Critical role of reactive oxygen species (ROS) for synergistic enhancement of apoptosis by vemurafenib and the potassium channel inhibitor TRAM-34 in melanoma cells.
Inhibition of MAP kinase pathways by selective BRAF inhibitors, such as vemurafenib and dabrafenib, have evolved as key therapies of BRAF-mutated melanoma. However, tumor relapse and therapy resistance have remained as major problems, which may be addressed by combination with other pathway inhibitors. Here we identified the potassium channel inhibitor TRAM-34 as highly effective in combination with vemurafenib. Thus apoptosis was significantly enhanced and cell viability was decreased. The combination vemurafenib/TRAM-34 was also effective in vemurafenib-resistant cells, suggesting that acquired resistance may be overcome. Vemurafenib decreased ERK phosphorylation, suppressed antiapoptotic Mcl-1 and enhanced proapoptotic Puma and Bim. The combination resulted in enhancement of proapoptotic pathways as caspase-3 and loss of mitochondrial membrane potential. Indicating a special mechanism of vemurafenib-induced apoptosis, we found strong enhancement of intracellular ROS levels already at 1 h of treatment. The critical role of ROS was demonstrated by the antioxidant vitamin E (α-tocopherol), which decreased intracellular ROS as well as apoptosis. Also caspase activation and loss of mitochondrial membrane potential were suppressed, proving ROS as an upstream effect. Thus ROS represents an initial and independent apoptosis pathway in melanoma cells that is of particular importance for vemurafenib and its combination with TRAM-34.
Department of Dermatology, Venerology und Allergology, Skin Cancer Center Charité, Charité - Universitätsmedizin Berlin, Berlin, Germany.|Molecular Medicine Master's Program, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Daniel
D
Bauer
Department of Dermatology, Venerology und Allergology, Skin Cancer Center Charité, Charité - Universitätsmedizin Berlin, Berlin, Germany.|Institute for Biochemistry and Biology, Faculty of Science, University of Potsdam, Potsdam, Germany.
Felix
F
Werth
Department of Dermatology, Venerology und Allergology, Skin Cancer Center Charité, Charité - Universitätsmedizin Berlin, Berlin, Germany.|Molecular Medicine Master's Program, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Ha An
HA
Nguyen
Department of Dermatology, Venerology und Allergology, Skin Cancer Center Charité, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Felix
F
Kiecker
Department of Dermatology, Venerology und Allergology, Skin Cancer Center Charité, Charité - Universitätsmedizin Berlin, Berlin, Germany.
Jürgen
J
Eberle
D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004357:Drug Synergism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008545:Melanoma / Q000188:drug therapy* / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D010091:Oximes / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides / Q000494:pharmacology*; D000077484:Vemurafenib; D014810:Vitamin E / Q000494:pharmacology
D007093:Imidazoles; D007211:Indoles; D010091:Oximes; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D011720:Pyrazoles; D017382:Reactive Oxygen Species; D013449:Sulfonamides; C411671:TRAM 34; D014810:Vitamin E; D000077484:Vemurafenib; D048493:Proto-Oncogene Proteins B-raf; D053148:Caspase 3; C561627:dabrafenib