Discovery of Novel Oxazolo[4,3-f]purine Derivatives as Antitumor Agents through PPIA Interaction

54 novel oxazolo [4,3-f]purine derivatives were designed, synthesized, and evaluated for antitumor activity, among which compound 20b exhibited potent activity against several cancer cell lines. Compound 20b inhibited cell metastasis, arrested the cell cycle in the G0/G1 phase, and induced apoptosis in HCT116 cells. Mechanistic studies revealed that 20b increased ROS levels and led to DNA damage, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction in HCT116 cells. Limited proteolysis-small molecule mapping (LiP-SMap), drug affinity responsive target stability (DARTS) assay, cellular thermal shift assay (CETSA), and surface plasmon resonance (SPR) experiments provided evidence that compound 20b bound to PPIA with a KD value of 0.52 μM. siRNA assay indicated that 20b-mediated antiproliferative and antimigration activities were abolished and that the PPIA/MAPK signaling pathway was inhibited when PPIA was silenced in HCT116 cells. Significantly, compound 20b presented significant anticolorectal cancer efficacy in vivo without obvious toxicity. These results indicate that 20b may serve as a novel anticancer agent targeting PPIA, meriting further attention in antitumor drug research.