro assays of 186 'hits' yielded over 30 active compounds, for four adenosine receptor subtypes. This search strategy may also be applicable to the discovery of new ligands via receptor homology data.

Adenosine-5'-(N-ethylcarboxamide)↗
PubMed1999

Selective A(3) adenosine receptor antagonists: water-soluble 3, 5-diacyl-1,2,4-trialkylpyridinium salts and their oxidative generation from dihydropyridine precursors.

A(3) adenosine receptor antagonists are sought for their potential antiinflammatory, antiasthmatic, and antiischemic properties. We have found that 3,5-diacyl-1,2,4-trialkyl-6-phenylpyridinium derivatives constitute a novel class of selective A(3) adenosine receptor antagonists. The structure-activity relationships of this class of antagonists, incorporating the 3-thioester, have been explored. The most potent analogue in this group was 2, 4-diethyl-1-methyl-3-(ethylsulfanylcarbonyl)-5-ethyloxycarbonyl -6-phe nylpyridinium iodide (11), which had an equilibrium inhibition constant (K(i)) value of 219 nM at human A(3) receptors (binding of [(125)I]AB-MECA (N(6)-(4-amino-3-iodobenzyl)-5'-N-methylcarbamoyladenosine)) expressed in Chinese hamster ovary (CHO) cells and >10 microM at rat brain A(1) and A(2A) receptors and at recombinant human A(2B) receptors. Compound 11 could be generated through oxidation of the corresponding 3,5-diacyl-1,2,4-trialkyl-6-phenyl-1,4-dihydropyridine, 24, with iodine or in the presence of rat brain homogenates. A 6-cyclopentyl analogue was shown to increase affinity at human A(3) receptors upon oxidation from the 1-methyl-1,4-dihydropyridine analogue, 25, to the corresponding pyridinium derivative, 23 (K(i) 695 nM), suggesting a prodrug scheme. Homologation of the N-methylpyridinium derivatives to N-ethyl and N-propyl at the 1-position caused a progressive reduction in the affinity at A(3) receptors. Modifications of the alkyl groups at the 2-, 3-, 4-, and 5-positions failed to improve potency in binding at A(3) receptors. The pyridinium antagonists are not as potent as other recently reported, selective A(3) receptor antagonists; however, they display uniquely high water solubility (43 mM for 11). Compound 11 antagonized the inhibition of adenylate cyclase elicited by IB-MECA in CHO cells expressing the human A(3) adenosine receptor, with a K(B) value of 399 nM, and did not act as an agonist, demonstrating that the pyridinium salts are pure antagonists.

Adenylyl Cyclase Inhibitors↗
PubMed1999

Differential expression of peroxiredoxin subtypes in human brain cell types.

The peroxiredoxin (Prx) protein is expressed widely in animal tissues and serves an antioxidant function associated with removal of cellular peroxides. We have cloned two Prx genes and observed differential expression of Prx-I and Prx-II (formerly NKEF-A and NKEF-B) in purified rat brain cell cultures (Sarafian et al. [1998] Mol. Chem. Neuropathol. 34:39-51). We have examined regional and cell-type-specific expression of Prx-I and Prx-II in paraffin sections of human brain using immunohistochemical methods. These studies revealed a clear segregation of expression of these two gene products in different brain cell types. In the cerebral cortex, cerebellum, basal ganglia, substantia nigra, and spinal cord, Prx-I was expressed primarily in astrocytes, while Prx-II was expressed exclusively in neurons. Prx-I was also prominently expressed in ependymal cells and subependymal matrix of substantia nigra and basal ganglia. Prx-II was not expressed at uniform density in all neurons. In general, small neurons such as cerebellar granule neurons displayed little or no staining, while large neurons, such as hippocampal pyramidal and Purkinje neurons were heavily stained. The absence of expression of Prx-I in neurons and the selective expression of Prx-II in large neurons suggest that these antioxidant enzymes serve distinct functional roles that may reflect the different functions and biochemical activities of these cell types. Restricted expression of these genes may also contribute to the selective vulnerability of these cells to a wide variety of neuropathologic conditions.

