Lack of drug penetration through the blood-brain barrier (BBB) represents a formidable hurdle to treatment of central nervous system (CNS) diseases and the development of CNS drugs. A significant amount of BBB penetration is blocked by an efflux transporter called the human multiple drug resistance 1 (MDR1) transporter. This transporter effluxes a wide range of chemically and structurally diverse compounds from epithelial cells within the BBB to the blood stream by ATP hydrolysis at nucleotide binding domains (NBDs) and conformational changes. Diphenylpropylamine derivatives, morphine alkaloids and triptans represent three chemical classes of CNS agonists that show large differences in their MDR1 efflux rates and transport properties within a chemical class, despite the similarities in their molecular structures. Although there have been numerous studies, the relationship between the agonist's molecular structure and transport rates remains to be clarified. The proposed work will test the central hypothesis that the agonist MDR1 transport rate is controlled by drug binding near the extracellular side (blood-side) of the membrane (near Y953) and without direct interaction with the NBDs. The proposal was divided into two specific aims: 1) to characterize the interaction of agonists with human MDR1, to determine their effect on ATP hydrolysis and to establish their transport rates with MDCK cells overexpressing human MDR1 and 2) to locate the agonist binding sites on human MDR1. Innovative NMR and computational methods will be used to explore the interaction between agonists and human MDR1. These technologies will open the door to screening a wide range of therapeutics with human MDR1. Understanding the relationship between molecular structure and transport rates will also fill significant gaps in our understanding of the transporter as wellas lead to novel neurotherapeutics, acceleration of CNS drug development and improvements in the effectiveness of current CNS drugs.