Cyproheptadine reduces the viability of myeloma and leukemia cell lines and primary patient samples. (A) Multiple myeloma cell lines (1.5 × 10⁴/well) were seeded in 96-well plates and then treated with increasing concentrations of cyproheptadine. Cell viability was measured at 72 hours by MTS assay. Cell viability is expressed as a mean percentage plus or minus SD (n = 3) relative to untreated cells. (B) Leukemia cell lines were treated with increasing concentrations of cyproheptadine. Cell viability was measured at 72 hours by MTS assay. Cell viability is expressed as a mean percentage plus or minus SD (n = 3) relative to untreated cells. (C) OCI-AML2 (AML2) leukemia and (D) LP-1 myeloma cells were treated with increasing concentrations of cyproheptadine. At increasing incubation time, cell viability was measured by MTS assay. Cell viability is expressed as a mean percentage plus or minus SD (n = 3) relative to untreated cells at that time point. (E) Mononuclear cells from the peripheral blood of patients with AML (n = 9), the marrow of patients with myeloma (n = 8), or from the peripheral blood of volunteers donating G-CSF–mobilized hematopoietic stem cells for allotransplantation (N-PBSC; n = 5) were treated with increasing concentrations of cyproheptadine for 48 hours. After treatment, apoptosis was measured by staining with annexin V-FITC. Mononuclear cells from the marrow of patients with multiple myeloma were costained with phycoerythrin-labeled anti-CD138 to identify the plasma cells and the percentage of CD138⁺/annexin V⁻ cells was quantified as a marker of myeloma cell viability. Data represent the mean percentage plus or minus SEM of viable cells relative to untreated control cells. (F) Mononuclear cells from patients with AML (n = 3) or from volunteers donating PBSC (n = 3) were treated with increasing concentrations of cyproheptadine for 24 hours. After treatment, cells were washed, plated in MethoCult, and counted as described in “Cell viability, apoptosis, proliferation, and clonogenic growth assays.” Data represent the mean percentage plus or minus SD of colonies relative to untreated control cells.