Figure 2.

Loss of inhibition with 8-Cl-ADO with prolonged incubation time: intracellular drug metabolism. A, 8-Cl-ADO (5 and 20 μm) was preincubated (minus cells) for 0–7 d at 37 C before its addition to cells for an additional 4 d; B, cells in 24-well culture plates were incubated with 8-Cl-ADO (20 μm) and [³H]thymidine (2 μCi per well) for 4 and 5 d. In some cultures, 8-Cl-ADO was replenished on d 4 and cultures assayed on d 5. Levels of intranuclear counts per minute (CPM) were determined by scintillation count, and values expressed as percent of control counts per minute. In A, Cell Titer 96 AQ solution was added 3.5 h before plates were read using an ELISA plate reader. Results are expressed as percentage of control absorbance. Points are mean ± sd of two experiments (A) and mean ± sem of three experiments (B); *, P = 0.032 (A); **, P < 0.0001 (B).