Isostearic acid is an active component of imiquimod formulations used to induce psoriaform disease models.

Topical imiquimod based creams are indicated as immune stimulants for papillomas and various skin neoplasms. Imiquimod is considered a TLR7 ligand. These creams are also used in research to induce skin inflammation in mice as a model for psoriasis. We observed that this inflammatory response was not strictly imiquimod dependent and we set out to establish which components drive the proinflammatory effects. To this end, we examined the induction response in a BALB/cJRj mouse model, in which 50 mg of cream is applied to 2 cm2 of skin (125 mg/kg imiquimod-5% W/V, and/or 625 mg/kg isostearic acid-25% W/V). Comparing cream formulations containing isostearic acid, imiquimod and the combination, we observed that isostearic acid causes skin inflammation within 2 days, whereas imiquimod requires up to 5 days for initial signs. Isostearic acid activated an inflammasome response, stimulated release of proinflammatory cytokines and upregulated the IL-23/17 axis. Animals treated with isostearic acid had enlarged livers (+ 40% weight), which was not observed with imiquimod alone. Imiquimod was readily metabolized and cleared from plasma and liver, but was maintained at high levels in the skin throughout the body (200 mM at area of application; 200 µM in untreated skin). Imiquimod application was associated with splenomegaly, cytokine induction/release and initial body weight loss over 3 days. Despite high imiquimod skin levels throughout the animal, inflammation was only apparent in the treated areas and was less severe than in isostearic acid groups. As the concentrations in these areas are well above the 10 µM required for TLR7 responses in vitro, there is an implication that skin inflammation following imiquimod is due to effects other than TLR7 agonism (e.g., adenosine receptor agonism). In brain, isostearic caused no major changes in cytokine expression while imiquimod alone sightly stimulated expression of IL-1ß and CCL9. However, the combination of both caused brain induction of CCL3, -9, CXCL10, -13, IL-1ß and TNFα. The implication of these data is that isostearic acid facilitates the entry of imiquimod or peripherally secreted cytokines into the brain. Our data suggest that psoriaform skin responses in mice are more driven by isostearic acid, than generally reported and that the dose and route used in the model, leads to profound systemic effects, which may complicate the interpretation of drug effects in this model.

Pharmacokinetic Optimization of Small Molecule Janus Kinase 3 Inhibitors to Target Immune Cells.

Modulation of Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling is a promising method of treating autoimmune diseases, and the profound potency of clinical compounds makes this mode of action particularly attractive. Other questions that remain unanswered also include: What is the ideal selectivity between JAK1 and JAK3? Which cells are most relevant to JAK blockade? And what is the ideal tissue distribution pattern for addressing specific autoimmune conditions? We hypothesized that JAK3 selectivity is most relevant to low-dose clinical effects and interleukin-10 (IL-10) stimulation in particular, that immune cells are the most important compartment, and that distribution to inflamed tissue is the most important pharmacokinetic characteristic for in vivo disease modification. To test these hypotheses, we prepared modified derivatives of JAK3 specific inhibitors that target C909 near the ATP binding site based on FM-381, first reported in 2016; a compound class that was hitherto limited in uptake and exposure in vivo. These limits appear to be due to metabolic instability of side groups binding in the selectivity pocket. We identified derivatives with improved stability and tissue exposure. Conjugation to macrolide scaffolds with medium chain linkers was sufficient to stabilize the compounds and improve transport to organs while maintaining JAK3 affinity. These conjugates are inflammation targeted JAK3 inhibitors with long tissue half-lives and high exposure to activated immune cells.