Agglomerated vesicle technology: a new class of particles for controlled and modulated pulmonary drug delivery

Pulmonary drug delivery devices and nanosystems as potential treatment strategies for acute respiratory distress syndrome (ARDS)

Despite advances in drug delivery technologies, treating acute respiratory distress syndrome (ARDS) is challenging due to pathophysiological barriers such as lung injury, oedema fluid build-up, and lung inflammation. Active pharmaceutical ingredients (API) can be delivered directly to the lung site of action with the use of aerosol-based drug delivery devices, and this circumvents the hepatic first-pass effect and improves the bioavailability of drugs. This review discusses the various challenges and barriers for pulmonary drug delivery, current interventions for delivery, considerations for effective drug delivery, and the use of nanoparticle drug delivery carriers as potential strategies for delivering therapeutics in ARDS. Nanosystems have the added benefit of entrapping drugs, increase pulmonary drug bioavailability, and using biocompatible and biodegradable excipients that can facilitate targeted and/or controlled delivery. These systems provide an alternative to existing conventional systems. An effective way to deliver drugs for the treatment of ARDS can be by using colloidal systems that are aerosolized or inhaled. Drug distribution to the deeper pulmonary tissues is necessary due to the significant endothelial cell destruction that is prevalent in ARDS. The particle size of nanoparticles (<0.5 μm) makes them ideal candidates for treating ARDS as they can reach the alveoli. A look into the various potential benefits and limitations of nanosystems used for other lung disorders is also considered to indicate how they may be useful for the potential treatment of ARDS.

Lessons from the history of inorganic nanoparticles for inhalable diagnostics and therapeutics

The respiratory tract is one of the most accessible ones to exogenous nanoparticles, yet drug delivery by their means to it is made extraordinarily challenging because of the plexus of aerodynamic, hemodynamic and biomolecular factors at cellular and extracellular levels that synergistically define the safety and efficacy of this process. Here, the use of inorganic nanoparticles (INPs) for inhalable diagnostics and therapies of the lung is viewed through the prism of the history of studies on the interaction of INPs with the lower respiratory tract. The most conceptually and methodologically innovative and illuminative studies are referred to in the chronological order, as they were reported in the literature, and the trends in the progress of understanding this interaction of immense therapeutic and toxicological significance are being deduced from it. The most outstanding actual trends delineated include the diminishment of toxicity via surface functionalization, cell targeting, tagging and tracking via controlled binding and uptake, hybrid INP treatments, magnetic guidance, combined drug and gene delivery, use as adjuvants in inhalable vaccines, and other. Many of the understudied research directions, which have been accomplished by the nanostructured organic polymers in the pulmonary niche, are discussed. The progress in the use of INPs as inhalable diagnostics or therapeutics has been hampered by their well-recognized inflammatory potential and toxicity in the respiratory tract. However, the annual numbers of methodologically innovative studies have been on the rise throughout the past two decades, suggesting that this is a prolific direction of research, its comparatively poor commercial takings notwithstanding. Still, the lack of consensus on the effects of many INP compositions at low but therapeutically effective doses, the plethora of contradictory reports on ostensibly identical chemical compositions and NP properties, and the many cases of antagonism in combinatorial NP treatments imply that the rational design of inhalable medical devices based on INPs must rely on qualitative principles for the most part and embrace a partially stochastic approach as well. At the same time, the fact that the most studied INPs for pulmonary applications have been those with some of the thickest records of pulmonary toxicity, e.g., carbon, silver, gold, silica and iron oxide, is a silent call for the expansion of the search for new inorganic compositions for use in inhalable therapies to new territories.

Development and application of ribonucleic acid therapy strategies against COVID-19

The Coronavirus disease 2019 (COVID-19) pandemic is caused by the severe acute respiratory syndrome 2 coronavirus (SARS-CoV-2), remaining a global health crisis since its outbreak until now. Advanced biotechnology and research findings have revealed many suitable viral and host targets for a wide range of therapeutic strategies. The emerging ribonucleic acid therapy can modulate gene expression by post-transcriptional gene silencing (PTGS) based on Watson-Crick base pairing. RNA therapies, including antisense oligonucleotides (ASO), ribozymes, RNA interference (RNAi), aptamers, etc., were used to treat SARS-CoV whose genome is similar to SARV-CoV-2, and the past experience also applies for the treatment of COVID-19. Several studies against SARS-CoV-2 based on RNA therapeutic strategy have been reported, and a dozen of relevant preclinical or clinical trials are in process globally. RNA therapy has been a very active and important part of COVID-19 treatment. In this review, we focus on the progress of ribonucleic acid therapeutic strategies development and application, discuss corresponding problems and challenges, and suggest new strategies and solutions.

