Date of Degree
PhD (Doctor of Philosophy)
Free Radical and Radiation Biology
Multiple myeloma (MM) is a prevalent B-cell neoplasm that remains incurable with currently available chemotherapeutic drugs. Existing drug regimens result in initial disease remission but MM often relapses with an aggressive, drug resistant phenotype with uniform mortality. Bortezomib (BTZ, proteasome inhibitor) is a frontline anti-MM drug that is used for treatment of newly diagnosed and relapsed MM. However both intrinsic and acquired BTZ resistance is observed. Hence, gaining a mechanistic understanding of BTZ-resistance can provide novel targets to increase and restore BTZ cytotoxicity in MM. Studies show that BTZ-mediated proteasome inhibition generates oxidative stress therefore, BTZ resistance can be caused by an increase in cellular antioxidant capacity of MM cells. Antioxidants like superoxide dismutases (SODs), glutathione (GSH), and glutathione peroxidases (GPxs) can maintain cellular redox homeostasis and confer resistance to oxidative stress. Additionally, an increased glucose metabolism can assist in maintaining low reactive oxygen species (ROS) levels formed as by-products of endogenous or therapy induced oxidative stress. This led us to test the hypothesis that BTZ resistance in MM is linked to redox regulation via the antioxidant network and generation of reducing equivalents. Retrospective analysis of clinically annotated MM dataset shows a correlation between SOD1 gene expression, MM progression, and poor overall and event free survival. In a MM cell line model with intrinsic or acquired BTZ resistance, our results show a correlation between half maximal inhibitory concentration (IC50) of BTZ and CuZnSOD activity. Upon inhibition of CuZnSOD activity with a clinically approved drug, disulfiram (DSF, Antabuse), BTZ cytotoxicity was increased. Furthermore, enforced overexpression of CuZnSOD conferred BTZ resistance in an otherwise BTZ sensitive MM cell line. MM cell lines with differential intrinsic BTZ cytotoxicity displayed a correlation between BTZ IC50 and GSH levels as well as GPx-1 activity. Gene expression profiling data from patients showed that poor prognosis associates with increased glycolytic gene expression in MM. Also, MM cell lines with intrinsic resistance toward BTZ exhibited increased glucose uptake, increased mRNA expression and activity of glucose-6-phosphate dehydrogenase (G6PD) with increased cytotoxicity with glucose deprivation or 2-deoxyglucose (2-DG) treatment. In conclusion, our results provide a rationale for utilizing redox-based combination protocols of clinically approved drugs (i.e. DSF and 2-DG) with BTZ to improve MM therapy responses.
Multiple myeloma (MM) is a blood cancer that shows uniform mortality. In the clinic, MM patients respond poorly to treatment or relapse with an aggressive disease that does not respond to treatment. We predicted that identifying parameters associated with therapy resistance could offer avenues to design combination therapies that would improve clinical outcome of MM. We used several human MM cell lines that were sensitive to treatment, that were innately resistant, and others that were adapted to acquire resistance to a commonly used MM drug. Our results showed that therapy resistant tumor cells display altered antioxidant levels and glucose metabolism. Upon combination with a drug already used in the treatment of alcoholism with an anti-myeloma drug, we were able to kill more of the resistant cells. Our studies provide preclinical rationale to develop combination chemotherapy protocols with drugs that perturb antioxidant levels and/or glucose metabolism such that MM prognosis can be improved.
publicabstract, Glucose, Multiple Myeloma, Redox, Superoxide Dismutase
xix, 201 pages
Includes bibliographical references (pages 172-201).
Copyright 2014 Kelley Salem