Optimization of folate-conjugated liposomal vectors for folate receptor-mediated gene therapy

Advances in Liposome-Encapsulated Phthalocyanines for Photodynamic Therapy

This updated review aims to describe the current status in the development of liposome-based systems for the targeted delivery of phthalocyanines for photodynamic therapy (PDT). Although a number of other drug delivery systems (DDS) can be found in the literature and have been studied for phthalocyanines or similar photosensitizers (PSs), liposomes are by far the closest to clinical practice. PDT itself finds application not only in the selective destruction of tumour tissues or the treatment of microbial infections, but above all in aesthetic medicine. From the point of view of administration, some PSs can advantageously be delivered through the skin, but for phthalocyanines, systemic administration is more suitable. However, systemic administration places higher demands on advanced DDS, active tissue targeting and reduction of side effects. This review focuses on the already described liposomal DDS for phthalocyanines, but also describes examples of DDS used for structurally related PSs, which can be assumed to be applicable to phthalocyanines as well.

Recent Advancements in Stimuli Responsive Drug Delivery Platforms for Active and Passive Cancer Targeting

The tumor-specific targeting of chemotherapeutic agents for specific necrosis of cancer cells without affecting the normal cells poses a great challenge for researchers and scientists. Though extensive research has been carried out to investigate chemotherapy-based targeted drug delivery, the identification of the most promising strategy capable of bypassing non-specific cytotoxicity is still a major concern. Recent advancements in the arena of onco-targeted therapies have enabled safe and effective tumor-specific localization through stimuli-responsive drug delivery systems. Owing to their promising characteristic features, stimuli-responsive drug delivery platforms have revolutionized the chemotherapy-based treatments with added benefits of enhanced bioavailability and selective cytotoxicity of cancer cells compared to the conventional modalities. The insensitivity of stimuli-responsive drug delivery platforms when exposed to normal cells prevents the release of cytotoxic drugs into the normal cells and therefore alleviates the off-target events associated with chemotherapy. Contrastingly, they showed amplified sensitivity and triggered release of chemotherapeutic payload when internalized into the tumor microenvironment causing maximum cytotoxic responses and the induction of cancer cell necrosis. This review focuses on the physical stimuli-responsive drug delivery systems and chemical stimuli-responsive drug delivery systems for triggered cancer chemotherapy through active and/or passive targeting. Moreover, the review also provided a brief insight into the molecular dynamic simulations associated with stimuli-based tumor targeting.

To Conjugate or to Package? A Look at Targeted siRNA Delivery Through Folate Receptors

RNA interference (RNAi) applications have evolved from experimental tools to study gene function to the development of a novel class of gene-silencing therapeutics. Despite decades of research, it was not until August 2018 that the US FDA approved the first-ever RNAi drug, marking a new era for RNAi therapeutics. Although there are many limitations associated with the inherent structure of RNA, delivery to target cells and tissues remains the most challenging. RNAs are unable to diffuse across cellular membranes due to their large size and polyanionic backbone and, therefore, require a delivery vector. RNAi molecules can be conjugated to a targeting ligand or packaged into a delivery vehicle. Alnylam has used both strategies in their FDA-approved formulations to achieve efficient delivery to the liver. To harness the full potential of RNAi therapeutics, however, we must be able to target additional cells and tissues. One promising target is the folate receptor α, which is overexpressed in a variety of tumors despite having limited expression and distribution in normal tissues. Folate can be conjugated directly to the RNAi molecule or used to functionalize delivery vehicles. In this review, we compare both delivery strategies and discuss the current state of research in the area of folate-mediated delivery of RNAi molecules.

Liposomal delivery of CRISPR/Cas9

Liposomes are one of the most widely investigated carriers for CRISPR/Cas9 delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic CRISPR/Cas9 delivery (long blood circulation, efficient tumor penetration, and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations, and ligand modifications. Cationic formulations dominate CRISPR/Cas9 delivery and neutral formulations also have good performance while anionic formulations are generally not proper for CRISPR/Cas9 delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal CRISPR/Cas9 delivery, outlined existing problems, and provided some future perspectives. Liposomes are one of the most widely investigated carriers for CRISPR/Cas9 delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic siRNA delivery (long blood circulation, efficient tumor penetration, and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations, and ligand modifications. Cationic formulations dominate CRISPR/Cas9 delivery and neutral formulations also have good performance while anionic formulations are generally not proper for CRISPR/Cas9 delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal CRISPR/Cas9 delivery, outlined existing problems, and provided some future perspectives.

