Zhou J1,2, Lu X1, Tan TZ1,3, Chng WJ1,2,4.
1 Cancer Science Institute of Singapore National University of Singapore14 Medical Drive, Centre for Translational Medicine, Singapore, 117599, Republic of Singapore.
1 Department of Medicine, Yong Loo Lin School of Medicine National University of Singapore, Singapore, 119074, Republic of Singapore.
1 Translational Centre for Development and Research, National University Health System MD11, #03-10, 10 Medical DriveSingapore, 117597, Republic of Singapore.
1 Department of Hematology-Oncology, National University Cancer Institute NUHS, Singapore, 119228, Republic of Singapore.
Acute myeloid leukemia (AML) is an aggressive disease with an increasing incidence and relatively low 5-year survival rate. Unfortunately, the underlying mechanism of leukemogenesis is poorly known, and there has been little progress in the treatment for AML. Studies have shown that X-Linked Inhibitor of Apoptosis (XIAP), one of the inhibitor of apoptosis proteins (IAPs), is highly expressed and contributes to chemoresistance in AML. Hence, a novel drug, RO6867520 (abbreviation: RO-BIR2), developed by Roche targeting the BIR2 domain in XIAP to reactivate blocked apoptosis, is a promising therapy for AML. The monotherapy of RO-BIR2 had minimal effect on most of the AML cell lines tested except U-937. In contrast to AML cell lines, in general, RO-BIR2 alone has been shown to inhibit proliferation of primary AML patient samples effectively and induced apoptosis in a dose-dependent manner. A combination of RO-BIR2 with TNF-related apoptosis inducing ligand (TRAIL) led to highly synergistic effect on AML cell lines and AML patient samples. This combination therapy is capable of inducing apoptosis, thereby leading to an increase in specific apoptotic cell population, along with the activation of caspase 3/7. A number of apoptotic-related proteins such as XIAP, cleavage of caspase 3, cleavage of caspase 7, and cleaved PARP were changed upon combination therapy. Combination of RO-BIR2 with Ara-C had similar effect as the TRAIL combination. Ara-C combination also led to synergistic effect on AML cell lines and AML patient samples with low combination indexes (CIs). We conclude that the combination of RO-BIR2 with either TRAIL or Ara-C represents a potent therapeutic strategy for AML and is warranted for further clinical trials to validate the synergistic benefits in AML patients, especially for the elderly who are abstaining from intensive chemotherapy.
KEYWORDS: TRAIL ; XIAP ; Acute myeloid leukemia (AML); Apoptosis; BIR2 domain; Cell Death; Chemotherapy; Combination therapy