Inhalable Retinoic Acid-loaded Nanoparticles as Host Directed Immunotherapy for Tuberculosis

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), is the top bacterial infectious disease killer and one of top ten causes of deaths worldwide. Multi drug resistant TB (MDR-TB) may arise because of poor patient adherence to treatment due to lengthy treatment duration and side effects. Delivering novel host directed therapies (HDT), like all trans retinoic acid (ATRA) may help to improve drug regimens and reduce the incidence of MDR-TB. ATRA is poorly soluble and has a short half-life. Therefore it requires a formulation step before it can be administered in vivo. ATRA loaded PLGA nanoparticles (ATRA-PLGA NPs) suitable for nebulization were manufactured using nanoprecipiation method. ATRA-PLGA NPs reduced bacterial growth in a dose dependent manner in H37Ra Mtb infected THP-1 cells. ATRA-PLGA NPs were then integrated with a vibrating mesh nebulizer (VMN) and the resulting aerosol had aerodynamic properties suitable for lung targeting. A scalable nanomanufacturing approach was optimized using microfluidics (MF) mixing. MF-ATRA-PLGA NPs demonstrated a dose dependent inhibition of Mtb growth in TB infected A549 alveolar epithelial cell model. In a preliminary study using Galleria mellonella (Gm) innovative in vivo model of TB infection, treatment with free ATRA or MF-ATRA-PLGA NPs did not improve colony forming units (CFU) or survival. Pre-treatment of BALB/c mice with free ATRA at 1.25 mg/kg 24 hrs before infection led to a decreased bacterial load trend in mice lungs 72 hrs post infection. Overall, the results of this project are promising for future research into ATRA as inhaled host directed therapies for TB. The data generated on the efficacy of inhalable, scalable and regulatory friendly ATRA-PLGA NPs formulation provides a foundation on which further pre-clinical testing can be built.