Immunologic consequences of nucleic acid therapy

DNA vaccines against viral diseases of farmed fish

Immunization by an antigen-encoding DNA was approved for commercial sale in Canada against a Novirhabdovirus infection in fish. DNA vaccines have been particularly successful against the Novirhabdoviruses while there are reports on the efficacy against viral pathogens like infectious pancreatic necrosis virus, infectious salmon anemia virus, and lymphocystis disease virus and these are inferior to what has been attained for the novirhabdoviruses. Most recently, DNA vaccination of Penaeus monodon against white spot syndrome virus was reported. Research efforts are now focused on the development of more effective vectors for DNA vaccines, improvement of vaccine efficacy against various viral diseases of fish for which there is currently no vaccines available and provision of co-expression of viral antigen and immunomodulatory compounds. Scientists are also in the process of developing new delivery methods. While a DNA vaccine has been approved for commercial use in farmed salmon in Canada, it is foreseen that it is still a long way to go before a DNA vaccine is approved for use in farmed fish in Europe.

Phase I clinical/pharmacokinetic and pharmacodynamic trial of the c-raf-1 antisense oligonucleotide ISIS 5132 (CGP 69846A)

PURPOSE

Raf-1 is a protein kinase that plays a broad role in oncogenic signaling and acts as a downstream effector of Ras in the mitogen-activated protein kinase pathway. The present study was designed to determine the maximum-tolerated dose (MTD), toxicity profile, pharmacokinetics, and antitumor activity of the c-raf-1 antisense oligodeoxynucleotide ISIS 5132 (CGP 69846A; ISIS Pharmaceuticals Inc, Carlsbad, CA). The effect of ISIS 5132 on c-raf-1 gene expression in peripheral-blood mononuclear cells (PBMCs) of treated patients was studied using a reverse transcriptase polymerase chain reaction assay.

PATIENTS AND METHODS

Patients with refractory malignancies received ISIS 5132 as a 2-hour intravenous infusion three times weekly for 3 consecutive weeks. Pharmacokinetic sampling was performed during the first cycle in all patients; PBMCs for c-raf-1 mRNA analysis were collected at baseline and on days 3, 5, 8, and 15 of cycle 1 and on day 1 of each cycle thereafter.

RESULTS

Thirty-one patients received ISIS 5132 at one of nine dose levels ranging from 0.5 mg/kg to 6.0 mg/kg. Clinical toxicities included fever and fatigue, but these were not dose limiting. A clinically defined MTD was not reached. The harmonic mean half-life of ISIS 5132 was 59.8 minutes (range, 35.5 to 107.3 minutes). The area under the concentration-time curve increased linearly with dose, and mean plasma clearance was 1.86 mL/kg/min (range, 1.21 to 2.41 mL/kg/min). Two patients experienced prolonged stable disease lasting more than 7 months, which was associated with persistent reduction in c-raf-1 expression in PBMCs. Significant decreases in c-raf-1 expression were identified at time points after the baseline value (P <.05) at doses >/= 2.5 mg/kg.

CONCLUSION

ISIS 5132 is well tolerated at doses up to 6.0 mg/kg when administered as a thrice weekly 2-hour infusion for 3 consecutive weeks. The pharmacokinetic behavior of the drug is reproducible, and suppression of target gene expression is observed in circulating PBMCs.

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.

DNA vaccines for viral diseases

DNA vaccines, with which the antigen is synthesized in vivo after direct introduction of its encoding sequences, offer a unique method of immunization that may overcome many of the deficits of traditional antigen-based vaccines. By virtue of the sustained in vivo antigen synthesis and the comprised stimulatory CpG motifs, plasmid DNA vaccines appear to induce strong and long-lasting humoral (antibodies) and cell-mediated (T-help, other cytokine functions and cytotoxic T cells) immune responses without the risk of infection and without boost. Other advantages over traditional antigen-containing vaccines are their low cost, the relative ease with which they are manufactured, their heat stability, the possibility of obtaining multivalent vaccines and the rapid development of new vaccines in response to new strains of pathogens. The antigen-encoding DNA may be in different forms and formulations, and may be introduced into cells of the body by numerous methods. To date, animal models have shown the possibility of producing effective prophylactic DNA vaccines against numerous viruses as well as other infectious pathogens. The strong cellular responses also open up the possibility of effective therapeutic DNA vaccines to treat chronic viral infections.

