Clinical Investigation of Mitochondrial Biogenesis in Multiple Myeloma

Background: Many cancers including multiple myeloma (MM) retain more cytosolic iron to promote tumor cell growth and drug resistance. Higher cytosolic iron promotes oxidative damages due to its interaction with reactive oxygen species generated by mitochondria. Though many other pre-clinical studies for targeting mitochondria have been reported in MM, it remains unclear whether the mitochondrial biogenesis is beneficial or detrimental for tumor cells is not clear. A better understanding of the genetic makeup of mitochondria in MM cells is required if we want to use mitochondria as specific targets.

Materials and Methods: Gene expression profiles (GEP) of highly purified bone marrow plasma cells were analyzed from 559 newly diagnosed patients with MM including 351 from total therapy 2 (TT2) and 208 from TT3 cohorts. Kaplan-Meier analyses of event-free survival (EFS) and overall survival (OS) about patients in the TT2 and TT3 cohorts were performed using methods implemented in the SurvExpress website. We performed GSEA and ssGSEA by using the applications available at the GenePattern platform of the Broad Institute of MIT and Harvard. Raw enrichment scores were subjected to Hierarchiacal Clustering analysis and heatmaps were generated by Hierachical Clustering Image module from Genepattern platform. For the MM murine model, NOD.Cγ-Rag1 mice 6-8 weeks old were injected intravenously or intraperitoneal injection with ARP1 MM cells expressing luciferase. After one-week injection of ARP1 cells, mice were treated with either PAA injected intraperitoneal once a day, 5 days every week for 3 weeks. The mice were euthanized when a humane endpoint was reached.

Results: The variation of mitochondrial biogenesis in different stages of MM disease was evaluated using gene expression profiles in a large clinical dataset. Sixteen of 18mitochondrial biogenesis related gene sets, including mitochondrial biogenesis signature and oxidative phosphorylation, were increased in myeloma cells compared with normal plasma cells and high expression was associated with an inferior outcome. Relapsed and drug resistant myeloma samples had higher expression of mitochondrial biogenesis signatures than newly diagnosed. The expression of mitochondrial biogenesis genes was regulated by the cellular iron content, which showed a synergistic effect in patient outcome in MM. Pharmacological ascorbic acid induced myeloma cell death by inhibition of mitochondria oxidative phosphorylation in an in vivo model.

Conclusion: Here, we identify that dysregulated mitochondrial biogenesis and iron homeostasis play a major role in myeloma progression and patient outcome and pharmacological ascorbic acid through cellular iron content and mitochondrial oxidative species should be considered as a novel treatment in myeloma including drug-resistant and relapsed patients.