Targeting peripheral 5-HT_2AR enhances antitumor immunity in colorectal cancer

Cancer remains a leading cause of morbidity and mortality worldwide. While classical psychedelics have been used clinically to treat cancer-associated psychiatric disorders, their impact on tumor progression is unclear. Here, we show that by targeting the serotonin receptor 5-HT_2AR, lysergic acid diethylamide (LSD) enhances CD8⁺ T cell-mediated antitumor immunity and suppresses colorectal cancer (CRC) growth. To harness this activity while avoiding psychedelic effects, we developed IHCH-8110, a non-brain-penetrant 5-HT_2AR agonist that selectively targets peripheral 5-HT_2AR. We show that IHCH-8110 inhibits CRC progression by activating 5-HT_2AR on enteric glial cells, thereby inducing CXCL10 and interleukin (IL)-18 expression to promote CD8⁺ T cell recruitment and effector polarization within the tumor microenvironment. By converting immune-cold CRC into a more immunologically responsive state, IHCH-8110 enhances the efficacy of PD-1 blockade. Together, our findings identify enteric 5-HT_2AR signaling as a regulator of antitumor immunity and support peripheral 5-HT_2AR agonists as a therapeutic strategy for CRC immunotherapy.