Identification and Characterization of Ovarian Cancer-Initiating Cells from Primary Human Tumors

TLDR

The study aimed to identify and characterize a self‑renewing subpopulation of human ovarian tumor cells (OCICs) capable of serially propagating the original tumor phenotype in animal models. Researchers isolated spheroid‑forming cells from serous adenocarcinomas, cultured them under stem‑cell selective conditions, performed immunostaining for CD44 and CD117, and assessed tumorigenicity via xeno‑engraftment, proliferation assays, and RT‑PCR. Only 100 spheroid or CD44⁺CD117⁺ cells formed tumors, whereas more than 10⁵ unselected or CD44⁻CD117⁻ cells did not, and OCICs displayed enhanced chemoresistance and up‑regulated stem‑cell markers, indicating that epithelial ovarian cancers arise from a CD44⁺CD117⁺ subpopulation that may be a therapeutic target. Cancer Research 2008;68(11):4311–20.

Abstract

Abstract The objective of this study was to identify and characterize a self-renewing subpopulation of human ovarian tumor cells (ovarian cancer-initiating cells, OCICs) fully capable of serial propagation of their original tumor phenotype in animals. Ovarian serous adenocarcinomas were disaggregated and subjected to growth conditions selective for self-renewing, nonadherent spheroids previously shown to derive from tissue stem cells. To affirm the existence of OCICs, xenoengraftment of as few as 100 dissociated spheroid cells allowed full recapitulation of the original tumor (grade 2/grade 3 serous adenocarcinoma), whereas >105 unselected cells remained nontumorigenic. Stemness properties of OCICs (under stem cell–selective conditions) were further established by cell proliferation assays and reverse transcription–PCR, demonstrating enhanced chemoresistance to the ovarian cancer chemotherapeutics cisplatin or paclitaxel and up-regulation of stem cell markers (Bmi-1, stem cell factor, Notch-1, Nanog, nestin, ABCG2, and Oct-4) compared with parental tumor cells or OCICs under differentiating conditions. To identify an OCIC cell surface phenotype, spheroid immunostaining showed significant up-regulation of the hyaluronate receptor CD44 and stem cell factor receptor CD117 (c-kit), a tyrosine kinase oncoprotein. Similar to sphere-forming OCICs, injection of only 100 CD44+CD117+ cells could also serially propagate their original tumors, whereas 105 CD44−CD117− cells remained nontumorigenic. Based on these findings, we assert that epithelial ovarian cancers derive from a subpopulation of CD44+CD117+ cells, thus representing a possible therapeutic target for this devastating disease. [Cancer Res 2008;68(11):4311–20]