Pristimerin, the methyl ester of celasterol, is a triterpenoid quinone methide isolated from Pristimerae indica. Pristimerin shows anticancer activity in vitro towards myeloma, prostate, breast, ovarian cancer cell lines and inhibits xenografted plasmacytoma tumors in mice. In a rat model of adjuvant arthritis, pristimerin effectively inhibited both arthritic inflammation and cartilage and bone damage in the joints. Pristimerin acts by inhibiting NF-kB signaling pathway and the 26S proteasome.