A sterically stabilized immunolipoplex for systemic administration of a therapeutic gene

PEGylation and folic-acid functionalization of cationic lipoplexes-Improved nucleic acid transfer into cancer cells

Efficient and reliable transfer of nucleic acids for therapy applications is a major challenge. Stabilization of lipo- and polyplexes has already been successfully achieved by PEGylation. This modification reduces the interaction with serum proteins and thus prevents the lipoplexes from being cleared by the reticuloendothelial system. Problematically, this stabilization of lipoplexes simultaneously leads to reduced transfer efficiencies compared to non-PEGylated complexes. However, this reduction in transfer efficiency can be used to advantage since additional modification of PEGylated lipoplexes with functional groups enables improved selective transfer into target cells. Cancer cells overexpress folate receptors because of a significantly increased need of folate due to high cell proliferation rates. Thus, additional folate functionalization of PEGylated lipoplexes improves uptake into cancer cells. We demonstrate herein that NHS coupling chemistries can be used to modify two commercially available transfection reagents (Fuse-It-DNA and Lipofectamine® 3000) with NHS-PEG-folate for increased uptake of nucleic acids into cancer cells. Lipoplex characterization and functional analysis in cultures of cancer- and healthy cells clearly demonstrate that functionalization of PEGylated lipoplexes offers a promising method to generate efficient, stable and selective nucleic acid transfer systems.

Single-Chain Fragment Variable: Recent Progress in Cancer Diagnosis and Therapy

Simple Summary

Recombinant antibody fragments have shown remarkable potential as diagnostic and therapeutic tools in the fight against cancer. The single-chain fragment variable (scFv) that contains the complete antigen-binding domains of a whole antibody, has several advantages such as a high specificity and affinity for antigens, a low immunogenicity, and the proven ability to penetrate tumor tissues and diffuse. This review provides an overview of the current studies on the principle, generation, and applications of scFvs, particularly in the diagnosis and therapy of cancer, and underscores their potential use in clinical trials.

Abstract

Cancer remains a public health problem worldwide. Although conventional therapies have led to some excellent outcomes, some patients fail to respond to treatment, they have few therapeutic alternatives and a poor survival prognosis. Several strategies have been proposed to overcome this issue. The most recent approach is immunotherapy, particularly the use of recombinant antibodies and their derivatives, such as the single-chain fragment variable (scFv) containing the complete antigen-binding domains of a whole antibody that successfully targets tumor cells. This review describes the recent progress made with scFvs as a cancer diagnostic and therapeutic tool, with an emphasis on preclinical approaches and their potential use in clinical trials.

The other side to the use of active targeting ligands; the case of folic acid in the targeting of breast cancer

Due to its overexpression in cancer cells, the folate receptor (FR) is heavily exploited in the active targeting of nanoparticles (NPs). Its ligand, folic acid (FA) is as a consequence widely used as a NP targeting ligand. Although rather popular and successful in principle, recent data has shown that FA may result in breast cancer initiation and progression, which questions the suitability of FA as NP cancer targeting ligand. In this work, intravenous administration of free FA to healthy female mice resulted in breast tissue dysplasia, hyperplasia and in the increased expression of human epidermal growth factor receptor-2 (HER2), folate receptor (FR), cancer antigen 15-3 (CA15.3), vascular endothelial growth factor (VEGF), signal transducer and activator of transcription 3 (STAT3) and the pro-inflammatory cytokines, tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6) and interleukin-1β. In addition to the reduction in IL2. To evaluate the suitability and safety of FA as NP targeting ligand in breast cancer, small (≈ 150 nm) and large (≈ 500 nm) chitosan NPs were formulated and decorated with two densities of FA. The success of active targeting by FA was confirmed in two breast cancer cell lines (MCF-7 and MDA-MB-231 cells) in comparison to HEK293 cells. FA modified NPs that demonstrated successful active targeting in-vitro were assessed in-vivo. Upon intravenous administration, large NPs modified with a high density of FA accumulated in the breast tissue and resulted in similar effects as those observed with free FA. These results therefore question the suitability of FA as a targeting ligand in breast cancer and shed light on the importance of considering the activity (other than targeting) of the ligands used in NP active targeting.

Lipid-Based Nanocarriers for The Treatment of Glioblastoma

Glioblastoma multiforme (GBM) is the most common and malignant neoplasia having origin in the brain. The current treatments involve surgery, radiotherapy, and chemotherapy, being complete surgical resection the best option for the patient survival chances. However, in those cases where a complete removal is not possible, radiation and chemotherapy are applied. Herein, the main challenges of chemotherapy, and how they can be overcome with the help of nanomedicine, are approached. Natural pathways to cross the blood-brain barrier (BBB) are detailed, and different in vivo studies where these pathways are mimicked functionalizing the nanomaterial surface are shown. Later, lipid-based nanocarriers, such as liposomes, solid lipid nanoparticles, and nanostructured lipid carriers, are presented. To finish, recent studies that have used lipid-based nanosystems carrying not only therapeutic agents, yet also magnetic nanoparticles, are described. Although the advantages of using these types of nanosystems are explained, including their biocompatibility, the possibility of modifying their surface to enhance the cell targeting, and their intrinsic ability of BBB crossing, it is important to mention that research in this field is still at its early stage, and extensive preclinical and clinical investigations are mandatory in the close future.

