In the quest to minimize the devastating collateral damage of chemotherapy and improve the precision of drug delivery, scientists at the University of California San Diego have pioneered a groundbreaking chemical tool known as TRACE (tetrazine release and activation by cellular enzymes). This innovation represents an extraordinary leap towards selective drug activation at the cellular level, whereby powerful therapeutic agents can be unleashed solely within targeted cells, radically reducing harm to healthy tissues and enhancing overall treatment efficacy.

Traditional chemotherapy agents face an inherent challenge: their lack of discrimination between malignant and normal cells frequently results in harmful side effects, sometimes severe enough to limit their clinical use. Innovative chemical strategies that can tightly control where and when drugs become active inside the human body have long been sought to address this issue. TRACE is a prime example of such innovation, utilizing the power of bioorthogonal chemistry—a cutting-edge approach that enables chemical reactions to proceed in living systems with unmatched selectivity and minimal biological interference.

Bioorthogonal chemistry involves the design of chemical moieties that react exclusively with each other within biological environments, effectively performing “click” reactions that attach diagnostic or therapeutic agents to biomolecules without disturbing native biochemical processes. Among the fastest and most versatile reagents in this realm are tetrazines—heterocyclic compounds known for their rapid and specific reactivity with their partner molecules. Since their introduction more than a decade ago by Neal K. Devaraj and Joseph M. Fox, tetrazine chemistry has revolutionized live-cell labeling, drug delivery systems, and materials functionalization.

Despite their speed and specificity, traditional tetrazine-based reactions have faced a crucial hurdle: they can activate indiscriminately across various cell types within complex biological milieus. This reduces the precision essential for many applications, such as targeted cancer therapy or real-time imaging of pathological processes, where only certain cells must be affected or visualized. Recognizing this limitation, Devaraj’s laboratory embarked on engineering a molecular “safe lock” to cage the reactive tetrazine, preventing it from interacting prematurely or non-selectively.

The breakthrough came in the form of enzyme-activated tetrazine cages. These cages encase the tetrazine molecules, rendering them inactive until they reach cells expressing specific enzymes capable of unlocking the cage. When the caged tetrazine encounters its target enzyme—often overexpressed in disease states like cancer—it undergoes rapid uncaging, liberating the reactive tetrazine to engage in its bioorthogonal “click” chemistry exclusively within the desired cells. This ingenious form of molecular programming imbues the chemical system with exquisite spatial resolution.

Achieving this level of cell-type specificity required extensive optimization. The researchers meticulously screened various tetrazine structures to identify candidates combining the fastest uncaging kinetics with rapid reaction turnover. To further sharpen targeting precision, they introduced tetrazine-reactive scavengers that mop up any prematurely released or non-target activated molecules, effectively suppressing background reactivity outside the enzyme-rich milieu. This elegant dual mechanism essentially narrows tetrazine activation to occur almost exclusively in the intended cellular population.

Proof-of-concept experiments employed enzymes uniquely abundant in certain pathological cells paired with doxorubicin (DOX), a potent but notoriously toxic chemotherapeutic drug. The caged tetrazine-DOX complex remained inert unless it encountered the activating enzyme, at which point doxorubicin was released to exert its cytotoxic effect precisely within the cancerous cells. This selective deployment mechanism holds immense promise for enhancing therapeutic windows, reducing systemic toxicity, and potentially overcoming drug resistance linked to broad drug exposures.

Beyond therapeutic applications, the TRACE platform also advances live-cell imaging capabilities. By integrating fluorescent probes within the tetrazine cages, the researchers devised a system where fluorescence switches on solely after enzymatic uncaging in targeted cells. This selective illumination enables unprecedented real-time visualization of enzymatic activity and cellular states, such as the detection of elevated alkaline phosphatase (ALP) activity—an important biomarker in various tumors—directly on the cell surface. Such precision could transform pathological diagnostics and allow monitoring of treatment responses with high fidelity.

This body of work reflects nearly two decades of pioneering research by Neal K. Devaraj in tetrazine chemistry and highlights the transformative potential of marrying chemical ingenuity with biological specificity. The ability to tailor chemical reactions to individual cell types within living organisms was once a distant dream; now, TRACE brings this vision within reach. By enhancing selectivity, reducing side effects, and enabling dynamic cellular imaging, this technology stands poised to redefine pharmaceutical delivery and molecular diagnostics.

Looking forward, Devaraj’s team is focused on refining the selectivity and general applicability of these enzymatic cages. The potential to customize cages responsive to a broad repertoire of cell-specific enzymes could open new frontiers in personalized medicine, allowing therapies to be fine-tuned not only to cancer cell types but to diverse pathological contexts, including infectious diseases and autoimmune disorders. The implications extend to improving the safety and effectiveness of treatments and to developing novel diagnostic tools adapted to complex biological systems.

At its core, TRACE exemplifies a paradigm shift: moving from broad-spectrum chemical interventions in biology to highly programmed, cell-specific molecular operations. This capability leverages the unique enzymatic fingerprints of different cell types to activate chemical functions only where needed, dramatically improving outcomes in both clinical and research settings. Such precision chemistry is rightly hailed as a game-changer in the science of drug delivery and bioimaging.

