Diaminododecane-based cationic bolaamphiphile as a non-viral gene delivery carrier

Cationic Amphiphilic Dendrons with Anticancer Activity

Cancer has become the leading cause of human death worldwide, and there is an urgent need to design and develop new oncology drugs. In this study, we report series of cationic amphiphilic dendrons with different hydrophobic alkyl chains (C_n) and different generations (G_x) and demonstrate their use for anticancer applications. The results revealed that lower-generation dendrons (G₁) with a longer hydrophobic alkyl chain (C₁₂ and C₁₈) have stronger antitumor activity. Among these dendrons, a lead candidate C₁₂-G₁ was identified that demonstrated excellent broad-spectrum antitumor activity in 7 cancer cell lines including highly metastatic tumor cells, while simultaneously, hemolysis was negligible. Mechanistic studies showed that C₁₂-G₁ could lead to cytoplasmic leakage and induce cancer cell necrosis through membrane disruption. In addition, C₁₂-G₁ showed potent inhibition of tumor growth in a B16-F10 melanoma model. In conclusion, these findings demonstrate that the cationic amphiphilic dendron might be a promising agent for anticancer application.

Biomedically Relevant Applications of Bolaamphiphiles and Bolaamphiphile-Containing Materials

Bolaamphiphiles (BAs) are structurally segmented molecules with rich assembly characteristics and diverse physical properties. Interest in BAs as standalone active agents or as constituents of more complex therapeutic formulations has increased substantially in recent years. The preorganized amphiphilicity of BAs allows for a range of biological activities including applications that rely on multivalency. This review summarizes BA-related research in biomedically relevant areas. In particular, we review BA-related literature in four areas: gene delivery, antimicrobial materials, hydrogels, and prodrugs. We also discuss several distinguishing characteristics of BAs that impact their utility as biomedically relevant compounds.

Sunlight-Mediated Thiol-Ene/Yne Click Reaction: Synthesis and DNA Transfection Efficiency of New Cationic Lipids

The design of green synthetic reaction conditions is very challenging, especially for biomaterials, but worthwhile if the compounds can be easily synthesized in the aqueous medium. Herein, we report the development of sunlight-mediated thiol-ene/yne click reaction in the presence of a catalytic amount of tert-butyl hydroperoxide (TBHP) in an aqueous medium. The optimized reaction conditions were successfully applied to synthesize a series of small molecules and lipids in a single step in the aqueous medium. The synthetic cationic lipid/co-lipid formed positively charged stable nanosized liposomes that effectually bind with the genetic materials. The in vitro DNA transfection and cellular uptake assays showed that the synthesized cationic lipids have comparable efficiency to commercially available Lipofectamine 2000. This mild synthetic strategy can also be used for smart design of novel or improvement of prevailing lipid-based nonviral gene delivery systems. Such chemical transformations in the aqueous medium are more environment-friendly than other reported thiol-ene/yne click reactions performed in an organic solvent medium.

In vitro cytotoxicity assay of D-limonene niosomes: an efficient nano-carrier for enhancing solubility of plant-extracted agents

The low solubility of the plant-extracted agent like D-limonene in cancer therapy is a critical problem. In this study, we prepared D-limonene-loaded niosomes (D-limonene/Nio) for cancer therapy through in vitro cytotoxicity assay of HepG2, MCF-7, and A549 cell lines. The niosomal formulation was prepared by film hydration technique with Span^® 40: Tween^® 40: cholesterol (35:35:30 molar ratio) and characterized for vesicle distribution size, morphology, entrapment efficiency (EE%), and in vitro release behaviour. The obtained niosomes showed a nanometric size and spherical morphology with EE% about 87 ± 1.8%. Remarkably prolonged release of D-limonene from niosomes compared to free D-limonene observed. The loaded formulation showed significantly enhanced cytotoxic activity with all three cancer cell lines (HepG2, Macf-7 and A549) at the concentration of 20 μM. These results indicated that niosome loaded with phytochemicals can be a promising nano-carrier for cancer therapy applications.

