Synthesis of poly(propylene glycol)-block-polyethylenimine triblock copolymers for the delivery of nucleic acids

LPEIs, which are efficient DNA transfection agents, were found to be far less effective for the delivery of siRNAs. Here, two amphiphilic triblock copolymers LPEI(50) -b-PPG(36) -b-LPEI(50) (2) and LPEI(14) -b-PPG(68) -b-LPEI(14) (4) have been synthesized. The transfection assays showed that compound 2 was efficient for DNA transfection whilst it was almost inactive for siRNA delivery. In contrast, polymer 4 was inefficient for DNA transfection while it showed capabilities for siRNA delivery. Taken together, our results indicate that the properties required for DNA and siRNA delivery are different. Moreover, we show that introduction of a hydrophobic segment that allows self-assembly confers siRNA delivery capacities.

Investigation of DNA condensing properties of amphiphilic triblock cationic polymers by atomic force microscopy

Introduction of nucleic acids into cells is an important biotechnology research field which also holds great promise for therapeutic applications. One of the key steps in the gene delivery process is compaction of DNA into nanometric particles. The study of DNA condensing properties of three linear cationic triblock copolymers poly(ethylenimine-b-propylene glycol-b-ethylenimine), namely, LPEI(50)-PPG(36)-LPEI(50), LPEI(19)-PPG(36)-LPEI(19), and LPEI(14)-PPG(68)-LPEI(14), indicates that proper DNA condensation is driven by both the charge and the size of the respective cationic hydrophilic linear polyethylenimine (LPEI) and neutral hydrophobic poly(propylene glycol) (PPG) parts. Atomic force microscopy was used to investigate the interactions of the triblock copolymers with plasmid DNA at the single molecule level and to enlighten the mechanism involved in DNA condensation.

Amphiphilic Poly[(propylene glycol)-block-(2-methyl-2-oxazoline)] Copolymers for Gene Transfer in Skeletal Muscle

Amphiphilic triblock copolymers such as poly(ethylene glycol-b-propylene glycol-b-ethylene glycol) PE6400 (PEG(13)-PPG(30)-PEG(13)) have been recently shown to promote gene transfer in muscle. Herein we investigated the effect of a chemical change of the PEG moiety on the transfection activity of these compounds. We synthesized new amphiphilic copolymers in which the PEG end blocks are replaced by more hydrophilic poly(2-methyl-2-oxazoline) (PMeOxz) chains of various lengths. The resulting triblock PMeOxz-PPG-PMeOxz compounds were characterized by NMR, SEC, TGA, and DSC techniques and assayed for in vivo muscle gene transfer. The results confirm both the block structure and the monomer unit composition (DP(PG)/DP(MeOxz)) of the new PPG(34)-PMeOxz(41) and PPG(34)-PMeOxz(21) triblock copolymers. Furthermore, in vivo experiments show that these copolymers are able to significantly increase DNA transfection efficiency, despite the fact that their chemical nature and hydrophilic character are different from the poloxamers. Overall, these results show that the capacity to enhance DNA transfection in skeletal muscle is not restricted to PEG-PPG-PEG arrangements.

Synthesis, characterization, and gene transfer application of poly(ethylene glycol-b-ethylenimine) with high molar mass polyamine block

The study of ethyloxazoline/methyloxazoline (EtOXZ/MeOXZ) copolymerization, initiated by methyl tosylate (MeOTs), showed that (i) incorporation of MeOXZ units into random copolymer becomes effective over DP = 100 and (ii) propagation process proceeds with negligible transfer to monomer up to a DP of 400 despite the presence of MeOXZ in the polymerization medium. These results produced random poly(EtOXZ-co-MeOXZ) copolymers with various molar composition ratios in alkyloxazoline units. The close values found for the comonomer reactivity ratios in acetonitrile (r(1MeOXZ) = 1.18; r(2EtOXZ) = 0.34) implied a random chain organization in short sequences of each repeating unit, which was an important parameter in view of the optimization of their subsequent modification: the alkaline hydrolysis was successfully achieved when the MeOXZ unit content of the polyoxazoline chains reached 75%. Using these results, the diblock copolymer poly(ethylene glycol-b-(ethyloxazoline-co-methyloxazoline)) (poly(EG-b-(EtOXZ-co-MeOXZ))) with high DP was synthesized by cationic copolymerization of EtOXZ/MeOXZ comonomers using CH(3)-PEG(2kDa)-Ts as macroinitiator. The comonomer composition of this new compound was adjusted in order to optimize the hydrolysis step and obtain finally the diblock copolymer poly(ethylene glycol-b-ethylenimine) (poly(EG-b-EI)). The high molar mass of this copolymer was confirmed both by (1)H NMR and SANS measurements. Gene delivery experiments showed that the copolymer has significant DNA transfection capacities.

