Effect of SU5416, SU5614, and GM-CSF on constitutive MAPK activation in cells expressing FLT3 ITD.

SU5416 and SU5614 inhibit constitutive MAPK activation in cells expressing FLT3 ITD; GM-CSF restores signaling. MV 4-11 (FLT3 ITD) cells were incubated with varying concentrations of inhibitor and stimulated with ligand. (A) MAPK was constitutively phosphorylated in these cells, and activation was not augmented by treatment with FL. This constitutive activation was inhibited by both SU5416 and SU5614 with an IC₅₀ of 100 nM and 10 nM, respectively. Despite the presence of activating RAS mutations in MV 4-11 (FLT3 ITD) cells, MAPK activation appeared to be dependent upon FLT3 activation. (B) Ligand-independent MAPK activation was completely inhibited by 1 μM concentrations of either SU5416 or SU5614. Treatment with FL did not induce additional MAPK phosphorylation. Stimulation with GM-CSF restored MAPK activation in cells pretreated with SU5416 or SU5614. Total MAPK protein was unaffected by treatment.