The Application of High-Content Analysis in the Study of Targeted Particulate Delivery Systems for Intracellular Drug Delivery to Alveolar Macrophages

Biomimetic Systems Involving Macrophages and Their Potential for Targeted Drug Delivery

The concept of targeted drug delivery can be described in terms of the drug systems' ability to mimic the biological objects' property to localize to target cells or tissues. For example, drug delivery systems based on red blood cells or mimicking some of their useful features, such as long circulation in stealth mode, have been known for decades. On the contrary, therapeutic strategies based on macrophages have gained very limited attention until recently. Here, we review two biomimetic strategies associated with macrophages that can be used to develop new therapeutic modalities: first, the mimicry of certain types of macrophages (i.e., the use of macrophages, including tumor-associated or macrophage-derived particles as a carrier for the targeted delivery of therapeutic agents); second, the mimicry of ligands, naturally absorbed by macrophages (i.e., the use of therapeutic agents specifically targeted at macrophages). We discuss the potential applications of biomimetic systems involving macrophages for new advancements in the treatment of infections, inflammatory diseases, and cancer.

Lipid-based particle engineering via spray-drying for targeted delivery of antibiotics to the lung

Pulmonary delivery of antibiotics for the treatment of tuberculosis provides several benefits compared to conventional oral and parenteral administration. API-loaded particles delivered directly to alveolar macrophages, where Mycobacterium tuberculosis resides, can reduce the required dose and decrease the severe side effects of conventional treatment. In this work, lipid-microparticles loaded with rifampicin were engineered via spray-drying to be administered as a carrier-free dry powder for inhalation. Although, it is well-known that spray-drying of lipid-based excipients is strongly limited, a completely lipid-based formulation using diglycerol full ester of behenic acid was produced. The solid state of the lipid, providing high melting temperature, absence of polymorphism and monophasic crystallization, led to high yield of spray-dried particles (83%). Inhalable particles of mass median aerodynamic diameter of 2.36 µm, median geometric size of 2.05 µm, and negative surface (-50.03 mV) were engineered. Such attributes were defined for deep lung deposition and targeted delivery of antibiotics to alveolar macrophages. Superior aerodynamic performance as carrier-free DPI was associated to a high fine particle fraction of 79.5 %. No in vitro cytotoxic effects were found after exposing epithelial cell lines and alveolar macrophages. In vitro uptake of particles into alveolar macrophages indicated the efficiency of their targeted delivery. The use of highly processable and safe lipid-based excipients for particle engineering via spray-drying can extend the availability of materials for functionalized applications for pulmonary delivery.

THP-1 cell line model for tuberculosis: A platform for in vitro macrophage manipulation

Macrophages are large mononuclear phagocytic cells that play a vital role in the immune response. They are present in all body tissues with extremely heterogeneous and plastic phenotypes that adapt to the organs and tissues in which they live and respond in the first-line against invading microorganisms. Tuberculosis (TB) is caused by the pathogenic bacteria Mycobacterium tuberculosis (Mtb), which is among the top 10 global infectious agents and the leading cause of mortality, ranking above human immunodeficiency virus (HIV), as a single infectious agent. Macrophages, upon Mtb infection, not only phagocytose the bacteria and present the antigens to T-cells, but also react rapidly by developing antimycobacterial immune response depending highly on the production of cytokines. However, Mtb is also capable of intracellular survival in instances of sub-optimal activation of macrophages. Hence, several systems have been established to evaluate the Mtb-macrophage interaction, where the THP-1 monocytes have been developed as an attractive model for in vitro polarized monocyte-derived macrophages. This model is extensively used for Mtb as well as other intracellular bacterial studies. Herein, we have summarized the updated implications of the THP-1 model for TB-related studies and discussed the pros and cons compared to other cell models of TB.

