Abstract
Abstract Tumorigenesis and malignant progression of cancers rely on a small subset of cells known as cancer stem cells (CSCs). In addition to forming primary tumors, metastasis and relapse, CSCs always display resistance to cytotoxins and this resistant feature protects CSCs during the course of chemotherapy. Glucosylceramide synthase (GCS) is a limited enzyme catalyzing the first glycosylation in glycosphingolipids synthesis. Glycosphingolipids are likely to play an essential role in maintaining the stemness of stem cells, since that deletion of GCS induces apoptosis of embryonic stem cell and stops embryo development in GCS knockout mice. The stage-specific embryonic antigens (SSEA-3, SSEA-4) are glycosphingolipids and serve as common pluripotent markers for human embryonic stem cells. In the present study, we have found that GCS modulates the formation and maintenance of breast cancer stem cells. GCS overexpression was interrelated to the increase of breast cancer stem cells (BCSCs) and drug resistance in human breast cancer MCF-7 cell lines after doxorubicin induction. In MCF-7/Dox (doxorubicin-resistant) cells, GCS protein was increased by 39-fold accompanied with enhanced enzyme activity, as compared to wild-type MCF-7 cell. Analyzed by using flow cytometry and immunostaining, the BCSCs with CD44+/CD24-/ESA+ phenotype were increased by 5-fold, and 3-fold in MCF-7/Dox and NCI-ADR/RES cell lines, as compared to MCF-7 cell lines, respectively. In BCSCs, GCS enzyme activity was 2-fold greater than other populations sorted from MCF-7/Dox. Silencing GCS by using mixed-backbone oligonucleotide (MBO-asGCS) significantly decreased the numbers of BCSCs in MCF-7/Dox cells. We observed tumorigenesis of NCI/ADR-RE/GCS (GCS overexpressed) and NCI/ADR-RE/asGCS (GCS silenced) in athymic nude mice. Aggressive tumors were found in all mice inoculated with NCI/ADR-RES and NCI/ADR-RE/GCS cells that were BCSC-enriched; however, no tumor or metastasis was observed in mice injected with NCI-ADR/asGCS cells. Furthermore, MBO-asGCS treatment (1 mg/kg) significantly decreased the numbers of BCSCs isolated from tumors of NCI-ADR/RES, as compared with control groups. Furthermore, BCSCs after MBO-asGCS treatment were more sensitive to doxorubicin. These results, for the first time, demonstrate that glycosphingolipid is involved in the regulation of cancer stem cell formation. Silencing GCS eliminates BCSCs, that can reverses drug resistance as well as prevent tumor relapse. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4282.
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