RNA-based gene therapy for HIV infection

Potential inhibition of HIV-1 encapsidation by oligoribonucleotide-dendrimer nanoparticle complexes

Background

Encapsidation, the process during which the genomic RNA of HIV is packaged into viral particles, is an attractive target for antiviral therapy. This study explores a novel nanotechnology-based strategy to inhibit HIV encapsidation by an RNA decoy mechanism. The design of the 16-mer oligoribonucleotide (RNA) decoy is based on the sequence of stem loop 3 (SL3) of the HIV packaging signal (Ψ). Recognition of the packaging signal is essential to the encapsidation process. It is theorized that the decoy RNA, by mimicking the packaging signal, will disrupt HIV packaging if efficiently delivered into lymphocytes by complexation with a carbosilane dendrimer. The aim of the study is to measure the uptake, toxicity, and antiviral activity of the dendrimer–RNA nanocomplex.

Materials and methods

A dendriplex was formed between cationic carbosilane dendrimers and the RNA decoy. Uptake of the fluorescein-labeled RNA into MT4 lymphocytes was determined by flow cytometry and confocal microscopy. The cytoprotective effect (50% effective concentration [EC₅₀]) and the effect on HIV replication were determined in vitro by the methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay and viral load measurements, respectively.

Results

Flow cytometry and confocal imaging demonstrated efficient transfection of lymphocytes. The dendriplex containing the Ψ decoy showed some activity (EC₅₀ =3.20 µM, selectivity index =8.4). However, there was no significant suppression of HIV viral load.

Conclusion

Oligoribonucleotide decoys containing SL3 of the packaging sequence are efficiently delivered into lymphocytes by carbosilane dendrimers where they exhibit a modest cytoprotective effect against HIV infection.

Targeting CCR5 for anti-HIV research

Highly active antiretroviral therapy (HAART) is the only approach for human immunodeficiency virus (HIV) infection treatment at present. Although HAART is effective in controlling the progression of infection, it is impossible to eradicate the virus from patients. The patients have to live with the virus. Alternative ways for the cure of HIV infection have been investigated. As the major co-receptor for HIV-1 infection, C-C motif chemokine receptor 5 (CCR5) is naturally an ideal target for anti-HIV research. The first CCR5 antagonist, maraviroc, has been approved for the treatment of HIV infection. Several other CCR5 antagonists are in clinical trials. CCR5 delta32 is a natural genotype, conferring resistance to CCR5 using HIV-1 strains. Gene therapy research targeting this mutant has been conducted for HIV infection treatment. A Berlin patient has been cured of HIV infection by the transplantation of stem cells from a CCR5 delta32 genotype donor. The infusion of an engineered zinc finger nuclease (ZFN)-modified autologous cluster of differentiation 4 (CD4) T cells has been proved to be a promising direction recently. In this study, the anti-HIV research targeting CCR5 is summarized, including CCR5 antagonist development, stem cell transplantation, and gene therapy.

Nanotechnology and the treatment of HIV infection

Suboptimal adherence, toxicity, drug resistance and viral reservoirs make the lifelong treatment of HIV infection challenging. The emerging field of nanotechnology may play an important role in addressing these challenges by creating drugs that possess pharmacological advantages arising out of unique phenomena that occur at the “nano” scale. At these dimensions, particles have physicochemical properties that are distinct from those of bulk materials or single molecules or atoms. In this review, basic concepts and terms in nanotechnology are defined, and examples are provided of how nanopharmaceuticals such as nanocrystals, nanocapsules, nanoparticles, solid lipid nanoparticles, nanocarriers, micelles, liposomes and dendrimers have been investigated as potential anti-HIV therapies. Such drugs may, for example, be used to optimize the pharmacological characteristics of known antiretrovirals, deliver anti-HIV nucleic acids into infected cells or achieve targeted delivery of antivirals to the immune system, brain or latent reservoirs. Also, nanopharmaceuticals themselves may possess anti-HIV activity. However several hurdles remain, including toxicity, unwanted biological interactions and the difficulty and cost of large-scale synthesis of nanopharmaceuticals.

Prevention of HIV-1 infection in human peripheral blood mononuclear cells by specific RNA interference

The RNA interference (RNAi) phenomenon is a recently observed process in which the introduction of a double-stranded RNA (dsRNA) into a cell causes the specific degradation of a mRNA containing the same sequence. The 21-23 nt guide RNAs, generated by RNase III cleavage from longer dsRNAs, are associated with sequence-specific mRNA degradation. Here, we show that dsRNA specifically suppresses the expression of HIV-1 genes. To study dsRNA-mediated gene interference in HIV-1-infected cells, we have designed six long dsRNAs containing the HIV-1 gag and env genes. HIV-1 replication was totally suppressed in a sequence-specific manner by the dsRNAs in HIV-1-infected cells. Especially, E2 dsRNA containing the major CD4-binding domain sequence of gp120, as the target of the HIV-1 env gene, dramatically inhibited the expression of the HIV-1 p24 antigen in PBMCs for a relatively long time. The dsRNA interference method seems to be a promising new strategy for anti-HIV-1 gene therapeutics.

siRNA-directed inhibition of HIV-1 infection

RNA interference silences gene expression through short interfering 21 23-mer double-strand RNA segments that guide mRNA degradation in a sequence-specific fashion. Here we report that siRNAs inhibit virus production by targeting the mRNAs for either the HIV-1 cellular receptor CD4, the viral structural Gag protein or green fluorescence protein substituted for the Nef regulatory protein. siRNAs effectively inhibit pre- and/or post-integration infection events in the HIV-1 life cycle. Thus, siRNAs may have potential for therapeutic intervention in HIV-1 and other viral infections.

The basis for HIV immunotherapeutic vaccines

The drug treatments introduced in recent years for HIV infection have enabled a marked reduction in morbidity and prolongation of life. These treatments, however, are often associated with acute and chronic toxicities, the development of resistant virus can limit their effectiveness, and they are too expensive and difficult to administer in most third world settings. A successful HIV immunotherapeutic vaccine has the potential to overcome these problems, and would be a valuable advance. The most promising approaches have induced the type of immune response found to correlate with reduced activity of HIV in man, especially cytotoxic T-cell responses, or have led to reduced HIV or SIV viral load and increased CD4 counts in non-human primates or man. The agents that have led to one or both of these effects have been selected for review, and include inactivated envelope depleted virus, recombinant envelope glycoprotein, DNA vaccines utilising HIV peptides or gene products, viral vectors, such as canarypox or attenuated vaccinia, with HIV core proteins. There are other approaches, such as alloimmunity, for which no candidate products yet exist, but which conceptually appear promising. Currently, however, only a few phase III studies of HIV therapeutic vaccines have been completed in man, and there has been a modest therapeutic effect. Further development of both existing and new candidates remains one of the key priorities in our fight against HIV.