Autophagy For Growth Research Articles

Azithromycin enhances the cytotoxicity of DNA-damaging drugs via lysosomal membrane permeabilization in lung cancer cells.

Cancer cells use autophagy for growth, survival, and cytoprotection from chemotherapy. Therefore, autophagy inhibitors appear to be good candidates for cancer treatment. Our group previously reported that macrolide antibiotics, especially azithromycin (AZM), have potent autophagy inhibitory effects, and combination treatment with tyrosine kinase inhibitors or proteasome inhibitors enhances their anti–cancer activity. In this study, we evaluated the effect of combination therapy with DNA‐damaging drugs and AZM in non–small‐cell lung cancer (NSCLC) cells. We found that the cytotoxic activities of DNA‐damaging drugs, such as doxorubicin (DOX), etoposide, and carboplatin, were enhanced in the presence of AZM in NSCLC cell lines, whereas AZM alone exhibited almost no cytotoxicity. This enhanced cell death was dependent on wild‐type‐p53 status and autophagosome‐forming ability because TP53 knockout (KO) and ATG5‐KO cells attenuated AZM‐enhanced cytotoxicity. DOX treatment upregulated lysosomal biogenesis by activating TFEB and led to lysosomal membrane damage as assessed by galectin 3 puncta assay and cytoplasmic leakage of lysosomal enzymes. In contrast, AZM treatment blocked autophagy, which resulted in the accumulation of lysosomes/autolysosomes. Thus, the effects of DOX and AZM were integrated into the marked increase in damaged lysosomes/autolysosomes, leading to prominent lysosomal membrane permeabilization (LMP) for apoptosis induction. Our data suggest that concomitant treatment with DNA‐damaging drugs and AZM is a promising strategy for NSCLC treatment via pronounced LMP induction.

Macroautophagy is dispensable for growth of KRAS mutant tumors and chloroquine efficacy

Macroautophagy is a key stress-response pathway that can suppress or promote tumorigenesis depending on the cellular context. Notably, Kirsten rat sarcoma (KRAS)-driven tumors have been reported to rely on macroautophagy for growth and survival, suggesting a potential therapeutic approach of using autophagy inhibitors based on genetic stratification. In this study, we evaluated whether KRAS mutation status can predict the efficacy to macroautophagy inhibition. By profiling 47 cell lines with pharmacological and genetic loss-of-function tools, we were unable to confirm that KRAS-driven tumor lines require macroautophagy for growth. Deletion of autophagy-related 7 (ATG7) by genome editing completely blocked macroautophagy in several tumor lines with oncogenic mutations in KRAS but did not inhibit cell proliferation in vitro or tumorigenesis in vivo. Furthermore, ATG7 knockout did not sensitize cells to irradiation or to several anticancer agents tested. Interestingly, ATG7-deficient and -proficient cells were equally sensitive to the antiproliferative effect of chloroquine, a lysosomotropic agent often used as a pharmacological tool to evaluate the response to macroautophagy inhibition. Moreover, both cell types manifested synergistic growth inhibition when treated with chloroquine plus the tyrosine kinase inhibitors erlotinib or sunitinib, suggesting that the antiproliferative effects of chloroquine are independent of its suppressive actions on autophagy.

Basal autophagy is negatively regulated by RIP1

Basal autophagy is negatively regulated by RIP1

Abstract B11: The early autophagy inhibitor verteporfin moderately enhances the antitumor activity of gemcitabine in a pancreatic ductal adenocarcinoma model

Abstract Autophagy, a cellular self-eating process that is activated by several cancer drugs and appears to function as a protective mechanism, is a promising therapeutic target. Pancreatic ductal adenocarcinoma (PDAC) is highly resistant to chemotherapy, and has been described as requiring elevated autophagy for growth. To date, all preclinical reports and clinical trials investigating pharmacological inhibition of autophagy have used chloroquine or hydroxychloroquine, which block autophagy at a late stage. Verteporfin is a newly discovered autophagy inhibitor that blocks autophagy at an early stage by inhibiting autophagosome formation. Here, we report that PDAC cell lines show variable sensitivity to verteporfin in vitro and that verteporfin inhibits autophagy stimulated by gemcitabine, the current standard treatment for PDAC. Pharmacokinetic and efficacy studies in a BxPC-3 xenograft mouse model demonstrate that verteporfin accumulated in tumors at autophagy-inhibiting levels but did not reduce tumor volume or increase survival as a single agent. However, in combination with gemcitabine, verteporfin moderately reduced tumor growth and enhanced survival compared to gemcitabine alone. Our results do not agree with the premise that autophagy inhibition is effective against PDAC as a single-modality treatment, but they support autophagy inhibition as an approach to sensitize PDAC to gemcitabine. Citation Format: Elizabeth Donohue, Anitha Thomas, Norbert Maurer, Irina Manisali, Magali Zeisser-Labouebe, Natalia Zisman, Hilary J. Anderson, Murray Webb, Marcel Bally, and Michel Roberge. The early autophagy inhibitor verteporfin moderately enhances the antitumor activity of gemcitabine in a pancreatic ductal adenocarcinoma model. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B11.