Adult↗
PubMed1999

Synthesis, CoMFA analysis, and receptor docking of 3,5-diacyl-2, 4-dialkylpyridine derivatives as selective A3 adenosine receptor antagonists.

3,5-Diacyl-2,4-dialkyl-6-phenylpyridine derivatives have been found to be selective antagonists at both human and rat A3 adenosine receptors (Li et al. J. Med. Chem. 1998, 41, 3186-3201). In the present study, ring-constrained, fluoro, hydroxy, and other derivatives in this series have been synthesized and tested for affinity at adenosine receptors in radioligand binding assays. Ki values at recombinant human and rat A3 adenosine receptors were determined using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)-5'-N-methylcarbamoyladenosine). Selectivity for A3 adenosine receptors was determined vs radioligand binding at rat brain A1 and A2A receptors, and structure-activity relationships at various positions of the pyridine ring (the 3- and 5-acyl substituents and the 2- and 4-alkyl substituents) were probed. At the 5-position inclusion of a beta-fluoroethyl (7) or a gamma-fluoropropyl ester (26) was favorable for human A3 receptor affinity, resulting in Ki values of 4.2 and 9.7 nM, respectively, while the pentafluoropropyl analogue was clearly less potent at human A3 receptors. At the 2-, 3-, and 4-positions, fluoro or hydroxy substitution failed to enhance potency and selectivity at human A3 receptors. Several analogues were nearly equipotent at rat and human A3 receptors. To further define the pharmacophore conformationally, a lactam, a lactone, and thiolactones were tested in adenosine receptor binding. The most potent analogue in this group was compound 34, in which a thiolactone was formed between 3- and 4-positions and which had a Ki value of 248 nM at human A3 receptors. Using affinity data and a general pharmacophore model for A3 adenosine receptor antagonists recently proposed, we applied comparative molecular field analysis (CoMFA) to obtain a three-dimensional quantitative structure-activity relationship for pyridine derivatives, having good predictability (r2pred = 0.873) for compounds in the test set. A rhodopsin-based model of the human A3 receptor was built, and the pyridine reference ligand 2,3,4, 5-tetraethyl-6-phenyl-pyridine-3-thiocarboxylate-5-carboxylate (MRS 1476) was docked in the putative ligand binding site. Interactions between receptor transmembrane domains and the steric and the electrostatic contour plots obtained from the CoMFA analysis were analyzed.

Animals↗
PubMed1999

Monoclonal anti-androgen receptor antibodies: production, characterization and potential diagnostic applications.

Several monoclonal antibodies (mAbs) and novel mAb-based assays for the androgen receptors (AR) have been developed. Large amounts of the recombinant human AR protein produced by a baculovirus expression system were used as an antigen to produce mAbs. Twenty-nine AR-specific mAbs were first confirmed by Western blot analysis and were then characterized for their immunoglobulin isotypes, epitopes, and epitope localization in AR. Novel assays using flow cytometry and sandwich enzyme-linked immunosorbent assays (ELISA) were established to detect AR-expressing cells and to quantify soluble AR protein, respectively. Using immunostaining, we identified several anti-AR mAbs exclusively recognizing AR within the nuclei of the prostate cancer cell line LNCaP and of prostate tissues in both frozen and paraffin-embedded sections, whereas other mAbs could detect AR in both nuclear and cytoplasmic compartments. Interestingly, certain mAbs, such as G122-25 and G122-77, could distinguish the androgen-bound AR from the unoccupied AR. In sum, many purified AR protein and anti-AR mAbs, together with the assays developed, could be powerful tools for the study of functional AR and for the diagnosis of prostatic cancers.

Animals↗
PubMed1999

Use of the triazolotriazine [3H]ZM 241385 as a radioligand at recombinant human A2B adenosine receptors.

