USP7 represents a therapeutic target for EGFR-driven and EGFR-TKI–resistance to EGFR mutations in lung cancer

Lung cancer remains one of the most formidable challenges in modern medicine, particularly a type known as non-small cell lung cancer. For many patients, the disease is driven by a specific protein on the surface of their cells called EGFR. This protein acts like a switch that, when stuck in the "on" position, tells the cell to grow and divide uncontrollably. Doctors have developed powerful drugs to turn this switch off, but the cancer often finds a way to bypass the blockade, continuing to grow despite the treatment. To understand why this happens and how to stop it, scientists must look deeper than just the switch itself. They need to understand the machinery that keeps the switch stable and the hidden pathways that allow the cancer to survive when the main route is blocked.

A team of researchers has now identified a crucial piece of this machinery. They found that a specific enzyme, which they call USP7, acts as a master regulator for the cancer's survival. In healthy cells, proteins are constantly being built and broken down in a controlled cycle. The researchers discovered that USP7 interferes with this cycle by removing the molecular tags that mark proteins for destruction. By doing so, it stabilizes two key proteins: the EGFR switch and another protein called c-Abl, which helps the cancer cell communicate and move. When USP7 is present, these proteins remain stable and active, fueling the tumor's growth. The study shows that when scientists remove USP7, the cancer proteins fall apart, and the tumor's ability to grow and spread collapses.

The investigation began by looking at tissue samples from forty-two patients with lung cancer. The researchers compared the genetic activity in the tumor tissue against the healthy tissue from the same patients. They found that in nearly three-quarters of the cases, the gene for USP7 was turned up much higher than normal. This high level of activity was not just a random occurrence; it was tightly linked to signs of aggressive disease, such as the cancer spreading to other parts of the body and a poorer outlook for the patient. The data suggested that tumors with high levels of USP7 were running a more dangerous program, one that relied heavily on the EGFR and c-Abl proteins to survive.

To prove that USP7 was actually causing the problem rather than just being a bystander, the scientists turned to laboratory experiments. They used a precise genetic tool to remove the USP7 gene from lung cancer cells grown in a dish. Without this enzyme, the cancer cells lost their ability to multiply and move. They could no longer form colonies or grow into three-dimensional spheres, which are models of how tumors behave inside the human body. When the researchers put these modified cells into mice, the tumors grew significantly slower and were much smaller than those formed by normal cancer cells. This confirmed that USP7 is essential for the cancer to thrive.

The team then dug into the molecular details to see exactly how this enzyme works. They found that USP7 physically grabs onto both the EGFR protein and the c-Abl protein. Once attached, it strips away the ubiquitin chains that would normally signal the cell to recycle these proteins. It is like a worker who removes the "dispose of" tags from a machine, ensuring it stays in operation. Because the proteins are no longer destroyed, they accumulate and form a powerful complex that sends constant growth signals to the cell. The researchers showed that this complex activates several downstream pathways, including those that control cell division and survival. When they restored the USP7 gene in the cells where it had been removed, the cancer cells immediately regained their aggressive behavior, proving that the enzyme was the missing link.

Perhaps the most significant finding was that this mechanism works even when the cancer has developed resistance to standard treatments. Many patients with lung cancer have mutations in their EGFR gene that make the cancer grow on its own, and they often take drugs designed to block these mutated switches. However, the cancer eventually learns to resist these drugs. The researchers tested their theory on cell lines that carried these specific, hard-to-treat mutations, including a complex mutation known as L858R/T790M/C797S. They found that even in these resistant cells, USP7 was still holding the EGFR and c-Abl proteins together. When they used a chemical inhibitor to block USP7, the mutant proteins destabilized and broke down, just like the normal ones. The cancer cells stopped growing and lost their ability to spread, regardless of the specific mutation they carried.

The study also tested a specific drug called P5091, which is designed to inhibit USP7. In the lab, this drug successfully reduced the levels of EGFR and c-Abl in both normal and mutated cancer cells. It suppressed the growth of tumors in a way that mimicked the genetic removal of the enzyme. The drug was effective at concentrations that did not immediately kill the cells, suggesting it targets a specific vulnerability rather than causing general toxicity. The researchers calculated that the drug was effective at very low concentrations, with some cell lines responding to levels as low as one micromolar. This indicates that targeting USP7 could be a viable strategy for patients whose cancer has stopped responding to current therapies.

The implications of these findings are substantial for the future of lung cancer treatment. The research suggests that the stability of the cancer's growth proteins is a critical weak point that has been overlooked. By focusing on the enzyme that keeps these proteins stable, doctors might be able to shut down the cancer's engine even when the usual switches are jammed. The study establishes that USP7 is a central hub that coordinates the cancer's ability to adapt and survive. While the work was conducted in cells and mice, the results provide a strong foundation for developing new medicines that could help patients who have run out of options. The researchers propose that blocking this enzyme could be a mutation-independent strategy, meaning it could work across different types of lung cancer, offering a new path forward for a disease that has long been difficult to cure.