Cationic inhalable particles for enhanced drug delivery to M. tuberculosis infected macrophages

Inhalable microparticle-based drug delivery platforms are being investigated extensively for Tuberculosis (TB) treatment as they offer efficient deposition in lungs and improved pharmacokinetics of the encapsulated cargo. However, the effect of physical parameters of microcarriers on interaction with Mycobacterium tuberculosis (Mtb) infected mammalian cells is underexplored. In this study, we report that Mtb-infected macrophages are highly phagocytic and microparticle surface charge plays a major role in particle internalization by infected cells. Microparticles of different sizes (0.5-2 μm) were internalized in large numbers by Mtb-infected THP-1 macrophages and murine primary Bone Marrow Derived Macrophages in vitro. Drastic improvement in particle uptake was observed with cationic particles in vitro and in mice lungs. Rapid uptake of rifampicin-loaded cationic microparticles allowed high intracellular accumulation of the drug and led to enhanced anti-bacterial function when compared to non-modified rifampicin-loaded microparticles. Cytocompatibility assay and histological analysis in vivo confirmed that the formulations were safe and did not elicit any adverse reaction. Additionally, pulmonary delivery of cationic particles in mice resulted in two-fold higher uptake in resident alveolar macrophages compared to non-modified particles. This study provides a framework for future design of drug carriers to improve delivery of anti-TB drugs inside Mtb-infected cells.

Alveolar macrophages: novel therapeutic targets for respiratory diseases

Alveolar macrophages (AMs) are lung-resident myeloid cells that sit at the interface of the airway and lung tissue. Under homeostatic conditions, their primary function is to clear debris, dead cells and excess surfactant from the airways. They also serve as innate pulmonary sentinels for respiratory pathogens and environmental airborne particles and as regulators of pulmonary inflammation. However, they have not typically been viewed as primary therapeutic targets for respiratory diseases. Here, we discuss the role of AMs in various lung diseases, explore the potential therapeutic strategies to target these innate cells and weigh the potential risks and challenges of such therapies. Additionally, in the context of the COVID-19 pandemic, we examine the role AMs play in severe disease and the therapeutic strategies that have been harnessed to modulate their function and protect against severe lung damage. There are many novel approaches in development to target AMs, such as inhaled antibiotics, liposomal and microparticle delivery systems, and host-directed therapies, which have the potential to provide critical treatment to patients suffering from severe respiratory diseases, yet there is still much work to be done to fully understand the possible benefits and risks of such approaches.

Recombinant ArgF PLGA nanoparticles enhances BCG induced immune responses against Mycobacterium bovis infection

Mycobacterium bovis (M. bovis) is a member of mycobacterium tuberculosis complex (MTBC), and a causative agent of chronic respiratory disease in a wide range of hosts. Bacillus Calmette-Guerin (BCG) vaccine is mostly used for the prevention of childhood tuberculosis. Further substantial implications are required for the development and evaluation of new tuberculosis (TB) vaccines as well as improving the role of BCG in TB control strategies. In this study, we prepared PLGA nanoparticles encapsulated with argF antigen (argF-NPs). We hypothesized, that argF nanoparticles mediate immune responses of BCG vaccine in mice models of M. bovis infection. We observed that mice vaccinated with argF-NPs exhibited a significant increase in secretory IFN-γ, CD4+ T cells response and mucosal secretory IgA against M. bovis infection. In addition, a marked increase was observed in the level of secretory IL-1β, TNF-α and IL-10 both in vitro and in vivo upon argF-NPs vaccination. Furthermore, argF-NPs vaccination resulted in a significant reduction in the inflammatory lesions in the lung's tissues, minimized the losses in total body weight and reduced M. bovis burden in infected mice. Our results indicate that BCG prime-boost strategy might be a promising measure for the prevention against M. bovis infection by induction of CD4+ T cells responses and mucosal antibodies.