Radiolabeled ZM 241385 (4-(2-[7-amino-2- ¿furyl¿¿1,2,4¿triazolo¿2,3-a¿¿1,3,5¿triazin-5-ylaminoethyl)p henol), has previously been used as a high affinity radioligand for the labeling of A2A adenosine receptors in cell membranes. Another subtype, the A2B receptor, is the least well-defined subtype of adenosine receptors and lacks selective pharmacological probes. In the present study, we have used [3H]ZM 241385 as a radioligand to label recombinant human A2B adenosine receptors in HEK-293 cell membranes, that do not express A2A adenosine receptors, and found that the pharmacological profile is consistent with the SAR of A2B receptors. Saturable, specific binding (Kd 33.6 nM, Bmax 4.48 pmol/mg protein) that was best described by a one-site model was found, and specific binding was approximately 75% of total binding. [3H]ZM 241385 binding was displaceable by a large number of compounds known to interact with A2B receptors; thus, this method has promise as a tool in the search for agonists and antagonists selective for this subtype. Xanthine analogs, which are antagonists, proved to be the most potent displacers. The Ki of XAC, xanthine amine congener, was 12.3 nM, while CPX (8-cyclopentyl-1,3-dipropylxanthine) was less potent. The non-selective triazoloquinazoline antagonist CGS 15943 (Ki 16.4 nM), which is similar in structure to ZM 241385, was slightly less potent than XAC. The non-xanthine A2B-antagonist alloxazine displaced [3H]ZM 241385-binding with a Ki of 462 nM, similar to its affinity in functional assays. Adenosine derivatives known to activate this receptor subtype, such as NECA (5'-N-ethylcarboxamidoadenosine) and R-PIA (N6-phenylisopropyladenosine), were considerably less potent than the 8-substituted xanthines examined.

Animals↗
PubMed1998

Structure-activity relationships and molecular modeling of 3, 5-diacyl-2,4-dialkylpyridine derivatives as selective A3 adenosine receptor antagonists.

The structure-activity relationships of 6-phenyl-1,4-dihydropyridine derivatives as selective antagonists at human A3 adenosine receptors have been explored (Jiang et al. J. Med. Chem. 1997, 39, 4667-4675). In the present study, related pyridine derivatives have been synthesized and tested for affinity at adenosine receptors in radioligand binding assays. Ki values in the nanomolar range were observed for certain 3,5-diacyl-2,4-dialkyl-6-phenylpyridine derivatives in displacement of [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)-5'-N-methylcarbamoyladenosine) at recombinant human A3 adenosine receptors. Selectivity for A3 adenosine receptors was determined vs radioligand binding at rat brain A1 and A2A receptors. Structure-activity relationships at various positions of the pyridine ring (the 3- and 5-acyl substituents and the 2- and 4-alkyl substituents) were probed. A 4-phenylethynyl group did not enhance A3 selectivity of pyridine derivatives, as it did for the 4-substituted dihydropyridines. At the 2- and 4-positions ethyl was favored over methyl. Also, unlike the dihydropyridines, a thioester group at the 3-position was favored over an ester for affinity at A3 adenosine receptors, and a 5-position benzyl ester decreased affinity. Small cycloalkyl groups at the 6-position of 4-phenylethynyl-1,4-dihydropyridines were favorable for high affinity at human A3 adenosine receptors, while in the pyridine series a 6-cyclopentyl group decreased affinity. 5-Ethyl 2, 4-diethyl-3-(ethylsulfanylcarbonyl)-6-phenylpyridine-5-carboxylate , 38, was highly potent at human A3 receptors, with a Ki value of 20 nM. A 4-propyl derivative, 39b, was selective and highly potent at both human and rat A3 receptors, with Ki values of 18.9 and 113 nM, respectively. A 6-(3-chlorophenyl) derivative, 44, displayed a Ki value of 7.94 nM at human A3 receptors and selectivity of 5200-fold. Molecular modeling, based on the steric and electrostatic alignment (SEAL) method, defined common pharmacophore elements for pyridine and dihydropyridine structures, e.g., the two ester groups and the 6-phenyl group. Moreover, a relationship between affinity and hydrophobicity was found for the pyridines.

