Characterization of A Novel, Potent and Selective Small Molecule Spleen Tyrosine Kinase (syk) Inhibitor in in Vitro and in Vivo Models of Asthma.

RationaleSpleen Tyrosine Kinase (SYK) is a key activator of signaling pathways downstream of multiple surface receptors implicated in asthma. SYK function has been extensively studied in mast cells downstream of the high affinity IgE-receptor (FcεR1). Most studies evaluating SYK function in preclinical models have relied on poorly selective compounds, anti-sense oligonucleotides or SYK knockout mice. Here we describe the characterization of MRK-A, a highly selective, potent small molecule SYK inhibitor in preclinical models of asthma.MethodsEnzyme potency and selectivity of MRK-A were evaluated. Functional inhibition of FcεR1 signaling was evaluated in primary human mast cells and in a rat airway passive sensitization model. Attenuation of allergic airway responses was evaluated in rat and sheep inhaled allergen challenge models.ResultsMRK-A inhibits SYK enzyme activity with an IC50 of 0.9 nM and is >100 fold selective against all other kinases tested in biochemical assays. MRK-A inhibited FcεR1 mediated mast cell degranulation with an EC50 of 27 nM, and dose-dependently blocked IgE-mediated tracheal extravasation in rat. In a rat ovalbumin-sensitized airway challenge model, oral dosing of MRK-A led to a dose-dependent attenuation of airway inflammation. Intravenous dosing of MRK-A was able to significantly inhibit both early and late allergen induced changes in airway resistance in an ascaris-sensitive sheep allergen challenge model.ConclusionsMRK-A is a potent and selective SYK inhibitor that can attenuate the endpoints in several in vivo models of allergic airways. This compound provides an important selective tool to interrogate the role of SYK signaling in disease biology. RationaleSpleen Tyrosine Kinase (SYK) is a key activator of signaling pathways downstream of multiple surface receptors implicated in asthma. SYK function has been extensively studied in mast cells downstream of the high affinity IgE-receptor (FcεR1). Most studies evaluating SYK function in preclinical models have relied on poorly selective compounds, anti-sense oligonucleotides or SYK knockout mice. Here we describe the characterization of MRK-A, a highly selective, potent small molecule SYK inhibitor in preclinical models of asthma. Spleen Tyrosine Kinase (SYK) is a key activator of signaling pathways downstream of multiple surface receptors implicated in asthma. SYK function has been extensively studied in mast cells downstream of the high affinity IgE-receptor (FcεR1). Most studies evaluating SYK function in preclinical models have relied on poorly selective compounds, anti-sense oligonucleotides or SYK knockout mice. Here we describe the characterization of MRK-A, a highly selective, potent small molecule SYK inhibitor in preclinical models of asthma. MethodsEnzyme potency and selectivity of MRK-A were evaluated. Functional inhibition of FcεR1 signaling was evaluated in primary human mast cells and in a rat airway passive sensitization model. Attenuation of allergic airway responses was evaluated in rat and sheep inhaled allergen challenge models. Enzyme potency and selectivity of MRK-A were evaluated. Functional inhibition of FcεR1 signaling was evaluated in primary human mast cells and in a rat airway passive sensitization model. Attenuation of allergic airway responses was evaluated in rat and sheep inhaled allergen challenge models. ResultsMRK-A inhibits SYK enzyme activity with an IC50 of 0.9 nM and is >100 fold selective against all other kinases tested in biochemical assays. MRK-A inhibited FcεR1 mediated mast cell degranulation with an EC50 of 27 nM, and dose-dependently blocked IgE-mediated tracheal extravasation in rat. In a rat ovalbumin-sensitized airway challenge model, oral dosing of MRK-A led to a dose-dependent attenuation of airway inflammation. Intravenous dosing of MRK-A was able to significantly inhibit both early and late allergen induced changes in airway resistance in an ascaris-sensitive sheep allergen challenge model. MRK-A inhibits SYK enzyme activity with an IC50 of 0.9 nM and is >100 fold selective against all other kinases tested in biochemical assays. MRK-A inhibited FcεR1 mediated mast cell degranulation with an EC50 of 27 nM, and dose-dependently blocked IgE-mediated tracheal extravasation in rat. In a rat ovalbumin-sensitized airway challenge model, oral dosing of MRK-A led to a dose-dependent attenuation of airway inflammation. Intravenous dosing of MRK-A was able to significantly inhibit both early and late allergen induced changes in airway resistance in an ascaris-sensitive sheep allergen challenge model. ConclusionsMRK-A is a potent and selective SYK inhibitor that can attenuate the endpoints in several in vivo models of allergic airways. This compound provides an important selective tool to interrogate the role of SYK signaling in disease biology. MRK-A is a potent and selective SYK inhibitor that can attenuate the endpoints in several in vivo models of allergic airways. This compound provides an important selective tool to interrogate the role of SYK signaling in disease biology.