Transfection by cationic gemini lipids and surfactants

Diseases that are linked to defective genes or mutations can in principle be cured by gene therapy, in which damaged or absent genes are either repaired or replaced by new DNA in the nucleus of the cell. Related to this, disorders associated with elevated protein expression levels can be treated by RNA interference via the delivery of siRNA to the cytoplasm of cells. Polynucleotides can be brought into cells by viruses, but this is not without risk for the patient. Alternatively, DNA and RNA can be delivered by transfection, i.e. by non-viral vector systems such as cationic surfactants, which are also referred to as cationic lipids. In this review, recent progress on cationic lipids as transfection vectors will be discussed, with special emphasis on geminis, surfactants with 2 head groups and 2 tails connected by a spacer.

Sensitization of Cancer Cells via Non-Viral Delivery of Apoptosis Inducing Proteins Using a Cationic Bolaamphiphile

Cationic bolaamphiphile polymers had been previously studied as efficient delivery system for the delivery of proteins with relatively low toxicity. Here, the authors investigate the use of a protein delivery system based on a cationic bolaamphiphile to sensitize cancer cells toward apoptosis-inducing drugs as a novel approach for cancer therapy. The authors demonstrates the efficacy of the system by two strategies. The first strategy involves delivery of a survivin antibody to inhibit survivin activity. Sensitization of MCF-7 cells to doxorubicin is observed by survivin inhibition by antibodies. The IC₅₀ of doxorubicin is reduced ≈2.5-fold after delivery of survivin antibodies to breast cancer cells and induction of apoptosis is shown by Western blotting with apoptosis specific antibodies. In a second approach, functional wild type p53 is delivered into p53-null liver cancer (Hep3B) cells, sensitizing the cells toward the p53 pathway drug, Nutlin. Nutlin reduced the viability of Hep3B cells by ≈42% at 15 μM concentration, demonstrating the effectiveness of p53 delivery. The expression of p21, a downstream target of p53 further confirmed the functional status of the delivered protein. In conclusion. The successful delivery of apoptosis inducing proteins and sensitization of cancer cells via cationic bolaamphiphile polymer represents a promising system for cancer therapeutics.

Dendritic peptide bolaamphiphiles for siRNA delivery to primary adipocytes

Obesity is a major risk factor for diabetes, heart disease and other health problems. Adipose tissue plays a central role in the development of obesity and obesity-associated diseases. Gene therapy targeting adipose tissue may provide a promising strategy for obesity treatment. However, nucleic acid delivery to adipose tissue or even cultured adipocytes is challenging due to low delivery efficacy and high toxicity of the current cationic lipid based delivery systems, or monoamphiphiles. Herein, we report using dendritic peptide bolaamphiphiles (bolas) to deliver siRNA to primary adipocytes and hepatocytes. The bola consists of two l-Lysine dendrons connected to a fluorocarbon core through disulfide linkages. The Lysine dendrons are functionalized with l-histidine and l-tryptophan to promote endosomal escape and cellular uptake. The bola exhibited over 70% knockdown of GAPDH gene in both primary adipocytes and hepatocytes. Importantly, different from Lipofectamine that significantly reduced genes involved in lipolysis, lipogenesis, fatty acid oxidation and ketogenesis, the bolas had little to no effect on these genes. These results demonstrate the bola as a promising new vector for clinical and experimental applications for delivery of siRNA to metabolic organs.

Functionalized Asymmetric Bola-Type Amphiphiles for Efficient Gene and Drug Delivery

