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At least 361 records · Page 20Linked to original sources
PubMed2006

IMRT delivery to a moving target by dynamic MLC tracking: delivery for targets moving in two dimensions in the beam's eye view.

A new modification of the dynamic multileaf collimator (dMLC) delivery technique for intensity-modulated therapy (IMRT) is outlined. This technique enables the tracking of a target moving through rigid-body translations in a 2D trajectory in the beam's eye view. The accuracy of the delivery versus that of deliveries with no tracking and of 1D tracking techniques is quantified with clinically derived intensity-modulated beams (IMBs). Leaf trajectories calculated in the target-reference frame were iteratively synchronized assuming regular target motion. This allowed the leaves defined in the lab-reference frame to simultaneously follow the target motion and to deliver the required IMB without violation of the leaf maximum-velocity constraint. The leaves are synchronized until the gradient of the leaf position at every instant is less than a calculated maximum. The delivered fluence in the target-reference frame was calculated with a simple primary-fluence model. The new 2D tracking technique was compared with the delivered fluence produced by no-tracking deliveries and by 1D tracking deliveries for 33 clinical IMBs. For the clinical IMBs normalized to a maximum fluence of 200 MUs, the rms difference between the desired and the delivered IMB was 15.6 +/- 3.3 MU for the case of a no-tracking delivery, 7.9 +/- 1.6 MU for the case where only the primary component of motion was corrected and 5.1 +/- 1.1 MU for the 2D tracking delivery. The residual error is due to interpolation and sampling effects. The 2D tracking delivery technique requires an increase in the delivery time evaluated as between 0 and 50% of the unsynchronized delivery time for each beam with a mean increase of 13% for the IMBs tested. The 2D tracking dMLC delivery technique allows an optimized IMB to be delivered to moving targets with increased accuracy and with acceptable increases in delivery time. When combined with real-time knowledge of the target motion at delivery time, this technique facilitates improved target conformality relative to no-tracking deliveries and allows PTV margin reduction.

Algorithms↗
PubMed2006

A tumor vasculature targeted liposome delivery system for combretastatin A4: design, characterization, and in vitro evaluation.

The objective of this study was to develop an efficient tumor vasculature targeted liposome delivery system for combretastatin A4, a novel antivascular agent. Liposomes composed of hydrogenated soybean phosphatidylcholine (HSPC), cholesterol, distearoyl phosphoethanolamine-polyethylene-glycol-2000 conjugate (DSPE-PEG), and DSPE-PEG-maleimide were prepared by the lipid film hydration and extrusion process. Cyclic RGD (Arg-Gly-Asp) peptides with affinity for alphavbeta3-integrins expressed on tumor vascular endothelial cells were coupled to the distal end of PEG on the liposomes sterically stabilized with PEG (long circulating liposomes, LCL). The liposome delivery system was characterized in terms of size, lamellarity, ligand density, drug loading, and leakage properties. Targeting nature of the delivery system was evaluated in vitro using cultured human umbilical vein endothelial cells (HUVEC). Electron microscopic observations of the formulations revealed presence of small unilamellar liposomes of approximately 120 nm in diameter. High performance liquid chromatography determination of ligand coupling to the liposome surface indicated that more than 99% of the RGD peptides were reacted with maleimide groups on the liposome surface. Up to 3 mg/mL of stable liposomal combretastatin A4 loading was achieved with approximately 80% of this being entrapped within the liposomes. In the in vitro cell culture studies, targeted liposomes showed significantly higher binding to their target cells than nontargeted liposomes, presumably through specific interaction of the RGD with its receptors on the cell surface. It was concluded that the targeting properties of the prepared delivery system would potentially improve the therapeutic benefits of combretastatin A4 compared with nontargeted liposomes or solution dosage forms.

Angiogenesis Inhibitors↗
PubMed1990

Quantitative analysis of retinal hemodynamics using targeted dye delivery.

