Drug Targeting Applications Research Articles

PEG-templated mesoporous silica nanoparticles exclusively target cancer cells

Mesoporous silica nanoparticles (MSNs) have been proposed as DNA and drug delivery carriers, as well as efficient tools for fluorescent cell tracking. The major limitation is that MSNs enter cells regardless of a target-specific functionalization. Here we show that non functionalized MSNs, synthesized using a PEG surfactant-based interfacial synthesis procedure, do not enter cells, while a highly specific, receptor mediated, cellular internalization of folic acid (FOL) grafted MSNs (MSN-FOL), occurs exclusively in folate receptor (FR) expressing cells. Neither the classical clathrin pathway nor macropinocytosis is involved in the MSN endocytic process, while fluorescent MSNs (MSN-FITC) enter cells through aspecific, caveolae-mediated, endocytosis. Moreover, internalized particles seem to be mostly exocytosed from cells within 96 h. Finally, cisplatin (Cp) loaded MSN-FOL were tested on cancerous FR-positive (HeLa) or normal FR-negative (HEK293) cells. A strong growth arrest was observed only in HeLa cells treated with MSN-FOL-Cp. The results presented here show that our mesoporous nanoparticles do not enter cells unless opportunely functionalized, suggesting that they could represent a promising vehicle for drug targeting applications.

Drug Targeting and other Recent Applications of Magnetic Carriers in Therapeutics

. Aqueous suspensions containing small magnetic particles have been increasingly used in biosciences and biotechnology. Magnetic particles develop magnetic polarization and magnetophoretic mobility, and because of such unique properties, these carriers may be eligible candidates for delivering drugs to specific sites within the body. Their special properties also allow other uses, such as those in embolization, radioisotope delivery, magnetic cell tracking for monitoring cell therapy, magnetofection, and hyperthermia. This review focuses on a discussion about magnetic particles, the properties and fate of magnetic carriers, the methods used to produce and characterize them, and their other uses in biotechnology.

MAGNETIC DRUG DELIVERY AND TARGETING: PRINCIPLES AND APPLICATIONS

Nanomaterials are at the leading edge of the rapidly developing field of nanotechnology. Magnetic nanoparticles for cancer therapy and diagnosis have been developed on the basis of their unique physico-chemical properties not present in other materials. Their versatility is widely exploited in such diverse techniques as cell and macromolecule separation and purification, immunoassays, targeted drug delivery, controlled material release, electromagnetic hyperthermia, gene therapy, or magnetic resonance imaging. In this review we concentrate on the physical principles of magnetic drug targeting and biomedical applications of this technique. We examined several databases, PubMed, ISI Web of Knowledge, and Scopus, for the period 1985-2009, with specific attention to studies that used targeting of magnetic nanoparticles especially in the therapy and diagnostics of tumors. We have also presented several of our own results on theoretical simulations of magnetic particle motion in external magnetic field. We found growing number of published papers in this field of nanomedicine, showing the almost unlimited potential of magnetic nanoparticles in the field of experimental and clinical oncology.

A Facile Approach to Fabrication of Bifunctional Magnetic-Optical Fe3O4@ZnS Microspheres

Bifunctional magnetic-optical Fe3O4@ZnS microspheres with core−shell heterostructures have been successfully fabricated by a simple chemical deposition method. The adsorption of sodium dodecyl sulfate (SDS) on the preformed magnetite microspheres played an essential role in directing the structure of the composites. The presented materials were characterized by FE-SEM, HRTEM, XRD, FTIR, fluorescence spectrophotometer, and SQUID MPMS. The results showed that spherical Fe3O4 cores were coated by a uniform ZnS layer. The saturation magnetization value of Fe3O4@ZnS core−shell microspheres is 52.5 emu g−1 at room temperature. Ultraviolet and visible light can be easily obtained by exposing the microspheres to different excitation wavelengths. The combined magnetic and fluorescent properties endow the microspheres with great potential applications in drug targeting, bioseparation and diagnostic analysis.

