Low proteasome activity as a means to track and target breast cancer stem cells in-vivo

• Published in: Cancer research (Chicago, Ill.) Vol. 69; no. 2_Supplement; p. 5055
• Main Authors: Lagadec, CH, Vlashi, E, Dolla Donna, L, McBride, W, Pajonk, F
• Format: Journal Article
• Language: English
• Published: 15.01.2009
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.SABCS-5055

Abstract Abstract #5055 Based on clinical observations, the existence of cancer stem cells (CSCs)/cancer initiating cells (CICs) in solid cancers has been postulated by radiation biologists and oncologists for decades. According to the stem cell hypothesis, only a small number of CSCs/CISs within a tumor have the ability to repopulate an entire tumor while their progeny does not. CSCs/CISs in solid tumors can now be identified prospectively in gliomas, head & neck cancers, pancreatic cancers, colon cancers, prostate cancers, melanomas, and in breast cancers. CSCs/CISs are thought to be mostly quiescent and relatively resistant to conventional anti-cancer therapy.
 Breast CSCs/CICs are enriched in cell populations with high CD44 and low or absent CD24 expression. Unfortunately, detection of breast CSCs/CISs, using CD44 and CD24 expression analysis, requires dissociation of the tumors and antibody staining for surface markers. We recently discovered that cancer stem cells, and specially breast CSCs/CICs, have low proteasome activity. In order to utilize this novel marker for the identification of breast CSCs/CICs, we developed retroviral vectors coding for fusion proteins between thymidine kinase (TK), the fluorescent protein ZsGreen and the c-terminal degron of murine ornithine decarboxylase (cODC). We stably transfected human breast cancer cells lines (MCF-7, MDA-MB-231, T47-D) with this reporter gene construct for 26S proteasome activity.
 Our reporter construct allowed us to track CSCs/CICs responses to radiation therapy in vivo via fluorescent imaging, but also to target them selectively using suicide gene (TK) therapy. Thus, the use of thymidine kinase in our fusion constructs allows for specific elimination of this cell population by ganciclovir preventing self-renewal in-vitro and causing T47-D and MDA-MB-231 tumor xenograft regression in vivo. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5055.