Synthesis and Structure-Activity Relationship Studies of Small Molecule Cancer Immunotherapies

Abstract

Inhibition of tyrosylprotein sulfotransferase-2 (TPST2) represents a promising strategy for cancer immunotherapy. TPST2-mediated sulfation of the interferon-γ receptor (IFNGR) suppresses IFN-γ signaling, which plays a crucial role in antigen processing and presentation. Therefore, inhibition of TPST2 enhances antitumor immunity by restoring and amplifying IFN-γ signaling. In a previous study, the importance of a hydrogen bond acceptor at the meta-position of the phenyl ring was revealed through the optimization process of a hit compound identified during screening. Compound 1, obtained after multiple optimization cycles, exhibited inhibition of TPST2 with an IC50 of 1.2 ± 0.3 μM. This study reports the design, synthesis, and in vitro enzyme assay evaluation of 1-phenyl-heterocyclic and 1-alkyl-heterocyclic derivatives as potent TPST2 inhibitors. Structure-activity relationship (SAR) analysis revealed that heterocycle-based derivatives, replacing the thiophene core, exhibited superior activity compared to thiophene derivatives, and an alkyl chain length of three carbons significantly enhanced inhibitory activity. Docking study showed that 7a and 11a were predicted to have similar binding poses in the active site of TPST2 while sharing a crucial hydrogen bond with the Lys300 residue. In vivo pharmacokinetic evaluation of compound 7a showed a bioavailability of 96.7%, supporting its potential as an orally administrable therapeutic candidate. Collectively, this study provides an important foundation for the development of small molecule cancer immunotherapy.