A novel core-shell structured magnetic organic-inorganic nanohybrid involving drug-intercalated layered double hydroxides coated on a magnesium ferrite core for magnetically controlled drug release

A novel magnetic nanohybrid involving non-steroid anti-inflammatory drug diclofenac (DIC) intercalated Mg–Al layered double hydroxides (LDH) coated on magnesium ferrite particles was assembled via a one step coprecipitation self-assembly method. The XRD, FT-IR and ICP measurements reveal that the magnetic nanohybrid consists of both DIC-LDH nanocrystallite and magnesium ferrite phases. The TEM image shows that the magnetic nanohybrid presents well-defined core-shell structure with diameter in the range of 90–150 nm. Compared to pure DIC-LDH, an obviously smaller dimension and less sharp hexagonal morphology of the coated DIC-LDH nanocrystallites in magnetic hybrids is observed due to a heterogeneous nucleation and crystal growth process with the introduction of the magnetic core. The in vitro drug release rate of the magnetic nanohybrid was thus enhanced owing to the much smaller size of the coated DIC-LDH nanoparticles on the surface of the magnetic core. However, under an external magnetic field of 0.15 Tesla, the drug release rate of the magnetic nanohybrid decreases dramatically owing to the aggregation of the magnetic nanohybrid particles triggered by non-contact magnetic force. The kinetic data reveal that the release of DIC from the magnetic nanohybrid is controlled by particle diffusion, and the release rate is mainly affected by the particle size and the aggregation extent of the hybrid magnetic particles. Additionally, the obtained nanohybrid has a strong magnetization response, implying the possibility of application in magnetic drug targeting.

Facile synthesis of ordered magnetic mesoporous γ-Fe 2O 3/SiO 2 nanocomposites with diverse mesostructures

On the basis of a sol–gel process, a facile, low cost, and one-step approach for preparing ordered magnetic mesoporous γ-Fe 2O 3/SiO 2 nanocomposites by an evaporation-induced self-assembly (EISA) approach is presented. Various mesostructured silica materials ( P6mm or Im3m) incorporated with different amounts of iron oxide ( n Si / n Fe = 9 / 1 , 8/2, 7/3, respectively) were synthesized and characterized by XRD, TEM, N 2-sorption analyses, and superconducting quantum interference device (SQUID) magnetometer. The HCl-leaching experiments together with TEM micrographs and nitrogen sorption analysis suggested that most of the γ-Fe 2O 3 domains of several nanometers were embedded in the silica walls, rather than dispersed in the mesopores, which could cause the significant pore clogging reported in some studies. The release behaviors of lysozyme from these magnetic porous nanocomposites were investigated for the possible application of drug targeting and control release. The influence of iron precursors was also studied and a possible mechanism was proposed. The hydrolysis of Fe 3+ ions under weakly acidic conditions and the induced formation of Si O Fe bonds may account for the synthesis of this kind of nanocomposite. These multifunctional nanostructured materials would have a wide range of applications in toxin removal, catalysis, waste remediation, and biological separation as well as novel drug-carrier technologies.

Design, Synthesis, and Characterization of pH-Sensitive PEG−PE Conjugates for Stimuli-Sensitive Pharmaceutical Nanocarriers: The Effect of Substitutes at the Hydrazone Linkage on the pH Stability of PEG−PE Conjugates

A set of aliphatic and aromatic aldehyde-derived hydrazone (HZ)-based acid-sensitive polyethylene glycol-phosphatidylethanolamine (PEG-PE) conjugates was synthesized and evaluated for their hydrolytic stability at neutral and slightly acidic pH values. The micelles formed by aliphatic aldehyde-based PEG-HZ-PE conjugates were found to be highly sensitive to mildly acidic pH and reasonably stable at physiologic pH, while those derived from aromatic aldehydes were highly stable at both pH values. The pH-sensitive PEG-PE conjugates with controlled pH sensitivity may find applications in biological stimuli-mediated drug targeting for building pharmaceutical nanocarriers capable of specific release of their cargo at certain pathological sites in the body (tumors, infarcts) or intracellular compartments (endosomes, cytoplasm) demonstrating decreased pH.

