PO-459 Unravelling endoglin as a potential therapeutic target for the treatment of uveal melanoma

Introduction Uveal Melanoma(UM) is a rare deadly tumour where, despite highly aggressive management of the primary disease, approximately 50% of patients develop metastases. Therapies directed towards systemic/metastatic disease have failed in the clinic.Endoglin (ENG),a co-receptor of TGF-β,plays an important role in tissue remodelling and cancer.A soluble form is produced upon proteolytic cleavage by matrix metalloprotease MMP14.Our work focuses on the role of ENG/MMP14, how they influence UM metastasis, and their potential as therapeutic targets. Material and methods Normalised gene expression data with patient follow-up from 80 primary UM tumours was downloaded from The Cancer Genome Atlas (TCGA) NIH Data Portal.mRNA/protein from UM and Ewing Sarcoma cell lines were isolated, and ENG/MMP14 levels were evaluated by q-RT-PCR/western blot. Immunohistochemistry analysis of ENG/MMP14 expression was performed in 2 independent patient cohorts.MTT assays were performed to evaluate proliferation inhibition after exposure to OMTX503 anti-ENG Antibody Drug Conjugate (ADC).CRISPR technology with high fidelity Cas9 was used to knockout MMP14/ENG, which was validated by mismatch-cleavage assays and by the loss of protein expression. Results and discussions Bioinformatics analysis showed that a higher expression of ENG correlated with worst disease-free survival (DFS)(p=0.00023), whereas MMP14 showed a similar trend without reaching statistical significance(p=0.077).These results differ from skin melanoma DFS(p=0.74 for ENG,p=0.22 for MMP14).Pathway enrichment analysis showed that higher ENG expression is associated with a higher abundance of CD8 + T-cells (p In vitro , cell line MUM2B expressed higher levels of ENG/MMP14.UM cell lines were highly sensitive to treatment with ADC OMTX503, with IC50 in the sub-nM range.Sensitivity was dependent on ENG expression.Knockout of MMP14 resulted in lack of protein expression in the single cell derived clones.The effect on ENG shedding and malignant features upon lack of MMP14 is currently being analysed. Conclusion ENG/MMP14 are expressed in UM cell lines and in patient tumour samples.Results suggest that higher levels of ENG are associated with a more aggressive phenotype.ENG is an attractive target, and ENG-targeting biologics such as OMTX503 show promising in vitro activity.In-depth evaluation of the role of ENG/MMP14 in UM is ongoing.