Dry Powder for Pulmonary Delivery: A Comprehensive Review

The pulmonary route has long been used for drug administration for both local and systemic treatment. It possesses several advantages, which can be categorized into physiological, i.e., large surface area, thin epithelial membrane, highly vascularized, limited enzymatic activity, and patient convenience, i.e., non-invasive, self-administration over oral and systemic routes of drug administration. However, the formulation of dry powder for pulmonary delivery is often challenging due to restrictions on aerodynamic size and the lung’s lower tolerance capacity in comparison with an oral route of drug administration. Various physicochemical properties of dry powder play a major role in the aerosolization, deposition, and clearance along the respiratory tract. To prepare suitable particles with optimal physicochemical properties for inhalation, various manufacturing methods have been established. The most frequently used industrial methods are milling and spray-drying, while several other alternative methods such as spray-freeze-drying, supercritical fluid, non-wetting templates, inkjet-printing, thin-film freezing, and hot-melt extrusion methods are also utilized. The aim of this review is to provide an overview of the respiratory tract structure, particle deposition patterns, and possible drug-clearance mechanisms from the lungs. This review also includes the physicochemical properties of dry powder, various techniques used for the preparation of dry powders, and factors affecting the clinical efficacy, as well as various challenges that need to be addressed in the future.

Prospects for RNAi Therapy of COVID-19

COVID-19 caused by the SARS-CoV-2 virus is a fast emerging disease with deadly consequences. The pulmonary system and lungs in particular are most prone to damage caused by the SARS-CoV-2 infection, which leaves a destructive footprint in the lung tissue, making it incapable of conducting its respiratory functions and resulting in severe acute respiratory disease and loss of life. There were no drug treatments or vaccines approved for SARS-CoV-2 at the onset of pandemic, necessitating an urgent need to develop effective therapeutics. To this end, the innate RNA interference (RNAi) mechanism can be employed to develop front line therapies against the virus. This approach allows specific binding and silencing of therapeutic targets by using short interfering RNA (siRNA) and short hairpin RNA (shRNA) molecules. In this review, we lay out the prospect of the RNAi technology for combatting the COVID-19. We first summarize current understanding of SARS-CoV-2 virology and the host response to viral entry and duplication, with the purpose of revealing effective RNAi targets. We then summarize the past experience with nucleic acid silencers for SARS-CoV, the predecessor for current SARS-CoV-2. Efforts targeting specific protein-coding regions within the viral genome and intragenomic targets are summarized. Emphasizing non-viral delivery approaches, molecular underpinnings of design of RNAi agents are summarized with comparative analysis of various systems used in the past. Promising viral targets as well as host factors are summarized, and the possibility of modulating the immune system are presented for more effective therapies. We place special emphasis on the limitations of past studies to propel the field faster by focusing on most relevant models to translate the promising agents to a clinical setting. Given the urgency to address lung failure in COVID-19, we summarize the feasibility of delivering promising therapies by the inhalational route, with the expectation that this route will provide the most effective intervention to halt viral spread. We conclude with the authors' perspectives on the future of RNAi therapeutics for combatting SARS-CoV-2. Since time is of the essence, a strong perspective for the path to most effective therapeutic approaches are clearly articulated by the authors.

Dry powder inhalers in COPD, lung inflammation and pulmonary infections

INTRODUCTION

The number of pulmonary diseases that are effectively treated by aerosolized medicine continues to grow.

