Membrane affinity fingerprints: A new tool for drug discovery

Kimberly Lynne Hauer, Purdue University

Abstract

Heterogeneity exists in the phospholipid bilayer of cells. One plausible role of this phospholipid heterogeneity is to regulate the distribution of drug molecules at both the cellular and tissue levels. In order to model the complex process of drug distribution among the endogenous lipid pools competing to sequester a drug molecule, pure lipid membrane surfaces, i.e. immobilized artificial membranes (IAMs), were used to develop a database of the membrane phospholipid affinities of approximately 300 commercially available drugs. This in vitro membrane binding model correlated phospholipid binding affinities with the in vivo activity of the drugs. Compounds within the same therapeutic class (e.g. anticonvulsant, antidepressant, anxiolytic, etc.) and compounds with the same molecular target (e.g. dopamine receptor, serotonin receptor, GABA receptor, etc.) exhibited membrane affinity fingerprints (MAFs) distinct from compounds in all other classes and mechanisms. The unique MAFs suggest that compounds comprising a therapeutic class or molecular target exhibit similar tendencies to distribute into tissue lipid pools where activity is then elicited. In addition to developing the in vitro membrane binding model, a new mechanism of action for the sleep inducing lipid oleamide was identified: inhibition of anandamide transport. Several analogs of oleamide were evaluated in vitro for inhibition of anandamide transport in order to explore the structure-activity relationship (SAR) with regard to fatty acid chain and carboxamide modifications. Of the primary fatty acid amides examined, 14:19 was the most potent monounsaturated inhibitor (IC50 = 5.6 μM) and 20:55,8,11,14,17 was the most potent polyunsaturated inhibitor (IC50 = 7.5 μM). Of the carboxamide modified oleamide derivatives, N-methyloleamide was the most potent inhibitor (IC50 = 5.40 μM). Several of the oleamide derivatives exhibited sedative behavior in vivo , with N,N-dimethyloleamide exhibiting a duration of sedation (40 min) twice as long as the endogenous oleamide. In addition, in vivo studies revealed that the sedative effects of oleamide and several analogs are potentiated two-fold in the presence of the cannabinoid (CB1) selective antagonist SR141716A. This potentiation taken together with the ability of oleamide to inhibit anandamide transport suggests that the cannabinoid system plays a crucial role in the physiological effects of oleamide.

Degree

Ph.D.

Advisors

Pidgeon, Purdue University.

Subject Area

Pharmacology

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