Optimized Doxorubicin Chemotherapy for Diffuse Large B-cell Lymphoma Exploits Nanocarrier Delivery to Transferrin Receptors

New treatments are needed to address persistent unmet clinical needs for diffuse large B-cell lymphoma (DLBCL). Overexpression of transferrin receptor 1 (TFR1) is common across cancer and permits cell-surface targeting of specific therapies in preclinical and clinical studies of various solid tumors. Here, we developed novel nanocarrier delivery of chemotherapy via TFR1-mediated endocytosis, assessing this target for the first time in DLBCL. Analysis of published datasets showed novel association of increased TFR1 expression with high-risk DLBCL cases. Carbon-nitride dots (CND) are emerging nanoparticles with excellent in vivo stability and distribution and are adaptable to covalent conjugation with multiple substrates. In vitro, linking doxorubicin (Dox) and transferrin (TF) to CND (CND-Dox-TF, CDT) was 10-100 times more potent than Dox against DLBCL cell lines. Gain- and loss-of-function studies and fluorescent confocal microscopy confirmed dependence of these effects on TFR1-mediated endocytosis. In contrast with previous therapeutics directly linking Dox and TF, cytotoxicity of CDT resulted from nuclear entry by Dox, promoting double-stranded DNA breaks and apoptosis. CDT proved safe to administer in vivo, and when incorporated into standard frontline chemoimmunotherapy in place of Dox, it improved overall survival by controlling patient-derived xenograft tumors with greatly reduced host toxicities. Nanocarrier-mediated Dox delivery to cell-surface TFR1, therefore, warrants optimization as a potential new therapeutic option in DLBCL. SIGNIFICANCE: Targeted nanoparticle delivery of doxorubicin chemotherapy via the TRF1 receptor presents a new opportunity against high-risk DLBCL tumors using potency and precision.

Nanoparticles for Targeting of Prostate Cancer

Prostate cancer (PCa) is the leading cause of death by cancer in men. Because of the drastic decline in the survival rate of PCa patients with advanced/metastatic disease, early diagnosis of disease and therapy without toxic side effects is crucial. Chemotherapy is widely used to control the progression of PCa at the later stages; however, it is associated with off-target toxicities and severe adverse effects due to the lack of specificity. Delivery of therapeutic or diagnostic agents by using targeted nanoparticles is a promising strategy to enhance accuracy and sensitivity of diagnosis of PCa and to increase efficacy and specificity of therapeutic agents. Numerous efforts have been made in past decades to create nanoparticles with different architectural bases for specific delivery payloads to prostate tumors. Major PCa associated cell membrane protein markers identified as targets for such purposes include folate receptor, sigma receptors, transferrin receptor, gastrin-releasing peptide receptor, urokinase plasminogen activator receptor, and prostate specific membrane antigen. Among these markers, prostate specific membrane antigen has emerged as an extremely specific and sensitive targetable marker for designing targeted nanoparticle-based delivery systems for PCa. In this article, we review contemporary advances in design, specificity, and efficacy of nanoparticles functionalized against PCa. Whenever feasible, both diagnostic as well as therapeutic applications are discussed.

Targeted Nanotechnology in Glioblastoma Multiforme

Gliomas, and in particular glioblastoma multiforme, are aggressive brain tumors characterized by a poor prognosis and high rates of recurrence. Current treatment strategies are based on open surgery, chemotherapy (temozolomide) and radiotherapy. However, none of these treatments, alone or in combination, are considered effective in managing this devastating disease, resulting in a median survival time of less than 15 months. The efficiency of chemotherapy is mainly compromised by the blood-brain barrier (BBB) that selectively inhibits drugs from infiltrating into the tumor mass. Cancer stem cells (CSCs), with their unique biology and their resistance to both radio- and chemotherapy, compound tumor aggressiveness and increase the chances of treatment failure. Therefore, more effective targeted therapeutic regimens are urgently required. In this article, some well-recognized biological features and biomarkers of this specific subgroup of tumor cells are profiled and new strategies and technologies in nanomedicine that explicitly target CSCs, after circumventing the BBB, are detailed. Major achievements in the development of nanotherapies, such as organic poly(propylene glycol) and poly(ethylene glycol) or inorganic (iron and gold) nanoparticles that can be conjugated to metal ions, liposomes, dendrimers and polymeric micelles, form the main scope of this summary. Moreover, novel biological strategies focused on manipulating gene expression (small interfering RNA and clustered regularly interspaced short palindromic repeats [CRISPR]/CRISPR associated protein 9 [Cas 9] technologies) for cancer therapy are also analyzed. The aim of this review is to analyze the gap between CSC biology and the development of targeted therapies. A better understanding of CSC properties could result in the development of precise nanotherapies to fulfill unmet clinical needs.

A Phase l Study of a Tumor-targeted Systemic Nanodelivery System, SGT-94, in Genitourinary Cancers

Gene therapy development has been limited by our inability to target multifocal cancer with systemic delivery. We developed a systemically administered, tumor-targeted liposomal nanodelivery complex (SGT-94) carrying a plasmid encoding RB94, a truncated form of the RB gene. In preclinical studies, RB94 showed marked cytotoxicity against tumor but not normal cells. SGT-94 was administered intravenously in a first-in-man study in metastatic genitourinary cancer. Minimal side effects were observed; dose-limiting toxicity (DLT) has not been reached in 11 evaluable patients. There was evidence of clinical activity at the 2.4 mg dose with one complete remission (CR) and one partial remission (PR). The patient in CR was retreated upon progression and had a second PR. Furthermore, there was tumor-specific targeting of the SGT-94 complex. One patient had wedge resections of two lung metastases which demonstrated RB94 expression at the DNA level by polymerase chain reaction (PCR) and at the protein level by Western blotting, with no RB94 present in normal contiguous lung. In conclusion, systemically delivered SGT-94 showed evidence of selective tumor targeting and was well tolerated with evidence of clinical activity. Additional studies are warranted to explore the activity of this drug as a single agent and in combination therapy.

