KW-2449, a Novel Multi-Kinase Inhibitor, Suppresses the Growth of Imatinib-Resistant Ph+ Leukemia Including BCR-ABL/T315I Both in Vitro and in Vivo.

Background: KW-2449 is a multi-kinase inhibitor against FLT3, ABL and ABL/T315I and Aurora kinases with IC₅₀ values of 0.007, 0.014, 0.004 and 0.048 micro mol/L, respectively. We reported a possible mode of action of KW-2449 with respect to its anti-leukemic effects on FLT3-mutated and FLT3-wild type leukemia cells via FLT3 and Aurora inhibition, respectively (1). Currently KW-2449 is being investigated in a Phase 1/2 study in patients with acute myeloid leukemia. In this report, we investigated the activity of KW-2449 or imatinib in imatinib-resistant leukemia with the T315I mutation.

Methods and results: We evaluated the effects of KW-2449 in vitro and in vivo on imatinib-resistant Ph+ leukemia. While imatinib suppressed the growth of K562 (Ph+CML with wild-type BCR-ABL) and TCC-Y (Ph+ALL with wild-type BCR-ABL) with GI50 values of 0.20 and 0.18 micro mol/L, it had little inhibitory effects on TCC-Y/sr (Ph+ALL with BCR-ABL/T315I) with a GI₅₀ value of 24 micro mol/L. On the other hand, KW-2449 showed equivalent growth inhibitory activities against K562, TCC-Y and TCC-Y/sr giving the GI₅₀ values of 0.2–0.6 micro mol/L. In addition, KW-2449 showed potent growth inhibitory activity against IL-3 dependent cells transfected with BCR-ABL and BCR-ABL/T315I with GI₅₀ values below 0.50 micro mol/L, whereas imatinib had no growth inhibition in BCR-ABL/T315I cells. When we examined the ABL-signaling pathway, imatinib had no effects on the expression of phosphorylated BCR-ABL (P-BCR-ABL) and STAT5 (P-STAT5), a key downstream signal molecules of BCR-ABL in TCC-Y/sr cells. Furthermore, no obvious apoptosis or cell cycle effects were observed in BCR-ABL/T315I cells after imatinib treatment. In addition, the exposure to KW-2449 induced reduction of P-BCR-ABL and P-STAT5 at 0.25 micro mol/L and induced G2/M arrest and apoptosis over the GI₅₀ value (0.50–1.0 micro mol/L). These data provide the evidence that BCR-ABL inhibition at a lower concentration of KW-2449 modulates its signaling pathway and that Aurora inhibition at a higher concentration may play a critical role in the anti-proliferative effects in imatinib-resistant CML and Ph+ALL. To assess the anti-leukemia activity of KW-2449 in vivo, the SCID mice intravenously inoculated with TCC-Y/sr leukemia were orally treated with KW-2449 or imatinib. While KW-2449 prolonged the survival, imatinib treatment had no effects in this model. Furthermore, anti-proliferative activity of KW-2449 was examined in primary samples from blast crisis CML patients who had BCR-ABL/T315I mutation. After inoculation of blast cells into NOG mice, KW-2449 or imatinib treatment started. In this model, oral treatments with KW-2449 decreased peripheral copy number of BCR-ABL mRNA and CD45+ blast cells in the bone marrow, though imatinib treatment showed limited activity.

Conclusion: KW-2449 demonstrated anti-leukemia activity against imatinib resistant leukemia both in vitro and in vivo. These results suggest that KW-2449 would be effective against imatinib-resistant CML or Ph+ALL because of its potent and unique kinase inhibition profile.