AREAS COVERED

These diseases include chronic obstructive pulmonary disease (COPD), lung inflammatory diseases (e.g., asthma) and pulmonary infections. Dry powder inhalers (DPIs) exhibit many unique advantages that have contributed to the incredible growth in the number of DPI pharmaceutical products. To improve the performance, there are a relatively large number of DPI devices available for different inhalable powder formulations. The relationship between formulation and inhaler device features on performance of the drug-device combination product is critical. Aerosol medicine products are drug-device combination products. Device design and compatibility with the formulation are key drug-device combination product aspects in delivering drugs to the lungs as inhaled powders. In addition to discussing pulmonary diseases, this review discusses DPI devices, respirable powder formulation and their interactions in the context of currently marketed DPI products used in the treatment of COPD, asthma and pulmonary infections.

EXPERT OPINION

There is a growing line of product options available for patients in choosing inhalers for treatment of respiratory diseases. Looking ahead, combining nanotechnology with optimized DPI formulation and enhancing device design presents a promising future for DPI development.

Liposomal formulations for inhalation

No marketed inhaled products currently use sustained release formulations such as liposomes to enhance drug disposition in the lung, but that may soon change. This review focuses on the interaction between liposomal formulations and the inhalation technology used to deliver them as aerosols. There have been a number of dated reviews evaluating nebulization of liposomes. While the information they shared is still accurate, this paper incorporates data from more recent publications to review the factors that affect aerosol performance. Recent reviews have comprehensively covered the development of dry powder liposomes for aerosolization and only the key aspects of those technologies will be summarized. There are now at least two inhaled liposomal products in late-stage clinical development: ARIKACE® (Insmed, NJ, USA), a liposomal amikacin, and Pulmaquin™ (Aradigm Corp., CA, USA), a liposomal ciprofloxacin, both of which treat a variety of patient populations with lung infections. This review also highlights the safety of inhaled liposomes and summarizes the clinical experience with liposomal formulations for pulmonary application.

Liposomal fasudil, a rho-kinase inhibitor, for prolonged pulmonary preferential vasodilation in pulmonary arterial hypertension

Current pharmacological interventions for pulmonary arterial hypertension (PAH) require continuous infusions, multiple inhalations, or oral administration of drugs that act on various pathways involved in the pathogenesis of PAH. However, invasive methods of administration, short duration of action, and lack of pulmonary selectivity result in noncompliance and poor patient outcomes. In this study, we tested the hypothesis that encapsulation of an investigational anti-PAH molecule fasudil (HA-1077), a Rho-kinase inhibitor, into liposomal vesicles results in prolonged vasodilation in distal pulmonary arterioles. Liposomes were prepared by hydration and extrusion method and fasudil was loaded by ammonium sulfate-induced transmembrane electrochemical gradient. Liposomes were then characterized for various physicochemical properties. Optimized formulations were tested for pulmonary absorption and their pharmacological efficacy in a monocrotaline (MCT) induced rat model of PAH. The entrapment efficiency of optimized liposomal fasudil formulations was between 68.1±0.8% and 73.6±2.3%, and the cumulative release at 37°C was 98-99% over a period of 5 days. Compared to intravenous (IV) fasudil, a ~10 fold increase in the terminal plasma half-life was observed when liposomal fasudil was administered as aerosols. The t1/2 of IV fasudil was 0.39±0.12 h. and when given as liposomes via pulmonary route, the t1/2 extended to 4.71±0.72 h. One h after intratracheal instillation of liposomal fasudil, mean pulmonary arterial pressure (MPAP) was reduced by 37.6±5.7% and continued to decrease for about 3 h, suggesting that liposomal formulations produced pulmonary preferential vasodilation in MCT induced PAH rats. Overall, this study established the proof-of-principle that aerosolized liposomal fasudil is a feasible option for a non-invasive, controlled release and pulmonary preferential treatment of PAH.

Non inflammatory boronate based glucose-responsive insulin delivery systems

Boronic acids, known to bind diols, were screened to identify non-inflammatory cross-linkers for the preparation of glucose sensitive and insulin releasing agglomerates of liposomes (Agglomerated Vesicle Technology-AVT). This was done in order to select a suitable replacement for the previously used cross-linker, ConcanavalinA (ConA), a lectin known to have both toxic and inflammatory effects in vivo. Lead-compounds were selected from screens that involved testing for inflammatory potential, cytotoxicity and glucose-binding. These were then conjugated to insulin-encapsulating nanoparticles and agglomerated via sugar-boronate ester linkages to form AVTs. In vitro, the particles demonstrated triggered release of insulin upon exposure to physiologically relevant concentrations of glucose (10 mmoles/L–40 mmoles/L). The agglomerates were also shown to be responsive to multiple spikes in glucose levels over several hours, releasing insulin at a rate defined by the concentration of the glucose trigger.