Adenosine↗
PubMed1998

Synthesis and biological activity of a new series of N6-arylcarbamoyl, 2-(Ar)alkynyl-N6-arylcarbamoyl, and N6-carboxamido derivatives of adenosine-5'-N-ethyluronamide as A1 and A3 adenosine receptor agonists.

A new series of 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ +-b earing N-arylureas or N-arylcarboxamido groups at the purine 6 position and N-arylureas combined with halogens or alkynyl chains at the 2 position have been synthesized and tested for affinity at A1 and A2A adenosine receptors in rat brain membranes and at cloned rat A3 receptors expressed in CHO cells. The derivatives contained the 5' substituent found in the potent, nonselective agonist 1-(6-amino-9H-purin-9-yl)-1-deoxy-N-ethyl-beta-D-ribofuranuronamide++ + (NECA). While the carboxamido derivatives (9-13) showed affinity for A1 receptors, the urea derivatives (30-45) showed different degrees of affinity and selectivity for the A3 adenosine receptor subtype. In particular the derivative bearing a p-sulfonamidophenyl-urea at the 6 position, 31 showed a high affinity (Ki = 9 nM) and selectivity for the A3 receptors compared to that of the reference compound 1-[6-[[(3-iodophenyl)methyl]amino]-9H-purin-9-yl]-1-deoxy-N-methyl-be ta-D-ribofuranuronamide (IB-MECA). Furthermore, the importance of the stereochemistry in the interaction of these ligands at the rat A3 adenosine receptors has been evaluated by introducing a chiral chain at the 6 position. The introduction of halogens or alkynyl chains at the purine 2 position of selected ureas did not give the expected enhancement of potency at A2A and/or A3 receptors but rather showed a dramatic reduction of A2A affinity, resulting in compounds with good A2A/A3 selectivity. For example, the 2-(3-hydroxy-3-phenyl-1-propyn-1-yl)-6-(4-methoxyphenylurea) derivative 61 showed the capability to bind simultaneously to A1 and A3 receptor subtypes, excluding the A2A receptor. Compound 31 was shown to be an agonist, 9-fold more potent than NECA, at A3 receptors in rat RBL-2H3 mast cell membranes through stimulation of binding of [35S]GTP-gamma-S.

Adenosine-5'-(N-ethylcarboxamide)↗
PubMed1998

Synthesis and adenosine receptor affinity of 7-beta-D-ribofuranosylxanthine.

7-beta-D-Ribofuranosylxanthine, a previously unreported isomer of xanthosine, was prepared in four steps from 7-benzylxanthine. The procedure, which involves the use of pivaloyloxymethyl groups to protect the xanthine ring, was also applied to preparation of some 1-N-alkyl derivatives of 7-ribosylxanthine. Adenosine receptor affinity for these compounds was determined. 7-beta-D-Ribofuranosylxanthine was found to have higher affinity and greater selectivity for the A1 receptor than previously reported xanthine nucleosides, and to be a partial agonist.

Animals↗
PubMed1998

Development and characterization of monoclonal antibodies specific to the serotonin 5-HT2A receptor.