A new method designed to allow repeated mapping of retinal hemodynamics on a macro- and microcirculatory level was evaluated in the primate eye. The method, called "targeted dye delivery," consists of encapsulating a fluorescent dye in temperature-sensitive liposomes, injecting the liposomes systemically, and using a light pulse from an argon laser to release a bolus of dye in a targeted retinal vessel. The follow-up of the well-defined dye front thus generated allows calculation of the blood flow and capillary transit time. Evaluation of targeted dye delivery in a monkey indicated that centerline blood velocity and the vessel diameter can be measured with a reproducibility of 10% and 4%, respectively, in vessels that are 40 microns and larger. These measurements yielded flow values that had a reproducibility of 10% on the same day and 13% on different days. The normalization of flow rate by the vessel diameter was consistent with theoretic estimates and promises to be a circulation indicator independent of variations between individual and species. The transit time across capillary beds at different locations was found to be similar, thus indicating that the method could be used to evaluate the local viability of the microcirculation.

Animals↗
PubMed2006

Formulation of functionalized PLGA-PEG nanoparticles for in vivo targeted drug delivery.

Nanoparticle (NP) size has been shown to significantly affect the biodistribution of targeted and non-targeted NPs in an organ specific manner. Herein we have developed NPs from carboxy-terminated poly(d,L-lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-b-PEG-COOH) polymer and studied the effects of altering the following formulation parameters on the size of NPs: (1) polymer concentration, (2) drug loading, (3) water miscibility of solvent, and (4) the ratio of water to solvent. We found that NP mean volumetric size correlates linearly with polymer concentration for NPs between 70 and 250 nm in diameter (linear coefficient=0.99 for NPs formulated with solvents studied). NPs with desirable size, drug loading, and polydispersity were conjugated to the A10 RNA aptamer (Apt) that binds to the prostate specific membrane antigen (PSMA), and NP and NP-Apt biodistribution was evaluated in a LNCaP (PSMA+) xenograft mouse model of prostate cancer. The surface functionalization of NPs with the A10 PSMA Apt significantly enhanced delivery of NPs to tumors vs. equivalent NPs lacking the A10 PSMA Apt (a 3.77-fold increase at 24h; NP-Apt 0.83%+/-0.21% vs. NP 0.22%+/-0.07% of injected dose per gram of tissue; mean+/-SD, n=4, p=0.002). The ability to control NP size together with targeted delivery may result in favorable biodistribution and development of clinically relevant targeted therapies.

Animals↗
PubMed2000

Targetable gene delivery vectors.

Adenoviral vectors, which have targeting ligands for tumor cells on the capsid, no natural tropism, and carry a therapeutic payload should be constructed soon and tested in pre-clinical models. Nevertheless, there are still important considerations for the design and therapeutic use of targetable vectors. Perhaps the single greatest challenge in the future, as it was in the past, will be finding ligands that have a higher apparent affinity for tumor and/or tumor endothelial cells then normal cells. However, the advent of many rapidly advancing technologies and information including the sequencing of the human genome, in vivo and in vitro phage display, rapid analysis of gene and protein expression in any context, and new cellular targets such as angiogenic endothelial cells, may provide many opportunities for the discovery of novel and useful ligands. In addition, the interests in targeting vectors are rapidly growing with new journals and meetings solely devoted to this subject increasing annually. Within the next 5 years, we should have meaningful clinical data on targetable vectors to reassess our progress.

Animals↗
PubMed2005

A multi-scale stochastic drug release model for polymer-coated targeted drug delivery systems.

