Peptide-mediated gene delivery: influence of peptide structure on gene expression

Cationic peptides possessing a single cysteine, tryptophan, and lysine repeat were synthesized to define the minimal peptide length needed to mediate transient gene expression in mammalian cells. The N-terminal cysteine in each peptide was either alkylated or oxidatively dimerized to produce peptides possessing lysine chains of 3, 6, 8, 13, 16, 18, 26, and 36 residues. Each synthetic peptide was studied for its ability to condense plasmid DNA and compared to polylysine19 and cationic lipids to establish relative in vitro gene transfer efficiency in HepG2 and COS7 cells. Peptides with lysine repeats of 13 or more bound DNA tightly and produced condensates that decreased in mean diameter from 231 to 53 nm as lysine chain length increased. In contrast, peptides possessing 8 or fewer lysine residues were similar to polylysine19, which bound DNA weakly and produced large (0.7-3 microns) DNA condensates. The luciferase expression was elevated 1000-fold after HepG2 cells were transfected with DNA condensates prepared with alkylated Cys-Trp-Lys18 (AlkCWK18) versus polylysine19. The gene transfer efficiencies of AlkCWK18 and cationic lipids were equivalent in HepG2 cells but different by 10-fold in COS 7 cells. A 40-fold reduction in particle size and a 1000-fold amplification in transfection efficiency for AlkCWK18 DNA condensates relative to polylysine19 DNA condensates suggest a contribution from tryptophan that leads to enhanced gene transfer properties for AlkCWK18. Tryptophan-containing cationic peptides result in the formation of small DNA condensates that mediate efficient nonspecific gene transfer in mammalian cells. Due to their low toxicity, these peptides may find utility as carriers for nonspecific gene delivery or may be developed further as low molecular weight DNA condensing agents used in targeted gene delivery systems.

Stability of peptide-condensed plasmid DNA formulations

Low molecular weight homogeneous peptides were used to form peptide/DNA condensates. A peptide possessing 18 lysines was found to protect plasmid DNA from serum endonuclease and sonicative-induced degradation whereas a shorter peptide possessing 8 lysines dissociated in 0.1 M sodium chloride and failed to protect DNA from enzymatic degradation. Peptide-condensed DNA showed no change in the ratio of supercoiled to circular DNA following 100 W sonication for up to 60 s and was able to transfect HepG2 cells with equivalent efficiency as untreated condensed plasmid DNA. Alternatively, uncondensed plasmid DNA was rapidly fragmented by sonication and serum endonucleases and resulted in negligible gene expression following condensation with peptide. Cationic lipid/DNA complexes were only partially effective at stabilizing DNA in serum compared to the complete stabilization afforded by peptide/DNA condensation. These results indicate that the stabilization afforded by condensation with a peptide protects DNA during formulation and preserves its structure in serum. These functions are important to achieve optimal gene expression from a nonviral gene delivery system.

Comparative gene transfer efficiency of low molecular weight polylysine DNA-condensing peptides

In a previous report (M.S. Wadhwa et al. (1997) Bioconjugate Chem. 8, 81-88), we synthesized a panel of polylysine-containing peptides and determined that a minimal repeating lysine chain of 18 residues followed by a tryptophan and an alkylated cysteine residue (AlkCWK18) resulted in the formation of optimal size (78 nm diameter) plasmid DNA condensates that mediated efficient in vitro gene transfer. Shorter polylysine chains produced larger DNA condensates and mediated much lower gene expression while longer lysine chains were equivalent to AlkCWK18. Surprisingly, AlkCWK18 (molecular weight 2672) was a much better gene transfer agent than commercially available low molecular weight polylysine (molecular weight 1000-4000), despite its similar molecular weight. Possible explanations were that the cysteine or tryptophan residue in AlkCWK18 contributed to the DNA binding and the formation of small condensates or that the homogeneity of AlkCWK18 relative to low molecular weight polylysine facilitated optimal condensation. To test these hypotheses, the present study prepared AlkCYK18 and K20 and used these to form DNA condensates and conduct in vitro gene transfer. The results established that DNA condensates prepared with either AlkCYK18 or K20 possessed identical particle size and mediated in vitro gene transfer efficiencies that were indistinguishable from AlkCWK18 DNA condensates, eliminating the possibility of contributions from cysteine or tryptophan. However, a detailed chromatographic and electrospray mass spectrometry analysis of low molecular weight polylysine revealed it to possess a much lower than anticipated average chain length of dp 6. Thus, the short chain length of low molecular weight polylysine explains its inability to form small DNA condensates and mediate efficient gene transfer relative to AlkCWK18 DNA condensates. These experiments further emphasize the need to develop homogenous low molecular weight carrier molecules for nonviral gene delivery.

Biodistribution, metabolism, and in vivo gene expression of low molecular weight glycopeptide polyethylene glycol peptide DNA co-condensates

The biodistribution, metabolism, cellular targeting, and gene expression of a nonviral peptide DNA gene delivery system was examined. (125)I-labeled plasmid DNA was condensed with low molecular weight peptide conjugates and dosed i.v. in mice to determine the influence of peptide DNA formulation parameters on specific gene targeting to hepatocytes. Optimal targeting to hepatocytes required the combined use of a triantennary glycopeptide (Tri-CWK(18)) and a polyethylene glycol-peptide (PEG-CWK(18)) to mediate specific recognition by the asialoglycoprotein receptor and to reduce nonspecific uptake by Kupffer cells. Tri-CWK(18)/PEG-CWK(18) DNA co-condensates were stabilized and protected from metabolism by glutaraldehyde crosslinking. An optimized formulation targeted 60% of the dose to the liver with 80% of the liver targeted DNA localized to hepatocytes. Glutaraldehyde crosslinking of DNA condensates reduced the liver elimination rate from a t((1/2)) of 0.8 to 3.6 h. An optimized gene delivery formulation produced detectable levels of human alpha1-antitrypsin in mouse serum which peaked at day 7 compared to no expression using control formulations. The results demonstrate the application of formulation optimization to improve the targeting selectivity and gene expression of a peptide DNA delivery system.

