title: A novel paradigm to trigger apoptosis in chronic lymphocytic leukemia.
abstract: Evasion of apoptosis is a hallmark of chronic lymphocytic leukemia (CLL), calling for new strategies to bypass resistance. Here, we provide first evidence that small-molecule X-linked inhibitor of apoptosis (XIAP) inhibitors in combination with the death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) present a novel approach to trigger apoptosis in CLL, including subgroups with resistant disease or unfavorable prognosis. XIAP, cellular IAP (cIAP) 1, and cIAP2 are expressed at high levels in primary CLL samples. Proof-of-concept studies in CLL cell lines show that subtoxic concentrations of XIAP inhibitors significantly enhance TRAIL-induced apoptosis and also sensitize for CD95-mediated apoptosis. Importantly also in primary CLL samples, XIAP inhibitor acts in concert with TRAIL to trigger apoptosis in 18 of 27 (67%) cases. This XIAP inhibitor-induced and TRAIL-induced apoptosis involves caspase-3 activation and is blocked by the caspase inhibitor zVAD.fmk. The cooperative interaction of XIAP inhibitor and TRAIL is even evident in distinct subgroups of patients with poor prognostic features (i.e., with 17p deletion, TP53 mutation, chemotherapy-refractory disease, or unmutated V(H) genes). Interestingly, cases with unmutated V(H) genes were significantly more sensitive to XIAP inhibitor-induced and TRAIL-induced apoptosis compared with V(H) gene-mutated samples, pointing to a role of B-cell receptor signaling in apoptosis regulation. By showing that XIAP inhibitors in combination with TRAIL present a new strategy to trigger apoptosis even in resistant forms and poor prognostic subgroups of CLL, our findings have important implications for the development of apoptosis-based therapies in CLL.
authors.affiliation: University Children's Hospital, Ulm, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Loeder
authors.forename: Thorsten
authors.initials: T
authors.lastname: Zenz
authors.forename: Andrea
authors.initials: A
authors.lastname: Schnaiter
authors.forename: Daniel
authors.initials: D
authors.lastname: Mertens
authors.forename: Dirk
authors.initials: D
authors.lastname: Winkler
authors.forename: Hartmut
authors.initials: H
authors.lastname: Döhner
authors.forename: Klaus-Michael
authors.initials: KM
authors.lastname: Debatin
authors.forename: Stephan
authors.initials: S
authors.lastname: Stilgenbauer
authors.forename: Simone
authors.initials: S
authors.lastname: Fulda
mesh_terms: D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001402:B-Lymphocytes / Q000187:drug effects; D045744:Cell Line, Tumor; D004357:Drug Synergism; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000037:antagonists & inhibitors*
chemical_list: D053221:TNF-Related Apoptosis-Inducing Ligand; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human