The studies of bolaamphiphile-based nanoparticles as delivery vectors are still rudimentary and under development. In this study, several asymmetric bolaamphiphiles containing lysine and another moiety with special functions, such as pH-sensitive or cell-targeting property, were designed and synthesized. The potentials of these bolaamphiphile-based nanoparticles as versatile vectors for both nucleic acids and chemical drugs were studied. With the presence of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), these amphiphiles could be prepared into bolasomes, which showed good DNA binding ability and could condense plasmid DNA into nanoparticles with appropriate size and surface potential. Lys-His, which has a pH-sensitive histidine on one head, exhibited higher transfection efficiency than the symmetric counterpart and comparable efficiency to commercially available transfection reagent. Mechanism studies confirmed that the bolaplexes formed from Lys-His might induce the highest cellular uptake and the best endosomal escape ability. On the other hand, these bolaamphiphiles also exhibited good drug loading ability. The self-assembly vesicles could efficiently encapsulate the hydrophobic anti-cancer drug doxorubicin (DOX) in aqueous solution with high drug loading content and encapsulation efficiency. Confocal laser scanning microscopy (CLSM) experiment and cell viability assay exhibited a controlled release of the drug with the assistance of bolasomes. It was shown that such bolaamphiphiles have great potential as nano-vectors for both drug and gene or their co-delivery.

Preparation and evaluation of a novel anticancer drug delivery carrier for 5-Fluorouracil using synthetic bola-amphiphile based on lysine as polar heads

A novel bolaamphiphile surfactant N,N'-(dodecane-1, 12-diyl) bis (2,6-diaminohexanamide) (DADL) was designed and synthesized using l-lysine and 1,12-diaminododecane as the hydrophilic and hydrophobic part, respectively. After separation and purification, the structure of the synthetic bolaamphiphile surfactant was verified by FTIR, MS and ¹H NMR. The synthetic bolaamphiphile was able to self-assemble to form vesicles. After formulation screening, vesicles loaded with 5-Fluorouracil (5-Fu) were prepared with Tween 60 and DADL by sonication and were examined by dynamic light scattering and transmission electron microscopy. Micro-FTIR was applied to investigate the conformation of the bola molecules within the vesicle membrane. The release profile of the vesicles showed a pH-sensitive and sustained release. No significant toxicity was observed in an in vitro cell viability assay. The antitumor efficacy of the 5-Fu-loaded vesicles on H₂₂ tumor-bearing mice was remarkably high due to the EPR effects. These results show that our novel bolaamphiphile derived from lysine has excellent potential as a pH-sensitive drug carrier.

Locally advanced vulva cancer: A single centre review of anovulvectomy and a systematic review of surgical, chemotherapy and radiotherapy alternatives. Is an international collaborative RCT destined for the "too difficult to do" box?

INTRODUCTION

Treatment of locally advanced vulva cancer (LAVC) remains challenging. Due to the lack of randomised trials many questions regarding the indications for different treatment options and their efficacy remain unanswered.

METHODS

In this retrospective study we provide the largest published series of LAVC patients treated with anovulvectomy, reporting oncological outcomes and morbidity. Additionally, a systematic literature review was performed for all treatment options 1946-2015.

RESULTS

In our case series, 57/70 (81%) patients were treated in the primary setting with anovulvectomy and 13 patients underwent anovulvectomy for recurrent disease. The median overall survival (OS) was 69months (1-336) with disease specific survival of 159months (1-336). Following anovulvectomy for primary disease, time to progression and OS were significantly higher in node negative disease (10 vs. 96months; 19 vs. 121months, p<0.0001). Post-surgical complications were observed in 36 (51.4%), the majority of which were Grade I/II infections. There was one peri-operative death. Review of the literature showed that chemotherapy, radiotherapy or combination treatments are alternatives to surgery. Evidence relating to all of these consisted mostly of small retrospective series, which varied considerably in terms of patient characteristics and treatment schedules. Significant patient and treatment heterogeneity prevented meta-analysis with significant biases in these studies. It was unclear if survival or morbidity was better in any one group with a lack of data reporting complications, quality of life, and long term follow-up. However, results for chemoradiation are encouraging enough to warrant further investigation.

CONCLUSIONS

There remains inadequate evidence to identify an optimal treatment for LAVC. However, there is sufficient evidence to support a trial of anovulvectomy versus chemoradiation. Discussions and consensus would be needed to determine trial criteria including the primary outcome measure. Neoadjuvant chemotherapy or radiotherapy alone may be best reserved for the palliative setting or metastatic disease.

