Critical role of reactive oxygen species (ROS) for synergistic enhancement of apoptosis by vemurafenib and the potassium channel inhibitor TRAM-34 in melanoma cells

Abstract

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.

Oridonin inhibits migration, invasion, adhesion and TGF‑β1‑induced epithelial‑mesenchymal transition of melanoma cells by inhibiting the activity of PI3K/Akt/GSK‑3β signaling pathway

“…Our data showed that the viability of A375 and B16-F10 melanoma cells were not allergic to ORI's treatment compared with other cancer cell lines (47,48). As the literature reported that ROS represents an initial and independent apoptosis pathway in melanoma cells (49). So we speculate that ORI can not trigger the ROS system inducing the apoptosis pathway in melanoma cells at lower concentrations (5 and 10 µM).…”

Crucial role of reactive oxygen species (ROS) for the proapoptotic effects of indirubin derivative DKP‐073 in melanoma cells

“…For ROS generation by DKP‐073, NOX enzymes may be involved as suggested by two used NOX inhibitors. The critical role of ROS in apoptosis regulation in melanoma cells was also seen, when other therapeutic strategies were applied, as chemotherapy and radiotherapy, elesclomol, PI3K inhibition, or BRAF inhibition …”

“…However, its relation to other described apoptosis pathways remained fragmentary so far. In melanoma cells, we have previously described enhanced ROS levels in response to inhibition of phospoinositol‐3 kinase (PI3K) as well as to inhibition of BRAF …”

“…In melanoma cells, we have previously described enhanced ROS levels in response to inhibition of phospoinositol-3 kinase (PI3K) as well as to inhibition of BRAF. 11,12 Both the death ligand TRAIL (TNF-related apoptosis-inducing ligand) and derivatives of indirubin may be considered as promising candidates for improving cancer therapy. TRAIL has been suggested as therapeutic approach because of its potential to selectively induce apoptosis in cancer cells.…”

Effects of 5‑hydroxy‑4'‑nitro‑7‑propionyloxy‑genistein on inhibiting proliferation and invasion via activating reactive oxygen species in human ovarian cancer A2780/DDP cells

“…It is well-known that mitochondria serve a crucial function in the extrinsic and intrinsic pathways of apoptosis; the structural integrity and normal function of mitochondrial membranes are critical for cell survival (22). Notably, if the structure and function of mitochondrial membranes sustain damage, for example through ultraviolet irradiation, genotoxic agents or oxidative stress, this will trigger a series of cellular events that will affect the basic characteristics of malignant tumors, such as the proliferation, invasion and metastasis, and even induce cells apoptosis or necrosis (23).…”