Deoxyribonuclease II is a lysosomal barrier to transfection

Decline in Exogenous Gene Expression in Primate Brain Following Intravenous Administration Is Due to Plasmid Degradation

PURPOSE

Nonviral gene transfer to the brain of adult Rhesus monkeys is possible with a single intravenous administration of plasmid DNA that is encapsulated in the interior of pegylated immunoliposomes, which are targeted across membrane barriers in vivo with a monoclonal antibody to the human insulin receptor.

METHODS

The present studies measure the rate of decay of luciferase gene expression in the Rhesus monkey with luciferase enzyme assays, Southern blotting, and real-time polymerase chain reaction.

RESULTS

Luciferase enzyme activity in frontal cortex, cerebellum, and liver decays with a t(1/2) of 2.1 +/- 0.1, 2.6 +/- 0.2, and 1.7 +/- 0.01 days, respectively. Luciferase plasmid in brain and liver was detectable by Southern blotting at 2 days, but not at 7 or 14 days. The concentration of luciferase plasmid DNA in brain and liver was measured by real-time polymerase chain reaction, and decayed with t(1/2) of 1.3 +/- 0.3 and 2.7 +/- 0.5 days, respectively.

CONCLUSIONS

The maximal concentration of luciferase plasmid DNA in Rhesus monkey brain was 3-4 molecules/cell following an i.v. administration of 12 microg/kg pegylated immunoliposome encapsulated plasmid DNA. These results demonstrate that the rate of loss of exogenous gene expression in the primate in vivo correlates with the rate of DNA degradation of the exogenous plasmid DNA.

DNase II and the Chk2 DNA Damage Pathway Form a Genetic Barrier Blocking Replication of Horizontally Transferred DNA

We have previously shown that DNA from dying tumor cells may be transferred to living cells via the uptake of apoptotic bodies and may contribute to tumor progression. DNA encoding H-ras(V12) and c-myc oncogenes may be transferred to the nucleus of the phagocyte but will only integrate and propagate in p53- and p21-deficient mouse embryonic fibroblasts, whereas normal cells are resistant to transformation. Here, we show that this protective mechanism (activation of p53 and p21 after uptake of apoptotic bodies) is dependent on DNA fragmentation, where inhibition of the caspase-activated DNase in the apoptotic cells, in conjunction with genetic ablation of lysosomal DNase II in the phagocytes, completely blocks p53 activation and consequently allows DNA replication of transferred DNA. We, therefore, suggest that there is a causal relationship between DNA degradation during apoptosis and p53 activation. In addition, we could further show that Chk2-/- cells were capable of replicating the hyg(R) gene taken up from engulfed apoptotic cells, suggesting involvement of the DNA damage response. These data show that the phagocytosing cell is sensing the degraded DNA within the apoptotic cell, hence preventing these genes from being replicated, probably through activation of the DNA damage response. We, therefore, hypothesize that DNase II together with the Chk2, p53, and p21 pathway form a genetic barrier blocking the replication of potentially harmful DNA introduced via apoptotic bodies, thereby preventing transformation and malignant development.

Nonionic amphiphilic block copolymers promote gene transfer to the lung

Various pulmonary disorders, including cystic fibrosis, are potentially amenable to a treatment modality in which a therapeutic gene is directly delivered to the lung. Current gene delivery systems, either viral or nonviral, need further improvement in terms of efficiency and safety. We reported that nonionic amphiphilic block copolymers hold promise as nonviral gene delivery systems for transfection of muscular tissues. To evaluate the efficiency of these vectors in the lung, intratracheal instillation or aerosolization of reporter genes complexed with Lutrol or PE6400 was performed. Lutrol-DNA and, to a lesser extent, PE6400-DNA complexes promoted efficient gene transfection into mouse airways in a dose-dependent manner. This improvement over naked DNA was observed irrespective of the reporter gene. Lutrol enabled us to deliver significantly higher DNA amounts than current nonviral vectors, with even greater increases in gene expression and without the formation of colloidally unstable complexes. Time course studies showed that Lutrol-DNA complexes permitted prolonged gene expression for up to 5 days whereas with poly(ethylenimine) (PEI)-DNA polyplexes, expression peaked on days 1-2 postinstillation, was strongly reduced by day 5, and reached background levels on day 7. Aerosolized delivery of Lutrol-DNA complexes, a less invasive approach to deliver genes to the lung, gave 5- to 15-fold higher reporter gene expression compared with PEI-DNA polyplexes administered via the same delivery route. After intratracheal instillation of Lutrol-DNA complexes, histochemical staining for beta-galactosidase expression showed the presence of large blue areas. Histopathological analysis showed that Lutrol alone did not elicit inflammation, and that the inflammatory response after intratracheal instillation of Lutrol-DNA complexes was reversible and was observed only with the highest amounts of DNA. We also found that Lutrol can efficiently deliver genes to the airways of cystic fibrosis mice. Thus, we conclude that Lutrol is a highly promising vector for gene delivery to the lung.

