Enhancements in gene expression by the choice of plasmid DNA formulations containing neutral polymeric excipients

Quality by design (QbD) approach of pharmacogenomics in drug designing and formulation development for optimization of drug delivery systems

Conventional approaches of drug discovery are very complex, costly and time consuming. But after the completion of human genome project, applications of pharmacogenomics in this area completely revolutionize the drug discovery and development process to produce a quality by design (QbD) approach based products. The applications of two areas of pharmacogenomics i.e. structural and functional pharmacogenomics excel the drug discovery process by employing genomic data in drug target identification and evaluation, lead optimization via high throughput screening, evaluation of drug metabolizing enzymes, drug transporters and drug receptors using computer aided technique and bioinformatics library data base. Pharmacogenomics also provides an important and reliable basis for evaluation and optimization of the dosage forms as well as repositioning of failed drugs for the treatment of new disease. Various dosage forms of category of drugs such as anticancer drugs, vaccines, gene and DNA delivery systems and immunological agents can be easily evaluated based on the genetic markers of the related disease. The effect of different formulation polymers on pharmacokinetic and pharmacodynamic properties of drugs can be assessed easily and therefore it plays an important role in formulation optimization. However, current applications of pharmacogenomics in drug discovery and formulation optimization are very limited because of costly and non accessible techniques for everyone, but in future, with the advancement in the technology; the application of genomic data in drug discovery will provide us with innovative, safer and more efficacious medicines.

Nanopolymeric micelle effect on the transdermal permeability, the bioavailability and gene expression of plasmid

This study attempts to investigate the transdermal permeability, the bioavailability and gene expression of plasmid formulated with nonionic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) polymeric micelles (PM). Dynamic light scattering (DLS) and atomic force microscopy (AFM) were used to analyze the PM formulated pCMV-Lac Z (P/PM) containing the gene for β-galactosidase (β-Gal) driven by cytomegalovirus early promoter. Franz diffusion cell was used for in vitro transdermal permeability analysis. Real-time PCR was used to quantify the permeated plasmid in vitro and in vivo. β-Gal activity assay was performed to evaluate transgene expression in vivo. The size of P/PM was ~50 nm with round shape. PM significantly enhanced the in vitro transdermal permeability of plasmid in a direction- and temperature-dependent manner. Following transdermal application of P/PM, higher area under the curve (AUC(P/PM): 98.34 h·ng/mL) and longer half-life of plasmid were detected compared with that of plasmid alone (AUC(P): 10.12 h·ng/mL). Additionally, the β-Gal activity was significantly increased in skin, stomach, brain and spinal cord at both 48 and 72 h after P/PM application and in testis and spleen at 72 h postapplication. In conclusion, PM formulation enhanced the permeation of plasmid through skin into blood circulation, increasing its absorption and the transgene expression in various tissues.

"Soft" calcium crosslinks enable highly efficient gene transfection using TAT peptide

PURPOSE

Typically, low molecular weight cationic peptides or polymers exhibit poor transfection efficiency due to an inability to condense plasmid DNA into small nanoparticles. Here, efficient gene delivery was attained using TAT/pDNA complexes containing calcium crosslinks.

METHODS

Electrostatic complexes of pDNA with TAT or PEI were studied with increasing calcium concentration. Gel electrophoresis was used to determine DNA condensation. The morphology of the complexes was probed by transmission electron microscopy. Transfection efficiency was assessed using a luciferase reporter plasmid. The accessibility of phosphate and amine groups within complexes was evaluated to determine the effect of calcium on structure.

RESULTS

TAT/pDNA complexes were condensed into small, 50-100 nm particles by optimizing the concentration of calcium. Complexes optimized for small size also exhibited higher transfection efficiency than PEI polyplexes in A549 cells. TAT and TAT complexes displayed negligible cytotoxicity up to 5 mg/mL, while PEI exhibited high cytotoxicity, as expected. Probing the TAT-Ca/pDNA structure suggested that calcium interacted with both phosphate and amine groups to compact the complexes; however, these "soft" crosslinks could be competitively disrupted to facilitate DNA release.