A multi-scale mathematical model for drug release of oral targeted drug delivery systems was developed and applied to a commercially available delayed release tablet (Asacol) that delivers 5-aminosalicyclic acid (5-ASA) to the colon. Underlying physical and biochemical principles governing the involved processes (diffusion and dissolution) were employed to develop the mathematical description. Finite element formulation was used to numerically solve the model equations. Molecular dynamics (MD) simulations were used to predict macro-scale transport properties of the drug and the biologic fluid. The effect of pH variability in the gastrointestinal tract environment on the dissolution of the polymeric enteric coating was investigated using the Monte Carlo method. The direct coupling method employed (MD) predicted a sufficiently accurate diffusion coefficient (5.7x10(-6) cm2 s-1) of the drug molecules in reasonable (3 h) computation times. The model was validated using experimental data from in vitro dissolution experiments and provided accurate prediction of the drug release from the delivery system (root mean square error of 5%). The amount of drug entering the systemic circulation, computed from the predicted drug release in varying pH environments in the small bowel, was 15-24%. This range was in good agreement with clinical in vivo data (13-36%) obtained from literature. This research shows that in silico experiments using mechanistic models and stochastic approaches can be used for drug design and optimization and as a decision making tool for physicians.

Administration, Oral↗
PubMed2001

Synthesis of galactosyl compounds for targeted gene delivery.

Cell-specific DNA delivery offers a great potential for targeted gene therapy. Toward this end, we have synthesized a series of compounds carrying galactose residues as a targeting ligand for asialoglycoprotein receptors of hepatocytes and primary amine groups as a functional domain for DNA binding. Biological activity of these galactosyl compounds in DNA delivery was evaluated in HepG2 and BL-6 cells and compared with respect to the number of galactose residues as well as primary amine groups in each molecule. Transfection experiments using a firefly luciferase gene as a reporter revealed that compounds with multivalent binding properties were more active in DNA delivery. An optimal transfection activity in HepG2 cells requires seven primary amine groups and a minimum of two galactose residues in each molecule. The transfection activity of compounds carrying multi-galactose residues can be inhibited by asialofetuin, a natural substrate for asialoglycoprotein receptors of hepatocytes, suggesting that gene transfer by these galactosyl compounds is asialoglycoprotein receptor-mediated. These results provide direct evidence in support of our new strategy for the use of small and synthetic compounds for cell specific and targeted gene delivery.

Animals↗
PubMed2005

Targeted drug delivery with dendrimers: comparison of the release kinetics of covalently conjugated drug and non-covalent drug inclusion complex.

Dendrimers have unique characteristics including monodispersity and modifiable surface functionality, along with highly defined size and structure. This makes these polymers attractive candidates as carriers in drug delivery applications. Drug delivery can be achieved by coupling a drug to polymer through one of two approaches. Hydrophobic drugs can be complexed within the hydrophobic dendrimer interior to make them water-soluble or drugs can be covalently coupled onto the surface of the dendrimer. Using both methods we compared the efficacy of generation 5 PAMAM dendrimers in the targeted drug delivery of methotrexate coupled to the polymer. The amine-terminated dendrimers bind to negatively charged membranes of cells in a non-specific manner and can cause toxicity in vitro and in vivo. To reduce toxicity and to increase aqueous solubility, modifications were made to the surface hydroxyl groups of the dendrimers. For targeted drug delivery, the dendrimer was modified to have a neutral terminal functionality for use with surface-conjugated folic acid as the targeting agent. The complexation of methotrexate within a dendrimer changes the water insoluble drug into a stable and readily water-soluble compound. When this dendrimer complexed drug, however, was placed in a solution of phosphate buffered saline, the methotrexate was immediately released and displayed diffusion characteristics identical to free methotrexate. Covalently coupled methotrexate dendrimer conjugates were stable under identical conditions in water and buffered saline. Cytotoxicity tests showed that methotrexate as the dendrimer inclusion complex had an activity identical to the free drug in vitro. In contrast, folic acid targeted dendrimer with covalently conjugated methotrexate specifically killed receptor-expressing cells by intracellular delivery of the drug through receptor-mediated endocytosis. This study demonstrates that while drug as a dendrimer inclusion complex is readily released and active in vitro, covalently conjugated drug to dendrimer is better suited for specifically targeted drug delivery.

