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

Jeanine Schibler,Douglas R Spitz,Michael K Schultz,Jessica L Reedy,Fenghuang Zhan,Ann M Tomanek-Chalkley,Apollina Goel,Rafael Moreno-Sanchez

doi:10.1371/journal.pone.0167323

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.

Highlights

Multiple myeloma (MM) is a debilitating plasma cell malignancy
Gene expression profiling has shown a higher expression of induced pluripotent stem cell genes in stem-like CD138- than bulk CD138+ cells isolated from Human MM cell lines (HMCLs) [63]
A low SDC1 expression confirmed that CD138low cells were genetically distinct and not comprised of MM cells that had shed surface CD138 (Table 1) [64]

Summary

Introduction

Multiple myeloma (MM) is a debilitating plasma cell malignancy. The American Cancer Society estimates that in the United States in 2016 approximately 30,000 new cancer diagnosis and 12,500 deaths will be linked with MM [1]. New pharmacological drugs (i.e. lenalidomide, pomalidomide, bortezomib, carfilzomib, ixazomib, panobinostat) show anti-MM activity and in combination with conventional therapies offer deep clinical remissions [2]. Most patients eventually relapse with aggressive drug-resistant MM disease [3]. Resistance to chemotherapy and MM relapse has been attributed to persistence of residual disease that contains drug-resistant phenotypes i.e. de-differentiated pre-plasma cells, genetically distinct clones, and stem-like tumor cells [4,5,6]. The cancer stem cell (CSC) hypothesis remains controversial in MM, several groups have demonstrated a distinct stem-like sub-population that displays increased clonogenicity, sustained self-renewal, differentiation towards CD138+ mature MM cells, and chemo-resistance [5, 7, 8]. Successful therapy requires an approach to induce cytotoxicity in the drug-resistant tumor cells with the overall objective to reduce MM recurrence

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Results

Conclusion