A novel photoaffinity probe for the LTD4 receptor

Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors

Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.

Enzyme occupancy measurement of intracellular protein tyrosine phosphatase 1B using photoaffinity probes

Protein tyrosine phosphatase 1B (PTP1B) is believed to be one of the enzymes involved in down-regulating the insulin receptor and is a drug target for the treatment of type II diabetes. To better understand the in vitro and in vivo behavior of PTP1B inhibitors, a cell-based assay to directly measure enzyme occupancy of PTP1B by inhibitors using photoaffinity labeling was developed. Two photoaffinity probes were synthesized containing the photolabile diazirine moiety. These photoprobes were specific for PTP1B and T-cell protein tyrosine phosphatase over CD45, with the most potent photoprobe having an IC(50) value of 0.2nM for PTP1B. Activation of the photoprobes with a 40-W UV lamp in the presence of purified AspTyrLysAspAspAspAspLys (Flag)-PTP1B formed a 1:1 irreversible adduct with the enzyme. The photolabeling was competed by known PTP1B inhibitors, vanadate, and the peptide inhibitor N-benzoyl-l-glutamyl-[4-phosphono(difluoromethyl)]-l-phenylalanyl-[4-phosphono(difluoromethyl)]l-phenylalanineamide (BzN-EJJ-amide). In HepG2 (human hepatoma cell line) cells, endogenous PTP1B was labeled by the UV-activated photoprobes in both lysed and intact cells. Enzyme occupancy measurements were conducted with a series of PTP1B inhibitors using the photoprobe affinity assay. Several compounds were shown to bind to endogenous PTP1B in the HepG2 intact cells.

Synthesis of a novel peptidic photoaffinity probe for the PTP-1B enzyme

The synthesis of a novel radioactive peptidic photoaffinity probe for the PTP-1B enzyme as well as some SAR leading to the choice of this compound as a photoaffinity probe are presented.

[(125)I]-N-[(3-azido-5-iodo)benzyl]dantrolene and [(125)I]-N-[[3-iodo-5-(3-trifluoromethyl-3H-diazirin-3-yl)]benzyl]dantrolene: photoaffinity probes specific for the physiological Ca(2+) release from sarcoplasmic reticulum of skeletal muscle

In order to capture and identify key molecules that regulate the release of Ca(2+) from the sarcoplasmic reticulum (SR) of skeletal muscle, we designed specific photoaffinity probes based on the structural modification of dantrolene. Thus, GIF-0082 and GIF-0276 possessing azido- and trifluoromethyldiazirinyl-benzyl groups, respectively, at the hydantoin moiety were found to have a highly selective inhibitory effect on physiological Ca(2+) release (PCR) without affecting Ca(2+)-induced Ca(2+) release (CICR). Successful realization of the sharp discrimination between PCR and CICR has led to the creation of [(125)I]GIF-0082 and [(125)I]GIF-0276, which were synthesized by substituting a stannyl group with (125)I in the corresponding phenylstannane precursors.