Alternatives to conventional suspensions for pulmonary drug delivery by nebulisers: a review

This review discusses the reports of alternative dosage forms to suspension formulations of hydrophobic drugs for nebulisers. Suspensions for nebulisers, although widely used over recent years, have several limitations which have led to pharmaceutical researchers looking for alternative, better performing preparations. Particular attention has been directed towards the use of nanoparticles as carriers of hydrophobic active ingredients. Several nanoformulations have been prepared and compared in vitro and/or in vivo with the corresponding microsuspension formulation. It is also clear that future studies in this field should address the parallel important aspects of safety and economical aspects of nanoparticualte formulations.

The effect of liposome encapsulation on the pharmacokinetics of recombinant secretory leukocyte protease inhibitor (rSLPI) therapy after local delivery to a guinea pig asthma model

PURPOSE

Inhaled recombinant Secretory Leukocyte Protease Inhibitor (rSLPI) has shown potential for treatment of inflammatory lung conditions. Rapid inactivation of rSLPI by cathepsin L (Cat L) and rapid clearance from the lungs have limited clinical efficacy. Encapsulation of rSLPI within 1,2-Dioleoyl-sn-Glycero-3-[Phospho-L-Serine]:Cholesterol liposomes (DOPS-rSLPI) protects rSLPI against Cat L inactivation in vitro. We aimed to determine the effect of liposomes on rSLPI pharmacokinetics and activity in vitro and after local delivery to the airways in vivo.

METHODS

Transport of DOPS-rSLPI and free-rSLPI across a polarised air-liquid epithelial monolayer was measured. An asthma guinea pig model was administered either DOPS-rSLPI liposomes or free-rSLPI by intratracheal instillation.

RESULTS

Apparent permeability (P(app)) of free-rSLPI was significantly higher at 4.9 x 10⁻⁶ cm/s than for DOPS-rSLPI, P(app) of 2.05 x 10⁻⁷ cm/s, confirmed by in vivo studies. Plasma rSLPI concentrations were highest in free-rSLPI-treated animals compared with those treated with DOPS-rSLPI; there also appeared to be a trend for higher intracellular rSLPI content in animals dosed with DOPS-rSLPI compared to free-rSLPI. Eosinophil influx was recorded as a measure of inflammation. Pre-dosing with either free-rSLPI or DOPS-rSLPI prevented inflammatory response to antigen challenge to levels comparable to control animals.

CONCLUSION

Encapsulation of rSLPI in DOPS:Chol liposomes improves stability, reduces clearance and increases residence time in the lungs after local delivery.

Nanosized rods agglomerates as a new approach for formulation of a dry powder inhaler

Background:

Nanosized dry powder inhalers provide higher stability for poorly water-soluble drugs as compared with liquid formulations. However, the respirable particles must have a diameter of 1–5 μm in order to deposit in the lungs. Controlled agglomeration of the nanoparticles increases their geometric particle size so they can deposit easily in the lungs. In the lungs, they fall apart to reform nanoparticles, thus enhancing the dissolution rate of the drugs. Theophylline is a bronchodilator with poor solubility in water.

Methods:

Nanosized theophylline colloids were formed using an amphiphilic surfactant and destabilized using dilute sodium chloride solutions to form the agglomerates.

Results:

The theophylline nanoparticles thus obtained had an average particle size of 290 nm and a zeta potential of −39.5 mV, whereas the agglomerates were 2.47 μm in size with a zeta potential of −28.9 mV. The release profile was found to follow first-order kinetics (r² > 0.96). The aerodynamic characteristics of the agglomerated nanoparticles were determined using a cascade impactor. The behavior of the agglomerate was significantly better than unprocessed raw theophylline powder. In addition, the nanoparticles and agglomerates resulted in a significant improvement in the dissolution of theophylline.

