Chloroquine synergizes with FTS to enhance cell growth inhibition and cell death
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Eran Schmukler1, Eya Wolfson1, Roni Haklai1, Galit Elad-Sfadia1, Yoel Kloog1 and Ronit Pinkas-Kramarski1
1 Department of Neurobiology. Tel-Aviv University, Ramat-Aviv, Israel.
Ronit Pinkas-Kramarski, email:
Keywords: Autophagy, Ras, Transformation, signal transduction
Received: October 14, 2013 Accepted: November 18, 2013 Published: November 20, 2013
The Ras family of small GTPases transmits extracellular signals that regulate cell growth, differentiation, motility and death. Ras signaling is constitutively active in a large number of human cancers. Ras can also regulate autophagy by affecting several signaling pathways including the mTOR pathway. Autophagy is a process that regulates the balance between protein synthesis and protein degradation. It is important for normal growth control, but may be defective in diseases. Previously, we have shown that Ras inhibition by FTS induces autophagy, which partially protects cancer cells and may limit the use of FTS as an anti-cancer drug. Since FTS is a non toxic drug we hypothesized that FTS and chloroquine (an autophagy inhibitor) will synergize in cell growth inhibition and cell death. Thus, in the present study, we explored the mechanism of each individual drug and their combined action. Our results demonstrate that in HCT-116 and in Panc-1 cells, FTS induces autophagy, which can be inhibited by chloroquine. Furthermore, the combined treatment synergistically decreased the number of viable cells. Interestingly, the combined treatment enhanced apoptotic cell death as indicated by increased sub-G1 cell population, increased Hoechst staining, activation of caspase 3, decrease in survivin expression and release of cytochrome c. Thus, chloroquine treatment may promote FTS-mediated inhibition of tumor cell growth and may stimulate apoptotic cell death.
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