Scientists describe roadmap for creating ‘Trojan horse’ peptides that cross biological barriers

A new review of research on cell-penetrating peptide (CPP) clusters by scientists from Macquarie University and the University of Oxford will provide a roadmap for biomedical scientists to develop the next generation of treatments for cancer and neurodegenerative diseases.

Biological barriers such as the blood-brain barrier and the plasma membrane, which protects neurons, prevent toxins from attacking the central nervous system, but they also stop potentially life-saving treatments from reaching their intracellular targets.

More than half of the structures in the body that can potentially be affected by drugs are found inside cells, making it vital to find ways to carry large molecules such as antibodies and gene treatments across these biological barriers.

CPPs were first discovered three decades ago as a possible answer to the problem. They are cheap to produce, have a long history in research and are easy to integrate into biologics, but problems with their efficacy have meant that no therapy using them has yet been approved by world regulatory bodies.

A major breakthrough came two years ago, in the form of CPP clusters that could be engineered to carry payloads of antibodies, proteins, enzymes and peptides across biological barriers.

Oxford University researchers created the first tricyclic CPP group, which was also the first in the world to transport functional antibodies into cells at low concentrations. At the same time, another research team from Nanyang Technological University in Singapore made a conceptually similar discovery, using a different agent to transport mRNA into cells.

Dr. Ole Tietz, one of the Oxford team, is now a Senior Research Fellow at Macquarie University’s Dementia Research Center (DRC). He says this discovery marked a fundamental shift in understanding how CPPs can be used.

“The key to successful CPP cluster transporters lies in arranging them in a specific configuration so that they can act as a switch to block the barrier,” he says. “These clusters are molecular Trojan horses, fooling the blood-brain barrier by allowing the molecules they carry to pass through.

“Until now, many therapies have had to be administered at very high doses for a small amount to pass through, and this can cause cytotoxicity, which can have very serious effects. There is a small therapeutic window with these treatments, after where you reach a concentration that is toxic and starts killing cells instead.

“These next-generation CPPs have the potential to allow us to deliver the minimum needed for treatment, which can dramatically improve patient outcomes.”

To help other biomedical scientists navigate the development and use of CPPs, Dr. Tietz has written a systematic review, published in the latest edition of Trends in Chemistry, that brings together all the research findings on this new class of CPP, effectively creating a roadmap for using the new paradigm.

Lead author Joseph Reeman, a Research Masters student at Macquarie Medical School, says one of the key aspects of the paper is providing a set of design criteria.

“These guidelines will help researchers develop the next generation of intracellular therapies, with a focus on translation into clinical practice,” he says.

“We cover how to use existing CPP clusters with payloads and how to create new clusters, the unsolved questions of what should happen in the field, as well as some of what we are currently addressing through our research program.”

The team is currently developing an array of CPPs that they hope can be used as a plug and play carrier for various types of intracellular treatments, including antibodies and gene therapies. Animal testing has already shown it can penetrate the brain, and they are now investigating whether it can transport an antibody across the blood-brain barrier and into a neuron.

If successful, it could be used to target pathogenic aggregates of brain proteins TDP-43 and tau that are associated with neurodegenerative diseases including Alzheimer’s disease, frontotemporal dementia and motor neuron disease, which are a key focus of research for DRC scientists.

This content was originally published on The Macquarie University Lighthouse.