Triplex-mediated genome targeting and editing

Triplex-forming oligonucleotides as an anti-gene technique for cancer therapy

Triplex-forming oligonucleotides (TFOs) can bind to the major groove of double-stranded DNA with high specificity and affinity and inhibit gene expression. Triplex-forming oligonucleotides have gained prominence because of their potential applications in antigene therapy. In particular, the target specificity of triplex-forming oligonucleotides combined with their ability to suppress oncogene expression has driven their development as anti-cancer agents. So far, triplex-forming oligonucleotides have not been used for clinical treatment and seem to be gradually snubbed in recent years. But triplex-forming oligonucleotides still represent an approach to down-regulate the expression of the target gene and a carrier of active substances. Therefore, in the present review, we will introduce the characteristics of triplex-forming oligonucleotides and their anti-cancer research progress. Then, we will discuss the challenges in their application.

Antiviral effects of hepatitis B virus S gene-specific anti-gene locked nucleic acid in transgenic mice

AIM

To assess the antiviral effects of hepatitis B virus (HBV) S gene-specific anti-gene locked nucleic acid (LNA) in transgenic mice.

METHODS

Thirty HBV transgenic mice were acclimatized to laboratory conditions and positive for serum HBV surface antigen (HBsAg) and HBV DNA, were randomly divided into 5 groups (n = 7), including negative control (blank control, unrelated sequence control), positive control (lamivudine, anti-sense-LNA), and anti-gene-LNA experimental group. LNA was injected into transgenic mice by tail vein while lamivudine was administered by gavage. Serum HBV DNA and HBsAg levels were determined by fluorescence-based PCR and enzyme-linked immune sorbent assay, respectively. HBV S gene expression amounts were assessed by reverse transcription polymerase chain reaction. Positive rates of HBsAg in liver cells were evaluated immunohistochemistry.

RESULTS

Average rate reductions of HBsAg after treatment on the 3^rd, 5^th, and 7^th days were 32.34%, 45.96%, and 59.15%, respectively. The inhibitory effect of anti-gene-LNA on serum HBsAg peaked on day 7, with statistically significant differences compared with pre-treatment (0.96 ± 0.18 vs 2.35 ± 0.33, P < 0.05) and control values (P < 0.05 for all). Average reduction rates of HBV DNA on the 3^rd, 5^th, and 7^th days were 38.55%, 50.95%, and 62.26%, respectively. This inhibitory effect peaked on the 7^th day after treatment with anti-gene-LNA, with statistically significant differences compared with pre-treatment (4.17 ± 1.29 vs 11.05 ± 1.25, P < 0.05) and control values (P < 0.05 for all). The mRNA levels of the HBV S gene (P < 0.05 for all) and rates of HBsAg positive liver cells (P < 0.05 for all) were significantly reduced compared with the control groups. Liver and kidney function, and histology showed no abnormalities.

CONCLUSION

Anti-gene-LNA targeting the S gene of HBV displays strong inhibitory effects on HBV in transgenic mice, providing theoretical and experimental bases for gene therapy in HBV.

Therapeutic genome mutagenesis using synthetic donor DNA and triplex-forming molecules

Genome mutagenesis can be achieved in a variety of ways, though a select few are suitable for therapeutic settings. Among them, the harnessing of intracellular homologous recombination affords the safety and efficacy profile suitable for such settings. Recombinagenic donor DNA and mutagenic triplex-forming molecules co-opt this natural recombination phenomenon to enable the specific, heritable editing and targeting of the genome. Editing the genome is achieved by designing the sequence-specific recombinagenic donor DNA to have base mismatches, insertions, and deletions that will be incorporated into the genome when it is used as a template for recombination. Targeting the genome is similarly achieved by designing the sequence-specific mutagenic triplex-forming molecules to further recruit the recombination machinery thereby upregulating its activity with the recombinagenic donor DNA. This combination of extracellularly introduced, designed synthetic molecules and intercellularly ubiquitous, evolved natural machinery enables the mutagenesis of chromosomes and engineering of whole genomes with great fidelity while limiting nonspecific interactions. Herein, we demonstrate the harnessing of recombinagenic donor DNA and mutagenic triplex-forming molecular technology for potential therapeutic applications. These demonstrations involve, among others, utilizing this technology to correct genes so that they become physiologically functional, to induce dormant yet functional genes in place of non-functional counterparts, to place induced genes under regulatory elements, and to disrupt genes to abrogate a cellular vulnerability. Ancillary demonstrations of the design and synthesis of this recombinagenic and mutagenic molecular technology as well as their delivery and assayed interaction with duplex DNA reveal a potent technological platform for engineering specific changes into the living genome.