Biomedical subjects

D Scherman

Publications and source records attributed to D Scherman.

At least 55 records · Page 3Linked to original sources

PubMed1999

High-efficiency gene transfer into skeletal muscle mediated by electric pulses.

Gene delivery to skeletal muscle is a promising strategy for the treatment of muscle disorders and for the systemic secretion of therapeutic proteins. However, present DNA delivery technologies have to be improved with regard to both the level of expression and interindividual variability. We report very efficient plasmid DNA transfer in muscle fibers by using square-wave electric pulses of low field strength (less than 300 V/cm) and of long duration (more than 1 ms). Contrary to the electropermeabilization-induced uptake of small molecules into muscle fibers, plasmid DNA has to be present in the tissue during the electric pulses, suggesting a direct effect of the electric field on DNA during electrotransfer. This i.m. electrotransfer method increases reporter and therapeutic gene expression by several orders of magnitude in various muscles in mouse, rat, rabbit, and monkey. Moreover, i.m. electrotransfer strongly decreases variability. Stability of expression was observed for at least 9 months. With a pCMV-FGF1 plasmid coding for fibroblast growth factor 1, this protein was immunodetected in the majority of muscle fibers subjected to the electric pulses. DNA electrotransfer in muscle may have broad applications in gene therapy and in physiological, pharmacological, and developmental studies.

Animals↗

PubMed1999

Structural characteristics of supramolecular assemblies formed by guanidinium-cholesterol reagents for gene transfection.

We have recently discovered that cationic cholesterol derivatives characterized by guanidinium polar headgroups are very efficient for gene transfection in vitro and in vivo. In spite of being based on some rationale at the molecular level, the development of these new synthetic vectors was nevertheless empirical. Indeed, the factors and processes underlying cationic lipid-mediated gene transfer are still poorly understood. Thus, to get a better insight into the mechanisms involved, we have examined the supramolecular structure of lipid/DNA aggregates obtained when using reagent bis(guanidinium)-tren-cholesterol (BGTC), either alone or as a liposomal formulation with the neutral phospholipid dioleoyl phosphatidylethanolamine (DOPE). We here report the results of cryotransmission electron microscopy studies and small-angle x-ray scattering experiments, indicating the presence of multilamellar domains with a regular spacing of 70 A and 68 A in BGTC/DOPE-DNA and BGTC-DNA aggregates, respectively. In addition, DNA lipoplexes with similar lamellar patterns were detected inside transfected HeLa cells by conventional transmission electron microscopy. These results suggest that DNA condensation by multivalent guanidinium-cholesterol cationic lipids involves the formation of highly ordered multilamellar domains, the DNA molecules being intercalated between the lipid bilayers. These results also invite further investigation of the intracellular fate of the internalized lipid/DNA structures during their trafficking toward the cell nucleus. The identification of the basic features of active complexes should indeed help in the design of improved guanidinium-based vectors.

Cholesterol↗

PubMed1999

Intracellular fate and nuclear targeting of plasmid DNA.

One of the major steps limiting nonviral gene transfer efficiency is the entry of plasmid DNA from the cytoplasm into the nucleus of the transfected cells. The nuclear localization signal (NLS) of the SV40 large T antigen is known to efficiently induce nuclear targeting of proteins. We have developed two chemical strategies for covalent coupling of NLS peptides to plasmid DNA. One method involves a site-specific labeling of plasmid DNA by formation of a triple helix with an oligonucleotide NLS peptide conjugate. After such modification with one NLS peptide per plasmid molecule, plasmid DNA remained fully active in cationic lipid-mediated transfection. In the other method, we randomly coupled 5-115 p-azidotetrafluorobenzyllissamine-NLS peptide molecules per plasmid DNA by photoactivation. Oligonucleotide-NLS and plasmid lissamine-NLS conjugates interacted specifically with the NLS-receptor importin alpha. Plasmid-lissamine-NLS conjugates were not detected in the nucleus, after cytoplasmic microinjection. Plasmids did not diffuse from the site of injection and plasmid-lissamine-NLS conjugates appeared to be progressively degraded in the cytoplasm. The process of plasmid DNA sequestration/degradation stressed in this study might be as important in limiting the efficiency of nonviral gene transfer as the generally recognized entry step of plasmid DNA from the cytoplasm into the nucleus.