Formulation Strategies for Folate-Targeted Liposomes and Their Biomedical Applications

The folate receptor (FR) is a tumor-associated antigen that can bind with folic acid (FA) and its conjugates with high affinity and ingests the bound molecules inside the cell via the endocytic mechanism. A wide variety of payloads can be delivered to FR-overexpressed cells using folate as the ligand, ranging from small drug molecules to large DNA-containing macromolecules. A broad range of folate attached liposomes have been proven to be highly effective as the targeted delivery system. For the rational design of folate-targeted liposomes, an intense conceptual understanding combining chemical and biomedical points of view is necessary because of the interdisciplinary nature of the field. The fabrication of the folate-conjugated liposomes basically involves the attachment of FA with phospholipids, cholesterol or peptides before liposomal formulation. The present review aims to provide detailed information about the design and fabrication of folate-conjugated liposomes using FA attached uncleavable/cleavable phospholipids, cholesterol or peptides. Advances in the area of folate-targeted liposomes and their biomedical applications have also been discussed.

Overcoming Endosomal Entrapment in Drug Delivery

Intracellular delivery of biological agents such as peptides, proteins, and nucleic acids generally rely on the endocytic pathway as the major uptake mechanism, resulting in their entrapment inside the endosome and lysosome. The recent discovery of cell-penetrating molecules of exceptionally high endosomal escape and cytosolic delivery efficiencies and elucidation of their mechanism of action represent major breakthroughs in this field. In this Topical Review, we provide an overview of the recent progress in understanding and enhancing the endosomal escape process and the new opportunities opened up by these recent findings.

Biotin conjugated organic molecules and proteins for cancer therapy: A review

The main transporter for biotin is sodium dependent multivitamin transporter (SMVT), which is overexpressed in various aggressive cancer cell lines such as ovarian (OV 2008, ID8), leukemia (L1210FR), mastocytoma (P815), colon (Colo-26), breast (4T1, JC, MMT06056), renal (RENCA, RD0995), and lung (M109) cancer cell lines. Furthermore, its overexpression was found higher to that of folate receptor. Therefore, biotin demand in the rapidly growing tumors is higher than normal tissues. Several biotin conjugated organic molecules has been reported here for selective delivery of the drug in cancer cell. Biotin conjugated molecules are showing higher fold of cytotoxicity in biotin positive cancer cell lines than the normal cell. Nanoparticles and polymer surface modified drugs and biotin mediated cancer theranostic strategy was highlighted in this review. The cytotoxicity and selectivity of the drug in cancer cells has enhanced after biotin conjugation.

Novel Water-Soluble Mucoadhesive Carbosilane Dendrimers for Ocular Administration

The purpose of this research was to determine the potential use of water-soluble anionic and cationic carbosilane dendrimers (generations 1-3) as mucoadhesive polymers in eyedrop formulations. Cationic carbosilane dendrimers decorated with ammonium -NH3(+) groups were prepared by hydrosylilation of Boc-protected allylamine and followed by deprotection with HCl. Anionic carbosilane dendrimers with terminal carboxylate groups were also employed in this study. In vitro and in vivo tolerance studies were performed in human ocular epithelial cell lines and rabbit eyes respectively. The interaction of dendrimers with transmembrane ocular mucins was evaluated with a surface biosensor. As proof of concept, the hypotensive effect of a carbosilane dendrimer eyedrop formulation containing acetazolamide (ACZ), a poorly water-soluble drug with limited ocular penetration, was tested after instillation in normotensive rabbits. The methodology used to synthesize cationic dendrimers avoids the difficulty of obtaining neutral -NH2 dendrimers that require harsher reaction conditions and also present high aggregation tendency. Tolerance studies demonstrated that both prototypes of water-soluble anionic and cationic carbosilane dendrimers were well tolerated in a range of concentrations between 5 and 10 μM. Permanent interactions between cationic carbosilane dendrimers and ocular mucins were observed using biosensor assays, predominantly for the generation-three (G3) dendrimer. An eyedrop formulation containing G3 cationic carbosilane dendrimers (5 μM) and ACZ (0.07%) (289.4 mOsm; 5.6 pH; 41.7 mN/m) induced a rapid (onset time 1 h) and extended (up to 7 h) hypotensive effect, and led to a significant increment in the efficacy determined by AUC0(8h) and maximal intraocular pressure reduction. This work takes advantage of the high-affinity interaction between cationic carbosilane dendrimers and ocular transmembrane mucins, as well as the tensioactive behavior observed for these polymers. Our results indicate that low amounts of cationic carbosilane dendrimers are well tolerated and able to improve the hypotensive effect of an acetazolamide solution. Our results suggest that carbosilane dendrimers can be used in a safe range of concentrations to enhance the bioavailability of drugs topically administered in the eye.

Targeted delivery of 5-fluorouracil to cholangiocarcinoma cells using folic acid as a targeting agent

There are limits to the standard treatment for cholangiocarcinoma (CCA) including drug resistance and side effects. The objective of this study was to develop a new technique for carrying drugs by conjugation with gold nanoparticles and using folic acid as a targeting agent in order to increase drug sensitivity. Gold nanoparticles (AuNPs) were functionalized with 5-fluorouracil (5FU) and folic acid (FA) using polyethylene glycol (PEG) shell as a linker (AuNPs-PEG-5FU-FA). Its cytotoxicity was tested in CCA cell lines (M139 and M213) which express folic acid receptor (FA receptor). The results showed that AuNPs-PEG-5FU-FA increased the cytotoxic effects in the M139 and M213 cells by 4.76% and 7.95%, respectively compared to those treated with free 5FU+FA. It is found that the cytotoxicity of the AuNPs-PEG-5FU-FA correlates with FA receptor expression suggested the use of FA as a targeted therapy. The mechanism of cytotoxicity was mediated via mitochondrial apoptotic pathway as determined by apoptosis array. In conclusion, our findings shed some light on the use of gold nanoparticles for conjugation with potential compounds and FA as targeted therapy which contribute to the improvement of anti-cancer drug efficacy. In vivo study should be warranted for its effectiveness of stability, biosafety and side effect reduction.