Extracellular matrix-inspired inhalable aerogels for rapid clearance of pulmonary tuberculosis

Tuberculosis (TB) remains a leading cause of death from a single infectious agent, and limiting the spread of multidrug-resistant TB (MDR-TB) is now an urgent global health priority. Essential to the persistence of this disease is the ability of Mycobacterium tuberculosis (Mtb) to circumvent host defenses by infecting lung macrophages to create a cellular niche for its survival and proliferation. This has urged the development of new therapeutic strategies that act through mechanisms distinct from conventional antibiotics, and thus are effective against MDR bacteria, while being able to efficiently kill persister Mtb cells in infected host macrophages. Here, we report a new class of gel-like microparticle aerosols, or 'aerogels', designed to exploit metabolic vulnerabilities of Mtb pathogens and TB-infected macrophages to enable preferential delivery of synergistic peptide-antibiotic combinations for potent and rapid antitubercular therapy. This is achieved by formulating aerogels through the supramolecular assembly of a de novo designed anti-TB peptide and the extracellular matrix (ECM)-derived polysaccharide, hyaluronic acid (HA). Importantly, HA serves as a nutrient source for Mtb cells during tissue invasion and proliferation, and is recognized by CD44 receptors highly expressed on lung macrophages during TB infection. By exploiting this metabolic substrate for pathogen targeting, HA aerogels are shown to avidly bind and kill both drug-sensitive and drug-resistant mycobacteria, while being efficiently internalized into macrophage host cells in vitro and in vivo to clear Mtb persisters. This multifaceted bioactivity suggests aerogels may serve as a versatile inhalable platform upon which novel biomaterials-enabled therapeutics can be developed to rapidly clear pulmonary MDR-TB.

In vitro toxicity screening of polyglycerol esters of fatty acids as excipients for pulmonary formulations

One of the main problems for the development of pulmonary formulations is the low availability of approved excipients. Polyglycerol esters of fatty acids (PGFA) are promising molecules for acting as excipient for formulation development and drug delivery to the lung. However, their biocompatibility in the deep lung has not been studied so far. Main exposed cells include alveolar epithelial cells and alveolar macrophages. Due to the poor water-solubility of PGFAs, the exposure of alveolar macrophages is expected to be much higher than that of epithelial cells. In this study, two PGFAs and their mixture were tested regarding cytotoxicity to epithelial cells and cytotoxicity and functional impairment of macrophages. Cytotoxicity was assessed by dehydrogenase activity and lactate dehydrogenase release. Lysosome function, phospholipid accumulation, phagocytosis, nitric oxide production, and cytokine release were used to evaluate macrophage function. Cytotoxicity was increased with the increased polarity of PGFA molecules. At concentrations above 1 mg/ml accumulation in lysosomes, impairment of phagocytosis, secretion of nitric oxide, and increased release of cytokines were noted. The investigated PGFAs in concentrations up to 1 mg/ml can be considered as uncritical and are promising for advanced pulmonary delivery of high powder doses and drug targeting to alveolar macrophages.

Nanomodulation of Macrophages in Multiple Sclerosis

Multiple Sclerosis (MS) is a chronic demyelinating autoimmune disease primarily affecting young adults. Despite an unclear causal factor, symptoms and pathology arise from the infiltration of peripheral immune cells across the blood brain barrier. Accounting for the largest fraction of this infiltrate, macrophages are functionally heterogeneous innate immune cells capable of adopting either a pro or an anti-inflammatory phenotype, a phenomenon dependent upon cytokine milieu in the CNS. This functional plasticity is of key relevance in MS, where the pro-inflammatory state dominates the early stage, instructing demyelination and axonal loss while the later anti-inflammatory state holds a key role in promoting tissue repair and regeneration in later remission. This review highlights a potential therapeutic benefit of modulating macrophage polarisation to harness the anti-inflammatory and reparative state in MS. Here, we outline the role of macrophages in MS and look at the role of current FDA approved therapeutics in macrophage polarisation. Moreover, we explore the potential of particulate carriers as a novel strategy to manipulate polarisation states in macrophages, whilst examining how optimising macrophage uptake via nanoparticle size and functionalisation could offer a novel therapeutic approach for MS.

