TY  - JOUR
A1  - Bauer, Daniel
A1  - Werth, Felix
A1  - Ha An Nguyen, 
A1  - Kiecker, Felix
A1  - Eberle, Jürgen
T1  - Critical role of reactive oxygen species (ROS) for synergistic enhancement of apoptosis by vemurafenib and the potassium channel inhibitor TRAM-34 in melanoma cells
JF  - Cell death & disease
N2  - 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 (alpha-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.
Y1  - 2017
U6  - https://doi.org/10.1038/cddis.2017.6
SN  - 2041-4889
VL  - 8
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Zhivkova, Veselina
A1  - Kiecker, Felix
A1  - Langer, Peter
A1  - Eberle, Jürgen
T1  - Crucial role of reactive oxygen species (ROS) for the proapoptotic effects of indirubin derivative DKP-073 in melanoma cells
JF  - Molecular carcinogenesis
N2  - Melanoma represents a prime example demonstrating the success of targeted therapy in cancer. Nevertheless, it remained a deadly disease until now, and the identification of new, independent strategies as well as the understanding of their molecular mechanisms may help to finally overcome the high mortality. Both indirubins and TNF-related apoptosis-inducing ligand (TRAIL) represent promising candidates. Here, the indirubin derivative DKP-073 is shown to trigger apoptosis in melanoma cells, which is enhanced by the combination with TRAIL and is accompanied by complete loss of cell viability. Addressing the signaling cascade, characteristic molecular steps were identified as caspase-3 activation, downregulation of XIAP, upregulation of p53 and TRAIL receptor 2, loss of mitochondrial membrane potential, and STAT-3 dephosphorylation. The decisive step, however, turned out to be the early production of ROS already at 1 h. This was proven by antioxidant pretreatment, which completely abolished apoptosis induction and loss of cell viability as well as abrogated all signaling effects listed above. Thus, ROS appeared as upstream of all proapoptotic signaling. The data indicate a dominant role of ROS in apoptosis regulation, and the new pathway may expose a possible Achilles heel of melanoma.
KW  - apoptosis
KW  - kinase pathway
KW  - melanoma
KW  - stat 3
Y1  - 2018
U6  - https://doi.org/10.1002/mc.22924
SN  - 0899-1987
SN  - 1098-2744
VL  - 58
IS  - 2
SP  - 258
EP  - 269
PB  - Wiley
CY  - Hoboken
ER  -