Synthesis and Metabolism of BTN3A1 Ligands: Studies on Diene Modifications to the Phosphoantigen Scaffold

Phosphoantigens (pAgs) are small organophosphorus compounds such as (E)-4-hydroxy-3-methyl-but-2-enyl diphosphate (HMBPP) that trigger an immune response. These molecules bind to butyrophilin 3A1 (part of the HMBPP receptor) and activate Vγ9Vδ2 T cells. To explore the structure-activity relationships underlying this process, we evaluated a series of novel diene analogs of HMBPP. Here we report that prodrug forms of [(1E)-4-methylpenta-1,3-dien-1-yl] phosphonic acid that lack the allylic alcohol of HMBPP but instead contained a diene scaffold exhibit mid-nanomolar potency for the activation of Vγ9Vδ2 T cells. The compounds also trigger the production of T-cell interferon γ upon exposure to loaded K562 cells. Although both the allylic alcohol and the diene scaffold boost pAg activity, the combination of the two decreases the activity and results in glutathione conjugation. Together, these data show that the diene scaffold results in intermediate pAgs that may have implications for the mechanisms regulating the HMBPP receptor.