Cambridge researchers develop tumor-targeted STING activator to safely boost cancer immunity

Researchers at Cambridge have engineered a fundamentally different approach to cancer immunotherapy—one that activates the body's defenses only where tumors exist, leaving healthy tissue untouched.

The work centers on a cellular pathway called STING, which functions as an internal alarm system. When activated, STING signals the immune system to mobilize and attack. Scientists have long recognized that drugs triggering this pathway could be powerful cancer fighters. But there has been a persistent problem: activate STING in normal tissue, and the results can be severe, even dangerous. The challenge has been precision—how to turn on the alarm only at the cancer site.

Professor Gonçalo Bernardes and his team at Cambridge's Yusuf Hamied Department of Chemistry solved this by designing what they call a prodrug: two separate, harmless chemical components that circulate through the body inert and useless on their own. Only when they encounter a tumor-specific enzyme called β-glucuronidase—which is rarely present in healthy tissue—does the first component unlock. Once unlocked, it immediately bonds with the second component, and together they form a potent STING activator. The two molecules are engineered to recognize and bind to each other with remarkable efficiency, so the reaction happens quickly and selectively inside the tumor itself.

"This is like sending two safe packages into the body that only unlock and combine when they meet the tumour's unique chemistry," Bernardes explained. "The result is a strong immune-activating drug that appears only where it is needed."

In laboratory tests, the individual components showed almost no activity. But when researchers exposed them to tumor conditions, the active compound formed and successfully triggered STING at very low concentrations. The real validation came in animal models. In zebrafish and mice engineered to produce β-glucuronidase, the drug activated almost exclusively in tumors while vital organs—liver, kidney, heart—remained protected. The findings, published in Nature Chemistry, represent a significant advance for STING-based therapies, which have historically struggled to distinguish between cancerous and healthy cells.

What makes this approach distinctive is its chemical simplicity. Rather than relying on complex biological engineering or artificial reactions, the Cambridge team achieved targeted immune activation through straightforward molecular design. Nai-Shu Hsu, the study's first author, noted that the discovery opens a broader conversation about drug safety: "This is exciting not only for cancer treatment, but also as a new way of thinking about how we make medicines safer and more precise."

The researchers believe the concept extends well beyond oncology. The principle of safe, inert components that only assemble into active drugs at disease sites could be adapted for other conditions where potent medications must be delivered with minimal collateral damage. This work suggests a new class of precision medicines may be emerging—one where the drug itself remains dormant until it reaches exactly where it needs to be.