Table 2.

Activity of PSI-352666 against genotype 1b, 2a, 3a, and 4a recombinant NS5BΔ21 polymerases and human RNA polymerase II and DNA polymerases α, β, and γ

Enzyme-based assay and genotype or enzyme	IC50 (μM)
	PSI-352666a	Positive controlb
HCV NS5B
1b	1.0 ± 0.2	0.1 ± 0.04
2a	4.7 ± 0.6	0.1 ± 0.02
3a	1.3 ± 0.5	0.03 ± 0.004
4a	4.2 ± 0.8	2.9 ± 0.6
Human polymerase
DNA Pol α	900 ± 140	16 ± 2
DNA Pol β	>1,000	9.0 ± 0.4
DNA Pol γ	>1,000	79 ± 4
RNA Pol II	>500	<1

^aHCV NS5B polymerase activity in the presence of PSI-352666 was determined by measuring the incorporation of [α-³²P]UTP into the RNA product using an HCV IRES template. The amount of product was quantified by phosphorimaging. Human DNA polymerase α, β, and γ activities were quantified by measuring the synthesized radiolabeled products with a filter binding assay. Human RNA polymerase II synthesized RNA products from in vitro transcription using HeLa nuclear extract were analyzed using a 6% polyacrylamide sequencing gel and phosphorimaging. Results were obtained from at least two independent experiments in duplicate and are reported as means ± standard deviations.

^bThe positive control for HCV NS5B was 3′-dCTP, that for DNA Pol α was aphidicolin, that for DNA Pols β and γ was d-ddFCTP, and that for RNA Pol II was α-amanitin.