Structure-activity relationship of tocopherol derivatives suggesting a novel non-antioxidant mechanism in antiprion potency.

Beneficial effects of tocopherols, or vitamin E, on degenerative brain conditions have been attributed mainly to their antioxidant effects. Non-antioxidant effects of the tocopherols have been shown to be mediated by inhibition of protein kinase C (PKC) signaling. Prion disease is a paradigmatic protein conformational disease characterized by the induced conversion of a normal host protein PrP(C) to adopt a pathogenic conformation PrP(Sc). The molecular regulation of prion replication is poorly understood. Here, we show that tocopherols inhibit prion replication by a structure-activity relationship for antiprion activity independent of antioxidant activity with tocopherol succinate (TS) posessing highest EC(50) at 7 microM. Only TS but not an equally antiprion active PKC inhibitor could be partially antagonized by substochiometric 1 nM rapamycin suggesting that there are pathways via mammalian target of rapamycin (mTOR) that interfere with tocopherol's biological effects. Interaction with the mTOR pathway is a yet undescribed characteristic of tocopherol derivatives, potentially significant for pathophysiological processes other than prion propagation.