Serotonin (5-hydroxytryptamine, 5-HT) mediates many functions of the central and peripheral nervous systems by its interaction with specific neuronal and glial receptors. Fourteen serotonin receptors belonging to seven families have been identified through physiological, pharmacological, and molecular cloning studies. Monoclonal antibodies (MAbs) specific for each of these receptor subtypes are needed to characterize their expression, distribution, and function in embryonic, adult, and pathological tissues. In this article we report the development and characterization of MAbs specific to the serotonin 5-HT2A receptor. To generate MAbs against 5-HT2AR, mice were immunized with the N-terminal domain of the receptor. The antigens were produced as glutathionine S-transferase (GST) fusion proteins in insect cells using a Baculovirus expression system. The hybridomas were initially screened by ELISA against the GST-5-HT2AR recombinant proteins and subsequently against GST control proteins to eliminate clones with unwanted reactivity. They were further tested by Western blotting against recombinant GST-5-HT2AR, rat and human brain lysate, and lysate from cell lines transfected with 5-HT2AR cDNA. One of the MAbs G186-1117, which recognizes a portion of the 5-HT2AR N-terminus, was selected for further characterization. G186-1117 reacted with a band of molecular size 55 kD corresponding to the predicted size of 5-HT2AR in lysates from rat brain and a 5-HT2AR-transfected cell line. Its specificity was further confirmed by adsorption of immunoreactivity with recombinant 5-HT2AR but not with recombinant 5-HT2BR and 5-HT2CR. Rat brain sections and Schwann cell cultures were immunohistochemically labeled with this MAb. G186-1117 showed differential staining in various regions of the rat brain, varying from regions with no staining to regions of intense reactivity. In particular, staining of cell bodies and dendrites of the pyramidal neurons in the cortex was observed, which is in agreement with observations of electrophysiological studies.

Aged↗
PubMed1997

Structure-activity relationships of 4-(phenylethynyl)-6-phenyl-1,4-dihydropyridines as highly selective A3 adenosine receptor antagonists.

4-(Phenylethynyl)-6-phenyl-1,4-dihydropyridine derivatives are selective antagonists at human A3 adenosine receptors, with Ki values in a radioligand binding assay vs [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)-5'-(N-methylcarbamoyl)adenosine) in the submicromolar range. In this study, structure-activity relationships at various positions of the dihydropyridine ring (the 3- and 5-acyl substituents, the 4-aryl substituent, and 1-methyl group) were probed synthetically. Using the combined protection of the 1-ethoxymethyl and the 5-[2-(trimethylsilyl)ethyl] ester groups, a free carboxylic acid was formed at the 5-position allowing various substitutions. Selectivity of the new analogues for cloned human A3 adenosine receptors was determined vs radioligand binding at rat brain A1 and A2A receptors. Structure-activity analysis at adenosine receptors indicated that pyridyl, furyl, benzofuryl, and thienyl groups at the 4-position resulted in, at most, only moderate selectivity for A3 adenosine receptors. Ring substitution (e.g., 4-nitro) of the 4-phenylethylnyl group did not provide enhanced selectivity, as it did for the 4-styryl-substituted dihydropyridines. At the 3-position of the dihydropyridine ring, esters were much more selective for A3 receptors than closely related thioester, amide, and ketone derivatives. A cyclic 3-keto derivative was 5-fold more potent at A3 receptors than a related open-ring analogue. At the 5-position, a homologous series of phenylalkyl esters and a series of substituted benzyl esters were prepared and tested. (Trifluoromethyl)-, nitro-, and other benzyl esters substituted with electron-withdrawing groups were specific for A3 receptors with nanomolar Ki values and selectivity as high as 37000-fold. A functionalized congener bearing an [(aminoethyl)amino]carbonyl group was also prepared as an intermediate in the synthesis of biologically active conjugates.

Adenosine↗
PubMed1997

The enhanced tumorigenic activity of a mutant epidermal growth factor receptor common in human cancers is mediated by threshold levels of constitutive tyrosine phosphorylation and unattenuated signaling.