Targeted siRNA Delivery Using a Lipo-Oligoaminoamide Nanocore with an Influenza Peptide and Transferrin Shell

Developing RNA-interference-based therapeutic approaches with efficient and targeted cytosolic delivery of small interfering RNA (siRNA) is remaining a critical challenge since two decades. Herein, a multifunctional transferrin receptor (TfR)-targeted siRNA delivery system (Tf&INF7) is designed based on siRNA complexes formed with the cationic lipo-oligoamino amide 454, sequentially surface-modified with polyethylene glycol-linked transferrin (Tf) for receptor targeting and the endosomolytic peptide INF7 for efficient cytosolic release of the siRNA. Effective Tf&INF7 polyplex internalization and target gene silencing are demonstrated for the TfR overexpressing tumor cell lines (K562, D145, and N2a). Treatment with antitumoral EG5 siRNA results in a block of tumor cell growth and triggered apoptosis. Tf-modified polyplexes are far more effective than the corresponding albumin- (Alb) or nonmodified 454 polyplexes. Competition experiments with excess of Tf demonstrate TfR target specificity. As alternative to the ligand Tf, an anti-murine TfR antibody is incorporated into the polyplexes for specific targeting and gene silencing in the murine N2a cell line. In vivo distribution studies not only demonstrate an enhanced tumor residence of siRNA in N2a tumor-bearing mice with the Tf&INF7 as compared to the 454 polyplex group but also a reduced siRNA nanoparticle stability limiting the in vivo performance.

Encapsulation of temozolomide in a tumor-targeting nanocomplex enhances anti-cancer efficacy and reduces toxicity in a mouse model of glioblastoma

Although temozolomide (TMZ) is the current first-line chemotherapy for glioblastoma multiforme (GBM), most patients either do not respond or ultimately fail TMZ treatment. Both intrinsic tumor resistance and limited access of TMZ to brain tumors as a result of the blood-brain barrier (BBB) contribute to poor response and ultimately to poor prognosis for GBM patients. We have developed a "dual-targeting" nanomedicine that both actively crosses the BBB and actively targets cancer cells once in the brain parenchyma. This nanomedicine (termed scL-TMZ) is sized ~40 nm and comprised of a cationic liposome (DOTAP:DOPE) encapsulating TMZ. The surface of liposome is decorated with anti-transferrin receptor single-chain antibody fragments to facilitate the crossing of the BBB by the scL-TMZ in addition to targeting GBM in the brain. This novel formulation was found to be markedly more effective than standard TMZ in both TMZ-resistant and TMZ-sensitive GBM. Encapsulation of TMZ also markedly enhanced its efficacy in killing a variety of non-GBM tumor cells. The scL-TMZ nanocomplex was shown to target cancer stem cells, which have been linked to both drug resistance and recurrence in GBM. Most significantly, systemically administered scL-TMZ significantly prolonged survival in mice bearing intracranial GBM tumors. The improved efficacy of scL-TMZ compared to standard TMZ was accompanied by reduced toxicity, so we conclude that the scL-TMZ nanomedicine holds great promise as a more effective therapy for GBM and other tumor types.

Promising approaches to circumvent the blood-brain barrier: progress, pitfalls and clinical prospects in brain cancer

Brain drug delivery is a major challenge for therapy of central nervous system (CNS) diseases. Biochemical modifications of drugs or drug nanocarriers, methods of local delivery, and blood-brain barrier (BBB) disruption with focused ultrasound and microbubbles are promising approaches which enhance transport or bypass the BBB. These approaches are discussed in the context of brain cancer as an example in CNS drug development. Targeting to receptors enabling transport across the BBB offers noninvasive delivery of small molecule and biological cancer therapeutics. Local delivery methods enable high dose delivery while avoiding systemic exposure. BBB disruption with focused ultrasound and microbubbles offers local and noninvasive treatment. Clinical trials show the prospects of these technologies and point to challenges for the future.

Endocytosis of a functionally enhanced GFP-tagged transferrin receptor in CHO cells

The endocytosis of transferrin receptor (TfR) has served as a model to study the receptor-targeted cargo delivery system for cancer therapy for many years. To accurately evaluate and optically measure this TfR targeting delivery in vitro, a CHO cell line with enhanced green fluorescent protein (EGFP)-tagged human TfR was established. A chimera of the hTfR and EGFP was engineered by fusing EGFP to the amino terminus of hTfR. Data were provided to demonstrate that hTfR-EGFP chimera was predominantly localized on the plasma membrane with some intracellular fluorescent structures on CHO cells and the EGFP moiety did not affect the endocytosis property of hTfR. Receptor internalization occurred similarly to that of HepG2 cells expressing wild-type hTfR. The internalization percentage of this chimeric receptor was about 81±3% of wild type. Time-dependent co-localization of hTfR-EGFP and PE-conjugated anti-hTfR mAb in living cells demonstrated the trafficking of mAb-receptor complexes through the endosomes followed by segregation of part of the mAb and receptor at the late stages of endocytosis. The CHO-hTfR cells preferentially took up anti-hTfR mAb conjugated nanoparticles. This CHO-hTfR cell line makes it feasible for accurate evaluation and visualization of intracellular trafficking of therapeutic agents conjugated with transferrin or Abs targeting the hTfRs.

Therapeutic efficacy of intravenously administered transferrin-conjugated dendriplexes on prostate carcinomas

AIM

Improved treatments for prostate cancer are critically needed in order to overcome metastasis and lethal recurrence. Intravenously administered gene therapy would be an attractive anticancer treatment strategy; however, the lack of suitable carrier systems able to selectively deliver therapeutic genes to tumors has so far limited this investigation. Given that transferrin receptors are overexpressed on prostate cancer cells, the purpose of this study is to determine whether transferrin-conjugated dendriplexes encoding TNF-α, TNF-related apoptosis-inducing ligand and IL-12 would suppress the growth of prostate cancer cell lines in vitro and in vivo.

MATERIALS & METHODS

Transferrin-conjugated dendriplexes encoding TNF-α, TNF-related apoptosis-inducing ligand and IL-12 were intravenously administered to mice bearing subcutaneous PC-3 and DU145 tumors.

RESULTS

The administration of the transferrin-conjugated generation 3 diaminobutyric polypropylenimine dendriplex encoding TNF-a resulted in tumor suppression for 60% of PC-3 and 50% of DU145 prostate tumors.

CONCLUSION

These dendriplexes hold great potential as a novel approach for prostate cancer therapy.

