title: Reactivation of Smac-mediated apoptosis in chronic lymphocytic leukemia cells: mechanistic studies of Smac mimetic.
abstract: Dysfunctional apoptotic machinery is a hallmark feature of chronic lymphocytic leukemia (CLL). Accordingly, targeting apoptosis regulators has been proven a rational approach for CLL treatment. We show that CLL lymphocytes express high levels of XIAP, cIAP1, and cIAP2 compared to normal lymphocytes. Smac mimetic, Smac066, designed to bind to BIR3-domain of IAPs, induce apoptosis in primary CLL cells (n=71; p<0.0001), irrespective of prognostic markers. Apoptosis was mediated by diminished levels of IAPs (XIAP-p=0.02; cIAP-p<0.0001) and increased activation of caspases-8,-9,-3. The caspase-cleavage was in direct association with the levels of apoptosis (r2=0.8 for caspases-8,-9,-3). Correlative analysis revealed a direct relationship between reduction in IAPs and degree of apoptosis (r2=0.6 (XIAP); 0.5 (cIAP2)). There was a strong association between apoptosis, IAP-degradation, and concurrent caspase-activation. Pan-caspase inhibitor Z-Vad-fmk reversed the degradation of Mcl-1, but not IAPs suggesting that smac066 is selective to IAPs, however, Mcl-1 degradation is through caspase-mediated cleavage. Immunoprecipitation experiments revealed physical interaction between caspase-3 and XIAP that was disrupted by smac066. Importantly, XIAP and cIAP2 were markedly induced in bone-marrow and lymph-node microenvironments, providing a basis for IAP antagonists as anti-tumor agents in CLL. Smac066 synergized with ABT-737, revealing a mechanistic rationale to jointly target BH3 and BIR3 domains.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.|Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Kumudha
authors.initials: K
authors.lastname: Balakrishnan
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Min
authors.initials: M
authors.lastname: Fu
authors.affiliation: Department of Hematology Unit, Fondazione IRCCS Ospedale Maggiore Policlinico, University of Milan, Milan, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Onida
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: William G
authors.initials: WG
authors.lastname: Wierda
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Keating
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.|Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
authors.forename: Varsha
authors.initials: V
authors.lastname: Gandhi
mesh_terms: D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D001713:Biphenyl Compounds / Q000737:chemistry; D001854:Bone Marrow Cells / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D018920:Coculture Techniques; D005347:Fibroblasts / Q000378:metabolism; D015973:Gene Expression Regulation, Leukemic; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D008207:Lymphatic Metastasis; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009596:Nitrophenols / Q000737:chemistry; D010879:Piperazines / Q000737:chemistry; D000072417:Protein Domains; D012044:Regression Analysis; D013449:Sulfonamides / Q000737:chemistry; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism
chemical_list: C501332:ABT-737; D051017:Apoptosis Regulatory Proteins; D001713:Biphenyl Compounds; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D009596:Nitrophenols; D010879:Piperazines; D013449:Sulfonamides; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D020169:Caspases
keywords: CLL; IAPs; Smac mimetic; XIAP; apoptosis