Arsenic trioxide uses caspase-dependent and caspase-independent death pathways in myeloma cells.
Arsenic trioxide (ATO) is emerging as a standard therapy for refractory acute promyelocytic leukemia. Consequently, ATO-based therapies are being investigated in other cancers. We have reported that the combination of ATO and ascorbic acid is an effective strategy in chemoresistant myeloma cell lines and in plasma cells from patients. ATO action is multimodal and appears to involve thiol depletion, increased reactive oxygen species production, loss of mitochondrial membrane potential (DeltaPsi(m)), and activation of caspases. To better define the ATO death pathway, we asked whether caspase activity is required for ATO-mediated cell death. Here we report that ATO exerts cytotoxic effects in myeloma cell lines via both caspase-dependent and caspase-independent pathways. We monitored ATO-induced changes in cell viability, caspase activity, superoxide production, and DeltaPsi(m) in the presence or absence of the caspase inhibitors t-butoxy carbonyl-Asp.fluoromethylketone (BocD.fmk) and Z-Val-Ala-Asp.fluoromethylketone (zVAD.fmk) and the anti-oxidant N-acetylcysteine. Consistent with glutathione levels dictating ATO action, N-acetylcysteine abrogated ATO-induced changes in cell death, caspase activation, free radical production, and loss of DeltaPsi(m) in all the cell lines we tested. Experiments with caspase inhibitors suggested at least two models for ATO death signaling. In 8226/S cells, blockade of caspases had no effect on loss of cell viability, increase in reactive oxygen species production, and minimal effects on the loss of DeltaPsi(m). In contrast, BocD.fmk or zVAD.fmk conferred significant protection from the effects of ATO in U266 cells and MM1.S cells. Chemoresistant variants of 8226/S and MM1.S displayed similar ATO-induced death pathways as their respective parental lines. Studies with myeloma cells from bone marrow biopsies indicated that ATO initiates a caspase-independent pathway in the majority of samples.
McCafferty-Grad
Jennifer
J
Sylvester Cancer Center, Department of Microbiology and Immunology, University of Miami School of Medicine, Miami, FL 33101, USA.
Bahlis
Nizar J
NJ
Krett
Nancy
N
Aguilar
Tatiana M
TM
Reis
Isildinha
I
Lee
Kelvin P
KP
Boise
Lawrence H
LH
D000111:Acetylcysteine / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D000077237:Arsenic Trioxide; D001152:Arsenicals / Q000494:pharmacology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D019008:Drug Resistance, Neoplasm; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000188:drug therapy* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D010087:Oxides / Q000494:pharmacology*; D010950:Plasma Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D014407:Tumor Cells, Cultured
D001152:Arsenicals; D061945:Caspase Inhibitors; D010087:Oxides; D013481:Superoxides; D020169:Caspases; D000077237:Arsenic Trioxide; D000111:Acetylcysteine