title: Obatoclax kills anaplastic thyroid cancer cells by inducing lysosome neutralization and necrosis.
abstract: Poorly differentiated and anaplastic thyroid carcinomas are very aggressive, almost invariably lethal neoplasms for which no effective treatment exists. These tumors are intrinsically resistant to cell death, even when their driver oncogenic signaling pathways are inhibited.We have undertaken a detailed analysis, in mouse and human thyroid cancer cells, of the mechanism through which Obatoclax, a pan-inhibitor of the anti-apoptotic proteins of the BCL2 family, effectively reduces tumor growth in vitro and in vivo.We demonstrate that Obatoclax does not induce apoptosis, but rather necrosis of thyroid cancer cells, and that non-transformed thyroid cells are significantly less affected by this compound. Surprisingly, we show that Obatoclax rapidly localizes to the lysosomes and induces loss of acidification, block of lysosomal fusion with autophagic vacuoles, and subsequent lysosomal permeabilization. Notably, prior lysosome neutralization using different V-ATPase inhibitors partially protects cancer cells from the toxic effects of Obatoclax. Although inhibition of autophagy does not affect Obatoclax-induced cell death, selective down-regulation of ATG7, but not of ATG5, partially impairs Obatoclax effects, suggesting the existence of autophagy-independent functions for ATG7. Strikingly, Obatoclax killing activity depends only on its accumulation in the lysosomes, and not on its interaction with BCL2 family members.Finally, we show that also other lysosome-targeting compounds, Mefloquine and LLOMe, readily induce necrosis in thyroid cancer cells, and that Mefloquine significantly impairs tumor growth in vivo, highlighting a clear vulnerability of these aggressive, apoptosis-resistant tumors that can be therapeutically exploited.
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Devora
authors.initials: D
authors.lastname: Champa
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Arturo
authors.initials: A
authors.lastname: Orlacchio
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Bindi
authors.initials: B
authors.lastname: Patel
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Michela
authors.initials: M
authors.lastname: Ranieri
authors.affiliation: Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Anton A
authors.initials: AA
authors.lastname: Shemetov
authors.affiliation: Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Vladislav V
authors.initials: VV
authors.lastname: Verkhusha
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Cuervo
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Antonio
authors.initials: A
authors.lastname: Di Cristofano
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D000071187:Autophagy-Related Protein 5 / Q000096:biosynthesis; D000071193:Autophagy-Related Protein 7 / Q000096:biosynthesis; D049109:Cell Proliferation; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007211:Indoles; D008247:Lysosomes / Q000378:metabolism*; D015767:Mefloquine / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D009336:Necrosis / Q000139:chemically induced*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors*; D011758:Pyrroles / Q000494:pharmacology*; D034622:RNA Interference; D034741:RNA, Small Interfering; D018874:Spheroids, Cellular; D065646:Thyroid Carcinoma, Anaplastic / Q000188:drug therapy*; D013964:Thyroid Neoplasms / Q000188:drug therapy*; D014407:Tumor Cells, Cultured
chemical_list: C502778:ATG5 protein, human; D000970:Antineoplastic Agents; D000071187:Autophagy-Related Protein 5; D004791:Enzyme Inhibitors; D007211:Indoles; D019253:Proto-Oncogene Proteins c-bcl-2; D011758:Pyrroles; D034741:RNA, Small Interfering; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; C520962:obatoclax; D015767:Mefloquine
keywords: autophagy; lysosomes; necrosis; obatoclax; thyroid cancer