title: Drug Synergism of Proteasome Inhibitors and Mitotane by Complementary Activation of ER Stress in Adrenocortical Carcinoma Cells.
abstract: Mitotane is the only drug approved for treatment of the orphan disease adrenocortical carcinoma (ACC) and was recently shown to be the first clinically used drug acting through endoplasmic reticulum (ER)-stress induced by toxic lipids. Since mitotane has limited clinical activity as monotherapy, we here study the potential of activating ER-stress through alternative pathways. The single reliable NCI-H295 cell culture model for ACC was used to study the impact MG132, bortezomib (BTZ) and carfilzomib (CFZ) on mRNA and protein expression of ER-stress markers, cell viability and steroid hormone secretion. We found all proteasome inhibitors alone to trigger expression of mRNA (spliced X-box protein 1, XBP1) and protein markers indicative of the inositol-requiring enzyme 1 (IRE1) dependent pathway of ER-stress but not phosphorylation of eukaryotic initiation factor 2α (eIF2α), a marker of the PRKR-like endoplasmic reticulum kinase (PERK)-dependent pathway. Whereas mitotane alone activated both pathways, combination of BTZ and CFZ with low-dose mitotane blocked mitotane-induced eIF2α phosphorylation but increased XBP1-mRNA splicing indicating that proteasome inhibitors can commit signalling towards a single ER-stress pathway in ACC cells. By applying the median effect model of drug combinations using cell viability as a read out, we determined significant drug synergism between mitotane and both BTZ and CFZ. In conclusion, combination of mitotane with activators of ER-stress through the unfolded protein response is synergistic in an ACC cell culture model. Since proteasome inhibitors are readily available clinically, they are attractive candidates to study for ACC treatment in clinical trials in combination with mitotane.
authors.affiliation: Comprehensive Cancer Center Mainfranken, University of Würzburg, Würzburg, Germany. Kroiss_M@ukw.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kroiss
authors.affiliation: Department of Internal Medicine I, Division of Endocrinology and Diabetes, University Hospital Würzburg, Oberrdürrbacher-Strasse 6, 97080, Würzburg, Germany.
authors.forename: Silviu
authors.initials: S
authors.lastname: Sbiera
authors.affiliation: Clinical Chemistry and Laboratory Medicine, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Sabine
authors.initials: S
authors.lastname: Kendl
authors.affiliation: Department of Internal Medicine I, Division of Endocrinology and Diabetes, University Hospital Würzburg, Oberrdürrbacher-Strasse 6, 97080, Würzburg, Germany.|Clinical Chemistry and Laboratory Medicine, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Kurlbaum
authors.affiliation: Comprehensive Cancer Center Mainfranken, University of Würzburg, Würzburg, Germany.|Department of Internal Medicine I, Division of Endocrinology and Diabetes, University Hospital Würzburg, Oberrdürrbacher-Strasse 6, 97080, Würzburg, Germany.|Clinical Chemistry and Laboratory Medicine, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Fassnacht
mesh_terms: D000306:Adrenal Cortex Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D018268:Adrenocortical Carcinoma / Q000188:drug therapy / Q000235:genetics* / Q000378:metabolism; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D000069286:Bortezomib / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D004722:Endoribonucleases / Q000235:genetics*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008939:Mitotane / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation; D061988:Proteasome Inhibitors / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D000071717:X-Box Binding Protein 1 / Q000235:genetics*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D015852:Eukaryotic Initiation Factor-2; D007976:Leupeptins; D009842:Oligopeptides; D061988:Proteasome Inhibitors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D000069286:Bortezomib; C524865:carfilzomib; D008939:Mitotane; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
keywords: Adrenal cancer; Synergism; Toxic lipids; Unfolded protein response