Gene Therapy: Non-Viral Vectors

(Posted on Tuesday, April 23, 2024)

This story is part of a series on the current progression in Regenerative Medicine. In 1999, I defined regenerative medicine as the collection of interventions that restore tissues and organs damaged by disease, injured by trauma, or worn by time to normal function. I include a full spectrum of chemical, gene, and protein-based medicines, cell-based therapies, and biomechanical interventions that achieve that goal.

In this subseries, we focus specifically on gene therapies. We explore the current treatments and examine the advances poised to transform healthcare. Each article in this collection delves into a different aspect of gene therapy’s role within the larger narrative of Regenerative Medicine. This piece continues s a miniseries on gene therapy vectors and their significance. Specifically, this piece begins with a two-part story on nonviral methods and vectors of gene therapy.

Modern medicine constantly searches for safer and more efficient ways to treat genetic disorders. One cutting-edge solution that has emerged is the use of non-viral vectors. These vectors have many benefits that have made them popular among researchers. 

The field explores the frontier science behind non-viral vectors such as liposomes, cationic polymers, gold nanoparticles, exosomes, ferritin, and red cell membranes. These vectors herald a new wave in delivering gene therapy’s promise to ailing cells, offering hope for a better future.

Liposomes: Cellular Delivery Reimagined

Thanks to their remarkable compatibility and efficacy, liposomes lead the charge as the most prevalent non-viral vectors. These microscopic, spherical shells, synthesized from naturally occurring lipids, encapsulate nucleic acids, offering a safe passage through the body’s immune defenses. Their dual-layered lipid structure seamlessly merges with cell membranes, introducing DNA and RNA directly into the cells’ sanctum—a neat trick devoid of immunogenic proteins. 

With a focused approach to developing specialized lipid nanoparticle (LNP) delivery systems for RNA-based therapeutics like small interfering RNA (siRNA), Alnylam has navigated many of the previously encountered limitations in this domain. Their strategies include the ingeniously designed cationic liposomes capable of DNA and RNA delivery, PEGylated liposomes for improved pharmacokinetics resulting in longer circulation times, and liposomes targeted with ligands for precise cellular engagement.

One exciting aspect of gene delivery is cationic liposomes (CLs), a lipid-based nanoparticle that can efficiently transport nucleic acids such as DNA and RNA into cells. One key advantage of CLs is their positive charge, allowing them to bond with the negatively charged strands of genetic blueprints effectively. This interaction between the CLs and the genetic material promotes cellular uptake and can enhance gene delivery efficiency. 

One notable success story involving liposomes as gene therapy vectors is their application in treating genetic ovarian cancers. In clinical trials, researchers have successfully employed liposomal vectors to deliver genetic material directly to the lungs of patients suffering from conditions like cystic fibrosis. 

Gold Nanoparticles: Precision Targeting in Gene Therapy

Gold nanoparticles are minuscule particles made of gold with distinct characteristics that make them very effective at carrying genetic sequences directly into cells. They become chameleons of sorts. They can be outfitted with positively charged components that magnetically draw in the negatively charged DNA strands, ensuring they can tightly hold onto the genetic sequences. These particles can be tethered to DNA or RNA, either solidly locked in via chemical bonding or attached more loosely, to ensure stability during delivery into cells.

To zero in on their cellular targets, gold nanoparticles can sport specialized ligands, like folic acid, fine-tuning their ability to deliver DNA to specific types of cells. Some nanoparticles are engineered to react to stimuli—like a red light or a shift in oxidation levels—activating DNA released right where it’s needed in the cell.

A new technology called “CRISPR-Gold” has been developed using gold nanoparticles. It can encapsulate the CRISPR components, including the Cas9 enzyme, guide RNA, and donor DNA. In a study, this system was delivered to mouse models of Duchenne muscular dystrophy (DMD) to correct the faulty dystrophin gene. This led to improved muscle strength and reduced fibrosis. The CRISPR-Gold approach showed high efficiency, with 5.4% of the dystrophin gene-corrected and minimal off-target effects.

