In vitro activity of inhalable microparticles containing anti-TB drugs and an efflux pump inhibitor against Mycobacteria infections
Irene Rossi1, Francesca Buttini1, Filippo Affaticati1, Fabio Sonvico1, Marco Pieroni1, Elliott K Miller2, Nitesh K Kunda2, Pavan Muttil2 & Ruggero Bettini1
1University of Parma, Food and Drug Department, Parco Area delle Scienze 27/A, Parma, PR, Italy
2University of New Mexico, College of Pharmacy, Department of Pharmaceutical Sciences, 2705 Frontier Avenue NE, Albuquerque, NM, USA
Mycobacterial efflux pumps inhibitors (EPIs), along with first-line antibiotics, are widely studied as a new strategy to increase intracellular drug concentration, enhance the efficacy of the treatment and reduce the generation of drug-resistant strains. More than 80% of Mycobacterium tuberculosis (Mtb) reside in the lungs after infection, especially inside macrophages . The aim of this work is to demonstrate the in vitro bactericidal activity of an innovative spray-dried formulation composed of low molecular weight hyaluronic acid nanoparticles encapsulating two first-line antibiotics and an efflux pump inhibitor, verapamil HCl. These formulations were evaluated for their efficacy against an intracellular nontuberculous mycobacterium (NTM; Mycobacterium smegmatis), used as a surrogate to Mtb. Powder 1 (P1), that contained the EPI verapamil HCl, was compared with the same formulation without the EPI (Powder 2, P2). The aerodynamic performance of P1 powder was better compared to P2 powder: (Fine Particle Fraction 78% (P1) vs 19% (P2)), although both powders presented a similar particle size distribution. Moreover, P1 powder showed increased bactericidal activity against Mycobacterium smegmatis after 48h of exposure, compared to P2. However, P1 powder was more toxic to macrophages than P2 powder at the 0.5 mg/mL concentration. In addition, P1 powder showed higher killing of the intracellular mycobacteria, even at concentrations below the minimum inhibitory concentrations of the encapsulated antibiotics.