Molecular requirements for inhibition of the chemokine receptor CCR8--probe-dependent allosteric interactions.

BACKGROUND AND PURPOSE: Here we present a novel series of CCR8 antagonists based on a naphthalene-sulfonamide structure. This structure differs from the predominant pharmacophore for most small-molecule CC-chemokine receptor antagonists, which in fact activate CCR8, suggesting that CCR8 inhibition requires alternative structural probes. EXPERIMENTAL APPROACH: The compounds were tested as inverse agonists and as antagonists against CCL1-induced activity in Gα(i) signalling and chemotaxis. Furthermore, they were assessed by heterologous competition binding against two radiolabelled receptor ligands: the endogenous agonist CCL1 and the virus-encoded antagonist MC148. KEY RESULTS: All compounds were highly potent inverse agonists with EC(50) values from 1.7 to 23 nM. Their potencies as antagonists were more widely spread (EC(50) values from 5.9 to 1572 nM). Some compounds were balanced antagonists/inverse agonists whereas others were predominantly inverse agonists with >100-fold lower potency as antagonists. A correspondingly broad range of affinities, which followed the antagonist potencies, was disclosed by competition with [(125)I]-CCL1 (K(i) 3.4-842 nM), whereas the affinities measured against [(125)I]-MC148 were less widely spread (K(i) 0.37-27 nM), and matched the inverse agonist potencies. CONCLUSION AND IMPLICATIONS: Despite highly potent and direct effects as inverse agonists, competition-binding experiments against radiolabelled agonist and tests for antagonism revealed a probe-dependent allosteric effect of these compounds. Thus, minor chemical changes affected the ability to modify chemokine binding and action, and divided the compounds into two groups: predominantly inverse agonists and balanced antagonists/inverse agonists. These studies have important implications for the design of new inverse agonists with or without antagonist properties.

Gallbladder visualization on routine lung perfusion imaging.

OBJECTIVE: Two routine lung SPECT studies showed what appeared to be uptake within the gallbladder. This finding was confirmed on coronal views and three-dimensional reconstruction. There was no contamination or problem with the radiopharmaceutical quality control. The patients had not had any prior nuclear procedures. Gallbladder visualization on routine lung imaging has not been previously observed. The purpose of this study was to ascertain the incidence of gallbladder uptake and to determine a possible mechanism. METHODS: Fifty-four patients referred for routine lung perfusion imaging were examined. At the end of the lung imaging, an anterior and/or right lateral 3-5 minute view of the abdomen was obtained. Patients too ill for additional imaging or those with prior cholecystectomies were excluded. RESULTS: Nineteen of the 54 patients showed activity within the gallbladder. Activity within the gut, kidneys, and urinary bladder also were observed. CONCLUSION: Gallbladder activity after Tc-99m macroaggregated albumin injection for lung perfusion studies, is a fairly common finding.