BAY 43-9006 exhibits broad spectrum oral antitumor activity and targets the RAF/MEK/ERK pathway and receptor tyrosine kinases involved in tumor progression and angiogenesis.

The RAS/RAF signaling pathway is an important mediator of tumor cell proliferation and angiogenesis. The novel bi-aryl urea BAY 43-9006 is a potent inhibitor of Raf-1, a member of the RAF/MEK/ERK signaling pathway. Additional characterization showed that BAY 43-9006 suppresses both wild-type and V599E mutant BRAF activity in vitro. In addition, BAY 43-9006 demonstrated significant activity against several receptor tyrosine kinases involved in neovascularization and tumor progression, including vascular endothelial growth factor receptor (VEGFR)-2, VEGFR-3, platelet-derived growth factor receptor beta, Flt-3, and c-KIT. In cellular mechanistic assays, BAY 43-9006 demonstrated inhibition of the mitogen-activated protein kinase pathway in colon, pancreatic, and breast tumor cell lines expressing mutant KRAS or wild-type or mutant BRAF, whereas non-small-cell lung cancer cell lines expressing mutant KRAS were insensitive to inhibition of the mitogen-activated protein kinase pathway by BAY 43-9006. Potent inhibition of VEGFR-2, platelet-derived growth factor receptor beta, and VEGFR-3 cellular receptor autophosphorylation was also observed for BAY 43-9006. Once daily oral dosing of BAY 43-9006 demonstrated broad-spectrum antitumor activity in colon, breast, and non-small-cell lung cancer xenograft models. Immunohistochemistry demonstrated a close association between inhibition of tumor growth and inhibition of the extracellular signal-regulated kinases (ERKs) 1/2 phosphorylation in two of three xenograft models examined, consistent with inhibition of the RAF/MEK/ERK pathway in some but not all models. Additional analyses of microvessel density and microvessel area in the same tumor sections using antimurine CD31 antibodies demonstrated significant inhibition of neovascularization in all three of the xenograft models. These data demonstrate that BAY 43-9006 is a novel dual action RAF kinase and VEGFR inhibitor that targets tumor cell proliferation and tumor angiogenesis.

FGF-2 antagonizes the TGF-beta1-mediated induction of pericyte alpha-smooth muscle actin expression: a role for myf-5 and Smad-mediated signaling pathways.

PURPOSE: Although the FGF and TGF-beta families are known to play an important role in regulating vascular endothelial and smooth muscle cell behavior, the influence of these matrix-binding growth factors on microvascular pericyte morphogenesis is not well understood. The current study was undertaken to examine the molecular mechanisms that mediate the effects of the endothelium-produced growth regulators FGF-2 and TGF-beta1 on retinal pericyte proliferation and contractile phenotype. METHODS: Using purified retinal pericytes, a series of assays were implemented, including RT-PCR, DNA binding, immunoprecipitation, electrophoretic mobility shift, and indirect immunofluorescence, in an attempt to elucidate the FGF/TGF-beta1 signaling cascades that mediate retinal microvascular cell growth and contractile phenotype. RESULTS: Treatment of retinal pericytes with FGF-2 and heparin stimulated nearly a log order increase in proliferation, whereas removal of FGF-2 or addition of TGF-beta1 caused withdrawal from the growth cycle, inducing a smooth-muscle-like contractile phenotype, as indicated by upregulation of alpha-smooth muscle actin (alpha-SMA). This switch from a growth-potentiated to a growth-arrested state followed induction of the transcriptional regulator myf-5, as well as the nuclear translocation of myf-5 and Smad2. CONCLUSIONS: Several critical features of the endothelial cell-extracellular matrix-pericyte molecular signaling axis were elucidated in the study that are likely to be responsible for regulating retinal microvascular morphogenesis during normal development, as well as the pathologic angiogenesis accompanying several ocular disorders, including diabetic retinopathy and age-related macular degeneration.