Use of peptide combinatorial libraries in drug design: the identification of a potent serotonin reuptake inhibitor derived from a tripeptide cassette library.

BACKGROUND: Medicinal chemistry traditionally requires the identification of biologically active molecules by synthesizing and screening each purified substrate. Further progress in drug discovery then requires definition of the structure-activity relationship of the lead compound. More recently, combinatorial chemistry has emerged as a way to examine structure-activity relationships by screening a large mixture of compounds synthesized in a predictably random manner, without the labor-intensive costs of molecular isolation and purification. We set out to use this approach to examine the structural requirements for peptide binding to serotonin and dopamine transporters. RESULTS: We screened a tripeptide cassette library for serotonin and dopamine reuptake inhibition using cloned transporter assay systems. The method has afforded a number of tripeptide pharmacophores with inhibitory IC50 values ranging from 10 microM to < 1 microM in the dopamine and serotonin reuptake systems. The conformation of one of these tripeptides, N-acetyl-D-Trp-L-Phe-D-Lys-CONH2 (which inhibits serotonin uptake with an IC50 of 10 microM) was compared to that of the serotonin uptake inhibitor s-fluoxetine, and was shown to be more similar in conformation to fluoxetine than was an analogous tripeptide containing L-Lys (IC50 > 50 microM). CONCLUSIONS: We have identified five tripeptides with inhibitory IC50 values of < 10 microM in the serotonin reuptake system. One tripeptide was predicted to have pharmacophore features similar to that of fluoxetine, a selective and potent non-peptide serotonin reuptake inhibitor. Our results suggest that tripeptides derived from combinatorial libraries will help to define the important structural elements of pharmacophores.

The rapid identification of HIV protease inhibitors through the synthesis and screening of defined peptide mixtures.

Small peptides with activity as enzyme inhibitors, hormone antagonists, or other peptide mimetics, can be identified by synthesizing and screening large numbers of peptides as defined mixtures. Several coupling reactions, each with a different amino acid, can be conducted simultaneously and then combined to generate a near equimolar mixture before coupling additional residues. The peptide mixtures are recovered free from the matrix and in quantities sufficient for screening in many assays. We describe the rapid identification of a potent peptide inhibitor of human immunodeficiency virus protease from twenty-two mixtures containing more than 240,000 tetrapeptides.