DEVELOPMENT OF UNIFIED MODELS OF CCK RECEPTOR SUBTYPE

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The general goal of the present study is to use 3D models of the CCK-B and CCK-A peptide pharmacophores, previously obtained by comparison of a parent peptide and its peptide analogs, as well as newly developed 3D models for CCK-B and CCK-A receptors themselves, to design non-peptide agonists and antagonists presumably binding to the same sites of the CCK-B and CCK-A receptors. The strategy we are going to follow in this project will be based on a rational design. Based on the results of the previous CCK project, we will extend the future studies in the following directions: (1) We will use the developed model for the CCK-B receptor-bound conformation for rational design of non-peptide agonists and antagonists with CCK-B selectivity. We will design these compounds by two convergent paths: (i) by rigidifying the proposed receptor-bound conformer (thus refining the model further), and, (ii) by modifying, in accordance with the model, known non-peptide CCK-B antagonists to obtain non-peptide agonists (there is no CCK-B non-peptide agonists discovered so far). These studies will open the route to lead compounds, which could be developed to the level of pharmaceuticals. (2). We will refine further the model of the CCK-A receptor-bound conformer by molecular modeling, synthesis and biological testing of conformationally constrained cyclic compounds. Then, this model will be used for design of CCK-A selective non-peptide agonists and antagonists. We will study also the conformational relationships between peptide (agonists and antagonists) and non-peptide antagonists (again, non-peptide agonists are not known) with CCK-A selectivity. (3) We will develop further the initial 3D models for CCK-B and CCK-A receptors suggested on the basis of the unique computer procedures available in our lab. These procedures include determining tof the ends for transmembrane helical segments in protein sequences, packing these segments together by special molecular recognition algorithm, and restoring the inter helical loops by residue-residue contact matrix technique. (4) We will use the obtained models for CCK-B and CCK-A peptide pharmacophores and for CCK-B and CCK-A receptors for national design of peptide and non-peptide ligands for both receptors. We will synthesize the designed compounds and will submit them for biological studies in vitro as well as in cell test systems with cloned and expressed mutants and chimeric CCK receptors.