Enrichment of Prostate Cancer Stem-Like Cells from Human Prostate Cancer Cell Lines by Culture in Serum-Free Medium and Chemoradiotherapy

Abstract

The discovery of rare subpopulations of cancer stem cells (CSCs) has created a new focus in cancer research. As CSCs demonstrate resistance to chemoradiation therapy relative to other cancer cells, this allows the enrichment of CSC populations by killing apoptosis-susceptible cancer cells. In this study, three commonly used human prostate cancer (PCa) cell lines (DU145, PC-3 and LNCaP) were examined for their expression of the putative stem cell markers CD133 and CD44 via flow cytometric analysis. Under normal culture conditions, CD133+/CD44+ cells were only present in the DU145 cell line, and comprised only a minor percentage (0.1% ± 0.01%) of the total population. However, the proportion of these CD133+/CD44+ prostate CSCs could be increased in these cell lines via culture in serum-free medium (SFM), or through chemotherapy or radiotherapy. Indeed, after culture in SFM, the proportion of CD133+/CD44+ cells in DU145 and PC-3 had increased to 10.3% and 3.0%, respectively. Moreover, the proportion had increased to 9.8% enriched by chemotherapy and 3.5% by radiotherapy in DU145. Colony-formation tests, cell invasion assays, and tumor xenografts in BALB/c nude mice were used to evaluate the stem cell properties of CD133+/CD44+ PCa cells that were isolated via fluorescence-activated cell sorting (FACS). CD133+/CD44+ cells had an enhanced colony-formation capability and invasive ability in vitro, and displayed greater tumorigenic properties in vivo. These results demonstrate the presence of CD133+/CD44+ prostate CSCs in established PCa cell lines and that populations of these cells can be enriched by culture in SFM or chemoradiotherapy. Finding novel therapies to override chemoradiation resistance in the prostate CSCs is the key to improve long-term results in PCa management.

Radiation induces the generation of cancer stem cells: A novel mechanism for cancer radioresistance

“…Al-Assar et al (88) reported that breast CSCs in xenografts exposed to radiation were enriched, as demonstrated by an increased number of CD24 − /epithelial-specific antigen + cancer cells, a marker of breast CSCs, in xenografts. The enrichment of breast CSCs in xenografts exposed to radiation was also considered as the result of different radioresistance between CSCs and adult cancer cells, which was consistent with the aforementioned speculation of Wang et al (87). This explanation was undoubtedly reasonable, but may be not complete.…”

“…It has been demonstrated that CSCs can be enriched both in vitro and in vivo by radiation, which indicates the possibility of radiation-induced generation of CSCs. Wang et al (87) demonstrated that the proportion of prostate cancer stem-like cells in a human prostate cancer cell culture increased significantly following exposure to radiation. The authors postulated that radiation eliminated the radiosensitive adult cancer cells in the culture by inducing apoptosis, which resulted in the enrichment of radioresistant CSCs.…”

“…Thus, there may be another reasonable source causing an increase in the absolute number of CSCs and subsequently resulting in CSCs enrichment upon radiation: Radiation-induced generation of CSCs. This source cannot be ignored, since the possibility that cancer cells without stemness markers could obtain stemness markers upon exposure to irradiation was not excluded in the aforementioned studies of Wang et al (87) and Al-Assar et al (88). …”

Induced cancer stem cells generated by radiochemotherapy and their therapeutic implications

“…In ovarian cancer cell lines, enrichment of CSCs was found in response to either cisplatin or paclitaxel or combination of both [51]. Similar results were reported in pancreatic cancer [44, 52], glioblastoma [53] and prostate cancer [54]. In our previous work, the combination of paclitaxel and serum-free medium cultivation enriched CSCs in lung adenocarcinoma A549 cells [55].…”

Isolation, Culture and Identification of Choriocarcinoma Stem-Like Cells from the Human Choriocarcinoma Cell-Line JEG-3

“…The serum-free suspension culture method is based on supplementation of culture medium with growth factors to promote proliferation of undifferentiated cells, concomitantly with the elimination of differentiated cells. In recent years, this approach has been used to isolate many kinds of CSCs including prostate [20], retinal [21], and prostate [22] cancer stem cells. Serum-free suspension culture may allow isolation and culture of choriocarcinoma stemlike cells (CSLCs) from human choriocarcinoma cell lines.…”