Cell Survival↗
PubMed2006

A RGD-containing oligopeptide (K)16GRGDSPC: a novel vector for integrin-mediated targeted gene delivery.

A 23 amino acid, bifunctional integrin-targeted synthetic oligopeptide was evaluated for ex vivo gene delivery to rabbit bone marrow stromal cells (BMSCs). Synthesis of the peptide (K)16GRGDSPC was performed on a solid-phase batch peptide synthesizer. BMSCs were transfected with plasmid DNA coding for luciferase by (K)16GRGDSPC and the transfection efficiency was assayed. The influences of chloroquine and polyethyleneimine on the transfection efficiency were also examined. The target specificity of (K)16GRGDSPC to mediate exogenous gene into BMSCs was analyzed using cell attachment test and gene delivery inhibition test. The results showed that the transfection efficiency of the oligopeptide vector was lower than that of Lipofectamine. But in the presence of endosomal buffer chloroquine or endosomal disrupting agent polyethyleneimine, the transfection efficiency of the vector was greatly enhanced. In addition, RGD-containing peptides inhibited BMSCs' attachment to the 96-well plates pretreated with fibronectin or vitronectin and significantly decreased the transfection efficiency of the oligopeptide vector. These studies demonstrated that oligopeptide (K)16GRGDSPC was an ideal novel targeted non-viral gene delivery vector, which was easy to be synthesized, high efficient and low cytotoxicity. The vector could effectively deliver exogenous gene into rat BMSCs.

Animals↗
PubMed2001

Development of colon targeted drug delivery systems for mebendazole.

The objective of the present study is to develop colon targeted drug delivery systems for mebendazole using guar gum as a carrier. Matrix tablets containing various proportions of guar gum were prepared by wet granulation technique using starch paste as a binder. The tablets were evaluated for drug content uniformity, and were subjected to in vitro drug release studies. The amount of mebendazole released from the matrix tablets at different time intervals was estimated by a high-performance liquid chromatography method. Guar gum matrix tablets released 8-15% of the mebendazole in the physiological environment of stomach and small intestine depending on the proportion of guar gum used in the formulation. When the dissolution study was continued in simulated colonic fluids the matrix tablets containing 20% of guar gum released another 83% of mebendazole after degradation into 2-3 pieces. The matrix tablets containing 30% of guar gum also released about 50% of mebendazole in simulated colonic fluids indicating the susceptibility of the guar gum formulations to the rat caecal contents. The results of the study show that matrix tablets containing either 20% or 30% of guar gum are most likely to provide targeting of mebendazole for local action in the colon. The mebendazole matrix tablets containing either 20% or 30% of guar gum showed no change either in physical appearance, drug content or dissolution pattern after storage at 45 degrees C/75% relative humidity for 3 months. Differential scanning calorimetry indicated no possibility of interaction between mebendazole and guar gum.

Animals↗
PubMed2004

Targeted gene delivery to human airway epithelial cells with synthetic vectors incorporating novel targeting peptides selected by phage display.

Human airway epithelial cell targeting peptides were identified by biopanning on 1HAEo-cells, a well characterised epithelial cell line. Bound phage were recovered after three rounds of binding, high stringency washing and elution, leading to the production of an enriched phage peptide population. DNA sequencing of 56 clones revealed 14 unique sequences. Subsequent binding analysis revealed that 13 of these peptides bound 1HAEo-cells with high affinity. Three peptides, SERSMNF, YGLPHKF and PSGAARA were represented at high frequency. Three clearly defined families of peptide were identified on the basis of sequence motifs including (R/K)SM, L(P/Q)HK and PSG(A/T)ARA. Two peptides, LPHKSMP and LQHKSMP contained two motifs. Further detailed sequence analysis by comparison of peptide sequences with the SWISSPROT protein database revealed that some of the peptides closely resembled the cell binding proteins of viral and bacterial pathogens including Herpes Simplex Virus, rotavirus, Mycoplasma pneumoniae and rhinovirus, the latter two being respiratory pathogens, as well as peptide YGLPHKF having similarity to a protein of unknown function from the respiratory pathogen Legionella pneumophila. Peptides were incorporated into gene delivery formulations with the cationic lipid Lipofectin and plasmid DNA and shown to confer a high degree of transfection efficiency and specificity in 1HAEo-cells. Improved transfection efficiency and specificity was also observed in human endothelial cells, fibroblasts and keratinocytes. Therefore, on the basis of clone frequency after biopanning, cell binding affinity, peptide sequence conservation and pathogenic similarity, we have identified 3 novel peptide families and 5 specific peptides that have the potential for gene transfer to respiratory epithelium in vivo as well as providing useful in vitro transfection reagents for primary human cell types of scientific and commercial interest.