Grapefruit-derived Nanovectors Delivering Therapeutic miR17 Through an Intranasal Route Inhibit Brain Tumor Progression

The lack of access to the brain is a major obstacle for central nervous system drug development. In this study, we demonstrate the capability of a grapefruit-derived nanovector (GNV) to carry miR17 for therapeutic treatment of mouse brain tumor. We show that GNVs coated with folic acid (FA-GNVs) are enhanced for targeting the GNVs to a folate receptor-positive GL-26 brain tumor. Additionally, FA-GNV-coated polyethylenimine (FA-pGNVs) not only enhance the capacity to carry RNA, but the toxicity of the polyethylenimine is eliminated by the GNVs. Intranasal administration of miR17 carried by FA-pGNVs led to rapid delivery of miR17 to the brain that was selectively taken up by GL-26 tumor cells. Mice treated intranasally with FA-pGNV/miR17 had delayed brain tumor growth. Our results demonstrate that this strategy may provide a noninvasive therapeutic approach for treating brain-related disease through intranasal delivery.

Folate-linked drugs for the treatment of cancer and inflammatory diseases

Folic acid, also known as vitamin B9 (Fig. 9.1), is an essential co-enzyme in one-carbon metabolism pathways, including the biosynthesis of nucleotides (i.e. purines, thymidine) and several amino acids. In general, two functionally different systems mediate the cellular uptake of folate: (1) the reduced folate carrier (RFC, Kd ∼ 10-6 M), an anion transporter that delivers folates across the plasma membrane in a bidirectional fashion, and (2) the folate receptor (FR, Kd ∼ 10-10 M), which internalizes folate through active receptor-mediated endocytosis. The RFC, a membrane-spanning anion transporter, is present in virtually all tissues and is responsible for the majority of folate transport in and out of cells. In contrast, FR expression is largely restricted to malignant cells, activated macrophages, and the proximal tubule cells of the kidneys. Because a variety of important diseases are caused by the former two cell types, interest in exploiting FR for drug targeting applications has rapidly increased. And achievement of this targeting objective, primarily through conjugation of drugs to folic acid is believed to enable (1) enhanced net drug uptake by pathologic cells, and more importantly (2) reduction in drug deposition into non-pathologic cells, thereby mitigating collateral toxicity to normal tissues.

Guiding principles in the design of ligand-targeted nanomedicines

Medicines for the treatment of most human pathologies are encumbered by unwanted side effects that arise from the deposition of an effective drug into the wrong tissues. The logical remedy for these undesirable properties involves selective targeting of the therapeutic agent to pathologic cells, thereby avoiding collateral toxicity to healthy cells. Since significant advantages can also accrue by incorporating a therapeutic or imaging agent into a nanoparticle, many laboratories are now combining both benefits into a single formulation. This review will focus on the major guiding principles in the design of ligand-targeted nanoparticles, including optimization of their chemical and physical properties, selection of the ideal targeting ligand, engineering of the appropriate surface passivation and linker strategies to achieve selective delivery of the entrapped cargo to the desired diseased cell.

Target delivery of MYCN siRNA by folate-nanoliposomes delivery system in a metastatic neuroblastoma model

Background

Folate-nanoliposomes delivery system has emerged recently as a specific and safety delivery method and gradually used as the carrier of a variety kinds of drugs including compounds, plasmids and siRNAs.

Methods

In this study, we established a bone marrow and bone metastasis xenograft mouse model by injecting the LA-N-5 cell into the bone marrow cavity. Fluorescence microscopy, TUNEL Assay, Quantitative RT-PCR and western blot were conducted to analysis the distribution of folate-nanoliposomes entrapped MYCN (V-myc myelocytomatosis viral related oncogene) siRNA in mice and the relevant suppression effect.

Results

The folate-nanoliposomes entrapped MYCN siRNA can be specifically distributed in tumor tissues. Further study shows that folate-nanoliposomes entrapped MYCN siRNA lead to MYCN mRNA expression significantly down-regulated (>50%, and p < 0.05) compared with negative control siRNA treatment. MYCN protein expression was inhibited about 60% in vivo, thus induced tumor cell apoptosis markedly.

Conclusion

This study point to a new way for treatment of metastatic neuroblastoma and could widen the application of folate-nanoliposomes delivery system in tumor therapy.

