In vitro activity: Oclacitinib (also known as PF-03394197) is a novel inhibitor of JAK (Janus kinase) family members with IC50 values ranging from 10 to 99 nM and JAK1-dependent cytokines with IC50 ranging from 36 to 249 nM. Oclacitinib did not inhibit a panel of 38 non-JAK kinases and is the most potent at inhibiting JAK1. Oclacitinib also inhibits the function of JAK1-dependent cytokines involved in allergy and inflammation as well as pruritus. Cclacitinib is a targeted therapy that selectively inhibits JAK1-dependent cytokines involved in allergy, inflammation, and pruritus and suggests these are the mechanisms by which oclacitinib effectively controls clinical signs associated with allergic skin disease in dogs. PF-03394197 inhibits JAK family members by 50% at concentrations ranging from 10 to 99 nM and does not inhibit a panel of 38 non-JAK kinases. PF-03394197 is most potent at inhibiting JAK1. PF-03394197 also inhibits the function of JAK1-dependent cytokines involved in allergy and inflammation as well as pruritus. PF-03394197 has minimal effects on cytokines which does not activate the JAK1 enzyme in cells.

Kinase Assay: Using isolated enzyme systems and in vitro human or canine cell models, potency and selectivity of Oclacitinib is determined against JAK family members and cytokines that trigger JAK activation in cells. Inhibitory activity of Oclacitinib against JAK family members is determined in isolated enzyme systems. Oclacitinib inhibits JAK1, JAK2, JAK3, and TYK2 by 50% at concentrations (IC50's) of 10, 18, 99, and 84 nM, respectively. Oclacitinib is most potent against the JAK1 enzyme, showing a 1.8-fold selectivity for JAK1 vs. JAK2 and 9.9-fold selectivity toward JAK1 vs. JAK3. Oclacitinib inhibits JAK family members by 50% at concentrations (IC50's) ranging from 10 to 99 nM and does not inhibit a panel of 38 non-JAK kinases (IC50's>1000 nM). Oclacitinib also inhibits the function of JAK1-dependent cytokines involved in allergy and inflammation (IL-2, IL-4, IL-6, and IL-13) as well as pruritus (IL-31) at IC50's ranging from 36 to 249 nM. Oclacitinib has minimal effects on cytokines that does not activate the JAK1 enzyme in cells (erythropoietin, granulocyte/macrophage colony-stimulating factor, IL-12, IL-23; IC50's>1000 nM). Topical treatment with Tofacitinib (0.1%) and Oclacitinib (0.1%) leads to significant reduction of cell migration from mouse ear explants compared with vehicle-treated ears (all P < 0.05). The cell counts of MHC class II positive cells (that is, Langerhans cells) are significantly lower in vehicle-treated compared with each JAK inhibitor–treated epidermis (all P<0.01).

Cell Assay: Oclacitinib has minimal effects on cytokines that does not activate the JAK1 enzyme in cells (erythropoietin, granulocyte/macrophage colony-stimulating factor, IL-12, IL-23; IC50's>1000 nM).