Mitochondrial-Targeted Decyl-Triphenylphosphonium Enhances 2-Deoxy-D-Glucose Mediated Oxidative Stress and Clonogenic Killing of Multiple Myeloma Cells

Abstract

Therapeutic advances have markedly prolonged overall survival in multiple myeloma (MM) but the disease currently remains incurable. In a panel of MM cell lines (MM.1S, OPM-2, H929, and U266), using CD138 immunophenotyping, side population staining, and stem cell-related gene expression, we demonstrate the presence of stem-like tumor cells. Hypoxic culture conditions further increased CD138low stem-like cells with upregulated expression of OCT4 and NANOG. Compared to MM cells, these stem-like cells maintained lower steady-state pro-oxidant levels with increased uptake of the fluorescent deoxyglucose analog. In primary human MM samples, increased glycolytic gene expression correlated with poorer overall and event-free survival outcomes. Notably, stem-like cells showed increased mitochondrial mass, rhodamine 123 accumulation, and orthodox mitochondrial configuration while more condensed mitochondria were noted in the CD138high cells. Glycolytic inhibitor 2-deoxyglucose (2-DG) induced ER stress as detected by qPCR (BiP, ATF4) and immunoblotting (BiP, CHOP) and increased dihydroethidium probe oxidation both CD138low and CD138high cells. Treatment with a mitochondrial-targeting agent decyl-triphenylphosphonium (10-TPP) increased intracellular steady-state pro-oxidant levels in stem-like and mature MM cells. Furthermore, 10-TPP mediated increases in mitochondrial oxidant production were suppressed by ectopic expression of manganese superoxide dismutase. Relative to 2-DG or 10-TPP alone, 2-DG plus 10-TPP combination showed increased caspase 3 activation in MM cells with minimal toxicity to the normal hematopoietic progenitor cells. Notably, treatment with polyethylene glycol conjugated catalase significantly reduced 2-DG and/or 10-TPP-induced apoptosis of MM cells. Also, the combination of 2-DG with 10-TPP decreased clonogenic survival of MM cells. Taken together, this study provides a novel strategy of metabolic oxidative stress-induced cytotoxicity of MM cells via 2-DG and 10-TPP combination therapy.

Alteration of mitochondrial biogenesis promotes disease progression in multiple myeloma

“…Our data show that the proteasome inhibitor bortezomib, a widely-used drug in MM, has no effect on AIF1 expression, cleavage and localization; suggesting that PAA could be applied in MM patients, who are resistant to bortezomib. Targeting mitochondria proteins, such as CDDO and 10-TPP, etc., have been shown to enhance the chemotherapeutic effects in pre-clinical and clinical MM studies [ 2 , 34 , 35 ]. Future work will focus on the selection of those promising agents which have specific toxicity to MM cells but spare normal tissues.…”

“…PAA-induced cell death depends on cellular iron content and cleavage of apoptosis-inducing factor 1 (AIF1), a mitochondrial biogenesis related gene [ 1 ]. Furthermore, increasing intracellular steady-state pro-oxidant levels in stem-like and mature MM cells using a mitochondrial-targeting agent decyl-triphenylphosphonium (10-TPP) promotes cancer cell death [ 2 ]. Though many pre-clinical studies for targeting mitochondria have been reported in MM [ 3 , 4 ], it remains unclear whether mitochondrial biogenesis is beneficial or detrimental for tumor cells.…”

Andrographolide, isolated from Andrographis paniculata, induces apoptosis in monocytic leukemia and multiple myeloma cells via augmentation of reactive oxygen species production

“…For example, ex vivo analysis showed that pharmacological-dosed ascorbic acid (PAA; ultra-high doses of vitamin C) selectively induced apoptosis in primary multiple myeloma cells while not significantly harming other bone marrow cells, and PAA-induced apoptosis in the multiple myeloma cell line OCI-MY5 could be inhibited by NAC (Xia et al, 2017). Furthermore, treatment with a mitochondrial-targeting agent decyltriphenylphosphonium (10-TPP) increased intracellular steady-state pro-oxidant levels and apoptosis in multiple myeloma cell lines (Schibler et al, 2016); 10-TPP is a lipophilic agent that associates directly with mitochondria, likely with the inner membrane (Murphy, 2008;Ross et al, 2008;Schibler et al, 2016). Dexamethasone, a glucocorticoid, is another hydrophobic lipophilic molecule that induced apoptotic cell death in multiple myeloma cell lines, and this effect could also be reduced by NAC (Bera et al, 2010); in sharp contrast, in normal cells dexamethasone was found to inhibit ROS generation (Dandona et al, 1999).…”

Andrographolide, isolated from Andrographis paniculata, induces apoptosis in monocytic leukemia and multiple myeloma cells via augmentation of reactive oxygen species production

“…For example, ex vivo analysis showed that pharmacological-dosed ascorbic acid (PAA; ultra-high doses of vitamin C) selectively induced apoptosis in primary multiple myeloma cells while not significantly harming other bone marrow cells, and PAA-induced apoptosis in the multiple myeloma cell line OCI-MY5 could be inhibited by NAC (Xia et al, 2017). Furthermore, treatment with a mitochondrial-targeting agent decyltriphenylphosphonium (10-TPP) increased intracellular steady-state pro-oxidant levels and apoptosis in multiple myeloma cell lines (Schibler et al, 2016); 10-TPP is a lipophilic agent that associates directly with mitochondria, likely with the inner membrane (Murphy, 2008;Ross et al, 2008;Schibler et al, 2016). Dexamethasone, a glucocorticoid, is another hydrophobic lipophilic molecule that induced apoptotic cell death in multiple myeloma cell lines, and this effect could also be reduced by NAC (Bera et al, 2010); in sharp contrast, in normal cells dexamethasone was found to inhibit ROS generation (Dandona et al, 1999).…”