Folate-equipped nanolipoplexes mediated efficient gene transfer into human epithelial cells

Since recombinant viral vectors have been associated with serious side effects, such as immunogenicity and oncogenicity, synthetic delivery systems represent a realistic alternative for achieving efficacy in gene therapy. A major challenge for non-viral nanocarriers is the optimization of transgene expression in the targeted cells. This goal can be achieved by fine-tuning the chemical carriers and the adding specific motifs to promote cellular penetration. Our study focuses on the development of novel folate-based complexes that contain varying quantities of folate motifs. After controlling for their physical properties, neutral folate-modified lipid formulations were compared in vitro to lipoplexes leading to comparable expression levels. In addition, no cytotoxicity was detected, unlike what was observed in the cationic controls. Mechanistically, the delivery of the transgene appeared to be, in part, due to endocytosis mediated by folate receptor targeting. This mechanism was further validated by the observation that adding free folate into the medium decreased luciferase expression by 50%. In vivo transfection with the folate-modified MM18 lipid, containing the highest amount of FA-PEG(570)-diether co-lipid (w:w; 90:10), at a neutral charge ratio, gave luciferase transgene expression. These studies indicate that modification of lipids with folate residues could enhance non-toxic, cell-specific gene delivery.

Development and characterization of hyaluronic acid decorated PLGA nanoparticles for delivery of 5-fluorouracil

The present investigation was aimed to develop and explore the prospective of engineered PLGA nanoparticles as vehicles for targeted delivery of 5-fluorouracil (5-FU). Nanoparticles of 5-FU-loaded hyaluronic acid-poly(ethylene glycol)-poly(lactide-co-glycolide) (HA-PEG-PLGA-FU) copolymer were prepared and characterized by FTIR, NMR, transmission electron microscopy, particle size analysis, DSC, and X-ray diffractometer measurement studies. The nanoparticulate formulation was evaluated for in vitro release, hemolytic toxicity, and hematological toxicity. Cytotoxicity studies were performed on Ehrlich ascites tumor (EAT) cell lines using MTT cell proliferation assay. Biodistribution studies of 99m Tc labeled formulation were conducted on EAT-bearing mice. The in vivo tumor inhibition study was also performed after i.v. administration of HA-PEG-PLGA-FU nanoparticles. The HA conjugated formulation was found to be less hemolytic but more cytotoxic as compared to free drug. The hematological data suggested that HA-PEG-PLGA-FU formulation was less immunogenic compared to plain drug. The tissue distribution studies displayed that HA-PEG-PLGA-FU were able to deliver a higher concentration of 5-FU in the tumor mass. In addition, the HA-PEG-PLGA-FU nanoparticles reduced tumor volume significantly in comparison with 5-FU. Thus, it was concluded that the conjugation of HA imparts targetability to the formulation, and enhanced permeation and retention effect ruled out its access to the non-tumor tissues, at the same time favored selective entry in tumors, thereby reducing the side-effects both in vitro and in vivo.

Electropolymerized molecularly imprinted polymer films of a bis-terthiophene dendron: folic acid quartz crystal microbalance sensing

A folic acid sensor was prepared via an electropolymerized molecularly imprinted polymer (E-MIP) film of a bis-terthiophene dendron on a quartz crystal microbalance (QCM). The cyclic voltammetry (CV) electrodeposition of the imprinted polymer film was monitored by electrochemical QCM or E-QCM, enabling in situ monitoring and characterization of E-MIP film formation and the viscoelastic behavior of the film. A key component of the E-MIP process is the use of a bifunctional monomer design to precomplex with the template and function as a cross-linker. The complex was electropolymerized and cross-linked by CV to form a polythiophene matrix. Stable cavities were formed that specifically fit the size and shape of the folic acid template. The same substrate surface was used for folic acid sensing. The predicted geometry of the 1:2 folic acid/terthiophene complex was obtained through semiempirical AM1 quantum calculations. The analytical performance, expressed through the figures of merit, of the sensor in aqueous solutions of the analyte was investigated. A relatively good linearity, R(2) = 0.985, was obtained within the concentration range 0-100 μM folic acid. The detection limit was found to be equal to 15.4 μM (6.8 μg). The relative cross selectivity of the folic acid imprinted polymer against the three molecules follows this trend: pteroic acid (= 50%) > caffeine (= 41%) > theophylline (= 6%). The potential and limitations of the E-MIP method were also discussed.

Silencing of the MYCN gene by siRNA delivered by folate receptor-targeted liposomes in LA-N-5 cells

INTRODUCTION

MYCN amplification is highly associated with malignancy and correlates with poor prognosis in patients with neuroblastoma.

MATERIALS AND METHODS

We developed a novel liposome-MYCN siRNA-folic acid complex, and the transfection efficacy was measured in LA-N-5 cells by cy-3 fluorescence density in each microgram of protein from the transfected cell lysate. MYCN expression and cell growth were studied with quantitative RT-PCR and MTT assays, and the expression of MYCN protein was studied with Western blot, respectively. An SCID mouse model with subcutaneous LA-N-5 xenografted tumor was established. The animals were divided into four groups (n = 5) and they were peritoneally injected with liposome-encapsulated MYCN siRNA (siRNA 125 μg/kg/day), lipid-encapsulated control siRNA, MYCN siRNA, or liposome only, respectively, for 5 consecutive days. The animals were killed 24 h after the last injection, and the expression of MYCN mRNA in tumor tissue was detected by RT-PCR.

