Celastrol inhibits the SmBiT–YAP1/LgBiT–TEAD interaction in a dose-dependent manner and inhibits YAP1/TAZ–TEAD biosensor activities in vitro and in vivoCelastrol significantly inhibited cell proliferation and decreased cell viability in H1299 lung and MDA–MB-231 breast cancer cells. It also significantly inhibited cell growth in H1299 (up to 88% reduction at 5 μM). The gene discussed is YAP1; the disease is breast carcinoma.