Figure 1. Chemical screen for compounds targeting leukemic cells identifies antimicrobial tigecycline.

(A) Drugs were added to TEX and ENL-1 cells (3 experiments each). Viability of cells after 72 hrs was determined by MTS staining and the results expressed as a percent of matching DMSO-treated controls (B) TEX, human and murine leukemia cells were incubated in triplicate experiments with drugs at concentrations shown for 72 hrs and viability was determined by MTS (human cells) or ViaCount (murine cells) staining and results expressed as a percent of results for untreated cells. (C) TEX cells were exposed to 5 or 10 μM of tigecycline (TIG) and Annexin V staining by flow cytometry was used to discriminate viable cells. Data represent the mean of Annexin V positive cells from a representative experiment (n=3). (D) Primary AML (1° AML) (n=20) and normal hematopoietic cells (n=5) were treated with increasing concentrations of tigecycline for 48 hrs. The proportion of viable cells was measured by Annexin-PI flow cytometry to calculate the yield of viable cells shown as a percent viable DMSO-treated cells in the same experiment. (E) Primary AML (n=7) and normal hematopoietic cells (n=5) were treated with 5 μM tigecycline and plated in clonogenic growth assays. Values shown are the percent of colonies obtained compared to DMSO-treated cells. (F) Cells from an AML patient and Lin⁻ CD34⁺ enriched human cord blood cells were treated with 5 μM tigecycline or DMSO for 48 hrs in vitro and then injected into femurs of irradiated NOD/SCID mice preconditioned with anti-CD122. Six weeks later, the percent of human CD45⁺CD33⁺CD19⁻ cells in femurs was measured by FACS. ***P < 0.0001, N.S. not significant P > 0.05 as determined by the unpaired student’s t test. Error bars represent mean +/− S.D. See also Table S1 and Figure S1.