The resonance of this innovation extends well beyond the confines of the laboratory. The principles underlying TRACE, including enzyme-activated molecular cages and bioorthogonal chemistry, could ultimately enable real-time, in vivo tracking and control of therapeutic agents in human patients, moving the field closer to the long-envisioned goal of “smart” medicines that dynamically respond to cellular environments. This research not only adds a powerful new tool to the chemical biology arsenal but underscores the untapped potential of chemistry to revolutionize medicine and healthcare.

In summation, the TRACE system is a monumental stride in the evolution of bioorthogonal chemistry, effectively combining precision chemical engineering with biological specificity to achieve selective drug delivery and imaging. By harnessing enzyme-mediated activation and molecular cages to control tetrazine activity, the Devaraj laboratory has unlocked unprecedented spatial and temporal control over chemical reactions in live cells. As discoveries continue, this chemical toolkit promises to provide clinicians and researchers with unparalleled control over therapeutic and diagnostic processes, heralding a future where side effects are minimized and treatment efficacy is maximized.

Subject of Research: Cells
Article Title: Achieving cell-type-specific bioorthogonal chemistry using enzyme-activated caged tetrazines
News Publication Date: 3-Jun-2026
Web References: https://doi.org/10.1038/s41589-026-02240-y
Image Credits: Devaraj lab / UC San Diego
Keywords: Organic chemistry, Click chemistry, Targeted drug delivery

A medical startup says it is using disembodied human brains in new drug development research targeting neurodegenerative diseases, a practice that may draw unsettling comparisons to the science fiction trope of a living brain in a jar. 

The brains of deceased donors are reportedly being used in the work by Bexorg, a Connecticut-based medical startup, building on successful attempts to restore limited function in pig brains.

A system dubbed BrainEx, a targeted life-support system for brains, is at the core of Bexorg’s work, restoring metabolic functions in donated organs and enabling extremely invasive research, albeit in a manner that has raised some ethical concerns.

Investigating the Human Brain

In their new process, Bexorg supplies recently deceased human brains with a blood substitute and other fluids that fuel metabolic processes, while anesthesia deadens their electrical activity. The artificially life-sustaining liquids, data, and drugs flow through four ports sutured into each brain, while apparatus mimicking the lungs and kidneys inject oxygen and remove waste. 

Bexborg says that the lack of neural firing in the brain, induced by the anesthetic drug propofol, means they do not experience consciousness. In a strange twilight state, the brain operates as though it were alive, allowing researchers to observe how it metabolizes experimental drugs, yet without the electrical activity that forms consciousness.

The shelf life of these brains is rather short; after only 24 hours, the researchers cut them into hundreds of pieces for a more detailed study. These investigations are targeting how ailments such as Parkinson’s, Alzheimer’s, or amyotrophic lateral sclerosis may respond to new treatments, allowing detailed information on duration, targeting, and potential side effects.

According to Bexborg, the greatest advantage of their work is in the deep complexities of how the human brain develops over decades. The real-world effects of genetics, environmental exposures, and drug histories are difficult to capture in simulated computer models, petri dish cells, or whole-animal brains.

Bexborg Grows

While their work has only recently come to public attention, Bexborg has been working in this space for five years now. They say early results show a close match between the responses displayed by preserved examples and those of living brains.

So far, only the company’s work with pig brains has been published, with their first human brain paper forthcoming. However, according to Bexborg, recent efforts to curb animal testing may potentially be a boon to the company, offering what they see as an ethical alternative.

As part of Bexborg’s upscaling, the company says it is developing new laboratory space where a robotic arm will automatically dissect more than 1,600 preserved brains per year.

Their public relations arm was working at full steam on a public presentation this week, aimed at assuaging those who feared that the brains might still possess some form of consciousness. Bexborg did not respond to inquiries from The Debrief about exactly where the brains used in the company’s research originate. However, the company has claimed that family members are informed about how the brains will be used.

Bringing Bexborg Results to Market

The first real-world application of Bexborg’s work is coming to fruition as their collaborator, Biohaven, begins clinical trials of a drug developed using Bexborg data. Bexborg claims that their work will enable safer clinical trials, as the results will be much closer to a treatment’s effect on actual human brains than those from animal testing or simulated models.

Biohaven praised the results from testing on 130 preserved brains, noting that a dose of their drugs 20 times lower than expected yielded optimal results in human brains, thereby minimizing the time required for clinical trials and potentially alleviating major side effects that could have occurred at the higher dose.

While the company is now focused on drug testing, they say expansion into more robust disease research could be on the horizon. They also note that, since electrical activity is not a major component of neurodegenerative diseases, the BrainEx could be the ideal platform for studying these maladies.

Still, some issues exist with BrainEx, limiting it from being a perfect representation of the human body. These artificial fluids, lungs, and kidneys are not exactly he same as the human originals, and the lack of electrical activity means that potential seizure risks would go unrecognized.

In the future, Bexorg is looking to expand in two directions. The first is exploring ways to extend the longevity of their preserved brains from 24 hours to two weeks, enabling more in-depth research. The second—and perhaps at odds with the company’s focus on the human brain—is NeuroLens, a machine-learning model for simulated drug testing.

Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.