HSB401 is an orally active FLT3 inhibitor with IC50 values of 28, 5, 72, and 51 nM for FLT3-WT, FLT3-D835Y, FLT3-ITD-F691L, and FLT3-ITD, respectively. It downregulates the FLT3 signaling pathway, inducing cell cycle arrest and apoptosis. HSB401 does not inhibit c-KIT, which reduces the risk of bone marrow suppression. In the MV4-11 xenograft mouse model, HSB401 significantly suppresses tumor growth and is applicable for research in acute myeloid leukemia (AML).

HSB401 exhibits a GI50 value of 0.772 μM in K562 cells and 0.027 μM in MV4-11 cells. At concentrations ranging from 20-500 nM over 2 hours, HSB401 inhibits FLT3 and its downstream pathways in MV4-11 cells. Within 24 hours at the same concentration range, it induces apoptosis in MV4-11 cells, activating caspase 7 and 9, and cleaving PARP-1 protein. HSB401 demonstrates nanomolar affinity for the recombinant human FLT3 kinase domain with a dissociation constant (K D) comparable to Gilteritinib. Additionally, HSB401 shows anti-proliferative activity similar to Gilteritinib in both MOLM13 cells and their resistant clones, with a selectivity ratio of 1. It reduces autophosphorylation of FLT3 at the Y589/591 sites in MOLM13 and Ba/F3 (FLT3-ITD) cell lines, and diminishes downstream FLT3 signaling in a concentration-dependent manner when used at 20-500 nM for 2 hours. Furthermore, at 6.25-100 nM for 24 hours, HSB401 specifically inhibits FLT3, inducing a dose-dependent increase in G1 phase cells in FLT3-dependent leukemia cell lines such as MV4-11 and MOLM-13.

HSB401 administered at 30 mg/kg orally once daily for 29 days demonstrated a statistically significant tumor growth inhibition (TGI) of 80.5% in the MV4-11 xenograft mouse model, with no adverse effects on body weight.