Specific inhibition of interleukin-10 production in murine macrophage-like cells by phosphorothioate antisense oligonucleotides

The effects of phosphorothioate antisense oligonucleotides (AS-S-oligos) directed against murine interleukin-10 (IL-10) mRNA on IL-10 production in RAW264.7 cells, a murine macrophage-like cell line, when stimulated by lipopolysaccharide (LPS) were examined. Of the six AS-S-oligos used, AS-S-oligos directed against the 3'-untranslated region (3'-UTR) of IL-10 mRNA (AS6-S-oligo) showed the strongest inhibitory effect on IL-10 production, and this inhibition was dose and time dependent. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that the antisense effect originated from a specific reduction of target IL-10 mRNA by hybridization with AS6-S-oligo. In addition, AS6-S-oligo did not affect tumor necrosis factor-alpha (TNF-alpha) production in cells stimulated by LPS, and S-oligos with control sequences did not affect IL-10 production. These findings suggested that AS6-S-oligo most powerfully inhibited IL-10 production in macrophages by an antisense mechanism.

Characterization and modulation of immune stimulation by modified oligonucleotides

Single-stranded oligodeoxynucleotides (ODNs) were tested for their ability to stimulate NK cells isolated from murine spleens to lyse target cells. Various sequences were evaluated, some of which have been shown previously to exhibit pharmacologic activity in murine model systems. It was confirmed that the CpG motif was stimulatory only in specific sequence contexts, and we found that phosphorothioate backbones were, in general, less stimulatory than phosphodiester backbones. In addition, this stimulation could be reduced by methylating the cytosine of the CpG and eliminated by modifying all of the cytosines contained in an ODN with methyl, bromo, or iodo modifications to the 5 position of the cytosine ring. These results were compared with the ability of a subset of these ODN sequences to stimulate B cell proliferation in vitro. In this comparison, phosphorothioate backbones were found to be required, and the context of the CpG motif was found to be less critical for activation. Finally, one of the most potent ODNs was shown to activate NK and B lymphocytes when administered in vivo.

Specific inhibition of nitric oxide production in macrophages by phosphorothioate antisense oligonucleotides

The effects of antisense oligonucleotides (ODNs) on nitric oxide (NO) production induced by lipopolysaccharide (LPS) were investigated using thioglycollate-induced mouse peritoneal macrophages. Antisense phosphorothioate ODNs (S-oligo) corresponding to a sequence in the neighborhood of the AUG initiation codon of a mouse inducible nitric oxide synthase (iNOS) mRNA, which has a G-quartet motif in its antisense sequence, inhibited NO induction in a dose-dependent manner. Antisense phosphodiester ODNs (D-oligo), 5'- and 3'-terminal phosphorothioate-modified antisense ODNs and control scramble and missense S-oligos had no such effect. In addition, control nonsense and two mismatched S-oligos, which include G-quartet motif in their sequences, inhibited NO induction to approximately 50% of those in the control. Antisense S-oligo showed the inhibitory effect on NO production by exposure of macrophages to various concentrations of LPS. Western blot analysis using anti-mouse inducible nitric oxide synthase (iNOS) antibody revealed that antisense S-oligo specifically removed an immunoreactive band at 130 kDa. In addition, the results of reverse transcription-polymerase chain reaction (RT-PCR) revealed that the antisense effect originated from a specific reduction of the targeted iNOS mRNA by hybridization with the antisense S-oligo. Furthermore, no ODNs affected beta-actin mRNA and tumor necrosis factor alpha (TNF-alpha) expression in macrophages stimulated by LPS. These findings demonstrated that antisense S-oligo inhibited NO production derived from iNOS expression in macrophages by an antisense mechanism, including the aptameric effect partially mediated by the G-quartet motif.

Pharmaceutical approach to somatic gene therapy

The pharmaceutical approach to somatic gene therapy is based on consideration of a gene as a chemical entity with specific physical, chemical and colloidal properties. The genes that are required for gene therapy are large molecules (> 1 x 10(6) Daltons, > 100 nm diameter) with a net negative charge that prevents diffusion through biological barriers such as an intact endothelium, the plasma membrane or the nuclear membrane. New methods for gene therapy are based on increasing knowledge of the pathways by which DNA may be internalized into cells and traffic to the nucleus, pharmaceutical experience with particulate drug delivery systems, and the ability to control gene expression with recombined genetic elements. This article reviews two themes in the development of gene therapies: first, the current approaches involving the administration of cells, viruses and plasmid DNA; second, the emerging pharmaceutical approach to gene therapy based on the pharmaceutical characteristics of DNA itself and methods for advanced drug delivery.