Amino Acid Sequence↗
PubMed2002

Design and in vitro evaluation of oral colon targeted drug delivery systems for tinidazole.

The aim of the present investigation is to develop colon targeted drag delivery sytems for tinidazole using guar gum as a carrier in the treatment of amoebiasis. Fast-disintegrating tinidazole core tablets were compression-coated with 55, 65 and 75% of guar gum. All the formulations were evaluated for the hardness, drug content uniformity, and subjected to in vitro drug release studies. The amount of tinidazole released from tablets at different time intervals was estimated by HPLC method. The compression-coated formulations released < 0.5% of tinidazole in the physiological environment of stomach and small intestine. When the dissolution study was continued in simulated colonic fluids, the compression coated tablet with 55% of guar gum coat released 99% of tinidazole after degradation by colonic bacteria at the end of 24 h of the dissolution study. The compression coated tablets with 65 and 75% of guar gum coat released about 67 and 20% of tinidazole, respectively in simulated colonic fluids indicating the susceptibility of the guar gum formulations to the rat caecal contents. The results of the study show that compression coated tinidazole tablets with either 55 or 65% of guar gum coat is most likely to provide targeting of tinidazole for local action in the colon owing to its minimal release of the drug in the first 5 h of physiological environment of stomach and small intestine. The tinidazole compression coated tablets showed no change either in physical appearance, drug content or in dissolution pattern after storage at 40 degrees C/75% RH for 6 months.

Animals↗
PubMed2005

The design and evaluation of a novel targeted drug delivery system using cationic emulsion-antibody conjugates.

In an attempt to design a targeted drug delivery system to tumors' over-expressing H-ferritin specifically recognized by a monoclonal antibody, AMB8LK, a cationic emulsion - AMB8LK conjugate was prepared. A novel cross-linker molecule bearing maleimide group was synthesized and added to cationic emulsion formulation for AMB8LK Fab' fragment covalent coupling. NMR spectroscopy confirmed the cross-linker synthesis and the preservation of the active maleimide function. SDS gel-electrophoresis results corroborated the formation of the Fab' fragment. Different densities of Fab' fragments (10-200 Fab'/oil droplet) were conjugated to emulsion droplet interface and no changes in the physico-chemical properties were observed ( approximately 120 nm size and zeta potential of approximately +30 mV). The coupling efficiency ranged from 55% to 70% and was visualized by TEM showing gold particles attached to the droplet interface. Cell culture studies demonstrated specific binding to cells as confirmed by the occurrence of the marked reduction in binding when free AMB8LK Mab was incubated before adding the AMB8LK-emulsion conjugate to the cells. The coupling of AMB8LK Fab' fragment to the cationic emulsion increased the cells uptake by 50% as compared to non-conjugated respective cationic emulsion. Appropriate conditions were, thus, identified for coupling AMB8LK Fab' fragment to cationic emulsion without altering the specificity and affinity of the Mab fragment to the tumor antigen.

Amines↗
PubMed1988

Evidence for targeted gene delivery to Hep G2 hepatoma cells in vitro.