CONCLUSION

Small and stable TAT-Ca/pDNA complexes were obtained via "soft" calcium crosslinks leading to sustained gene expression levels higher than observed for control PEI gene vectors. TAT-Ca/pDNA complexes were stable, maintaining particle size and transfection efficiency even in the presence of 10% of FBS. TAT-Ca complexes offer an effective vehicle offering potential for translatable gene delivery.

An overview of condensing and noncondensing polymeric systems for gene delivery

INTRODUCTIONSelf-assembling synthetic vectors for DNA delivery are designed to fulfill several biological functions. They must be able to deliver their genetic payload specifically to the target tissue/cells in a site-specific manner, while protecting the genetic material from degradation by metabolic or immune pathways. Furthermore, they must exhibit minimal toxicity and be proven safe enough for therapeutic use. Ultimately, they must have the capability to express a therapeutic gene for a finite period of time in an appropriate, regulated fashion. The DNA encapsulated in these vectors may be in a condensed or noncondensed form, depending on the nature of the polymer and the technique used for formulating the vector system. The whole process presents many barriers at both tissue and cellular levels. Overcoming these hurdles is the principal objective for efficient polymer-based DNA therapeutics.

A stopped-flow kinetic study of the assembly of nonviral gene delivery complexes

Stopped-flow circular dichroism and fluorescence spectroscopy are used to characterize the assembly of complexes consisting of plasmid DNA bound to the cationic lipids dimethyldioctadecylammonium bromide and 1, 2-dioleoyl- 3-trimethylammonium-propane and a series of polyamidoamine dendrimers. The kinetics of complexation determined from the stopped-flow circular dichroism measurements suggests complexation occurs within 50 ms. Further analysis, however, was precluded by the presence of mixing (shear) artifacts. Stopped-flow fluorescence employing the high-affinity DNA dyes Hoechst 33258 and YOYO-1 was able to resolve two sequential steps in the assembly of complexes that are assigned to binding/dehydration and condensation events. The rates of each process were determined over the temperature range of 10-50 degrees C and activation energies were determined from the slope of Arrhenius plots. The behavior of polyamidoamine dendrimers can be separated into two classes based on their differing binding modes: generation 2 and the larger generations (G4, G7, and G9). The larger generations have activation energies for binding that follow the trend G4 > G7 > G9. The activation energies for condensation (compaction) of complexes composed of these same dendrimers have the opposite trend G9 > G7 > G4. It is postulated that a balance between a more energetically favorable condensation and less favorable binding may prove beneficial in enhancing gene delivery.

Degradation kinetics of high molecular weight poly(L-lactide) microspheres and release mechanism of lipid:DNA complexes

Plasmid DNA encoding the green lantern protein was ion-paired with 1,2-dioleoyl, 3-trimethylammonium propane (DOTAP) at a (+/-) charge ratio of (1:1) to form a hydrophobic ion-pair (HIP) complex using the Bligh and Dyer method, and transferred into methylene chloride. Precipitation with a compressed antisolvent (PCA) was then employed to encapsulate plasmid DNA into poly(L-lactide) (PLLA) microspheres. The hydrophobicity of DOTAP:DNA complexes allowed consistently high encapsulation efficiencies (>70%) to be achieved. Release of the DOTAP:DNA complex from PLLA microspheres exhibited minimal burst and a short (ca. 1 week) lag phase, followed by sustained release over a 20 week period. Release kinetics were consistent with a simple Fickian diffusion model. No correlation was identified between release rate of soluble poly(L-lactide) species (< or =10 lactate units) from PLLA and the DNA release kinetics. Only approximately 12% of the polymer was degraded into soluble poly(L-lactide) over the time frame where approximately 90% of the plasmid load had been released.

Controlled plasmid gene transfer to murine renal carcinoma by hexadecylphosphocholine

We report here that the anticancer drug hexadecylphosphocholine (HPC) can control plasmid DNA-mediated gene transfer to renal carcinoma following intratumoral administration. Significant improvement of gene expression levels could be achieved depending on HPC dose administered. Optimal concentration of HPC co-injected with plasmid DNA was found to be 0.2% (w/v) showing up to a 10-fold increase in reporter gene expression levels when compared to DNA administered alone. In vivo gene transfer activity of HPC was not affected by the nature of the diluent used, i.e. glucose-based or saline-based isotonic solutions. Although in vitro transfection activity of HPC formulations could not be evidenced, a liposome leakage assay revealed that HPC could significantly destabilize stable lipid membranes suggesting that a possible membrane permeation enhancer activity of HPC combined to the physical stress induced by the intratumor injection may facilitate plasmid DNA entry inside the cells resulting in increased gene expression. HPC/plasmid formulations represent new and attractive non-viral gene delivery systems with potential in cancer gene therapy and vaccination.

