TABLE 1

K_i and Gibbs free energy values for inhibition of hCNT2-mediated Urd uptake in S. cerevisiae by Urd analogs

The uptake of 1 μM [³H]Urd into yeast (fui1::HIS3) expressing pYPhCNT2 was measured over 20 min in the presence of graded concentrations of nonradioactive Urd or Urd analogs. IC₅₀ values (mean ± S.E., n = 3-4) were determined using Prism version 3.0 software (GraphPad Software Inc., San Diego, CA) and were converted to K_i values (Cheng and Prusoff, 1973) using K_m values (mean ± S.E., n = 3) of 29 ± 7 μM for recombinant hCNT2. ΔG⁰ was calculated from ΔG⁰ = −RTln(K_i).

Urd Compounds	IC₅₀	K_i	ΔG⁰	δ(ΔG⁰)
	μM
Urd	29 ± 3	28 ± 3	23.8	0
Base modification
FUrd	63 ± 13	61 ± 13	22.1	1.7
IUrd	371 ± 51	358 ± 50	18.1	5.7
BrUrd	238 ± 4	230 ± 4	19.1	4.7
MeUrd	165 ± 0.3	160 ± 1	19.9	3.9
3MeUrd	581 ± 151	562 ± 146	17.1	6.7
Sugar modification
2′-dUrd	76 ± 8	73 ± 8	21.7	2.1
5′-dUrd	>3000^a	>3000^a	<13.3	>10.5
3′-dUrd	>3000^b	>3000^b
araU	>3000^a	>3000^a
xyloU	>3000^a	>3000^a
2′,5′-ddUrd	>3000^a	>3000^a
3′,5′-ddUrd	>3000^a	>3000^a
2′,3′-ddUrd	>3000^b	>3000^b
2′-OMeUrd	>1000^a	>1000^a	<15.8	>8.0
5′-OMeUrd	>3000^a	>3000^a
3′-OMeUrd	>3000^a	>3000^a
2′-AzdUrd	>3000^b	>3000^b
3′-AzdUrd	>3000^a	>3000^a
5′-AzdUrd	>3000^a	>3000^a
5′-CldUrd	>1000^a	>1000^a
iPUrd	>3000^a	>3000^a
Base and sugar modifications
FdUrd	156 ± 7	151 ± 7	20.0	3.8
BrdUrd	272 ± 75	263 ± 72	18.8	5.0
IdUrd	303 ± 20	293 ± 11	18.5	5.3
EtdUrd	353 ± 40	341 ± 39	18.2	5.6
5-Fluoro-5′-deoxyuridine	>3000^b	>3000^b
Thd	586 ± 20	566 ± 20	17.0	6.8
AZT	>3000^b	>3000^b

↵ a No obvious inhibition was observed.
↵ b Inhibition of <50% was observed.