sirolimus and Mastocytosis--Systemic

Mast cell disorders are defined by an abnormal accumulation of tissue mast cells in one or more organ systems. Clinical symptoms in mastocytosis result from mast cells derived mediators and, less frequently, from destructive infiltration of mast cells. Systemic mastocytosis is regressive among children, whereas the disease is persistent among adults. A clonal haematological non-mast cell lineage disease can be associated. The clinical course in these patients is variable ranging from asymptomatic for years to highly aggressive and rapidly devastating. Until recently, the only treatment of this incurable disease was symptomatic.. Recent advances were done in understanding the physiopathology of this myeloproliferative syndrome which results from an activating mutation of the stem cell factor receptor: C-Kit. A somatic C-Kit mutation is usually detectable in mast cells and their progenitors. Different mutations were found and the mutation D816V is the most frequent. Their specific transduction paths were also studied. Diagnosis of systemic mastocytosis does not only rest upon pathological examination but also on molecular as well as immunological and immunochemical tools.. Physiopathological advancements led to suggest new treatments in order to directly inhibit proliferative paths of masts cells such as tyrosine kinase inhibitors and rapamycin.

Topics: Adult; Boronic Acids; Bortezomib; Child; Forecasting; Humans; Immunohistochemistry; Immunosuppressive Agents; Mastocytosis, Systemic; Mutation; Prognosis; Protease Inhibitors; Proto-Oncogene Proteins c-kit; Pyrazines; Sirolimus; Stem Cell Transplantation; Transduction, Genetic; World Health Organization

KIT D816V mutation has been observed in more than 90% of patients with systemic mastocytosis (SM). This mutation constitutively activates the mammalian target of rapamycin (mTOR) signaling pathway. We tested the efficacy of everolimus (RAD001), a novel oral mTOR inhibitor, at a dose of 10 mg daily in an open label, non-comparative Phase II trial for patients with SM. Ten patients were enrolled from April 2007 to October 2008. Median age was 55 years, four were males, seven had indolent and three aggressive SM, and six were previously treated with other agents. Median duration of therapy was 4 months (range 0.2-18). No objective responses were noted. Four patients had a short-lasting subjective improvement in symptoms for a median duration of 3 months (range 3-15). Grade 1-3 diarrhea, mucositis, and neutropenia were the most common adverse effects. No Grade 4 toxicity was noted. In conclusion, everolimus does not result in appreciable clinical activity in patients with SM.

Topics: Administration, Oral; Adult; Aged; Diarrhea; Everolimus; Fatigue; Female; Follow-Up Studies; Humans; Immunosuppressive Agents; Intracellular Signaling Peptides and Proteins; Male; Mastocytosis, Systemic; Middle Aged; Mucositis; Mutation; Neutropenia; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins c-kit; Sirolimus; TOR Serine-Threonine Kinases; Treatment Outcome

Increased mast cell burden is observed in the inflamed tissues and affected organs and tissues of patients with mast cell proliferative disorders. However, normal mast cells participate in host defense, so approaches to preferentially target clonally expanding mast cells are needed. We found that mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) are up-regulated in neoplastic and developing immature mast cells compared with their terminally differentiated counterparts. Elevated mTOR mRNA was also observed in bone marrow mononuclear cells of patients exhibiting mast-cell hyperplasia. Selective inhibition of mTORC1 and mTORC2 through genetic and pharmacologic manipulation revealed that, whereas mTORC1 may contribute to mast-cell survival, mTORC2 was only critical for homeostasis of neoplastic and dividing immature mast cells. The cytostatic effect of mTORC2 down-regulation in proliferating mast cells was determined to be via inhibition of cell-cycle progression. Because mTORC2 was observed to play little role in the homeostasis of differentiated, nonproliferating, mature mast cells, these data provide a rationale for adopting a targeted approaching selectively inhibiting mTORC2 to effectively reduce the proliferation of mast cells associated with inflammation and disorders of mast cell proliferation while leaving normal differentiated mast cells largely unaffected.