Modified cells as potential ocular drug delivery systems

Drug delivery to ocular targets is problematic, especially in retinal disease treatment. Therefore, targeted drug delivery, prolonged drug action, and minimally invasive treatments are needed. In this review, we describe cell technologies for drug delivery. These technologies are based on genetic engineering and nongenetic-based approaches for cell modification. In principle, cell technologies enable targeted delivery, long drug action, and minimally invasive administration, but they have only been sparsely studied for ocular drug delivery. Herein, these technologies are discussed in the ocular context.

Knockdown of Gene Expression in Macrophages by microRNA Mimic-Containing Poly (Lactic-co-glycolic Acid) Microparticles

Background: microRNA (miRNA) regulate target gene expression through translational repression and/or mRNA degradation and are involved in the regulation of inflammation. Macrophages are key inflammatory cells that are important in chronic inflammatory lung diseases such as cystic fibrosis (CF). Macrophage-expressed miRNA represent therapeutic drug targets, yet delivery of nucleic acids to macrophages has proved challenging. Methods: miRNAs were encapsulated in poly (lactic-co-glycolic acid) (PLGA)-based microparticles using double emulsion solvent evaporation and characterised for physicochemical features. Phorbol myristic acetate (PMA)-differentiated U937 macrophages were transfected with empty PLGA microparticles or those encapsulating a premiR-19b-3p or scrambled control miRNA mimic. miRNA internalisation and knockdown of a miR-19b-3p target gene, secretory leucoprotease inhibitor (SLPI), were determined by qRT-PCR. Results: Microparticle formulations were consistently found to be 2⁻3μm and all had a negative ζ potential (-5 mV to -14 mV). Encapsulation efficiency of premiR-19b-3p was 37.6 ± 13.4%. Levels of mature miR-19b-3p were higher in macrophages after delivery of premiR-19b-3p microparticles compared to empty or scrambled control miRNA-containing microparticles. Significant SLPI knockdown was achieved 72 hours post-delivery of premiR-19b-3p microparticles compared to controls. Conclusions: miRNA-encapsulating PLGA microparticles offer a new treatment paradigm for delivery to macrophages that could potentially be administered to CF lungs via inhalation.

Inhalable poly(lactic-co-glycolic acid) (PLGA) microparticles encapsulating all-trans-Retinoic acid (ATRA) as a host-directed, adjunctive treatment for Mycobacterium tuberculosis infection

Ending the tuberculosis (TB) epidemic by 2030 was recently listed in the United Nations (UN) Sustainable Development Goals alongside HIV/AIDS and malaria as it continues to be a major cause of death worldwide. With a significant proportion of TB cases caused by resistant strains of Mycobacterium tuberculosis (Mtb), there is an urgent need to develop new and innovative approaches to treatment. Since 1989, researchers have been assessing the anti-bacterial effects of the active metabolite of vitamin A, all trans-Retinoic acid (ATRA) solution, in Mtb models. More recently the antibacterial effect of ATRA has been shown to regulate the immune response to infection via critical gene expression, monocyte activation and the induction of autophagy leading to its application as a host-directed therapy (HDT). Inhalation is an attractive route for targeted treatment of TB, and therefore we have developed ATRA-loaded microparticles (ATRA-MP) within the inhalable size range (2.07 ± 0.5 µm) offering targeted delivery of the encapsulated cargo (70.5 ± 2.3%) to the site of action within the alveolar macrophage, which was confirmed by confocal microscopy. Efficient cellular delivery of ATRA was followed by a reduction in Mtb growth (H37Ra) in THP-1 derived macrophages evaluated by both the BACT/ALERT® system and enumeration of colony forming units (CFU). The antibacterial effect of ATRA-MP treatment was further assessed in BALB/c mice infected with the virulent strain of Mtb (H37Rv). ATRA-MP treatments significantly decreased the bacterial burden in the lungs alongside a reduction in pulmonary pathology following just three doses administered intratracheally. The immunomodulatory effects of targeted ATRA treatment in the lungs indicate a distinct yet effective mechanism of action amongst the formulations. This is the first study to-date of a controlled release ATRA treatment for TB suitable for inhalation that offers improved targeting of a HDT, retains antibacterial efficacy and improves pulmonary pathology compared to ATRA solution.