Liquid chromatography-tandem mass spectrometric quantitation of cyclophosphamide and its hydroxy metabolite in plasma and tissue for determination of tissue distribution

Cyclophosphamide (CP) and its metabolite, hydroxycyclophosphamide (OH-CP) have been quantitated in mouse plasma and tissue by derivatization combined with liquid chromatography-tandem mass spectrometry (LC-MS-MS). The derivatization was conducted immediately upon sample collection, to trap the OH-CP metabolite intermediate prior to further conversion to phosphoramide mustard or other reaction products. This simple and straightforward derivatization procedure, combined with sample extraction via protein precipitation, allowed quantitation of CP and the oxime derivative of OH-CP in plasma for concentrations ranging from approximately 12.5-3333 ng/ml, and in spleen tissue for concentrations of 1,250-50,000 ng/g. The short cycle time (2.5 min) of the LC-MS-MS method allowed high throughput analysis with minimal matrix interference. Mouse plasma levels were quantitated for doses of 40, 65 and 120 mg/kg; spleen concentrations were determined for mice dosed at 120 mg/kg. The CP and oxime plasma levels correlated well with dose amounts. The CP levels in the spleen and plasma were similar while the oxime levels in the spleen were significantly lower than the plasma.

Virus-free adenocarcinoma of the frog (summer phase tumor) transcribes Lucké tumor herpesvirus-specific RNA

[(3)H]RNA isolated from "virus-free," summer phase, renal adenocarcinomas of Rana pipiens labeled with [(3)H]uridine hybridizes with DNA of herpesvirus particles isolated from the winter phase Lucké tumor. Transcription of the herpesvirus genome in virus-free tumors provides additional evidence for the viral etiology of this tumor.

Animal Health Modeling & Simulation Society: a new society promoting model-based approaches in veterinary pharmacology

The Animal Health Modeling & Simulation Society (AHM&S) is a newly founded association (2012) that aims to promote the development, application, and dissemination of modeling and simulation techniques in the field of Veterinary Pharmacology and Toxicology. The association is co-chaired by Pr. Johan Gabrielsson (Europe), Pr. Jim Riviere (USA), and secretary Dr. Jonathan Mochel (Switzerland). This short communication aims at presenting the membership, rationale and objectives of this group.

Prediction of formulation effects on dermal absorption of topically applied ectoparasiticides dosed in vitro on canine and porcine skin using a mixture-adjusted quantitative structure permeability relationship

Topical application of ectoparasiticides for flea and tick control is a major focus for product development in animal health. The objective of this work was to develop a quantitative structure permeability relationship (QSPeR) model sensitive to formulation effects for predicting absorption and skin deposition of five topically applied drugs administered in six vehicle combinations to porcine and canine skin in vitro. Saturated solutions (20 μL) of (14) C-labeled demiditraz, fipronil, permethrin, imidacloprid, or sisapronil were administered in single or binary (50:50 v/v) combinations of water, ethanol, and transcutol (6 formulations, n = 4-5 replicates per treatment) nonoccluded to 0.64 cm(2) disks of dermatomed pig or dog skin mounted in flow-through diffusion cells. Perfusate flux over 24 h and skin deposition at termination were determined. Permeability (logKp), absorption, and penetration endpoints were modeled using a four-term Abrahams and Martin (hydrogen-bond donor acidity and basicity, dipolarity/polarizability, and excess molar refractivity) linear free energy QSPeR equation with a mixture factor added to compensate for formulation ingredient interactions. Goodness of fit was judged by r(2) , cross-validation coefficient, coefficients (q(2) s), and Williams Plot to visualize the applicability domain. Formulation composition was the primary determinant of permeation. Compounds generally penetrated dog skin better than porcine skin. The vast majority of permeated penetrant was deposited within the dosed skin relative to transdermal flux, an attribute for ectoparasiticides. The best QSPeR logKp model for pig skin permeation (r(2) = 0.86, q(2) s = 0.85) included log octanol/water partition coefficient as the mixture factor, while for dogs (r(2) = 0.91, q(2) s = 0.90), it was log water solubility. These studies clearly showed that the permeation of topical ectoparasiticides could be well predicted using QSPeR models that account for both the physical-chemical properties of the penetrant and formulation components.

Synthesis of homogeneous glycopeptides and their utility as DNA condensing agents

Two glycopeptides were synthesized by attaching purified glycosylamines (N-glycans) to a 20 amino acid peptide. Triantennary and Man9 Boc-tyrosinamide N-glycans were treated with trifluoroacetic acid to remove the Boc group and expose a tyrosinamide amine. The amine group was coupled with iodoacetic acid to produce N-iodoacetyl-oligosaccharides. These were reacted with the sulfhydryl group of a cysteine-containing peptide (CWK18), resulting in the formation of glycopeptides in good yield that were characterized by 1H NMR and ESIMS. Both glycopeptides were able to bind to plasmid DNA and form DNA condensates of approximately 110 nm mean diameter with zeta potential of +31 mV. The resulting homogeneous glycopeptide DNA condensates will be valuable as receptor-mediated gene-delivery agents.