Scientists Develop 'Molecular Glue' to Destroy Undruggable Cancer Protein

Colorectal cancer is the second leading cause of cancer-related deaths globally, and roughly 10% of patients carry a specific genetic error known as a BRAF mutation. This mutation acts as an always-on switch for cell division, driving aggressive tumor growth and signaling a poor prognosis for those diagnosed.[2][6]

While targeted BRAF inhibitors have transformed the treatment of melanoma, they frequently fail in colorectal cancer. When treated, these tumors quickly adapt by utilizing a feedback loop involving the epidermal growth factor receptor (EGFR) to reactivate the MAPK signaling pathway. Consequently, patients often develop resistance and relapse within four to six months.[2][6]

Researchers have long known that an RNA-binding protein called HuR (encoded by the ELAVL1 gene) plays a critical role in this resistance. HuR stabilizes the messenger RNA that produces these escape pathways, allowing the tumor to survive. However, because HuR lacks the deep structural pockets required for traditional small-molecule drugs to bind, the pharmaceutical industry has historically classified it as "undruggable."[1][2]

A study published in the journal Nature by researchers at ShanghaiTech University and Degron Therapeutics has introduced a breakthrough solution to this bottleneck. Rather than attempting to block HuR's function, the team developed a "molecular glue degrader" designed to destroy the protein entirely.[1][3]

Molecular glues represent a paradigm shift in drug discovery. Instead of inhibiting a protein's active site, they act as chemical matchmakers. The newly discovered compound, optimized as dHuR-2, forces the HuR protein to bind with Cereblon (CRBN), a component of the cell's natural E3 ubiquitin ligase system.[1][2]

Cryo-electron microscopy revealed that the molecular glue uses a benzofuran core to bridge the gap between CRBN and HuR. Once this unnatural ternary complex is formed, the system tags HuR with a chain of ubiquitin molecules. This acts as a molecular "kiss of death," directing the cell's proteasome to shred the HuR protein into harmless peptides.[1][2]

The genetic consequences of destroying HuR are profound. The Nature study provides strong evidence that HuR normally binds to a specific sequence within the BRAF pre-mRNA. When HuR is degraded, the alternative splicing of the BRAF genetic instructions is severely altered, specifically causing the skipping of exon 18.[1][6]

This splicing error results in a truncated, highly unstable version of the BRAF protein that is incapable of driving tumor growth. Simultaneously, the degradation of HuR lowers the expression of EGFR, effectively shutting down the tumor's primary escape route and preventing the MAPK pathway from reactivating.[1][2]

Preclinical evidence demonstrates the potency of this approach. In patient-derived xenograft (PDX) models—where human colorectal tumors are grown in mice—the molecular glue showed significant anti-tumor activity on its own.[1][3]

Crucially, unbiased CRISPR screening and in vivo tests revealed that combining the HuR degrader with existing BRAF, EGFR, or MEK inhibitors creates a massive synergistic effect. The combination therapy suppressed tumor progression far more effectively than any single agent, offering a clear strategy to overcome acquired drug resistance.[1][2]

The evidence has already catalyzed clinical translation. Based on the discovery of dHuR-2, Degron Therapeutics developed a clinical-grade molecular glue candidate named DEG6498.[2][5]

This compound has received Investigational New Drug (IND) clearance from both the U.S. Food and Drug Administration and China's National Medical Products Administration. It marks a significant milestone as the first molecular glue targeting an RNA-binding protein to reach clinical development.[2][5]

A Phase 1 clinical trial is currently underway to evaluate the safety, tolerability, and preliminary efficacy of DEG6498. The study is enrolling patients with advanced solid tumors, specifically targeting those with BRAF-mutant colorectal cancer who have exhausted standard treatment options.[2][4]

Despite the robust preclinical data, transparent uncertainty remains regarding the drug's future in humans. Phase 1 trials are designed primarily to assess safety and toxicity. Because HuR is a fundamental RNA-binding protein that stabilizes various mRNAs in healthy cells, systemic degradation could potentially yield unforeseen off-target effects or dose-limiting toxicities.[4][6]

If DEG6498 proves safe and effective, the implications extend far beyond colorectal cancer. The successful degradation of HuR validates the molecular glue platform as a viable strategy for targeting the vast universe of RNA-binding proteins, potentially unlocking treatments for dozens of previously "undruggable" genetic drivers of disease.[3][6]