Polylysine activates membrane-bound adenylyl cyclase from Xenopus laevis oocytes through the Gs transducing protein

Influence of Poly(Amino Acid) Composition on the Complexation of Plasmid DNA and Transfection Efficiency

Random copolymers of poly[(Lys, Ala) 1: 1], poly[(Lys, Ala) 2: 1], poly[(Lys, Ala) 3: 1], poly[(Lys, Ser) 3: 1] and poly[(Arg, Ser) 3: 1] (ratios designate the feed comonomer composition), were complexed with plasmid DNA pRL CMV luc at different weight per weight DNA: polymer ratios. The physicochemical properties of the complexes were evaluated by gel retardation assay, Zeta potential measurements and photon correlation spectroscopy. The extent of DNA protection against nucleases was determined by a nuclease assay. Cell viability and transfection efficiency of the DNA/polymer complexes were determined by MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-4-sulfophenyl)-2-H -tetrazolium) and luciferase assays, respectively. Regardless of the amino acid feed composition, neutral complexes were formed between 2: 1 and 1: 1 DNA: polymer ratios. The particle sizes of the complexes were in the range of 100-300 nm with complexes with more DNA gave a larger particle size than those with a higher proportion of polymer. Compared to other copolymers, lower amounts of poly[(Lys, Ser) 3: 1] were required to protect the DNA against degradation. The presence of arginine residues increased the transfection efficiency of the complexes by 2-3 orders of magnitude. Results suggest that the amino acid composition of the copolymers has an impact on protection of DNA against degradation by the nucleases, cytotoxicity and transfection efficiency.

Polyhistidine-PEG:DNA nanocomposites for gene delivery

Complexation of plasmid DNA with polycations is a popular method by which to transfer therapeutic nucleic acid sequences to cells. One caveat of the approach is that the positive zeta potential of the complexes facilitates interaction with blood constituents, leading to serum protein adsorption and complement activation. As a countermeasure, investigators have developed polycations combined with polyethylene glycol (PEG) to create complexes with reduced protein adsorption potential. We have designed and synthesized PEG-polyhistidine conjugates to evaluate the material class as potential gene delivery vehicles. Two conjugate architectures (comb-shaped and linear A-B block copolymers) were synthesized and formulated with plasmid DNA. The complexes were characterized with respect to DNA complexation capacity, hydrodynamic diameter, zeta potential, in vitro cytotoxicity and transfection capacity in a model cell line. PEG content of the conjugate significantly influenced the hydrodynamic diameter of the DNA:conjugate composite in aqueous solution. For comb-shaped conjugates steric hindrance attributed to PEG led to a direct relationship between the PEG content and the complex size. Both architectures could condensed plasmid DNA into complexes with hydrodynamic diameters <150 nm. Complexation of DNA with the polyhistidine-PEG conjugates resulted in nanocomposites with negative zeta potentials that retarded DNase I-mediated hydrolysis, and all conjugates showed low cytotoxicity to macrophages cultured in vitro. The transfection efficiency was approximately equivalent to DNA:polylysine complexes. The formulation characteristics and low cytotoxicity suggest that polyhistidine-PEG conjugates may be useful for gene delivery.

Polymer-based gene delivery with low cytotoxicity by a unique balance of side-chain termini

Protein expression after delivery of plasmid DNA to the cell nucleus depends on the processes of transcription and translation. Cytotoxic gene-delivery systems may compromise these processes and limit protein expression. This situation is perhaps most prevalent in current nonviral polycationic gene-delivery systems in which the polycationic nature of the delivery system can lead to cytotoxicity. To approach the problem of creating nontoxic but effective gene-delivery systems, we hypothesized that by optimizing the balance between polymer cationic density with endosomal escape moieties, effective gene transfer with low cytotoxicity could be created. As a model system, we synthesized a series of polymers whose side-chain termini varied with respect to the balance of cationic centers and endosomal escape moieties. Specifically, by polymer-analogous amidation we conjugated imidazole groups to the epsilon-amines of polylysine in varying mole ratios (73.5 mol % imidazole, 82.5 mol % imidazole, and 86.5 mol % imidazole). The primary epsilon-amine terminus of polylysine served as a model for the cationic centers, whereas the imidazole groups served as a model for the endosomal escape moieties. These polymers condensed plasmid DNA into nanostructures <150 nm and possessed little cytotoxicity in vitro. Transfection efficiency, as measured by luciferase protein expression, increased with increasing imidazole content of the polymers in a nonlinear relationship. The polymer with the highest imidazole content (86.5 mol %) mediated the highest protein expression, with levels equal to those mediated by polyethylenimine, but with little to no cytotoxicity.