3T3 Cells↗

PubMed1999

Synthetic DNA-compacting peptides derived from human sequence enhance cationic lipid-mediated gene transfer in vitro and in vivo.

Cationic lipids can deliver genes efficiently in vitro, but are generally inhibited by the presence of serum, and their efficiency in vivo is much lower than in vitro. An attractive strategy is to induce strong DNA compaction by its association with proteins, before addition of lipids. However the use of whole proteins might present both production and immunological limitations. We have devised a system in which DNA is associated with short peptides derived from human histone or protamine, before the addition of a cationic lipid or polymer. Peptides strongly associating with DNA confer to such peptide-DNA-lipid particles an enhanced in vitro transfection efficiency over that observed with classical DNA/lipid lipoplexes, and particularly confer the capacity to transfect in the presence of serum. This acquisition of serum resistance is cell type-independent, and observed with all four lipopolyamines tested and polyethylenimine. Precompacting DNA with a histone H1-derived peptide enhances cationic lipid RPR 115335-mediated gene transfer in an in vivo model of Lewis lung carcinoma. Apart from their use in peptide-DNA-lipid association, such peptides could be useful as part of chimeric gene delivery vectors presenting a DNA-binding moiety that can be easily associated with other functional domains.

3T3 Cells↗

PubMed1999

Minicircle: an improved DNA molecule for in vitro and in vivo gene transfer.

Minicircles are a new form of supercoiled DNA molecule for nonviral gene transfer which have neither bacterial origin of replication nor antibiotic resistance marker. They are thus smaller and potentially safer than the standard plasmids currently used in gene therapy. They were obtained in E. coli by att site-specific recombination mediated by the phage lambda integrase, which was used to excise the expression cassette from the unwanted plasmid sequences. We produced two minicircles containing the luciferase or beta-galactosidase gene under the control of the strong human cytomegalovirus immediate-early enhancer/promoter. Comparing maximal differences, these minicircles gave 2.5 to 5.5 times more reporter gene activity than the unrecombined plasmid in the NIH3T3 cell line and rabbit smooth muscle cells. Moreover, injection in vivo into mouse cranial tibial muscle, or human head and neck carcinoma grafted in nude mice resulted in 13 to 50 times more reporter gene expression with minicircles than with the unrecombined plasmid or larger plasmids. Histological analysis in muscle showed there were more transfected myofibers with minicircles than with unrecombined plasmid.

3T3 Cells↗

PubMed1999

pCOR: a new design of plasmid vectors for nonviral gene therapy.

A totally redesigned host/vector system with improved properties in terms of safety has been developed. The pCOR plasmids are narrow-host range plasmid vectors for nonviral gene therapy. These plasmids contain a conditional origin of replication and must be propagated in a specifically engineered E. coli host strain, greatly reducing the potential for propagation in the environment or in treated patients. The pCOR backbone has several features that increase safety in terms of dissemination and selection: (1) the origin of replication requires a plasmid-specific initiator protein, pi protein, encoded by the pir gene limiting its host range to bacterial strains that produce this trans-acting protein; (2) the plasmid's selectable marker is not an antibiotic resistance gene but a gene encoding a bacterial suppressor tRNA. Optimized E. coli hosts supporting pCOR replication and selection were constructed. High yields of supercoiled pCOR monomers were obtained (100 mg/l) through fed-batch fermentation. pCOR vectors carrying the luciferase reporter gene gave high levels of luciferase activity when injected into murine skeletal muscle.

Drug Design↗

PubMed1998

Cationic lipid-mediated gene transfer: effect of serum on cellular uptake and intracellular fate of lipopolyamine/DNA complexes.

