Inhalational Delivery of a JAK3 Inhibitor for the Novel Treatment of Asthma and the Investigation of Pharmaceutical Salts in HFA Propellant Systems

Abstract

Asthma is a significant lung disease involving chronic inflammation and remodeling of the airways, resulting in reduced quality of life for those who suffer from the condition. Current therapeutic guidelines suggest the use of inhaled corticosteroids for long-term anti-inflammatory relief to manage moderate to severe chronic asthma; however, inhaled corticosteroids fail to provide prophylactic or reversal treatment of damaged airways incurred by chronic asthma as well as exhibiting adverse side effects (skeletal complications, diabetes, and weight gain).Therefore, there is a need for a new type of drug therapy to address these gaps in the treatment of chronic asthma. There is growing interest aimed towards the inhibition of the Janus Kinase and Signal Transducer and Activator of Transcription (JAK-STAT) pathway for the treatment of asthma. Despite the promising opportunity to investigate this new pathway towards this clinical application, no published work is available using an established and characterized JAK 1/3 inhibitor for the treatment of chronic asthma delivered via inhalation. This work investigated tofacitinib citrate, a selective JAK 3 inhibitor, and its potential to be delivered locally to the lungs for the treatment of chronic asthma. Several preformulation studies were conducted to determine the basic physical and chemical properties of the compound and its free base, tofacitinib, for proper inhalational formulation development. The drug was delivered to BALB/c mice challenged with house dust mite (HDM) allergen via nebulization utilizing a nose-only chamber. After a three week dosing schedule, mice treated with tofacitinib citrate exhibited an increase in monocyte cell numbers with a simultaneous decrease in eosinophil cell count, gathered from BAL fluid. Further, the experimental groups treated with tofacitinib citrate had a decrease in total protein concentrations in comparison to the experimental groups that were only challenged with HDM or were both exposed to HDM and vehicle. These findings demonstrated that the proper formulation was developed for nebulized delivery of tofacitinib citrate, and that the compound was capable of reducing total protein concentrations and eosinophil cell recruitment, both recognized as biomarkers for an asthmatic response. Although significant work is still needed to be done, these data hold promise for the potential of a locally delivered JAK 3 inhibitor as a treatment for chronic asthma. Further, the solubility of tofacitinib citrate and five other pharmaceutical salts were determined in HFA 134a, HFA 227, and DFP with varying cosolvent content (0-20% v/v ethanol). The experimental solubilities of the free acid and base compounds were larger than the solubilities of their respective salts in all three systems for tofacitinib, albuterol, and salicylic acid. Warfarin, phenytoin, and ciprofloxacin had similar solubilities with their respective salt forms. Solubilities also increased with increasing cosolvent concentration for all compounds investigated. The model propellant, DFP, provided a slightly stronger correlation of solubility values with HFA 134a in comparison to HFA 227. The observed solubility values were also compared to calculated values obtained from the ideal solubility model, where it was determined that the observed solubility was indeed also dependent on its surrounding solvent interactions and not solely on its ideal solubility (melting point). While some physical changes were observed for the pharmaceutical salts in HFA 134a and 227, more quantitative studies are needed for a larger database of compounds to better understand the factors that contribute to the solubility of pharmaceutical salts (and their correlation to DFP), in HFA-based systems. This information could potentially contribute to a predictive model, saving time and money during the process of pMDI formulation development.