APcK 110, a novel Inhibitor of Kit, Extends Survival of NOD-SCID Mice in An AML Xenograft Model.

Abstract 1045

Poster Board I-67

Kit is a type III receptor protein tyrosine kinase and membrane receptor for stem cell factor (SCF). Tight regulation of the activity of kit is a crucial component of normal hematopoiesis. Mutations of the KIT gene have been identified in blasts of patients with AML predominantly those with core-binding factor leukemias. As the presence of mutations of KIT has been associated with higher likelihood of relapse and shorter survival, targeting Kit may be of therapeutic benefit. Therapeutic activity may extend to cases with Kit overexpression. We have recently described the activity of APcK110, a novel inhibitor of Kit, in vitro where we have shown potent proapoptotic and antiproliferative effects in AML cell lines and primary AML samples irrespective of mutation status but with measurable expression of Kit (Faderl S et al. Cancer Res 2009; 69: 3910-3917). Here we extend our investigations to the activity of APcK110 in vivo in a xenograft mouse model. After exposure of 8-weeks-old female NOD-SCID mice (NOD.CB17-PRKDS SCID\J) to 30cGy sub-lethal WBXRT, 1 × 10⁵ OCI/AML3 cells (human AML cell line) were injected I.V. Ten days later, the mice were injected I.P. every other day with the same volume of either APcK110 or PBS. The mice were sacrificed according to experimental protocol or when they became moribund, unable to obtain food or water, or if they lost > 20% of their body weight. Necropsy was performed on all animals. Marrow, blood and organs were preserved in formalin for histological analysis. Kaplan-Meier estimates were applied to calculate survival of the mice. We could show that 1) all mice injected with OCI/AML3 cells developed a clinical and histological picture consistent with AML. Wright stains of blood and marrow confirmed presence of a large, heterogeneous blast population, which was negative for myeloperoxidase, but stained positive for butyrate and anti-human CD45. Histological analysis of lung and liver tissue revealed dense infiltration with AML blasts as confirmed by anti-human CD45-positive sheets of cells in these tissues; 2) survival of APcK110-treated mice was significantly improved compared with mice which were injected with PBS (p=.02); 3) Marrow histology showed residual AML following injection of mice with APcK110. In conclusion, APcK110 is a novel kit kinase inhibitor with anti-AML activity in vitro and in vivo. Further evaluation in toxicology and clinical studies should be pursued.