Most of the cationic lipids used for gene transfer experiments drastically lose their efficiency in the presence of serum. We used a cationic lipid with a spermine head group and its fluorescent analog to study the cellular uptake and the intracellular fate of lipoplexes in the presence and absence of serum. We found that the amount of DNA and lipid taken up by the cells was not related to the efficacy of the gene transfer. When the lipofection was performed in the presence of serum, lipoplexes were contained within small intracellular vesicles. In the absence of serum, the vesicles were larger and heterogeneous in size and shape. By analysis of their size distribution, we showed that lipoplexes preformed in the absence of serum tended to aggregate. This aggregation was inhibited in the presence of serum. We used a carbonate formulation that led to the preformation of large particles: those large particles gave a high lipofection efficiency in the presence of serum and their intracellular distribution was identical to that observed in the absence of serum.

3T3 Cells↗

PubMed1998

Synthesis, activity, and structure--activity relationship studies of novel cationic lipids for DNA transfer.

We have designed and synthesized original cationic lipids for gene delivery. A synthetic method on solid support allowed easy access to unsymmetrically monofunctionalized polyamine building blocks of variable geometries. These polyamine building blocks were introduced into cationic lipids. To optimize the transfection efficiency in the novel series, we have carried out structure-activity relationship studies by introduction of variable-length lipids, of variable-length linkers between lipid and cationic moiety, and of substituted linkers. We introduce the concept of using the linkers within cationic lipids molecules as carriers of side groups harboring various functionalities (side chain entity), as assessed by the introduction of a library composed of cationic entities, additional lipid chains, targeting groups, and finally the molecular probes rhodamine and biotin for cellular traffic studies. The transfection activity of the products was assayed in vitro on Hela carcinoma, on NIH3T3, and on CV1 fibroblasts and in vivo on the Lewis Lung carcinoma model. Products from the series displayed high transfection activities. Results indicated that the introduction of a targeting side chain moiety into the cationic lipid is permitted. A primary physicochemical characterization of the DNA/lipid complexes was demonstrated with this leading compound. Selected products from the series are currently being developed for preclinical studies, and the labeled lipopolyamines can be used to study the intracellular traffic of DNA/cationic lipid complexes.

3T3 Cells↗

PubMed1998

Production of a new DNA vehicle for gene transfer using site-specific recombination.

Supercoiled DNA molecules, minicircles, were produced by in vivo site-specific recombination. They contained exclusively the desired excisable fragment. Recombination was driven by bacteriophage lambda integrase from a plasmid substrate containing the attP and attB recombination sites in the same orientation. Conditions for minicircle production within the lysogen Escherichia coli D1210HP were optimised. Up to 1.5 mg minicircles could be produced per litre bacterial culture, and the remaining, unrecombined plasmid comprised less than about 15% of the minicircle produced. However minicircle multimers were also produced, and comprised up to 30% of all minicircles synthesised. The par ABCDE' locus from plasmid RK2 was introduced into the minicircle fragment, resulting in minicircle dimers being reduced to less than 2% of all minicircles. The par A gene encodes a resolvase that catalyses recombination at the multimer resolution site in the parABCDE' locus. Minicircle multimers were also resolved when par A was introduced downstream from the integrase gene of the lambda pL transcript in D1210HP together with a multimer resolution site carried by the minicircle fragment.

DNA, Circular↗

PubMed1998

Long-term, high level in vivo gene expression after electric pulse-mediated gene transfer into skeletal muscle.

Gene delivery to skeletal muscle is a promising strategy for the treatment of muscle disorders and for the local or systemic secretion of therapeutic proteins. However, current DNA delivery technologies have to be improved. We report very efficient luciferase gene transfer into muscle fibres obtained through the delivery of square-wave electric pulses of moderate field strength (100-200 V/cm) and of long duration (20 ms) to muscle previously injected with plasmid DNA. This intramuscular 'electrotransfer' method increases reporter gene expression by more than 100 times. It is noteworthy that this expression remains high and stable for at least 9 months. Moreover, intramuscular electrotransfer strongly decreases the interindividual variability usually observed after plasmid DNA injection into muscle fibres. Therefore, DNA electrotransfer in muscle possesses broad potential applications in gene therapy and for physiological, pharmacological and developmental studies.

Animals↗

PubMed1998

Application of lipids and plasmid design for gene delivery to mammalian cells.

