2-Pyrazolyl-N(6)-substituted adenosine derivatives as high affinity and selective adenosine A(3) receptor agonists.

We describe the synthesis of new high affinity and selective A(3)-adenosine receptor (A(3)-AdoR) agonists. Introduction of a methyl group at the N(6)-position of the A(2A)-AdoR selective 2-pyrazolyl-adenosine analogues (Figure 2) brought about a substantial increase in the A(3)-AdoR binding affinity and selectivity. While the N(6)-desmethyl analogues 3a and 4 were inactive at the A(3)-AdoR (K(i) > 10 microM), the corresponding N(6)-methyl analogues 5 and 22 showed good binding affinity at the A(3)-AdoR (K(i) = 73 and 97 nM, respectively). Replacement of the carboxamide group in 5 with different heteroaryl groups resulted in analogues with high affinities and selectivity for the A(3)-AdoR. (2R,3S,4R)-tetrahydro-2-(hydroxymethyl)-5-(6-(methylamino)-2-(4-(pyridin-2-yl)-1H-pyrazol-1-yl)-9H-purin-9-yl)furan-3,4-diol (15, K(i) = 2 nM) displayed high selectivity for the A(3)-AdoR versus A(1)- and A(2A)-AdoRs (selectivity ratios of 1900 and >2000, respectively).

Synergy between A2B adenosine receptors and hypoxia in activating human lung fibroblasts.

Chronic inflammatory airway diseases, such as asthma, chronic obstructive pulmonary disease and pulmonary fibrosis, are associated with subepithelial fibroblast activation, myofibroblast hyperplasia, hypoxia, and increase in interstitial adenosine concentrations. The goal of this study was to determine the effect of adenosine and its receptors on activation of human lung fibroblasts under normoxia (21% O2) and hypoxia (5% O2). Under the normoxic condition, adenosine and its stable analog, 5'-(N-ethylcarboxamido)-adenosine, via activation of A2B adenosine receptors, increased the release of interleukin (IL)-6 by 14-fold and induced the differentiation of human lung fibroblasts to myofibroblasts. This latter effect of 5'-(N-ethylcarboxamido)-adenosine was abolished by an IL-6-neutralizing antibody. Hypoxia increased the release of IL-6 by 2.8-fold, and there was a synergy between hypoxia and activation of A2B adenosine receptors to increase the release of IL-6 and to induce differentiation of fibroblasts into myofibroblasts. Hypoxia increased the expression of A2B adenosine receptors by 3.4-fold. Altogether, these data suggest that hypoxia amplifies the effect of adenosine on the release of IL-6 and cell differentiation by upregulating the expression of A2B adenosine receptors. Our findings provide a novel mechanism whereby adenosine participates in the remodeling process of inflammatory lung diseases.

The discovery of a selective, high affinity A(2B) adenosine receptor antagonist for the potential treatment of asthma.

Adenosine has been suggested to play a role in asthma, possibly via activation of A(2B) adenosine receptors on mast cells and other pulmonary cells. We describe our initial efforts to discover a xanthine based selective A(2B) AdoR antagonist that resulted in the discovery of CVT-5440, a high affinity A(2B) AdoR antagonist with good selectivity (A(2B) AdoR K(i)=50 nM, selectivity A(1)>200: A(2A)>200: A(3)>167).

A(2B) adenosine receptors increase cytokine release by bronchial smooth muscle cells.

Adenosine (Ado) has been suggested to play a role in inflammatory airway diseases such as asthma and chronic obstructive pulmonary disease. The goal of this study was to determine the effect of Ado and its receptor subtypes on cytokine release by bronchial smooth muscle cells. The A2B Ado receptor (AdoR) was expressed at the highest level among the four AdoR subtypes. Activation of the A2B AdoR by an Ado analog, 5'-(N-ethylcarboxamido)-adenosine (NECA), increased cAMP accumulation with potency (EC50 value) of 21.2 +/- 0.2 microM. The effect of NECA on the expression of the inflammatory cytokines was determined using a cDNA array consisting of 23 cytokine genes and confirmed using real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. NECA increased the release of interleukin-6 and monocyte chemotactic protein-1 proteins with EC50 values of 1.26 +/- 0.25 microM and 0.40 +/- 0.08 microM, respectively, and the maximal folds of induction were 20.8 +/- 1.7- and 6.4 +/- 0.7-fold, respectively. Selective agonists for the A1, A2A, and A3 AdoR subtypes had no effect on cytokine release. The effects of NECA were attenuated by selective antagonists of the A2B AdoR. Thus, Ado increases the release of interleukin-6 and monocyte chemotactic protein-1 from bronchial smooth muscle cells via activation of the A2B AdoR. Our findings provide a novel mechanism whereby Ado acts as a proinflammatory mediator in the airway.

Structure-affinity relationships of 5'-aromatic ethers and 5'-aromatic sulfides as partial A1 adenosine agonists, potential supraventricular anti-arrhythmic agents.

Atrial fibrillation (AF) is the most commonly encountered sustained clinical arrhythmia with an estimated 2.3 million cases in the US (2001). A(1) adenosine receptor agonists can slow the electrical impulse propagation through the atrioventricular (AV) node (i.e., negative dromotropic effect) resulting in prolongation of the stimulus-to-His bundle (S-H) interval to potentially reduce ventricular rate. Compounds that are full agonists of the A(1) adenosine receptor can cause high grade AV block. Therefore, it is envisioned that a compound that is a partial agonist of the A(1) adenosine receptor could avoid this deleterious effect. 5(') Phenyl sulfides (e.g., 17, EC(50)=1.26 microM) and phenyl ethers (e.g., 28, EC(50)=0.2 microM) are partial agonists with respect to their AV nodal effects in guinea pig isolated hearts. Additional affinity, GTPgammaS binding data suggesting partial activity of the A(1) adenosine receptor, and PK results for 5(') modified adenosine derivatives are shown.