We’ve all heard of the ancient myth of the Trojan horse, a famous tale of deception. But have you heard of molecular Trojan horses, the new way to trick the blood-brain barrier? Could this hold the key to treating many neurological diseases once thought untreatable?
What is the blood-brain barrier?
When it comes to protecting vital organs, the human body pulls out all the stops, and nowhere is this more evident than the brain. Guarded by the remarkable blood-brain barrier (BBB) – a tightly packed network of endothelial cells – almost all molecules are stopped at the door.
Historically, 100% of large-molecule and 98% of small-molecule drugs have been unable to penetrate this tight network of endothelial cells.1 With the BBB being just as picky as Goldilocks, most molecules have been either too big, too hydrophilic or too fragile.
For decades, this has been the ultimate hurdle in treating neurological disorders. But a new class of clever delivery systems, known as molecular Trojan horses, are finally giving scientists a path into the highly protected brain.
From myth to molecule
The name says it all. Much like the ancient Greek myth in which the people of Troy were deceived by a giant wooden horse, molecular Trojan horses are ingeniously engineered delivery systems that disguise therapeutic agents.
These engineered molecules use ligands or antibodies that bind to receptors naturally found on the BBB, such as the transferrin receptor or insulin receptor. Therapeutics (enzymes, RNA, small molecules, or even gene therapies) are hitched onto these carriers. Once bound, the whole package is taken up and transported across the BBB via receptor-mediated transcytosis.2
It’s a strategy that doesn’t force the barrier open. Instead, the therapeutic agents travel through the front door (with an invitation)!
Real world impact
What started as a bold idea in the lab is now moving into the real world. In recent years, we’ve seen growing momentum behind this approach. For example, Denali Therapeutics is developing biologics that cross the BBB via receptors, targeting neurodegenerative diseases like Parkinson's and Alzheimer's.
These innovations aren’t limited to classic brain diseases, either. Applications span brain cancers, lysosomal storage disorders and even psychiatric conditions, areas currently underserved by traditional drug delivery systems.
But there are some barriers yet to fall
Of course, we’re not over the finish line just yet. Several challenges remain:
- Target specificity: It is difficult to ensure the therapeutic payload stays intact until it reaches the site in the brain.
- Immunogenicity: It is thought repeated exposure to engineered proteins or nanoparticles could trigger an immune response. What if the immune system starts producing antibodies against these therapeutic drugs? What if patients cannot switch back to their previous therapy due to this?
- Manufacturing complexity: Producing multifunctional molecules at commercial scale is no small feat.
But as technologies like protein engineering, nanotech, and gene editing continue to evolve, the path ahead for many diseases is becoming brighter.
A glimpse into the future
We’re not quite at the stage of BBB delivery systems becoming the standard of care for neurological diseases, but we’re getting close. Molecular Trojan horses offer a compelling glimpse into the future: one where precision neuroscience is not only possible but expected.
Imagine a world where patients with Alzheimer’s receive early, targeted therapies that halt disease progression. Where glioblastoma treatments arrive directly at the tumour site, bypassing the systemic toxicity of chemo. Where RNA therapies for rare brain diseases aren’t blocked by biology’s most stubborn barrier.
It’s not wishful thinking, and it’s within reach.
Here at TVF we’re watching this space closely, because what was once considered science fiction is fast becoming tomorrow’s standard of care. If you would like to find out more about our expertise in neurological diseases, please don’t hesitate to reach out.
By Katie Rowe
References
- Pardridge WM. The blood-brain barrier: bottleneck in brain drug development. NeuroRx. 2005;2(1):3-14. doi:10.1602/neurorx.2.1.3
- Jones AR, Shusta EV. Blood-brain barrier transport of therapeutics via receptor-mediation. Pharm Res. 2007 Sep;24(9):1759-71. doi: 10.1007/s11095-007-9379-0.
- Denali Therapeutics Inc. Denali Therapeutics announces key anticipated 2024 milestones and priorities to further advance its therapeutics portfolio for neurodegeneration and lysosomal storage diseases. GlobeNewswire. Published January 8, 2024. Accessed September 23, 2025. https://www.globenewswire.com/en/news-release/2024/01/08/2805400/0/en/Denali-Therapeutics-Announces-Key-Anticipated-2024-Milestones-and-Priorities-to-Further-Advance-Its-Therapeutics-Portfolio-for-Neurodegeneration-and-Lysosomal-Storage-Diseases.html