RESULTS

Our results are as follows: the transfect efficacy reached 1808.5 ± 140.2 pg siRNA/μg protein in LA-N-5 lysates after treatment with 100 nmol/L MYCN siRNA encapsulated with lipid, and fluorescence could be visualized in 92% of LA-N-5 cells after transfection. At 72 h post-transfection, MYCN mRNA expression in LA-N-5 cells was downregulated by 79.2%, MYCN protein was downregulated by 71.3% and cell growth was inhibited by 66.2%, as measured by MTT assay. In the in vivo study, MYCN mRNA expression was knocked down 53.1% in tumor tissues with injection of liposome-encapsulated MYCN siRNA as compared to control siRNA.

CONCLUSION

These results suggest that targeted delivery of MYCN siRNA by folate receptor-targeted lipid vesicles into LA-N-5 cells is efficacious and capable of suppressing MYCN mRNA expression both in vitro and in vivo.

Preliminary studies on the selective accumulation of vitamin-targeted polymers within tumors

Many different cancer types have previously been found to show increased uptake of the vitamins folate, vitamin B12, and biotin; however, it is not known whether these tumor lines show increased uptake of one or more of the vitamins. The current study was designed to examine the relative uptake of the three vitamins in 10 different types of cell lines. Rhodamine-labeled hydroxypropyl-methacrylamide (HPMA) was targeted with vitamin B(12), folate, or biotin, and the uptake of the labeled polymer was compared both in in vitro cell cultures and in mice-bearing tumors from a variety of tumor cell lines. Fluorescent microscopy of cell cultures and histological examination of tumor sections showed greatly increased uptake of the fluorescently labeled polymer in many tumors when the polymer was targeted with folate, biotin, or vitamin B(12). Tumors with enhanced uptake of vitamin B(12)- or folate-targeted rhodamine-HPMA also showed increased uptake of biotin-Rho-HPMA. In contrast, tumors with increased uptake of folate-Rho-HPMA did not show increased uptake of vitamin B12 (VB(12))-HPMA and vice versa. These findings suggest that vitamin-targeted polymers may greatly increase the uptake of drug-polymer complexes in certain tumors, which may result in an increased efficacy of antitumor agents, and which may allow for easier imaging of both the primary and metastatic tumors.

One-step synthesis of folic acid protected gold nanoparticles and their receptor-mediated intracellular uptake

We report here a facile method to obtain folic acid (FA)-protected gold nanoparticles (Au NPs) by heating an aqueous solution of HAuCl(4)/FA in which FA acts as both the reducing and stabilizing agent. The successful formation of FA-protected Au NPs is demonstrated by UV/Vis spectroscopy, transmission electron microscopy (TEM), selected-area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The intracellular uptake of these nanoparticles is facilitated by HeLa cells overexpressing the folate reporter, which itself is significantly inhibited by free FA in a competitive assay as quantified by inductively coupled plasma mass spectroscopy (ICP-MS). This simple one-step approach affords a new perspective for creating functional nanomaterials, and the resulting biocompatible, functional Au NPs may find some prospective applications in various biomedical fields.

Synthesis, characterization and transfection of a novel folate-targeted multipolymeric nanoparticles for gene delivery

Novel folate-conjugated biodegradable multipolymeric nanoparticles (NPs) were constructed and evaluated for potential use in gene delivery to human cervical carcinomas Hela cells, which overexpressed folate receptors. Folate-poly(ethylene glycol)-poly(D: , L: -lactic-co-glycolic acid) (PELGA-F) was synthesized and collaborated with poly-L: -lysine (PLL) to form polymer-polycationic peptide-DNA (PPD) NPs. Fluorescein sodium and polylysine-condensed DNA (PD) were encapsulated in both PELGA nanoparticles (PELGA-NPs) and folate modified nanoparticles (PELGA-F-NPs), which were prepared by a modified solvent extraction/evaporation method. Effects of the folate conjugation and PLL introduction on the uptake of NPs was qualified by fluorescent invert microscopy and quantified by spectrofluorometric measurement, while effect on the gene expression was measured by X-gal staining and luciferase assay, both using Hela cells as an in vitro model. Results showed that cellular uptake of NPs was enhanced by folate modification, but had no difference after PLL encapsulation. In transfection tests, increased gene expression also confirmed the different functions of folate and PLL introduction. It is feasible that folate-linked multipolymeric NPs should be an efficient targeted carrier for gene delivery.

