Monitoring multiple myeloma through tumor-derived exosomes

Tumor-derived exosomes (TDEs) play a pivotal role in tumor establishment and progression, and are emerging biomarkers for tumor diagnosis in personalized medicine. To date, there is a lack of efficient technology platforms for exosome isolation and characterization. Multiple myeloma (MM) is an incurable B-cell malignancy due to the rapid development of drug-resistance. MM-released exosomes express the immunoglobulin B-cell receptor (Ig-BCR) of the tumor B-cells, which can be targeted by Idiotype-binding peptides (Id-peptides).

In this study, researchers at Magna Græcia University analyzed the production of MM-released exosomes in the murine 5T33MM multiple myeloma model as biomarkers of tumor growth. To this end, they selected Id-peptides by screening a phage display library using as bait the Ig-BCR expressed by 5T33MM cells. By FACS, the FITC-conjugated Id-peptides detected the MM-released exosomes in the serum of 5T33MM-engrafted mice, levels of which are correlated with tumor progression at an earlier time point compared to serum paraprotein. These results indicate that Id-peptide-based recognition of MM-released exosomes may represent a very sensitive diagnostic approach for clinical evaluation of disease progression.

Workflow of the experimental design

exosomes

The Igs secreted by 5T33MM cells were purified from cell supernatant using Protein G affinity chromatography, and used as bait to isolate phage ligands from the C7C phage-displayed peptide library fused to the M13 minor coat protein. ELISA was performed to select ligands with distinct affinities for their cognate Ig-BCR. Synthetic peptides corresponding to the peptide insert of phage clones were assayed for their antigenic properties out of the phage context. The purified 5T33MM-released exosomes were characterized by scanning electron microscopy (SEM), Zetasizer and Western blotting analysis. SMNPs were decorated with biotinylated anti-CD63, incubated with RED-EXO-labeled exosomes, and analyzed for the binding of FITC-conjugated Id-peptides by flow cytometry. For in vivo analysis, 5T33MM cells (1 × 106) were intravenously injected in C57BL/KaLwRij mice (10 females at 8 weeks of age). Tumor-derived exosomes and paraprotein levels in peripheral blood were monitored every 7 days up to 35 days post-inoculation

Iaccino E, Mimmi S, Dattilo V, Marino F, Candeloro P, Di Loria A, Marimpietri D, Pisano A, Albano F, Vecchio E, Ceglia S, Golino G, Lupia A, Fiume G, Quinto I, Scala G. (2017) Monitoring multiple myeloma by idiotype-specific peptide binders of tumor-derived exosomes. Mol Cancer 16(1):159. [article]

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