Researchers at the University of Bath have developed a new technology that uses bacteria to build, chemically stabilise, and test millions of potential drug molecules inside living cells, making it much quicker and easier to discover new treatments for difficult-to-treat cancers.
- The technology uses bacteria to produce vast libraries of peptide molecules, and chemically stabilise (or ‘staple’) them into defined shapes while they are being tested inside the cell.
- Only bacteria that produce peptides which are both effective and non-toxic survive, allowing researchers to rapidly identify the most promising potential drug candidates.
- By combining chemical modification and biological testing in a single step, the approach streamlines drug discovery and lets biology do the hard work.
- The team has used the technology to identify peptide inhibitors of transcription factor CREB1, which is overactive in a broad range of cancers including colorectal cancer.
- They have shown these peptides can enter human cancer cells grown in the lab, shut down CREB1-controlled pathways, and selectively kill cancer cells.
Scientists based at the University’s Department of Life Sciences are investigating peptides – short chains of amino acids, the building blocks of proteins – as potential drugs for a family of notoriously ‘undruggable’ cancer drivers known as transcription factors. These proteins act as master switches that control gene activity and are frequently overactive in cancer.
Chemical "staple" stabilises peptide
In their latest study, published in Cell Chemical Biology, the team has created a bacterial system in which each bacterium produces a different peptide, which is then chemically modified inside the living cell. This chemical step acts like a molecular staple, locking each peptide into a defined shape that it would not normally adopt.
Crucially, this chemical ‘stapling’ happens after the peptide is made but while it is still inside the cell, allowing the researchers to test millions of structurally stabilised peptides directly in a biological setting.
Because the chemistry occurs inside living cells, the approach is also cleaner, greener, and cheaper than conventional peptide drug discovery. It avoids the toxic solvents and multi-step chemical processes usually required to make and ‘staple’ peptides in the lab.
Traditional methods require peptides to be made, purified, chemically modified, and then purified again. In contrast, the stapled peptides can be recovered directly from the cell in a single, simplified step. This simplicity also makes the approach inherently scalable, as the same bacterial processes used for discovery could, in principle, be adapted for larger-scale peptide production and manufacturing.
Survival of the best blocker
The modified peptides are then screened for activity using a technique developed by the team called the Transcription Block Survival (TBS) assay. In this system, bacteria can only survive if the peptide they produce successfully blocks the cancer-causing transcription factor.
By combining chemical peptide stabilisation with the TBS assay, the researchers can simultaneously make and screen tens of millions of different stapled peptide variants for their ability to switch off a transcription factor target in a single experiment.
Because survival depends on successful target blocking, the most effective stapled peptides quickly dominate the bacterial population. At the same time, any peptides that are unstable, ineffective, or toxic are automatically eliminated during the process.
Dr Andrew Brennan, from the University of Bath’s Department of Life Sciences and first author of the paper, said:
“Some cancers are driven by transcription factors that are stuck in the ‘on’ position, causing cancer cells to grow and spread when they shouldn’t. This uncontrolled growth is what drives tumours to form and metastasise.
“Our approach uses peptides to interfere with these faulty switches. What’s new is that we can chemically stabilise tens of millions of different peptides inside the cell while we test them, rather than doing this later in the lab.
“Only the bacteria producing peptides that are both stable and effective survive, so the best candidates naturally rise to the top.
It’s a powerful way of letting biology and chemistry work together.
Potential new cancer therapeutics
The team demonstrated the power of technology by discovering peptide inhibitors of a transcription factor called CREB1, which is overactive in a broad range of cancers including colorectal cancer.
They showed that the most promising peptides can enter human cancer cells grown in the laboratory, shut down CREB1-controlled pathways, and selectively kill cancer cells.
The next step will be to test whether these peptide inhibitors are effective in more complex tissue models and animal studies.
Professor Jody Mason, from the University of Bath’s Department of Life Sciences and the Institute of Sustainability and Climate Change, said:
“What excites us is that we’re not just finding peptides that bind a target, but peptides that are chemically stabilised, resistant to breakdown, and functional inside live cells.
“This opens up a completely new way to go after cancer targets that have long been considered undruggable.”
Funding The research was funded by a Biotechnology and Biological Sciences Research Council Responsive Mode Grant and a Medical Research Council World Class Labs Award.
Translation and commercial development The platform reported in this study forms the scientific basis of Revolver Therapeutics, a University of Bath spin-out company established to translate intracellular peptide discovery technologies into new cancer medicines.
The Transcription Block Survival (TBS) assay and the in-cell peptide stapling technology are exclusively licensed to Revolver Therapeutics, where they are being developed for progression toward preclinical and clinical evaluation.