RNA silencing technology could be the future of medicine

Onpattro has Canadian roots and is the first FDA-approved RNAi treatment

RNA silencing technology could be the future of medicine

In August, Alnylam Pharmaceuticals released patisiran, trade name ONPATTRO, an injectable drug that treats hereditary transthyretin (ATTR) amyloidosis.

While this may seem like just another experimental drug release among tens and hundreds each year, this one is particularly notable: it’s the first RNA interference (RNAi) therapy approved by the US Food and Drug Administration.

RNAi silences specific messenger RNAs (mRNA), transcribed from DNA, before they have a chance to be used for protein synthesis. As such, it can be used to prevent the translation of otherwise defective proteins.

Hereditary ATTR amyloidosis causes a buildup of a protein known as amyloid in the nervous system. When amyloid accumulates, it can cause debilitating damage to the nervous system and more serious cases can result in death.

The technology for patisiran was first developed in the laboratory of University of British Columbia (UBC) Professor Pieter Cullis in collaboration with UBC Professor Marco Ciufolini.

Patients in trials reported significant improvements in motor skills, reflexes, and other essential functions of the nervous system after 18 months of treatment.

Many therapies have sought to target DNA and RNA as a permanent treatment to various diseases and conditions, although this becomes more complicated, since there are several categories of RNA. It would be difficult to cast a net that is wide enough to target genetic abnormalities, but selective enough to not destroy pathways necessary for proper functioning.

This is where RNAi therapy comes in.

On their way to being translated into proteins, an enzyme known as Dicer typically intercepts sections of RNA and cuts them in two; one half is degraded immediately, while the other half is shuffled into a complex called the RNA-induced silencing complex (RISC).

But during RNAi, specific messenger RNAs are silenced after DNA has been transcribed to RNA. Dicer selectively targets certain pieces of RNA. The RISC, now containing this small piece of RNA, can use it as a template to target and degrade similar pieces of RNA, which allows silencing of specific RNA sections throughout a cell — sometimes even an organism as a whole — and inhibits the production of disease-causing proteins.

RNAi technology is useful for pinpointing a gene’s function. In fact, U of T Professor Jason Moffat’s lab is working on identifying genes in human cancer cell lines using RNAi, among other methods. U of T Professor Andrew Fraser uses RNAi to ‘turn off’ genes in worms to identify potential mutations in the human genetic code.

RNAi can be manipulated for the treatment of genetic and hereditary diseases and, with the correct specificity, could revolutionize medicine.

Op-ed: Minding our makeup

Considering the pros and cons of DNA editing

Op-ed: Minding our makeup

Not too long ago, ‘designer babies,’ genome editing and gene therapy were futuristic and expensive ideas that were available only to the most affluent elite.

Yet, today, this baffling feat is becoming shockingly affordable. In the last few years you may have been hearing about the new technology known as CRISPR/cas9, more commonly referred to as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats). It is a new, precise, and efficient method for editing DNA.

Since its initial debut in 2012, CRISPR’s capabilities have leapt forward every year. Some highlights include modifications of genomes in non-viable human embryos by Chinese scientists, modifications in pig embryos by US scientists in an effort to create pig organs viable for human organ transplants, and more recently, the authorization for UK scientists to begin experimentation in modifying viable human embryos.

CRISPR/Cas9 is not without its drawbacks. Although its precision has improved since its first introduction, the risk of off-target cuts exists and can range from 0.1 per cent to more than 60 per cent, depending on the target cell and sequence used in the experiment. Its power to wipe out entire species in under a year can be disastrous and have widespread effects on entire ecosystems.

For example, scientists have shown that by mutating a single gene in a single mosquito to render it sterile, they could essentially kill off all mosquitos in roughly 12 generations (36 weeks). But what does that mean for bats who rely on mosquitos as a food source? Use in human embryos could lead to ‘designer babies’ with the ability to pick and choose certain traits, consequently reducing genetic variation in populations.

It is a rather inexpensive and simple technique that can be easily accessed, and dangerous if not regulated. There has been such an explosive reaction to this new technique that it has outpaced our ability to create legal and ethical guidelines, and mandates for its use.

CRISPR has opened up new avenues for researching genetic diseases and gene therapy. While there are a number of concerns that accompany this research, the potential advantages are notable. CRISPR is more precise, efficient, and affordable than past methods of gene editing. There is still a lot of work to be done but initial studies have shown promising results.

In Toronto, CRISPR gene editing is currently being tested as a way to prevent and eliminate hereditary diseases like cystic fibrosis or muscular dystrophy, which do not currently have cures. It also has the potential to regulate genes instead of simply editing them. This means that it could activate some genes and silence others (like those which fuel cancer growth). 

CRISPR technology is propelling genetics research forward. There are a number of ethical concerns accompanying this advancement, and regulatory bodies need to catch up. As the leading agency responsible for regulating health products, Health Canada’s responsibility for creating a comprehensive regulatory framework will ultimately determine how CRISPR’s capabilities will affect our society.

