LCL/LBH is active against primary CD138⁺ MM cells and reduces the primitive progenitor cell–enriched CD138⁻/CD19⁺/CD20⁺/CD27⁺ population while sparing normal CD34⁺ cells. (A) Representative primary bone marrow cells from a patient with MM (relapse and refractory [RR]; prior bortezomib) were exposed to LBH (5 nM) ± LCL (5 µM) for 24 hours, after which the cells were stained with CD138-PE and Annexin V (Ann V)-FITC. Images were obtained with an IX71-Olympus inverted system microscope at 20× magnification. Flow cytometric analysis was performed to determine the CD138⁺ population. (B) After exposure to LBH (5 nM) ± LCL (5 µM) for 24 hours, the percentage of primitive CD138^–/CD19⁺/CD20⁺/CD27⁺ cells in bone marrow mononuclear cells from a primary MM sample was determined by multi-color flow cytometry. The percentage of viable cells shown in red boxes (as Annexin V^–/7-AAD^–) is displayed after normalization of viable cells in untreated samples to 100%. The viability of the treated samples was calculated related to values for the untreated sample. (C) Flow cytometry comparison of effects of LCL161/LBH589 on primary CD138⁺ MM cells (left) and cord blood (CB) CD34⁺ cells (right). (D) Parallel experiments were conducted with 31 primary samples. Viability of CD138⁺ cells was analyzed by using multi-color flow cytometry determination of Annexin V-FITC. Lines indicate means and standard deviations (P < .001 or P < .0013). (E) After exposure to LBH (5-10 nM) ± LCL (5 µM) for 24 hours, apoptosis of CD138^–/CD19⁺/CD20⁺/CD27⁺ cells (n = 23) was analyzed by Annexin V-FITC staining and quantitated by using multi-color flow cytometry (P < .0001 or P < .0078). (F) Parallel experiments were conducted with 6 primary CB CD34⁺ samples (n = 6; P = .0661 or P = .2290). FSC, forward scatter; SSC, side scatter.