TABLE 2.

IC₅₀ values in HeLa cells cultured for 96–120 h with 50 µM deoxyuridine or 50 µM uridine¹

	IC50 relative to control (no nucleosides)
Treatment	50 µM uridine	50 µM deoxyuridine	P (comparison between nucleotide treatments)
5-Fluorouracil	1.30 ± 0.18	0.77 ± 0.20	P < 0.01
Methotrexate	1.16 ± 0.12	0.85 ± 0.26	P = 0.03

¹Values are means ± SDs of the normalized ratio of 4 independent experiments. IC₅₀ curves were generated by using 0.1–1000 µM 5-fluorouracil and 0.001–0.5 µM methotrexate; viability was measured by using the MTT assay. IC₅₀ values for each treatment were normalized to IC₅₀ of control (no nucleoside supplementation). IC₅₀, concentration of an inhibitor where the response is reduced by half; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.