Factors modulating the delivery and effect of enzymatic cargo conjugated with antibodies targeted to the pulmonary endothelium

Vascular drug targeting may improve therapies, yet a thorough understanding of the factors that regulate effects of drugs directed to the endothelium is needed to translate this approach into the clinical domain. To define factors modulating the efficacy and effects of endothelial targeting, we used a model enzyme (glucose oxidase, GOX) coupled with monoclonal antibodies (anti-TM 34 or anti-TM 201) to distinct epitopes of thrombomodulin, a surface determinant enriched in the pulmonary endothelium. GOX delivery results in conversion of glucose and oxygen into H 2O 2 leading to lung damage, a clear physiologic endpoint. Results of in vivo studies in mice showed that the efficiency of cargo delivery and its effect are influenced by a number of factors including: 1) The level of pulmonary uptake of the targeting antibody (anti-TM 201 was more efficient than anti-TM 34); 2) The amount of an active drug delivered to the target; 3) The amount of target antigen on the endothelium (animals with suppressed TM levels showed less targeting); and, 4) The substrate availability for the enzyme cargo in the target tissue (hyperoxia augmented GOX-induced injury). Therefore, both activities of the conjugates and biological factors control targeting and effects of enzymatic cargo. Understanding the nature of such “modulating biological factors” will hopefully allow optimization and ultimately applications of drug targeting for “individualized” pharmacotherapy.

Preparation and characterization of magnetic PLA–PEG composite nanoparticles for drug targeting

A series of biodegradable block copolymers of poly- d, l-lactide-co-polyethylene glycol (PLA–PEG) was prepared by ring-opening polymerization of d, l-lactide with stannous caprylate (Sn(Oct) 2) as catalyst, then composite particles were prepared using PLA–PEG copolymers and magnetic Fe 3O 4 by a phase separation method. The average molecular weight and structure of PLA–PEG were determined by gel permeation chromatography (GPC), nuclear magnetic resonance ( 1H NMR) and differential scanning calorimeter (DSC). The sizes and its distributions of the composite particles were investigated by laser particle size analyzer. The morphologies of prepared particles were observed by transmission electron microscopy (TEM). The contents of Fe in the composite particles were determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES). The magnetic susceptibilities were measured by nephelometery. The magnetic particles prepared were spherical with size range of 100–200 nm. The sizes of spheres were influenced by PLA, PEG chain length and block ratio. The magnetic properties of composite particles increased with increasing PEG chain length and PEG content. Particles with Fe content ranging from 0.5% to 5.2% were prepared. The properties of magnetic composite particles were controlled by altering the block ratio and the length of PLA–PEG copolymer to meet more requirements. The prepared Fe 3O 4/PLA–PEG particles with magnetic properties and biodegradable properties would provide practical applications in drug targeting and controlled drug release.

Preparation and in vivo evaluation of PEGylated spherulite formulations

Spherulites are multilamellar vesicles obtained by shearing a lamellar phase of lipids and surfactants. They consist of concentric bilayers of amphiphiles alternating with layers of aqueous medium in which hydrophilic drugs can be sequestered with high yield. To be useful for drug targeting applications, spherulites should be small and long circulating. The objectives of this work were threefold. First, the spherulite size was optimized to obtain a mean diameter of less than 300 nm. Second, the vesicle composition was adjusted to minimize in vitro leakage of internal content. Third, the spherulites were coated with 1,2-distearoyl- sn-glycero-3-phosphatidylethanolamine- N-[methoxy poly(ethylene glycol)] (DSPE-PEG) to impart them with a long half-life. Then, the PEGylated spherulites (Phospholipon 90G/Solutol HS15/cholesterol/DSPE-PEG 2000 or 5000) were loaded with 1-β- d-arabinofuranosylcytosine (ara-C) and injected intravenously to rats. They were compared to uncoated spherulites and to an ara-C solution. The surface-modified vesicles exhibited long circulation times with areas under the blood concentration vs. time curve exceeding by 3.1- to 6.9-fold that of uncoated spherulites. Similarly, blood levels of ara-C encapsulated in PEGylated vesicles were higher than those of the controls, but they did not parallel the carrier pharmacokinetics. Two hours post-injection, most of the drug was cleared from the systemic circulation, reflecting rapid leakage of ara-C from the vesicles.

