Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer
By: Linkoping University
Introduction
In a landmark development that could reshape the landscape of pediatric oncology, researchers have announced a significant breakthrough in targeting a protein long considered "undruggable." This discovery offers new hope for children suffering from aggressive cancers, particularly Ewing sarcoma, a disease that has historically resisted traditional treatment methods.
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
The challenge of "undruggable" proteins has loomed large over cancer research for decades. While targeted therapies have revolutionized the treatment of many adult cancers—such as lung cancer and melanoma—pediatric cancers often operate through different biological mechanisms. These childhood cancers are frequently driven by "transcription factors": proteins that bind to DNA and turn genes on or off. Because these proteins lack the deep pockets or crevices that small-molecule drugs typically latch onto, pharmaceutical companies have largely viewed them as impossible to treat with medication.
However, a new study published in a leading oncology journal details a novel strategy that bypasses this structural hurdle, effectively neutralizing the cancer-causing protein driving tumor growth.
The Elusive Target: EWS-FLI1
At the heart of this research is a specific aberration found in Ewing sarcoma, a rare but devastating bone and soft tissue cancer that primarily affects children and adolescents. In approximately 85% of Ewing sarcoma cases, a genetic accident causes the 'EWSR1' gene to fuse with the *FLI1* gene. The result is a mutant fusion protein, known as EWS-FLI1.
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
This fusion protein acts as a master switch. Once activated, it hijacks the cell's genetic machinery, turning off genes that suppress tumors and turning on genes that drive uncontrolled cell division. Because EWS-FLI1 is a transcription factor, it is inherently disordered; it does not have a fixed, rigid structure. This "floppiness" makes it incredibly difficult to design a drug that can stick to it.
"For years, EWS-FLI1 has been the 'Holy Grail' of pediatric cancer research," explains the study’s lead author. "We knew it was the engine driving the cancer, but we had no way to turn the engine off. We were trying to shoot a moving target that had no surface to grab onto."
A New Strategy: Protein Degradation
Faced with the failure of traditional inhibition, the research team turned to a cutting-edge approach known as "Targeted Protein Degradation (TPD)". Instead of trying to inhibit the protein's function—which requires binding to a specific active site—this new class of drugs aims to destroy the protein entirely.
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
The technique utilizes a mechanism called a "PROTAC" (Proteolysis Targeting Chimera). Think of a PROTAC as a molecular bridge. On one end, it latches onto the cancer-causing protein (EWS-FLI1). On the other end, it binds to an E3 ligase, an enzyme naturally present in the cell that acts as a garbage disposal tagger.
Once connected, the E3 ligase tags the "undruggable" protein with a molecule called ubiquitin. This tag signals the cell's proteasome—the waste management system—to recognize the protein as trash and degrade it.
"This is fundamentally different from how standard chemotherapy or even standard targeted therapy works," the researchers note. "We aren't just putting the brake on the protein; we are removing it from the cell entirely. Without the EWS-FLI1 protein, the cancer cells essentially forget who they are and stop growing."
Overcoming Skepticism
The path to this discovery was fraught with skepticism. For many years, the pharmaceutical industry avoided investing in transcription factors, deeming them too risky. The biological dogma suggested that without a defined binding pocket, drug interaction was impossible.
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
However, the team persisted by exploring previously ignored "cryptic" pockets—tiny, transient grooves on the surface of the protein that appear for only fractions of a second. Using advanced computational modeling and X-ray crystallography, they were able to map these fleeting structures and design a molecule that could exploit them.
Furthermore, the researchers discovered that EWS-FLI1 relies on a network of partner proteins to function. By disrupting the interaction between the fusion protein and its RNA helicase partners, they destabilized the entire cancer-driving complex.
Promising Pre-Clinical Results
The study reports impressive results in pre-clinical models. In laboratory cell lines derived from Ewing sarcoma patients, the new degrader molecule rapidly reduced EWS-FLI1 protein levels. Within hours, the genetic signature of the cancer cells reverted to a normal state, and the cells began to die (apoptosis).
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
Crucially, the treatment was tested in mouse models harboring human Ewing sarcoma tumors. In these models, the drug led to significant tumor regression without displaying the severe toxicity often associated with chemotherapy. Because EWS-FLI1 is not present in healthy cells (it exists only as a result of the cancer mutation), the drug acts as a "guided missile," sparing the patient's healthy tissue.
"The selectivity is remarkable," the team observed. "We are hitting a target that exists only in the tumor. This suggests we could potentially treat patients with much lower doses, avoiding the harsh side effects that plague childhood cancer survivors later in life."
Implications Beyond Ewing Sarcoma
While the immediate focus is on Ewing sarcoma, the implications of this research extend far beyond a single disease. The "undruggable" label applies to many other pediatric cancers, such as certain forms of leukemia, neuroblastoma (driven by the MYCN protein), and medulloblastoma.
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
By proving that transcription factors can be effectively degraded using heterobifunctional molecules, this study opens the door for a whole new class of therapeutics. The research team is already investigating whether similar degraders can be designed to target MYCN in neuroblastoma, another aggressive childhood cancer with limited treatment options.
"This validates the concept that if we can understand the biology of the protein well enough, we can find a way to drug it," the authors conclude. "It removes the excuse that these targets are inaccessible."
The Road Ahead
Despite the excitement, the researchers caution that there is a long road ahead before this drug reaches the clinic. The next phase involves optimizing the chemical structure of the degrader to ensure it remains stable in the body and can effectively penetrate tumor tissue.
| Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer |
Following pre-clinical optimization, the team hopes to move into Phase 1 clinical trials within the next few years. These trials will determine the safety profile of the drug in humans and establish the appropriate dosage levels.
For the families of children diagnosed with Ewing sarcoma, this research represents a beacon of hope. Current treatments involve a grueling combination of chemotherapy, radiation, and surgery, which often leaves survivors with lifelong disabilities and secondary health issues. A targeted therapy that specifically eliminates the cancer cells while preserving healthy tissue could radically improve the quality of life for these children.
In the fight against cancer, the "undruggable" barrier has been the most formidable fortress. With this new approach, scientists have finally breached the walls, signaling a new era in the war on childhood cancer.
Labels: Targeting the Untargetable: Scientists Break Through the "Undruggable" Barrier in Childhood Cancer
