A High-Throughput Assay to Identify Specific Nascent Chain Inhibitors

Many of the proteins that keep our bodies running are like locked safes: they have no obvious handle or keyhole on their surface for a medicine to grab onto. For decades, drug developers have struggled to create treatments that can stop these "undruggable" proteins, because the standard approach relies on finding a specific spot on a finished, folded protein to block. However, proteins do not appear fully formed; they are built piece by piece inside the cell's factories, stretching out like a long string before they curl up into their final shape. During this brief moment of construction, the protein exists in a different form, one that might expose a temporary opening that disappears once the protein is finished. If scientists could find a way to catch these proteins while they are still being built, they might be able to stop them before they ever become a threat.

A team of researchers has now created a new tool designed to hunt for exactly this kind of intervention. They developed a method to watch proteins being made in a test tube, using a system that mimics the human body's own machinery for reading genetic instructions and assembling proteins. In this setup, the researchers can see the protein appear in real time by watching it glow with a fluorescent light. The goal is to find tiny chemical compounds that act like a brake, stopping the production of a specific protein only while it is still a nascent chain, or a growing string, without interfering with the production of other proteins. To ensure the tool is precise, the scientists built in a second check to compare results, making sure any compound found is truly targeting the specific protein of interest and not just shutting down the entire factory.

The researchers fine-tuned this system to be incredibly sensitive and affordable, costing only about one cent per test, which makes it possible to screen thousands of chemicals at once. They first tested the method using a known compound called PF846 on a protein called PCSK9 to prove the system worked. Then, they put the method to the test with a large collection of 1,760 different compounds, aiming to find inhibitors for two specific targets: a variant of a protein linked to cancer known as KRAS A146T, and a protein called ApoC3. The results showed that the system was robust and reliable, capable of handling large-scale searches with high consistency.

When the screening campaign concluded, the researchers found that sixteen of the compounds successfully stopped the production of proteins, but they did so by halting the entire translation process, meaning they acted as general inhibitors rather than precise tools. Crucially, none of the compounds met the strict criteria for selectively stopping only the specific proteins the team was targeting. While the study did not yield the specific "nascent chain" inhibitors the researchers were hoping to find, it successfully demonstrated that the platform itself is ready for much larger and more extensive searches. The work establishes a solid, working foundation that allows scientists to continue looking for those elusive compounds that can catch proteins in the act of being built.