title: Proteasome inhibitors against amelanotic melanoma.
abstract: The incidence of malignant melanoma, the most aggressive skin cancer, is increasing constantly. Despite new targeted therapies, the prognosis for patients with metastatic disease remains poor. Thus, there is a need for new combinational treatments, and antineoplastic agents potentially valuable in this approach are inhibitors of the ubiquitin-proteasome system (UPS). In this work, we analyze the cytotoxicity mechanisms of proteasome inhibitors (MG-132, epoxomicin, and lactacystin) in a specific form of melanoma which does not synthesize melanin-the amelanotic melanoma (Ab cells). We found that the most cytotoxic of the compounds tested was epoxomicin. Caspase-9 activation as well as cytochrome C and AIF release from mitochondria indicated that exposure to epoxomicin induced the mitochondrial pathway of apoptosis. Epoxomicin treatment also resulted in accumulation of Bcl-2 family members-proapoptotic Noxa and antiapoptotic Mcl-1, which were postulated as the targets for bortezomib in melanoma. Inhibition of caspases by BAF revealed that cell death was partially caspase-independent. We observed no cell cycle arrest preceding the apoptosis of Ab cells, even though cdk inhibitors p21Cip1/Waf1and p27Kip1were up-regulated. The cell cycle was blocked only after inactivation of caspases by the pan-caspase inhibitor BAF. In summary, this is the first study exploring molecular mechanisms of cell death induced by epoxomicin in melanoma. We found that Ab cells died on the mitochondrial pathway of apoptosis and also partially by the caspase-independent way of death. Apoptosis induction was fast and efficient and was not preceded by cell cycle arrest.
authors.affiliation: Department of Anatomy and Neurobiology, Medical University of Gdansk, Gdansk, Poland. j.sidor@gumed.edu.pl.
authors.forename: Justyna
authors.identifier: 0000-0001-5747-4782
authors.initials: J
authors.lastname: Sidor-Kaczmarek
authors.affiliation: Department of Embryology, Medical University of Gdansk, Gdansk, Poland.
authors.forename: Mirosława
authors.initials: M
authors.lastname: Cichorek
authors.affiliation: Department of Anatomy and Neurobiology, Medical University of Gdansk, Gdansk, Poland.
authors.forename: Jan Henryk
authors.initials: JH
authors.lastname: Spodnik
authors.affiliation: Department of Anatomy and Neurobiology, Medical University of Gdansk, Gdansk, Poland.
authors.forename: Sławomir
authors.initials: S
authors.lastname: Wójcik
authors.affiliation: Department of Anatomy and Neurobiology, Medical University of Gdansk, Gdansk, Poland.
authors.forename: Janusz
authors.initials: J
authors.lastname: Moryś
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D006224:Cricetinae; D008297:Male; D018328:Melanoma, Amelanotic / Q000188:drug therapy* / Q000201:enzymology* / Q000473:pathology; D008647:Mesocricetus; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors / Q000494:pharmacology*; D012878:Skin Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000473:pathology
chemical_list: D000970:Antineoplastic Agents; D061988:Proteasome Inhibitors; D046988:Proteasome Endopeptidase Complex
keywords: Apoptosis; Cancer; Melanoma; Proteasome inhibitors