Prognostication of uveal melanoma patients: are exosomes the solution?

Abstract

Purpose : Uveal melanoma (UM) is the most common primary intraocular malignancy in adults. It is a highly aggressive cancer in which nearly 50% of patients die from liver metastasis. UM patients can be divided into 3 groups based on their genetic profile and disease free survival; the low metastatic risk, intermediate metastatic risk and high metastatic risk tumours. Since tumour tissue is not always available and biopsies are not without risk, it is important to develop a method that can identify high risk patients in a non-invasive manner. Exosomes are an excellent candidate for this application.

Methods : We isolated exosomes from conditioned cell culture medium from non-metastatic and metastatic UM cell lines by ultracentrifugation and an Optiprep density gradient. To confirm the presence of exosomes in our sample, we performed flow cytometry, electron microscopy and Nanosight Tracking Analysis. Subsequently we isolated and analysed the RNA and protein content of the UM exosomes by sequencing, qPCR and mass spectrometry, respectively.

Results : mRNA and cDNA sequencing of exosomal RNA identified UM-specific mutations in EIF1AX, SF3B1 and BAP1. Mass spectrometry analysis of the exosomal surface proteins, did not only identify exosomal markers such as CD81, CD9 and CD63 but also melanocyte-specific proteins such as Melan-A and GP100.

Conclusions : The expression of melanocyte-specific markers on the exosome surface might make it possible to enrich for UM exosomes from blood. Analyzing the genomic content of these exosomes allows us to determine the patients’ metastatic risk. These results highlight the potential of exosomes as non-invasive predictors of disease free survival in UM. Detecting UM-specific mutations in exosomal mRNA derived from plasma, will enable us to provide all UM patients with a prognosis and may also lead to future therapeutic targets.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.