Abstract C175: Effective targeting of PI3K/mTOR pathways with GDC-0980 in FLT-3 mutant pediatric leukemia.

Introduction: FLT-3 is a receptor tyrosine kinase that is abnormally activated in a significant percentage of pediatric acute myeloid leukemia (AML) and infant ALL. Previous studies have shown that FLT-3 aberration with deregulated PI3K/Akt and mTOR signaling pathways have significantly poor outcome. GDC-0980 is an orally bioavailable inhibitor with selective and potent activity against PI3K and mTOR kinases with the capacity to target two crucial pathway nodes to produce the strongest accessible inhibition of signaling by these mechanisms. Methods: A panel of pediatric cell lines with FLT-3 mutations (N=3), ITD (n=3), Wt (n=2) and primary specimens (n=4) were evaluated. Cells were cultured with GDC-0980 and after four days in culture, growth inhibition was quantified by Alamar blue assay. Changes in activity of FLT-3 and various associated intracellular signaling components were evaluated by Western blot analysis. Similarly, the induction of apoptosis was measured by the activation of various caspases, Bcl-2 and PARP cleavage. Actin was used for loading control. Results: GDC-0980 induced effective cytotoxicity in all of the leukemia cell lines (mean IC₅₀ = 0.65 uM range 0.2 - 1uM). The sensitivity was highest in cells with FLT-3 over-expression followed by ITD and then wild-type (wt). As expected, changes in the modulators of apoptosis such as caspases and PARP were noted although PARP cleavage was observable at much lower drug concentrations (0.01uM). At IC₅₀ concentrations GDC-0980 mediated a decrease in active mTOR. The effect on markers of PI3K/mTOR activity (loss of pS6 and p-AKT) was more pronounced in cells with aberrant FLT-3 than those with wt FLT-3. Meanwhile, in all leukemic cells the levels of active PTEN, ERK, JAK and STAT-5 remained unchanged following treatment with similar drug concentrations. Unexpectedly, GDC-0980 induced FLT-3 de-phosphorylation in cells with FLT-3 over-expression and ITD, but this effect was not noted in leukemia cells with wt FLT-3. Discussion: Our data indicate the potential of the PI3K/mTOR inhibitor GDC-0980 to affect specific intracellular signaling pathways in pediatric leukemia cells with abnormal FLT-3. We also provide evidence for the unique ability of GDC-0980 to directly target constitutively active FLT-3 suggesting its effective use in specific leukemia sub-types. These data, in addition to the identification of the targets that are modified by this agent, provide rationale for additional pre-clinical experiments and the subsequent formulation of clinical studies for the treatment of such refractory leukemias in infants and children.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C175.

Citation Format: Meaghan Hagerty, Aarthi Jayanthan, Yibing Ruan, Tanya Trippett, Aru Narendran. Effective targeting of PI3K/mTOR pathways with GDC-0980 in FLT-3 mutant pediatric leukemia. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C175.