Progresses towards safe and efficient gene therapy vectors

The emergence of genetic engineering at the beginning of the 1970′s opened the era of biomedical technologies, which aims to improve human health using genetic manipulation techniques in a clinical context. Gene therapy represents an innovating and appealing strategy for treatment of human diseases, which utilizes vehicles or vectors for delivering therapeutic genes into the patients' body. However, a few past unsuccessful events that negatively marked the beginning of gene therapy resulted in the need for further studies regarding the design and biology of gene therapy vectors, so that this innovating treatment approach can successfully move from bench to bedside. In this paper, we review the major gene delivery vectors and recent improvements made in their design meant to overcome the issues that commonly arise with the use of gene therapy vectors. At the end of the manuscript, we summarized the main advantages and disadvantages of common gene therapy vectors and we discuss possible future directions for potential therapeutic vectors.

Bolaamphiphile-based nanocomplex delivery of phosphorothioate gapmer antisense oligonucleotides as a treatment for Clostridium difficile

Despite being a conceptually appealing alternative to conventional antibiotics, a major challenge toward the successful implementation of antisense treatments for bacterial infections is the development of efficient oligonucleotide delivery systems. Cationic vesicles (bolasomes) composed of dequalinium chloride ("DQAsomes") have been used to deliver plasmid DNA across the cardiolipin-rich inner membrane of mitochondria. As cardiolipin is also a component of many bacterial membranes, we investigated the application of cationic bolasomes to bacteria as an oligonucleotide delivery system. Antisense sequences designed in silico to target the expression of essential genes of the bacterial pathogen, Clostridium difficile, were synthesized as 2'-O-methyl phosphorothioate gapmer antisense oligonucleotides (ASO). These antisense gapmers were quantitatively assessed for their ability to block mRNA translation using luciferase reporter and C. difficile protein expression plasmid constructs in a coupled transcription-translation system. Cationic bolaamphiphile compounds (dequalinium derivatives) of varying alkyl chain length were synthesized and bolasomes were prepared via probe sonication of an aqueous suspension. Bolasomes were characterized by particle size distribution, zeta potential, and binding capacities for anionic oligonucleotide. Bolasomes and antisense gapmers were combined to form antisense nanocomplexes. Anaerobic C. difficile log phase cultures were treated with serial doses of gapmer nanocomplexes or equivalent amounts of empty bolasomes for 24 hours. Antisense gapmers for four gene targets achieved nanomolar minimum inhibitory concentrations for C. difficile, with the lowest values observed for oligonucleotides targeting polymerase genes rpoB and dnaE. No inhibition of bacterial growth was observed from treatments at matched dosages of scrambled gapmer nanocomplexes or plain, oligonucleotide-free bolasomes compared to untreated control cultures. We describe the novel application of cationic bolasomes to deliver ASOs into bacteria. We also report the first successful in vitro antisense treatment to inhibit the growth of C. difficile.

Cationic Nanoparticles Assembled from Natural-Based Steroid Lipid for Improved Intracellular Transport of siRNA and pDNA

Developing new functional biomaterials from biocompatible natural-based resources for gene/drug delivery has attracted increasing attention in recent years. In this work, we prepared a series of cationic nanoparticles (Diosarg-DOPE NPs) by assembly of a natural steroid diosgenin-based cationic lipid (Diosarg) with commercially-available helper lipid 1,2-dioleoyl-sn-glycero-3-phosphorethanolamine (DOPE). These cationic Diosarg-DOPE NPs were able to efficiently bind siRNA and plasmid DNA (pDNA) via electrostatic interactions to form stable, nano-sized cationic lipid nanoparticles instead of lamellar vesicles in aqueous solution. The average particle size, zeta potentials and morphologies of the siRNA and pDNA complexes of the Diosarg-DOPE NPs were examined. The in vitro cytotoxicity of NPs depends on the dose and assembly ratio of the Diosarg and DOPE. Notably, the intracellular transportation efficacy of the exogenesis siRNA and pDNA could be greatly improved by using the Diosarg-DOPE NPs as the cargoes in H1299 cell line. The results demonstrated that the self-assembled Diosarg-DOPE NPs could achieve much higher intracellular transport efficiency for siRNA or pDNA than the cationic lipid Diosarg, indicating that the synergetic effect of different functional lipid components may benefit the development of high efficiency nano-scaled gene carriers. Moreover, it could be noted that the traditional "lysosome localization" involved in the intracellular trafficking of the Diosarg and Diosarg-DOPE NPs, indicating the co-assembly of helper lipid DOPE, might not significantly affect the intracellular localization features of the cationic lipids.

