Abstract POSTER-BIOL-1345: SUSD2 inhibits spheroids from breaching the mesothelium: a mechanism for increased longevity of patients with SUSD2-expressing high-grade ovarian serous carcinoma

Abstracts: 10th Biennial Ovarian Cancer Research Symposium; September 8-9, 2014; Seattle, WA The cause of death among the majority of epithelial ovarian cancer (EOC) patients involves metastasis and subsequent invasion of cancer cells into organs enclosed and adjacent to the abdominal cavity, which can lead to deadly health complications such as bowel obstruction. Thus, it is important to identify the factors that contribute to metastasis and invasion including those that facilitate adhesion to the mesothelium. The anatomical location of the ovary and the fallopian tube within the peritoneal cavity facilitates metastasis of ovarian cancer without involvement of the vasculature. EOC cells exfoliate from the fallopian tube or ovary, disseminate within the peritoneal cavity as free-floating single cells or spheroids and invade mesothelium-covered organs including the bowel. To identify potential immunotherapy targets for epithelial cancers, we generated a cDNA library enriched with genes encoding membrane and secreted proteins that are highly expressed in cancer with minimal expression in normal essential tissues. From this library we identified Sushi Domain Containing 2 (SUSD2), a type I transmembrane protein that localizes to the cell surface and contains several functional domains inherent to adhesion molecules. To determine the expression pattern of SUSD2 in normal and carcinoma ovarian tissues, an immunohistochemical analysis was performed on ovarian tissue samples from patients using an anti-SUSD2 antibody. Weak to no staining was observed in normal epithelial cells. In contrast, various intensities of positive staining for SUSD2 were observed in several types of EOC, including serous, mucinous, endometrioid and transitional adenocarcinomas. A high-grade serous ovarian carcinoma (HGSOC) tissue microarray containing samples from 128 patients was stained with an anti-SUSD2 antibody. A pathologist scored the intensity of SUSD2 staining, and results were correlated with patient outcome. A Kaplan-Meier curve indicated a significant separation for patients with weak SUSD2 staining, median survival 31.7 months, versus patients with strong SUSD2 staining, median survival 49.1 months (p-value = 0.0083). This data suggests that low SUSD2 levels in HGSOC tumors are associated with a poorer prognosis for the patient. To investigate the role of SUSD2 in HGSOC, stable SUSD2 knock-down (KD) and non-targeting (NT) OVCAR3 cell lines were generated. Boyden chamber and wound healing assays were used to assess the effect of SUSD2 on migration. OVCAR3 SUSD2-KD cells migrated at significantly higher rates than the OVCAR3-NT cells suggesting that the presence of SUSD2 in OVCAR3 cells inhibits cell migration. In addition, attenuation of SUSD2 levels in OVCAR3 cells significantly increased mesothelial clearance. Altogether, our findings indicate that SUSD2 negatively impacts the ability of OVCAR3 cells to breach the mesothelium, which defines a mechanism for the increased longevity of patients with SUSD2-expressing HGSOC. Citation Format: Jordan N. Sheets, Marcin Iwanicki, Joyce Liu, Ronny Drapkin, Kristi A. Egland. SUSD2 inhibits spheroids from breaching the mesothelium: a mechanism for increased longevity of patients with SUSD2-expressing high-grade ovarian serous carcinoma [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1345.