Table 1.

Binding affinities of monosubstituted adenosine derivatives (N⁶-substituted) at the human A₃AR expressed in CHO cells and at A₁ and A_2A ARs, and maximal A₃AR agonist effect

Compound	Substitution R1 =	pKi at A1ARa	pKi at A2AARa	pKi at A3ARa	%Activation, A3ARa
6	CH3	7.22b	<5b	8.03	96
7	CH2CH3	8.31b	5.05b	8.34	102
8	OCH3	6.65b	<5b	7.55	107
9		9.15b	5.76b	8.19	100
10		9.35b	6.34b	7.14	97
11		9.05b	6.28b	7.14	76
12		8.48b	6.18b	7.83	102
13		6.76b	6.55b	7.38	55
14		7.35	<5b	8.36	80
15		7.89, 7.89b	7.17, 7.17b	8.68, 6.62b	84
16		6.91	5.60	9.06	101
17		6.98	5.60	8.72	101
18		7.82b	5.52b	9.20	100
19		7.93b	5.60b	7.62	87
20		8.15	6.24	7.04	100
21		7.30	6.29	8.41	0
22		6.31	<5	5.48	87
23		7.85	6.84	9.04	99

^aA₃AR binding experiments were performed with membranes prepared from adherent CHO cells stably transfected with cDNA encoding the human A₃AR, using as radioligand [¹²⁵I]N⁶-(4-amino-3-iodobenzyl)adenosine-5′-N-methyluronamide ([¹²⁵I]I–AB–MECA; 2000 Ci/mmol) at a final concentration of 0.5 nM, in Tris·HCl buffer (50 mM, pH 8.0) containing 10mM MgCl₂, 1mM EDTA. Nonspecific binding was determined using 10 μM Cl–IB–MECA. The mixtures were incubated at 25°C for 60 min. Maximal A₃AR agonist effect is the inhibition of forskolin-stimulated adenylate cyclase at 10 μM using a reference value for Cl–IB–MECA of 100%. (Gao et al. 2003; Tchilibon et al. 2004).

^bIn rat brain (Gao et al. 2003; Tchilibon et al. 2004).