The role of ELTD1/ADGRL4 in tumour angiogenesis


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Koon Hwee Ang1
1University of Oxford

Abstract

Background

ELTD1/ADGRL4, is an orphan adhesion GPCR. ELTD1 is expressed in endothelial and vascular smooth muscle cells but its expression in the tumour vasculature is significantly increased. Our aims were to analyse ELTD1’s function in endothelial cells and breast cancer to explore its potential as an anti-cancer therapeutic target.

Method

Primary human breast cancers (n=245) and matched primary & nodal secondary breast cancers (n=79) were stained for ELTD1. Staining intensity was scored and compared with survival. ELTD1 was expressed in breast cancer cell lines to assess the effect on tumour growth in xenograft experiments and knockout mice were generated with 1) tamoxifen-inducible knockout of Eltd1 in all tissues 2) constitutive Eltd1 knockout in vessels or 3) inducible Eltd1 knockout in vessels. Extracellular vesicles (EV’s) were harvested from ELTD1 expressing cells and their effects assessed in vitro and in vivo.

Results

Human breast cancer staining revealed a higher intensity vascular ELTD1 staining within the tumour stroma compared to normal stroma and ~15% of the tumours had ELTD1 expression within tumour cells. Higher ELTD1 expression in both the tumour stroma vasculature (n=241; HR=0.68; p=0.04) and within the subset of tumour positive cases (n=24; HR=0.3; p=0.02) correlated with improved relapse free survival (RFS). ELTD1 expression in human breast cancer cell lines did not affect proliferation or spheroid growth, but reduction in tumour growth was seen in xenograft models. Tumours grown in the constitutive and inducible Eltd1 knockout mice showed no difference in growth but marked changes in vasculature and necrosis. ELTD1 is incorporated into EV’s. Vesicles isolated from ELTD1 overexpressing breast cancer cell lines and HUVECs were pro-angiogenic in vitro and reduced tumour growth when injected into xenografts.

Conclusion

Eltd1 knockdown affects tumour vasculature, particularly in inducible models suggesting that monoclonal antibodies targeted the calcium binding EGF domain should be considered for further therapeutic development.