Engineered subtilisin protease degrades active KRAS in cancer cells leading to differential cell targeting

Inside the cells that make up every living thing, there is a complex system of switches that tells the cell when to grow and when to stop. One of the most important of these switches is a protein called RAS. In a healthy cell, RAS acts like a careful manager, turning on only when it receives a specific signal to help the cell divide, and then turning off just as quickly. However, when the gene that makes RAS becomes mutated, the switch gets stuck in the "on" position. This causes the cell to grow and divide without stopping, leading to cancer. For decades, scientists have struggled to find a way to fix this broken switch. The protein is slippery and lacks the deep pockets where most medicines usually latch on, making it notoriously difficult to target with traditional drugs. While some progress has been made with small molecules that block the switch, a more direct approach has remained largely unexplored: simply cutting the broken switch out of the cell entirely.

A team of researchers at the University of Maryland has taken a bold step toward this direct approach by engineering a biological tool designed to hunt down and destroy the active, cancer-causing version of RAS. They created a custom-made enzyme, a type of protein cutter, that acts like a molecular pair of scissors. This tool was built to recognize a specific shape that only the active, dangerous form of RAS takes. When the enzyme finds this shape, it snips the protein, breaking it apart and rendering it useless. The researchers tested this tool in cancer cells that rely entirely on this broken switch to survive, and the results were striking: the cells died rapidly, while normal cells remained unharmed.

The story of this discovery begins with the nature of the RAS protein itself. RAS exists in two main states: an inactive state, where it is bound to a molecule called GDP, and an active state, where it is bound to GTP. In the active state, the protein changes its shape slightly, exposing a hidden region that is normally tucked away. This exposed region is the key. The researchers realized that if they could build a cutter that only recognizes this exposed shape, they could target the dangerous, active RAS while leaving the harmless, inactive RAS alone. They turned to a natural enzyme found in a bacterium called Bacillus subtilis, known as subtilisin. This enzyme is a powerful cutter, but in its natural form, it is too broad and would cut many things it shouldn't. The team re-engineered this enzyme to be highly specific, training it to look only for the exposed region on the active RAS protein. They named their creation RASProtease, or RASp for short.

To make sure this new tool could be controlled, the scientists added a safety switch. They designed the enzyme so that it would only become active if a specific helper molecule was present. They created two versions: one that required a chemical called imidazole to turn on, and another that required nitrite. Nitrite is a substance that occurs naturally in the body and is often found in higher concentrations in cancer cells, while imidazole is not naturally present in human cells. By using these helpers, the researchers could control exactly when and where the enzyme would start cutting. In their initial tests, they found that the version requiring nitrite was far more efficient at its job, cutting through its target much faster than the version requiring imidazole.

The researchers then moved from simple chemical tests to living cells to see if their tool could work in a real biological environment. They started with a common laboratory cell line called HEK 293T, which contains normal, healthy RAS. They introduced the enzyme into these cells and watched what happened. When the enzyme was turned on, it successfully cut the RAS protein, but the cells themselves did not die. This was an important finding because it suggested that the enzyme was not just randomly destroying everything in the cell; it was doing its job without causing immediate chaos to normal cells that did not depend on RAS for their survival.

Next, the team turned their attention to a much more dangerous target: a pancreatic cancer cell line called MIA PaCa-2. These cells are driven by a specific mutation in the RAS gene, known as G12C, which locks the protein in the active, cancer-causing state. These cells are entirely dependent on this broken switch to grow and survive. The researchers introduced their nitrite-dependent enzyme into these cancer cells and activated it. The result was dramatic. Within 24 hours, the enzyme had found and cut the active RAS proteins. As the RAS proteins were destroyed, the signals that told the cancer cells to grow and divide were cut off. The cancer cells, unable to function without their primary driver, began to die. The researchers observed that nearly all the cancer cells were gone within a day, a level of destruction that far exceeded what happened in the normal cells.

To understand exactly how this happened, the scientists looked closely at the signals inside the cells. They found that when the enzyme cut the RAS protein, the entire chain of communication that followed it also shut down. This included a pathway involving proteins called MEK and ERK, which are crucial for telling the cell to divide. By removing the source of the signal, the enzyme effectively silenced the cancer's growth engine. They also saw that another pathway involving a protein called AKT, which helps cells survive, was also shut down. This confirmed that the enzyme was not just cutting a single protein but was dismantling the entire network that the cancer cells relied on.

One of the most significant aspects of this work is the precision of the attack. The researchers discovered that the enzyme's ability to target the active form of RAS depended on how much enzyme was present. When they used a large amount of enzyme, it cut both the active and inactive forms of the protein. However, when they used a very small, limited amount—more like what would happen in a real treatment—the enzyme became highly selective. It ignored the inactive, normal RAS and focused its energy almost exclusively on the active, cancer-causing version. This selectivity is crucial because it means the treatment could potentially kill cancer cells while sparing healthy ones, which is the holy grail of cancer therapy.

The study also explored how the enzyme behaves in different environments. They found that the enzyme worked well in cell extracts and in living cells, proving that it could function in the complex soup of a real biological system. They used a technique called nuclear magnetic resonance to watch the enzyme interact with the protein in real-time, confirming that the enzyme was indeed binding to the specific shape of the active protein before cutting it. This level of detail gave them confidence that the mechanism was working exactly as they had designed it.

The implications of this work are significant for the future of cancer treatment. For a long time, the idea of using an enzyme to cut a specific protein inside a human cell was considered too difficult to achieve. This research shows that it is possible to design a molecular tool that can find a specific target, recognize its shape, and destroy it with high precision. While this study was conducted in a laboratory setting using cell cultures, it provides a strong foundation for developing new types of therapies. The ability to selectively target the active form of a protein that is responsible for many cancers offers a new way to think about fighting disease. Instead of trying to block a protein with a drug, scientists might be able to design tools that simply remove the problem entirely.

The researchers also noted that their tool could be adapted to target other proteins or even different types of cancer. The design of the enzyme is flexible, meaning it could potentially be retrained to recognize other shapes or mutations. This opens up a new avenue for creating personalized treatments that are tailored to the specific genetic makeup of a patient's tumor. The fact that the enzyme can be controlled by a helper molecule adds another layer of safety, allowing doctors to turn the treatment on and off as needed.

In the end, this paper demonstrates a powerful new strategy for controlling cancer. By engineering a protein cutter that hunts down the active form of a critical cancer protein, the researchers have shown that it is possible to selectively destroy cancer cells while leaving healthy ones alone. The work moves beyond the limitations of traditional drugs and offers a glimpse into a future where we can precisely edit the molecular machinery of disease. The results are not just a theoretical possibility but a measured reality in the lab, showing that with the right design, we can outsmart the very mechanisms that drive cancer.