Cationic lipids are widely used for in vitro gene transfer due to their efficiency. The major challenges for the improvement of in vivo cationic lipid-mediated gene delivery reside in the design of more biocompatible lipoplexes mimicking viral-mediated gene delivery and in understanding the fate of the lipoplexes within the cells.

Animals↗

PubMed1998

Cationic lipid-mediated gene transfer: analysis of cellular uptake and nuclear import of plasmid DNA.

Cationic lipids are widely used for gene transfer in vitro and show promise as vectors for in vivo gene therapy applications. However, there is limited understanding of the cellular mechanisms involved in nonviral gene transfer. We investigated two major steps that could be limiting barriers to cationic lipid-mediated gene transfer in vitro. We used a fluorescent plasmid to study the cellular uptake and the intracellular fate of lipoplexes during in vitro transfection of fibroblast cells and found that 100% of the cells take up lipoplexes. The intracellular staining observed with lipoplexes was clearly different from that obtained with endocytosed fluorescent dextran. This suggests that cells readily take up lipoplexes by a mechanism that could be different from endocytosis in our conditions. However, the escape of DNA from intracellular vesicles could be a major limiting barrier to gene transfer. Direct injection of plasmid DNA into the nucleus and cytoplasm of cells indicated that DNA traffic from the cytoplasm to the nucleus might be also an important limiting step.

Animals↗

PubMed1998

Novel non-viral vectors for gene delivery: synthesis of a second-generation library of mono-functionalized poly-(guanidinium)amines and their introduction into cationic lipids.

The development of new gene delivery technologies is a prerequisite towards gene therapy clinical trials. Because gene delivery mediated by viral vectors remains of limited scope due to immunological and propagation risks, the development of new non-viral gene delivery systems is of crucial importance. We have synthesized a secondary library of mono-functionalized poly-(guanidinium)amines generated from a library of mono-functionalized polyamines applying the concept of "libraries from libraries." The method allows a quick and easy access to mono-functionalized geometrically varied poly-(guanidinium)amines. The new building blocks were introduced into cationic lipids to obtain novel poly-(guanidinium)amine lipids, which are potential DNA vectors for gene delivery.

Chlorides↗

PubMed1997

Virus-sized self-assembling lamellar complexes between plasmid DNA and cationic micelles promote gene transfer.

Gene therapy is based on the vectorization of genes to target cells and their subsequent expression. Cationic amphiphile-mediated delivery of plasmid DNA is the nonviral gene transfer method most often used. We examined the supramolecular structure of lipopolyamine/plasmid DNA complexes under various condensing conditions. Plasmid DNA complexation with lipopolyamine micelles whose mean diameter was 5 nm revealed three domains, depending on the lipopolyamine/plasmid DNA ratio. These domains respectively corresponded to negatively, neutrally, and positively charged complexes. Transmission electron microscopy and x-ray scattering experiments on complexes originating from these three domains showed that although their morphology depends on the lipopolyamine/plasmid DNA ratio, their particle structure consists of ordered domains characterized by even spacing of 80 A, irrespective of the lipid/DNA ratio. The most active lipopolyamine/DNA complexes for gene transfer were positively charged. They were characterized by fully condensed DNA inside spherical particles (diameter: 50 nm) sandwiched between lipid bilayers. These results show that supercoiled plasmid DNA is able to transform lipopolyamine micelles into a supramolecular organization characterized by ordered lamellar domains.

DNA, Circular↗

PubMed1997

Triple helix formation on plasmid DNA determined by a size-exclusion chromatographic method.

