Abstract 1376: Identification of selective inhibitors of ovarian cancer stem cells by high-throughput screening
Authors: Ertem Server Adil , Zehir Ahmet , Moore Malcolm AS 
Published: June 2012

Metastasis of cancer cells into the peritoneal cavity is a clinical manifestation of advanced-stage ovarian cancer and is associated with poor survival.

We have identified a novel cellular structure consisting of a chain of 4-72 cells with a pericellular glycocalyx, free-floating in the ascites of NOD/SCIDIL2Rγ-/- mice with intraperitoneal human serous ovarian adenocarcinoma (OvCa) xenografts. We have termed these “catenae” (Latin for “chains”). Catenae develop clonally and are exclusively composed of stem cells since a single catena cell forms intraperitoneal tumor. We can expand catenae in vitro (∼10,000 fold in 7-9 days) for prolonged periods with all cells retaining CSC function. To our knowledge, this is the first report to show isolation of a homogeneous population of CSC, that can be expanded extensively in vitro without differentiation, yet retain the capacity to fully differentiate to all cellular components of the original tumor.

At high cell density, catenae develop into spheroids by a process of “rolling up”. Spheroids contain ∼10% CSC while epithelial and mesenchymal tumor monolayers have 1–5% CSC.

By gene expression and proteomics analysis we have identified hyaluronan and collagen as major components of the protective glycocalyx. Catena with its intact pericellular coat represents a unique in vitro system that is more relevant to the clinical setting than conventional high throughput screening (HTS) methods. We have adapted the catena and spheroid system for HTS for identification of compounds that specifically inhibit CSC by inducing apoptosis, proliferation inhibition or differentiation. This HTS method allows rapid assessment of the effectiveness of a test compound against ovarian cancer stem cell existing in different cellular entities (catena, spheroids or monolayers).

We have shown that CSC drug sensitivity is context dependent. Ovarian CSCs (catenae) with an established protective glycocalyx were significantly more resistant to all compounds tested when compared to epithelial or mesenchymal ovarian cancer monolayer cells. The drug resistance of catenae was more pronounced with microtubule stabilizers such as Paclitaxel, 9,10-dEpothiloneB and Fludelone (up to 8,000,000-folds). Disruption of the glycocalyx by PEGylated hyaluronidase and PEGylated collagenase enzymes overcame this resistance. In some cases, spheroids formation conferred an additional 10-fold resistance.

The glycocalyx and catena-spheroid transition provide mechanisms for resistance to small molecule, antibody and immune cell-mediated killing. This may explain the incurable nature of advanced stage ovarian cancer. The catena model can be used for identification and validation of novel therapeutics that target the CSC. Our results suggest that combination therapies of PEGylated hyaluronidase, PEGylated collagenase and chemotherapeutic agents could be effective in treatment of ovarian cancer.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1376. doi:10.1158/1538-7445.AM2011-1376