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 IC 50 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 IC 50 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 IC 50 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 GI 50 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 GI 50 values below 0.05 μmol/L. It also inhibited the growth of FLT3 wild type human leukemia RS4;11 cells giving the GI 50 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 GI 50 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.