Relationship between the extent of lipid substitution on poly(L-lysine) and the DNA delivery efficiency

Poly(L-lysine) (PLL) is a commonly used polymer for nonviral gene delivery. However, the polymer exhibits significant toxicity and is not very effective for transgene expression. To enhance the gene delivery efficiency of the polymer, we imparted an amphiphilic property to PLL by substituting approximately 10% of epsilon-NH2 with several endogenous lipids of variable chain lengths (lipid carbon chain ranging from 8 to 18). Lipid-modified PLL with high molecular weight (approximately 25 vs 4 kDa) was found to be more effective in delivering plasmid DNA intracellularly in clinically relevant bone marrow stromal cells (BMSC). For lipid-substituted 25 kDa PLL, a correlation between the extent of lipid substitution and the plasmid DNA delivery efficiency was obtained. Additionally, transgene expression by BMSC significantly increased (20-25%) when amphiphilic PLLs were used for plasmid delivery as compared to native PLL and the commercial transfection agent Lipofectamine-2000. The transfection efficiency of the polymers was positively correlated with the extent of lipid substitution. The amphiphilic polymers were able to modify the cells up to 7 days after transfection, after which the expression was decreased to background levels within 1 week. We conclude that lipid-substituted PLL can be used effectively as a nonviral carrier for DNA, and the extent of lipid substitution was an important determinant of gene delivery.

Interactive transport, subcellular relocation and enhanced phototoxicity of hypericin encapsulated in guanidinylated liposomes via molecular recognition

Hypericin (HYP), a photocytotoxic phenanthroperylenquinone was encapsulated in liposomes outfitted with guanidinium-bearing lipids to ensure efficient cell binding through molecular recognition with anionic groups resident on the plasma membrane. The uptake of HYP encapsulated in these liposomes by DU145 human prostate cancer cells, was studied employing fluorescence, versus nonguadinylated liposomes and free HYP. The subcellular localization was in all cases studied by confocal microscopy employing specific subcellular organelle probes. The photocytotoxicity of HYP was assessed, 24 h following irradiation with 15 mWcm(-2) light through a GG 495 Schott filter, by a standard tetrazolium to formazan assay (XTT). HYP uptake by DU145 cells was found to be profoundly enhanced by using guanidinylated liposomes. Also the distance of the guanidinium group from the liposomal surface was found to significantly affect HYP loading, subcellular localization and phototoxicity. The two different modes of liposome cell internalization observed, i.e. plasma membrane fusion and endocytosis, were found to greatly affect the phototoxicity of HYP. Molecular recognition was overall appraised as a promising, novel route for photodynamic therapy, profoundly enhancing its efficacy. HYP encapsulated in liposomes-bearing guanidinium groups was more efficiently taken up by cells, leading to enhanced phototoxicity, in contrast to HYP encapsulated in their nonguanidinylated counterparts.

Targeted drug delivery via folate receptors

Targeted delivery via selective cellular markers can potentially increase the efficacy and reduce the toxicity of therapeutic agents. The folate receptor (FR) has two glycosyl phosphatidylinositol (GPI)-anchored isoforms, alpha and beta. FR-alpha expression is frequently amplified in epithelial cancers, whereas FR-beta expression is found in myeloid leukemia and activated macrophages associated with chronic inflammatory diseases. Conjugates of folic acid and anti-FR antibodies can be taken up by cancer cells via receptor-mediated endocytosis, thus providing a mechanism for targeted delivery to FR+ cells. The aim of this article is to provide a brief overview of applications of FR targeting in drug delivery, with an emphasis on the strategy of using folate as a targeting ligand. In order to do this, recent literature is surveyed on targeted delivery via both FR sub-types, as well as new findings on selective receptor upregulation in the targeted cells. A wide variety of molecules and drug carriers, including imaging agents, chemotherapeutic agents, oligonucleotides, proteins, haptens, liposomes, nanoparticles and gene transfer vectors have been conjugated to folate and evaluated for FR-targeted delivery. Substantial targeting efficacy has been found both in vitro and in vivo. In addition, mechanisms and methods for selective FR upregulation have been uncovered, which might enhance the effectiveness of the FR-targeted delivery strategy. FR-alpha serves as a useful marker for cancer, whereas FR-beta serves as a marker for myeloid leukemia and chronic inflammatory diseases. FR-targeted agents have shown promising efficacy in preclinical models and significant potential for future clinical application in a wide range of diseases.

Quantum dots – Nano-sized probes for the exploration of cellular and intracellular targeting

Nanoparticles emerged as promising tool in drug targeting, since, after appropriate modification, they are able to deliver their payload to specific sites, like tissues, cells, or even certain cellular organelles. In this context, the delivery of nanoparticles from the circulation into the target cells represents a crucial step. Here, model drug delivery systems such as quantum dots are ideal candidates to elucidate this process in more detail, since they provide outstanding features like a small and uniform size, unique optical properties for most sensitive detection and modifiable surfaces. Recent progress in the surface chemistry of quantum dots expanded their use in biological applications, reduced their cytotoxicity and rendered quantum dots a powerful tool for the investigation of distinct cellular processes, like uptake, receptor trafficking and intracellular delivery. In this review, we will not only describe the ideal attributes of QDs for biological applications and imaging but also their distinct specific and non-specific pathways into the cells as well as their intracellular fate.