Fusogenic liposome delivers encapsulated nanoparticles for cytosolic controlled gene release

Therapeutic agents based on DNA or RNA oligonucleotides (e.g., antisense DNA oligonucleotide, small interfering RNA) require a regulation of their kinetics in cytoplasm to maintain an optimal concentration during the treatment period. In this respect, delivery of functional nanoparticles containing these drugs into cytoplasm has been thought to have a potential for the cytosolic controlled gene release. In this study, we establish a protocol for the encapsulation of nanoparticles into liposome, which is further fused with ultra violet-inactivated Sendai virus to compose fusogenic liposomes. When nanoparticles were encapsulated in conventional liposomes, endocytosis-mediated uptake of nanoparticles was observed. In contrast, numerous amounts of nanoparticles were delivered into the cytoplasm without any cytotoxicity when the particles were encapsulated in fusogenic liposomes. Additionally, fusogenic liposome showed a high ability to deliver nanoparticles containing DNA oligonucleotides into cytoplasm. These results indicate that this combinatorial nanotechnology using fusogenic liposome and nanoparticle is a valuable system for regulating the intracellular pharmacokinetics of gene-based drugs.

“Diffusible‐PEG‐Lipid Stabilized Plasmid Lipid Particles”

Many viral and non-viral gene transfer systems suffer from common pharmacological issues that limit their utility in a systemic context. By application of the liposomal drug delivery paradigm, many of the limitations of the first generation non-viral delivery systems can be overcome. Encapsulation in small, long-circulating particles called stabilized plasmid lipid particles (SPLP) results in enhanced accumulation at disease sites and selective protein expression. This work compares the detergent dialysis method of SPLP manufacture with an alternative method, spontaneous vesicle formation by ethanol dilution. The pharmacology of SPLP, as determined by monitoring lipid label and quantitative real time PCR, is also presented.

FRET-FCS as a tool to evaluate the stability of oligonucleotide drugs after intracellular delivery

The intracellular degradation of single-stranded, double-labeled oligonucleotides (ONs) was studied by following the disappearance of Fluorescence Resonance Energy Transfer (FRET) between the rhodamine green and Cy5 fluorophores attached to respectively the 3' and 5' end of the ONs. The green and red fluorescence intensities upon rhodamine green excitation were monitored using the ultra-sensitive detectors of a dual-color Fluorescence Correlation Spectroscopy (FCS) instrument. The ratio of the red to green fluorescence (R/G ratio) as obtained from such FRET-FCS measurements showed to give accurate information on the integrity of the ONs, without the need for additional auto- or cross-correlation analysis of the registered fluorescence intensity fluctuations. Intracellular measurements revealed that most of the 40mer phosphodiester ONs were degraded before they entered the nucleus. For the 20mer phosphodiester ONs, this degradation occurred more slowly, and both intact and degraded ONs entered the nucleus. For the 20mer phosphorothioate ONs, no intracellular degradation was observed during the measured time period. The sensitive detection of the intracellular fluorescence by the FCS setup will be particularly useful in situations where the expected fluorescence is too low to be detected by FRET-imaging as may occur after intracellular delivery of ONs by cationic carriers.

Polyfection as Nonviral Gene Transfer Method —Design of Novel Nonviral Vector Using α-Cyclodextrin—

Due to the growing concerns over the toxicity and immunogenicity of viral DNA delivery systems, DNA delivery via nonviral routes has become more desirable and advantageous. In particular, polycation complexes with DNA (polyplex) are attractive nonviral vectors. To design novel polycationic vectors, we prepared polyamidoamine starburst dendrimer (dendrimer) conjugates with three cyclodextrins (CDE conjugates) and three generations (G2, G3, and G4) of dendrimers. Of seven CDE conjugates, an alpha-CDE conjugate (G3) with an average degree of substitution (DS) of alpha-CyD of 2.4 [alpha-CDE conjugate (G3, DS 2.4)] showed greater gene transfer activity than dendrimers and other alpha-CDE conjugates with less cytotoxicity. These results suggest the potential use of alpha-CDE conjugate (G3, DS 2.4) as a polycationic vector in vitro and in vivo. Herein, I review a recent polyfection method, with special focus on alpha-CDE conjugate (G3, DS 2.4).