Abstract A71: Expression of Sushi Domain Containing 2 (SUSD2) in high-grade ovarian serous carcinoma correlated with increased longevity of patients

Abstract

Abstract Despite research in therapeutic strategies, ovarian cancer (OvCa) remains the most lethal gynecologic malignancy. The anatomical location of the ovaries within the peritoneal cavity facilitates metastasis by allowing tumor cells sloughed from the main tumor on the ovary to bind to the peritoneum or organs within the peritoneal cavity. These tumor cells are released from the main tumor either as single cells or as spheroids, the latter of which have been shown to be more effective at metastasizing and invading into the mesothelial lining. To identify novel tumor markers and therapeutic targets for epithelial cancers, a cDNA library enriched for cancer genes that encode membrane and secreted proteins was generated. The 18th most abundant gene represented in this library was Sushi Domain Containing 2 (SUSD2), which encodes an 822 amino acid membrane surface protein. To begin defining the role of SUSD2 in OvCa, stable SUSD2-expressing and vector control A2780 cell lines were generated. To examine whether SUSD2 affects the growth of OvCa cells, cellular proliferation assays were performed. There was no significant difference in growth rates with SUSD2 over-expression compared to the vector control cell lines. A Boyden chamber assay was performed to analyze the effect of SUSD2 on cell migration. A2780-SUSD2 cell lines and vector-only controls were plated on membranes and allowed to migrate toward a chemoattractant in a lower chamber. SUSD2 over-expression significantly increased migration by greater than 2-fold. In addition, a scratch wound-healing assay was performed, and after 24 hours the A2780-SUSD2 cell line had 2-fold more cells within the wound compared to the A2780-vector control cells (P<0.05). Consistently, agarose beads containing either A2780-SUSD2 or vector cells were grown in chemoattractant containing media. The distance the escaped cells traveled from the bead was measured. A2780-SUSD2 cells traveled farther away from the bead compared to the vector control (717 μm compared to 125 μm, respectively, P<0.05). Spheroid-forming ability was analyzed, and A2780-SUSD2 cells formed smaller and looser spheroids (length and width average of 933 μm) compared to A2780-vector control cells (length and width average of 1237 μm, P=0.025). To correlate OvCa patient outcome with the presence of SUSD2 in the corresponding tumor, a tissue microarray containing high-grade ovarian serous carcinoma core samples from 128 patients was stained with an anti-SUSD2 antibody. The intensity of SUSD2 staining was scored by a pathologist, and results were correlated with patient outcome. A Kaplan-Meier curve indicated a significant separation for patients with low SUSD2 levels, median survival 31.7 months, versus patients with strong SUSD2 staining, median survival 49.1 months (P=0.0083). This data suggests that low SUSD2 levels in OvCa tumors are associated with a poorer prognosis for the patient. Our in vitro assays indicate that expression of SUSD2 in A2780 cells increased the ability of the cells to migrate and caused the formation of smaller spheroids. Because spheroids are better able to resist chemotherapy and invade the mesothelium, the decreased spheroid size of SUSD2-expressing cells may allow for a better patient prognosis. Citation Format: Jennifer A. A. Gubbels, Elizabeth M. Hultgren, Jessica Johnson, Emily Johnson, Jeffrey Sachs, Michelle S. Hirsch, Joyce Liu, Ronny Drapkin, Kristi A. Egland. Expression of Sushi Domain Containing 2 (SUSD2) in high-grade ovarian serous carcinoma correlated with increased longevity of patients. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr A71.