Discovery and development of folic-acid-based receptor targeting for imaging and therapy of cancer and inflammatory diseases

In order to avoid the toxicities associated with prescription drug use today, we have explored novel methods for delivering drugs selectively to pathologic cells, thereby avoiding the collateral damage that accompanies their uptake by healthy cells. In this Account, we describe our quest for the ideal targeted therapeutic agent. This effort began with a search for ligands that would bind selectively to pathologic cells, displaying no affinity for healthy cells. After identification of an optimal targeting ligand, effort was focused on construction of linkers that would carry the attached drug to pathologic cells with receptors for the selected ligand. In the case of cancer, we exploited the well-characterized up-regulation of folate receptors on malignant cells to target folate-linked pharmaceuticals to cancer tissues in vivo. Drugs that have been linked to folic acid for tumor-selective drug delivery to date include (i) protein toxins, (ii) chemotherapeutic agents, (iii) gene therapy vectors, (iv) oligonucleotides (including small interfering RNA (siRNA)), (v) radioimaging agents, (vi) magnetic resonance imaging (MRI) contrast agents, (vii) liposomes with entrapped drugs, (viii) radiotherapeutic agents, (ix) immunotherapeutic agents, and (x) enzyme constructs for prodrug therapy. Current clinical trials of four folate-linked drugs demonstrate that folate receptor-targeting holds great promise for increasing the potency while reducing toxicity of many cancer therapies. In the course of developing folate-conjugated drugs for cancer, we discovered that folate receptors are also overexpressed on activated (but not resting or quiescent) macrophages. Recognizing that activated macrophages either cause or contribute to such diseases as rheumatoid arthritis, Crohn's disease, atherosclerosis, lupus, inflammatory osteoarthritis, diabetes, ischemia reperfusion injury, glomerulonephritis, sarcoidosis, psoriasis, Sjogren's disease, and vasculitis, we initiated studies aimed at developing folate-conjugated imaging and therapeutic agents for the diagnosis and treatment of such diseases. In very brief time, significant progress has been made towards identification of clinical candidates for targeted treatment of several inflammatory and autoimmune diseases. This Account summarizes the discovery and development of a variety of folate-targeted drugs for the diagnosis and therapy of cancers and inflammatory/autoimmune diseases.

Ligand based dendritic systems for tumor targeting

Medications that can selectively target tumors at the same time avoid access of the drug to nontarget areas, employ utilization of homing devices termed as ligands, that can bind to specific epitopes expressed on the surface of the necrotic mass of cells. Molecular signatures for transferrin, Epidermal Growth Factor, Sialic Lewis and folic acid are expressed on the surface of these cells. Dendrimers are nanosized, non-immunogenic, and hyper-branched vehicles that can be efficiently tailored for spatial distribution of bioactives, thereby reducing untoward cytotoxicity on normal cells. These nanoparticulate drug delivery vehicles provide a unique platform that has precisely placed functional groups so that multiple copies of ligands can be attached to it and facilitate targeting to the tumor surface or neo-vascularizing vessels proliferating around these cells. The article reviews the scope of ligand based dendritic system as a prospective for delivery of anti-cancer drugs, via active targeting with interception of minimal side effects.

Palmitic acid substitution on cationic polymers for effective delivery of plasmid DNA to bone marrow stromal cells

Nonviral gene carriers are actively explored in gene therapy due to safety concerns of the viral carriers. To design effective gene carriers for modification of bone marrow stromal cells (BMSC), an important cell phenotype for clinical application of gene therapy, cationic polymers polyethyleneimine (PEI), and poly-L-Lysine (PLL) were substituted with palmitic acid (PA) via amide linkages. Depending on the reaction conditions, PEI and PLL was substituted with 2.2-5.2 and 13.4-16.2 PA per polymer chain. The PA substituted polymers displayed slightly lower binding efficiency towards a plasmid containing Enhanced Green Fluorescent Protein (pEGFP) in an agarose gel binding assay. The cell binding of PLL-PA, but not PEI-PA, was particularly enhanced, resulting in higher percentage of the cells displaying a significant polymer uptake. pEGFP delivery into the BMSC was also significantly increased with the PLL-PA (vs. PLL), but not PEI-PA (vs. PEI). The transfection efficiency of PLL-PA was significantly higher ( approximately fivefold) than the unmodified polymer. We conclude that PA substitution on PLL provides an effective carrier for transfection of primary cells derived from the bone marrow.

pH-sensitive liposomes--principle and application in cancer therapy

The purpose of this review is to provide an insight into the different aspects of pH-sensitive liposomes. The review consists of 6 parts: the first introduces different types of medications made in liposomal drug delivery to overcome several drawbacks; the second elaborates the development of pH-sensitive liposomes; the third explains diverse mechanisms associated with the endocytosis and the cytosolic delivery of the drugs through pH-sensitive liposomes; the fourth describes the role and importance of pH-sensitive lipid dioleoylphosphatidylethanolamine (DOPE) and research carried on it; the fifth explains successful strategies used so far using the mechanism of pH sensitivity for fusogenic activity; the final part is a compilation of research that has played a significant role in emphasizing the success of pH-sensitive liposomes as an efficient drug delivery system in the treatment of malignant tumours. pH-Sensitive liposomes have been extensively studied in recent years as an amicable alternative to conventional liposomes in effectively targeting and accumulating anti-cancer drugs in tumours. This research suggests that pH-sensitive liposomes are more efficient in delivering anti-cancer drugs than conventional and long-circulating liposomes due to their fusogenic property. Research focused on the clinical and therapeutic side of pH-sensitive liposomes would enable their commercial utility in cancer treatment.

