Apoptosis following MGd exposure. Flow cytometry to measure annexin V expression was performed following 24-hour, 48-hour, and 72-hour exposure to MGd in the (A) chemotherapy-sensitive cell line, 8226-RPMI, and the (B) highly chemotherapy-resistant line, DOX-10V; +ve indicates positive. The asterisk indicates that analysis not performed because all cells were dead at this time point. Results showing means and SD are the average of triplicate measurements at each time point. In panel C, annexin V studies were done on fresh patient myeloma cells with plasma cells defined as cells that express high levels of CD38 and no or low levels of CD45 (see “Materials and methods”). Cells were treated for 48 hours with 50μM MGd and 100 μM ascorbate (right) and ascorbate 100 μM control (left). Events in the upper right quadrant represent CD38+ cells that are annexin V+ as measured by flow cytometric analysis. Data presented are representative of independent experiments from 3 untreated multiple myeloma patients.