birinapant and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

Second mitochondria-derived activator of caspase (SMAC) mimetics (SMs) targeting inhibitor of apoptosis proteins (IAPs) activate cell death pathways, and are currently being evaluated in clinical trials. Their successful therapeutic implementation requires upfront identification of patients who could benefit from a SM-based treatment but biomarkers for SM sensitivity have not yet been described. Here, we analyzed the intrinsic activity of two monovalent (AT406 and LCL161) and two bivalent (Birinapant and BV6) SMs on unselected patient-derived pediatric precursor B-cell acute lymphoblastic leukemia (BCP-ALL) identifying a subset of patient samples to be particularly sensitive to SM-induced cell death. This subset was defined by a characteristic gene expression signature with 127 differentially regulated genes, amongst them TNFRSF1A encoding TNFR1, and a critical role of TNFR1 in SM-induced cell death in sensitive BCP-ALL was confirmed on the functional level. Interestingly, samples with intermediate or low sensitivity to SMs were sensitized to SM-induced cell death by inhibition of caspases using zVAD.fmk or Emricasan, a pan-caspase inhibitor in clinical trials. When we compared our expression data to published data sets, we identified an overlap of four genes to be commonly differentially regulated in SM-sensitive BCP-ALL, that is, TSPAN7, DIPK1C, MTX2 and, again, TNFRSF1A. Functional testing revealed that this set of genes identified samples with high sensitivity to SM treatment. In summary, our data suggest using this gene signature as biomarker predicting response to SM treatment and point to the development of new combinatorial treatments consisting of SMs and pan-caspase inhibitors for a successful clinical implementation of SMs in treatment of BCP-ALL.

Topics: Animals; Apoptosis; Apoptosis Regulatory Proteins; Azocines; Benzhydryl Compounds; Caspase Inhibitors; Cell Line, Tumor; Dipeptides; Female; Humans; Indoles; Inhibitor of Apoptosis Proteins; Mice; Mice, Inbred NOD; Mice, SCID; Mitochondrial Proteins; Oligopeptides; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Precursor Cells, B-Lymphoid; Receptors, Tumor Necrosis Factor, Type I; Thiazoles; Xenograft Model Antitumor Assays

More precise treatment strategies are urgently needed to decrease toxicity and improve outcomes for treatment-refractory leukemia. We used ex vivo drug response profiling of high-risk, relapsed, or refractory acute lymphoblastic leukemia (ALL) cases and identified a subset with exquisite sensitivity to small-molecule mimetics of the second mitochondria-derived activator of caspases (SMAC) protein. Potent ex vivo activity of the SMAC mimetic (SM) birinapant correlated with marked in vivo antileukemic effects, as indicated by delayed engraftment, decreased leukemia burden, and prolonged survival of xenografted mice. Antileukemic activity was dependent on simultaneous execution of apoptosis and necroptosis, as demonstrated by functional genomic dissection with a multicolored lentiCRISPR approach to simultaneously disrupt multiple genes in patient-derived ALL. SM specifically targeted receptor-interacting protein kinase 1 (RIP1)-dependent death, and CRISPR-mediated disruption of RIP1 completely blocked SM-induced death yet had no impact on the response to standard antileukemic agents. Thus, SM compounds such as birinapant circumvent escape from apoptosis in leukemia by activating a potent dual RIP1-dependent apoptotic and necroptotic cell death, which is not exploited by current therapy. Ex vivo drug activity profiling could provide important functional diagnostic information to identify patients who may benefit from targeted treatment with birinapant in early clinical trials.

Topics: Animals; Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Cell Line, Tumor; Dipeptides; Drug Synergism; Humans; Indoles; Inhibitor of Apoptosis Proteins; Intracellular Signaling Peptides and Proteins; Mice; Mitochondrial Proteins; Necrosis; Nuclear Pore Complex Proteins; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Receptor-Interacting Protein Serine-Threonine Kinases; RNA-Binding Proteins; Tumor Necrosis Factor-alpha

Ph-like acute lymphoblastic leukemia (ALL) is a genetically defined high-risk ALL subtype with a generally poor prognosis. In this study, we evaluated the efficacy of birinapant, a small-molecule mimetic of the apoptotic regulator SMAC, against a diverse set of ALL subtypes. Birinapant exhibited potent and selective cytotoxicity against B-cell precursor ALL (BCP-ALL) cells that were cultured ex vivo or in vivo as patient-derived tumor xenografts (PDX). Cytotoxicity was consistently most acute in Ph-like BCP-ALL. Unbiased gene expression analysis of BCP-ALL PDX specimens identified a 68-gene signature associated with birinapant sensitivity, including an enrichment for genes involved in inflammatory response, hematopoiesis, and cell death pathways. All Ph-like PDXs analyzed clustered within this 68-gene classifier. Mechanistically, birinapant sensitivity was associated with expression of TNF receptor TNFR1 and was abrogated by interfering with the TNFα/TNFR1 interaction. In combination therapy, birinapant enhanced the in vivo efficacy of an induction-type regimen of vincristine, dexamethasone, and L-asparaginase against Ph-like ALL xenografts, offering a preclinical rationale to further evaluate this SMAC mimetic for BCP-ALL treatment. Cancer Res; 76(15); 4579-91. ©2016 AACR.

Topics: Animals; Apoptosis; Cell Line, Tumor; Dipeptides; Female; Gene Expression; Humans; Indoles; Mice; Mice, Inbred NOD; Mice, SCID; Precursor Cell Lymphoblastic Leukemia-Lymphoma