INHIBITION OF CL-36(-) INFLUX AND [S-35] TBPS BINDING IN THE RAT-BRAIN BY LEUMEDINS - A NOVEL CLASS OF ANTIINFLAMMATORY AGENTS

The leumedins, a series of N-(fluorenyl-9-methoxycarbonyl) amino acids , are putative anti-inflammatory agents that have been shown to inhibi t leukocyte recruitment into inflammed tissue. While the exact mechani sm of action of these agents is unknown, there are some reports sugges ting that leumedins selectively block transmembrane ion flux in neutro phils. In order to examine the possibility that the leumedins may inte ract with chloride transport mechanisms, we evaluated representative l eumedins for their ability to interact with the GABA/benzodiazepine ch loride ionophore in rat brain. NPC 17923, at micromolar concentrations , was found to compete for 2 nM [S-35]TBPS binding (IC50 = 16 mu M) an d inhibit Cl-36(-) influx (IC50 = 133 mu M) in rat brain. Saturation s tudies indicated that NPC 17923 inhibited [S-35]TBPS binding in a nonc ompetitive fashion. Other less potent leumedins also inhibited [S-35]T BPS binding in a concentration-dependent fashion. The leumedins had no significant activity at other GABA/benzodiazepine recognition sites l abeled by [H-3]muscimol, [H-3]flunitrazepam, or [H-3]RO15-4513. The tw o most potent leumedins effectively attenuated Cl-36(-) influx into ra t brain, while all of the leumedins examined blocked Cl-36(-) influx i nto guinea pig neutrophils at moderate micromolar concentrations. The present data offer the first demonstration that the leumedins can bloc k chloride flux at the rat brain GABA/benzodiazepine chloride ionophor e and in guinea pig neutrophils at similar concentrations required to produce anti-inflammatory actions on human neutrophils. These results show that while the leumedins can block chloride flux in both neurons and neutrophils, the relative low affinity of the leumedins to produce this effect suggests an apparent nonselective interaction at a number of different chloride transporters similar to that found with the dis ulfonic stilbene derivative chloride channel blockers. (C) 1995 Wiley- Liss, Inc.