The ability of tolfenamic acid to penetrate the brain: a model for testing the brain disposition of candidate Alzheimer's drugs using multiple platforms.

Evidence from our laboratory suggests that tolfenamic acid has a potential for slowing the progression of Alzheimer's disease (AD) through lowering cortical levels of the ß-amyloid precursor protein (APP) and its pathogenic amyloid beta (Aß) intermediates [1]. In this study, we examined the ability of tolfenamic acid to cross the blood brain barrier (BBB) by predicting its logBB and logPS values, the indexes of BBB permeability, using computational models. We also determined, via in vitro methods, the brain penetration capacity factor [(K(IAM)/MW(4))x10(10)] using phosphatidylcholine column chromatography. The obtained logBB, logPS and (K(IAM)/MW(4))x10(10) values predicted that tolfenamic acid can passively transfer into the central nervous system (CNS). These results were validated in vivo using LC-MS analysis after administration of tolfenamic acid intravenously to guinea pigs and mice. The present study provides the first evidence of the ability of tolfenamic acid to cross the BBB and offers a comparative analysis of approaches used to predict the ability of compounds to penetrate into the brain.

Mechanism and uses of a membrane peptide that targets tumors and other acidic tissues in vivo.

The pH-selective insertion and folding of a membrane peptide, pHLIP [pH (low) insertion peptide], can be used to target acidic tissue in vivo, including acidic foci in tumors, kidneys, and inflammatory sites. In a mouse breast adenocarcinoma model, fluorescently labeled pHLIP finds solid acidic tumors with high accuracy and accumulates in them even at a very early stage of tumor development. The fluorescence signal is stable for >4 days and is approximately five times higher in tumors than in healthy counterpart tissue. In a rat antigen-induced arthritis model, pHLIP preferentially accumulates in inflammatory foci. pHLIP also maps the renal cortical interstitium; however, kidney accumulation can be reduced significantly by providing mice with bicarbonate-containing drinking water. The peptide has three states: soluble in water, bound to the surface of a membrane, and inserted across the membrane as an alpha-helix. At physiological pH, the equilibrium is toward water, which explains its low affinity for cells in healthy tissue; at acidic pH, titration of Asp residues shifts the equilibrium toward membrane insertion and tissue accumulation. The replacement of two key Asp residues located in the transmembrane part of pHLIP by Lys or Asn led to the loss of pH-sensitive insertion into membranes of liposomes, red blood cells, and cancer cells in vivo, as well as to the loss of specific accumulation in tumors. pHLIP nanotechnology introduces a new method of detecting, targeting, and possibly treating acidic diseased tissue by using the selective insertion and folding of membrane peptides.