Residence time and uptake of porous and cationic maltodextrin-based nanoparticles in the nasal mucosa: Comparison with anionic and cationic nanoparticles

Different types of biodegradable nanoparticles (NP) have been studied as nasal mucosa cell delivery systems. These nanoparticles need to strongly interact with mucosa cells to deliver their payload. However, only a few simultaneous comparisons have been made and it is therefore difficult to determine the best candidate. Here we compared 5 types of nanoparticles with different surface charge (anionic or cationic) and various inner compositions as potential vectors: cationic and anionic liposomes, cationic and anionic PLGA (Poly Lactic co-Glycolic Acid) NP and porous and cationic maltodextrin NP (cationic surface with an anionic lipid core: NPL). We first quantified their nasal residence time after nasal administration in mice using in vivo live imaging and NPL showed the longest residence time. In vitro endocytosis on mucosal cells (airway epithelial cells, macrophages and dendritic cells) using labeled nanoparticles were performed by flow cytometry and confocal microscopy. Among the 5 nanoparticles, NPL were taken up to the greatest extent by the 3 different cell lines and the endocytosis mechanisms were characterized. Taken together, we observed that the nanoparticles' cationic surface charge is insufficient to improve mucosal residence time and cellular uptake and that the NPL are the best candidates to interact with airway mucosal cells.

Local delivery of siRNA-loaded calcium phosphate nanoparticles abates pulmonary inflammation

The local interference of cytokine signaling mediated by siRNA-loaded nanoparticles might be a promising new therapeutic approach to dampen inflammation during pulmonary diseases. For the local therapeutic treatment of pulmonary inflammation, we produced multi-shell nanoparticles consisting of a calcium phosphate core, coated with siRNAs directed against pro-inflammatory mediators, encapsulated into poly(lactic-co-glycolic acid), and coated with a final outer layer of polyethylenimine. Nasal instillation of nanoparticles loaded with a mixture of siRNAs directed against different cytokines to mice suffering from T_H1 cell-mediated lung inflammation, or of siRNA directed against NS-1 in an influenza infection model led to a significant reduction of target gene expression which was accompanied by distinct amelioration of lung inflammation in both models. Thus, this study provides strong evidence that the specific and local modulation of the inflammatory response by CaP/PLGA nanoparticle-mediated siRNA delivery could be a promising approach for the treatment of inflammatory disorders of the lung.

Preclinical safety of solid lipid nanoparticles and nanostructured lipid carriers: Current evidence from in vitro and in vivo evaluation

Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) were designed as exceptionally safe colloidal carriers for the delivery of poorly soluble drugs. SLN/NLC have the particularity of being composed of excipientsalready approved for use in medicines for human use, which offers a great advantage over any other nanoparticulate system developed from novel materials. Despite this fact, any use of excipients in new route of administration or in new dosage form requires evidence of safety. After 25 years of research on SLN and NLC, enough evidence on their preclinical safety has been published. In the present work, published data on in vitro and in vivo compatibility of SLN/NLC have been surveyed, in order to provide evidence of high biocompatibility distinguished by intended administration route. We also identified critical factors and possible weak points in SLN/NLC formulations, such as the effect of surfactants on the cell viability in vitro, which should be considered for further development.

Sharpening nature's tools for efficient tuberculosis control: A review of the potential role and development of host-directed therapies and strategies for targeted respiratory delivery

Centuries since it was first described, tuberculosis (TB) remains a significant global public health issue. Despite ongoing holistic measures implemented by health authorities and a number of new oral treatments reaching the market, there is still a need for an advanced, efficient TB treatment. An adjunctive, host-directed therapy designed to enhance endogenous pathways and hence compliment current regimens could be the answer. The integration of drug repurposing, including synthetic and naturally occurring compounds, with a targeted drug delivery platform is an attractive development option. In order for a new anti-tubercular treatment to be produced in a timely manner, a multidisciplinary approach should be taken from the outset including stakeholders from academia, the pharmaceutical industry, and regulatory bodies keeping the patient as the key focus. Pre-clinical considerations for the development of a targeted host-directed therapy are discussed here.

