Table 1.

In vitro pharmacological data for UTP (1) and its analogues in the stimulation of PLC at recombinant human P2Y₂ and P2Y₄ receptors expressed in astrocytoma cells

Compound	Modification	Structure	EC50 at hP2Y2 receptor (µM)a	Relative to UTP	EC50 at hP2Y4 receptor (µM)a	Relative to UTP
Native ribonucleoside-5′-triphosphates
1 UTP			0.049 ± 0.012	1	0.073 ± 0.02	1
2 ATP			0.085 ± 0.012	1.7	Antagonistb
3a CTP			5.63 ± 0.30	110	Antagonistb
3b GTP			2.64 ± 0.30	54	6.59b	90
Ribose-modified UTP analogues
4	2′-Deoxy	RII = H	1.08 ± 0.28	22	1.9 ± 0.5	26
5	2′-Deoxy-2′-methoxy	RII = OCH3	14.3 ± 7.7	290	8.2 ± 2.1	110
6	3′-Deoxy-3′-methoxy	RIII = OCH3	NE	>1000	NE	>1000
7	2′-Amino-2′-deoxy	RII = NH2	0.062 ± 0.008	1.3	1.2 ± 0.3	16
8	2′-Azido-2′-deoxy	RII = N3	5.0 ± 2.1	100	1.1 ± 0.1	15
9	2′-Deoxy-2′-fluoro	RII = F	0.78 ± 0.11	16	0.54 ± 0.14	7.4
10	Arabino	RII = H, RARA = OH	0.087 ± 0.010	1.8	0.71 ± 0.08	9.7
11	2′-Deoxy-arabino-2′-fluoro-	RII = H, RARA = F	0.52 ± 0.15	11	0.52 ± 0.08	7.1
Uracil-modified UTP analogues
12	5-Bromo	R5 = Br	0.75 ± 0.1	15	2.1 ± 0.7	29
13	5-Iodo	R5 = I	0.83 ± 0.1	17	4.0 ± 1.7	55
14	5-Methyl	R5 = CH3	0.48 ± 0.1	9.8	3.9 ± 1.6	53
15	2-Thio	R2 = S	0.035 ± 0.004	0.71	0.35 ± 0.01	4.8
16	4-Thio	R4 = S	0.026 ± 0.01	0.53	0.023 ± 0.005	0.32
17	6-Aza	X = N	8.6 ± 3.7	180	NE	>1000
18	3-Methyl	R3 = CH3	1.20 ± 0.20	24	3.4 ± 0.8	47
19	Zebularine analogue	R4 = H, H	8.9 ± 0.5	180	NE	>1000
20	Pseudouridine	c	0.78 ± 0.5	16	3.0 ± 0.3	41
Phosphate-modified UTP analogues
21	Rp-α-thio	RR = S	5.4 ± 1.5	110	27 ± 5	370
22	Sp-α-thio	RS = S	14 ± 5.5	290	81 ± 8	1100
23	2′-Deoxy-Rp-α-thio-triphosphate	RR = S, RII = H	12.5 ± 6.7	260	NE	>1000
24	2′-Deoxy-Sp-α-thio triphosphate	RS = S RII = H	NE	>1000	NE	>1000

NE: no effect at 10 µM.

^aAgonist potencies were calculated using a four-parameter logistic equation and the GraphPad software package (GraphPad, San Diego, CA). EC₅₀ values (mean ± S.E.) represent the concentration at which 50% of the maximal effect is achieved. EC₅₀ is also expressed relative to the value for UTP at each receptor. Relative efficacies (%) were determined by comparison with the effect produced by a maximal effective concentration of reference agonist (UTP) in the same experiment. For all of the nucleotides, except 22 and 23, for which an EC₅₀ is reported in this table, ~100% efficacy was achieved.

^bATP antagonized the human P2Y₄ receptor with a K_B of 0.708 µM. CTP (100 µM) inhibited the response to an EC₅₀ concentration of UTP by ~40% [11].

^cCompound 20 has the following structure: