TY - JOUR
T1 - Reactivation of smac-mediated apoptosis in chronic lymphocytic leukemia cells
T2 - Mechanistic studies of smac mimetic
AU - Balakrishnan, Kumudha
AU - Fu, Min
AU - Onida, Francesco
AU - Wierda, William G.
AU - Keating, Michael J.
AU - Gandhi, Varsha
N1 - Funding Information:
The authors thank Benjamin Hayes for coordinating the blood sample collection and Susan C Smith for providing information on patient characteristics. This work was supported in part by a CLL Global Research Foundation grant to K.B. and a CLL Research Consortium grant from the National Institutes of Health (P01-CA081534). K.B., W.G.W. and V.G. are members of the CLL Research Consortium.
PY - 2016
Y1 - 2016
N2 - 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-Vadfmk 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.
AB - 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-Vadfmk 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.
KW - Apoptosis
KW - CLL
KW - IAPs
KW - Sac mimetic
KW - XIAP
UR - http://www.scopus.com/inward/record.url?scp=84982899270&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84982899270&partnerID=8YFLogxK
U2 - 10.18632/oncotarget.8462
DO - 10.18632/oncotarget.8462
M3 - Article
C2 - 27223062
AN - SCOPUS:84982899270
SN - 1949-2553
VL - 7
SP - 39458
EP - 39472
JO - Oncotarget
JF - Oncotarget
IS - 26
ER -