We'd all like to see groundbreaking solutions to brain cancer and neurodegenerative diseases such as Parkinson's or Alzheimer's. But perhaps, appropriately enough, accessing the brain can be a perplexing business. It's protected by a mechanism called the blood-brain barrier, meant to keep out unwanted pathogens and toxins. Unfortunately, in the process, it also prevents about 95 percent of intended medicines and therapeutic treatments from reaching their target.
Now through novel approaches and groundbreaking research, scientists at the National Research Council of Canada (NRC) are helping bring the dream of more effective brain treatments one step closer to reality.
A team of researchers at the Therapeutics Beyond Brain Barriers program within the NRC's Human Health Therapeutics Research Centre have developed a novel approach that is allowing scientists to predict which therapeutics, intended to target the central nervous system, will be able to successfully cross the blood-brain barrier. It could lead to a range of new treatments for a variety of conditions, such as Alzheimer's, amyotrophic lateral sclerosis (ALS), dementia, epilepsy, neural infections and even the Zika virus. At the core of the new approach is a breakthrough in transforming human amniotic fluid cells to produce a unique kind of stem cell that can be differentiated into any cell type in the body, known as induced pluripotent stem cells (iPSCs).
"With induced pluripotent stem cells, we have the capability to generate all the different cell types we want to study in the brain," says NRC research scientist Dr. Anna Jezierski.
A Model for Success
This breakthrough research holds great promise as a tool for advancing medical and pharmaceutical applications – from modelling and understanding disease processes to the creation of vaccines and personalized medicines. The predictive model also allows researchers to rank and optimize lead candidates earlier in the design process, thereby reducing costs.
The development of the stem cell-derived blood-brain barrier model was pioneered by the late Dr. Mahmud Bani-Yaghoub, Team Leader of the HHT In Vitro Pharmacology Group. The process involves 2 steps – developing the induced pluripotent stems cells (iPSCs) and then differentiating them into the blood-brain barrier model itself. By reprogramming amniotic fluid cells into iPSCs and treating them with a cocktail of growth factors and media, Dr. Bani-Yaghoub and his team were able to induce the cells to differentiate into brain endothelial cells. These are the same kind of cells that form the blood-brain barrier, and therefore mimic many of its properties.
"Our approach offers several advantages over existing protocols: it's simplified and streamlined, less labour intensive, and highly reproducible. Most importantly, it's very efficient and the final cell types we obtain are very pure," emphasizes Dr. Jezierski.
The model itself is created by seeding a layer of the endothelial cells onto a semipermeable insert, which acts as a proxy for the blood-brain barrier. Cells hidden behind the barrier, such as human neurons (also iPSC-derived), are placed in a bottom compartment. Therapeutics, diagnostics and infectious agents are then tested not only for their ability to pass through, but also for their effectiveness in treating target cells.
Accelerating Canadian Biopharmaceutical Innovation
The NRC has already put its new blood-brain barrier model into action. Its Therapeutics Beyond Brain Barriers program is one of a very few in Canada – and the world – that has a human iPSC-derived blood-brain barrier model available to industry, government, and university researchers to gauge the success of therapeutics in crossing the blood-brain barrier. Canadian companies such as Cyclenium Pharma and ViDa Therapeutics have already accessed the lab's expertise and received support and advice on innovation through the NRC Industrial Research Assistance Program.
"The benefits of having access to the relevant and reliable assay for blood-brain barrier penetration, as well as the exceptional expertise at the NRC, are numerous," says Mark Peterson, Chief Operating Officer of Cyclenium Pharma. "In particular, the model has allowed us to assess a critical new characteristic of our designed macrocyclic molecules and been essential in our drug discovery projects that target the central nervous system."
The new model is also front and centre in supporting exciting research into Zika virus infections. In collaboration with NRC researchers Dr. Judie Alimonte and Dr. Wayne Conlan, it was used to demonstrate that Zika virus can, in fact, cross the blood-brain barrier without disrupting its integrity—thereby infecting brain cells. By the same token, the model will also serve as an essential tool as industry and government researchers work to develop and screen antiviral therapeutics aimed at limiting the disease process of Zika virus in the brain.
New Frontiers: From 2D to 3D
Creating an effective 2D predictive model is a remarkable feat, but what if researchers could take it one step further and create models in three dimensions? That's exactly what the NRC, in partnership with Aspect Biosystems, is aiming to do. Through a collaboration made possible via funding from the Build in Canada Innovation Program, NRC researchers will be among the first in the world to harness microfluidic 3D bioprinting technology to create multicellular 3D tissue of the iPSC blood-brain barrier model.
This innovative approach is essential because there's more to the blood-brain barrier than just endothelial cells. The actual barrier is made up of a complex biological structure consisting of astrocytes, pericytes and other cell types, referred to as the neuro-vascular unit. 3D bioprinting will allow researchers to create actual structures that mimic not only the biological cell properties of the barrier, but also their anatomical and physiological context.
"By employing the use of groundbreaking new bioprinting technology we're actually printing living cells," says Dr. Betty Li, who recently joined the NRC as a postdoctoral fellow and will be spearheading efforts to create the 3D model. "In turn, this will allow us to create a living model of the blood-brain barrier that will deepen our understanding of this complex system and make our screening process even better able to predict the effectiveness of potential therapeutics."
Overall, finding novel ways to get past the blood-brain barrier will have a significant impact on the development of drugs to treat diseases that affect the central nervous system, such as Alzheimer's.
"The blood-brain barrier exists in a 3D micro-environment that is critical to its function," explains Jezierski. "By creating a model in three dimensions that can reproduce the architecture and cellular diversity of the in vivo blood-brain barrier, we can better understand the interactions that will potentially occur between the barrier and intended therapeutics. We're excited to be at the forefront of this promising new research."
Note: This article reflects the work pioneered and led by 2 of the NRC's Senior Human Health Therapeutics research officers, Dr. Mahmud Bani-Yaghoub (1964–2016) and Dr. Judie Alimonte, (1960–2017), who will be fondly remembered for their devoted work in developing the human blood-brain barrier model and understanding of Zika virus pathogenesis.