Synthesis and evaluation of novel lipopeptide as a vehicle for efficient gene delivery and gene silencing

Nucleic acid-based therapeutics have recently emerged as a new class of next generation agents for treatment and prevention of viral infection, cancer, and genetic disorders, but their wide use is limited by their relatively weak delivery into target cells. Usage of synthetic cationic amphiphiles with peptide hydrophilic domain as agents for non-viral gene delivery is an attractive approach. We developed the schemes for the synthesis of aliphatic peptides with different length of the hydrocarbon chains in hydrophobic domains and different amino acids in polar head. For the obtained derivatives we determined transfection efficiency, critical vesicle concentration, particle size, ζ-potential and aggregates stability. We have found that the transfection efficiency is increased if the ornithine is a part of polar head in an amphiphile. The most promising amphiphile for liposomal formation OrnOrnGlu(C16H33)2 was examined more carefully. It has been shown that the lipopeptide possesses low toxicity (in vitro and in vivo) and high transfection efficiency with pDNA and siRNA in different cell lines. In addition, the production of liposomes based on this lipopeptide is simple, quick and cheap. Thus OrnOrnGlu(C16H33)2 is a promising vehicle for gene delivery and gene silencing.

Interaction between a cationic bolaamphiphile and DNA: The route towards nanovectors for oligonucleotide antimicrobials

Bacterial resistance to antimicrobials is a global threat that requires development of innovative therapeutics that circumvent its onset. The use of Transcription Factor Decoys (TFDs), DNA fragments that act by blocking essential transcription factors in microbes, represents a very promising approach. TFDs require appropriate carriers to protect them from degradation in biological fluids and transfect them through the bacterial cell wall into the cytoplasm, their site of action. Here we report on a bolaform cationic surfactant, [12-bis-THA]Cl2, with proven transfection activity in vivo. By studying the physical-chemical properties of its aqueous solutions with light scattering, cryo-TEM, ζ-potential, absorption and fluorescence spectroscopies, we prove that the bolaamphiphiles associate into transient vesicles which convert into one-dimensional elongated structures over time. These surfactant assemblies complex TFDs with extremely high efficiency, if compared to common cationic amphiphiles. At Z+/-=11, the nanoplexes are stable and have a size of 120nm, and they form independently of the original morphology of the [12-bis-THA]Cl2 aggregate. DNA is compacted in the nanoplexes, as shown through CD spectroscopy and fluorescence, but is readily released in its native form if sodium taurocholate is added.

Enhanced siRNA delivery of a cyclododecylated dendrimer compared to its linear derivative

Lipid modification has been widely applied to improve the gene delivery efficacy of cationic polymers.

Structure-Based Design of Dendritic Peptide Bolaamphiphiles for siRNA Delivery

Development of safe and effective delivery vectors is a critical challenge for the application of RNA interference (RNAi)-based biotechnologies. In this study we show the rational design of a series of novel dendritic peptide bolaamphiphile vectors that demonstrate high efficiency for the delivery of small interfering RNA (siRNA) while exhibiting low cytotoxicity and hemolytic activity. Systematic investigation into structure-property relationships revealed an important correlation between molecular design, self-assembled nanostructure, and biological activity. The unique bolaamphiphile architecture proved a key factor for improved complex stability and transfection efficiency. The optimal vector contains a fluorocarbon core and exhibited enhanced delivery efficiency to a variety of cell lines and improved serum resistance when compared to hydrocarbon analogues and lipofectamine RNAiMAX. In addition to introducing a promising new vector system for siRNA delivery, the structure-property relationships and "fluorocarbon effect" revealed herein offer critical insight for further development of novel materials for nucleic acid delivery and other biomaterial applications.