Preparation and characterization of magnetic PLA–PEG composite particles

A series of biodegradable block copolymers of poly- d, l-lactide-co-polyethylene glycol (PLA–PEG) were prepared out by ring-opening polymerization of d, l-lactide with stannous caprylate (Sn(Oct) 2) as catalyst, then the PLA–PEG copolymers and magnetic Fe 3O 4 were made into composite particles by phase separation method. The sizes and distribution of composite particles were investigated by laser particle size analyzer. The morphologies of the prepared particles were examined by TEM. The contents of Fe in composite particles were detected by ICP. The magnetic susceptibilities were measured by nephelometery and VSM. The particles prepared were spherical with a size range of 100–200 nm. The sizes of the particles were influenced by PEG molecular weights and block ratio. The magnetic properties of composite particles increased with the increase of PEG molecular weights and block ratio. The properties of magnetic composite particles were controlled by altering the block ratio and the molecular weight of PLA–PEG copolymer. The prepared Fe 3O 4/PLA–PEG particles with magnetic properties and biodegradable properties would provide useful applications in drug targeting and drug controlling release.

Analyzing ferrofluid transport for magnetic drug targeting

Experimental and numerical investigations of magnetically induced localization of ferrofluid and its subsequent dispersion are performed in a forced flow. The ferrofluid accumulation behaves as a solid obstacle in the flow as the competing magnetic and fluid shear forces give rise to a rigidly bound core region followed by a washaway region at its wake. Results of the analysis provide meaningful information on ferrofluid transport for various magnetic drug targeting applications.

Pegylated Poly(Lactide) and Poly(Lactide-Co-Glycolide) Nanoparticles: Preparation, Properties and Possible Applications in Drug Delivery

The preparation, properties and potential applications in drug delivery of biocompatible and biodegradable PLA-PEG and PLGA-PEG nanoparticles are discussed. PLA-PEG and PLGA-PEG nanoparticles have been produced by emulsification-solvent evaporation, solvent displacement and salting out methods. The nanoparticles can be stored as freeze-dried powders, but an adequate amount of a suitable lyoprotectant should be added prior lyophilisation to prevent nanoparticle aggregation and retain nanoparticle redispersibility. The nanoparticles have a core-shell structure with a PLA core and a PEG coating. Their basic colloidal properties and degradation depend on copolymer composition. The PLA-PEG and PLGA-PEG nanoparticles exhibit prolonged blood circulation following intravenous administration to animals. The composition of the nanoparticles determine their biodistribution properties, probably through its effects on the effectiveness of the PEG steric barrier and the size of the nanoparticles. The ability of the PLA-PEG and PLGA-PEG nanoparticles to evade rapid phagocytocis has extended the range of sites within the body that the nanoparticles can reach, which has significant implications with regard to their application in controlled drug delivery and targeting. The PLA-PEG and PLGA-PEG nanoparticles can be loaded with a variety of bioactive agents achieving satisfactory loading, especially in the case of hydrophobic drugs. The nanoparticles have been investigated for the treatment of infectious diseases and cancer, the intravenous and mucosal delivery of proteins, and oligonucleotide and gene delivery. The results have been encouraging and PLA-PEG and PLGA-PEG nanoparticle formulations, improving the therapeutic potential of both established and new drugs, may be expected to be available in the near future.

Investigation of Surface Properties of Biodegradable Albumin Microspheres via Phagocytosis Phenomena

The phagocytosis of biodegradable albumin (Alb) microspheres by peripheral blood cells (neutrophils and monocytes) and mouse macrophage cells (peritoneal and lung macrophages) as a carrier matrix in drug targeting applications was investigated. Glutaraldehyde crosslinking was used to produce albumin microspheres with different sizes. Plain (nonmodified) microspheres with diameters of1, 2, and 4 mm were cultured with cells and their uptake was determined as 8, 5, and 1 particles/cell, respectively. Albumin microspheres (2 mm diameter) were also modified with various opsonization and passivation agents, such as fibronectin (Fn), amicasine, and poly(ethylene glycol) (PEG). Plain, Alb-PEG, Alb-Fn, and Alb-amicasine microspheres were phagocytized by monocytes and neutrophils and the number of particles taken up by each cell significantly increased for Alb-Fn microspheres with respect to the plain microspheres. No significant phagocytosis was observed for Alb-PEG microspheres. The number of particles taken up by each cell was less than the plain and amikacin modified albumin microspheres. Almost zero uptake was obtained for the phagocytosis of Alb-PEG microspheres with lung and peritoneal macrophages. For phagocytosis of plain and other modified particles by the macrophages, although the number of particles taken up by each cell increased with respect to those with neutrophils and monocytes, similar tendencies were also obtained.

