Glutathione and Bcl-2 targeting facilitates elimination by chemoradiotherapy of human A375 melanoma xenografts overexpressing bcl-xl, bcl-2, and mcl-1

Abstract

BackgroundBcl-2 is believed to contribute to melanoma chemoresistance. However, expression of Bcl-2 proteins may be different among melanomas. Thus correlations among expression of Bcl-2-related proteins and in vivo melanoma progression, and resistance to combination therapies, was investigated.MethodsHuman A375 melanoma was injected s.c. into immunodeficient nude mice. Protein expression was studied in tumor samples obtained by laser microdisection. Transfection of siRNA or ectopic overexpression were applied to manipulate proteins which are up- or down-regulated, preferentially, during melanoma progression. Anti-bcl-2 antisense oligonucleotides and chemoradiotherapy (glutathione-depleting agents, paclitaxel protein-binding particles, daunorubicin, X rays) were administered in combination.ResultsIn vivo A375 cells down-regulated pro-apoptotic bax expression; and up-regulated anti-apoptotic bcl-2, bcl-xl, and mcl-1, however only Bcl-2 appeared critical for long-term tumor cell survival and progression in vivo. Reduction of Bcl-2, combined with partial therapies, decreased melanoma growth. But only Bcl-2 targeting plus the full combination of chemoradiotherapy eradicated A375 melanoma, and led to long-term survival (> 120 days) without recurrence in 80% of mice. Tumor regression was not due to immune stimulation. Hematology and clinical chemistry data were within accepted clinical toxicities.ConclusionStrategies to target Bcl-2, may increase the effectiveness of antitumor therapies against melanomas overexpressing Bcl-2 and likely other Bcl-2-related antiapoptotic proteins.

Oxidative stress and antioxidants in the pathophysiology of malignant melanoma

“…Interestingly, Bcl-2 specifically inhibits GSH efflux from melanoma cells thereby facilitating its intracellular accumulation (Ortega et al, 2003). All facts coherent with observations indicating that Bcl-2-overexpressing melanomas appear more aggressive (Trisciuoglio et al, 2005;Mena et al, 2012); and that in melanoma, the mitochondrial apoptosis pathways and Bcl-2 proteins appear of particular importance for apoptosis resistance (Eberle and Hossini, 2008).…”

Anti-apoptotic proteins on guard of melanoma cell survival

“…This was also supported by the report showing that silencing Bcl-2 resulted in moderate apoptosis per se but sensitized melanoma cells to low doses of cisplatin [30]. Importantly, Bcl-2 was shown to be a critical regulator of melanoma growth in vivo that could not be substituted by Bcl-X L or Mcl-1 [31].…”

Glucocorticoid Receptor Knockdown Decreases the Antioxidant Protection of B16 Melanoma Cells: An Endocrine System-Related Mechanism that Compromises Metastatic Cell Resistance to Vascular Endothelium-Induced Tumor Cytotoxicity

“…Notably, Blc-2, in particular, can inhibit GSH efflux and, thus, favors GSH accumulation within the cancer cell [4]. This conclusion has experimental and clinical relevance as different Bcl-2 over-expressing melanomas have been observed to exhibit more aggressive behavior [67].…”