Treatment of Mycobacterium tuberculosis-Infected Macrophages with Poly(Lactic-Co-Glycolic Acid) Microparticles Drives NFκB and Autophagy Dependent Bacillary Killing

The emergence of multiple-drug-resistant tuberculosis (MDR-TB) has pushed our available repertoire of anti-TB therapies to the limit of effectiveness. This has increased the urgency to develop novel treatment modalities, and inhalable microparticle (MP) formulations are a promising option to target the site of infection. We have engineered poly(lactic-co-glycolic acid) (PLGA) MPs which can carry a payload of anti-TB agents, and are successfully taken up by human alveolar macrophages. Even without a drug cargo, MPs can be potent immunogens; yet little is known about how they influence macrophage function in the setting of Mycobacterium tuberculosis (Mtb) infection. To address this issue we infected THP-1 macrophages with Mtb H37Ra or H37Rv and treated with MPs. In controlled experiments we saw a reproducible reduction in bacillary viability when THP-1 macrophages were treated with drug-free MPs. NFκB activity was increased in MP-treated macrophages, although cytokine secretion was unaltered. Confocal microscopy of immortalized murine bone marrow-derived macrophages expressing GFP-tagged LC3 demonstrated induction of autophagy. Inhibition of caspases did not influence the MP-induced restriction of bacillary growth, however, blockade of NFκB or autophagy with pharmacological inhibitors reversed this MP effect on macrophage function. These data support harnessing inhaled PLGA MP-drug delivery systems as an immunotherapeutic in addition to serving as a vehicle for targeted drug delivery. Such “added value” could be exploited in the generation of inhaled vaccines as well as inhaled MDR-TB therapeutics when used as an adjunct to existing treatments.

Dual-functionalisation of gelatine nanoparticles with an anticancer platinum(ii)–bisphosphonate complex and mineral-binding alendronate

Mineral-binding gelatine nanoparticles can be loaded with tailored amounts of anticancer molecules, which may benefit the development of bone-seeking carriers for targeted delivery of drugs to treat bone tumours.

Early-stage development of novel cyclodextrin-siRNA nanocomplexes allows for successful postnebulization transfection of bronchial epithelial cells

BACKGROUND

Successful delivery of small interfering RNA (siRNA) to the lungs remains hampered by poor intracellular delivery, vector-mediated cytotoxicity, and an inability to withstand nebulization. Recently, a novel cyclodextrin (CD), SC12CDClickpropylamine, consisting of distinct lipophilic and cationic subunits, has been shown to transfect a number of cell types. However, the suitability of this vector for pulmonary siRNA delivery has not been assessed to date. To address this, a series of high-content analysis (HCA) and postnebulization assays were devised to determine the potential for CD-siRNA delivery to the lungs.

METHODS

SC12CDClickpropylamine-siRNA mass ratios (MRs) were examined for size and zeta potential. In-depth analysis of nanocomplex uptake and toxicity in Calu-3 bronchial epithelial cells was examined using IN Cell(®) HCA assays. Nebulized SC12CDClickpropylamine nanocomplexes were assessed for volumetric median diameter (VMD) and fine particle fraction (FPF) and compared with saline controls. Finally, postnebulization stability was determined by comparing luciferase knockdown elicited by SC12CDClickpropylamine nanocomplexes before and after nebulization.

RESULTS

SC12CDClickpropylamine-siRNA complexation formed cationic nanocomplexes of ≤200 nm in size depending on the medium and led to significantly higher levels of siRNA associated with Calu-3 cells compared with RNAiFect-siRNA-treated cells at all MRs (p<0.001, n=3×4), with evidence of toxicity only at MRs 50-100. Nebulization of SC12CDClickpropylamine nanocomplexes using the Aeroneb(®) Pro resulted in VMDs of ∼4 μm and FPFs of ∼57% at all MRs. SC12CDClickpropylamine-siRNA-mediated luciferase knockdown was found to be 39.8±3.6% at MR=20 before and 35.6±4.55% after nebulization, comparable to results observed using unnebulized commercial transfection reagent, RNAiFect.

