Abstract
Cancer stem cells (CSC) are the primary cell type responsible for metastasis and relapse. ABC-transporters are integral membrane proteins involved in the translocation of substrates across membranes protecting CSC from chemotherapeutic agents. A plant extract derived from C. spinosa (P2Et) previously investigated for its antitumor activity has been shown to reduce lung and spleen metastasis in mice that have been transplanted with breast cancer cells, suggesting that P2Et has a significant activity against cancer stem cells (CSC). P2Et extract was thoroughly characterized by HPLC/MS. The cytotoxicity of P2Et extract was evaluated using a MTT assay in human and murine cell lines with different profiles of resistance, by Pgp overexpression or by enrichment in cancer stem cells. The synergistic effect of P2Et with doxorubicin was evaluated in vitro in several cell lines and in vivo in mice transplanted with TS/A cells, a highly resistant cell line and enriched in CD44[Formula: see text]CD24[Formula: see text]CSC. The chromatographic fingerprint of P2Et extract revealed 13 gallotannins. We also found that P2Et extract was cytotoxic to cells regardless of their resistant phenotype. Similarly, complementary activities were observed as drug efflux reversion and antioxidant activity. Short-treatment with P2Et extract, revealed a synergistic effect with doxorubicin in resistant cell lines. In vivo the P2Et increases mice survival in a TS/A breast cancer model associated with augmentation of calreticulin expression. Our results suggest that P2Et treatment could be used as adjuvant along with conventional chemotherapy to treat tumors with a MDR phenotype or with high frequency of CSC.
Highlights
Over the last century, the goal of conventional medicine has been to identify or create molecules that act on single molecular targets with high efficiencies and few side effects; this concept was postulated by Ehrlich and is referred to as the “magic bullet” (Strebhardt and Ullrich, 2008)
Eight of the identified compounds were assigned to HPLC fingerprint as follows (Fig. 1): 1. n-O-galloylquinic; 2. gallic acid; 3. di-O-galloylquinic acid; 4. galloylquinic acid ethyl ester; 5. tri-O-galloylquinic acid; 6. tetra-O-galloylquinic acid; 7. tri-O-galloyquinic acid; 8. ethyl gallate
A significant synergistic activity with doxorubicin was observed after treating mice that were transplanted with doxorubicin resistant breast cancer cells (TSA)
Summary
The goal of conventional medicine has been to identify or create molecules that act on single molecular targets with high efficiencies and few side effects; this concept was postulated by Ehrlich and is referred to as the “magic bullet” (Strebhardt and Ullrich, 2008). This reductionist approach is not effective for treating complex diseases where multiple mechanisms are responsible for development, progression and resistance (Efferth and Koch, 2011). Certain compounds, such as gallic acid derivatives, reverse resistance in cancer cells (Kitagawa et al, 2005) and are good candidates for this specific activity
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