Indoleamine 2,3-dioxygenase (IDO), an immune checkpoint, is a promising target for cancer immunotherapy. However, current IDO inhibitors are not approved for clinical use yet; therefore, new IDO inhibitors are still demanded. To identify new IDO inhibitors, we have built naive Bayesian (NB) and recursive partitioning (RP) models from a library of known IDO inhibitors derived from recent publications. Thirteen molecular fingerprints were used as descriptors for the models to predict IDO inhibitors. An in-house compound library was virtually screened using the best machine learning model, which resulted in 50 hits for further enzyme-based IDO inhibitory assays. Consequently, we identified three new IDO inhibitors with IC values of 1.30, 4.10, and 4.68 μM. These active compounds also showed IDO inhibitory activities in cell-based assays. The compounds belong to the tanshinone family, a typical scaffold family derived from Danshen (a Chinese herb), the dried root of , which has been widely used in China, Japan, the United States, and other European countries for the treatment of cardiovascular and cerebrovascular diseases. Thus, we discovered a new use for Danshen using machine learning methods. Surface plasmon resonance (SPR) experiments proved that the inhibitors interacted with the IDO target. Molecular dynamic simulations demonstrated the binding modes of the IDO inhibitors.

No abstract

(+)-Rutamarin inhibits EBV lytic DNA replication with an IC of 7.0 μM. (-)-Chalepin, a (-)-rutamarin derivative, was isolated from the whole plant of Ruta graveolens and used as a precursor of (-)-rutamarin. Altogether, 28 (-)-rutamarin derivatives were synthesized starting from (-)-chalepin. Of these, 16 compounds (2a-e, 3b-e, 3g, 4f, 4k, 4m-p) were found to be more potent against EBV lytic DNA replication than (-)-chalepin. Compounds 4m, 4n, and 4p exhibited IC values of 1.5, 0.32, and 0.83 μM and showed selectivity index values (SI) of 801, 211, and >120, respectively. Thus, compounds 4m, 4n, and 4p are considered promising leads for further laboratory investigation.

No abstract