title: The Bcl-2 repertoire of mesothelioma spheroids underlies acquired apoptotic multicellular resistance.
abstract: Three-dimensional (3D) cultures are a valuable platform to study acquired multicellular apoptotic resistance of cancer. We used spheroids of cell lines and actual tumor to study resistance to the proteasome inhibitor bortezomib in mesothelioma, a highly chemoresistant tumor. Spheroids from mesothelioma cell lines acquired resistance to bortezomib by failing to upregulate Noxa, a pro-apoptotic sensitizer BH3-only protein that acts by displacing Bim, a pro-apoptotic Bax/Bak-activator protein. Surprisingly, despite their resistance, spheroids also upregulated Bim and thereby acquired sensitivity to ABT-737, an inhibitor of anti-apoptotic Bcl-2 molecules. Analysis using BH3 profiling confirmed that spheroids acquired a dependence on anti-apoptotic Bcl-2 proteins and were 'primed for death'. We then studied spheroids grown from actual mesothelioma. ABT-737 was active in spheroids grown from those tumors (5/7, ∼70%) with elevated levels of Bim. Using immunocytochemistry of tissue microarrays of 48 mesotheliomas, we found that most (33, 69%) expressed elevated Bim. In conclusion, mesothelioma cells in 3D alter the expression of Bcl-2 molecules, thereby acquiring both apoptotic resistance and sensitivity to Bcl-2 blockade. Mesothelioma tumors ex vivo also show sensitivity to Bcl-2 blockade that may depend on Bim, which is frequently elevated in mesothelioma. Therefore, mesothelioma, a highly resistant tumor, may have an intrinsic sensitivity to Bcl-2 blockade that can be exploited therapeutically.
authors.affiliation: Lung Biology Center, San Francisco General Hospital, University of California-San Francisco, 1001 Potrero Avenue, San Francisco, CA 94110, USA. dario.barbone@ucsf.edu
authors.forename: D
authors.initials: D
authors.lastname: Barbone
authors.forename: J A
authors.initials: JA
authors.lastname: Ryan
authors.forename: N
authors.initials: N
authors.lastname: Kolhatkar
authors.forename: A D
authors.initials: AD
authors.lastname: Chacko
authors.forename: D M
authors.initials: DM
authors.lastname: Jablons
authors.forename: D J
authors.initials: DJ
authors.lastname: Sugarbaker
authors.forename: R
authors.initials: R
authors.lastname: Bueno
authors.forename: A G
authors.initials: AG
authors.lastname: Letai
authors.forename: L M
authors.initials: LM
authors.lastname: Coussens
authors.forename: D A
authors.initials: DA
authors.lastname: Fennell
authors.forename: V C
authors.initials: VC
authors.lastname: Broaddus
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001713:Biphenyl Compounds / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008654:Mesothelioma / Q000378:metabolism* / Q000473:pathology*; D009596:Nitrophenols / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018874:Spheroids, Cellular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: C501332:ABT-737; D001713:Biphenyl Compounds; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides