title: Lucanthone is a novel inhibitor of autophagy that induces cathepsin D-mediated apoptosis.
abstract: Cellular stress induced by nutrient deprivation, hypoxia, and exposure to many chemotherapeutic agents activates an evolutionarily conserved cell survival pathway termed autophagy. This pathway enables cancer cells to undergo self-digestion to generate ATP and other essential biosynthetic molecules to temporarily avoid cell death. Therefore, disruption of autophagy may sensitize cancer cells to cell death and augment chemotherapy-induced apoptosis. Chloroquine and its analog hydroxychloroquine are the only clinically relevant autophagy inhibitors. Because both of these agents induce ocular toxicity, novel inhibitors of autophagy with a better therapeutic index are needed. Here we demonstrate that the small molecule lucanthone inhibits autophagy, induces lysosomal membrane permeabilization, and possesses significantly more potent activity in breast cancer models compared with chloroquine. Exposure to lucanthone resulted in processing and recruitment of microtubule-associated protein 1 light chain 3 (LC3) to autophagosomes, but impaired autophagic degradation as revealed by transmission electron microscopy and the accumulation of p62/SQSTM1. Microarray analysis, qRT-PCR, and immunoblotting determined that lucanthone stimulated a large induction in cathepsin D, which correlated with cell death. Accordingly, knockdown of cathepsin D reduced lucanthone-mediated apoptosis. Subsequent studies using p53(+/+) and p53(-/-) HCT116 cells established that lucanthone induced cathepsin D expression and reduced cancer cell viability independently of p53 status. In addition, lucanthone enhanced the anticancer activity of the histone deacetylase inhibitor vorinostat. Collectively, our results demonstrate that lucanthone is a novel autophagic inhibitor that induces apoptosis via cathepsin D accumulation and enhances vorinostat-mediated cell death in breast cancer models.
authors.affiliation: Department of Medicine, Institute for Drug Development, Cancer Therapy and Research Center, The University of Texas Health Science Center, San Antonio, Texas 78245, USA.
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Carew
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Espitia
authors.forename: Juan A
authors.initials: JA
authors.lastname: Esquivel
authors.forename: Devalingam
authors.initials: D
authors.lastname: Mahalingam
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Kelly
authors.forename: Guru
authors.initials: G
authors.lastname: Reddy
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Giles
authors.forename: Steffan T
authors.initials: ST
authors.lastname: Nawrocki
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000819:agonists / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D002402:Cathepsin D / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004357:Drug Synergism; D020869:Gene Expression Profiling; D006801:Humans; D006877:Hydroxamic Acids / Q000819:agonists / Q000494:pharmacology; D007425:Intracellular Membranes / Q000378:metabolism; D008154:Lucanthone / Q000819:agonists / Q000494:pharmacology*; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010539:Permeability / Q000187:drug effects; D010588:Phagosomes / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012556:Schistosomicides / Q000819:agonists / Q000494:pharmacology*; D000071456:Sequestosome-1 Protein; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D000077337:Vorinostat
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D006877:Hydroxamic Acids; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; C099718:SQSTM1 protein, human; D012556:Schistosomicides; D000071456:Sequestosome-1 Protein; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D000077337:Vorinostat; C533922:CTSD protein, human; D002402:Cathepsin D; D008154:Lucanthone