miRNA in Serum and Bone Marrow Plasma Cells From Multiple Myeloma Patients.

Multiple myeloma (MM) is a clonal B-cell malignancy characterized by the aberrant expansion of clonal plasma cells (PCs) within the bone marrow. Malignant PCs produce intact or partial monoclonal immunoglobulin (M protein) and cause organ damage. More than 20,000 new cases of multiple myeloma (MM) are diagnosed every year in the US with approximately 10,700 deaths occurring. The pathogenesis of MM is still largely unclear, but several reports suggest that interaction of tumor cells with the bone marrow microenvironment and microRNAs (miRNAs) deregulation may play a role in the etiology and progression of MM. miRNAs are small non-coding RNAs capable of regulating protein expression by binding to mRNA, and have been implicated in the development of MM. First identified inside cells, miRNAs can also be detected in body fluids, including serum and plasma, and may be a valid biomarker. Few studies have investigated the agreement between circulating miRNAs and intracellular myeloma PC miRNAs at diagnosis.

Using Nano-String nCounter technology we first performed a screening analysis on serum samples obtained from MM patients and healthy controls. We identified a candidate set of miRNAs differentially expressed in the serum of MM patients. The levels of these miRNA markers were validated by RT-PCR in both serum and bone marrow PCs from the same cohort. Agreement of the quantitative miRNA marker levels between sample types was evaluated using intraclass correlation coefficients (ICC) (both for normalized and log2 measures).

Thirty-nine MM patients (21 male, 18 female) with a median age of 72 years (range: 65 – 83) were included in the analysis. Most were ISS stage I or II (59% vs. 41% ISS stage III) and 39% were high risk according to FISH abnormalities – 21% of patients carried del17p, 24% t(4;14) and 5% t(14;16). Medians and ranges for lab markers were as follows: hemoglobin 10.0 g/dl (7.2 to 15.1), beta2-microglobulin 5.18 ug/ml (1.38 – 12.1), creatinine 0.94 mg/dl (0.65 – 2.49), CRP = 1.6 mg/dl (0.02 – 116.0). Nine age-matched healthy controls were also used for the analysis. After the screening analysis, the following miRNAs were differentially expressed between healthy subjects and MM patients in serum samples: miR-92a, miR-451, miR-19b, miR-21, miR-16, miR-25, miR-30a, and miR-126. There was no significant agreement or correlation between serum and myeloma cell samples using either untransformed as well as log₂measures (all p>0.40) (Table 1).

Our preliminary results suggest a difference between circulating miRNAs in myeloma patients from controls. This indicates that future studies are needed to better define the role of miRNAs in the peripheral blood as a prognostic and even diagnostic biomarker in myeloma. From our preliminary data it also appears that circulating miRNAs are not simply secreted into the peripheral blood by myeloma PCs as it seems that circulating miRNAs do not reflect those of myeloma PCs. Differential expression could be determined by other cells that can release and or modify their miRNA expression in response to MM. Ongoing studies are examining the origin and function of miRNAs in the peripheral blood.

No relevant conflicts of interest to declare.