Uptake and transfection efficiency of PEGylated cationic liposome-DNA complexes with and without RGD-tagging

Steric stabilization of cationic liposome-DNA (CL-DNA) complexes is required for in vivo applications such as gene therapy. PEGylation (PEG: poly(ethylene glycol)) of CL-DNA complexes by addition of PEG2000-lipids yields sterically stabilized nanoparticles but strongly reduces their gene delivery efficacy. PEGylation-induced weakening of the electrostatic binding of CL-DNA nanoparticles to cells (leading to reduced uptake) has been considered as a possible cause, but experimental results have been ambiguous. Using quantitative live-cell imaging in vitro, we have investigated cell attachment and uptake of PEGylated CL-DNA nanoparticles with and without a custom synthesized RGD-peptide grafted to the distal ends of PEG2000-lipids. The RGD-tagged nanoparticles exhibit strongly increased cellular attachment as well as uptake compared to nanoparticles without grafted peptide. Transfection efficiency of RGD-tagged PEGylated CL-DNA NPs increases by about an order of magnitude between NPs with low and high membrane charge density (σM; the average charge per unit area of the membrane; controlled by the molar ratio of cationic to neutral lipid), even though imaging data show that uptake of RGD-tagged particles is only slightly enhanced by high σM. This suggests that endosomal escape and, as a result, transfection efficiency of RGD-tagged NPs is facilitated by high σM. We present a model describing the interactions between PEGylated CL-DNA nanoparticles and the anionic cell membrane which shows how the PEG grafting density and membrane charge density affect adhesion of nanoparticles to the cell surface.

Ligand-targeted particulate nanomedicines undergoing clinical evaluation: current status

Since the introduction of Doxil® on the market nearly 20years ago, a number of nanomedicines have become part of treatment regimens in the clinic. With the exception of antibody-drug conjugates, these nanomedicines are all devoid of targeting ligands and rely solely on their physicochemical properties and the (patho)physiological processes in the body for their biodistribution and targeting capability. At the same time, many preclinical studies have reported on nanomedicines exposing targeting ligands, or ligand-targeted nanomedicines, yet none of these have been approved at this moment. In the present review, we provide a concise overview of 13 ligand-targeted particulate nanomedicines (ligand-targeted PNMs) that have progressed into clinical trials. The progress of each ligand-targeted PNM is discussed based on available (pre)clinical data. Main conclusions of these analyses are that (a) ligand-targeted PNMs have proven to be safe and efficacious in preclinical models; (b) the vast majority of ligand-targeted PNMs is generated for the treatment of cancer; (c) contribution of targeting ligands to the PNM efficacy is not unambiguously proven; and (d) targeting ligands do not cause localization of the PNM within the target tissue, but rather provide benefits in terms of target cell internalization and target tissue retention once the PNM has arrived at the target site. Increased understanding of the in vivo fate and interactions of the ligand-targeted PNMs with proteins and cells in the human body is mandatory to rationally advance the clinical translation of ligand-targeted PNMs. Future perspectives for ligand-targeted PNM approaches include the delivery of drugs that are unable or inefficient in passing cellular membranes, treatment of drug resistant tumors, targeting of the tumor blood supply, the generation of targeted vaccines and nanomedicines that are able to cross the blood-brain barrier.

Delivery of therapeutic nucleic acids via transferrin and transferrin receptors: lipoplexes and other carriers

INTRODUCTION

The overexpression of transferrin (Tf) receptors on cancer cells renders them a useful target for the delivery of small-molecule drugs and nucleic acid therapeutics to these cells. This approach could alleviate the non-target effects of the drugs.

AREAS COVERED

The function of the Tf receptor, the development of Tf-lipid-DNA complexes (Tf lipoplexes), therapeutic use of lipoplexes and polymer-DNA complexes (poylplexes), and the therapeutic use of Tf-lipoplexes and anti-Tf-receptor antibody-lipoplexes are outlined. The literature search for this review was based primarily on the terms 'lipoplexes,' 'lipopolyplexes' 'transferrin,' 'transferrin receptor,' and 'gene therapy.' However, the review was not intended to be comprehensive.

EXPERT OPINION

Complexes of Tf with cationic liposomes and nucleic acids, or liposomes with covalently attached Tf or anti-transferrin receptor antibodies have been used for the delivery of therapeutic genes, antisense oligodeoxynucleotides, and short interfering RNA. Although such targeted nonviral delivery vehicles may benefit from further enhancement of their efficacy, current achievements at the cell culture and animal model level should be translated into clinical applications, restricted initially to localized delivery into accessible tissues to avoid potential systemic side-effects and non-target delivery.

Phase I study of a systemically delivered p53 nanoparticle in advanced solid tumors

Selective delivery of therapeutic molecules to primary and metastatic tumors is optimal for effective cancer therapy. A liposomal nanodelivery complex (scL) for systemic, tumor-targeting delivery of anticancer therapeutics has been developed. scL employs an anti-transferrin receptor (TfR), scFv as the targeting molecule. Loss of p53 suppressor function, through mutations or inactivation of the p53 pathway, is present in most human cancers. Rather than being transiently permissive for tumor initiation, persistence of p53 dysfunction is a continuing requirement for maintaining tumor growth. Herein, we report results of a first-in-man Phase I clinical trial of restoration of the normal human tumor suppressor gene p53 using the scL nanocomplex (SGT-53). Minimal side effects were observed in this trial in patients with advanced solid tumors. Furthermore, the majority of patients demonstrated stable disease. One patient with adenoid cystic carcinoma had his status changed from unresectable to resectable after one treatment cycle. More significantly, we observed an accumulation of the transgene in metastatic tumors, but not in normal skin tissue, in a dose-related manner. These results show not only that systemically delivered SGT-53 is well tolerated and exhibits anticancer activity, but also supply evidence of targeted tumor delivery of SGT-53 to metastatic lesions.

