Abstract 906: Targeting CD166 to overcome platinum resistance in ovarian cancer
Authors: Atwani Rula , Prasad Mayuri , Sandusky George E , Condello Salvatore 
Published: June 2022

Abstract
Background: Ovarian cancer (OC) is the most lethal gynecological cancer, characterized by chemoresistance and fatal tumor recurrence after primary treatment. The development of intra-peritoneal metastases is correlated with the formation of multicellular spheroids by OC cells disseminated in the peritoneal fluid. Within a spheroid, OC cells undergo an epithelial-to-mesenchymal transition (EMT), which involves changes in the expression of cell adhesion molecules (CAMs) and acquisition of cancer stem cell (CSC) characteristics, therefore protecting OC cells during chemotherapy. Cluster of differentiation 166 (CD166) is one of the CAMs involved in tumor progression and its modulation impacts cell-cell adhesion, leading to impaired ability of tumor cells to metastasize. However, limited number of studies are available on the functional role of CD166 in the initiation, progression, and chemoresistance of OC. Our goal was to investigate the contribution of CD166 in supporting chemoresistance and the tumorigenic OCSC phenotype, thus proposing this molecule as a potential new therapeutic target in OC.
Methods: We compared CD166 expression in primary OC cells grown as spheroids and monolayers and in chemoresistant versus sensitive OC cell lines by q-PCR and Western Blot (WB). CD166 blockade by shRNA knockdown (KD) or anti-CD166 inhibitory antibody (clone AZN-L50) was evaluated on spheroid assay and colony formation. Combinatorial carboplatin and AZN-L50 treatment was assessed on spheroid assays and by WB of pro-apoptotic proteins. Chromatin immunoprecipitation (ChIP) assay detected the interaction between the β-catenin and the CD166 promoter.
Results: OC cells grown as spheroids showed a significant increase in CD166 expression compared to monolayers. Our results also demonstrated an increase in CD166 expression levels in chemoresistant OC cell lines when compared to the chemosensitive counterpart. A comparison of normal adjacent ovarian epithelium, localized, and metastatic OC tissues on a multitissue array revealed that CD166 expression coincided with an advanced promigratory phenotype (n=88, P&lt;0.001), correlating with poor outcome. CD166 blockade by either shRNA-mediated KD or AZN-L50 treatment in combination with carboplatin led to a significant decrease in the expression levels of stemness-related genes, spheroid and colony formation. The combination of carboplatin and CD166 blockade increased cleaved-PARP and -caspase-3 levels compared to single agent alone, indicating sustained DNA damage. Mechanistically, β-catenin-KD decreased CD166 expression levels and β-catenin coimmunoprecipitated with the CD166 promoter, suggesting that CD166 is a direct β-catenin target.
Conclusions: CD166 is strongly linked to chemoresistance and is regulated by the oncogenic β-catenin pathway. Our data suggest that inhibition of CD166 along with carboplatin treatment could be a potential combination therapy in OC.
Citation Format: Rula Atwani, Mayuri Prasad, George E Sandusky, Salvatore Condello. Targeting CD166 to overcome platinum resistance in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 906.