EGFR overexpressing cells and tumors are dependent on autophagy for growth and survival

Background and purposeThe epidermal growth factor receptor (EGFR) is overexpressed, amplified or mutated in various human epithelial tumors, and is associated with tumor aggressiveness and therapy resistance. Autophagy activation provides a survival advantage for cells in the tumor microenvironment. In the current study, we assessed the potential of autophagy inhibition (using chloroquine (CQ)) in treatment of EGFR expressing tumors. Material and methodsQuantitative PCR, immunohistochemistry, clonogenic survival, proliferation assays and in vivo tumor growth were used to assess this potential. ResultsWe show that EGFR overexpressing xenografts are sensitive to CQ treatment and are sensitized to irradiation by autophagy inhibition. In HNSSC xenografts, a correlation between EGFR and expression of the autophagy marker LC3b is observed, suggesting a role for autophagy in EGFR expressing tumors. This observation was substantiated in cell lines, showing high EGFR expressing cells to be more sensitive to CQ addition as reflected by decreased proliferation and survival. Surprisingly high EGFR expressing cells display a lower autophagic flux. ConclusionsThe EGFR high expressing cells and tumors investigated in this study are highly dependent on autophagy for growth and survival. Inhibition of autophagy may therefore provide a novel treatment opportunity for EGFR overexpressing tumors.

Abstract 2041: Inhibition of autophagy in melanoma: using cell lines to model chloroquine sensitivity.

Abstract Metastatic melanoma offers an ongoing clinical challenge. According to the American Cancer Society, the 5-year survival rate in 2012 for stage IV melanoma is only about 15% even with therapies. To improve outcomes, it is important to investigate new pathways involved in the regulation of metastasis as possible targets for prevention or treatment, such as autophagy. Autophagy (self-eating pathway) destroys a cell's damaged proteins and organelles through lysosomal degradation and has been shown to play roles in a wide variety of normal physiological processes including energy metabolism, nutrient or stress responses, growth regulation, and aging. The role of dysregulated autophagy in melanoma has not been well characterized. Preliminary research found cutaneous malignant melanoma cells display high levels of autophagy suggesting that this cellular process may provide an active metabolic state for invasive and metastatic melanoma. Chloroquine (CLQ), a classic antimalarial agent, is a potent inhibitor of autophagy and has been used safely in human patients for decades. This study is designed to dissect the role of autophagy in melanoma using melanoma cell lines (e.g. SK-Mel 19, 103, and 147), and primary melanocytes as controls to determine whether these cell types respond to CLQ as measured by cell viability . Similar to pancreatic and prostate cancer cell lines, our preliminary results indicate that metastatic melanoma cells require autophagy for growth and show high sensitivity to CLQ at doses as low as 20uM which resulted in greater than 60% decreases in cell viability. These findings suggest that metastatic melanoma cell lines rely on lysosomal degradation to a greater extent than what has been reported for other cell types. In addition, both N-ras mutation and androgen deprivation mitigate the effects of CLQ on melanoma cells. Ongoing experiments will confirm the expression of autophagy related genes, as well as imaging to determine the rate of autophagy in these cell lines. Finally, we will introduce stripped hormonal factors including vitamin D and estrogen, to evaluate whether this addition will progressively restore the original chloroquine sensitive phenotype. Findings from this work have the potential to be immediately translatable to patients as CLQ is already approved for therapeutic use in other human diseases. Citation Format: Kirsten A. White, Salina M. Torres, Natalia J. Gurule, Marianne Berwick, Chien-An A. Hu. Inhibition of autophagy in melanoma: using cell lines to model chloroquine sensitivity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2041. doi:10.1158/1538-7445.AM2013-2041