Imaging gene expression in the brain with peptide nucleic acid (PNA) antisense radiopharmaceuticals and drug targeting technology

Antisense oligomers are potential pharmaceutical and radiopharmaceutical agents that can be used to modulate and image gene expression. Progress with in vivogene targeting using antisense-based therapeutics has been slower than expected during the last decade, owing to poor trans-cellular delivery of antisense agents. This chapter suggests that if antisense pharmacology is merged with drug targeting technology, then membrane barriers can be circumvented and antisense agents can be delivered to tissues in vivo. Without the application of drug targeting, the likelihood of success for an antisense drug development program is low, particularly for the brain which is protected by the blood-brain barrier (BBB). Among the different classes of antisense agents, peptide nucleic acids (PNA) present advantages for in vivoapplications over conventional and modified oligodeoxynucleotides (ODN), including phosphorothioates (PS)-ODN. Some advantages of PNAs include their electrically neutral backbone, low toxicity to neural cells, resistance to nucleases and peptidases, and lack of binding to plasma proteins. PNAs are poorly transported through cellular membranes, however, including the BBB and the brain cell membrane (BCM). Because the mRNA target for the antisense agent lies within the cytosol of the target cell, the BBB and the BCM must be circumvented in vivo, which ispossible with the use of chimeric peptide drug targeting technology. Chimeric peptides are formed by conjugation of a non-transportable drug, such as a PNA, to a drug delivery vector. The vector undergoes receptor-mediated transcytosis (RMT) through the BBB and receptor-mediated endocytosis through the BCM in vivo. When labeled with a radioisotope (e.g., 125I or 111In), the antisense chimeric peptide provides imaging of gene expressionin the brain in vivoin a sequence-specific manner. Further development of antisense radiopharmaceutical agents may allow for in vivoimaging of genes in pathological states, and may provide tools for the analysis of novel genes with functional genomics.

Novel polyester-polysaccharide nanoparticles.

The aim of the present study was to develop a new type of core-shell nanoparticles from a family of novel amphiphilic copolymers, based on dextran (DEX) grafted with poly(epsilon-caprolactone) (PCL) side chains (PCL-DEX). A family of PCL-DEX copolymers was synthesized in which both the molecular weight and the proportion by weight of DEX in the copolymer were varied. The nanoparticles were prepared by a technique derived from emulsion-solvent evaporation, during which emulsion stability was investigated using a Turbiscan. The nanoparticle size distribution, density, zeta potential, morphology, and suitability for freeze-drying were determined. Because of their strongly amphiphilic properties, the PCL-DEX copolymers were able to stabilize o/w emulsions without the need of additional surfactants. Nanoparticles with a controlled mean diameter ranging from 100 to 250 nm were successfully prepared. A mechanism of formation of these nanoparticles was proposed. Zeta potential measurements confirmed the presence of a DEX coating. A new generation of polysaccharide-decorated nanoparticles has been successfully prepared from a family of PCL-DEX amphiphilic copolymers. They may have potential applications in drug encapsulation and targeting.

Construction of tumor-specific cells expressing a membrane-anchored single-chain Fv of anti-ErbB-2 antibody

Cells expressing a membrane-anchored single-chain fragment variable (scFv) domain against a tumor-specific antibody were fabricated. These cells were able to bind to cells of a human colon cancer line (BM314) expressing the erbB-2 proto-oncogene. A plasmid, pMFverbB, was first constructed in which the anti-ErbB-2 scFv gene was cloned in-frame between a signal peptide sequence and the platelet-derived growth factor receptor (PDGFR) transmembrane domain gene to express scFv on the cell surface. An African green monkey cell line, COS-1, was stably transfected with pMFverbB. Immunofluorescence assay experiments and microscopic observation showed that the cells expressing scFv bound to the human tumor cells overexpressing the ErbB-2 protein as well as to cells of a mouse fibroblast line (NIH-3T3) transfected with the erbB-2 gene. The cells expressing scFv could take up magnetite cationic liposomes as a model of particle-type drug and retained the ability to target ErbB-2-expressing cells. The fabricated cells have the potential to serve as drug carriers in drug targeting applications.