Overall, gold nanoparticles have promising applications in gene delivery. Potential side effects must be thoroughly investigated and mitigated, especially at high concentrations or with improper design. When combined with techniques such as electroporation or ultrasound, they can take advantage of the EPR effect (enhanced permeability and retention) in pathological tissues, allowing them to accumulate in higher concentrations at the disease site. The EPR effect occurs because of the unique properties of pathological tissues characterized by compromised vasculature. The blood vessels of these tissues have gaps between cells. This makes them leaky and allows larger particles like gold nanoparticles to enter more easily.

Electroporation

Electroporation is a pivotal technique in gene therapy, enabling the transfer of genetic material into cells with an efficiency once thought unattainable. The fundamental principle of electroporation lies in applying high-voltage electric pulses that transiently disrupt the phospholipid bilayer of cell membranes. This temporary disruption manifests as pores forming within the membrane, allowing molecules such as DNA and RNA, which typically cannot permeate the membrane easily, to slip into the cellular interior.

Controlled electrical pulses form these “electropores,” their size and lifetime can be adjusted by manipulating pulse parameters. By fine-tuning the voltage, pulse duration, and the number of pulses, the process can be optimized for various cell types and materials intended for internalization, making the method both precise and versatile.

Several strengths have bolstered Electroporation’s strategic role in gene therapy. It enhances transfection rates, even for recalcitrant cells, optimizes the in vitro and in vivo application for numerous therapeutic scenarios, and skirts many safety issues commonly associated with viral vectors. Electroporation’s versatility is also evident as it allows for various modes of gene transfer, catering to the specific needs of in vivo or ex vivo protocols.

Gene therapy has been revolutionized by electroporation, which has improved safety, efficacy, and flexibility. However, we are now exploring natural intracellular communication methods such as exosomes as gene manipulation technology advances.

Exosomes: Nature’s Ingenious Messengers

Exosomes are tiny vesicles naturally produced by cells and play a vital role in intercellular communication. These lipid packages contain various biomolecules, including proteins, lipids, and nucleic acids. They also play a role in many biological processes, such as immune responses, tissue repair, and gene regulation.

Recent research has shown that exosomes can also be used as vehicles for gene therapy. By engineering these vesicles, it’s possible to capitalize on their unique ability to traverse biological barriers and deliver therapeutic nucleic acids to targeted regions. The conversion of exosomes into gene therapy vehicles requires careful manipulation of their lipid composition and surface proteins. 

Ferritin: Ironclad Delivery

The human body’s iron storage system, ferritin, has been found to have a unique ability to act as a carrier for nucleic acids. This carrier technology involves modifying ferritin to act as a vector, which allows it to specifically target and bind to cellular receptors, promoting receptor-mediated uptake of healing genes into target cells.

This innovative technology protects against the immune system’s surveillance, preventing it from recognizing and attacking therapeutic nucleic acids. This, in turn, enables these nucleic acids to reach their intended target more efficiently. By working as a Trojan horse for nucleic acids, this technology has the potential to revolutionize gene therapy and treat various genetic disorders. Unfortunately, we have not yet found any explicit successful cases of using these vectors outside of cancer therapy and chemotherapy treatments. However, the potential of this technology is promising.

Challenges and Opportunities

Non-viral vectors are emerging as a promising approach for gene therapy. Unlike viral vectors, they do not carry the same potential safety risks associated with viral infections. Non-viral vectors can be formulated with various materials such as lipids, polymers, peptides, and inorganic nanoparticles. They have the potential to carry large gene sequences, lower immune responses, and enable large-scale production.

However, non-viral vectors face several challenges that limit their efficacy. One significant challenge is the low efficiency of cellular uptake, which means that only a tiny fraction of the administered vector reaches the target cells. Another challenge is the clearance of the vector by immune surveillance, which recognizes the vector as a foreign entity and clears it from the body. Additionally, non-viral vectors can be degraded within the body before they reach their intended target. Despite these challenges, we are continuously making progress in developing non-viral vectors for gene therapy.

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