Polymer-based gene delivery with low cytotoxicity by a unique balance of side-chain termini

Protein expression after delivery of plasmid DNA to the cell nucleus depends on the processes of transcription and translation. Cytotoxic gene-delivery systems may compromise these processes and limit protein expression. This situation is perhaps most prevalent in current nonviral polycationic gene-delivery systems in which the polycationic nature of the delivery system can lead to cytotoxicity. To approach the problem of creating nontoxic but effective gene-delivery systems, we hypothesized that by optimizing the balance between polymer cationic density with endosomal escape moieties, effective gene transfer with low cytotoxicity could be created. As a model system, we synthesized a series of polymers whose side-chain termini varied with respect to the balance of cationic centers and endosomal escape moieties. Specifically, by polymer-analogous amidation we conjugated imidazole groups to the epsilon-amines of polylysine in varying mole ratios (73.5 mol % imidazole, 82.5 mol % imidazole, and 86.5 mol % imidazole). The primary epsilon-amine terminus of polylysine served as a model for the cationic centers, whereas the imidazole groups served as a model for the endosomal escape moieties. These polymers condensed plasmid DNA into nanostructures <150 nm and possessed little cytotoxicity in vitro. Transfection efficiency, as measured by luciferase protein expression, increased with increasing imidazole content of the polymers in a nonlinear relationship. The polymer with the highest imidazole content (86.5 mol %) mediated the highest protein expression, with levels equal to those mediated by polyethylenimine, but with little to no cytotoxicity.

mu-opioid receptor regulates CFTR coexpressed in Xenopus oocytes in a cAMP independent manner

The objective of this study was to characterize the signaling mechanisms of the mu-opioid receptor in its coupling to the cystic fibrosis transmembrane conductance regulator (CFTR) when coexpressed in Xenopus oocytes. Because oocytes do not contain endogenous cAMP-regulated ion channels, the cAMP-modulated CFTR was coexpressed with receptors as a 'reporter' channel. Agonist treatment of oocytes coexpressing mu-opioid receptors, beta2-adrenergic receptors and CFTR produced Cl- currents in a dose-related manner and immunocytochemical analysis confirmed receptor expression. These data suggest that opioid agonists could activate adenylyl cyclase in this system to elevate cAMP levels. Heterotrimeric G protein betagamma-subunits acting on adenylyl cyclase type II would increase cAMP levels. The probable presence of adenylyl cyclase type II and other components of opioid signal transduction such as G(i alpha2), were demonstrated by RT-PCR. However, measurement of cAMP levels in individual oocytes by radioimmunoassay showed that opioid agonist application to oocytes expressing mu-opioid receptors, beta2-adrenergic receptors and CFTR did not increase cAMP levels, whereas application of the beta2-adrenergic agonist, isoproterenol, or IBMX alone did increase cAMP levels. Opioid-induced CFTR activation was not affected by either application of the broad spectrum kinase inhibitor, H7, nor by application of the specific PKA inhibitor, KT5720. Injection of free betagamma-subunits, which could activate the endogenous type II cyclase, was unable to produce measurable currents in oocytes expressing the CFTR. These studies indicate that opioid activation of the CFTR is not mediated through a cAMP/PKA pathway, by either betagamma-subunit activation of an adenylyl cyclase type II or promiscuous coupling to G(s alpha).