UC Irvine researchers have developed a new method designed to activate chemotherapy drugs more precisely within cancer cells, aiming to reduce damage to healthy tissues. The findings, published in Signal Transduction and Targeted Therapy, detail a strategy that turns a cell’s own protein-recycling machinery into a trigger for drug activation.
The new approach addresses a fundamental challenge in chemotherapy: highly potent drugs that kill cancer cells can also harm healthy tissue. Researchers at UC Irvine designed an experimental prodrug, which is a pharmacologically inert compound, to become active only when it encounters specific conditions within a cancer cell.
At the core of this strategy is the immunoproteasome, a specialized component of the cellular mechanism responsible for breaking down proteins. Immunoproteasome activity can be elevated in various cancers and inflammatory conditions. The research team connected an extremely toxic anticancer agent, monomethyl auristatin E (MMAE), to a short peptide. While this peptide is attached, MMAE is effectively “caged,” which limits its ability to harm cells. When elevated immunoproteasome activity is detected inside a cancer cell, the immunoproteasome cuts the peptide, thereby releasing the active MMAE. This mechanism allows the drug to activate selectively where it is needed.
Darci Trader, UC Irvine associate professor of pharmaceutical sciences and vice chair of postgraduate studies in that department, explained that the goal is to leverage existing differences in cancer cells to activate a drug precisely where its toxic effects are desired. This method involves “harnessing the unique immunoproteasome activity as a prodrug trigger,” rather than relying on traditional enzyme inhibitors.
This strategy differs from many existing targeted cancer therapies, which typically use antibodies to recognize specific proteins, or antigens, on the surface of cancer cells. While such antibody-drug conjugates have transformed treatment for some cancers by carrying a toxic drug directly to cells displaying a specific marker, not all cancers present suitable surface targets. The UC Irvine approach instead investigates what is happening inside the cancer cell, exploiting internal biological differences.
Experiments demonstrated that the immunoproteasome could recognize the specially designed peptide and release MMAE. Cancer cells that exhibited high immunoproteasome activity were highly sensitive to the prodrug. In contrast, healthy cells with low immunoproteasome activity remained viable, indicating a potential way to create a therapeutic window that attacks cancer while limiting healthy tissue exposure.
Claudia Benavente, UC Irvine associate professor of pharmaceutical sciences and a member of the Chao Family Comprehensive Cancer Center, noted that this work expands the understanding of targeted therapy. She stated that cancer cells are not defined solely by their surface characteristics; important biological differences in their function can reveal therapeutic vulnerabilities.
Researchers, including study leader Cody A. Loy, who recently earned a Ph.D. in pharmaceutical sciences from UC Irvine, next tested the method in small cell lung cancer, an aggressive form of the disease with limited treatment options. Laboratory studies confirmed that the experimental prodrug maintained strong cancer-killing activity in these cells. Moving into a preclinical model, the team found that treatment with the prodrug led to a significant reduction in tumor volume without substantial toxicities. This provides early evidence that immunoproteasome activity can function as an internal switch for selective drug delivery in a living system.
The work remains in the preclinical stage, and further research is necessary before this approach can be evaluated as a treatment for patients. Researchers also need to identify which specific cancers possess sufficiently high immunoproteasome activity to benefit from this strategy. However, given that elevated immunoproteasome activity occurs across multiple cancer types, the researchers believe the concept could extend beyond small cell lung cancer.
This research was supported by startup funding from the UC Irvine School of Pharmacy & Pharmaceutical Sciences and the Chao Family Comprehensive Cancer Center, which provided resources for investigating the immunoproteasome. Additional funding came from the National Institutes of Health, National Cancer Institute, National Institute of Allergy and Infectious Diseases, American Lung Association, and UC Irvine’s Vertex Diversity Graduate Research Program. The study involved researchers across multiple disciplines at UC Irvine, including pharmaceutical sciences, cancer biology, physiology and biophysics, and developmental and cell biology. Darci Trader emphasized that this progression, from understanding cellular machinery to controlling drug activation, demonstrates how fundamental discoveries can lead to entirely new possibilities for drug development.
