MGd cytotoxicity in chemotherapy-sensitive and highly resistant myeloma cell lines. Cell number as determined by Coulter counting following 24-hour, 48-hour, and 72-hour exposure to 50 μM MGd (▵) in the chemotherapy-sensitive cell line, 8226-RPMI (A), and the highly chemotherapy-resistant line, DOX-10V (B). Varying concentrations of ascorbate (Asc) were added to cell cultures at time 0 (50 μM, ○; 100μM, ×). Mannitol control is indicated by ⋄; ascorbate control, by □. PI was measured by flow cytometric analysis under the same conditions in 8226-RPMI (C) and DOX-10V (D). A dose-response analysis was completed at 48 hours using increasing MGd doses with a constant ascorbate concentration (50 μM) in 8226-RPMI cells (E). Control consisted of mannitol/ascorbate and MGd alone (data not shown). Results showing the mean and the SD were obtained from triplicate measurements at each time point.