Effects of HMA on sorafenib-resistant cell line M13-RE. (A) Sorafenib (10 nM) and HMA (10 μM) inhibited leukemia growth and (B) induced apoptosis of M13 (fold change normalized to vehicle control) with combined sorafenib and HMA treatment resulting in more pronounced inhibition. Note that HMA but not sorafenib inhibited leukemia growth and induced apoptosis in M13-RE. (C) In M13, HMA modestly inhibited FLT3 signaling and potentiated sorafenib-induced inhibition of downstream signaling. (D) M13-RE was resistant to sorafenib but sensitive to the combination of HMA and sorafenib. Densitometric analysis of the bands was performed by ImageJ. The ratios of phosphorylated to total proteins are shown at the top of each lane. (E) Effects of HMA (10 μM) and sorafenib (10 nM) on FLT3 signaling (i, p-STAT; ii, p-AKT; iii, p-ERK [extracellular signal-regulated kinase]) evaluated quantitatively by phosphoflow. Sorafenib induced significantly stronger inhibition in M13 than M13-RE. Combination of sorafenib with HMA resulted in significant inhibition of FLT3 signaling in both M13 and M13-RE.