Effect of Notch-1 activation on resistance to drug-induced apoptosis. Notch-1 activation in myeloma cells increased resistance to drug-induced apoptosis. Myeloma H929 (A-B), HS-Sultan (C), or U266 (D) cells were incubated on the monolayer of 3T3-Jagged or control fibroblasts for 24 hours. H929 cells (E) were treated with 50 μM Jagged-1 or scrambled peptide for 24 hours followed by drug or vehicle control exposure for another 24 hours. Myeloma cells were then collected, and apoptosis was measured by flow cytometry with the use of the TUNEL assay (A-B) or annexin V-binding assay (C-E). Similar results were obtained for H929 cells with the use of the annexin V-binding assay. All experiments were repeated 4 times with similar results. ^*Statistically significant differences from cells cultured on 3T3-Jagged stroma or with Jagged-1 peptide, P < .05. In panel F, H929 cells were treated with 50 μM Jagged-1 (○) or scrambled peptide (•) for 24, 48, or 72 hours, and the cell number was calculated in triplicates. Error bars indicate standard deviation.