Quercetin inhibits N-SMase activity and exerts combinatorial anti-AML efficacy with Lip-C6. (a) N-SMase inhibition by quercetin was confirmed by measuring N-SMase activity in AML cell lines (KG-1, 32D-FLT3-ITD) following 4-hour exposure to respective controls, 10 μM liposomal C6-ceramide (Lip-C6), 10 μM quercetin, or the combination of both. Activity (fluorescence) per total protein content was normalized to the untreated controls, and a heat map was generated (pink: high activity, blue low activity). (b) Cellular cysteine sulfenic acid content (oxidation) was determined by ELISA. Following 4-hour exposure of KG-1 and 32D-FLT3-ITD cells to respective controls (white bar: untreated, gray bar: empty/ghost liposomes), 10 μM Lip-C6 (blue bar), 10 μM quercetin (green bar), or the combination of both (purple bar) (1-way ANOVA, *p<0.05 compared with both controls, n=4)). (c) Cellular viability was determined by MTS assay following 48-hour exposure of KG-1 cells to quercetin (green line), Lip-C6 (blue line), or the combination of both (dashed green line). Cyanidin (purple line), or a combination of cyaniding and Lip-C6 (dashed purple line) was used to compare a distinct polyphenol also found in the blueberry. (d) In a similar manner, cellular viability was assessed using the 32D-FLT3-ITD cell line.