Abstract A41: ROR1 is associated with ovarian cancer progression and chemoresistance

Background: New targets for ovarian cancer treatment are critically needed. The Wnt receptors ROR1 and ROR2 are overexpressed in all subtypes of ovarian cancer and appear to play a role in both the tumor and surrounding microenvironment (1). In vitro studies support the approach of targeting these receptors together to inhibit ovarian cancer migration and invasion (2, 3). Aim: To investigate the role of ROR1 and ROR2 in ovarian cancer progression, survival and chemoresistance, to determine their feasibility as therapeutic targets. Methods: Analysis of RNA-Seq data from publicly available ovarian cancer datasets was performed to determine associations with overall survival and platinum resistance. ROR1 IHC using a recently released monoclonal antibody (4A5, BD Bioscience) was performed on a cohort of ovarian cancer patients. ROR1 and/or ROR2 were silenced in a unique preclinical organotypic model of platinum-resistant ovarian cancer metastasis. Results: There is a significant increase (p=0.01) in ROR1 expression in both primary resistant and acquired resistant (p=0.03) high-grade serous ovarian cancer (HGSOC). ROR2 expression is not significantly associated with chemoresistance. High ROR1 (P=0.002, HR 1.93) or high ROR2 (P=0.004, HR 1.9) expression is associated with a significantly shorter overall survival (OS) in the Tothill cohort (4). Patients expressing both high ROR1 and high ROR2 have the shortest OS (P=0.0003, HR 2.38). ROR1 protein expression was detected in 97% of HGSOC patients via IHC, with 59% of HGSOC expressing “high ROR1” (IHC score 2 or 3). Overall, patients with higher-grade tumors expressed significantly higher ROR1 levels (P=0.001) than patients with low-grade tumors. Silencing ROR1 and ROR2 in combination inhibits adhesion and invasion of platinum resistant ovarian cancer in a 3D organotypic coculture model. Conclusion: Our data support targeting both ROR1 and ROR2 as a new approach to treating ovarian cancer. The development of a number of monoclonal antibodies targeting ROR1 and ROR2 that are currently in phase 1 trials for other tumor types makes this clinically feasible in the future. These data also suggest that this may be most effective in the context of HGSOC with platinum resistance. References: 1. Henry CE et al. Distinct patterns of stromal and tumor expression of ROR1 and ROR2 in histological subtypes of epithelial ovarian cancer. Transl Oncol 2017;10(3):346-56. 2. Henry C, Hacker NF, Ford CE. Silencing ROR1 and ROR2 inhibits invasion and adhesion in an organotypic model of ovarian cancer metastasis. Oncotarget 2017;8(68):112727-38. 3. Henry C et al. ROR1 and ROR2 are upregulated in chemoresistant ovarian cancer and promote migration and invasion. Oncogenesis 2016;5(5):doi: 10.1038/oncsis.2016.32. 4. Tothill RW et al. Novel molecular subtypes of serous and endometrioid ovarian cancer linked to clinical outcome. Clin Cancer Res 2008;14(16):5198-208. Citation Format: Dongli Liu, Miya John, Claire E. Henry, Elizabeth L. Christie, David D.L. Bowtell, Kristina Tang, Viola Heinzelmann-Schwarz, Catherine Kennedy, Jessica Boros, Anna DeFazio, Caroline E. Ford. ROR1 is associated with ovarian cancer progression and chemoresistance [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr A41.