Digoxigenin-labeled phosphorothioate oligonucleotides: a new tool for the study of cellular uptake

Versatile Peptide Dendrimers for Nucleic Acid Delivery

Dendrimers are nonviral vectors that have attracted interest on account of a number of features. They are structurally versatile because their size, shape, and surface charge can be selectively altered. Here we examine the functions of a new family of composite dendrimers that were synthesized with lipidic amino acid cores. These dendrimers are bifunctional because they are characterized by positively charged (lysine) modules for interaction with nucleic acids and neutral lipidic moieties for membrane lipid-bilayer transit. We assessed their structure-function correlations by a combination of molecular and biophysical techniques. Our assessment revealed an unexpected pleitropy of functions subserved by these vectors that included plasmid and oligonucleotide delivery. We also generated a firefly luciferase cell line in which we could modulate luciferase activity by RNA interference. We found that these vectors could also mediate RNA suppression of luciferase expression by delivering double-stranded luciferase transcripts generated in vitro. The structural uniqueness of these lipidic peptide dendrimers coupled with their ease and specificity of assembly and the versatility in their choice of cargo, puts them in a new category of macromolecule carriers. These vectors, therefore, have potential applications as epigenetic modifiers of gene function.

Cellular pathway of plasmids vectorized by cholesterol-based cationic liposomes

We investigated by transmission electron microscopy the cellular route in tumor MCF7 cells of DNA labeled with digoxigenin, carried by cationic liposomes (Lip+) prepared from TMAEC-Chol [3 beta(N-(N',N',N'-trimethylaminoethane)-carbamoyl)cholesterol iodide] and TEAPC-Chol [3 beta(N-(N',N',N'-triethylaminopropane)-carbamoyl)cholesterol iodide], two cholesterol-based cationic lipids containing a quaternary ammonium. In a previous work we showed the pathway of cationic lipid/plasmid complexes from the beginning of endocytosis until their entry into the perinuclear area. Beyond this limit, unlabeled exogenous plasmids cannot be distinguished with nuclear DNA. This work dealt with the cellular fate of cationic liposome-vectorized plasmids labeled with digoxigenin using an immunogold procedure. Early after the beginning of transfection (30 min, 1 hr, 5 hr), gold particles were observed only in the cytoplasm and in endosome-like vesicles, whereas after 24 hr gold particles were densely present in the nucleus. These results demonstrate the nuclear localization of plasmids vectorized by the cationic liposomes used. The results are discussed in comparison with transfection efficiency measurements.

Impaired endocytosis may represent an obstacle to gene therapy in polycystic kidney disease

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease and a frequent cause of chronic renal failure. The cloning of the PKD1 and PKD2 genes, which are mutated in the great majority of patients with this disease, opens up the opportunity for somatic gene therapy by introduction of the wild-type gene or cDNA. Several publications have provided evidence, that many portions of the nephron and the collecting duct can form cysts, including the proximal tubule. Alterations in the proximal tubule may prevent the efficient endocytosis of filtered proteins and thus contribute to proteinuria, a frequent symptom in patients with polycystic kidney disease. At the same time this may also negatively affect various gene therapy strategies, since endocytosis is important for the uptake of foreign DNA at least under some circumstances. In the (cy/+) rat, a widely used animal model for ADPKD, cysts almost exclusively develop from proximal tubules, and we have therefore investigated whether proteinuria and defective endocytosis also occur in this model.

METHODS

Proteinuria was demonstrated by direct measurement and by protein gel electrophoresis of urines from 16 week-old (cy/+) rats. Endocytosis was investigated by injection of FITC-dextran and immunohistochemical staining with anti-ClC-5 and anti-megalin antibodies.

RESULTS

Similar to the observations made in ADPKD patients, proteinuria also develops in the (cy/+) rat. Using FITC-labeled dextran as an in vivo tracer for renal tubular endosomal function, we could show that portions of cyst-lining epithelia from proximal tubules have lost the ability to endocytose, which is necessary for the reabsorption of albumin and lower-molecular-weight proteins. By immunohistochemistry the expression of other proteins implicated in endocytosis, such as the chloride channel ClC-5 and the albumin receptor megalin, correlated well with the presence and absence of FITC-dextran in cyst wall epithelia.

CONCLUSION

These data indicate that proteinuria and albuminuria in the (cy/+) rat model for ADPKD are due to a loss of the endocytic machinery in epithelia of proximal tubular cysts. Such a defect may also reduce the efficacy of certain gene therapy protocols.

Studies on uptake, sub-cellular trafficking and efflux of antisense oligodeoxynucleotides in glioma cells using self-assembling cationic lipoplexes as delivery systems

The cellular uptake of antisense oligodeoxynucleotides (ODNs) may be enhanced by the use of carriers such as cationic liposomes or lipoplexes, but little is known about the intracellular fate and subcellular trafficking of these systems in target cells. In this study, we report on the cellular uptake and biodistribution of ODNs in the presence and absence of optimised self-assembled cationic lipoplexes using the C6 glioma cell line as an in vitro model. Biotin or radiolabelled 15-mer phosphorothioate (PS) ODNs were synthesised and their cellular uptake and subcellular biodistribution characterised in the presence and absence of an optimised cationic lipoplex delivery system using studies ranging from cellular association, cellular efflux and transmission electron microscopy (TEM). Ultrastructural studies clearly showed PS ODNs in the absence of liposomal delivery to be sequestered within endosomal and lysosomal vesicular bodies indicative of endocytic uptake. ODNs were also visible, to a lesser extent, in the nucleus and cytoplasm. By employing DOSPA (2'-(1",2"-dioleoyloxypropyldimethyl-ammonium bromide)-N-ethyl-6-amidospermine tetra trifluoroacetic acid) and DOPE (dioleoylphosphatidylethanolamine) complex in a 3 : 1 ratio, as a delivery system for ODNs at a optimal lipid/DNA charge ratio of 1 : 1, the level of ODN cellular association was significantly increased by approximately 10-12 fold with a concomitant change in subcellular distribution of PS ODN. TEM studies indicated enhanced penetration of ODN within the cytosol and the cell nucleus with reduced presence in vesicular compartments. Efflux studies confirmed that cationic lipoplexes promoted entry of ODNs into 'deeper' cellular compartments, consistent with endosomal release. Optimised cationic lipoplexes improved cellular delivery of ODNs by enhancing cell association, uptake and by favourably modulating the intracellular trafficking and distribution of ODNs into non-vesicular compartments including the cytosol and nucleus.

