CSCs resemble cells that have undergone epithelial–mesenchymal transition (EMT) with regard to their invasiveness and motility. EMT, which is associated with a key step in tumor metastasis via induction of a highly invasive phenotype, has been intensely studied. And CSCs have been found to transiently acquire stem cell-like properties as a consequence of EMT. CSCs also are inherently chemoresistant and radioresistant. Recently, side population (SP) cells have been shown to express increased levels of MDR1 (multidrugresistance protein 1) and ABCG2 (ATP-binding cassette, sub-family G, member 2) transporters, which can extrude certain chemotherapeutic agents and have been implicated in drug resistance. Importantly, SP cells appear to be enriched in stem cells. Although this issue remains controversial, identifying and characterizing human ovarian CSCs would provide a critical step toward the identification of drugs with therapeutic efficacy against CSCs and the development of novel therapeutic strategies for the long-term control of cancer.
- Heterogeneous populations may contain subpopulations with different phenotypic and genetic profiles. Among these are cancer stem cell-like cells (CSCs), a dynamically changing subpopulation of cancer-initiating cells (CICs) that arises due to the acquisition of malignant cellular transformations as part of a biological evolutionary process. Although, in theory, many tumors contain limited minority of CSCs, in practice, it is difficult to identify the cells that acquire the genetic/epigenetic alterations that lead to tumor initiation. As the name suggests, the CSC hypothesis describes a process driven by rare cellular components that display stem cell properties of self-renewal and differentiation: self-renewal promotes tumorigenesis, whereas differentiation contributes to the phenotypic heterogeneity of tumors.
- The role of CSCs as adverse factors in ovarian cancer may reflect their suggested origin from aberrant CICs. Consistent with this, a subpopulation of cells isolated from mouse ovarian cancer cell lines and ascites of human ovarian cancer patients phenotypically resemble stem cells. CSCs are thought to be self-renewing and possess multipotency. This latter property enables CSCs to differentiate into diverse cells that display histologic heterogeneity and tumorigenicity, even in a subpopulation or a small minority of cells.
▶ Ovarian tumor was comprised of both phenotypically and genetically distinct subpopulations according to spatial zones.
▶ Phenotypes of SP cells in heterogeneous clones of human ovarian cancer.
▶ Chromosomal alterations in SP cells relative to NSP cells were closely related to the novel core networks of CSCs, such as cycle checkpoint regulation, notch, PTEN, wnt/β-catenin, PI3K/AKT, integrin, and cytokine and chemokine signaling
▶ This study is the first document to define molecular portrait of ITH according to in intratumoral spatial difference. Clones from front zone revealed genetically distinct populations with relatively higher SP proportions, stemness gene expression, frequent chromosomal aberrance by aCGH, and chemotherapeutic resistance. Furthermore, CD24+ cells could be strong potential for tumor progression, drug resistance and clonal asynchronous evolution affecting ITH in consequence. Our evidence for frequent genetic alterations in SP cells compared with NSP cells also suggests that the observed ITH in a single human ovarian cancer tumor specimen could be an effect of clonally diverse evolution from CSCs
Characterization of heterogeneous clones generated from different tumor zones. (a) Cell proliferation assays performed at 0, 24, 48, 72, and 96 h after cell seeding confirmed that each clone exhibited a distinctive growth rate and doubling time. (b) Comparison of cell growth property in heterogeneous clones generated from different tumor zones, front and rear, at 96 h. (c) H&E staining was performed to compare differences in morphology at approximately 10 passages. (d) Conventional RT-PCR analyses of the expression of candidate CSC markers. (e) Conventional RT-PCR analyses of the expression of stem cell-related genes. GAPDH was used as an internal control. (f) Cell cycle distribution analysis. All experiments were performed in triplicate. (p<0.05)
- Ovarian cancer cells isolated from ovarian tumor specimens of a patient were heterogeneous in growth rate, cell cycle distribution, and expression profile of genes and proteins.
- CD24, CD44, ESA, and CD117 are potential surface marker to identify ovarian cancer stem-like cells.
- The analysis of array comparative genomic hybridization (aCGH) and IPA indicated that novel core networks and molecules closely related to CSCs, such as Notch signaling, Wnt/β-catenin signaling, PTEN signaling, G1/S and G2/M checkpoint regulation, PI3K/AKT signaling, and p53 signaling, were involved in the different functions of SP and NSP isolated from ovarian cancer.
Altogether, these observations suggest human ovarian tumor cells are organized as a hierarchy and CD24 demarcates an ovarian cancer-initiating cell population. These findings will have important clinical applications for developing effective therapeutic strategies to treat ovarian cancer.
Results (I) : Clone derivation with different characteristics
Results (II) :Identification of ovarian cancer stem cells