Gene Therapy for Cardiovascular Diseases

Madiha Khalid07-arid-1610

Gene therapy 

Use of DNA as a pharmaceutical agent to treat disease.

The most common form involves DNA that encodes a functional, therapeutic gene to replace a mutated gene.

Other forms involve using DNA that encodes a therapeutic protein drug.

Once inside, the DNA becomes expressed by the cell machinery, resulting in the production of therapeutic protein, which in turn treats the patient's disease.

How it works

A vector delivers a therapeutic gene into patient’s target cell.

Functional proteins are created from therapeutic gene causing cells to return to a normal state.

Types of gene therapy

Gene therapy may be classified into the two following types Somatic gene therapy

In somatic gene therapy, the therapeutic genes are transferred into the somatic cells (non sex-cells), or body, of a patient.

Germ line gene therapy

In germ line gene therapy, germ cells(sperm or eggs), are modified by the introduction of functional genes, which are integrated into their genomes.

Methods Adopted

Ex vivo: where cells are modified outside the body and then transplanted again.

In vivo: which means interior,where genes are changed in cells still in body

Cardiovascular disease

Cardiovascular disease remains the leading cause of morbidity and mortality in developed countries.

The emergence of human gene therapy in the early 1990s led to numerous attempts, both experimental and clinical, to treat cardiovascular disease with gene therapy strategies. 

Gene therapy holds considerable promise for the treatment of cardiovascular disease and may provide novel therapeutic solutions for both genetic disorders and acquired pathophysiologies such as arteriosclerosis and heart failure

Recombinant DNA technology and the sequencing of the human genome have made candidate therapeutic genes available for cardiovascular diseases.

However, progress in the field of gene therapy for cardiovascular disease has been modest.

one of the key reasons is the lack of gene delivery systems for localizing gene therapy to specific sites to optimize transgene expression and efficacy.

Because cardiovascular disease is characteristically localized, the site-specific targeting of gene therapy for the cardiovascular system is necessary.

Barriers of gene therapy for cardiovasculardiseases

For efficient delivery of therapeutic genes to the cardiovascular system, a series of barriers have to be overcome.

The gene vectors need to pass through the endothelial barriers in capillary walls when systemically injected.

Plasmid faces a threat of being degraded rapidly by the immune system or DNAse in serum before transfection.

Viral gene vectors need to avoid the immunoreaction in circulation and transduction of non-target organs, mainly liver and spleen.

The plasmid needs to avoid being entrapped into lysosome or the endosome, where it will be degraded.

The gene vector has to penetrate the nuclear membrane to achieve the goal of gene therapy.

Candidate transgenes for cardiovascular gene transfer

A variety of cardiovascular therapeutic gene constructs have been studied in vitro and in vivo.

These constructs can be categorized into several groups

The tumor-suppressor p53 Metalloprotease inhibitor 3 hepatocyte growth factor superoxide dismutase [SOD]   sarcoplasmic/endoplasmic reticulum calcium ATPase 2

Gene vectors

Mostly 2 types of vectors are used Non-viral gene vectors Plasmid DNA Antisense and decoy RNA

Viral gene verctors Retroviruses and lentiviruses Adenoviruses Adeno-associated viruses 

Plasmid DNA Low toxicity,

Considered to be the safest choice for therapeutic gene transfer

 Unfortunately, the inherently low expression

limited clinical situations in which low and transient expression of the transgene is required. 

Ongoing efforts to optimize the plasmid backbone via:

tissue-specific enhancers

prevent premature silencing

It increase and stabilize the levels of transgene expression obtainable with non-viral vectors.

Antisense and decoy RNA

Inactivates gene involved in disease process

Antisense specific to target gene disrupts the translation of faulty gene

Liposomes

Aqueous compartments enclose by membrane

Protect DNA from undesirable degradation during transfection

Plasmid can be covered with lipids to form micelles or liposomes

Low efficiency due to lack of ability in term of ‘ endosomal escape.

Viral vectors

Risks associated with viral vectors

Can infect more than one type of cell New gene can be inserted into wrong position in the cell DNA can unintentionally be inserted into patient’s

reproductive system and resultant changes will pass to next generation

Transferred gene can be over expressed Protein in excess will be harmful Could cause an immune reaction

Gene delivery systems

 The main purpose is: To provide the method of transport to deliver the

formulation containing the gene vector to the intended site of action.

Minimizing the contact between the gene vector and bodily fluids prior to arrival at the intended location

Reducing this contact decreases the dilution of the vector and protects the surface of the vector from non-specific interactions that are typically detrimental to its activity.

Needle injections

The most straightforward approach to myocardial gene delivery is the direct needle injection of the vector

However, this approach has low efficiency; transduced cells are typically observed only along the needle track 

 But transgene expression is usually low because of the rapid removal of the vector, which is intensified by the local inflammatory reaction initiated by needle-related tissue damage

Antegrade Arterial Infusion

Coronary artery catheterization is:

Minimally invasive and well-established procedure that allows homogenous gene delivery to each territory of the heart

The major advantages of this approach are that it is minimally invasive and relatively safe

Thus, it is especially attractive for patients with end-stage heart failure.

Intravenous infusion

Simplest and less invasive method

Among current available methods of cardiac gene delivery

In rodents, injection into the tail vein results in successful cardiac gene expression

Dilution by the systemic blood circulation compromises the vector concentration in the cardiac circulation, uptake by other organs such as liver, lung, and spleen before the vectors reach the heart is another issue

Ultrasound targeted microbubble destruction (UTMD)

UTMD is an immense potential target-specific gene delivery tool.

Microbubbles (MBs) of UTMD, which may consist of lipids, albumin, saccharide, biocompatible polymers and other materials are traditionally used as ultrasound contrast agents due to their physical property of reflecting ultrasound.

Microbubble as cavitation nucleus could expand and contract under the effect of ultrasound, and disrupted when the acoustic pressure reaches a much higher level.

The mechanism is based on the specific response of the microbubbles upon exposure to ultrasound,namely sonoporation.

Microbubbles may oscillate when exposed to ultrasound, and then these oscillating microbubbles may rupture. So, the gene therapy vector incorporated with microbubbles can be released with high local concentrations at the site of interest.

Meanwhile, the destruction of MBs may transiently induce transient holes in membranes and cause entry of gene into target cells.

The advantages of UTMD techniques

Low toxicity Low immunogenicity Low invasiveness MB can be intravenously injected Great potential for repetitive application Organs can be targeted with high specificity Improve the efficiency Regarded as a new choice for gene therapy

Conclusion

UTMD constitutes the most efficient method to deliver transgene up till now.

Translation of gene therapies into routine medical practice will require the development and optimization of novel delivery systems capable control of gene vector biodistribution and activity.

References

Zhi-Yi Chen1, Yan Lin1, Feng Yang1, Lan Jiang1 and Shu ping Ge2Gene therapy for cardiovascular disease mediated by ultrasound and microbubbles, Chen et al. Cardiovascular Ultrasound 2013, 11:11.

Lisa Tilemann, Kiyotake Ishikawa, Thomas Weber, and Roger J. Hajjar, Gene Therapy for Heart Failure, Circ Res. 2012 March 2; 110(5): 777–793.

Julie A. Wolfram, PhD; J. Kevin Donahue, MD, Gene Therapy to Treat Cardiovascular Disease

Elizabeth G. Nabel MD,Gene Therapy for Cardiovascular Disease,2013

Ilia Fishbein, Michael Chorny, and Robert J Levy,Site-specific gene therapy for cardiovascular disease,March 2010