Background Uveal melanoma is a poor prognosis cancer. Ergolide, a sesquiterpene lactone
isolated from Inula Brittanica , exerts anti-cancer properties. The objective of this
study was to 1) evaluate whether ergolide reduced metastatic uveal melanoma (MUM)
cell survival/viability in vitro and in vivo ; and 2) to understand the molecular
mechanism of ergolide action. Methods Ergolide bioactivity was screened via long-term
proliferation assay in UM/MUM cells and in zebrafish MUM xenograft models. Mass spectrometry
profiled proteins modulated by ergolide within whole cell or extracellular vesicle
(EVs) lysates of the OMM2.5 MUM cell line. Protein expression was analyzed by immunoblots
and correlation analyses to UM patient survival used The Cancer Genome Atlas (TCGA)
data. Results Ergolide treatment resulted in significant, dose-dependent reductions
(48.5 to 99.9%; p <0.0001) in OMM2.5 cell survival in vitro and of normalized primary
zebrafish xenograft fluorescence (56%; p <0.0001) in vivo , compared to vehicle controls.
Proteome-profiling of ergolide-treated OMM2.5 cells, identified 5023 proteins, with
52 and 55 proteins significantly altered at 4 and 24 hours, respectively ( p <0.05;
fold-change >1.2). Immunoblotting of heme oxygenase 1 (HMOX1) and growth/differentiation
factor 15 (GDF15) corroborated the proteomic data. Additional proteomics of EVs isolated
from OMM2.5 cells treated with ergolide, detected 2931 proteins. There was a large
overlap with EV proteins annotated within the Vesiclepedia compendium. Within the
differentially expressed proteins, the proteasomal pathway was primarily altered.
Interestingly, BRCA2 and CDKN1A Interacting Protein (BCCIP) and Chitinase Domain Containing
1 (CHID1), were the only proteins significantly differentially expressed by ergolide
in both the OMM2.5 cellular and EV isolates and they displayed inverse differential
expression in the cells versus the EVs. Conclusions Ergolide is a novel, promising
anti-proliferative agent for UM/MUM. Proteomic profiling of OMM2.5 cellular/EV lysates
identified candidate pathways elucidating the action of ergolide and putative biomarkers
of UM, that require further examination.
