Antisense approach for the treatment of cytomegalovirus infection

Focused Update on AAV-Based Gene Therapy Clinical Trials for Inherited Retinal Degeneration

Inherited retinal diseases (IRDs) comprise a clinically and genetically heterogeneous group of disorders that can ultimately result in photoreceptor dysfunction/death and vision loss. With over 270 genes known to be involved in IRDs, translation of treatment strategies into clinical applications has been historically difficult. However, in recent years there have been significant advances in basic research findings as well as translational studies, culminating in an increasing number of clinical trials with the ultimate goal of reducing vision loss and associated morbidities. The recent approval of Luxturna^® (voretigene neparvovec-rzyl) for Leber congenital amaurosis type 2 (LCA2) prompts a review of the current clinical trials for IRDs, with a particular focus on the importance of adeno-associated virus (AAV)-based gene therapies. The present article reviews the current state of AAV use in gene therapy clinical trials for IRDs, with a brief background on AAV and the reasons behind its dominance in ocular gene therapy. It will also discuss pre-clinical progress in AAV-based therapies aimed at treating other ocular conditions that can have hereditable links, and what alternative technologies are progressing in the same therapeutic space.

Towards Zwitterionic Oligonucleotides with Improved Properties: the NAA/LNA-Gapmer Approach

Oligonucleotides (ON) are promising therapeutic candidates, for instance by blocking endogenous mRNA (antisense mechanism). However, ON usually require structural modifications of the native nucleic acid backbone to ensure satisfying pharmacokinetic properties. One such strategy to design novel antisense oligonucleotides is to replace native phosphate diester units by positively charged artificial linkages, thus leading to (partially) zwitterionic backbone structures. Herein, we report a "gapmer" architecture comprised of one zwitterionic central segment ("gap") containing nucleosyl amino acid (NAA) modifications and two outer segments of locked nucleic acid (LNA). This NAA/LNA-gapmer approach furnished a partially zwitterionic ON with optimised properties: i) the formation of stable ON-RNA duplexes with base-pairing fidelity and superior target selectivity at 37 °C; and ii) excellent stability in complex biological media. Overall, the NAA/LNA-gapmer approach is thus established as a strategy to design partially zwitterionic ON for the future development of novel antisense agents.

Cellular delivery of cationic lipid nanoparticle-based SMAD3 antisense oligonucleotides for the inhibition of collagen production in keloid fibroblasts

SMAD3 is a key player in the TGFβ signaling pathway as a primary inducer of fibrosis. The inhibition of SMAD3 production is one strategy to alleviate fibrosis in keloid fibroblasts. In the present study, antisense oligonucleotides (ASOs) against SMAD3 were designed to specifically block the expression of SMAD3. The cationic lipid nanoparticles (cLNs) were formulated to enhance an intracellular activity of SMAD3 ASOs in keloid fibroblasts. This formulation was prepared using melt-homogenization method, composed of 3-[N-(N',N'-dimethylaminoethane)-carbamol] cholesterol (DC-Chol), dioleoylphosphatidylethanolamine (DOPE), Tween20, and trimyristin as a lipid core (1:1:1:1.3, w/w). The size and zeta potential of cLNs and cLN/ASO complexes were measured using light scattering. AFM was used to confirm the morphology and the size distribution of cLNs and cLN/ASO complexes. The prepared cLNs had a nano-scale sized spherical shape with highly positive charge, which were physically stable without aggregation during the storage. The cLN/SMAD3 ASO complexes were successfully generated and internalized onto keloid fibroblasts without toxicity. After the treatment with cLN/ASO complexes, SMAD3 was inhibited and collagen type I was also significantly suppressed in keloid fibroblasts. These results suggest that SMAD3 ASOs complexed with cLNs have a therapeutic potential to suppress collagen deposition in fibrotic diseases. Therefore, this strategy might be developed to lead to anti-fibrotic therapies.

Antiviral Chemistry & Chemotherapy's Current Antiviral Agents FactFile (2nd Edition): DNA Viruses

Although most of the recent attempts to develop new antiviral agents have been focussed on RNA viruses (in particular, HIV and hepatitis C virus), a few new compounds are now awaiting their entry into the field of DNA viruses, particularly poxviruses, such as variola virus, because of the bioterrorist context, and herpesviruses, such as herpes simplex virus and cytomegalovirus, where the market scene has for many years been dominated by acyclovir, penciclovir and ganciclovir and their respective orally bioavailable prodrugs: valaciclovir, famciclovir and valganciclovir. Here, we review the current ‘state of the art’ with old compounds ready to rotate off and new compounds eagerly awaiting to appear on the continuously evolving scene of antiviral drug development.

Synthesis of N-alkyl substituted indolocarbazoles as potent inhibitors of human cytomegalovirus replication

The synthesis and antiviral evaluation of unsymmetrical indolocarbazole derivatives of Arcyriaflavin A, substituted with a range of alkyl groups at the indole nitrogen, is described. Structure-activity relationships in this series against human cytomegalovirus (HCMV) replication in cell culture are reported. Compound 4b was identified as potent inhibitor of HCMV (IC(50)=19 nM), which retained activity against a range of HCMV strains including ganciclovir resistant isolates.

Fomivirsen

Fomivirsen (ISIS 2922) is an antisense oligonucleotide which specifically inhibits replication of human cytomegalovirus. It achieves this by binding to complementary sequences on messenger RNA transcribed from the major immediate-early transcriptional unit of the virus. It is being developed for the treatment of cytomegalovirus retinitis. Mean maximum retinal concentrations of fomivirsen occurred approximately 2 days after a single intravitreal injection in monkeys. The elimination half-life of fomivirsen (after a single 115 microg dose) in monkey retina was 78 hours. Fomivirsen, administered as an intravitreal injection, significantly delayed progression of cytomegalovirus retinitis in patients with AIDS in preliminary clinical trials. In 18 patients with newly diagnosed, unilateral, peripheral cytomegalovirus retinitis treated with fomivirsen 165 microg once weekly for 3 weeks, then 165 microg every second week, the median time to disease progression was significantly longer than in 10 patients in whom fomivirsen treatment was deferred until early disease progression (71 vs 14 days). In patients with advanced, refractory, sight-threatening disease, treatment with fomivirsen 330 microg once weekly for 3 weeks and then 330 microg every 2 weeks (n = 34) or 330 microg on days 1 and 15 and then monthly (n = 20) significantly delayed disease progression. The interpolated median time to disease progression was 90 days in both treatment groups. The most common adverse events reported in clinical trials of fomivirsen were increased intraocular pressure and mild to moderate intraocular inflammation. These events were generally transient or reversible with topical steroid treatment.