The PD169540 ErbB inhibitor potentiates dexamethasone and anti–IL-6–induced apoptosis of primary myeloma cells. Mononuclear cells from 8 patients with MM were cultured at 5 × 105 cells/mL in RPMI 1640 medium and 5% FCS with either the PD169540 ErbB inhibitor (1 μM) or anti–IL-6 MoAb (B-E8; 10 μg/mL) or dexamethasone (DEX, 10–6 M), alone or in combination, for 5 days. As endogenous production of IL-6 is highly variable in short-term culture of patients' bone marrow, 1 ng/mL recombinant IL-6 was added to eliminate this source of variability. In each culture group, viability and cell counts were assayed and myeloma cells were stained with an anti-CD138–PE antibody. Results are median values of the numbers of myeloma (A) or nonmyeloma cells (B), compared with that of the control group, which assigned the value of 100%. Only the 6 responder patients listed in Table 1 are represented there. *Indicates a statistically significant difference of the median value compared with that of the control group using a Wilcoxon test for pairs (P ≤ .05). **Indicates a statistically significant difference of the median value compared with that obtained with the anti–IL-6 MoAb or the DEX groups using a Wilcoxon test for pairs (P ≤ .05).
