The Novel Aurora Kinase Inhibitor AS703569 Shows Potent Anti-Tumor Activity in Acute Myeloid Leukemia (AML).

Aurora kinases have been implicated in the onset of several human cancers. They are overexpressed in different tumor types including colon, breast, and pancreatic cancers, as well as in leukemias. AS703569 (formerly known as R763) is an orally bioavailable inhibitor of all three Aurora kinase isoforms (A, B and C), and is currently in Phase I clinical studies for both solid tumors and hematological malignancies. AS703569 also exhibits potent inhibition of the receptor tyrosine kinase FLT3. FLT3 is postulated to play an important role in the pathogenesis of AML. Somatic mutations and internal tandem duplications in FLT3 resulting in constitutive kinase activation are the most commonly acquired genomic abnormalities found in this disease. The potential therapeutic benefits of AS703569 as a dual Aurora kinase/FLT3 inhibitor is being explored in AML. The anti-proliferative effect of AS703569 has been tested in a panel of AML cell lines harboring different genetic defects. All cell lines were potently inhibited by AS703569 with IC₅₀s between 0.7nM and 1 μM. The MV4-11 cell line possessing the FLT3 ITD was the most sensitive. Examination of cell cycle profiles demonstrated that AS703569 induced a block in the G₂/M phase with a subsequent accumulation of cells in sub G (indicative of apoptosis). Dose-dependent induction of endoreduplication was observed in a subset of the cell lines tested. The pro-apoptotic role for the compound was further supported by the observation that increasing concentrations of AS703569 led to a significant increase in Caspase-3 cleavage and Annexin-V staining. AS703569 treatment led to a dose-dependent inhibition of FLT3 and Histone H3 phosphorylation, suggesting that modulation of both FLT3 and Aurora kinase B are implicated in the observed anti-proliferative, pro-apoptotic activity of AS703569 in these cell lines. To extend our investigation from cell lines to primary patient samples, AML blasts isolated from 15 patients were exposed ex vivo to increasing concentrations of AS703569 or Ara-C. In every case, AS703569 induced a dose-dependent decrease in viability that was more potent than Ara-C. We also tested the anti-tumor activity of AS703569 in two leukemia xenograft mouse models: MV4-11 and HL-60. In the MV4-11 model, tumors were grown to different sizes: 230, 750, and 1100 mm3, and in all three experimental conditions, tumor regression was seen after one dose (75 mg/kg) of AS703569. We found that a weekly dosing schedule is best tolerated by mice and reproducibly shows potent anti-tumor activity. Consistent with our in vitro data, AS703569 was less potent in the HL-60 xenograft model where the FLT3 mutation is absent. In this model, AS703569 only partially inhibited tumor growth (data not shown). Taken together, our data suggest that AS703569 shows particularly promising therapeutic activity in AML, especially cases presenting FLT3 mutations.