In-vitroevaluation of a new potent, selective pan-Janus kinase (JAK) inhibitor VR588

Rationale: Janus kinases (JAK) transduce multiple cytokine receptors reported to play an important role in asthma and COPD disease progression. VR588 is promising pan-JAK inhibitor suited to inhalation delivery. These studies were designed to characterise the in-vitro kinase inhibition profile of VR588 and to determine its selectivity versus non-JAK kinases. Methods: Kinase activity was assessed in a non-cell (Z9Lyte™ Florescence assay) and in cell based assays using stimulation of human whole blood (IL-2 stimulated INFγ production and JAK1/JAK3 and pSTATa/b activation and IL-6 stimulated pSTAT3 to assess JAK1, JAK2 and Tyk2 activity). In addition, the selectivity of VR588 (1mM) against a panel of 93 human kinases was assessed. Results: VR588 potently inhibited JAK1, 2, 3 and Tyk2 kinases (IC 50 4.2, 0.7, 2.1 & 6 nM respectively) in the non-cell based assay and showed poor inhibitory activity against non–JAK kinases FLT3, PDGFB, JNK2 and Syk (IC 50 247, 2350,4000, 8900 nM respectively). This potent and broad JAK inhibition was confirmed in the cell based assays with inhibition of IL-2 stimulated INFγ, IL-2 stimulated pSTATa/b & IL-6 stimulated pSTAT3 demonstrating IC 50 values of 209, 29 & 62 nM respectively. Selectivity versus human kinases revealed no relevant off-target effects. Conclusions: VR588 represents a potent, selective and balanced pan-JAK inhibitor and the lack of off-target effects mitigates the potential for unwanted kinase activity. These results suggest VR588 may have utility as a pharmacological treatment for asthma and COPD and have prompted the characterisation of absorption, distribution, metabolism, and excretion (ADME) and in vivo efficacy via the inhaled route.