Effects of IGFs, insulin, and IL-6 on growth inhibition induced by PPP. (A) Karpas 707 and (B) RPMI 8226 cells were treated for 48 hours with PPP alone (□) or in the presence of IGF-1 (•), IGF-2 (○), LongR3-IGF-1 (▴), or insulin (▵). In control cultures (C) Karpas 707 and (D) RPMI 8226, cells were treated for 72 hours with the indicated ligands alone (□) or with the addition of 1 μM dexamethasone (▪). Each ligand was added at the concentration 100 nM and always 1 hour before treatment with PPP/dexamethasone was initiated. The 4 IL-6–dependent/responsive MM cell lines (E) U-1957, (F) U-1958, (G) U-1996, and (H) U-266-1970 were treated for 48 hours with PPP alone (□) or in the presence of IL-6 at 10 ng/mL (○) or 100 ng/mL (•). IL-6 was added 1 hour before treatment with PPP, at indicated concentrations, was initiated. (I) As a control experiment the IL-6–dependent U-1958 cell line was treated with increasing concentrations of IL-6. Three independent experiments were performed in triplicate and 1 representative is shown. Data are presented as means ± SD. Error bars not visible are included within the symbols.