Gene Augmentation vs. Silencing in Therapy Design

Basic Introduction - What is Gene Therapy

Gene therapy introduces a modified gene into diseased cells to treat a genetic-based disease. The new gene usually contains a functioning gene to correct the effects of a disease-causing mutation, which may be either spontaneous or inherited. In the past few decades, gene therapy has made significant progress in the treatment of genetic diseases. In practice, scientists apply genomic and proteomic methods to identify the disease-causing gene, subsequently verifying the target gene with in vitro and in vivo experiments. With this methodology, scientists have published many high-impact gene therapy research articles.

Over the last decade, Cyagen has delivered hundreds of genetically modified animal models and virus packaging services to researchers for gene therapy applications. By the end of 2020, Cyagen’s products and services have been cited in over 4,750 publications across highly reputed peer-reviewed journals, such as Nature, Cell, Science, and more. With our expertise, Cyagen provides guaranteed genetically engineered animal models and viral packaging services for gene therapy research. The use of such models are known to to improve clinical transformation of gene therapy.

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If you have questions about choosing the right animal models for gene therapy research, contact us for complimentary support, consultations, and project strategy design.

Gene Therapy Strategy

Gene therapies are powerful research tools which deliver nucleic acids into diseased cells to directly treat illness – these are also being tested in human clinical trials for a range of applications. A thorough understanding of the currently available gene therapy methods is critical for successfully developing new gene therapy strategies and projects. Herein, we will discuss 4 gene therapy strategies: gene augmentation, gene silencing/inhibition, genome editing and gene suicide. Note that the last two options – genome editing and gene suicide – are both used to induce targeted death of diseased cells. Since gene suicide is mainly used to destroy tumor cells with an oncolytic virus, this article will not explore this topic in detail.

Gene Augmentation

Gene augmentation therapy is used to treat diseases caused by loss-of-function mutations, which prevent the gene from producing a functional product. This gene therapy technique introduces DNA containing a functional version of the lost gene into the cell and aims to produce a functioning product at sufficient levels to replace the protein that was originally missing.

Gene augmentation therapy is the most common treatment option for spinal muscular atrophy (SMA). SMA is caused by a deficiency of a motor neuron protein called SMN1, so the basic concept of gene therapy treatment is to insert the normal SMN1 gene into the diseased cell. Importantly, vector AAV9 can deliver cDNA of SMN1 gene to the cells. The first gene therapy treatment for SMA was approved by the Food and Drug Administration (FDA) in 2019. Despite being an effective option to minimize the progression of SMA and improve survival, this treatment is costly. At present, the commonly used strategies of gene augmentation therapies include delivering of a new protein-coding gene, increasing the expression of growth factors and cytokines, as well as cellular cytokines and autophagy activation of the diseased protein.

Gene Silencing

In cases where the addition of a functional gene does not resolve the disease phenotype, gene silencing therapy may be used to shut down (silence) the expression of an abnormal gene. For diseases caused by dominantly inherited disorders, just one abnormal allele can manifest the disease phenotype and related dysfunctionality of cells or organs. A common example is the constitutive expression of oncogene mutations in tumor cells, which requires gene therapy to inhibit the function and expression of pathogenic genes. RNA interference (RNAi) therapy has been applied in research across many polyglutamine (PolyQ)-related diseases, including Huntington’s disease (HD) and spinocerebellar ataxias (SCAs), with the aim to reduce the expression of toxic proteins. Although single-stranded ASOs can mediate gene silencing – small/short interfering RNA (siRNA), short hairpin RNA (shRNA), and microRNA (miRNA) therapies typically provide stronger inhibitory function and durability.

Polygultamine-related diseases that can potentially be treated with gene silencing

Gene Editing

In gene therapy applications, the use of gene editing technology has been closely tied to the development of Targeted Gene Editing-Cas9 technology, which has made gene editing in organisms much easier and inexpensive. Importantly, Targeted Gene Editing-Cas9 gene editing technology has become widely used in gene therapy and served as a breakthrough approach to many previous restrictions, such as the limitations by disease type (recessive or dominant disease), gene length, and in vitro or in vivo experimental model development. Those experimental limitations and others could be solved by gene editing (Targeted Gene Editing-Cas9) technology. Below are four key gene editing strategies for gene therapy:

(1) Directly inhibiting the expression of pathogenic genes, which is used for dominant diseases treatments;

(2) Correcting the faulty gene via single base editing or direct knockouts (KOs);

(3) Using homologous fragment repair strategy, which depends on the improvement of homologous recombination efficiency;

(4) Introducing the normal gene by homologous recombination at the safe site, similar to gene augmentation.

Gene Editing Applications in Rare Disease Research

More than 80% of rare diseases are caused by genetic disorders. With the development of a gene therapy for a rare disease, it can provide hope of a one-time treatment for numerous rare diseases that currently have no specific therapeutic options.

At present, there are gene editing-based gene therapy R&D pipelines in progress for several rare diseases, including Duchenne muscular dystrophy (DMD), congenital immune deficiency, hepatitis B, hemophilia, and cystic fibrosis.

With Cyagen’s professional gene editing platform, we provide accurate genetic engineering disease models to help researchers explore key information on rare disease mechanisms and potential treatment approaches. Our model services may be customized to support drug development programs more efficiently transition from gene discovery and validation to pre-clinical safety and efficacy evaluations.

Customer Case Study of Gene Therapy

The research groups of Dr. Bin Zhou (Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences) and Dr. Hefeng Huang (International Peace Maternity and Child Health Hospital, Shanghai Jiao Tong University) co-published an article titled “In Vivo AAV-Targeted Gene Editing/Cas9-mediated Gene Editing Ameliorates Atherosclerosis in Familial Hypercholesterolemia” in the journal Circulation.

In this study, researchers find that adeno-associated virus (AAV) delivers Targeted Gene Editing/Cas9 to achieve Ldlr gene correction that can partially rescue LDLR expression and effectively ameliorate atherosclerosis phenotypes in Ldlr mutant mice generated by Cyagen. The nonsense point mutation mouse line, LdlrE208X, is based on a gene mutation relevant to familial hypercholesterolemia - providing a potential therapeutic approach for the treatment of patients with the rare disease.

The Research Map