Topics: Adaptor Proteins, Signal Transducing; Animals; Antibiotics, Antineoplastic; Blotting, Western; Bone Marrow Cells; Carrier Proteins; Cell Cycle; Cell Proliferation; Cell Survival; Cells, Cultured; Gene Expression Profiling; Homeostasis; Humans; Mast Cells; Mastocytosis, Systemic; Mechanistic Target of Rapamycin Complex 1; Mice; Mice, Transgenic; Multiprotein Complexes; Naphthyridines; Proteins; Rapamycin-Insensitive Companion of mTOR Protein; Regulatory-Associated Protein of mTOR; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Sirolimus; TOR Serine-Threonine Kinases; Tumor Cells, Cultured

Oncogenic activation loop KIT mutations are observed in acute myeloid leukemia (AML) and systemic mastocytosis (SM); however, unlike the KIT juxtamembrane mutants, the activation loop mutants are insensitive to imatinib mesylate. Furthermore, as prior studies primarily used heterologous cell lines, the molecular mechanism(s) underlying oncogenic KIT-induced transformation in primary cells is poorly understood. We demonstrate that expression of KITD814V in primary hematopoietic stem/progenitor cells (HSC/Ps) and mast cell progenitors (MCps) induces constitutive KIT autophosphorylation, supports ligand-independent hyperproliferation, and promotes promiscuous cooperation with multiple cytokines. Genetic disruption of p85 alpha, the regulatory subunit of class IA lipid kinase phosphoinositol-3-kinase (PI3K), but not of p85 beta, or genetic disruption of the hematopoietic cell-specific Rho GTPase, Rac2, normalizes KITD814V-induced ligand-independent hyperproliferation. Additionally, deficiency of p85 alpha or Rac2 corrects the promiscuous hyperproliferation observed in response to multiple cytokines in both KITD814V-expressing HSC/Ps and MCps. Treatment of KITD814V-expressing HSC/Ps with a Rac inhibitor (NC23766) or with rapamycin showed a dose-dependent suppression in ligand-independent growth. Taken together, our results identify p85 alpha and Rac2 as potential novel therapeutic targets for the treatment of KITD814V-bearing AML and SM.

Topics: Amino Acid Substitution; Animals; Antibiotics, Antineoplastic; Benzamides; Cell Proliferation; Cell Transformation, Neoplastic; Cytokines; Drug Resistance, Neoplasm; Enzyme Inhibitors; Hematopoietic Stem Cells; Imatinib Mesylate; Leukemia, Myeloid, Acute; Mastocytosis, Systemic; Mice; Mice, Knockout; Mutation, Missense; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Piperazines; Protein Subunits; Proto-Oncogene Proteins c-kit; Pyrimidines; rac GTP-Binding Proteins; RAC2 GTP-Binding Protein; Sirolimus

Two classes of oncogenic mutations of the c-kit tyrosine kinase have been described: the juxtamembrane domain V560G mutation, which is preferentially found in gastrointestinal stromal tumors (GISTs), and the kinase domain D816V mutation, which is highly representative of systemic mastocytosis (SM). Here we show that both mutations constitutively activate the mammalian target of rapamycin (mTOR) signaling pathway. Surprisingly, the mTOR inhibitor rapamycin induces only apoptosis in HMC-1 cells bearing the D816V but not the V560G mutation. In support of this unexpected selectivity, rapamycin inhibits the phosphorylation of 4E-BP1, a downstream substrate of the mTOR pathway, but only in D816V HMC-1 cells. Importantly, D816V mast cells isolated from SM patients or from transgenic mice are sensitive to rapamycin whereas normal human or mouse mast cells are not. Thus, rapamycin inhibition appears specific to the D816V mutation. At present there is no effective cure for SM patients with the D816V mutation. The data presented here provide a rationale to test whether rapamycin could be a possible treatment for SM and other hematologic malignancies with the D816V mutation.

Topics: Animals; Apoptosis; Cell Proliferation; Cell Survival; Humans; Mast Cells; Mastocytosis, Systemic; Mice; Mice, Transgenic; Mutation, Missense; Pharmacogenetics; Protein Kinases; Proto-Oncogene Proteins c-kit; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tumor Cells, Cultured