Sensitization of EBV lymphoma cells to GCV-mediated killing by brief exposure to HDAC inhibitors. (A) Three hundred thousand P3HR1 cells in a 1-mL volume were treated with 20nM LBH589 for the indicated period of time in the presence or absence of 40μM GCV. The culture medium was completely removed after centrifugation at the end of incubation with LBH589 and replenished with fresh growth medium with or without GCV, as indicated. Media for all cells were replaced again at 72 hours. Cells were counted at 144 hours (day 6). (B) Similar protocol as in panel A, but MS275 was evaluated at 3 different concentrations. The overwhelming toxicity after exposure to MS275 at 5μM for 48 or 72 hours precluded any meaningful cell count. Cells exposed to sodium butyrate at 1mM were used as an internal control. The number above the HDAC + GCV bar represents the percentage of cells surviving relative to the cell count after exposure to the HDAC inhibitor alone (assigned a value of 100%). Experiments were repeated 3 times and error bars represent SDs in individual experiments.