TABLE 1.

Effect of natural pyrimidine and purine derivatives on the cytostatic activity of 3F-3DUrd and other antimetabolite drugs in CEM cell culture

Addition of natural DNA/RNA precursors	IC50a
	3F-3DUrd	3-DUrd	Pyrazofurin	6-Aza-Urd	K-oxonate	A77 1726
	μm
As such	19 ± 8.6	7.4 ± 3.1	0.24 ± 0.09	0.63 ± 0.28	204 ± 43	47 ± 41
+ Urd 500 μm	>250	>250	>250	>250	>250	>250
+ Urd 100 μm	>250	>250	>250	>250	>250	>250
+ Cyd 500 μm	>250	>250	123 ± 121	>250	>250	>250
+ Cyd 100 μm	>250	>250	99 ± 85	>250	>250	>250
+ Orotic acid 500 μm	13 ± 8.5	≥27	0.24 ± 0.15	0.62 ± 0.30	>250	>250
+ Orotic acid 100 μm	10 ± 8.6	12 ± 5.8	0.26 ± 0.17	0.53 ± 0.25	≥250	153
+ Orotidine 100 μm	6.8 ± 2.7	17 ± 10.3	0.079 ± 0.01	0.37 ± 0.17	149 ± 47	132
+ dThd 10 μm	11 ± 1.4	9 ± 4.0	0.20 ± 0.01	0.69 ± 0.06	82 ± 9.9	32 ± 6.1
+ dThd 5 μm	19 ± 8.6	9.6 ± 0.64	0.18 ± 0.11	0.75 ± 0.17	121 ± 82	61 ± 45
+ Hpx 100 μm	0.79 ± 0.44	3.55 ± 0.29	0.013 ± 0.007	0.045 ± 0.002	13 ± 2.3	114
+ Hpx 20 μm	2.2 ± 0.50	4.31 ± 0.88	0.12 ± 0.009	0.15 ± 0.01	105 ± 80	110
+ Gua 100 μm	4.9 ± 2.8	0.89 ± 0.16	0.17 ± 0.07	0.15 ± 0.07	42 ± 6.0	>50
+ Gua 20 μm	9.3 ± 0.47	10 ± 2.4	0.25 ± 0.13	0.54 ± 0.13	≥250	106
+ Ado 500 μm	0.31 ± 0.13	2.0 ± 1.5	0.026 ± 0.015	0.031 ± 0.008	12 ± 2.1	18 ± 13
+ Ado 100 μm	0.87 ± 0.02	2.9 ± 0.69	0.082 ± 0.014	0.089 ± 0.012	76 ± 16	62 ± 48
+ Ade 500 μm	0.25 ± 0.18	2.3 ± 1.9	0.011 ± 0	0.013 ± 0	6.2 ± 1.1	31 13
+ Ade 100 μm	0.53 ± 0.33	4.0 ± 0.95	0.020 ± 0.005	0.031 ± 0.003	19 ± 13	31 ± 10
+ Ade 20 μm	3.2 ± 2.9	4.2 ± 2.4	0.14 ± 0.07	0.22 ± 0.09	150 ± 141	22.4
+ Guo 20 μm	16 ± 11	3.3 ± 3.1	0.29 ± 0.01	0.32 ± 0.22	≥208	117
+ Ino 100 μm	1.3 ± 0.19	3.3 ± 0.0	0.031 ± 0.005	0.054 ± 0.021	29 ± 11	105
+ Ino 20 μm	3.5 ± 0.47	3.3 ± 0.05	0.11 ± 0	0.22 ± 0.007	110 ± 9.9	126 ± 9.9

^a 50% Inhibitory concentration or compound concentration required to inhibit CEM cell proliferation by 50%.