Transferrin receptor targeting nanomedicine delivering wild-type p53 gene sensitizes pancreatic cancer to gemcitabine therapy

To overcome gene therapy barriers such as low transfection efficiency and nonspecific delivery, liposomal nanoparticles targeted by a single-chain antibody fragment to the transferrin receptor (TfRscFv) delivering wild-type (wt) human p53 (SGT-53) were developed for tumor-specific targeting. We hypothesize that SGT-53 in combination with gemcitabine will demonstrate enhanced therapeutic benefit in an in vivo metastatic pancreatic cancer model. Intrasplenic injection of 1 × 10(6) Panc02 murine pancreatic cancer cells was used to generate in vivo hepatic metastatic tumors. Nanoparticle localization was assessed by tail vein injection of TfRscFv with fluorescently labeled oligonucleotides (6-carboxyfluorescein phosphoramidite (6FAM) ODN) imaged by Xenogen IVIS 200 scan. SGT-53 (equivalent to 30 μg of p53 intravenously) and gemcitabine (20 mg/kg intraperitoneally) alone and in combination were administered biweekly and compared with untreated mice. Survival was determined by blinded daily assessment of morbidity. Human wtp53 expression and transferrin levels in the tumors were assessed by western blot analysis. Tumor burden was quantified by liver weight. Xenogen imaging demonstrated tumor-specific uptake of TfRscFv-6FAM ODN. Exogenous human wtp53 protein was detected in the SGT-53-treated tumors compared with control. Compared with untreated mice with metastatic tumors demonstrating median survival of 20 days, SGT-53, gemcitabine and the combination demonstrated improved median survival of 29, 30 and 37 days, respectively. The combination treatment prolonged median survival when compared with single drug treatment and decreased tumor burden. The tumor targeting liposomal-based SGT-53 nanoparticle is capable of sensitizing pancreatic cancer to conventional chemotherapy in pancreatic cancer models. This approach has the potential to be translated into a new, more effective therapy for pancreatic cancer. Further optimization is ongoing, moving towards a Phase 1B/2 clinical trial.

Endosomal escape and transfection efficiency of PEGylated cationic liposome-DNA complexes prepared with an acid-labile PEG-lipid

Cationic liposome-DNA (CL-DNA) complexes are being pursued as nonviral gene delivery systems for use in applications that include clinic trials. However, to compete with viral vectors for systemic delivery in vivo, their efficiencies and pharmacokinetics need to be improved. The addition of poly (ethylene glycol)-lipids (PEGylation) prolongs circulation lifetimes of liposomes, but inhibits cellular uptake and endosomal escape of CL-DNA complexes. We show that this limits their transfection efficiency (TE) in a manner dependent on the amount of PEG-lipid, the lipid/DNA charge ratio, and the lipid membrane charge density. To improve endosomal escape of PEGylated CL-DNA complexes, we prepared an acid-labile PEG-lipid (HPEG2K-lipid, PEG MW 2000) which is designed to lose its PEG chains at the pH of late endosomes. The HPEG2K-lipid and a similar but acid-stable PEG-lipid were used to prepare PEGylated CL-DNA complexes. TLC and dynamic light scattering showed that HPEG2K-CL-DNA complexes are stable at pH 7.4 for more than 24 h, but the PEG chains are cleaved at pH 5 within 1 h, leading to complex aggregation. The acid-labile HPEG2K-CL-DNA complexes showed enhanced TE over complexes stabilized with the acid-stable PEG-lipid. Live-cell imaging showed that both types of complexes were internalized to quantitatively similar particle distributions within the first 2 h of incubation with cells. Thus, we attribute the increased TE of the HPEG2K-CL-DNA complexes to efficient endosomal escape, enabled by the acid-labile HPEG2K-lipid which sheds its PEG chains in the low pH environment of late endosomes, effectively switching on the electrostatic interactions that promote fusion of the membranes of complex and endosome.

The transferrin receptor and the targeted delivery of therapeutic agents against cancer

BACKGROUND

Traditional cancer therapy can be successful in destroying tumors, but can also cause dangerous side effects. Therefore, many targeted therapies are in development. The transferrin receptor (TfR) functions in cellular iron uptake through its interaction with transferrin. This receptor is an attractive molecule for the targeted therapy of cancer since it is upregulated on the surface of many cancer types and is efficiently internalized. This receptor can be targeted in two ways: 1) for the delivery of therapeutic molecules into malignant cells or 2) to block the natural function of the receptor leading directly to cancer cell death.

SCOPE OF REVIEW

In the present article we discuss the strategies used to target the TfR for the delivery of therapeutic agents into cancer cells. We provide a summary of the vast types of anti-cancer drugs that have been delivered into cancer cells employing a variety of receptor binding molecules including Tf, anti-TfR antibodies, or TfR-binding peptides alone or in combination with carrier molecules including nanoparticles and viruses.

MAJOR CONCLUSIONS

Targeting the TfR has been shown to be effective in delivering many different therapeutic agents and causing cytotoxic effects in cancer cells in vitro and in vivo.

GENERAL SIGNIFICANCE

The extensive use of TfR for targeted therapy attests to the versatility of targeting this receptor for therapeutic purposes against malignant cells. More advances in this area are expected to further improve the therapeutic potential of targeting the TfR for cancer therapy leading to an increase in the number of clinical trials of molecules targeting this receptor. This article is part of a Special Issue entitled Transferrins: molecular mechanisms of iron transport and disorders.

