TPO receptor-dependent cell proliferation and STAT5 phosphorylation. (A) UT-7/TPO and (B) UT-7/EPO cells were cultured for 4 days with various doses of rhTPO, TA-316, eltrombopag, or rhEPO, and the number of cells were counted using the WST-8 assay. (C) Ba/F3 cells, Ba/F3 cells with human c-MPL (Ba/F3-HuMpl), and Ba/F3 cells with murine c-MPL (Ba/F3-MuMpl) were similarly cultured and counted after 4 days with rmIL-3 (1 ng/mL), rhTPO (100 ng/mL), TA-316 (1 ng/mL), or eltrombopag (ChemScene; 100 ng/mL). (D) Ba/F3-HuMpl cells were similarly cultured and counted after 4 days with various doses of rhTPO, TA-316, or eltrombopag (ChemScene). (E) STAT5 phosphorylation in UT-7/TPO cells stimulated for 15 to 360 minutes with rhTPO (100 ng/mL), TA-316 (100 ng/mL), eltrombopag (ChemScene; 1000 ng/mL), or DMSO (vehicle) were evaluated using BD Phosflow (STAT5, pY694). △MFI values of pSTAT5 are shown as relative values to that of vehicle treatment. Data represent the mean and SD; *P < .05, †P < .05. MFI, mean fluorescence intensity; min, minutes; O.D., optical density; pSTAT5, phosphorylated STAT5.