DNA Nanoparticles Show Promise in CF Treatment
Boosting gene therapy with approved drugs may offer long-lasting help
Gene therapy holds great promise in treating a number of childhood diseases, including respiratory illnesses. But delivering treatment to the right cells, and without long-term toxicity, remains a difficult task.
One delivery system showing promise is nucleic acid nanoparticles that range in size from one-hundredth to one-thousandth the width of a human hair. They deliver nucleic acids (either DNA or RNA) to cells by compacting them into a tiny delivery system. This allows the nucleic acids to be taken up by cells, and protects the acids from being destroyed by the body’s natural defense systems. Assem Ziady, PhD, in the Division of Pulmonary Medicine at Cincinnati Children’s, helped develop the nanoparticle delivery system with other scientists some 18 years ago.
The biggest challenge in gene therapy is to be able to take DNA or RNA (which are very large molecules) and shrink enough to deliver it to a cell, and to protect them enough so they’re not destroyed on their way to the cell of interest. Developing nanoparticles made this possible, and allowed us to think about using nucleic acid as a vehicle of therapy.
Assem Ziady, PhD
The method is not without its drawbacks, however. “There is no vector that currently comes even close to being perfect, and this is still an imperfect vector. For others, immunity and safety might be a problem. For us, the problem is the efficiency of the particles, once inside the cells, is low.”
His team is working to combine the nanoparticles with drugs already approved for use in humans to enhance delivery, an approach that so far is pointing the way to success.
Nanoparticles came about as an alternative to viruses as vectors for gene therapy. Viruses were once heralded as the ideal vectors for their ability to penetrate cells and deliver therapies effectively. But results from early viral gene therapy trials showed the therapies were susceptible to immune responses, cytotoxicity, and even caused cancer. Some viral vectors were so toxic that, in the U.S. alone, at least one patient died as a result of treatment, and several other deaths are suspected to be linked to treatment. This resulted in a moratorium on gene therapy research in the early 2000s.
DNA nanoparticles have so far eliminated the risks of toxicity and immune response. In fact, they deliver on every one of what Ziady terms the “canonical four” criteria for gene therapy: They are able to target specific cells and enter them; they remain intact long enough to work within the cell; their beneficial effects can last for an extended period of time; and finally, they do not provoke immune response or toxicity.
On the downside, says Ziady, nanoparticles do not work as effectively as the viral delivery system once inside the cells. But he and his research team are working to change that.
“Our recent work is focused on understanding the cellular biology of the nanoparticles so we can manipulate it with pharmacology. Instead of changing the particle so it loses many of it advantages, we are trying to understand how we can boost its efficacy by simultaneously administering a drug to change the biology it encounters and enhance its uptake.”
Ziady and his team added the particles to cells, let them go to work, and then arrested the process, breaking the cells apart and extracting the particles to see what proteins were “stuck” to them. “This lets us see what they interacted with,” Ziady says. “I call it the ‘transfectome,’ the pathways the particles take to transfect cells.”
Ziady and his team have found 546 proteins that interact with the particle in the process of getting into the cell and traveling to their site of activity (either the nucleus or ribosome). “We can track the particles throughout the cell by understanding which proteins are interacting with them.”
And what are these 546 proteins doing? That depends, says Ziady. “When we put in a nanoparticle, some of them go to ‘traps,’ places where they aren’t going to be efficacious, given their composition. So we thought, we might want to interfere with the directing of the particles to those places where we don’t want them to go and boost their routing to those places where we do want them to go.”
By analyzing the 546 proteins, the researchers learned what pathways they sit in and what FDA approved drugs modulate them. They then discovered that by using these drugs – sometimes drugs that the patients are already taking – they can manipulate the transfectome and allow the particles to work more effectively.
“We don’t have to alter the particle – we can manipulate the biology the particle is going to be in within the patients, with one dosing of a drug, since it takes hours, not days, for the particles to travel to their site of function. This eliminates long-term treatment with the drug and drastically reduces any harmful effects.”
Ziady says they are seeing as much as a fifty-fold improvement in effectiveness with this method.
The researchers believe they could be ready for clinical trials by next year, and are currently seeking to fund their studies. DNA nanoparticles have already been tested in humans in a 2004 study, so Ziady has all the data and the safety results. He believes the setup of a second trial will go smoothly.
“We know the vector is safe and the FDA approved drugs we are proposing are safe when used correctly, so now we have to look at the safety of the combination therapy.”