Chloroquine synergizes with FTS to enhance cell growth inhibition and cell death

Abstract

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.

Impact of Autophagy Inhibition at Different Stages on Cytotoxic Effect of Autophagy Inducer in Glioblastoma Cells

“…Interestingly, autophagy inhibitor and autophagy inducer, two kinds of contradictory drugs, sometimes produce synergistic effect on cancer therapy when used in combination [19,20]. By far, numbers of basic studies and clinical trials evaluating such effect in cancer treatment are in progress [11,19,20,21,22,23,24,25,26].…”

“…By far, numbers of basic studies and clinical trials evaluating such effect in cancer treatment are in progress [11,19,20,21,22,23,24,25,26]. However, the published results were in conflict.…”

Ras and autophagy in cancer development and therapy

“…FTS was shown to exhibit anti-tumorigenic effects in vitro and in vivo [66-69]. Treatment with FTS was shown to activate autophagy in wild-type MEF cells and in cancer cell lines harboring a K-Ras mutation (HCT-116, DLD-1, and Panc-1) [70, 71] The effect of FTS on autophagy may depend on mTOR1 inhibition, at least in certain cell types. Knockout of Atg5 sensitizes MEF cells to FTS-induced growth inhibition and cell death.…”

“…Thus, FTS-induced autophagy seems to play a pro-tumorigenic role. Interestingly, rat fibroblasts transformed with oncogenic H-Ras G12V are more sensitive to the combined treatment with FTS and autophagy inhibitors compared to normal fibroblasts, indicating the specificity of the treatment [70, 71]. …”

Targeting KRAS-mutant non-small cell lung cancer: challenges and opportunities

“…Although there is lack of explanation in the literature, this observation could suggest that using farnesyl mimics alone is probably not sufficient to significantly degrade active KRAS via targeting its localization, and/or targeting KRAS membrane localization alone may not be sufficient to result in clinical significance. In fact, several studies have proposed combining salirasib with other strategies for KRAS-mutant cancers [38][39][40]. Nevertheless, the above-mentioned unsuccessful clinical trials, together with the tremendous challenge of designing a direct RAS inhibitor, make targeting its downstream signaling pathway the most clinically applicable approach.…”