Development of Novel Models to Study Ovarian Cancer Stem Cells.

Abstract

Cancer stem cells (CSC) are rare cells within a tumor reported to be resistant to standard chemotherapy, which can serve to populate the bulk of a tumor with more differentiated daughter cells and potentially contribute to recurrent disease and metastasis. A better understanding of ovarian CSC could lead to novel therapeutic approaches to specifically target CSC. We developed two in vivo models for the study of ovarian CSC. We first generated a human embryonic stem cell derived teratoma (hESCT) tumor model, creating a human tumor microenvironment for CSC growth. We demonstrate that unlike other tumor models, this model has human tumor vessels, a critical part of the CSC niche. These vessels express tumor vascular specific markers (TVMs). We showed the ability of the hESCT model, with human tumor vascular niche, to enhance the engraftment rate of primary human ovarian cancer stem-like cells. Furthermore, this model can be used to test anti-human specific TVM immunotherapeutics. Unfortunately, the study of human CSC can be hampered by heterogeneity of primary tumor samples, long requirements for tumor growth in vivo, and the need for tumor growth in immune-deficient mice. We therefore evaluated CSC in a transgenic murine model of ovarian cancer. Using flow cytometry to characterize a cell line derived from this tumor model we identified that CD24+ cells have a enhanced ability to form tumor spheres, to passage, and to initiate tumors in vivo; hallmarks of CSC. CD24+ cells preferentially express stem cell markers Nanog and c-myc and demonstrate preferential phosphorylation of STAT3. Suggesting an important role for STAT3 in CD24+ CSC, CD24+ cells were preferentially sensitive to inhibition of STAT3 phosphorylation with the JAK2 inhibitor TG101209. Finally, in vivo therapy with TG101209 appeared to decrease tumor metastasis and combined with chemotherapy, prolonged overall survival. Furthermore, preliminary data suggests a role of CD24+ cells in tumor migration. Combined we have characterized two distinct models for the characterization of ovarian CSC targeted therapeutics.