Temperature-tuned DNA condensation and gene transfection by PEI-g-(PMEO(2)MA-b-PHEMA) copolymer-based nonviral vectors

In this work, thermoresponsive diblock copolymers, poly[2-(2-methoxyethoxy) ethyl methacrylate]-b-poly(2-hydroxyethyl methacrylate) (PMEO(2)MA-b-PHEMA) with low polydispersity were synthesized by atomic transfer radical polymerization(ATRP). Low molecular weight (LWM) polyethylenimine (PEI, 1200Da) was then grafted to 1,1'-carbonyldiimidazole (CDI)-activated PMEO(2)MA-b-PHEMA to fabricate PEI-g-(PMEO(2)MA-b-PHEMA) (PEIMH) copolymer vectors. The LCSTs of PEIMHs with 3 and 8 grafted PEI side chains, separately termed as PEIMH-1 and PEIMH-2, were 32.5 and 38.7 degrees C in PBS solution. Variable temperature agarose retardation, Zeta potential and time-resolved fluorescence assays were performed to elucidate the temperature sensitive DNA condensation. It showed that DNA was condensed more efficiently by PEIMH, and the collapse of PMEO(2)MA chains led to more exposure of surface positive charges of PEIMH-1/pDNA complexes while temperature was above LCST. Variable temperature time-resolved fluorescence measurement of lifetimes of bound and free ethidium bromide (EB) unveiled that the population of EB at different states was dependent on temperature. At a temperature above LCST, the collapsed PMEO(2)MA polymer chains squeezed the loosely bound EB out of complex to become free species; thereby DNA was more tightly packaged by PEIMH-1. Temporary cooling was shown to improve the transfection efficiency of PEIMH-1 in COS-7 and HEK293 cell lines. The variable temperature protocol is more efficient in improving gene expression level in HEK293 cells. The transfection efficiency was equivalent or superior to that of PEI25K at an optimal weight ratio of vector/DNA. Furthermore, the cytotoxicity of PEIMH-1 was considerably lower than that of control PEI25K.

Lipidic systems for in vivo siRNA delivery

The ability of small-interfering RNA (siRNA) to silence specific target genes not only offers a tool to study gene function but also represents a novel approach for the treatment of various human diseases. Its clinical use, however, has been severely hampered by the lack of delivery of these molecules to target cell populations in vivo due to their instability, inefficient cell entry, and poor pharmacokinetic profile. Various delivery vectors including liposomes, polymers, and nanoparticles have thus been developed in order to circumvent these problems. This review presents a comprehensive overview of the barriers and recent progress for both local and systemic delivery of therapeutic siRNA using lipidic vectors. Different strategies for formulating these siRNA-loaded lipid particles as well as the general concern about their safe use in vivo will also be discussed. Finally, current advances in the targeted delivery of siRNA and their impacts on the field of RNA interference (RNAi)-based therapy will be presented.

Lipid-based nanoparticles as pharmaceutical drug carriers: from concepts to clinic

In recent years, various nanotechnology platforms in the area of medical biology, including both diagnostics and therapy, have gained remarkable attention. Moreover, research and development of engineered multifunctional nanoparticles as pharmaceutical drug carriers have spurred exponential growth in applications to medicine in the last decade. Design principles of these nanoparticles, including nanoemulsions, dendrimers, nano-gold, liposomes, drug-carrier conjugates, antibody-drug complexes, and magnetic nanoparticles, are primarily based on unique assemblies of synthetic, natural, or biological components, including but not limited to synthetic polymers, metal ions, oils, and lipids as their building blocks. However, the potential success of these particles in the clinic relies on consideration of important parameters such as nanoparticle fabrication strategies, their physical properties, drug loading efficiencies, drug release potential, and, most importantly, minimum toxicity of the carrier itself. Among these, lipid-based nanoparticles bear the advantage of being the least toxic for in vivo applications, and significant progress has been made in the area of DNA/RNA and drug delivery using lipid-based nanoassemblies. In this review, we will primarily focus on the recent advances and updates on lipid-based nanoparticles for their projected applications in drug delivery. We begin with a review of current activities in the field of liposomes (the so-called honorary nanoparticles), and challenging issues of targeting and triggering will be discussed in detail. We will further describe nanoparticles derived from a novel class of amphipathic lipids called bolaamphiphiles with unique lipid assembly features that have been recently examined as drug/DNA delivery vehicles. Finally, an overview of an emerging novel class of particles (based on lipid components other than phospholipids), solid lipid nanoparticles and nanostructured lipid carriers will be presented. We conclude with a few examples of clinically successful formulations of currently available lipid-based nanoparticles.

Physical approaches for nucleic acid delivery to liver

The liver is a key organ for numerous metabolic pathways and involves many inherited diseases that, although being different in their pathology, are often caused by lack or overproduction of a critical gene product in the diseased cells. In principle, a straightforward method to fix such problem is to introduce into these cells with a gene-coding sequence to provide the missing gene product or with the nucleic acid sequence to inhibit production of the excessive gene product. Practically, however, success of nucleic acid-based pharmaceutics is dependent on the availability of a method capable of delivering nucleic acid sequence in the form of DNA or RNA to liver cells. In this review, we will summarize the progress toward the development of physical methods for nucleic acid delivery to the liver. Emphasis is placed on the mechanism of action, pros, and cons of each method developed so far. We hope the information provided will encourage new endeavor to improve the current methodologies or develop new strategies that will lead to safe and effective delivery of nucleic acids to the liver.

Imaging of cationic multifunctional liposome-mediated delivery of COX-2 siRNA

Liposomes are a useful means of delivering molecular targeting agents such as small interfering RNA (siRNA) to downregulate specific pathways important in cancer growth and progression. The ability to non-invasively image these carriers is important to ascertain their delivery within the tumor. As cyclooxygenase-2 (COX-2) is an important therapeutic target in cancer, we investigated loading COX-2-specific siRNA into cationic liposomes containing MR contrast agents for imaging delivery in cancer cells and tumors. COX-2 and GAPDH siRNA, as well as Magnevist or Feridex, were loaded directly into the liposomes. These lipoplexes were used for cell transfection of the poorly differentiated and highly metastatic breast cancer cell line MDA-MB-231. PEGylated liposomes loaded with Feridex and fluorescently labeled COX-2 siRNA were used for in vivo delivery of lipoplexes in MDA-MB-231 breast cancer xenografts in female SCID mice. Transient transfection assays demonstrated potent and specific downregulation of the COX-2 protein in cells in culture. Tail vein injections of PEGylated COX-2 lipoplexes resulted in intratumoral delivery of siRNA. Biodistribution studies showed significant localization in the lung, liver and kidney at 24 h. These data demonstrate the feasibility of liposomal-mediated delivery of COX-2-specific siRNA to downregulate COX-2 in cancer cells, and multi-modality imaging of the delivery of specific siRNA in tumors.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Does a targeting ligand influence nanoparticle tumor localization or uptake?

