title: GX15-070 (obatoclax) induces apoptosis and inhibits cathepsin D- and L-mediated autophagosomal lysis in antiestrogen-resistant breast cancer cells.
abstract: In estrogen receptor-positive (ER+) breast cancer cells, BCL2 overexpression contributes to antiestrogen resistance. Direct targeting of the antiapoptotic BCL2 members with GX15-070 (obatoclax), a BH3-mimetic currently in clinical development, is an attractive strategy to overcome antiestrogen resistance in some breast cancers. Recently, GX15-070 has been shown to induce both apoptosis and autophagy, yet the underlying cell death mechanisms have yet to be elucidated. Here, we show that GX15-070 is more effective in reducing the cell density of antiestrogen-resistant breast cancer cells versus sensitive cells and that this increased sensitivity of resistant cells to GX15-070 correlates with an accumulation of autophagic vacuoles. Formation of autophagosomes in GX15-070-treated cells was verified by changes in expression of the lipidation of microtubule-associated protein-1 light chain-3 and both confocal and transmission electron microscopy. While GX15-070 treatment promotes autophagic vacuole and autolysosome formation, p62/SQSTM1, a marker for autophagic degradation, levels accumulate. Moreover, GX15-070 exposure leads to a reduction in cathepsin D (CTSD) and L (CTSL1) protein expression that would otherwise digest autolysosome cargo. Thus, GX15-070 has dual roles in promoting cell death: (i) directly inhibiting antiapoptotic BCL2 family members, thereby inducing apoptosis; and (ii) inhibiting downstream CTSD and CTSL1 protein expression to limit the ability of cells to use degraded material to fuel cellular metabolism and restore homeostasis. Our data highlight a new mechanism of GX15-070-induced cell death that could be used to design novel therapeutic interventions for antiestrogen resistant breast cancer.
authors: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University School of Medicine, Washington, DC 20057, USA.
authors: Jessica L
authors: JL
authors: Schwartz-Roberts
authors: Ayesha N
authors: AN
authors: Shajahan
authors: Katherine L
authors: KL
authors: Cook
authors: Anni
authors: A
authors: Wärri
authors: Mones
authors: M
authors: Abu-Asab
authors: Robert
authors: R
authors: Clarke
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects; D000071186:Beclin-1; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism*; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000378:metabolism*; D056668:Cathepsin L / Q000037:antagonists & inhibitors / Q000378:metabolism*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007211:Indoles; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism; D011758:Pyrroles / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D000071456:Sequestosome-1 Protein; D014183:Transplantation, Heterologous
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; D004965:Estrogen Antagonists; D007211:Indoles; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D011758:Pyrroles; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; D056668:Cathepsin L; D002402:Cathepsin D; C520962:obatoclax
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