CONCLUSIONS

SC12CDClickpropylamine nanocomplexes can be effectively nebulized for pulmonary delivery of siRNA using Aeroneb technology to mediate knockdown in airway cells. To the best of our knowledge, this is the first study examining the suitability of SC12CDClickpropylamine-siRNA nanocomplexes for pulmonary delivery. Furthermore, this work provides an integrated nanomedicine-device combination for future in vitro and in vivo preclinical and clinical studies of inhaled siRNA therapeutics.

Non-genetic engineering of cells for drug delivery and cell-based therapy

Cell-based therapy is a promising modality to address many unmet medical needs. In addition to genetic engineering, material-based, biochemical, and physical science-based approaches have emerged as novel approaches to modify cells. Non-genetic engineering of cells has been applied in delivering therapeutics to tissues, homing of cells to the bone marrow or inflammatory tissues, cancer imaging, immunotherapy, and remotely controlling cellular functions. This new strategy has unique advantages in disease therapy and is complementary to existing gene-based cell engineering approaches. A better understanding of cellular systems and different engineering methods will allow us to better exploit engineered cells in biomedicine. Here, we review non-genetic cell engineering techniques and applications of engineered cells, discuss the pros and cons of different methods, and provide our perspectives on future research directions.

High-content analysis for drug delivery and nanoparticle applications

High-content analysis (HCA) provides quantitative multiparametric cellular fluorescence data. From its origins in discovery toxicology, it is now addressing fundamental questions in drug delivery. Nanoparticles (NPs), polymers, and intestinal permeation enhancers are being harnessed in drug delivery systems to modulate plasma membrane properties and the intracellular environment. Identifying comparative mechanistic cytotoxicity on sublethal events is crucial to expedite the development of such systems. NP uptake and intracellular routing pathways are also being dissected using chemical and genetic perturbations, with the potential to assess the intracellular fate of targeted and untargeted particles in vitro. As we discuss here, HCA is set to make a major impact in preclinical delivery research by elucidating the intracellular pathways of NPs and the in vitro mechanistic-based toxicology of formulation constituents.

Inhalable microparticles of nitric oxide donors induce phagosome maturation and kill Mycobacterium tuberculosis

Nitric oxide (NO) kills Mycobacterium tuberculosis (Mtb) in vitro, but gaseous NO is difficult to administer to patients. We evaluated the consequences of intracellular delivery of NO using inhalable microparticles (MP) containing NO donors. MP containing 10% w/w of NO donors alone, or in addition to 25% each of isoniazid (INH) and rifabutin (RFB) in a polylactide-co-glycolide (PLGA) matrix were prepared by spray drying. THP-1-derived macrophages infected with Mtb H37Rv were exposed to MP or soluble NO donors. Phagosome-lysosome fusion (PLF) and bacterial killing were monitored. Colony forming units (cfu) in lungs and spleen of mice infected with a low-dose aerosol and administered inhalations of MP were enumerated. Bacterial DNA in these tissues was estimated by real-time PCR. In vitro studies indicated a bacteriostatic effect of NO donors despite significant enhancement of PLF. Daily inhalation of MP containing 10% diethylenetriamine nitric oxide adduct (DETA/NO) alone reduced log10 cfu in the lungs from 6.1 to 4.4 at the highest dose in four weeks, but did not significantly affect cfu in the spleen. Inhalations of MP containing DETA/NO in combination with INH and RFB significantly (P < 10(-5), ANOVA) reduced cfu in lungs and spleens by 4 log. Gross morphology and histology of the lungs and spleen indicated that inhaled particles were well-tolerated. Inhalable MP containing NO donors need further investigation as an adjunct to standard anti-tuberculosis chemotherapy.

