Background: Several studies have demonstrated that aberrant expression of microRNAs in multiple myeloma (MM) cells is associated with the pathogenesis and development of MM. Recently, circulating serum microRNAs have been recognized as novel biomarkers in tumor biology and have predictive value in determining the efficacy of various drugs. However, little is known regarding the role of circulating serum microRNAs in patients with MM in terms of MM biology and the clinical efficacy of anti-MM drugs. In this study, we evaluated the expression levels of serum microRNAs in patients with MM, including newly diagnosed (ND) and relapsed and/or refractory (RR) cases. We also evaluated the correlation of the expression levels of serum microRNAs with the clinical efficacy of bortezomib (BTZ)-containing treatment.
Materials & Methods: Fifteen serum samples from healthy donors and 62 from 10 patients with NDMM and 52 patients with RRMM were collected and subjected to comprehensive microRNA analysis using next-generation sequencing (NGS). First, we compared the microRNA expression levels between healthy donors and patients with MM. Next, using 52 serum samples collected from patients with NDMM and RRMM who received BTZ plus low-dose dexamethasone (Bd) therapy, the correlation between the response to Bd therapy and specific serum microRNA expression profiles was determined.
Results: Approximately 150-250 microRNAs were detected by small RNA analysis of serum samples using NGS. The expression levels of 32 serum microRNAs were higher in MM than in healthy donors (Mann-Whitney U test, P < 0.05). Among them, 5 microRNAs (mir-10a, 10b, 92a, 378a, and 378d) had higher expression in RRMM than in NDMM. These microRNAs are involved in the biology and oncogenesis of several solid tumors, including MM. The mir-92a expression level has been associated with the response to chemotherapy and disease progression in MM.
Regarding the correlation between microRNA expression levels and the clinical efficacy of Bd therapy, expression levels of 14 microRNAs were associated with progression-free survival (PFS) in Bd therapy (Spearmanfs rho < -0.2, P < 0.05). Among them, 5 microRNAs (mir-22, 146a, 193b, 584, and 1307) showed high correlation with PFS (Spearmanfs rho < -0.4, P < 0.002). These microRNAs are involved in angiogenesis, proliferation, and apoptosis in several solid tumors and MM. Next, we divided the 52 samples into two groups according to PFS: short (<6 months; n = 27) or long (≥6 months; n = 25). The short-PFS group showed lower expression of 5 microRNAs (mir-22, 146a, 193b, 320b, and 320c) than the long-PFS group did (Mann-Whitney U test, P < 0.01).
Among them, mir-146a can regulate TRAF6, NF-kB, and TNF-axis, and is regulated by the c-Myc at the transcriptional level. c-Myc-mediated mir-146a overexpression can reduce CXCR4 expression. Several studies suggest that CXCR4 expression is an important factor for MM cells to migrate and interact with stromal cells; lower expression is recognized as a poor prognostic factor in the survival of patients with MM. Therefore, we hypothesized that BTZ-insensitive clone has high mir-146a expression along with low CXCR4 expression, suggesting that low dependence on stromal cells may contribute to the resistance to BTZ activity.
Conclusion: We have demonstrated that the expression levels of several serum microRNAs are associated with the progression of MM and may serve as predictive markers in BTZ-containing therapies in MM. Further validation studies in a larger number of patients is needed and the origin of these serum microRNAs, together with the functional consequences of aberrant expression, must be pursued. Our findings can contribute in developing circulating microRNA analysis as a potential strategy in determining useful biomarkers for diagnosis and therapeutic outcomes in MM.
Ishida:Celgene KK: Research Funding; Kyowa Hakko Kirin, Co., Ltd.: Honoraria, Research Funding; Bayer Pharma AG: Research Funding. Iida:Celgene: Honoraria, Research Funding; Janssen Pharmaceuticals: Honoraria, Research Funding.
Asterisk with author names denotes non-ASH members.