Microsphere-liposome complexes protect adenoviral vectors from neutralising antibody without losses in transfection efficiency, in-vitro

Preparation of microspheres encapsulating a recombinant TIMP-1 adenovirus and their inhibition of proliferation of hepatocellular carcinoma cells

OBJECTIVE

The study aim was to prepare poly-DL-lactide-poly (PELA) microspheres encapsulating recombinant tissue inhibitors of metalloproteinase-1 (TIMP-1) in an adenovirus to investigate its inhibition on the proliferation of hepatocellular carcinoma cells HepG2.

METHODS

Microspheres were prepared by encapsulating the recombinant TIMP-1 adenovirus into biodegradable PELA. The particle size, viral load, encapsulation efficiency and in-vitro release were measured. Microspheres were used to infect HepG2 cells, then infection efficiency was examined under a fluorescent microscope and ultrastructural changes assessed by TEM. Expression of TIMP-1 mRNA in HepG2 cells was examined by semi-quantitative RT-PCR and proliferation by MTT and cell growth curve assays.

RESULTS

We successfully prepared microspheres encapsulating recombinant TIMP-1 adenovirus with a diameter of 1.965μm, an encapsulation efficiency of 60.0%, a viral load of 10.5?108/mg and approximate 60% of virus release within 120 h, the total releasing time of which was longer than 240 h. The microspheres were confirmed to be non-toxic with blank microspheres. Infected HepG2 cells could stably maintain in-vitro expression of TIMP-1, with significantly effects on biological behaviour.

CONCLUSION

PELA microspheres encapsulating a recombinant TIMP-1 adenovirus can markedly inhibit the proliferation of HepG2 cells, which provides an experimental basis for polymer/chemistry-based gene therapy of hepatocellular carcinomas.

Biosafety studies of carrier cells infected with a replication-competent adenovirus introduced by IAI.3B promoter

The use of carrier cells infected with oncolytic viruses in cancer gene therapy is an attractive method because it can overcome viral immunogenicity and induce tumor immunity and significant antitumor activity. To enable human clinical trials of this treatment, acute and chronic toxicity tests must first be performed to ensure safety. IAI.3B promoter, oncolytic adenovirus AdE3-IAI.3B introduced by IAI.3B promoter, and A549 carrier cells infected with AdE3-IAI.3B were highly active in cancer cells but not in normal cells. Freeze-thawing increased the antitumor effect of A549 carrier cells by promoting the translocation of oncolytic adenovirus particles from the nucleus to the cytoplasm following the rupture of the nuclear membranes. No deaths or abnormal blood test data resulted from acute toxicity tests conducted in nude mice after a single dose. In chronic toxicity tests in rabbits, there were no serious side effects after eight doses of 1.25 × 10⁷ cells/kg or less for 4 weeks; a significant immune response is known to elicit increased numbers of antiadenovirus antibodies and enlarge the spleen. From these results, it could be concluded that cancer gene therapy of recurrent solid tumors using carrier cells can be safely trialed in humans.

Suppression of ovarian cancer growth via systemic administration with liposome-encapsulated adenovirus-encoding endostatin

Gene therapy using adenoviral vector containing the endostatin gene is a promising strategy for advanced cancers. However, host immune response to adenovirus and the lack of the requisite coxsackie-adenovirus receptor (CAR) in many primary cells limit the in vivo application. Liposome-complexed adenoviral vectors have proven to be useful for enhancing gene delivery in target cells that lack adenoviral receptors and avoiding a neutralizing antibody response. Here, we investigated antitumor effects of intravenous administration with PEG-PE cationic liposome-encapsulated recombinant human endostatin adenovirus (Ad-hEndo) on CAR-negative ovarian cancer. Electron micrography (EM) showed that these liposomes efficiently encapsulated the vectors, allowing CAR-independent adenovector transduction. The results showed that the complex enhanced transfection efficiency of recombinant adenovirus. Prolonged systemic administration was performed in immunocompetent mice and did not induce significant antibody response. The antitumor effect with PEG-PE cationic liposome encapsulated with Ad-hE (Ad-hE/lipo) was evaluated in the human ovarian cancer model. Systemic administration was well tolerated and resulted in marked suppression of tumor growth in an established ovarian cancer model, which was associated with a decreased number of micro-vessels and increased apoptosis of tumor cells. Our study shows that PEG-PE cationic liposome-encapsulated Ad-hE (Ad-hE/Lipo) can be administrated intravenously and lastingly to inhibit angiogenesis, thus showing promising clinical application.

