Host directed therapy delivery system based on M.tb-mimicking metal organic framework for tuberculosis
Presenting Author: Ailin Guo, South Dakota State University, USA
Co-Authors: Mikhail Durymanov, Moscow Institute of Physics and Technology, Russia; Angelika Mielcarek, Institut des Materiaux Poreux de Paris, France; Christian Serre, Institut des Materiaux Poreux de Paris, France; Joshua Reineke, South Dakota State University, USA

Introduction
Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (M.tb) with an estimated 1.5 million deaths and 10 million infections each year. Due to the complications and length of treatment required for TB (3 to 6 drugs to be taken for up to 9 months), inadequate or improper administration of anti-TB drugs use is common. This has led a rise in drug-resistant M.tb strains. Multidrug-resistant TB (MDR-TB) remains a public health threat, and only one third of infected people enroll in treatment. Improved therapeutic approaches are needed to avoid drug resistance. One promising approach is to use host-directed therapy (HDT) to activate and enhance the host’s response to TB infection rather than targeting bacterium itself. However, the major concern of the HDT approach is the systematic host effects. M.tb can survive and replicate inside infected macrophages which are expected to kill bacteria. Here, we propose the implementation of biomimetic microparticles as host-directed therapy drugs carriers to overcome systemic host concerns by targeting infected cells. Metal organic frameworks (MOFs) are porous hybrid inorganic-organic materials which have been increasingly explored as a drug delivery system. We developed the MOF MIL-88A which is non-toxic, highly porous, biodegradable, and consists of surface chemistries versatile for coating. Additionally, it can be synthesized to be rod-shaped and with a size similar to M.tb. In this study, we aim to develop a drug delivery system that mimics the behaviors of M.tb and delivers a HDT drug to enhance host cells’ response to a M.tb infection. This work builds on our studies evaluating biomimetic MOFs and alveolar macrophage interactions.

Methods
MIL-88A(Fe) was built up from oxo-centered trimers of iron (III) in octahedral coordination that are bridged by fumaric acids. Mannose, as model ligand was first conjugated with MOFs via EDC/NHS coupling reaction. MOF particles were coated with lipids including mycolic acid; the major M.tb cell wall component, to enhance the bacterium mimicking properties. Surface functionalization of particles was developed based on direct coordination of phenolic lipid (DPGG) with iron through phase transfer reaction. Mycolic acid coated particles were obtained from DPGG-coated MOF particles via hydrophobic interaction of lipids. Particle size and lipid coating were characterized by scanning electron microscopy and transmission electron microscopy (TEM), respectively. Zeta potential of particles before and after coating was measured by ZetaSizer. Metformin-loaded particles were prepared by coprecipitation. Drug loading was confirmed by TEM elemental analysis and HPLC. The cytotoxicity, stability, internalization mechanisms, cell uptake kinetics, cellular transport, and organelle localization of the mimetic particles have been studied in the non-infected macrophage cell model.

Results
The synthesized MIL-88A (Fe) particles were similar to M.tb with rod-shaped and positively charged with size of (2.6±0.2) × (0.6±0.1) μm. The study of cellular viability and degradation behavior of MOFs indicated particles were nontoxic and stable. The coating with lipids on MOFs was confirmed by TEM and negative surface charge. The elemental dispersive spectroscopy and HPLC analysis indicate that metformin, as a model HDT agent for tuberculosis, was encapsuled into the biomimetic particles. The result of internalization mechanism characterization suggests that the uptake process is energy-dependent, and phagocytosis is the major endocytic pathway. The study of intracellular trafficking shows that particles accumulated in acidic compartments of alveolar macrophages. Increased cell uptake was observed in MOF particles with mannose and M.tb specific lipids.

Conclusions
Mannoslyated- and bacterial lipid coated- MOF particles were successfully synthesized. We successfully coated particles with bacterial outer component to form M.tb -mimetic MOFs. The M.tb -mimetic particles with HDT drug have similar alveolar macrophage uptake and trafficking as M.tb which may enable effective localized treatment.

Ailin Guo MSc

South Dakota State University

Appearances