Program: Oral and Poster Abstracts
Session: 652. Myeloma: Pathophysiology and Pre-Clinical Studies, excluding Therapy: Poster I
Methods: Liquid Chromatography Mass Spectrometry (MS) and Label-free relative quantitation were used to assess the protein content of MM EV and cellular lysates. Cryo-Transmission Electron Microscopy (cryo-TEM) and Nanoparticle Tracking Analysis were used to assess size distribution and specific EV surface markers in EV isolated from the supernatant of MM cell lines and from the serum of non-cancer, MGUS, smoldering MM and active MM donors. Western blot and enzyme-linked immunosorbent assays were used to validate MS data in a bigger cohort of primary MM patients and to assess the biological effect of MM derived EV in the BM stromal cells.
Results: Our data show that the Major Histocompatibility Complex Class I (MHCI) and its associated binding protein β2-microglobulin (β2-MG) are the most abundant communally enriched proteins in the EV derived from MM cell lines and from the serum of MM patients. Although it is well known that the serum level of β2-MG is an important prognostic factor in MM, our data indicate that β2-MG represents only a small percentage of the total serum β2-MG, suggesting that two separate β2-microglobulin populations coexist in the serum of patients. Additionally, we show that the main receptor of hyaluronic acid, CD44, is highly expressed in the EVs isolated from the corticosteroid resistant MM cell line, MM.1R, and is a protein that is differentially expressed in EVs isolated from newly diagnosed MM patients and which seems to play a key role in communicating with the BM microenvironment. By using a large cohort of serum obtained from MM patients prospectively treated on a randomized phase 3 trial (233), we establish the potential of serum CD44 as a predictive biomarker of overall survival. These results support the analysis of EVs as easily accessible MM biomarker.
Conclusions: Our results generate a foundation for the potential use of circulating EVs as novel serum markers of MM and provide the rationale to further explore previously unconsidered molecular players associated with MM disease.
Disclosures: Palumbo: Array BioPharma: Consultancy ; Onyx Pharmaceuticals: Consultancy ; Millennium Pharmaceuticals Inc., a wholly owned subsidiary of Takeda Pharmaceutical Company Limited: Consultancy , Honoraria ; Janssen-Cilag: Consultancy , Honoraria ; Genmab A/S: Consultancy ; Bristol-Myers Squibb: Consultancy ; Amgen: Consultancy ; Sanofi Aventis: Consultancy .
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