Many physiologically important receptors and enzymes are regulated by their endogenous ligands and inhibitors. Nature chose to utilize these p- tides as chemical switches since they can be efficiently synthesized and - graded in cells, thus providing an immediate response to a fast changing environment. Such properties, so critical in cell survival, make peptides less than ideal drug candidates. Other frequently desired properties in drug m- ecules include oral bioavailability, the ability to cross membranes, including the blood-brain barrier, and sufficient stability for administration 1-2...

Many physiologically important receptors and enzymes are regulated by their endogenous ligands and inhibitors. Nature chose to utilize these p- tides as chemical switches since they can be efficiently synthesized and - graded in cells, thus providing an immediate response to a fast changing environment. Such properties, so critical in cell survival, make peptides less than ideal drug candidates. Other frequently desired properties in drug m- ecules include oral bioavailability, the ability to cross membranes, including the blood-brain barrier, and sufficient stability for administration 1-2...