Popular Antidepressants May Enhance the Immune System's Ability to Fight Cancer

Recent research from UCLA suggests that commonly used antidepressants, specifically selective serotonin reuptake inhibitors (SSRIs), could play a role in boosting the immune system's capacity to combat cancer. The study demonstrated that SSRIs significantly improved the effectiveness of T cells — key immune cells involved in attacking tumors — across various cancer models in both mice and humans.

This discovery is promising because SSRIs, such as Prozac and Celexa, are already widely prescribed for depression and have a well-established safety profile. These drugs work by increasing serotonin levels in the brain through inhibition of the serotonin transporter (SERT). While serotonin is traditionally associated with mood regulation, it also influences numerous bodily processes, including immune response.

The research team initially focused on serotonin's role in immune function after observing elevated levels of serotonin-regulating molecules in immune cells from tumor sites. Their previous work revealed that T cells produce the enzyme MAO-A to break down serotonin, which can hinder their ability to fight cancer. Blocking MAO-A improved T cell activity but posed safety concerns due to side effects. Therefore, the team shifted focus to targeting SERT with SSRIs, which are safer and have fewer adverse effects.

In experiments, SSRIs decreased tumor size by over 50% and enhanced T cell activity against cancer cells, including in models of melanoma, breast, prostate, colon, and bladder cancers. Furthermore, combining SSRIs with immune checkpoint therapies, like anti-PD-1 antibodies, resulted in significant tumor reduction and instances of complete remission. These findings imply that SSRIs could make existing cancer treatments more effective.

The implications are substantial, considering that about 20% of cancer patients in the U.S. are prescribed antidepressants. The possibility of repurposing SSRIs as adjuncts to cancer therapy offers a cost-effective and swift pathway to new treatment strategies. The researchers are planning clinical trials to examine if cancer patients taking SSRIs experience better outcomes, especially in conjunction with immunotherapies.

Overall, this study highlights the potential of leveraging existing FDA-approved drugs to enhance anti-cancer immunity and improve patient responses, marking a significant step forward in cancer research and treatment options.

Source: https://medicalxpress.com/news/2025-05-common-antidepressants-immune-cancer.html