Decreased bone resorption, osteoclast differentiation, and expression of vacuolar H+-ATPase in antisense DNA-treated mouse metacarpal and calvaria cultures ex vivo

Expression and function of vacuolar H(+)-ATPase, a key enzyme in bone resorption, were monitored in antisense DNA-treated bone organ cultures ex vivo. A novel fluoroimmunoassay was used to quantitate mRNA levels after treatment with various antisense, sense, or random DNA oligonucleotides. Conventional slot blots and in vitro translation experiments were used to monitor the efficiency of the antisense molecules. In cell cultures, the used antisense molecules were transported into osteoclasts and a population of mononuclear cells. A significant decrease in bone resorption and in the expression of the 16 kDa, 31 kDa, 42 kDa, 60 kDa, 70 kDa, and 116 kDa subunits of V-ATPase was seen after antisense treatment. Also, osteoclast differentiation was decreased in antisense-treated mouse metacarpal cultures. These data show that the proper function of V-ATPase in osteoclasts requires expression of the 16 kDa, 31 kDa, 42 kDa, 60 kDa, 70 kDa, and 116 kDa subunits of V-ATPase. Antisense DNA molecules can be used to inhibit osteoclast differentiation and function in tissue cultures, in which the physical and chemical cellular environment resembles that in vivo. However, more studies are needed to learn if antisense DNA molecules can be used for inhibiting bone resorption also in vivo.

Synthesis of achiral linker reagents for direct labelling of oligonucleotides on solid supports

Full experimental procedures for the synthesis of a series of new functional linker reagents (14-16) and solid supports (11-13) are reported. The achiral linker reagents and supports can be used for high yield incorporation of free amino groups, fluorescein or biotin into DNA oligomers.

Phosphorothioate antisense oligonucleotides induce the formation of nuclear bodies

Antisense oligonucleotides are powerful tools for the in vivo regulation of gene expression. We have characterized the intracellular distribution of fluorescently tagged phosphorothioate oligodeoxynucleotides (PS-ONs) at high resolution under conditions in which PS-ONs have the potential to display antisense activity. Under these conditions PS-ONs predominantly localized to the cell nucleus where they accumulated in 20-30 bright spherical foci designated phosphorothioate bodies (PS bodies), which were set against a diffuse nucleoplasmic population excluding nucleoli. PS bodies are nuclear structures that formed in cells after PS-ON delivery by transfection agents or microinjection but were observed irrespectively of antisense activity or sequence. Ultrastructurally, PS bodies corresponded to electron-dense structures of 150-300 nm diameter and resembled nuclear bodies that were found with lower frequency in cells lacking PS-ONs. The environment of a living cell was required for the de novo formation of PS bodies, which occurred within minutes after the introduction of PS-ONs. PS bodies were stable entities that underwent noticeable reorganization only during mitosis. Upon exit from mitosis, PS bodies were assembled de novo from diffuse PS-ON pools in the daughter nuclei. In situ fractionation demonstrated an association of PS-ONs with the nuclear matrix. Taken together, our data provide evidence for the formation of a nuclear body in cells after introduction of phosphorothioate oligodeoxynucleotides.

Intracellular distribution of oligonucleotides delivered by cationic liposomes: light and electron microscopic study

Synthesized oligonucleotides are used in anti-sense and anti-gene technology to control gene expression. Because cells do not easily take up oligonucleotides, cationic liposomes have been employed to facilitate their transport into cells. Although cationic liposomes have been used in this way for several years, the precise mechanisms of the delivery of oligonucleotides into cells are not known. Because no earlier reports have been published on the liposomal delivery of oligonucleotides at the ultrastructural level, we performed a study, using electron microscopy, on the cellular uptake and intracellular distribution of liposomal digoxigenin-labeled oligodeoxynucleotides (ODNs) at several concentrations (0.1, 0.2, an 1.0 microM) in CaSki cells. Two cationic lipids (10 microM) were compared for transport efficiency: polycationic 2,3-dioleoyloxy-N-[2(sperminecarboxamido)ethyl]-N,N-dimethyl -1-propanaminium trifluoroacetate (DOSPA) and monocationic dimethyl-dioctadecylammonium bromide (DDAB). Both liposomes contained dioleoyl-phosphatidylethanolamine (DOPE) as a helper lipid. Endocytosis was found to be the main pathway of cellular uptake of liposomal ODNs. After release from intracellular vesicles, ODNs were carried into the perinuclear area. The nuclear membrane was found to be a barrier against the penetration of ODNs delivered by liposomes into the nucleus. Release from vesicles and transport into the nuclear area was faster when the oligo-DDAB/DOPE complex had a positive net charge (0.1 and 0.2 microM ODN concentrations), and only under this condition were some ODNs found in nucleoplasm. Although DOSPA/DOPE could also efficiently deliver ODNs into the cytosol, no ODNs were found in nucleoplasm. These findings suggest that both the type of liposome and the charge of the oligo-liposome complex are important for determination of the intracellular distribution of ODNs.