Inclusion of a tumor-targeting molecule in nanosized delivery systems increases their in vivo efficacy. However, the biodistribution and pharmacokinetics of the uptake of such particles have not yet been well addressed. Several recent papers have suggested that tumor-targeting ligands function primarily to increase intracellular uptake of the nanocomplex and do not influence tumor localization. However, other reports indicate that they do play a role in the accumulation in the tumor. One difference might be the presence or absence of poly-[ethylene glycol] (PEG) in the complex and its impact on the enhanced permeability and retention (EPR) effect. Further studies are clearly needed to more fully elucidate the influence of composition on tumor-targeted, systemic delivery of nanoparticles.

Progress in developing cationic vectors for non-viral systemic gene therapy against cancer

Initially, gene therapy was viewed as an approach for treating hereditary diseases, but its potential role in the treatment of acquired diseases such as cancer is now widely recognized. The understanding of the molecular mechanisms involved in cancer and the development of nucleic acid delivery systems are two concepts that have led to this development. Systemic gene delivery systems are needed for therapeutic application to cells inaccessible by percutaneous injection and for multi-located tumor sites, i.e. metastases. Non-viral vectors based on the use of cationic lipids or polymers appear to have promising potential, given the problems of safety encountered with viral vectors. Using these non-viral vectors, the current challenge is to obtain a similarly effective transfection to viral ones. Based on the advantages and disadvantages of existing vectors and on the hurdles encountered with these carriers, the aim of this review is to describe the "perfect vector" for systemic gene therapy against cancer.

Clostridium neurotoxin fragments as potential targeting moieties for liposomal gene delivery to the CNS

Targeted transfection of the CNS with synthetic, nonviral vectors represents a huge technical challenge. The approach explored here attempts to combine self-assembly ABCD nanoparticles (Kostarelos and Miller, Chem. Soc. Rev. 2005, 34, 970), with the potential of Clostridium neurotoxin fragments to effect receptor-mediated transfection of neuronal cells. Cationic liposome-plasmid DNA complexes were first modified with a PEG stealth layer, before the addition of C-terminal fragments of tetanus toxin (TH(C)), botulinum toxin (BH(C)) or the truncated C-terminal domain of TH(C) as biological "targeting" ligands. First-generation nanoparticles were identified for the transfection of two neuronal cell lines (human SH-5YSY and rat/mouse hybrid N18-RE105); control studies were also performed with HeLa cells. ABCD nanoparticle transfections of the neuronal cell lines were up to 30-fold higher than corresponding control transfections with nanoparticles that lacked the protein ligand. We also demonstrate apparent receptor-mediated uptake by means of competition-binding and real-time confocal experiments. By contrast, nanoparticle transfection of HeLa cells appeared to involve alternative nonspecific enhanced cellular uptake mechanism(s). Receptor-mediated and nonspecific mechanisms appear to be in competition, potentially harming the capacity of receptor-mediated delivery to effect proper targeted delivery of nucleic acids to cells ex vivo and in vivo.

PEGylated synthetic surfactant vesicles (Niosomes): novel carriers for oligonucleotides

Polyethylene glycol (PEG) modified cationic niosomes were used to improve the stability and cellular delivery of oligonucleotides (OND). PEGylated cationic niosomes, composed of DC-Chol, PEG2000-DSPE and the non-ionic surfactant-Span, offer some advantages as gene carriers. Complexes of PEGylated cationic niosomes and OND showed a neutral zeta potential with particle size about 300 nm. PEG-modification significantly decreased the binding of serum protein and prevented particle aggregation in serum. The loaded nuclear acid drug exhibited increased resistance to serum nuclease. Compared with cationic niosomes, the PEGylated niosomes showed a higher efficiency of OND cellular uptake in serum. Therefore, in terms of their stable physiochemical properties in storage and physiological environment, as well as low-cost and widely available materials, PEGylated cationic niosomes are promising drug delivery systems for improved OND potency in vivo.

Bio-nanocapsule conjugated with liposomes for in vivo pinpoint delivery of various materials

Bio-nanocapsules (BNCs) consisting of hepatitis B virus (HBV) surface antigen (HBsAg) are approximately 50-nm hollow particles displaying a human hepatocyte-recognizing molecule (pre-S1 peptide). They have been used as an HB vaccine for the last two decades. Original BNC can incorporate various payloads (e.g., drugs, genes) by electroporation and deliver them to human hepatocytes specifically by utilizing the HBV infection mechanism. Here, we developed a new BNC conjugated with liposomes and succeeded in incorporating large materials (100-nm fluorescence-labeled polystyrene beads and >30 kbp plasmids) into the BNC-liposome complex. The complex delivered these large materials to human hepatocytes specifically ex vivo and in vivo. The transfection efficiency of the BNC-liposome complex was significantly higher than that of the original BNC. These results indicated that BNC confers the tissue- and cell-specificity on the conventional liposomes and raises new possibilities for drug delivery systems, gene delivery systems, and bio-imaging systems in vivo.

