The PD169540 ErbB inhibitor has no effect on the growth of the hematopoietic progenitors or on the adhesion of MM cells to stromal cells. (A) Bone marrow mononuclear cells from 5 patients with MM were grown in a semisolid culture medium with hematopoietic cytokines for 14 days. Cells were treated with either the PD169540 pan-ErbB inhibitor (1μM) or anti–IL-6 MoAb (B-E8; 10 μg/mL) or 10^–6 M dexamethasone (DEX), alone or in combination. The number of granulocyte-macrophage colonies was counted on day 14 of incubation. Data are means ± SD of the number of colonies determined on 2 different culture plates for each condition. (B) XG-11 cells were cultured with either BMSC-coated (▪) or noncoated culture plates (□), without or with 1μM PD169540 for 24 hours. Nonadherent cells were counted and adherent cells were trypsinized and counted. In the 2 cell populations, GFP⁺ stromal cells were quantified with FACS analysis. Results are expressed as percentage of bound plasma cells ± SDs. The percentage was calculated as follows: percentage bound cells = ([input cells] – [nonadherent cells]/[input cells]) × 100. Results are of one experiment representative of 3.