Deregulation of signaling by the epidermal growth factor receptor (EGFR) is common in human malignancy progression. One mutant EGFR (variously named DeltaEGFR, de2-7 EGFR, or EGFRvIII), which occurs frequently in human cancers, lacks a portion of the extracellular ligand-binding domain due to genomic deletions that eliminate exons 2 to 7 and confers a dramatic enhancement of brain tumor cell tumorigenicity in vivo. In order to dissect the molecular mechanisms of this activity, we analyzed location, autophosphorylation, and attenuation of the mutant receptors. The mutant receptors were expressed on the cell surface and constitutively autophosphorylated at a significantly decreased level compared with wild-type EGFR activated by ligand treatment. Unlike wild-type EGFR, the constitutively active DeltaEGFR were not down-regulated, suggesting that the altered conformation of the mutant did not result in exposure of receptor sequence motifs required for endocytosis and lysosomal sorting. Mutational analysis showed that the enhanced tumorigenicity was dependent on intrinsic tyrosine kinase activity and was mediated through the carboxyl terminus. In contrast with wild-type receptor, mutation of any major tyrosine autophosphorylation site abolished these activities suggesting that the biological functions of DeltaEGFR are due to low constitutive activation with mitogenic effects amplified by failure to attenuate signaling by receptor down-regulation.

Amino Acid Sequence↗
PubMed1997

Pharmacological characterization of novel A3 adenosine receptor-selective antagonists.

The effects of putative A3 adenosine receptor antagonists of three diverse chemical classes (the flavonoid MRS 1067, the 6-phenyl-1,4-dihydropyridines MRS 1097 and MRS 1191, and the triazoloquinazoline MRS 1220) were characterized in receptor binding and functional assays. MRS1067, MRS 1191 and MRS 1220 were found to be competitive in saturation binding studies using the agonist radioligand [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)adenosine-5'-N-methyluronamide) at cloned human brain A3 receptors expressed in HEK-293 cells. Antagonism was demonstrated in functional assays consisting of agonist-induced inhibition of adenylate cyclase and the stimulation of binding of [35S]guanosine 5'-O-(3-thiotriphosphate) ([35S]GTP-gamma-S) to the associated G-proteins. MRS 1220 and MRS 1191, with KB values of 1.7 and 92 nM, respectively, proved to be highly selective for human A3 receptor vs human A1 receptor-mediated effects on adenylate cyclase. In addition, MRS 1220 reversed the effect of A3 agonist-elicited inhibition of tumor necrosis factor-alpha formation in the human macrophage U-937 cell line, with an IC50 value of 0.3 microM.

Adenosine↗
PubMed1996

6-phenyl-1,4-dihydropyridine derivatives as potent and selective A3 adenosine receptor antagonists.

An approach to designing dihydropyridines that bind to adenosine receptors without binding to L-type calcium channels has been described. 1,4-Dihydropyridine derivatives substituted with beta-styryl or phenylethynyl groups at the 4-position and aryl groups at the 6-position were synthesized and found to be selective for human A3 receptors. Combinations of methyl, ethyl, and benzyl esters were included at the 3- and 5-positions. 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-carboxyethyl)phenyl]ethylamino]-5'- (N-ethylcarbamoyl)adenosine], respectively. Affinity was determined at cloned human and rat A3 receptors using [125I]AB-MECA [N6-(4-amino-3-iodobenzyl)-5'-(N-ethylcarbamoyl)-adenosine]. Structure-activity analysis indicated that substitution of the phenyl ring of the beta-styryl group but not of the 6-phenyl substituent was tolerated in A3 receptor selective agents. Replacement of the 6-phenyl ring with a 3-thienyl or 3-furyl group reduced the affinity at A3 receptors by 4- and 9-fold, respectively. A 5-benzyl ester 4-trans-beta-styryl derivative, 26, with a Ki value of 58.3 nM at A3 receptors, was > 1700-fold selective vs either A1 receptors or A2A receptors. Shifting the benzyl ester to the 3-position lowered the affinity at A3 receptors 3-fold. A 5-benzyl, 3-ethyl ester 4-phenylethynyl derivative, 28, displayed a Ki value of 31.4 nM at A3 receptors and 1300-fold selectivity vs A1 receptors. The isomeric 3-benzyl, 5-ethyl diester was > 600-fold selective for A3 receptors. Oxidation of 28 to the corresponding pyridine derivative reduced affinity at A3 receptors by 88-fold and slightly increased affinity at A1 receptors.

Animals↗