A new study from UCLA has revealed that common antidepressants may help the immune system fight cancer.
Researchers found that selective serotonin reuptake inhibitors (SSRIs)—medications like Prozac and Celexa—boost the ability of certain immune cells, called T cells, to attack cancer cells.
The findings, published in the journal Cell, suggest that these widely used drugs could open new doors in cancer treatment.
SSRIs work by increasing serotonin levels in the brain, which improves mood. But serotonin also plays important roles in other parts of the body, including the immune system. The UCLA team, led by Dr. Lili Yang, discovered that SSRIs help make T cells more active against tumors.
They tested these drugs in lab models of various cancers, including breast, prostate, colon, bladder, and skin cancer. The results were striking: tumors shrank by more than 50%, and killer T cells became stronger and more effective.
“It turns out SSRIs don’t just make our brains happier—they also make our T cells happier, even while they’re fighting tumors,” said Dr. Yang. She is a senior researcher at UCLA’s Broad Center of Regenerative Medicine and a professor of microbiology, immunology, and molecular genetics.
Because SSRIs have been used safely for decades to treat depression, repurposing them for cancer treatment could be faster and less expensive than developing a brand-new drug.
The research started when the team noticed that immune cells in tumors had higher levels of proteins related to serotonin control. In earlier work, the scientists had studied a protein called MAO-A, which breaks down serotonin and other brain chemicals.
They found that when T cells made more MAO-A, it weakened their ability to fight cancer. Blocking this protein helped the T cells work better. But MAO inhibitors (MAOIs), which treat depression by blocking MAO-A, can have serious side effects.
This time, the team focused on a different target: SERT, the serotonin transporter protein that SSRIs block. SERT only controls serotonin, so drugs targeting it are safer and have fewer side effects. Dr. Bo Li, the study’s first author, explained that SERT made a perfect target for cancer research.
When mice were given SSRIs, their tumors got smaller and their T cells became more energized. These results suggest that SSRIs make the tumor environment less toxic for immune cells, allowing them to survive longer and attack harder.
The team also tested what happens when SSRIs are combined with existing cancer treatments. They added an anti-PD-1 antibody—a common immunotherapy drug—to the SSRIs. This combination had even better results: tumors shrank dramatically, and some mice experienced complete remission.
“Immune checkpoint blockades like anti-PD-1 work for fewer than 25% of patients,” said researcher James Elsten-Brown. “If SSRIs can help these drugs work better, it could change the lives of many cancer patients.”
To move this research forward, the team wants to study cancer patients who are already taking SSRIs. Since about 20% of cancer patients also take antidepressants, they see a unique chance to compare outcomes. Dr. Yang said the next step is designing a clinical trial to compare how cancer patients with and without SSRIs respond to treatment.
Repurposing approved drugs like SSRIs could also save a lot of time and money. Developing a new cancer drug costs around $1.5 billion. In contrast, using existing drugs might cost about $300 million. This makes the approach both promising and practical.
A patent has been filed for this strategy by the UCLA Technology Development Group. It names Dr. Yang and Dr. Li as co-inventors. With such encouraging results, this research may lead to faster, safer, and more affordable cancer treatments in the near future.
If you care about cancer, please read studies about Research finds a new cause of cancer growth and findings of Scientists find the missing link between autoimmune diseases and blood cancer.
For more about cancer, please read studies about A common blood thinner can help fight cancer and findings of Heavy alcohol drinking is common in cancer patients.
The study is published in Cell.
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