Antitubercular nanocarrier monotherapy: Study of In Vivo efficacy and pharmacokinetics for rifampicin

Abstract

Tuberculosis represents a major global health problem for which improved approaches are needed to shorten the course of treatment and to combat the emergence of resistant strains. The development of effective and safe nanobead-based interventions can be particularly relevant for increasing the concentrations of antitubercular agents within the infected site and reducing the concentrations in the general circulation, thereby avoiding off-target toxic effects. In this work, rifampicin, a first-line antitubercular agent, was encapsulated into biocompatible and biodegradable polyester-based nanoparticles. In a well-established BALB/c mouse model of pulmonary tuberculosis, the nanoparticles provided improved pharmacokinetics and pharmacodynamics. The nanoparticles were well tolerated and much more efficient than an equivalent amount of free rifampicin.

Introduction

Tuberculosis (TB) represents a global health problem, although a potentially curative therapy has been available for approximately 50 years [[1], [2], [3]]. TB has killed millions of people over the past centuries and remains among the leading causes of infectious morbidity. This intracellular disease affects approximately 1 in 3 people worldwide, with over 10 million new cases per year and one death every three minutes [4].

TB can usually be treated with a 6- to 9-month course of combined therapy. Rifampicin (RIF), isoniazid, pyrazinamide and ethambutol are core drugs used for this purpose. However, the necessity of using a cocktail of anti-TB drugs and the long-term treatment schedules required for conventional therapy result in poor patient compliance; therefore, the risk of treatment failure and relapse is higher. Improved drug delivery strategies for the existing drugs can be exploited to shorten TB treatment duration and to avoid the selection of drug-resistant mutants [5].

Nanoparticle (NP) technology has emerged as one of the most promising approaches for overcoming the above-listed shortcomings associated with TB therapy thanks to the unique physicochemical properties of nanomaterials. These include their small size, allowing them to reach the intracellular level, and their ability to be modified to control their biorelevant behavior. Also note that nanobead-based interventions allow the improvement of aqueous solubility of drugs, drug protection, selective transport to the sites of infection and controlled release. [6] Utilizing nanocarriers for drug delivery into the lungs, which is the primary site of TB infection, offers an elegant way to circumvent the numerous difficulties associated with conventional therapy. [[6], [7], [8]] Within the sites of inflammation, the endothelium becomes permeable due to pathologic processes. Nanobead-based structures follow the route of particulate patterns, including intracellular pathogens, and they are preferentially taken up by phagocytes, which further enhance their targeting [1]. Thus, these approaches enhance the therapeutic effectiveness and minimize the undesirable side effects of numerous antibacterial drugs [3,9].

In this context, several types of anti-TB nanoformulations, including solid lipid nanoparticles [6,10], inorganic nanoparticles [7,11,12], micelles [13], and polymeric nanoparticles [[14], [15], [16], [17], [18]], have been utilized. All of these “future medicines” for use in TB regimens, however, still require financial support and further preclinical studies to move on to the next developmental step and reach patients [19]. Despite the fact that handling both animals and pathogens requires specific facility and biosafety conditions, there are studies (e.g. [12,15,18,[20], [21], [22], [23]],) describing the antitubercular activity in vivo. Most of these promising matrices are not, however, approved by regulatory authorities and, thus, have a lower chance of reaching clinical studies [19]. In this context, the toxicity studies required would increase the final cost of a novel intervention.

Recently, we described an intervention based on FDA-approved [24] biocompatible and biodegradable methoxy poly(ethylene oxide)-block-poly(ε-caprolactone) (MPEO-b-PCL) nanoparticles loaded with RIF, a cornerstone of modern antitubercular therapy. In these previous studies, we showed that the RIF-loaded nanoparticles were efficiently taken up by Raw 264.7 macrophage-like cells and efficiently killed the intracellularly persistent mycobacteria (nontuberculous Mycobacterium sp. as well as M. tuberculosis H37Rv). We also demonstrated in a zebrafish model of tuberculosis that the nanoparticles were well tolerated, had a curative effect and were significantly more efficient compared to a free form of RIF.

Considering these previous findings [17,18], we chose the most promising RIF-loaded nanoformulation, which was based on the MPEO_5k-b-PCL_4k copolymer, to test its biorelevant properties. We analyzed the pharmacokinetics and the effects of a RIF-loaded nanoformulation (NPs-RIF), a RIF-free nanoformulation (NPs), and free RIF on artificially induced tuberculous infection using a clinically relevant in vivo model.