Primary CD138⁺ MM cells display selective sensitivity to UCN-01/UO126–induced apoptosis.

CD138⁺ and CD138⁻ cells were isolated from the bone marrow of MM patients as described in “Materials and methods.” The cells were exposed individually or in combination to drugs as follows: UO126 (A: 25 μM; B and C: 20 μM); UCN-01 (A: 150 nM; B: 250 nM; C: 100 nM). After 24 hours' treatment, the extent of apoptosis was determined by evaluating Wright-Giemsa–stained cytospin preparations as described previously. Values represent the means ± SD for more than 20 randomly selected fields encompassing more than 300 cells. Representative microphotographs of cells obtained from patient #2 are shown in D, a: early apoptotic cells; b: late apoptotic cells; c: postapoptotic (ghost) cells.