Inhibiting miR-25 Could Improve Immunotherapy Response in Cold Tumors

Immune checkpoint therapy, a type of cancer immunotherapy that helps the immune system recognize and attack tumors, has transformed cancer treatment. While these therapies can produce long-lasting benefits for some patients, many cancers either fail to respond or become resistant over time. One major challenge is the tumor microenvironment - the network of cells and signals  surrounding tumors that can weaken immune cells  and protect cancer from treatment. This protective environment can act like a shield that prevents immunotherapy from working effectively.

Researchers at University of California San Diego investigated whether microRNAs - small RNA molecules that help control gene activity - play a role in creating this treatment-resistant environment. The team focused on microRNA-25 (miR-25), which stood out after analyses showed that its levels changed in tumors that responded to immunotherapy. Across several mouse cancer models, blocking miR-25 did not significantly affect tumor growth on its own, but it greatly improved how well tumors responded to immunotherapy.

Further analyses showed that removing miR-25 reshaped the environment around the tumor and activated several anti-tumor immune responses. Removing miR-25 appeared to help the immune system attack cancer cells by changing the environment surrounding tumors. Researchers identified a mechanism involving a protein called Syndecan-3 (SDC3), which miR-25 suppresses. Editing the miR-25 binding site restored SDC3 activity and reproduced the therapeutic effects seen with miR-25 deletion, suggesting this pathway may be a critical driver of treatment resistance.

The findings suggest that future therapies targeting the miR-25–SDC3 pathway could help convert immunotherapy-resistant “cold” tumors into more immune-active “hot” tumors that respond better to treatment. The work may eventually help make immunotherapy effective for more cancer patients.