KW-2449, a Novel Multi-Kinase Inhibitor Against FLT3, Abl, FGFR1 and Aurora, Suppresses the Growth of AML Both In Vitro and In Vivo.

Constitutive activation of FLT3 kinase is associated with poor prognosis in AML and is present in 30–40% of AML patients. KW-2449 is a multi-kinase inhibitor against FLT3, FGFR1, Abl and Abl-T315, tyrosine kinases with IC₅₀ values of 0.007, 0.036, 0.014 and 0.004 μmol/L, respectively. While it has inhibitory activity against c-Src, JAK2 and c-Kit tyrosine kinases with IC₅₀ values between 0.15–0.40 μmol/L, it has little effect on kinase activity of PDGFR, Fms, IGF1R, and EGFR at a concentration of 1.0 μmol/L. KW-2449 uniquely inhibits Aurora A serine threonine kinase with IC₅₀ of 0.048 μmol/L. Since KW-2449 possesses potent FLT3 as well as Aurora inhibition activity, we studied its possible mode of actions for anti-leukemic effects in both in FLT3 constitutively activated and FLT3 wild type leukemia cell lines. In FLT3-ITD (+) MOLM-13 cells, the exposure of KW-2449 induced a concentration-dependent reduction of phosphorylated FLT3 (P-FLT3) and STAT5 (P-STAT5), a key downstream signal molecules of FLT3. In MOLM-13 cells, KW-2449 also induced G1 arrest and apoptosis over the GI₅₀ value (0.01 - 0.02 μmol/L). In addition, KW-2449 showed potent growth inhibitory activity against 32D cells transfected with FLT3-ITD, FLT3-D835Y or WTFLT3 plus FL, with GI₅₀ values below 0.05 μmol/L. It also inhibited the growth of FLT3 wild type human leukemia RS4;11 cells giving the GI₅₀ value of 0.23 μmol/L. Exposure of RS4;11 cells to KW-2449 also induced the reduction of phosphorylated Histone H3 which is a key downstream signal for Aurora kinase, as well as G2/M arrest and apoptosis over the GI₅₀ value. These data provide additional evidence that Aurora inhibition may play a critical role in the anti-proliferative effects of KW-2449 in FLT3 wild type leukemia. To assess the anti-leukemia activity of KW-2449 in vivo, the SCID mice subcutaneously inoculated with MOLM-13 leukemia were treated with oral KW-2449 bid for 14 days. Dose- dependent tumor growth inhibitory activity was observed at doses ranging from 2.5 to 20 mg/kg. Treatment with 20 mg/kg bid induced complete remission of inoculated tumour in all mice in the cohort without causing significant body weight loss. A PK/PD study using this model revealed significant decreases of P-FLT3 and P-STAT5 in tumors 4 to 8 hours after KW-2449 treatment at 20 mg/kg. In addition, oral administration of 20 mg/kg of KW-2449 showed the survival-prolongation effect in two xenograft models in which the mice were intravenously inoculated with MOLM-13 or 32D/FLT3-D835Y. Furthermore, anti-proliferative activity of KW-2449 was examined in primary samples from AML patients with FLT3 mutation or wildtype. The concentration-dependent growth inhibitory effects that were correlated with P-FLT3 and P-STAT5 reduction were observed in the primary leukemia cells with FLT3 activating mutation. Since KW-2449 shows a potent and unique kinase inhibition profile, it is expected that it could be effective not only in the treatment of AML with FLT3 mutations, but also in FLT3 wild-type AML, imatinib-resistant chronic myeloid leukemia (CML), ALL, and other hematological malignancies. KW-2449 is being investigated in a Phase I, open label, single agent, dose-escalation, multi-center study in patients with relapsed and refractory AML, MDS, CML and ALL.