Abstract
Purpose :
Exosomes secreted from tumors have been suggested as a mean by which tumors prepare their target organs to accept metastases. The purpose of this study was to evaluate the possibility to extract exosomes from frozen archival sera of uveal melanoma patients and to use an exosomal analysis from the first visit as a predictive marker for the metastatic disease.
Methods :
Sera of uveal melanoma patients were collected at the initial visit when uveal melanoma was diagnosed and on every follow-up visit. Samples were separated and kept frozen in (-70) degrees Celsius. Exosomes were extracted from archival sera of the diagnostic visit by a series of ultracentrifugations. The vesicular nature and size of the purified exosomes were confirmed by electron microscopy (EM). Exosomal size, counts, and concentrations were quantified using a Tunable Resistive Pulse Sensing (TRPS) method.
Results :
Twelve samples from patients who developed metastases and twelve who were metastasis-free for over 5 years were analyzed. The exosomes mean size (± SD) was greater in sera from patients who developed metastases (126 ± 23 microns vs. 110 ± 15 microns, respectively, p=0.047). The mean mode size (± SD) was similar between the tested groups (114 ± 15 vs. 105 ± 15 microns, respectively, p=0.13). The mean (± SD) counts were 1.54 E+10 ± 1.76 E+10 particles/mL for the patients who have not developed metastases and 5.81 E+11 ± 1.90 E+12 particles/mL for the patients who developed metastases, with medians of 9.1 E+9 particles/mL and 10 E+9 particles/mL, respectively (p=0.31). There was no correlation between the exosomal count and the time the sera were frozen.
Conclusions :
This preliminary study proved that exosomes can be extracted from archival samples. In sera from the first visit of uveal melanoma patients who developed metastases, there were larger exosomes, but the mode size and counts were similar. The preliminary findings of this study require further analysis in a larger group before this analysis is used as a prognostic test.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.