New “lock-and-key” chemistry

(Press-News.org) Many therapeutic molecules used in cancer treatments are highly toxic, often harming healthy tissues and causing significant side effects. This creates a critical need for strategies that localize their toxic activity to tumors. What if cancer drugs could stay dormant until they reach cancer cells? A new study by Syracuse University researchers demonstrates a promising chemistry-based strategy that could do just that.

Xiaoran Hu, assistant professor of chemistry in the College of Arts & Sciences (A&S), and his team introduced a prototyping “lock-and-key” system that holds therapeutic drugs in an inactive, caged form until a separate chemical trigger releases them at a specific site. The study was published in Angewandte Chemie International Edition. It introduces a new platform to control when and where chemical bonds break inside living systems. “We are developing a broadly applicable tool that has the potential to regulate the activity of different types of therapeutics” Hu says. “Think of this as a tool, like a hammer, that could be used on different nails.”

A New Kind of Chemistry to Regulate Drug Activity

The cornerstone of this work is the concept of biorthogonal chemistry, which describes chemical reactions that proceed in a highly selective fashion such that these reactions can be conducted in biological systems (e.g., within cells or the body) without disturbing native biological processes—and, at the same time, the complex biological environment doesn’t interfere with the reactions. This “biorthogonal” approach would allow researchers to control specific chemical actions inside cells and tissues with great precision.

In Hu’s study, a drug molecule is caged in a safe, inactive form, so it cannot harm healthy tissues. Once this caged drug encounters a “trigger” molecule, they will rapidly and selectively react with each other and release the toxic drug within this triggering environment. If the “trigger” is introduced to a specific location, like a tumor, it will enable localized drug release.

“Our drug-activation chemistry can be conducted in complex biological environments and does not perturb native biomolecules and cellular processes,” Hu says. “In the future, this process could improve treatment precision and reduce side effects from drugs acting in the wrong places.”

More specifically, this platform uses biorthogonal supramolecular chemistry, which allow specific “host” molecules to recognize and connect with their complementary “guest” partners in a highly selective manner so that they can be reliably conducted in complex biological environments. These interactions act as the “key” to release the drug.

This new system could address dangerous side effects in cancer treatments. Many treatments fail because they damage healthy tissues. Chemotherapy drugs circulate throughout the body, often leading to severe side effects. A system that allows drugs to remain inactive until they reach the disease site could help eliminate that damage.

“In cell-based experiments, we controlled the release of different cancer-therapeutic agents and dialed cancer cell killing up or down, suggesting new possibilities for better controlled therapies,” says Hu. “You could have special control over the turn-on of a therapy’s cytotoxicity—where and when you want it to occur, typically in cancer or tumor cells, but the rest of the human body will not have this cytotoxic effect.”

Removing Treatment Obstacles

Hu’s strategy keeps the drug inactive by “caging” a drug precursor through supramolecular interactions between a host-guest pair. But at normal body temperature (37 degrees Celsius; 98.6 degrees Fahrenheit), these interactions weaken, and therefore, could allow some drug to slowly “leak” out from the “cage” before reaching the intended triggering environment. A premature release reduces the therapeutic control and could pose increased safety risks.

“One of the biggest challenges is the stability of the host-guest complex under physiological conditions,” Hu says. “The molecular interaction that we rely on to lock this bioactive molecule is sufficient for a proof-of-concept demonstration, but at physiological temperatures and pH, the interaction is weaker. We still need to improve on the host-guest binding strength so that we can minimize premature release under therapeutically practical conditions.”

Fixing this issue is a major focus for the team. Future research will aim to strengthen the locking interactions so that the drug stays inactive while circulating and only activates when triggered.

Importantly, this platform isn’t just for cancer drugs. Because it works independently of specific biological targets, it could be adapted to a variety of therapies.

While clinical applications remain years away, the study lays the groundwork for a new way of thinking about drugs—not just as active compounds, but as programmable systems whose effects can be switched on precisely when and where they are needed.

The study was supported in part by the Syracuse University Office of Undergraduate Research and Creative Engagement.

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