Linear Topology Confers in Vivo Gene Transfer Activity to Polyethylenimines

Although polyethylenimines (PEIs) are frequently used transfection agents, it is still unclear which of their properties are required for efficient gene delivery. This is even more striking when working in vivo since some PEIs are able to generate significant gene expression, whereas others are not. To facilitate a rational development of compounds with improved transfection activities, studies aimed at identifying the properties involved in the transfection process seem indispensable. In the present work, we investigated how transfection with linear PEI of 22 kDa allows for high reporter gene expression in lungs after intravenous injection, whereas the branched PEI of 25 kDa does not. To this end, we synthesized L-PEI derivatives that are intermediates between linear and branched PEIs. Our results show that the topology plays a crucial role in obtaining in vivo reporter gene expression, whereas the content of primary, secondary, and tertiary amines is only of minor importance.

Synthesis of linear polyethylenimine derivatives for DNA transfection

A series of linear polymers containing varying amounts of ethylenimine or N-propylethylenimine units were synthesized by hydrolysis and/or reduction of polyethyloxazolines. The pK(a)s of the polyamines were determined potentiometrically. Gel mobility shift assay showed that the efficiency of DNA complexation was related to the fraction of amino groups that are protonated at neutral pH. The effects of cationic charge density and molar weight of the polymers on the transfection efficiency were evaluated on HepG2 cells. The results obtained with different copolymers show that the transfection efficiency primarily depends on the fraction of ethylenimine units included in the polymer albeit the molar weight is also of importance. On the basis of the results obtained with poly(N-propylethylenimines), we also demonstrate that the high transfection efficiency of polyethylenimines does not solely rely on their capacity to capture protons which are transferred into the endo-lysosomes during acidification.

Dns-Gly-(p-NO2)Phe-beta Ala, a specific fluorogenic substrate for neutral endopeptidase 24.11

A novel fluorogenic peptide, dansyl-Gly-(p-NO2) Phe-beta Ala (DGNPA), was synthesized as a selective substrate for neutral endopeptidase 24.11, an enzyme involved in enkephalin and atrial natriuretic peptide degradation and a marker of differentiation (CD10) on the surface of lymphohematopoietic cells. Cleavage of the substrate Gly-(p-NO2)Phe amide bond leads to an increase in fluorescence related to the disappearance of the intramolecular quenching of the dansyl fluorescence by the nitrophenyl residue. This new fluorogenic substrate is an improvement over the commercially available dansyl-D-Ala-Gly-(p-NO2)Phe-Gly, as the Gly4 residue of the latter has been replaced by a beta-alanine, therefore eliminating a residual sensitivity of the peptide toward angiotensin converting enzyme. Moreover, deletion of the D-Ala2 residue was shown to increase the quenching efficiency, thus raising the sensitivity of the assay, which was further improved by stopping the reaction with dioxane. The present substrate has improved affinity (Km = 37 microM, V = 0.72 mumol min-1 mg protein-1), selectivity, and sensitivity over its precursor and was used in automated assays using 96-well microplates and a fluorescence plate reader.

Investigation of the structural parameters involved in the delta-opioid selectivity of several families of opioid peptides

Three series of highly delta-opioid selective peptides are now available, and each family is used as template to investigate the structural parameters involved in delta-receptor recognition and in the modulation of the selectivity of the parent peptide. The first series includes cyclic derivatives such as Tyr-D-Pen-Gly-Phe-D-Pen(DPDPE) and Tyr-D-Pen-Gly-Phe-Pen(DPLPE); the second are the synthetic linear constrained peptides [Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr(DSTBULET), Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr (OtBu)(BUBU) and especially Tyr-D-Cys(StBu)-Gly-Phe-Leu-Thr(OtBu) (BUBUC)] and the last one the natural peptides [Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2 (deltorphin or dermenkephalin) and Tyr-D-Ala-Phe-Asp-Val-Val-GlyNH2 ([D-Ala2] deltorphin I)]. In the present study, the possibly of transposing some of the decisive factors of delta-selectivity evidenced in the two other families, to the linear constrained peptides series was examined. With this aim in view, residues such as Phe3, pClPhe4 or Asp were introduced in the sequence of DSTBULET, BUBU or BUBUC. Direct comparison between the biochemical profiles of the [pClPhe4] analogs of the linear constrained peptides and their parent compounds shows that the addition of an electronegative atom on the Phe4 residue of enkephalin sequences is not an absolute parameter for delta-selectivity improvement. The hydrophobic delta-receptor subsite seems able to receive a range of molecular volumes and electronegativities. By contrast, this subsite cannot interact with a Phe3 aromatic ring introduced in this series of peptides. Moreover, the results obtained with linear peptides including additional negatively charged residues demonstrate that the proposed location of the delta-receptors in a cationic membrane environment is not adequate to explain the selectivity profile of a number of compounds.