Conclusion:

The results obtained lend support to the hypothesis that controlled agglomeration strategies provide an efficient approach for the delivery of poorly water-soluble drugs into the lungs.

Targeted drug delivery of Rifampicin to the lungs: formulation, characterization, and stability studies of preformed aerosolized liposome and in situ formed aerosolized liposome

PURPOSE

This study aimed at the preparation and characterization of preformed and in situ formed liposomes for sustained delivery to the lungs.

METHODS

Two different liposome formulations were prepared and subjected to characterization of physical parameters and drug release profile (% cumulative drug release and % drug retained). Formulations were then subjected to accelerated stability studies as per ICH guidelines.

RESULTS

In situ formed liposome showed better sustained release profile than the preformed liposome as it released sufficient amount of drug while retaining considerable amount of drug. Upon subjection to accelerated conditions for 60 days, preformed liposome lost the objective of being controlled release formulation.

A dry powder formulation of liposome-encapsulated recombinant secretory leukocyte protease inhibitor (rSLPI) for inhalation: preparation and characterisation

Inhaled recombinant secretory leukocyte protease inhibitor (rSLPI) has shown potential for the treatment of inflammatory lung conditions. Rapid inactivation of rSLPI by cathepsin L (Cat L) and rapid clearance from the lungs has limited clinical efficacy to date. Previous studies by us have shown that encapsulation of rSLPI within1,2-dioleoyl-sn-glycero-3-[phospho-L-serine]/cholesterol (DOPS/Chol) liposomes protects rSLPI against Cat L inactivation in vitro. Liquid DOPS-rSLPI preparations were found to be unstable upon long-term storage and nebulisation. The aim of this study was therefore to develop a method of manufacture for preparing DOPS-rSLPI liposomes as a dry powder for inhalation. DOPS-rSLPI dry powders were lyophilised and subsequently micronised with a novel micronisation aid. The effects of formulation and processing on rSLPI stability, activity, and uniformity of content within the powders were characterised. Using D-mannitol as the micronisation aid, dry powder particles in the inhalable size range (<5 μm) were prepared. By optimising process parameters, up to 54% of rSLPI was recovered after micronisation, of which there was no significant loss in anti-neutrophil elastase activity and no detectable evidence of protein degradation. Aerosolisation was achieved using a dry powder inhaler, and mass median aerodynamic diameter (MMAD) was evaluated after collection in a cascade impactor. Aerosolisation of the DOPS-rSLPI dry powder yielded 38% emitted dose, with 2.44 μm MMAD. When challenged with Cat L post-aerosolisation, DOPS-rSLPI dry powder was significantly better at retaining a protective function against Cat L-induced rSLPI inactivation compared to the aqueous DOPS-rSLPI liposome dispersion and was also more stable under storage.

Redox-sensitive disassembly of amphiphilic copolymer based micelles

Amphiphilic polymers of different hydrophilic-lipophilic ratios were prepared by free radical polymerization using two monomers consisting of triethylene glycol as the hydrophilic part and an alkyl chain connected by disulfide bond as the hydrophobic part. These polymers form micelle-like nanoassemblies in aqueous media and can encapsulate hydrophobic drug molecules up to 14% of their mass. In a reducing environment, these polymeric micelles disassemble and dissolve in water, since the amphiphilic polymers are converted into hydrophilic polymers upon cleavage of the disulfide bond. This disassembly event results in the release of hydrophobic molecules that had been encapsulated inside the micelle, the rate of which was found to be dependent on the concentration of the reducing agent, glutathione (GSH). In vitro experiments also show that the GSH-dependent release of the doxorubicin can be used to effect cytotoxicity in MCF-7 cells.

