Neurofibromatosis type 2 (NF2) is a genetic syndrome that predisposes individuals to multiple benign tumors of the central and peripheral nervous systems, including vestibular schwannomas. Currently, there are no FDA approved drug therapies for NF2. Loss of function of merlin encoded by the NF2 tumor suppressor gene leads to activation of multiple mitogenic signaling cascades, including platelet-derived growth factor receptor (PDGFR) and SRC in Schwann cells. The goal of this study was to determine whether ponatinib, an FDA-approved ABL/SRC inhibitor, reduced proliferation and/or survival of merlin-deficient human Schwann cells (HSC). Merlin-deficient HSC had higher levels of phosphorylated PDGFRα/β, and SRC than merlin-expressing HSC. A similar phosphorylation pattern was observed in phospho-protein arrays of human vestibular schwannoma samples compared to normal HSC. Ponatinib reduced merlin-deficient HSC viability in a dose-dependent manner by decreasing phosphorylation of PDGFRα/β, AKT, p70S6K, MEK1/2, ERK1/2 and STAT3. These changes were associated with decreased cyclin D1 and increased p27Kip1levels, leading to a G1 cell-cycle arrest as assessed by Western blotting and flow cytometry. Ponatinib did not modulate ABL, SRC, focal adhesion kinase (FAK), or paxillin phosphorylation levels. These results suggest that ponatinib is a potential therapeutic agent for NF2-associated schwannomas and warrants further in vivo investigation.

Midostaurin is a multitargeted tyrosine kinase inhibitor (TKI) that potently inhibits activated fms-related tyrosine kinase 3 (FLT3) in the nanomolar range and other kinases including platelet-derived growth factor receptors α (PDGFR- α) and β (PDGFR- β), cyclin-dependent kinase, proto-oncogene tyrosine-protein kinase Src, tyrosine-protein kinase Fgr, spleen tyrosine kinase (Syk), KIT proto-oncogene receptor tyrosine kinase and the major vascular endothelial growth factor receptor (VEGFR). Activating mutations in FLT3, which is one of the more common acute myeloid leukemia (AML) mutations, particularly those that result in an FLT3-ITD (internal tandem duplication) mutation, confer poor prognosis and represent a therapeutic target. Small molecule TKIs that vary in potency and selectivity for FLT3 are under investigation. Here, we provide a comprehensive review of the preclinical and clinical activity of midostaurin, a recently approved drug indicated to be used in combination with cytarabine and daunorubicin induction and cytarabine consolidation chemotherapy for the treatment of AML featuring an FLT3 mutation.