Evidence is accumulating that solid tumors contain a rare phenotypically distinct population of cells, termed cancer stem cells (CSC), which give rise to and maintain the bulk of the tumor. These CSC are thought to be resistant to current chemotherapeutic strategies due to their intrinsic stemlike properties and thus may provide the principal driving force behind recurrent tumor growth. Given the high frequency of recurrent metastasis associated with human ovarian cancer, we sought to determine whether primary human ovarian tumors contain populations of cells with enhanced tumor-initiating capacity, a characteristic of CSC. Using an in vivo serial transplantation model, we show that primary uncultured human ovarian tumors can be reliably propagated in NOD/SCID mice, generating heterogeneous tumors that maintain the histological integrity of the parental tumor. The observed frequency of tumor engraftment suggests only certain subpopulations of ovarian tumor cells have the capacity to recapitulate tumor growth. Further profiling of human ovarian tumors for expression of candidate CSC surface markers indicated consistent expression of CD133. To determine whether CD133 expression could define a tumor-initiating cell population in primary human ovarian tumors, fluorescence-activated cell sorting (FACS) methods were employed. Injection of sorted CD133 1 and CD133 2 cell populations into NOD/SCID mice established that tumor-derived CD133 1 cells have an increased tumorigenic capacity and are capable of recapitulating the original heterogeneous tumor. Our data indicate that CD133 expression defines a NOD/SCID tumor initiating subpopulation of cells in human ovarian cancer that may be an important target for new chemotherapeutic strategies aimed at eliminating ovarian cancer.

BackgroundRecent data provide significant evidence to support the hypothesis that there are sub-populations of cells within solid tumors that have an increased tumor initiating potential relative to the total tumor population. CD133, a cell surface marker expressed on primitive cells of neural, hematopoietic, endothelial and epithelial lineages has been identified as a marker for tumor initiating cells in solid tumors of the brain, colon, pancreas, ovary and endometrium. Our objectives were to assess the relative level of CD133 expressing cells in primary human endometrial tumors, confirm their tumorigenic potential, and determine whether CD133 expression was epigenetically modified.MethodsWe assessed CD133 expression in primary human endometrial tumors by flow cytometry and analyzed the relative tumorigenicity of CD133+ and CD133- cells in an in vivo NOD/SCID mouse model. We assessed potential changes in CD133 expression over the course of serial transplantation by immunofluorescence and flow cytometry. We further examined CD133 promoter methylation and expression in normal endometrium and malignant tumors.ResultsAs determined by flow cytometric analysis, the percentage of CD133+ cells in primary human endometrial cancer samples ranged from 5.7% to 27.4%. In addition, we confirmed the tumor initiating potential of CD133+ and CD133- cell fractions in NOD/SCID mice. Interestingly, the percentage of CD133+ cells in human endometrial tumor xenografts, as evidenced by immunofluorescence, increased with serial transplantation although this trend was not consistently detected by flow cytometry. We also determined that the relative levels of CD133 increased in endometrial cancer cell lines following treatment with 5-aza-2'-deoxycytidine suggesting a role for methylation in the regulation of CD133. To support this finding, we demonstrated that regions of the CD133 promoter were hypomethylated in malignant endometrial tissue relative to benign control endometrial tissue. Lastly, we determined that methylation of the CD133 promoter decreases over serial transplantation of an endometrial tumor xenograft.ConclusionsThese findings support the hypotheses that CD133 expression in endometrial cancer may be epigenetically regulated and that cell fractions enriched for CD133+ cells may well contribute to endometrial cancer tumorigenicity, pathology and recurrence.

Background: Pre-clinical studies have demonstrated that natural and synthetic histone deacetylase (HDAC) inhibitors can impede the in vitro and in vivo growth of cell lines from a variety of gynecologic and other malignancies. We investigated the anti-tumor activity of panobinostat (LBH589) both in vitro and in vivo as either a single agent or in combination with conventional cytotoxic chemotherapy using patient-derived xenograft (PDX) models of primary serous ovarian tumors. Methods: The ovarian cancer cell lines OVCAR8, SKOV3 and their paclitaxel-resistant derivatives OVCAR8-TR and SKOV3-TR were treated with increasing doses of LBH589. The effect of LBH589 on cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Serially transplanted primary human high-grade serous ovarian adenocarcinoma tissue was utilized to generate xenografts in 6-week old female NOD/ SCID mice. The mice were then randomized into one of 4 treatment groups: (1) vehicle control; (2) paclitaxel and carboplatin (P/C); (3) LBH589; or (4) P/C + LBH589. Mice were treated for 21 days and tumor volumes and mouse weights were obtained every 3 days. These experiments were performed in triplicate with three different patient derived tumors. Wilcoxan rank-sum testing was utilized to assess tumor volume differences.