Lipid-based nanoparticles for nucleic acid delivery

Lipid-based colloidal particles have been extensively studied as systemic gene delivery carriers. The topic that we would like to emphasize is the formulation/assembly of lipid-based nanoparticles (NP) with diameter under 100 nm for delivering nucleic acid in vivo. NP are different from cationic lipid-nucleic acid complexes (lipoplexes) and are vesicles composed of lipids and encapsulated nucleic acids with a diameter less than 100 nm. The diameter of the NP is an important attribute to enable NP to overcome the various in vivo barriers for systemic gene delivery such as: the blood components, reticuloendothelial system (RES) uptake, tumor access, extracellular matrix components, and intracellular barriers. The major formulation factors that impact the diameter and encapsulation efficiency of DNA-containing NP include the lipid composition, nucleic acid to lipid ratio and formulation method. The particle assembly step is a critical one to make NP suitable for in vivo gene delivery. NP are often prepared using a dialysis method either from an aqueous-detergent or aqueous-organic solvent mixture. The resulting particles have diameters about 100 nm and nucleic acid encapsulation ratios are >80%. Additional components can then be added to the particle after it is formed. This ordered assembly strategy enables one to optimize the particle physico-chemical attributes to devise a biocompatible particle with increased gene transfer efficacy in vivo. The components included in the sequentially assembled NP include: poly(ethylene glycol) (PEG)-shielding to improve the particle pharmacokinetic behavior, a targeting ligand to facilitate the particle-cell recognition and in some case a bioresponsive lipid or pH-triggered polymer to enhance nucleic acid release and intracellular trafficking. A number of groups have observed that a PEG-shielded NP is a robust and modestly effective system for systemic gene or small interfering RNA (siRNA) delivery.

Use of nanoparticles for drug delivery in glioblastoma multiforme

Treatment of glioblastoma multiforme (GBM), a primary malignant tumor of the brain, is one of the most challenging problems as no currently available treatment is curative. Surgery remains the basic treatment in which the bulk of the tumor is removed and the peripheral infiltrating part is the target of supplementary treatments. The currently available anticancer therapeutics have less than optimal usefulness for GBM, mainly owing to delivery problems to the tumor, including those due to blood-brain barrier. Several new therapies in development for GBM will require innovative methods of delivery besides the current practice of direct introduction of drugs and devices into the tumor. Nanobiotechnology, particularly nanoparticles, is making a significant contribution to the improvement of drug delivery in cancer and many of these technologies can be applied to GBM. Nanobiotechnology can provide a platform for combination of diagnostics, therapeutics, and its delivery to the tumor with subsequent monitoring of response. These technologies are reviewed and the prospects of improvement of therapeutic delivery to the brain are excellent during the next 5 years. Curing of GBM, however, depends on discovery of an anticancer agent that will destroy GBM completely.

Cell and tissue targeting of nucleic acids for cancer gene therapy

Tumor targeting--per definition--includes any strategy to improve the specificity of the therapeutic nucleic acid towards the tumor site, while highest biological activity should be maintained. Targeting has been successfully achieved at the transcriptional, transductional or delivery level. For tumor-specific delivery, physical targeting methods like electroporation, hyperthermia, magnetofection, photochemical internalization or ultrasound, and biological targeting systems, including active and passive tumor targeting, have been developed. Therapeutic effects could be demonstrated with various targeted nucleic acid formulations, such as tumor-targeted DNA plasmids expressing p53 or tumor necrosis factor alpha, small interfering RNAs knocking down gene expression from tumor specific chromosomal translocations or gene expression of tumor neoangiogenic processes, as well as double stranded RNA poly inosine-cytosine which triggers apoptosis in targeted tumor cells.

Recent developments in the application of plasmid DNA-based vectors and small interfering RNA therapeutics for cancer

Increased understanding of the molecular pathological mechanisms of cancer, the advent of novel molecular tools such as synthetic small interfering RNA (siRNA) or plasmid DNA-based vectors (pDNA), and technology for the in vivo delivery of such biomolecular therapeutics have provided an encouraging perspective for cancer therapy. Numerous pDNAs and siRNAs have been tested in preclinical cancer models, and these first approaches have reached clinical evaluation. The therapeutic effector mechanisms include interference with neoangiogenesis, blockage of cell division, promotion of apoptosis and sensitization to chemotherapy, delivery of cytotoxic genes, and activation of anticancer immune responses. Physical methods have been developed for highly effective regional delivery. A series of innovative "smart" formulations directs the current development toward safe and effective systemic tumor-targeted delivery of pDNA and siRNA.

Surface-modified LPD nanoparticles for tumor targeting

We have developed a tumor-targeted LPD formulation (liposome-polycation-DNA complex) for siRNA. With surface modification, the targeted, PEGylated LPD increased the delivery efficiency by four-fold and the gene-silencing effect by two- to three-fold. Downregulation of survivin in human lung cancer cells by targeted LPD induced 90% of apoptosis and sensitized the cells to cisplatin by four-fold. PEGylated LPD formulation also significantly improved the tumor localization of siRNA in the NCI-H460 human lung cancer xenograft model. The tumor appeared to be the major uptake organ for siRNA formulated in surface-modified LPD. Our encouraging results indicate that surface-modified LPD may be a potent carrier for RNAi-based tumor therapy.

Chemically modified short interfering hybrids (siHYBRIDS): nanoimmunoliposome delivery in vitro and in vivo for RNAi of HER-2

A blunt-ended 19-mer short interfering hybrid (siHybrid) (H) comprised of sense-DNA/antisense-RNA targeting HER-2 mRNA was encapsulated in a liposomal nanoplex with anti-transferrin receptor single-chain antibody fragment (TfRscFv) as the targeting moiety for clinically relevant tumor-specific delivery. In vitro delivery to a human pancreatic cell line (PANC-1) was shown to exhibit sequence-specific inhibition of 48-h cell growth with an IC50 value of 37 nM. The inhibitory potency of this siHybrid was increased (IC50 value of 7.8 nM) using a homologous chemically modified siHybrid (mH) in which the 19-mer sense strand had the following pattern of 2 '-deoxyinosine (dI) and 2 '-O-methylribonucleotide (2 '-OMe) residues: 5'-d(TITIT)-2'OMe(GCGGUGGUU)-d(GICIT). These modifications were intended to favor antisense strand-mediated RNAi while mitigating possible sense strand-mediated off-target effects and RNase H-mediated cleavage of the antisense RNA strand. The presently reported immunoliposomal delivery system was successfully used in vivo to inhibit HER-2 expression, and thus induce apoptosis in human breast carcinoma tumors (MDA-MB-435) in mice upon repeated i.v. treatment at a dose of 3 mg/kg of H or mH. The in vivo potency of modified siHybrid mH appeared to be qualitatively greater than that of H, as was the case in vitro.