Abstract #181: Identification and characterization of serous ovarian cancer-initiating cells
Authors: Jocelyn Stewart, Patricia Shaw, James Greenaway, Barry Rosen, Benjamin Neel
Journal: Cancer Research (2009)

Serous ovarian cancer (SOC) patients typically present with advanced disease. Current therapy increases overall survival, yet the majority of patients (70-90%) recur within five years and die of their disease. The cancer-initiating cell (CIC) hypothesis holds that only a subset of cells within tumors have the potential to extensively self-renew and give rise to other tumor cells. Because their properties may differ from bulk tumor cells, CIC might be spared by available therapies. Previous reports suggest the presence of CIC in human/murine ovarian cancer, but these findings remain to be validated in multiple primary human samples. Identification and characterization of CIC may lead to more effective therapeutic strategies for SOC. Primary SOC samples were mechanically/enzymatically dissociated and depleted of CD45+ leukocytes. The expression of cell surface (CD133, CD44, CD117, CDCP1, MUC-1, VEGFR2) and functional (ALDH1) markers was examined by flow cytometry on 70 samples (tumor and ascites). All markers demonstrated intra-/inter-tumoral heterogeneity; however, only CD133, VEGFR2 and ALDH marked minority populations present in all samples. Notably, in contrast to a recent report that CD44+/CD117+ cells contain ovarian CIC, CD117 is present on only half of all SOC samples examined (n=60) and only one quarter have a CD44+/CD117+ population. Concomitantly, we tested four injection sites (ovarian bursa, intraperitoneal, mammary fat pad and renal capsule) for their ability to support the growth of 10 6  tumor cells and to recapitulate primary tumor histology. The fat pad was superior based on tumor take (94%) and the shorter time to tumor palpation (4-6 weeks) and was therefore used for all other experiments. Limiting dilution analysis for each primary sample estimated the bulk CIC frequency to be ~1/40,000 (n=10). The CIC frequency was estimated to be significantly higher (~1/6,000) in palliative ascites from treated patients (n=9, p=0.02), suggesting that CIC may be enriched after chemotherapy; however, this must be tested in matched samples. Xenografts could be passaged at least three times, providing evidence of self-renewal. In addition, samples sorted for CD133, VEGFR2 or ALDH1 demonstrated CIC enrichment, although to variable degrees. Initial data indicate that CD133+ cells from both primary tumors and ascites are enriched for CIC (1/500-1/1500; 4-50 fold enrichment). VEGFR2+ and ALDH1+ were also enriched for CIC, although enrichment appears to be far less than observed for CD133. We also find evidence for a hierarchy in three syngeneic, mouse ovarain surface epithelial cell (MOSEC) models of ovarian cancer. In conclusion, our data indicate a tumor hierarchy in SOC that is consistent with the CIC hypothesis. VEGFR2, ALDH1 and in particular, CD133 enrich for CIC in all cases examined. If, as reported, CD44+/CD117+ enriches for CIC in some SOC, there must be different subtypes of SOC with phenotypically distinct CIC.   Citation Information:  In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 181.