Clinical Applications of Magnetic Drug Targeting

Cancer patients often present with localized disease. Yet, surgical eradication or radiation treatment is not always possible or meaningful. Site-directed drug targeting is one way of local or regional antitumor treatment. Magnetically controlled drug targeting is one of the various possibilities of drug targeting. This technology is based on binding established anticancer drugs with ferrofluids that concentrate the drug in the area of interest (tumor site) by means of magnetic fields. Then, the drug desorbs from the ferrofluid and enfolds its mechanism of action. This paper gives the reader an overview of current applications of ferrofluids (magnetic liquids) in conjunction with magnetic fields as they relate to the latest advances in medical applications and in particular to anticancer treatment.

Glycohistochemistry: the why and how of detection and localization of endogenous lectins.

The central dogma of molecular biology limits the downstream flow of genetic information to proteins. Progress from the last two decades of research on cellular glycoconjugates justifies adding the enzymatic production of glycan antennae with information-bearing determinants to this famous and basic pathway. An impressive variety of regulatory processes including cell growth and apoptosis, folding and routing of glycoproteins and cell adhesion/migration have been unravelled and found to be mediated or modulated by specific protein (lectin)-carbohydrate interactions. The conclusion has emerged that it would have meant missing manifold opportunities not to recruit the sugar code to cellular information transfer. Currently, the potential for medical applications in anti-adhesion therapy or drug targeting is one of the major driving forces fuelling progress in glycosciences. In histochemistry, this concept has prompted the introduction of carrier-immobilized carbohydrate ligands (neoglycoconjugates) to visualize the cells' capacity to be engaged in oligosaccharide recognition. After their isolation these tissue lectins will be tested for ligand analysis. Since fine specificities of different lectins can differ despite identical monosaccharide binding, the tissue lectins will eventually replace plant agglutinins to move from glycan profiling and localization to functional considerations. Namely, these two marker types, i.e. neoglycoconjugates and tissue lectins, track down accessible binding sites with relevance for involvement in interactions in situ. The documented interplay of synthetic organic chemistry and biochemistry with cyto- and histochemistry nourishes the optimism that the application of this set of innovative custom-prepared tools will provide important insights into the ways in which glycans can act as hardware in transmitting information during normal tissue development and pathological situations.

Estimation of the Poly(ethylene glycol) Chain Length of L-Polylactide-Polyethylene Glycol in Aqueous Dispersions Using Viscoelastic Measurements

A range of novel, biodegradable block copolymers have been produced, consisting of polylactidepolyethylene glycol (PLA-PEG)AB block copolymers, as possible drug delivery systems for drug targeting applications. These copolymers form particles in aqueous dispersions, with the PLA in the core and the hydrophilic PEG chains surrounding the core and extending into the media. The viscoelastic properties of an aqueous dispersion of one such copolymer, synthesized from L-polylactide (LPLA-PEG) were investigated to estimate the PEG chain length. This value would give an indication of the steric stability of the particle and hence the ability to avoid uptake by the reticuloendothelial system (RES). A range of volume fractions, O, of the copolymer were studied, with a strain sweep and frequency sweep being performed at each concentration. The results were typical for a viscoelastic system, with the storage modulus, G', becoming greater than the loss modulus, G'', on increasing in the volume fraction, indicating interaction between the PEG chains. The critical volume fraction, O eff (where G'=G''), is the point where overlap of the PEG chains commences. These data, in conjunction with the known hydrodynamic radius of the particles, determined from photon correlation spectroscopy (PCS), gave a PEG chain length estimate of 6.4 nm. It is hoped that the ability to estimate the PEG chain length by this method will lead to greater understanding of the role of PEG in drug targeting and the design of future drug delivery systems