Micelle-like luminescent nanoparticles as a visible gene delivery system with reduced toxicity

Luminescent nanoparticles (TPEI) were synthesized to tackle the undesired cytotoxicity of cationic polymers and were also used for visible gene transfection.

Assembly of plasmid DNA with pyrene-amines cationic amphiphiles into nanoparticles and their visible lysosome localization

In this study, we constructed a visible model for drug/gene dual delivery.

Glial cell line-derived neurotrophic factor gene delivery via a polyethylene imine grafted chitosan carrier

Parkinson’s disease is known to result from the loss of dopaminergic neurons. Direct intracerebral injections of high doses of recombinant glial cell line-derived neurotrophic factor (GDNF) have been shown to protect adult nigral dopaminergic neurons. Because GDNF does not cross the blood–brain barrier, intracerebral gene transfer is an ideal option. Chitosan (CHI) is a naturally derived material that has been used for gene transfer. However, the low water solubility often leads to decreased transfection efficiency. Grafting of highly water-soluble polyethylene imines (PEI) and polyethylene glycol onto polymers can increase their solubility. The purpose of this study was to design a non-viral gene carrier with improved water solubility as well as enhanced transfection efficiency for treating Parkinsonism. Two molecular weights (Mw =600 and 1,800 g/mol) of PEI were grafted onto CHI (PEI600-g-CHI and PEI1800-g-CHI, respectively) by opening the epoxide ring of ethylene glycol diglycidyl ether (EX-810). This modification resulted in a non-viral gene carrier with less cytotoxicity. The transfection efficiency of PEI600-g-CHI/deoxyribonucleic acid (DNA) polyplexes was significantly higher than either PEI1800-g-CHI/DNA or CHI/DNA polyplexes. The maximal GDNF expression of PEI600-g-CHI/DNA was at the polymer:DNA weight ratio of 10:1, which was 1.7-fold higher than the maximal GDNF expression of PEI1800-g-CHI/DNA. The low toxicity and high transfection efficiency of PEI600-g-CHI make it ideal for application to GDNF gene therapy, which has potential for the treatment of Parkinson’s disease.

Novel gemini cationic lipids with carbamate groups for gene delivery

To obtain efficient non-viral vectors, a series of Gemini cationic lipids with carbamate linkers between headgroups and hydrophobic tails were synthesized. They have the hydrocarbon chains of 12, 14, 16 and 18 carbon atoms as tails, designated as G12, G14, G16 and G18, respectively. These Gemini cationic lipids were prepared into cationic liposomes for the study of the physicochemical properties and gene delivery. The DNA-bonding ability of these Gemini cationic liposomes was much better than their mono-head counterparts (designated as M12, M14, M16 and M18, respectively). In the same series of liposomes, bonding ability declined with an increase in tail length. They were tested for their gene-transferring capabilities in Hep-2 and A549 cells. They showed higher transfection efficiency than their mono-head counterparts and were comparable or superior in transfection efficiency and cytotoxicity to the commercial liposomes, DOTAP and Lipofectamine 2000. Our results convincingly demonstrate that the gene-transferring capabilities of these cationic lipids depended on hydrocarbon chain length. Gene transfection efficiency was maximal at a chain length of 14, as G14 can silence about 80 % of luciferase in A549 cells. Cell uptake results indicate that Gemini lipid delivery systems could be internalised by cells very efficiently. Thus, the Gemini cationic lipids could be used as synthetic non-viral gene delivery carriers for further study.

Cyclen-based cationic lipids with double hydrophobic tails for efficient gene delivery

The gene transfection abilities and structure–activity relationship of newly designed cationic lipids were studied in detail.

