Parathyroid hormone (PTH) secretion is regulated by a cell surface Ca 2؉ receptor that detects small changes in the level of plasma Ca 2؉ . Because this G protein-coupled receptor conceivably provides a distinct molecular target for drugs useful in treating bone and mineral-related disorders, we sought to design small organic molecules that act on the Ca 2؉ receptor. We discovered that certain phenylalkylamine compounds, typified by NPS R-568 and its deschloro derivative NPS receptor are termed calcimimetics. The discovery of calcimimetic compounds with potent and selective activity enables a pharmacological approach to regulating plasma levels of PTH. Calcimimetic compounds could conceivably provide a specific medical therapy for primary hyperparathyroidism.The concentration of ionized calcium (Ca 2ϩ ) in plasma is regulated largely by parathyroid hormone (PTH), which acts on the kidney and on bone to increase the level of plasma Ca The Ca 2ϩ receptor is a member of the G protein-coupled receptor superfamily and possesses an unusually large extracellular domain, the characteristic seven transmembrane domain, and a relatively long cytoplasmic tail. In these topological aspects, the Ca 2ϩ receptor is similar to metabotropic glutamate receptors (mGluR), although the sequence homology between these receptors is only about 25%. The human (1,078 amino acids) and bovine (1,085 amino acids) parathyroid cell Ca 2ϩ receptors are glycosylated proteins of ϳ120 kDa and are 93% identical (5). The Ca 2ϩ receptor expressed on authentic parathyroid cells or in heterologous cellular systems couples to phospholipase C and, when activated by increased concentrations of extracellular Ca 2ϩ , elicits rapid increases in inositol 1,4,5-trisphosphate and [Ca 2ϩ ] i (2, 4, 6). Thus, in its functional and structural properties, the parathyroid Ca 2ϩ receptor is akin to other cell surface receptors that initially transduce extracellular signals into functional cellular responses. The difference is that the physiological ligand for the Ca 2ϩ receptor is an inorganic ion, rather than an organic molecule.G protein-coupled receptors have been a classic site of action for drugs useful in treating various diseases. As a member of the G protein-coupled receptor superfamily, the Ca 2ϩ receptor is seemingly an ideal target for new pharmaceuticals useful in treating disorders of bone and mineral metabolism, such as hyperparathyroidism and osteoporosis. At present, however, the only ligands known to act on the Ca 2ϩ receptor are other inorganic di-and trivalent cations (2, 7) and organic polycations (8-10) that are nonselective and lack utility as systematic therapeutics. The present report describes the results of our initial efforts to devise a small organic compound that selectively acts on the parathyroid Ca 2ϩ receptor yet lacks a polycationic structure. NPS R-467 and NPS R-568 (Fig. 1) are two compounds that emerged from this effort. They are potent and selective activators of the Ca 2ϩ receptor and inhibit PTH secretion in vitro....

Generating highly selective probes to interrogate protein kinase function in biological studies remains a challenge and new strategies are required. Herein, we describe the development of the first highly selective and cell permeable inhibitor of c-Src, a key signaling kinase in cancer. Our strategy involves extension of traditional inhibitor design by appending functionality proposed to interact with the phosphate-binding loop of c-Src. Using our selective inhibitor, we demonstrate that selective inhibition is significantly more efficacious than pan-kinase inhibition in slowing the growth of cancer cells. We also show that inhibition of c-Abl kinase, an off-target of most c-Src inhibitors, promotes oncogenic cell growth.

On the basis of synergism observed between a selective c-Src kinase inhibitor with an HDAC inhibitor, the development of the first chimeric c-Src kinase and HDAC inhibitor is described. The optimized chimeric inhibitor is shown to be a potent c-Src and HDAC inhibitor. Chimeric inhibitor 4 is further shown to be highly efficacious in cancer cell lines and significantly more efficacious than a dual-targeting strategy using discrete c-Src and HDAC inhibitors.

We have developed the first irreversible inhibitors of wild-type c-Src kinase. We demonstrate that our irreversible inhibitors display improved potency and selectivity relative to their reversible counterparts. Our strategy involves modifying a promiscuous kinase inhibitor with an electrophile to generate covalent inhibitors of c-Src. We applied this methodology to two inhibitor scaffolds that exhibit increased cellular efficacy when rendered irreversible. In addition, we have demonstrated the utility of irreversible inhibitors in studying the conformation of an important loop in kinases that can control inhibitor selectivity and cause drug resistance. Together, we have developed a general and robust framework for generating selective irreversible inhibitors from reversible, promiscuous inhibitor scaffolds.

Loss-of-function mutations in the human melanocortin-4 receptor (MC4R) are associated with obesity. Previous work has implicated a C-terminal di-isoleucine motif at residues 316/317 in MC4R cell surface targeting.