The Raf Inhibitor BAY 43-9006 (Sorafenib) Induces Caspase-Independent Apoptosis in Melanoma Cells

Abstract

Mitogen-activated protein kinase (MAPK) is activated in the majority of melanomas, and its activity is essential for cell survival. In this report, we examined the effects of a novel raf inhibitor BAY 43-9006 on melanoma cell viability and intracellular signaling and found that it induces apoptosis through a caspase-independent mechanism. At concentrations that suppress extracellular signal-regulated kinase (ERK) phosphorylation, BAY 43-9006 dephosphorylates Bad on Ser 75 and Ser 99 , activates Bak and Bax, and reduces the mitochondrial transmembrane potential. BAY 43-9006 (sorafenib) down-modulates the levels of Bcl-2 and Bcl-X L in a MAPK-independent manner in A2058 and SKMEL5 melanoma cells but not in the more resistant A375 cells. Of the three lines tested, only A375 cells were rescued from BAY 43-9006-induced apoptosis by knocking down Bad. BAY 43-9006 induced poly(ADP-ribose) polymerase cleavage and the mitochondrial release of cytochrome c and SMAC. However, the pan-caspase inhibitor Z-VAD-fmk had only a modest protective effect against the drug, suggesting that BAY 43-9006-induced apoptosis is largely caspase independent. BAY 43-9006 but not the MAP/ERK kinase inhibitors PD98059 or U0126 induced the nuclear translocation of apoptosisinducing factor (AIF) in A2058 and SKMEL5 cells, and the introduction of a small interfering RNA (siRNA) for AIF partially protected these cells from BAY 43-9006-induced apoptosis. The AIF siRNA had little effect in A375 cells, in which drug-induced AIF release was negligible. These data indicate that in sensitive cell lines, BAY 43-9006-induced apoptosis is independent of Bad dephosphorylation and caspase activation and largely mediated through the nuclear translocation of AIF. (Cancer Res 2006; 66(3): 1611-9)

Oncogenic BRAF regulates β-Trcp expression and NF-κB activity in human melanoma cells

“…Pretreatment of 1205Lu human melanoma cells with BAY 43-9006 led to a significant increase in the number of apoptotic cells (Figure 4b). These data are consistent with the recently demonstrated apoptotic effects of prolonged treatment with BAY 43-9006 (Panka et al, 2006) and with regression in cell and tumor growth upon RNAi-mediated knock-down of BRAF (Sharma et al, 2005;Hoeflich et al, 2006). They also indicate that mutationally activated BRAF plays an important role in the survival of melanoma cells.…”

“…Whereas BAY 43-9006 was shown to downregulate the expression of Bcl-X L (an NF-kB target protein), the mechanisms by which this agent promotes apoptosis in human melanoma cells are complex (Panka et al, 2006) and cannot be attributed solely to NF-kB inhibition. Future basic and translational research efforts are warranted to delineate additional mechanisms by which inhibition of oncogenic BRAF, on the one hand, and effects of available Raf and IKK inhibitors, on the other hand, mediate melanoma cell death and tumor regression.…”

The multikinase inhibitor sorafenib induces caspase-dependent apoptosis in PC-3 prostate cancer cells

“…In more sensitive cell lines, such as Jurkat leukaemia cells or SKMEL5 melanoma cells, sorafenib-induced apoptosis is largely caspase independent because Z-VAD-FMK is not inhibitory and AIF translocation has an essential role in the apoptotic process [23,38]. A previous study observed a higher rate of sorafenib-induced apoptosis than that observed in this study: ∼80% cell death for Jurkat cells at 15 µmol L −1 and 80.9% cell death for SKEML5 cells at 20 µmol L −1 (27.7% cell death was observed for PC-3 cells at 10 µmol L −1 in the current study).…”

Sorafenib in advanced melanoma: a Phase II randomised discontinuation trial analysis

“…cells of the tumour vasculature to inhibit angiogenesis (Wilhelm et al, 2004). Sorafenib also induces apoptosis in several human cancer cell lines (Rahmani et al, 2005;Yu et al, 2005), including melanoma cells (Panka et al, 2006b). Sorafenib downregulates Mcl-1 protein levels in a time-and dose-dependent manner to induce apoptosis in renal, colon and breast tumour lines (Rahmani et al, 2005;Yu et al, 2005).…”

“…This effect involves enhanced proteasomal degradation of Mcl-1, which could be the consequence of RAF-1 inhibition. Finally, sorafenib induces caspase-independent apoptosis in A2058 and SKMEL5 melanoma cell lines (Panka et al, 2006a). However, the multiple molecular targets of sorafenib, and its dual effects on the tumour cell and the vascular endothelium, make it difficult to determine the mechanism of effect of this multikinase inhibitor in different tumour types, particularly in the absence of validated biomarkers.…”