Rifampicin-loaded liposomes for the passive targeting to alveolar macrophages: in vitro and in vivo evaluation

Mycobacterium avium complex (MAC), the most frequent cause of opportunistic nontuberculous pulmonary infection, is made up of a group of intracellular pathogens that are able to survive and multiply inside lung alveolar macrophages. As nebulized liposomes are reported to be effective to target antibacterial agents to macrophages, in this work we have prepared and characterized re-dispersible freeze-dried rifampicin (RFP)-loaded vesicles by using soy lecithin (SL) and a commercial, enriched mixture of soy phosphatidylcholine (Phospholipon 90, P90) with or without cholesterol. The obtained results showed that RFP could be loaded stably in SL vesicles only when cholesterol was not present in the film preparation, whereas with P90 vesicles, the highest stability was obtained with formulations prepared with P90/cholesterol 7:1 or 4:1 molar ratios. RFP-liposome aerosols were generated using an efficient high-output continuous-flow nebulizer, driven by a compressor. After the experiments, nebulization efficiency (NE%) and nebulization efficiency of the encapsulated drug (NEED%) were evaluated. The results of our study indicated that nebulization properties and viscosity of formulations prepared with the low-transition-temperature phospholipids, SL and P90, are affected by vesicle composition. However, all formulations showed a good stability during nebulization and they were able to retain more than 65% of the incorporated drug. The effect of liposome encapsulation on lung levels of RFP following aerosol inhalation was determined in rats. The in vitro intracellular activity of RFP-loaded liposomes against MAC residing in macrophage-like J774 cells was also evaluated. Results indicated that liposomes are able to inhibit the growth of MAC in infected macrophages and to reach the lower airways in rats.

Comparison of ciprofloxacin hydrochloride-loaded protein, lipid, and chitosan nanoparticles for drug delivery

The aim of the present study was to develop single dose delivery systems based on nanotechnology for prolonged antibiotic release in a controlled manner. Five different drug-carrier ratios of ciprofloxacin hydrochloride-loaded nanoparticles of albumin, gelatin, chitosan (CS), and lipid [solid lipid nanoparticles (SLNs)] were prepared and characterized. Average particle size was found to be in the range of 73 +/- 2 to 98 +/- 44 nm for SLNs, 140 +/- 7 to 175 +/- 24 nm for albumin nanoparticles, 143 +/- 18 to 184 +/- 27 nm for gelatin nanoparticles, and 247 +/- 48 to 322 +/- 52 nm for CS nanoparticles. A drug-to-carrier ratio of 0.5:1 was preferred for CS nanoparticles having zeta potential of >20 mV and drug encapsulation of 35.01% +/- 2.66%. Similarly, 0.6:1 ratio was preferred for albumin nanoparticles with zeta potential >16 mV and drug encapsulation 48.20% +/- 3.01%. Zeta potentials of gelatin nanoparticles loaded with ciprofloxacin suggested that they were unstable and prone to flocculation. SLN with 0.25:1 drug carrier ratio showed 38.71% +/- 2.38% drug entrapment and -28 +/- 1 mV surface charge. All the nanoparticles showed sustained drug release avoiding "burst effect" of the free drugs for up to 120 h for albumin nanoparticles, 96 h for CS and gelatin nanoparticles, and 80 h for SLNs. The drug release profiles followed Higuchi model. Results suggest that CS nanoparticles and SLNs can act as promising carriers for sustained ciprofloxacin release in infective conditions.

Optimization of Formulation Components and Characterization of Large Respirable Powders Containing High Therapeutic Payload

The aim of the study was to optimize and characterize high therapeutic payload large respirable powders prepared by spray-drying technique for maximum fine particle fraction with minimum quantities of excipients. Influence of formulation components was optimized by a three-factor, five-level central composite design having different proportions of L-leucine (X1), tobramycin sulfate (X2), and poloxamer-188 (X3) as the independent variables and fine particle fraction as a response variable (Y). Large respirable powders were characterized for particle size, size distribution, moisture, crystallinity, and morphology. In vitro aerosol performance of powders was determined by an eight-stage Andersen cascade impactor using the Rotahaler. Mathematical model elucidated for Y was Y = 56.2068 + 5.7481 X1 - 3.0531 X2 + 0.8468 X3 + 1.1737 X1 X2 - 0.5012 X1 X3 - 0.7412 X2 X3 - 0.7149 X1(2) - 1.9212 X2(2) - 1.6187X3(2). The component of greatest influence on product performance (response variable) was found to be L-leucine. Lack of fit was not significant (p = 0.08), and regression equation predicted response for Y was in reasonably good agreement with experimental values (p = 0.01; R2 = 0.92). The optimal model predicted with a fine particle fraction of 62.8 +/- 2.6% with X1, X2, X3 levels of 20, 45.71, and 5.51 respectively. Large respirable powders with TB load of 45.7% w/w were prepared; they had smooth surface texture, dimpled spherical shape, roundness value close to 1(1.048 +/- 0.032) and were found to possess bulk tap densities of 0.04 g/cc, geometric particle sizes of 6-7 micro m, and emitted dose of 92%. The results of the studies suggest that in vitro aerosol performance was affected significantly by small and deliberate change of specific formulation components and its proportions. It may be concluded that appropriate type and proportion of excipients is necessary to obtain maximum fine particle fraction of large respirable powders containing high therapeutic payloads.

