The novel Raf inhibitor Raf265 decreases Bcl-2 levels and confers TRAIL-sensitivity to neuroendocrine tumour cells

Abstract

The tumour-selective death receptor ligand tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent for the treatment of human cancer. However, many tumours have evolved mechanisms to resist TRAIL-induced apoptosis. A number of studies have demonstrated that aberrant PI(3)K-Akt-mTOR survival signalling may confer TRAIL resistance by altering the balance between pro-and anti-apoptotic proteins. Here, we show that neuroendocrine tumour (NET) cell lines of heterogeneous origin exhibit a range of TRAIL sensitivities and that TRAIL sensitivity correlates with the expression of FLIP S , caspase-8, and Bcl-2. Neither single mTOR inhibition by everolimus nor dual mTOR/PI(3)K inhibition by NVP-BEZ235 was able to enhance TRAIL susceptibility in any of the tested cell lines. In contrast, dual PI(3)K-Akt-mTOR and Raf-MEK-Erk pathway inhibition by the IGF-1R inhibitor NVP-AEW541 effectively restored TRAIL sensitivity in NCI-H727 bronchus carcinoid cells. Furthermore, blocking Raf-MEK-Erk signalling by the novel Raf inhibitor Raf265 significantly enhanced TRAIL sensitivity in NCI-H727 and CM insulinoma cells. While having no effect on FLIP S or caspase-8 expression, Raf265 strongly decreased Bcl-2 levels in those cell lines susceptible to its TRAIL-sensitizing action. Taken together, our findings suggest that combinations of Raf-MEK-Erk pathway inhibitors and TRAIL might offer a novel therapeutic strategy in NET disease.

Cytotoxic Effects of Valproic Acid on Neuroendocrine Tumour Cells

“…Recently, it has been shown that GOT1 cells are resistant to death receptor signalling induced by TRAIL [37]. GOT1 cells express low levels of caspase-8 and high levels of the anti-apoptotic proteins CFLAR and Bcl-2 compared to NET cells of pancreatic and broncho-pulmonary origin [37]. Our data suggest that VPA exerts a TRAIL-sensitizing effect through downregulation of CFLAR .…”

“…A detailed analysis of the transcriptional response in GOT1 cells confirmed that there was a correlation between growth inhibition and activation of death receptor signalling and mitochondria-mediated apoptosis. Recently, it has been shown that GOT1 cells are resistant to death receptor signalling induced by TRAIL [37]. GOT1 cells express low levels of caspase-8 and high levels of the anti-apoptotic proteins CFLAR and Bcl-2 compared to NET cells of pancreatic and broncho-pulmonary origin [37].…”

Ouabain downregulates Mcl-1 and sensitizes lung cancer cells to TRAIL-induced apoptosis

“…An increase of c-FLIP protein was shown to suppress TRAILinduced gallbladder cancer cell death (41) and a decrease in c-FLIP enhanced TRAIL-mediated apoptosis in breast cancer cells (7). Likewise, Bcl-2 family proteins, namely Bcl-2 and Mcl-1, exert their inhibitory functions on TRAIL-induced apoptosis (38,40). Recently, Mcl-1 has gained increasing attention as many researchers have reported that decreasing Mcl-1 could sensitize cancer cells to TRAIL-induced apoptosis (13,14).…”

The Novel Cyclin-Dependent Kinase 4/6 Inhibitor Ribociclib (LEE011) Alone and in Dual-Targeting Approaches Demonstrates Antitumoral Efficacy in Neuroendocrine Tumors in vitro

“…8 ). Many studies indicate the importance of the Ras-Raf-MEK-ERK and the PI3K-Akt-mTOR molecular signaling pathway for NET cell growth, invasion, and proliferation [16,[40][41][42][43][44][45][46] . In addition, 5-FU showed cooperative downregulating effects with LEE011 on cell cycle components such as oncogenic cyclin D1 ( Fig.…”

“…Single-substance treatment with everolimus has been shown to lead to resistance mechanisms in many tumor entities, including pNETs [58][59][60][61] . Dual-targeted therapy approaches to overcome possible resistance mechanisms and feedback loops have shown promising results in NETs [40,62] . In PI3K inhibitor-resistant cancer cells, combined treatment with a CDK4/6 inhibitor re-sensitized cancer cells to PI3K inhibition [63] .…”