Table 1. Competitive Binding Results for Nucleoside Derivatives at Three AR Subtypes^a.

compd	A1AR, % inhibition or Ki (nM)	A2AAR, Ki (nM)	A3AR, Ki (nM)
1	380	70	570
3a	500 ± 72	23.0 ± 6.7	207 ± 47
3b	(30 ± 5%)	4360 ± 760	1810 ± 470
3c	(37 ± 5%)	3280 ± 680	1960 ± 100
5	1890 ± 670	267 ± 66	171 ± 6

^aBinding in membranes of CHO or HEK293 (A_2A only) cells stably expressing one of three hAR subtypes. The binding affinity for hA₁, A_2A, and A₃ARs was expressed as K_i values (mean of 3–4 determinations ± SEM) using agonists [³H]N⁶-R-phenylisopropyladenosine 8 ([³H]R-PIA), [³H]2-[p-(2-carboxyethyl)phenyl-ethylamino]-5′-N-ethylcarboxamidoadenosine 1, or [¹²⁵I]N⁶-(4-amino-3-iodobenzyl)adenosine-5′-N-methyluronamide 9 ([¹²⁵I]I-AB-MECA), respectively. A percent in parentheses refers to inhibition of binding at 10 μM. Competition was performed at a concentration range of 1 nM to 10 μM against the selective radioligand agonist for each subtype. Nonspecific binding was determined using 10 μM 5′-N-ethylcarboxamidoadenosine 10. Values for 1 are from ref (21).