FLT3-IN-3 is an effective FLT3 inhibitor, and the IC50s of FLT3 WT and FLT3 D835Y are 13 and 8 nM, respectively.

FLT3 (WT):13 nM, FLT3 (D835Y):8 nM

FLT3-IN-3 inhibits the proliferation of FLT3-ITD positive MV4-11 and MOLM-13 cell lines very effectively at low nanomolar concentrations (GI50 values 2 and 1 nM, respectively). FLT3-IN-3 (1 nM, 10nM, 100 nM, 1 μM and 10 μM; 72 hours) inhibits the Ba/F3 FLT3-ITD cells with the GI50 of 0.034±0.015 μM, and inhibits the parental Ba/F3 cells with the GI50 value of 1.136±0.389 μM. Concentrations as low as 1 nM are sufficient to block the autophosphorylation of the FLT3 receptor tyrosine kinase at three different tyrosine residues (589, 591, and 842). Moreover, this inhibition suppresses phosphorylation of several downstream targets of FLT3. Notably, FLT3-IN-3 (0.01, 0.1, 1, 10 and 100 nM; 1 hours) abolishes phosphorylation of STAT5 at Y694, which is a direct substrate of the oncogenic FLT3-ITD variant. The second pathway affected is the MAPK cascade: Two key components of this signaling pathway, ERK1/2 (T202/Y204) and MEK1/2 (S217/221), exhibit reduced phosphorylation upon treatment with FLT3-IN-3. FLT3-IN-3 also interfers with PI3K/AKT pathway which is confirmed by reduced phosphorylation of AKT at S473.

A single dose of FLT3-IN-3 in mice with subcutaneous MV4-11 xenografts results in sustained inhibition of FLT3 and STAT5 phosphorylation for 48 hours.