Targeting B-Raf inhibitor resistant melanoma with novel cell penetrating peptide disrupters of PDE8A – C-Raf

Abstract

BackgroundRecent advances in the treatment of melanoma that involve immunotherapy and B-Raf inhibition have revolutionised cancer care for this disease. However, an un-met clinical need remains in B-Raf inhibitor resistant patients where first-generation B-Raf inhibitors provide only short-term disease control. In these cases, B-Raf inhibition leads to paradoxical activation of the C-Raf – MEK – ERK signalling pathway, followed by metastasis. PDE8A has been shown to directly interact with and modulate the cAMP microdomain in the vicinity of C-Raf. This interaction promotes C-Raf activation by attenuating the PKA-mediated inhibitory phosphorylation of the kinase.MethodsWe have used a novel cell-penetrating peptide agent (PPL-008) that inhibits the PDE8A – C-Raf complex in a human malignant MM415 melanoma cell line and MM415 melanoma xenograft mouse model to investigate ERK MAP kinase signalling.ResultsWe have demonstrated that the PDE8A – C-Raf complex disruptor PPL-008 increased inhibitory C-Raf-S259 phosphorylation and significantly reduced phospho-ERK signalling. We have also discovered that the ability of PPL-008 to dampen ERK signalling can be used to counter B-Raf inhibitor-driven paradoxical activation of phospho-ERK in MM415 cells treated with PLX4032 (Vemurafenib). PPL-008 treatment also significantly retarded the growth of these cells. When applied to a MM415 melanoma xenograft mouse model, PPL-008C penetrated tumour tissue and significantly reduced phospho-ERK signalling in that domain.ConclusionOur data suggests that the PDE8A-C-Raf complex is a promising therapeutic treatment for B-Raf inhibitor resistant melanoma.Electronic supplementary materialThe online version of this article (10.1186/s12885-019-5489-4) contains supplementary material, which is available to authorized users.

Novel LRRFIP2‐RAF1 fusion identified in an acral melanoma: A review of the literature on melanocytic proliferations with RAF1 fusions and the potential therapeutic implications

“…26,27 Newly discovered cellpenetrating peptide agents that target CRAF have been shown to disrupt ERK signaling and reduce the rate of cell growth in a human melanoma cell line and xenograft mouse model. 28 These promising results raise hope that novel peptide disrupters could be used therapeutically for patients with BRAF inhibitor-resistant melanomas as well as advanced RAF1 fusion melanomas. RAF1 alterations have also been identified in extracutaneous neoplasms including papillary thyroid carcinoma, 11 breast cancer, 29 prostatic adenocarcinoma, 6,11 pancreatic acinar cell carcinoma, 30 anaplastic pleomorphic xanthoastrocytoma, 31 pilocytic glioma, 20,32 and in a family of monomorphic spindle cell mesenchymal tumors resembling low-grade malignant peripheral nerve sheath tumors.…”

“…There has also been a recent enthusiasm for developing agents targeting CRAF for the treatment of BRAF inhibitor‐resistant melanomas since patients who receive BRAF inhibitors show paradoxical activation of the CRAF‐MEK‐ERK signaling pathway, which could account for disease progression following the short‐term disease control experienced 26,27 . Newly discovered cell‐penetrating peptide agents that target CRAF have been shown to disrupt ERK signaling and reduce the rate of cell growth in a human melanoma cell line and xenograft mouse model 28 . These promising results raise hope that novel peptide disrupters could be used therapeutically for patients with BRAF inhibitor‐resistant melanomas as well as advanced RAF1 fusion melanomas.…”

Peptides derived from the SARS-CoV-2 receptor binding motif bind to ACE2 but do not block ACE2-mediated host cell entry or pro-inflammatory cytokine induction

“…In total, the FP data suggested that we were successful in designing short sequence linear RBM-derived peptides capable of directly binding ACE2. Previous work using the peptide array approach has reliably generated highly-selective decoy peptides against pathological PPIs in a broad context of disease-indications, including heart failure (HSP20 –PDE4D) [ 29 , 30 ], schizophrenia (DISC1 –FBWX7) [ 31 ], and cancer (c-Raf–PDE8A) [ 21 , 32 , 33 ]. All identified RBM peptides discovered in this study were tested as potential SARS-CoV-2 viral cell-entry inhibitors.…”

Cyclic adenosine monophosphate (cAMP) signaling in melanocyte pigmentation and melanomagenesis

“…Pharmacological disruption of this PDE8A-CRAF complex with PPL-008 attenuates downstream MAPK signaling and decreases cell proliferation in vitro (Blair, Walsh, Littman, Marcoux, & Baillie, 2019).…”

“…Several studies also suggest a role of PDE8 in CRAF activation, as PDE8A directly interacts with CRAF to protect CRAF from PKA‐mediated inhibition (Brown et al., 2013; Maurice, 2013). Pharmacological disruption of this PDE8A‐CRAF complex with PPL‐008 attenuates downstream MAPK signaling and decreases cell proliferation in vitro (Blair, Walsh, Littman, Marcoux, & Baillie, 2019 ) . This reinforces the concept that impairment in cAMP signaling by increased PDE activity is associated with CRAF activation and oncogenic progression, while restoration of cAMP signaling is protective.…”