Silencing of episomal transgene expression by plasmid bacterial DNA elements in vivo

We previously demonstrated that sustainable enhanced levels of transgene products could be expressed from a bacterial DNA-free expression cassette either formed from a fragmented plasmid in mouse liver or delivered as a minicircle vector. This suggested that bacterial DNA sequences played a role in episomal transgene silencing. To further understand the silencing mechanism, we systematically altered the DNA components in both the expression cassette and the bacterial backbone, and compared the gene expression profiles from mice receiving different DNA forms. In nine vectors tested, animals that received the purified expression cassette alone always expressed persistently higher levels of transgene compared to 2fDNA groups. In contrast, animals that received linearized DNA by a single cut in the bacterial backbone had similar expression profiles to that of intact plasmid groups. All three linear DNAs formed large concatemers and small circles in mouse liver, while ccDNA remained intact. In all groups, the relative amount of vector DNA in liver remained similar. Together, these results further established that the DNA silencing effect was mediated by a covalent linkage of the expression cassette and the bacteria DNA elements.

Water-Soluble and Nonionic Polyphosphoester: Synthesis, Degradation, Biocompatibility and Enhancement of Gene Expression in Mouse Muscle

A nonionic and water-soluble polyphosphoester, poly(2-hydroxyethyl propylene phosphate) (PPE3), was synthesized by chlorination of poly(4-methyl-2-oxo-2-hydro-1,3,2-dioxaphospholane), followed by esterification with 2-benzyloxyethanol and deprotection of the hydroxyl group by catalytic hydrogenation in the presence of Pd-C. PPE3 degraded rapidly in PBS 7.4 at 37 degrees C. The cytotoxicity and tissue compatibility assays suggested good biocompatibility of PPE3 in vitro and in vivo. The expression of pVR1255 Luc plasmid in mouse muscle after intramuscular (i.m.) injection of DNA formulated with PPE3 solution in saline was enhanced up to 4-fold compared with that of naked DNA. These results suggest the potential of this polyphosphoester for naked DNA-based gene therapy. The advantages of this polymer design include the biodegradability of the polyphosphoester and its structural versatility, which allows the fine-tuning of the physicochemical properties to optimize the enhancement of gene expression in muscle.

A survey of the year 2002 literature on applications of isothermal titration calorimetry

Isothermal titration calorimetry (ITC) is becoming widely accepted as a key instrument in any laboratory in which quantification of biomolecular interactions is a requisite. The method has matured with respect to general acceptance and application development over recent years. The number of publications on ITC has grown exponentially over the last 10 years, reflecting the general utility of the method. Here all the published works of the year 2002 in this area have been surveyed. We review the broad range of systems to which ITC is being directed and classify these into general areas highlighting key publications of interest. This provides an overview of what can be achieved using this method and what developments are likely to occur in the near future.

Barriers to nonviral gene delivery

The use of various synthetic lipids and polymers to deliver DNA for gene therapy applications has been the subject of intense examination for the last 15 years. Our understanding of the processes involved in the delivery of DNA, although still limited, can be described in terms of specific physical and chemical barriers encountered along the delivery pathway. Successful engagement of this pathway involves avoiding inactivation in the extracellular compartment and initial favorable interactions with the cell surface. Internalization of the delivery system by endocytosis results in a poorly defined endosomal trafficking process which, if not escaped, leads to degradation of the therapeutic DNA in lysosomes. For the small fraction of material that is able to escape this vesicular trafficking pathway, the cytosol provides additional physical and metabolic barriers to further trafficking to the nucleus. Finally, nuclear uptake has been demonstrated to be a significant barrier to gene delivery. In this review, we outline in greater detail the various processes involved in each step and describe various formulation variables that have been explored to overcome these delivery barriers to nonviral gene delivery.