KW-3902, a selective high affinity antagonist for adenosine A1 receptors

Abstract

1. We demonstrate that 8-(noradamantan-3-yl)-1,3-dipropylxanthine (KW-3902) is a very potent and selective adenosine A1 receptor antagonist, assessed by radioligand binding and cyclic AMP response in cells. 2. In rat forebrain adenosine A1 receptors labelled with [3H]-cyclohexyladenosine (CHA), KW-3902 had a K(i) value of 0.19 nM, whereas it showed a K(i) value of 170 nM in rat striatal A(2A) receptors labelled with [3H]-2-[p-(2-carboxyethyl)-phenethylamino]-5'N-ethylcarboxamidoadenosine (CGS21680), indicating 890 fold A1 receptor selectivity versus the A(2A) receptor. KW-3902 at 10 μM showed no effect on recombinant rat A3 receptors expressed on CHO cells. 3. Saturation studies with [3H]-KW-3902 revealed that it bound with high affinity (K(d) = 77 pM) and limited capacity (B(max) = 470 fmol mg-1 of protein) to a single class of recognition sites. A high positive correlation was observed between the pharmacological profile of adenosine ligands inhibiting the binding of [3H]-KW-3902 and that of [3H]-CHA. 4. KW-3902 showed potent A1 antagonism against the inhibition of forskolin-induced cyclic AMP accumulation in DDT1 MF-2 cells by the A1-selective agonist, cyclopentyladenosine with a dissociation constant (K(B) value) of 0.34 nM. KW-3902 antagonized 5'-N-ethylcarboxamidoadenosine-elicited cyclic AMP accumulation via A(2B) receptors with a K(B) value of 52 nM. 5. KW-3902 exhibited marked species-dependent differences in the binding affinities. The highest affinity was for the rat A1 receptor (K(i) = 0.19 nM) and these values for guinea-pig and dog A1 receptors were 1.3 and 10 nM, respectively.