Nasal delivery of an adenovirus-based vaccine bypasses pre-existing immunity to the vaccine carrier and improves the immune response in mice

Pre-existing immunity to human adenovirus serotype 5 (Ad5) is common in the general population. Bypassing pre-existing immunity could maximize Ad5 vaccine efficacy. Vaccination by the intramuscular (I.M.), nasal (I.N.) or oral (P.O.) route with Ad5 expressing Ebola Zaire glycoprotein (Ad5-ZGP) fully protected naïve mice against lethal challenge with Ebola. In the presence of pre-existing immunity, only mice vaccinated I.N. survived. The frequency of IFN-γ+ CD8+ T cells was reduced by 80% and by 15% in animals vaccinated by the I.M. and P.O. routes respectively. Neutralizing antibodies could not be detected in serum from either treatment group. Pre-existing immunity did not compromise the frequency of IFN-γ+ CD8+ T cells (3.9±1% naïve vs. 3.6±1% pre-existing immunity, PEI) nor anti-Ebola neutralizing antibody (NAB, 40±10 reciprocal dilution, both groups). The number of INF-γ+ CD8+ cells detected in bronchioalveolar lavage fluid (BAL) after I.N. immunization was not compromised by pre-existing immunity to Ad5 (146±14, naïve vs. 120±16 SFC/million MNCs, PEI). However, pre-existing immunity reduced NAB levels in BAL by ∼25% in this group. To improve the immune response after oral vaccination, the Ad5-based vaccine was PEGylated. Mice given the modified vaccine did not survive challenge and had reduced levels of IFN-γ+ CD8+ T cells 10 days after administration (0.3±0.3% PEG vs. 1.7±0.5% unmodified). PEGylation did increase NAB levels 2-fold. These results provide some insight about the degree of T and B cell mediated immunity necessary for protection against Ebola virus and suggest that modification of the virus capsid can influence the type of immune response elicited by an Ad5-based vaccine.

Carrier Cell–mediated Delivery of a Replication-competent Adenovirus for Cancer Gene Therapy

Although replication-competent viruses have been developed to treat cancers, their cytotoxic effects are insufficient, as infection is inhibited by the generation of neutralizing antibodies. To address this limitation, we developed a carrier cell system to deliver a replication-competent adenovirus. Carrier cells infected with replication-competent adenovirus were incubated with target cancer cells in a high titer of anti-adenovirus antibody. Carrier cells were injected into syngeneic subcutaneous tumors after immunization with adenovirus. Carrier cell-derived cell fragments containing viral particles were engulfed by proliferative target cancer cells. This engulfment-mediated transfer of adenovirus was not inhibited by the anti-adenovirus antibody and enabled repetitive infection. After the induction of anti-adenoviral cytotoxic T-lymphocyte (CTL) responses by immunization with adenovirus, administration of carrier cells infected with a replication-competent adenovirus induced complete tumor regression. Adenovirus-GM-CSF augmented the anti-tumor effect of carrier cells by increasing anti-adenoviral and anti-tumoral CTL responses and decreased the number of injections of carrier cells required to induce complete tumor regression. This novel carrier cell-mediated viral transfection system might prove useful in a variety of cancer therapies.

Structure-based identification of a major neutralizing site in an adenovirus hexon

Virus-specific neutralizing antibodies present an obstacle to the effective use of adenovirus vectors for gene therapy and vaccination. The specific sites recognized by neutralizing antibodies have not been identified for any adenovirus, but they have been proposed to reside within the hexon, in small regions of the molecule that are exposed on the capsid surface and possess sequences that vary among serotypes. We have mapped the epitopes recognized by a panel of seven hexon-specific monoclonal antibodies that neutralize the chimpanzee adenovirus 68 (AdC68). Surface plasmon resonance experiments revealed that the antibodies compete for a single hexon binding site, and experiments with synthetic peptides indicated that this site resides within just one small surface loop. Mutations within this loop (but not in other surface loops) permitted virus to escape neutralization by all seven monoclonal antibodies and to resist neutralization by polyclonal antisera obtained from animals immunized against AdC68. These results indicate that a single small surface loop defines a major neutralization site for AdC68 hexon.

Increased tumor localization and reduced immune response to adenoviral vector formulated with the liposome DDAB/DOPE

We aimed to increase the efficiency of adenoviral vectors by limiting adenoviral spread from the target site and reducing unwanted host immune responses to the vector. We complexed adenoviral vectors with DDAB-DOPE liposomes to form adenovirus-liposomal (AL) complexes. AL complexes were delivered by intratumoral injection in an immunocompetent subcutaneous rat tumor model and the immunogenicity of the AL complexes and the expression efficiency in the tumor and other organs was examined. Animals treated with the AL complexes had significantly lower levels of beta-galactosidase expression in systemic tissues compared to animals treated with the naked adenovirus (NA) (P<0.05). The tumor to non-tumor ratio of beta-galactosidase marker expression was significantly higher for the AL complex treated animals. NA induced significantly higher titers of adenoviral-specific antibodies compared to the AL complexes (P<0.05). The AL complexes provided protection (immunoshielding) to the adenovirus from neutralizing antibody. Forty-seven percent more beta-galactosidase expression was detected following intratumoral injection with AL complexes compared to the NA in animals pre-immunized with adenovirus.

CONCLUSIONS

Complexing of adenovirus with liposomes provides a simple method to enhance tumor localization of the vector, decrease the immunogenicity of adenovirus, and provide protection of the virus from pre-existing neutralizing antibodies.