Microenvironmental screen identifies FGF2 as a protective molecule for K562 cells in the presence of IM; FGF2 promotes long-term K562 outgrowth and IM resistance. (A) K562 cells were added to a 384-well plate containing cytokines, chemokines, growth factors, and small proteins to screen for factors that would promote growth in the presence of 1 μM IM. Viability was measured using MTS reagent and the results sorted according to viability at 100 ng/mL concentration. The highest 2% of values are indicated in red and lowest 2% in white, with gradients indicating subsequent highest and lowest values, respectively. (B) K562 cells were cultured in 10, 1, and 0.1 ng/mL of recombinant proteins plus 1 μM IM. Viability was assessed after 48 hours with MTS reagent and data plotted as percent of the respective untreated control. All wells were plated in triplicate with standard deviation (stdev) indicated in error bars. The red line represents 2 standard deviations of IM-treated K562 cells (11.8%, n = 9). (C) K562 cells were cultured in 1 μM IM alone and with FGF2, IFN-γ, or G-CSF as indicated. Fresh media, IM, and cytokine were replaced every 2-3 days over the indicated time. Viable cells were analyzed using Guava ViaCount. EGF, epidermal growth factor; GM-CSF, granulocyte macrophage colony-stimulating factor; IGF, insulin-like growth factor; IL, interleukin; Neg, negative control; OSM, oncostatin M.