P-077: Bone marrow microenvironment analysis of exosomal microRNAs in multiple myeloma, extramedullary disease and plasma cell leukemia

Background Multiple myeloma (MM) is a heterogeneous plasma cell (PC) malignancy. These malignant PC are dependent on the bone marrow (BM) microenvironment. However, a subclone of PCs can escape the BM microenvironment and infiltrate soft tissues and organs in the so-called extramedullary disease (EMD). This subclone may also escape to peripheral blood; if there are more than 20% of circulating PC (cPC), the disease is reclassified as plasma cell leukemia (PCL). All cells in the BM microenvironment release exosomes. Exosomes are small membranous vesicles that originate from internal multivesicular bodies; they are found in all body fluids, including peripheral blood, breast milk, etc. Exosomes are important in intercellular communication, and they have been implicated in disease relapse, resistance to chemotherapy and many other processes important for tumorigenesis. They contain proteins and nucleic acids, such as microRNAs (miRNAs) - short non-coding RNA molecules that are involved in many physiological and pathological processes. Aims The aim of this work was to analyze expression of exosomal miRNAs in BM plasma samples of MM, EMD and PCL patients. Methods Exosomes were isolated using qEV columns. MiRNAs were isolated from exosomes using qEV original Size Exclusion Columns, following miRNA isolation using miRNeasy Micro Kit. For next generation sequencing (NGS), 8 MM, 7 EMD and 8 PCL samples were used. Results from NGS were validated on 40 MM, 25 EMD and 21 PCL samples by RT-qPCR using Taqman Advanced MiRNA Assays. Results NGS analysis showed 1128 different miRNAs that were present in analyzed samples. Out of these, 239 miRNAs were found in at least 8 samples and had more than 1 read per million; thus, they were included in subsequent analysis. Out of these miRNAs, there are 6 miRNAs (p Conclusions Using NGS, we showed that they are differentially expressed exosomal miRNAs between MM, EMD and PCL patients suggesting their role in pathogenesis of these diseases. This work was supported by AZV 17-29343A and AZV 18-003-00203.