Figure 2.

5-Fluorouracil (5-FU) derived from 5-fluorocytosine (5-FC) was cytotoxic in vitro. The “bystander effect” of the cytosine deaminase (CD) produced by the F3.CD cells was confirmed using a coculture system. MDA-MB-435, PC14PE6, or K1735 cells and F3 or F3.CD cells were seeded in 96-well plates (total 5 × 10³ cells per well, tumor cell:F3 or F3.CD cell = 100:0, 75:25, 50:50, 25:75, or 0:100). After 24 hours in coculture, cells were treated with 0.5 mmol/l 5-FC for 72 hours and cell viability determined (each group, n = 3). Survival (%) = percentage of the control viability (tumor cell only, = 100%). Columns = mean, bars = SD, ^*P < 0.05.