title: Coordinate autophagy and mTOR pathway inhibition enhances cell death in melanoma.
abstract: The phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway promotes melanoma tumor growth and survival while suppressing autophagy, a catabolic process through which cells collect and recycle cellular components to sustain energy homeostasis in starvation. Conversely, inhibitors of the PI3K/AKT/mTOR pathway, in particular the mTOR inhibitor temsirolimus (CCI-779), induce autophagy, which can promote tumor survival and thus, these agents potentially limit their own efficacy. We hypothesized that inhibition of autophagy in combination with mTOR inhibition would block this tumor survival mechanism and hence improve the cytotoxicity of mTOR inhibitors in melanoma. Here we found that melanoma cell lines of multiple genotypes exhibit high basal levels of autophagy. Knockdown of expression of the essential autophagy gene product ATG7 resulted in cell death, indicating that survival of melanoma cells is autophagy-dependent. We also found that the lysosomotropic agent and autophagy inhibitor hydroxychloroquine (HCQ) synergizes with CCI-779 and led to melanoma cell death via apoptosis. Combination treatment with CCI-779 and HCQ suppressed melanoma growth and induced cell death both in 3-dimensional (3D) spheroid cultures and in tumor xenografts. These data suggest that coordinate inhibition of the mTOR and autophagy pathways promotes apoptosis and could be a new therapeutic paradigm for the treatment of melanoma.
authors: The Cancer Institute of New Jersey, New Brunswick, NJ, USA.
authors: Xiaoqi
authors: X
authors: Xie
authors: Eileen P
authors: EP
authors: White
authors: Janice M
authors: JM
authors: Mehnert
mesh_terms: D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001343:Autophagy / Q000187:drug effects*; D000071193:Autophagy-Related Protein 7; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D004357:Drug Synergism; D055785:Gene Knockdown Techniques; D006801:Humans; D006886:Hydroxychloroquine / Q000494:pharmacology; D008297:Male; D008545:Melanoma / Q000473:pathology*; D051379:Mice; D008819:Mice, Nude; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000031:analogs & derivatives / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D044764:Ubiquitin-Activating Enzymes / Q000172:deficiency / Q000235:genetics
chemical_list: D006886:Hydroxychloroquine; C401859:temsirolimus; D058570:TOR Serine-Threonine Kinases; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; D044764:Ubiquitin-Activating Enzymes; D020123:Sirolimus
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