Unleashing the Impact of Exosomes Derived from Human Placental Mesenchymal Stem Cells (hPMSCs) on U-266 Myeloma Cell Line

Multiple myeloma (MM) is a malignancy of plasma cells, terminally differentiated B cells, with complications like hypercalcemia, renal failure, anemia, and bone disease, which are also known as CRAB criteria. MM develops from monoclonal gammopathy of unknown significance (MGUS), a pre-malignant plasma cell dyscrasia. Over some time, MGUS has the potential to progress into smoldering multiple myeloma (SMM), which can evolve into MM. MM rarely progresses into plasma cell leukemia (PCL), a condition in which malignant plasma cells no longer stay in the bone marrow niche and circulate in the peripheral blood. In MM, various soluble factors play important roles, and interleukin-6 has different vital roles.  Interleukin-6, an inflammatory cytokine, has significant roles in the growth, survival, angiogenesis, metastasis, and apoptosis resistance in MM. Interleukin-6 is produced and secreted by both autocrine from myeloma cells and paracrine from bone marrow stromal cells. To tackle MM, various therapeutic approaches were applied over many years, and according to the results, most patients with MM can respond well to first-line treatment. However, the majority of patients may relapse as conventional treatment may not be curative. So, there is an urgent need for novel cell-based and cell-free therapeutic strategies, such as mesenchymal stem cell-based therapies and their products to offer new therapeutic strategies for MM. Materials and Methods: In the present study, we investigated the impacts of exosomes derived from human placental mesenchymal stem cells (hPMSCs) on apoptosis and interleukin-6 expression in a myeloma cell line, U-266, for the first time. hPMSCs were isolated from the human placenta and cultured in a DMEM medium. After characterizing the cells and acknowledging their identity, they underwent several passages and their supernatant was collected to harvest exosomes. The exosomes were isolated by ultracentrifugation and characterized by DLS and TEM, and their concentration was measured by BCA protein assay. U266 cells were treated with different concentrations of exosomes and then MTT and annexin/propidium iodide flow cytometry tests were performed to evaluate cell viability. Afterward, a real-time PCR test was performed to evaluate interleukin-6 gene expression. Results: According to our findings, treatment of U-266 cells with hPMSCS-derived exosomes led to the preservation of myeloma cells without changes in their cell cycle. Surprisingly, treatments did not hinder the expression of interleukin-6 in the myeloma cells. Conclusion: In MM patients, interleukin-6 plays different roles, and it is a desirable target to design new therapeutic strategies. To evaluate the effects of new therapeutic strategies, we designed and performed our study to estimate the effects of cell-free therapeutic strategy.  In the present study, the impacts of hPMSCS-derived exosomes on the viability of MM cells and interleukin-6 gene expression were evaluated. The results showed that hPMSCS-derived exosomes resulted in the perseverance of myeloma cells without changes in the cell cycle.  Furthermore, the interleukin-6 gene expression level showed no significant change.