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 (IC₅₀ 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 (IC₅₀ 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 IC₅₀ 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.