MAPK8 and osteosarcoma: It was found that pentacyclic triterpenoids can inhibit JNK1 activity: oleanolic acid acetate, isoxazole ursolic amide (IUA) and celastrol were shown to significantly inhibit phosphorylation of c-Jun, a downstream effector of JNK1, in leukemia THP-1, osteosarcoma HOS and Saos-2 cells and cerebral ischemia, respectively [89,90,91].