Gene set enrichment analysis (GSEA) revealed that, of the 2414 curated gene sets from the Molecular Signatures Database tested (version 6.2) (10), those reflecting the response of HL-60 promyelocytic leukemia cells to the aminopeptidase inhibitor tosedostat (11), and arterial endothelial cells to hypoxia (12), were the most significantly enriched among both up- and downregulated genes in daunorubicin-resistant versus sensitive K562 cells (Figure 2D and Supplemental Figure 1A). This evidence concerns the gene CPQ and acute promyelocytic leukemia.