‘Smart’ non-viral delivery systems for targeted delivery of RNAi to the lungs

The emergence of RNAi offers a potentially exciting new therapeutic paradigm for respiratory diseases. However, effective delivery remains a key requirement for their translation into the clinic and has been a major factor in the limited clinical success seen to date. Inhalation offers tissue-specific targeting of the RNAi to treat respiratory diseases and a diminished risk of off-target effects. In order to deliver RNAi directly to the respiratory tract via inhalation, ‘smart’ non-viral carriers are required to protect the RNAi during delivery/aerosolization and enhance cell-specific uptake to target cells. Here, we review the state-of-the-art in therapeutic aerosol bioengineering, and specifically non-viral siRNA delivery platforms, for delivery via inhalation. This includes developments in inhaler device engineering and particle engineering, including manufacturing methods and excipients used in therapeutic aerosol bioengineering that underpin the development of smart, cell type-specific delivery systems to target siRNA to respiratory epithelial cells and/or alveolar macrophages.

A DNA vaccination regime including protein boost and electroporation protects cattle against foot-and-mouth disease

Protection against foot-and-mouth disease (FMD) using DNA technology has been documented for sheep and pigs but not for the highly susceptible species of cattle. Twenty-five Holstein Friesian cross-bred cattle were vaccinated twice, 21 days apart, with a DNA vaccine containing the capsid coding region (P1) along with the non-structural proteins 2A, 3C and 3D (pcDNA3.1/P1-2A3C3D) of O(1) Kaufbeuren alone or coated onto PLG (d,l-lactide-co-glycolide) microparticles. In some pcDNA3.1/P1-2A3C3D was also combined with an adjuvant plasmid expressing bovine granulocyte macrophage colony stimulating factor (GM-CSF). DNA vaccinations were administered intramuscularly with, or without, the use of electroporation and at 42 days post primary vaccination cattle received a protein boost of 146S FMD virus (FMDV) antigen and non-structural protein 3D. For comparison, four cattle were vaccinated with a conventional FMD vaccine and two more included as unvaccinated controls. Apart from those immunised with PLG microparticles all cattle were challenged with 10(5) TCID(50) cattle adapted O(1) Lausanne FMDV virus at day 93 post primary vaccination. All DNA vaccinated cattle regardless of regime developed good humoral and cell mediated responses prior to challenge. The best overall virus neutralising antibody, IFN-γ and clinical protection (75%) were seen in the cattle whereby the DNA was delivered by electroporation. In contrast, only 25% of cattle vaccinated with the DNA vaccine without electroporation were clinically protected. The addition of GM-CSF in combination with electroporation further improved the efficacy of the vaccine, as demonstrated from the reduction of clinical disease and virus excretions in nasal swabs. We thus demonstrate for the first time that cattle can be clinically protected against FMDV challenge following a DNA prime-protein boost strategy, and particularly when DNA vaccine is combined with GM-CSF and delivered by electroporation.

Therapeutic aerosol bioengineering of targeted, inhalable microparticle formulations to treat Mycobacterium tuberculosis (MTb)

Therapeutic aerosol bioengineering (TAB) of Mycobacterium tuberculosis (MTb) therapies using inhalable microparticles offers a unique opportunity to target drugs to the site of infection in the alveolar macrophages, thereby increasing dosing in the lungs and limiting systemic exposure to often toxic drugs. Previous work by us used sophisticated, high content analysis to design the optimal poly(lactide-co-glycolic) acid (PLGA) microparticle for delivery of drugs to alveolar macrophages. Herein, we applied this technology to three different anti-MTb drugs. These formulations were then tested for encapsulation efficiency, drug-release, in vitro killing against MTb and aerosol performance. Methods for encapsulating each of the drugs in the PLGA microparticles were successfully developed and found to be capable of controlling the release of the drug for up to 4 days. The efficacy of each of the encapsulated anti-MTb drugs was maintained and in some cases enhanced post-encapsulation. A method of processing these drug-loaded microparticles for inhalation using standard dry powder inhaler devices was successfully developed that enabled a very high respirable dose of the drug to be delivered from a simple dry powder inhaler device. Overall, TAB offers unique opportunities to more effectively treat MTb with many potential clinical and economic benefits resulting.