title: RIP1 is required for IAP inhibitor-mediated sensitization of childhood acute leukemia cells to chemotherapy-induced apoptosis.
abstract: Evasion of apoptosis may contribute to poor treatment response in pediatric acute lymphoblastic leukemia (ALL), calling for novel treatment strategies. Here, we report that inhibitors of apoptosis (IAPs) at subtoxic concentrations cooperate with various anticancer drugs (that is, AraC, Gemcitabine, Cyclophosphamide, Doxorubicin, Etoposide, Vincristine and Taxol) to induce apoptosis in ALL cells in a synergistic manner as calculated by combination index and to reduce long-term clonogenic survival. Importantly, we identify RIP1 as a critical regulator of this synergism of IAP inhibitors and AraC that mediates the formation of a RIP1/FADD/caspase-8 complex via an autocrine/paracrine loop of tumor necrosis factor-α (TNFα). Knockdown of RIP1 abolishes formation of this complex and subsequent activation of caspase-8 and -3, mitochondrial perturbations and apoptosis. Similarly, inhibition of RIP1 kinase activity by Necrostatin-1 or blockage of TNFα by Enbrel inhibits IAP inhibitor- and AraC-triggered interaction of RIP1, FADD and caspase-8 and apoptosis. In contrast to malignant cells, IAP inhibitors and AraC at equimolar concentrations are non-toxic to normal peripheral blood lymphocytes or mesenchymal stromal cells. Thus, our findings provide first evidence that IAP inhibitors present a promising strategy to prime childhood ALL cells for chemotherapy-induced apoptosis in a RIP1-dependent manner. These data have important implications for developing apoptosis-targeted therapies in childhood leukemia.
authors.affiliation: University Children's Hospital, Ulm, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Löder
authors.forename: M
authors.initials: M
authors.lastname: Fakler
authors.forename: H
authors.initials: H
authors.lastname: Schoeneberger
authors.forename: S
authors.initials: S
authors.lastname: Cristofanon
authors.forename: J
authors.initials: J
authors.lastname: Leibacher
authors.forename: N
authors.initials: N
authors.lastname: Vanlangenakker
authors.forename: M J M
authors.initials: MJ
authors.lastname: Bertrand
authors.forename: P
authors.initials: P
authors.lastname: Vandenabeele
authors.forename: I
authors.initials: I
authors.lastname: Jeremias
authors.forename: K-M
authors.initials: KM
authors.lastname: Debatin
authors.forename: S
authors.initials: S
authors.lastname: Fulda
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3 / Q000378:metabolism; D053181:Caspase 8 / Q000378:metabolism; D045744:Cell Line, Tumor; D002648:Child; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors* / Q000502:physiology; D028861:Nuclear Pore Complex Proteins / Q000235:genetics / Q000502:physiology*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000473:pathology; D016601:RNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000502:physiology
chemical_list: C119724:AGFG1 protein, human; D000970:Antineoplastic Agents; D051034:Inhibitor of Apoptosis Proteins; D028861:Nuclear Pore Complex Proteins; D016601:RNA-Binding Proteins; D014409:Tumor Necrosis Factor-alpha; D053148:Caspase 3; D053181:Caspase 8