Delivery of reprogramming factors into fibroblasts for generation of non-genetic induced pluripotent stem cells using a cationic bolaamphiphile as a non-viral vector

Protein delivery allows a clinical effect to be directly realized without genetic modification of the host cells. We have developed a cationic bolaamphiphile as a non-viral vector for protein delivery application. The relatively low toxicity and efficient protein delivery by the cationic bolaamphiphile prompted us to test the system for the generation of induced pluripotent stem cells (iPSCs) as an alternative to the conventional vector-based genetic approach. Studies on the kinetics and cytotoxicity of the protein delivery system led us to use an optimized cationic bolaamphiphile-protein complex ratio of 7:1 (wt/wt) and a 3 h period of incubation with human fibroblasts, to ensure complete and non-toxic protein delivery of the reprogramming proteins. The reprogrammed cells were shown to exhibit the characteristics of embryonic stem cells, including expression of pluripotent markers, teratoma formation in SCID mice, and ability to be differentiated into a specific lineage, as exemplified by neuronal differentiation.

Disulfide cross-linked low generation dendrimers with high gene transfection efficacy, low cytotoxicity, and low cost

Cationic poly(amidoamine) (PAMAM) dendrimers were widely used as nonviral gene carriers. PAMAM dendrimer-based products such as Superfect and Priofect were already commercially available gene transfection reagents. However, these products are based on high generation dendrimers with high cost and serious cytotoxicity. In this study, we prepared high efficient gene carriers using disulfide cross-linked low generation (generation 2, G2) PAMAM dendrimers. These synthesized materials can effectively condense DNA into ~200 nm polyplexes and degrade into G2 dendrimers after cellular uptake. Confocal laser scanning microscope studies revealed high cellular uptake behavior of disulfide cross-linked G2 PAMAM dendrimers. Compared to G2 and G5 PAMAM dendrimers, disulfide cross-linked G2 PAMAM dendrimers showed much improved gene transfection efficacy (both EGFP and luciferase gene) and low cytotoxicity on both HEK293 and HeLa cell lines. The disulfide cross-linked G2 dendrimer prepared at a linker/dendrimer molar ratio of 1:1 showed the highest gene transfection efficacy and exhibited comparable efficacy to branched PEI with a molecular weight of 25 kD, a commercially available nonviral gene vector. Our study demonstrated that disulfide cross-linked low generation PAMAM dendrimers with high transfection efficacy, low cytotoxicity, and low cost are efficient alternatives to high generation PAMAM dendrimers in gene delivery.

Nanostructured PEG-based hydrogels with tunable physical properties for gene delivery to human mesenchymal stem cells

Effective delivery of DNA to direct cell behavior in a well defined three dimensional scaffold offers a superior approach in tissue engineering. In this study, we synthesized biodegradable nanostructured hydrogels with tunable physical properties for cell and gene delivery. The hydrogels were formed via Michael addition chemistry by reacting a four-arm acrylate-terminated PEG with a four-arm thiol-functionalized PEG. Nanosized micelles self-assembled from the amphiphilic PEG-b-polycarbonate diblock copolymer, having reactive end-groups, were chemically incorporated into the hydrogel networks at various contents. The use of Michael addition chemistry allows for in situ hydrogel formation under the physiological conditions. Mechanical property analysis of the hydrogels revealed a correlation between the content of micelles and the storage modulus of the hydrogels. Internal morphology of hydrogels was observed using a field emission scanning electron microscope, which showed that the number and/or size of the pores in the hydrogel increased with increasing micelle content due to reduced crosslinking degree. There exists an optimal micelle content for cell proliferation and gene transfection. MTT assays demonstrated the highest cell viability in the hydrogel with 20% micelles. The gene expression level in hMSCs in the hydrogel with 20% micelles was also significantly higher than that in the hydrogel without micelles. The enhanced cell viability and gene expression in the hydrogel with the optimized micelle content are likely attributed to the physical properties that provide a better environment for cell-matrix interactions. Therefore, incorporating micelles into the hydrogel is a good strategy to control cellular behavior in 3-D through changes in physical properties of the microenvironment.