The agency has prioritized a sub-program for Biologics and Radiopharmaceuticals for 2015-2016 (which covers gene therapy products) with the goal of generating a regulatory framework to develop, maintain, and implement the program. As the CRISPR technology is moving forward rapidly in Canada and abroad, this regulatory framework is urgently needed.

Health Canada must ensure that the regulatory framework adequately addresses the concerns that are surfacing with the development of CRISPR, both domestically and internationally. Harmonization of CRISPR regulations and requirements will be necessary to ensure equal protection for citizens and reduce medical tourism. Countries are moving forward at different paces — the United Kingdom for example has already approved use of CRISPR for research on human embryos.

In December 2015, the National Academy of Sciences (NAS) held an international summit on Human Gene Editing after the Chinese Academy of Scientists asked for a ban on clinical use of human germ line editing. The meeting concluded that research should continue with proper oversight, and that editing germ line cells should not proceed until safety and efficacy concerns have been resolved. These discussions should continue to form the basis of a comprehensive regulatory framework for the use of CRISPR worldwide.

So why does CRISPR matter to us as students? CRISPR is not elusive technology. It is already being used in many labs at the university because of its broad range of applications and its ability to rapidly create animal models for testing. Students have an obligation to understand the benefits of CRISPR technology and the current debates surrounding its application.

Students have an important voice to advocate for how CRISPR technology can be used in the future because its implications will directly affect our generation. CRISPR offers substantial benefits and holds promise as an inexpensive treatment for a variety of genetic disorders. However, its powers should be used cautiously so as to not let it become a destructive villain.

Anna Foster and Parmida Jafari are on the advocacy sub-committee of IMAGINE at U of T, a student-run community health initiative aimed at promoting and discussing healthcare in Toronto.

Shape-shifting cancer

U of T’s Institute of Biomaterials and Biomedical Engineering researchers have discovered a way to make nanoparticles “shape-shift”

Shape-shifting cancer

Dr. Warren Chan of UofT’s  Institute of Biomaterials and Biomedical Engineering, along with PhD student Dylan Glancy and postdoctoral fellow Seiichi Ohta, have managed to “shape-shift” nanoparticles in their most recent study.

Extensive research on nanoparticles has demonstrated a strong potential for the small objects to contribute to the highly localized delivery of drugs in the treatment of cancer. Some researchers speculate that within half a century, we will look back at the practice of injecting freely transported drugs into our circulatory system as a crude convention of the past. While having Aspirin molecules freely floating in your blood is usually benign, one cannot say the same for commonly used chemotherapy drugs. 

Nanoparticle design has two primary issues: first finding, and then interacting with the correct cell and not its neighbours.

Nanoparticles must survive the trip through the blood stream, evade the body’s immune system, and, in the case of cancer, penetrate deep into dense tumor tissue and into individual cells. 

Once there, the right cell is targeted through the use of  “lock and key” arrangements, where the nanoparticle snugly latches on to a specific molecule, unique to the affected cells.

Unlike most nanoparticles, those developed by Dr. Chan and his associates have the ability to switch shapes, from a rod to a sphere. “Rod-shaped nanoparticles for example are good at penetrating tumors, while spherically shaped ones are absorbed by cells more easily.” explained Glancy. “Most of the currently existing dynamic nanoparticles might permanently lose an outer layer or increase in size under different conditions, but they don’t change shape, and they definitely don’t do it reversibly.”

This reversibility will be helpful in the removal of the nanoparticles from out of the tumor and into the blood stream after they have done their job.

This shape change is brought about by the use of flexible adhesive strands of DNA known as “biological Velcro.” There are two core nanoparticles of different sizes strung together by DNA, with the larger core being “orbited” by smaller “satellite” particles. All of the particles have sticky DNA threads attached to their surface. 

Introduction of loose DNA can help link the DNA on the satellites simultaneously to both core particles, and not just one. The introduction of additional competitive loose DNA helps break the linkage between the satellite particles and the larger core by removing the original linker DNA. This graceful displacement, described by Glancy as “DNA origami,” results in an elongation of the resultant structure from a sphere to a rod and vice versa. 

The beauty of using DNA is that it can be designed to simultaneously adhere to specific DNA molecules expressed by faulty cancer cells. Alternatively, the particles can additionally be decorated with proteins that are known to interact with other proteins found on the surface of cancer cells, due to the large surface area of the nanoparticles. Examples of “lock and key” pairs suggested by Dr. Chan include the popular antibiotic Herceptin and HER2 receptors, as well as folic acid and folate receptors, both of which are receptors commonly displayed in breast cancer cells. 

“This can be very useful in targeting cancer cells that have metastasized, which are extremely hard to localize through surgery for example” added Glancy, “and since they are usually found closer to blood vessels, they can fortunately be easily reached by the blood transported nanoparticles.”

Once the nanoparticles are engulfed by oblivious cancer cells, they can release their drug “pay-load.”

Good things come in small packages, and thanks to the pioneering work of Dr. Chan and his associates, our newest way to attack cancer may come in a small, shape-shifting, package.