We have developed a system for targeting foreign DNA to hepatocytes in vitro using a soluble DNA carrier that takes advantage of receptor-mediated endocytosis to achieve internalization. The idea is based on the fact that hepatocytes possess a unique receptor that binds and internalizes galactose-terminal (asialo)glycoproteins. To create a targetable carrier system that could bind DNA in a nondeforming manner, we used poly(L-lysine) to bind DNA in a strong but noncovalent interaction. An asialoglycoprotein, asialoorosomucoid (AsOR), was chemically coupled to poly(L-lysine) to form an asialoorosomucoid-poly(L-lysine) conjugate. Various proportions of conjugate to DNA were tested to determine conditions that maximized DNA content in a soluble complex and that limited solubility of complexes. To test the targetable gene delivery system, AsOR-poly(L-lysine) conjugate was complexed to the plasmid pSV2 CAT containing the gene for chloramphenicol acetyltransferase (CAT) driven by an SV-40 promoter. We tested this complex using a model system consisting of human hepatoma cell line Hep G2 [asialoglycoprotein receptor (+)], hepatoma SK-Hep 1, IMR-90 fibroblasts, and uterine smooth muscle [receptor (-)] cells. Each cell line was incubated with 0.2 micron filtered AsOR-poly(L-lysine)-DNA complex or controls consisting of DNA plus AsOR, DNA plus poly(L-lysine), or DNA alone. Cells were assayed for the presence of CAT activity as a measure of gene transformation. SK-Hep 1, IMR-90, and smooth muscle [receptor (-)] cells produced no detectable acetylated chloramphenicol derivatives under any of these conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyltransferases↗
PubMed2006

Nanotechnology and site-targeted drug delivery.

Nanotechnology, building on its ability to control or manipulate structures at the atomic level, promises to develop effective drug-delivery systems. This is to be achieved through creating structures that have novel properties because of their small size. This is not an entirely new concept in site-targeted drug delivery, and this critical review examines recent contributions made by 'nanotechnology' to solve critical issues concerning the development of therapeutically effective and acceptable site-targeted drug delivery systems. It is shown that very little progress has been made. For nanotechnology rationally to generate materials useful in human therapy it will need to progress in full recognition of all the requirements biology places on the acceptability of exogenous materials.

Drug Delivery Systems↗
PubMed2003

Cell type specific targeted intracellular delivery into muscle of a monoclonal antibody that binds myosin IIb.

Methods for cell type specific targeted intracellular delivery of proteins in vivo remain limited. A murine monoclonal anti-dsDNA antibody, mAb 3E10, was selectively transported into skeletal muscle cells in vivo. The antibody bound a 200 kDa protein only found in lysates of skeletal muscle by Western blotting. The 200 kDa protein was purified from muscle lysate by antibody affinity chromatography and identified as the skeletal muscle specific heavy chain of myosin IIb by electrospray mass spectrometry. Antibody binding specificity for myosin IIb was demonstrated in Western blots by binding myosin in skeletal muscle lysates from mice null for myosin IId but not in mice null for myosin IIb. Myosin IIb is implicated in the specific targeting of mAb 3E10 to skeletal muscle.

Amino Acid Sequence↗
PubMed1994

Strategies to achieve targeted gene delivery via the receptor-mediated endocytosis pathway.

Gene transfer to eukaryotic cells may be accomplished by capitalizing on endogenous cellular pathways of macromolecular transport. In this regard, molecular conjugate vectors have been developed which deliver DNA via the receptor-mediated endocytosis pathway. An attractive feature of this vector system is the potential to achieve targeted gene delivery based upon flexible incorporation of a targeting ligand. In this review we describe steps that have been taken to optimize this vector system. Specific strategies include the incorporation of mechanisms to achieve conjugate escape from the endosome and the derivation of methods to eliminate sources of nonspecificity. These developments have demonstrated the potential to construct a vector system in which multiple independent components may function in a concerted manner to accomplish targeted high efficiency gene delivery. In their present state of development, molecular conjugate vectors may have many potential applications for in vitro use.

Adenoviridae↗