Chloroquine enhances temozolomide cytotoxicity in malignant gliomas by blocking autophagy

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>In a recent clinical trial, patients with newly diagnosed glioblastoma multiforme benefited from chloroquine (CQ) in combination with conventional therapy (resection, temozolomide [TMZ], and radiation therapy). In the present study, the authors report the mechanism by which CQ enhances the therapeutic efficacy of TMZ to aid future studies aimed at improving this therapeutic regimen.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Using in vitro and in vivo experiments, the authors determined the mechanism by which CQ enhances TMZ cytotoxicity. They focused on the inhibition-of-autophagy mechanism of CQ by knockdown of the autophagy-associated proteins or treatment with autophagy inhibitors. This mechanism was tested using an in vivo model with subcutaneously implanted U87MG tumors from mice treated with CQ in combination with TMZ.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>Knockdown of the autophagy-associated proteins (GRP78 and Beclin) or treatment with the autophagy inhibitor, 3-methyl adenine (3-MA), blocked autophagosome formation and reduced CQ cytotoxicity, suggesting that autophagosome accumulation precedes CQ-induced cell death. In contrast, blocking autophagosome formation with knockdown of GRP78 or treatment with 3-MA enhanced TMZ cytotoxicity, suggesting that the autophagy pathway protects from TMZ-induced cytotoxicity. CQ in combination with TMZ significantly increased the amounts of LC3B-II (a marker for autophagosome levels), CHOP/GADD-153, and cleaved PARP (a marker for apoptosis) over those with untreated or individual drug-treated glioma cells. These molecular mechanisms seemed to take place in vivo as well. Subcutaneously implanted U87MG tumors from mice treated with CQ in combination with TMZ displayed higher levels of CHOP/GADD-153 than did untreated or individual drug-treated tumors.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Taken together, these results demonstrate that CQ blocks autophagy and triggers endoplasmic reticulum stress, thereby increasing the chemosensitivity of glioma cells to TMZ.</jats:p></jats:sec>

New derivatives of the antimalarial drug Pyrimethamine in the control of melanoma tumor growth: an in vitro and in vivo study

“…Apoptosis and autophagy are closely intertwined processes and the shift apoptosis/autophagy is extremely delicate and highly dependent on metabolic interactions [33]. Previously, we reported that Pyr (as TMZ and other chemotherapeutic drugs) is able to induce autophagy at the early stage of treatment of tumor cells [33, 47, 48]. In this context, the Food and Drug Administration (FDA) have currently approved the use of CQ in combination with conventional therapies to counteract the mechanisms of cell survival in cancer treatment (source http://www.fda.gov).…”

“…In this context, the Food and Drug Administration (FDA) have currently approved the use of CQ in combination with conventional therapies to counteract the mechanisms of cell survival in cancer treatment (source http://www.fda.gov). Therefore, based primarily on the ability to inhibit autophagy, CQ and its derivative, hydroxychloroquine, are currently being investigated as adjuvant therapy in multiple clinical trials for cancer treatment [47], leading to their use as potential chemotherapy and radiotherapy sensitizers rather than antineoplastic. In agreement with these findings, when we combined CQ with Pyr, we found an enhanced cytotoxic effect and block of the autophagic flux.…”

Re-purposing Chloroquine for Glioblastoma: Potential Merits and Confounding Variables

“…Most of the existing studies addressing the effects of CHQ in glioma cells have used conventional serum-dependent cell lines that lack stemness properties and/or poorly recapitulate characteristic features of human GBs. For example, the human glioma cell line U87MG, which has been widely used as an experimental model for investigating biological responses mediated by CHQ (21, 22, 29, 30, 81, 82) does not reproduce certain characteristic traits of GBs such as an invasive tumor phenotype, intra-tumoral heterogeneity and high degree of intrinsic radio-resistance. Considering that GSCs are fundamentally distinct from non-stem glioma cells, it is conceivable that their responses to CHQ might also differ from those operating in the latter ones.…”

Chloroquine Enhances the Radiosensitivity of Bladder Cancer Cells by Inhibiting Autophagy and Activating Apoptosis

“…Due to its chemical properties as a weak base, it can inhibit H+-ATPase to increase the lysosomal pH, thus inhibiting enzymatic activity of lysosomal hydrolases and preventing the fusion of autophagosome and lysosome for lysosomotropic properties [18, 19]. Now, several studies have reported that chloroquine could enhance the efficiency of present tumor therapies in many cancers [20-23]. Qin et al [20] found that chloroquine enhanced the efficacy of cisplatin in human adrenocortical carcinoma treatment by blocking autophagy.…”

“…Qin et al [20] found that chloroquine enhanced the efficacy of cisplatin in human adrenocortical carcinoma treatment by blocking autophagy. In addition, Golden et al [23] suggested that chloroquine blocked autophagy and triggered endoplasmic reticulum stress, thereby increasing the chemosensitivity of glioma cells to temozolomide. In addition, Ye et al [21] showed that chloroquine enhanced the radiosensitivity of glioma initiating cells.…”