Abstract 584: Doppel, an exosome mediated biomarker specific to tumor endothelial cells
Authors: Kim Byoungmo , Lee Ha Kyeong , Byun Youngro , Hwang Seung Rim , Kim Sang Yoon 
Published: April 2023

Abstract
The difficulty of finding a biomarker that is both specific and ubiquitous in cancer presents a barrier to targeted drug delivery. Some tumor-associated antigens are also found in normal tissue and contribute to “on-target toxicities”. Tumors are also heterogenous and plastic in nature, thus biomarkers often represent only a subset of the tumor cells. Despite such heterogenicity, however, all cancers share functional characteristics in order to support its rapid growth. One such example is angiogenesis. The endothelium itself is also a heterogenous, variable population of cells sharing the same function. This is in part because it is heavily affected by its surroundings and the cells that it supports. In particular, because of the heavy burden placed upon it, tumor-associated blood vessels and their endothelium have unique morphologies and transcription profiles. Previous studies have identified Doppel, a membrane protein that is expressed only in tumor tissues and in particular tumor blood vessels, but not in normal adult tissues (except the testis). Further studies showed that the expression of Doppel promoted blood vessel development and that the inhibition of Doppel led to the suppression of angiogenesis. Considering Doppel’s role in angiogenesis and its localization in both tumor and tumor-associated endothelial cells, we hypothesized that exosomes are responsible for the transfer of Doppel from tumor cells to nearby blood vessels, converting normal endothelial cells to pathological tumor endothelial cells. In order to prove this experimentally, exosomes were isolated from the conditioned media of HCT116 human colon cancer cell line via ultracentrifugation and size exclusion chromatography (HCT116 exosomes). Isolated exosomes were characterized with nanoparticle tracking analysis, western blot, and Transmission Electron Microscopy. Western blot and nano-flow cytometry revealed that HCT116 exosomes express Doppel on its surface. HUVEC cells incubated with HCT116 exosomes express higher levels of Doppel when analyzed with flow cytometry and western blot. Live-cell confocal imaging with fluorescently labeled HCT116 exosomes shows internalization of Doppel-expressing exosomes. Finally, HUVEC cells co-cultured with HCT116 cells show higher expression of Doppel. This is meaningful because it sheds light on the mechanism behind angiogenesis in cancer and hints at Doppel’s potential as both a diagnostic marker and a druggable target specific to the tumor endothelium. Targeting the tumor endothelium is advantageous because it reflects a common need of all tumors and because of its proximity to the bloodstream. An antibody-drug conjugate to Doppel is already in the early stages of development.
Citation Format: Byoungmo Kim, Ha Kyeong Lee, Youngro Byun, Seung Rim Hwang, Sang Yoon Kim. Doppel, an exosome mediated biomarker specific to tumor endothelial cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 584.