RESUMO
The hepatitis C virus (HCV) NS4B protein is an antiviral therapeutic target for which small-molecule inhibitors have not been shown to exhibit in vivo efficacy. We describe here the in vitro and in vivo antiviral activity of GSK8853, an imidazo[1,2-a]pyrimidine inhibitor that binds NS4B protein. GSK8853 was active against multiple HCV genotypes and developed in vitro resistance mutations in both genotype 1a and genotype 1b replicons localized to the region of NS4B encoding amino acids 94 to 105. A 20-day in vitro treatment of replicons with GSK8853 resulted in a 2-log drop in replicon RNA levels, with no resistance mutation breakthrough. Chimeric replicons containing NS4B sequences matching known virus isolates showed similar responses to a compound with genotype 1a sequences but altered efficacy with genotype 1b sequences, likely corresponding to the presence of known resistance polymorphs in those isolates. In vivo efficacy was tested in a humanized-mouse model of HCV infection, and the results showed a 3-log drop in viral RNA loads over a 7-day period. Analysis of the virus remaining at the end of in vivo treatment revealed resistance mutations encoding amino acid changes that had not been identified by in vitro studies, including NS4B N56I and N99H. Our findings provide an in vivo proof of concept for HCV inhibitors targeting NS4B and demonstrate both the promise and potential pitfalls of developing NS4B inhibitors.
Assuntos
Antivirais/farmacologia , Farmacorresistência Viral/genética , Hepacivirus/efeitos dos fármacos , Hepatite C/tratamento farmacológico , Imidazóis/farmacologia , Piridinas/farmacologia , RNA Viral/antagonistas & inibidores , Animais , Antivirais/síntese química , Linhagem Celular Tumoral , Avaliação Pré-Clínica de Medicamentos , Expressão Gênica , Genótipo , Hepacivirus/genética , Hepacivirus/crescimento & desenvolvimento , Hepatite C/patologia , Hepatite C/virologia , Hepatócitos/efeitos dos fármacos , Hepatócitos/patologia , Hepatócitos/virologia , Humanos , Imidazóis/síntese química , Camundongos , Camundongos Transgênicos , Mutação , Piridinas/síntese química , RNA Viral/biossíntese , RNA Viral/genética , Replicon/efeitos dos fármacos , Resultado do Tratamento , Carga Viral/efeitos dos fármacos , Proteínas não Estruturais Virais , Replicação Viral/efeitos dos fármacosRESUMO
The RAS-RAF-mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway provides numerous opportunities for targeted oncology therapeutics. In particular, the MEK enzyme is attractive due to high selectivity for its target ERK and the central role that activated ERK plays in driving cell proliferation. The structural, pharmacologic, and pharmacokinetic properties of RDEA119/BAY 869766, an allosteric MEK inhibitor, are presented. RDEA119/BAY 869766 is selectively bound directly to an allosteric pocket in the MEK1/2 enzymes. This compound is highly efficacious at inhibiting cell proliferation in several tumor cell lines in vitro. In vivo, RDEA119/BAY 869766 exhibits potent activity in xenograft models of melanoma, colon, and epidermal carcinoma. RDEA119/BAY 869766 exhibits complete suppression of ERK phosphorylation at fully efficacious doses in mice. RDEA119/BAY 869766 shows a tissue selectivity that reduces its potential for central nervous system-related side effects. Using pharmacokinetic and pharmacodynamic data, we show that maintaining adequate MEK inhibition throughout the dosing interval is likely more important than achieving high peak levels because greater efficacy was achieved with more frequent but lower dosing. Based on its longer half-life in humans than in mice, RDEA119/BAY 869766 has the potential for use as a once- or twice-daily oral treatment for cancer. RDEA119/BAY 869766, an exquisitely selective, orally available MEK inhibitor, has been selected for clinical development because of its potency and favorable pharmacokinetic profile.