IL-6 fails to protect dexamethasone-sensitive and -resistant MM cells from the lethal actions of UCN-01/PD184352.

Logarithmically growing dexamethasone-sensitive (MM.1S; Figure 9A) and -resistant MM cells (MM.1R; Figure 9B) were exposed to 10 μM PD184352 + 150 nM UCN-01 or 10 μM dexamethasone in the presence or absence of 100 ng/mL IL-6 for 24 to 72 hours, after which the percentage of apoptotic cells was determined by examining Wright-Giemsa–stained cytospin preparations. Alternatively, MM.1S and MM.1R cells were treated as above for 24 or 48 hours, after which the percentage of cells displaying a reduction in ΔΨm was determined (panel C) as described in “Materials and methods.” For panels A and B: ■ indicates Control; ▪, PD + UCN; ░, PD + U + IL-6; ▨, Dex; ▩, Dex + IL-6. For panel C: ■ indicates Control; ░, PD184352; ▧, UCN-01; ▪, PD + UCN; ▤, PD + UCN + IL-6. For all panels, values represent the means ± SD for 3 separate experiments performed in triplicate.