Triple-helix-forming oligodeoxynucleotides are receiving considerable attention due to their potential applications for the inhibition of specific genes in vivo. However, their development is impaired by the lack of triple helix formation under physiological conditions. It is thus crucial to be able to quantitatively assay triple helix formation of various oligodeoxynucleotides on different target sequences. Usual methods to detect triple helix formation are restricted under the experimental conditions that can be studied. In addition, quantitative techniques are limited. We present a novel method for rapid detection and quantification of triple helix formation between an oligodeoxynucleotide and a plasmid carrying a target sequence. The oligodeoxynucleotide was radiolabeled and, after incubation with the target plasmid, the unbound oligodeoxynucleotide was separated from the mixture of plasmids and plasmid-bound oligodeoxynucleotides by rapid gel filtration spun columns. The formation of a triple helix between a target plasmid and several oligodeoxynucleotides was demonstrated and compared. Temperature, sequence and ionic dependencies, and kinetics of association were analyzed. This new technique can be used under a variety of conditions and should allow the rapid determination of optimal conditions required for triple helix formation, as well as the easy selection of an oligodeoxynucleotide that specifically binds with the highest affinity to a target double-stranded sequence.

Cations↗

PubMed1997

Synthesis of O-methylsulfonyl derivatives of D-glucose as potential alkylating agents for targeted drug delivery to the brain. Evaluation of their interaction with the human erythrocyte GLUT1 hexose transporter.

In order to obtain hydrophilic analogues of 1,4-dimethylsulfonyloxybutane (busulfan) with enhanced selectivity and improved brain penetration, we have synthesized 6-O-methylsulfonyl-D-glucose, 3-O-methylsulfonyl-D-glucose, 3,6-di-O-methylsulfonyl-D-glucose, 4-O-methylsulfonyl-D-glucose, and 4,6-di-O-methylsulfonyl-D-glucose, and we have studied their interactions with the human erythrocyte GLUT1 hexose transport system. Mesylation of OH-4 and OH-6 of glucose resulted in a slightly diminished affinity for the GLUT1 glucose transporter, whereas mesylation of OH-3 led to complete loss of affinity.

Antineoplastic Agents, Alkylating↗

PubMed1997

Synthesis and conformational analysis of peptide inhibitors of farnesyltransferase.

Farnesylation of the ras oncogene product by Farnesyl Transferase (FTase) is known to be a critical step in cell transformation leading to uncontrolled proliferation. The peptide CysValTicMet is a potent FTase inhibitor, but its degradation by amino-peptidases and its only weak internalization into cells make it a bad candidate for a future cancer drug. We have prepared improved CysValTicMet analogues using several approaches: (i) amino terminal modifications or introduction of pseudopeptides or non-natural amino acids to increase proteolytic stability, (ii) introduction of hydrophobic aliphatic chains to increase cell internalization and metabolic stability and (iii) transformation into prodrugs. Additionally, we have carried out comparative conformational analysis studies by molecular dynamics of some of the here presented peptides and of our recently described peptidomimetic inhibitors of FTase.

Alkyl and Aryl Transferases↗

PubMed1997

Efficient purification of plasmid DNA for gene transfer using triple-helix affinity chromatography.

Plasmid DNA used for nonviral therapeutic gene transfer or nucleic acid vaccination has to be highly purified devoid of contaminating components such as bacterial proteins, endotoxins, or bacterial chromosomal DNA. We have developed a new affinity chromatography technique for plasmid DNA purification: triple-helix affinity chromatography (THAC). This technique is based on the sequence-specific interaction of an oligonucleotide forming a triple-helix with plasmid DNA. The oligonucleotide was covalently linked to a chromatographic matrix, thus providing a reusable affinity support. By inserting a suitable homopurine sequence in the plasmid DNA, it is possible to obtain a triple-helix interaction that will only be stable at mild acidic pH and that will dissociate in alkaline conditions. A crude lysate from a recombinant E. coli, or a pre-purified plasmid DNA, is thus applied at acidic pH on to a THAC column. After extensive washing of the column, purified plasmid DNA is eluted using an alkaline buffer. The binding conditions of the plasmid DNA on to the column have been optimized, as well as the hybridization sequence and the linker group between the matrix and the third strand oligonucleotide. The THAC technique makes it possible to purify in one step supercoiled plasmid DNA, and to significantly reduce the level of contaminating RNA, endotoxins and chromosomal DNA. In particular, a 100-fold reduction of chromosomal DNA contamination over that obtained with conventional techniques can be achieved through a single additional THAC step. Further improvements of THAC technology are possible, and we anticipate that this technique can be scaled up for integration into a full commercial-scale DNA production process.

3T3 Cells↗