Intracellular trafficking of plasmids for gene therapy: mechanisms of cytoplasmic movement and nuclear import

Under physiologically relevant conditions, the levels of non-viral gene transfer are low at best. The reason for this is that many barriers exist for the efficient transfer of genes to cells, even before any gene expression can occur. While many transfection strategies focus on DNA condensation and overcoming the plasma membrane, events associated with the intracellular trafficking of the DNA complexes have not been as extensively studied. Once internalized, plasmids must travel potentially long distances through the cytoplasm to reach their next barrier, the nuclear envelope. This review summarizes the current progress on the cytoplasmic trafficking and nuclear transport of plasmids used for gene therapy applications. Both of these processes utilize specific and defined mechanisms to facilitate movement of DNA complexes through the cell. The continued elucidation and exploitation of these mechanisms will lead to improved strategies for transfection and successful gene therapy.

Cationic liposomes for gene delivery

Cationic liposome-DNA complexes (lipoplexes) constitute a potentially viable alternative to viral vectors for the delivery of therapeutic genes. This review will focus on various parameters governing lipoplex biological activity, from their mode of formation to in vivo behaviour. Particular emphasis is given to the mechanism of interaction of lipoplexes with cells, in an attempt to dissect the different barriers that need to be surpassed for efficient gene expression to occur. Aspects related to new trends in the formulation of lipid-based gene delivery systems aiming at overcoming some of their limitations will be covered. Finally, examples illustrating the potential of cationic liposomes in clinical applications will be provided.

Galactosylated polyethylenimine-graft-poly(vinyl pyrrolidone) as a hepatocyte-targeting gene carrier

Polyethylenimine (PEI) has been used for the gene delivery system in vitro and in vivo since it has high transfection efficiency owing to proton buffer capacity. However, the use of PEI for gene delivery is limited due to cytotoxicity, non-specificity and unnecessary interaction with serum components. To overcome cytotoxicity and non-specificity, PEI was coupled with poly(vinyl pyrrolidone) (PVP) as the hydrophilic group to reduce cytotoxicity and lactose bearing galactose group for hepatocyte targeting. The galactosylated-PEI-graft-PVP (GPP) was complexed with DNA, and GPP/DNA complexes were characterized. GPP showed good DNA binding ability, high protection of DNA from nuclease attack. The sizes of DNA complexes show tendency to decrease with an increase of charge ratio and had a minimum value around 59 nm at the charge ratio of 40 for the GPP-1/DNA complex (PVP content: 4.1 mol%). The GPP showed low cytotoxicity. And GPP/DNA complexes were mediated by asialoglycoprotein receptors (ASGP-R)-mediated endocytosis. Also, the transfection efficiency of GPP-1/DNA complex at charge ratio of 40 in the HepG2 was higher than that of PEI/DNA one.

Folate Receptor-Mediated Drug Targeting: From Therapeutics to Diagnostics

Folate targeted drug delivery has emerged as an alternative therapy for the treatment and imaging of many cancers and inflammatory diseases. Due to its small molecular size and high binding affinity for cell surface folate receptors (FR), folate conjugates have the ability to deliver a variety of molecular complexes to pathologic cells without causing harm to normal tissues. Complexes that have been successfully delivered to FR expressing cells, to date, include protein toxins, immune stimulants, chemotherapeutic agents, liposomes, nanoparticles, and imaging agents. This review will summarize the applications of folic acid as a targeting ligand and highlight the various methods being developed for delivery of therapeutic and imaging agents to FR-expressing cells.

Quantitative aspects of endocytic activity in lipid-mediated transfections

Variation in transfection efficiency observed in different cell-types is poorly understood. To investigate the influence of endocytic activity on lipid-mediated transfections, we have monitored both the processes in 12 different cell-types. The endocytic activity shows a strong positive correlation (P < 0.01), with transfection efficiency. Treatment with wortmannin resulted in cell-type-dependent inhibition of transfection. Studies on M-phase cells by confocal microscopy show that compared to interphase cells, uptake of cationic liposomes was substantially reduced. In addition, transfection efficiency of cells in mitotic phase was inhibited by >70% compared to controls. Our study based on several cell-types demonstrates for the first time that quantitative aspects of endocytosis have decisive influence on the overall process of lipid-mediated transgene expression.