The BH3 Mimetic Obatoclax Accumulates in Lysosomes and Causes Their Alkalinization

Obatoclax belongs to a class of compounds known as BH3 mimetics which function as antagonists of Bcl-2 family apoptosis regulators. It has undergone extensive preclinical and clinical evaluation as a cancer therapeutic. Despite this, it is clear that obatoclax has additional pharmacological effects...

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Veröffentlicht in:PloS one 2016-03, Vol.11 (3), p.e0150696-e0150696
Hauptverfasser: Stamelos, Vasileios A, Fisher, Natalie, Bamrah, Harnoor, Voisey, Carolyn, Price, Joshua C, Farrell, William E, Redman, Charles W, Richardson, Alan
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container_start_page e0150696
container_title PloS one
container_volume 11
creator Stamelos, Vasileios A
Fisher, Natalie
Bamrah, Harnoor
Voisey, Carolyn
Price, Joshua C
Farrell, William E
Redman, Charles W
Richardson, Alan
description Obatoclax belongs to a class of compounds known as BH3 mimetics which function as antagonists of Bcl-2 family apoptosis regulators. It has undergone extensive preclinical and clinical evaluation as a cancer therapeutic. Despite this, it is clear that obatoclax has additional pharmacological effects that contribute to its cytotoxic activity. It has been claimed that obatoclax, either alone or in combination with other molecularly targeted therapeutics, induces an autophagic form of cell death. In addition, obatoclax has been shown to inhibit lysosomal function, but the mechanism of this has not been elucidated. We have evaluated the mechanism of action of obatoclax in eight ovarian cancer cell lines. Consistent with its function as a BH3 mimetic, obatoclax induced apoptosis in three cell lines. However, in the remaining cell lines another form of cell death was evident because caspase activation and PARP cleavage were not observed. Obatoclax also failed to show synergy with carboplatin and paclitaxel, chemotherapeutic agents which we have previously shown to be synergistic with authentic Bcl-2 family antagonists. Obatoclax induced a profound accumulation of LC-3 but knockdown of Atg-5 or beclin had only minor effects on the activity of obatoclax in cell growth assays suggesting that the inhibition of lysosomal function rather than stimulation of autophagy may play a more prominent role in these cells. To evaluate how obatoclax inhibits lysosomal function, confocal microscopy studies were conducted which demonstrated that obatoclax, which contains two basic pyrrole groups, accumulates in lysosomes. Studies using pH sensitive dyes demonstrated that obatoclax induced lysosomal alkalinization. Furthermore, obatoclax was synergistic in cell growth/survival assays with bafilomycin and chloroquine, two other drugs which cause lysosomal alkalinization. These studies explain, for the first time, how obatoclax inhibits lysosomal function and suggest that lysosomal alkalinization contributes to the cytotoxic activity of obatoclax.
doi_str_mv 10.1371/journal.pone.0150696
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It has undergone extensive preclinical and clinical evaluation as a cancer therapeutic. Despite this, it is clear that obatoclax has additional pharmacological effects that contribute to its cytotoxic activity. It has been claimed that obatoclax, either alone or in combination with other molecularly targeted therapeutics, induces an autophagic form of cell death. In addition, obatoclax has been shown to inhibit lysosomal function, but the mechanism of this has not been elucidated. We have evaluated the mechanism of action of obatoclax in eight ovarian cancer cell lines. Consistent with its function as a BH3 mimetic, obatoclax induced apoptosis in three cell lines. However, in the remaining cell lines another form of cell death was evident because caspase activation and PARP cleavage were not observed. Obatoclax also failed to show synergy with carboplatin and paclitaxel, chemotherapeutic agents which we have previously shown to be synergistic with authentic Bcl-2 family antagonists. Obatoclax induced a profound accumulation of LC-3 but knockdown of Atg-5 or beclin had only minor effects on the activity of obatoclax in cell growth assays suggesting that the inhibition of lysosomal function rather than stimulation of autophagy may play a more prominent role in these cells. To evaluate how obatoclax inhibits lysosomal function, confocal microscopy studies were conducted which demonstrated that obatoclax, which contains two basic pyrrole groups, accumulates in lysosomes. Studies using pH sensitive dyes demonstrated that obatoclax induced lysosomal alkalinization. Furthermore, obatoclax was synergistic in cell growth/survival assays with bafilomycin and chloroquine, two other drugs which cause lysosomal alkalinization. These studies explain, for the first time, how obatoclax inhibits lysosomal function and suggest that lysosomal alkalinization contributes to the cytotoxic activity of obatoclax.</abstract><cop>United States</cop><pub>Public Library of Science</pub><pmid>26950068</pmid><doi>10.1371/journal.pone.0150696</doi><tpages>e0150696</tpages><oa>free_for_read</oa></addata></record>
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identifier ISSN: 1932-6203
ispartof PloS one, 2016-03, Vol.11 (3), p.e0150696-e0150696
issn 1932-6203
1932-6203
language eng
recordid cdi_plos_journals_1771230385
source MEDLINE; DOAJ Directory of Open Access Journals; Public Library of Science (PLoS) Journals Open Access; EZB-FREE-00999 freely available EZB journals; PubMed Central; Free Full-Text Journals in Chemistry
subjects Antagonists
Antineoplastic agents
Apoptosis
Autophagy
Bcl-2 protein
Biological Transport
Biology and Life Sciences
Biomimetic Materials - metabolism
Biomimetic Materials - pharmacology
Biotechnology
Cancer
Cancer therapies
Carboplatin
Caspase
Cathepsins - antagonists & inhibitors
Cell cycle
Cell death
Cell Death - drug effects
Cell Line, Tumor
Cell survival
Chemotherapy
Chloroquine
Complications and side effects
Confocal microscopy
Cytotoxicity
Dosage and administration
Drugs
Genetic aspects
Health aspects
Humans
Hydrogen-Ion Concentration
Inhibitor drugs
Kinases
Lysosomes
Lysosomes - chemistry
Lysosomes - drug effects
Lysosomes - metabolism
Medicine
Medicine and Health Sciences
Microscopy
Ovarian cancer
Ovarian carcinoma
Paclitaxel
pH effects
Phagocytosis
Pharmacology
Pharmacy
Physiological aspects
Poly(ADP-ribose) polymerase
Proto-Oncogene Proteins c-bcl-2 - antagonists & inhibitors
Pyrroles - metabolism
Pyrroles - pharmacology
Regulators
Research and Analysis Methods
Science
Tumor cell lines
title The BH3 Mimetic Obatoclax Accumulates in Lysosomes and Causes Their Alkalinization
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