CXCR4 pepducins enhance rituximab-mediated cytotoxicity in lymphoma cells. (A) Raji cells were treated overnight with vehicle (0.3% DMSO), PZ-218 (10μM), or PZ-210 (10μM) in the absence or presence of rituximab (10 μg/mL). Samples were dual stained with annexin V–FITC and PI and evaluated for apoptotic/dead cells by flow cytometry. The x-axis depicts annexin V and y-axis depicts PI. Experiments were repeated 3 times with similar results. Representative dot plots are shown. (B) Raji cells were treated with the indicated concentrations of pepducins and plerixafor (AMD) for 24 hours in the presence (+) or absence (−) of rituximab (10 μg/mL). The percentage of apoptotic/dead cells was determined by annexin V/PI staining and flow cytometry. Data represent means of the sum of annexin V⁺/PI⁺/annexin V⁺PI⁺ cells ± 1 seconds (n = 3), with assays done in duplicate. *P < .05 and ** P < .01 compared with rituximab-treated samples. (C) CXCR4 pepducins inhibit stromal-mediated protective effect of rituximab and enhance rituximab-induced apoptosis. Raji cells were cocultured with or without M2-10B4 stromal cells and treated with 10μM concentrations of pepducins or vehicle control in the presence (+) or absence (−) of rituximab. Samples were dual stained with annexin V–FITC and PI and evaluated for apoptotic/dead cells by flow cytometry.