Chemical modification of therapeutic drugs or drug vector systems to achieve targeted therapy: looking for the grail

Most therapeutic drugs distribute to the whole body, which results in general toxicity and poor acceptance of the treatments by patients. The targeted delivery of chemotherapeutics to defined cells, either stromal or cancer cells in cancer lesions, or defined inflammatory cells in immunological disorders, is one of the main challenges and a very active field of research in the development of treatment strategies to minimize side-effects of drugs. Disease-associated cells express molecules, including proteases, receptors, or adhesion molecules, that are different or differently expressed than their normal counterparts. Therefore one goal in the field of targeted therapies is to develop chemically derivatized drugs or drug vectors able to target defined cells via specific recognition mechanisms and also able to overcome biological barriers. This article will review the approaches which have been explored to achieve these goals and will discuss in more detail three examples (i) the use of nanostructures to take advantage of increased vascular permeability in some human diseases, (ii) the targeting of therapeutic drugs to an organ, the brain, protected against foreign molecules by the blood-brain barrier, and (iii) the use of the folate receptor to target either tumor cells or activated macrophages.

Triggered release of inhaled insulin from the agglomerated vesicles: Pharmacodynamic studies in rats

An aerosol insulin carrier based on the agglomerated vesicle technology that the authors have previously advanced [E. Karathanasis et al. J. Control. Release 103 (2005) 159-175] was evaluated in vivo. The carrier consisted of insulin-loaded liposomes cross-linked via chemical bridges cleavable by cysteine. It was speculated that the cleavage of the cross links released internal surface area and possibly resulted in the disruption of the liposomal walls. The result was a rapid release of encapsulated insulin upon contact of the insulin carrier with cysteine. The particles exhibited a small aerodynamic diameter within the respirable range suggesting deposition into the deep lung of humans along with a large geometrical diameter, consistent with long residence time. Indeed the endotracheal instillation of the particles into hyperglycemic rats decreased the glucose levels rapidly while delivery of cysteine triggered a further drop of glucose implying acceleration of insulin release from the carrier. Euglycemic clamp studies verified the accelerated insulin release upon application of cysteine.

Preparation of in vivo cleavable agglomerated liposomes suitable for modulated pulmonary drug delivery

In an attempt to achieve post-inhalation modulation of drug release rate, Bhavane et al. have recently proposed a microparticle agglomerate of nano-sized liposomal particles, with the agglomeration process consisting of chemical cross-linkages that are capable of cleavage [Bhavane et al. J. Cont. Rel 93 (2003) 15-28.]. There, the in vitro modulation of release from agglomerated liposomes encapsulating the antibiotic ciprofloxacin was demonstrated. However, the cleaving agents used in the previous studies are not acceptable for in vivo use. In the present work therefore, a new generation of in vivo compatible agglomerated liposomes has been developed. The release rate of encapsulated compounds from these carriers can be modulated by the addition of mild thiolytic cleaving agents such as cysteine. Specifically, an amino terminated PEG conjugate has been successfully synthesized, similar to the conjugate proposed by Zalipsky [Bioconjugate Chemistry, 10 (5) (1999) 703-707.]. This conjugate contains a dithiobenzyl urethane linkage between the lipid and the PEG, cleavable by the addition of cysteine. The amines at the distal ends of the PEG are used to cross-link the liposomes into agglomerates by the addition of a suitable cross-linking agent reactive towards amines. The cross-linkages were cleaved by cysteine at the DTB sites, resulting in changes in the size distribution of the agglomerates, as well as changes in the release rate of the encapsulated drug.