Kerry J. Koller

Comparative gene expression profiles of ABC transporters in brain microvessel endothelial cells and brain in five species including human

While P-glycoprotein (PGP, ABCB1) is known to play an important role in drug exclusion at the blood brain barrier (BBB), less is known about the contribution of other members in the ATP-binding cassette (ABC) transporter family to BBB drug efflux, or whether these transporters are expressed differently in humans and in mammalian species of pharmacological interest. We used quantitative real-time PCR to determine mRNA expression levels for the majority of ABC family members in brain and in isolated brain microvessel endothelial capillary cells (BMEC) from human, rat, mouse, pig and cow. We confirmed BBB expression of several well-characterized ABC family members that are implicated in xenobiotic exclusion from the brain, including ABCB1 (PGP), ABCG2 (BCRP), ABCC1 (MRP1), ABCC4 (MRP4), and ABCC5 (MRP5). In addition, we detected high expression and enrichment in BMEC of several less well-characterized ABC transporters in one or more species, including ABCA2-4, ABCB4, ABCB6-8, ABCB10, ABCC3, ABCC6, ABCC10, and ABCE1. We also uncovered species differences in the expression of a number of transporters, including ABCG2 and ABCC4. This study identifies several additional ABC family members that may contribute to xenobiotic efflux at the human BBB, and compares the expression of a broad array of efflux transporters between human and four other species relevant to pharmacological research.

Peptides Which Bind to E-selectin and Block Neutrophil Adhesion

E-selectin is an inducible cell adhesion molecule which mediates rolling of neutrophils on the endothelium, an early event in the development of an inflammatory response. Inhibition of selectin-mediated rolling is a possible means for controlling inflammation-induced diseases, and several classes of compounds have been tested for this use. We describe here the use of recombinant peptide library screening for identification and optimization of novel ligands which bind to E-selectin. Several of these peptides bind with K values in the low nanomolar range and block E-selectin-mediated adhesion of neutrophils in static and flow-cell assays. Administration of the peptide to mice undergoing an acute inflammatory response reduced the extent of neutrophil transmigration to the site of inflammation, demonstrating the utility of this compound as a potential therapeutic. The identification of a peptide ligand for E-selectin suggests that the complete natural ligand for this adhesion molecule may include protein as well as carbohydrate moieties.

Arbaclofen Placarbil, a Novel R-Baclofen Prodrug: Improved Absorption, Distribution, Metabolism, and Elimination Properties Compared with R-Baclofen

Baclofen is a racemic GABAB receptor agonist that has a number of significant pharmacokinetic limitations, including a narrow window of absorption in the upper small intestine and rapid clearance from the blood. Arbaclofen placarbil is a novel transported prodrug of the pharmacologically active R-isomer of baclofen designed to be absorbed throughout the intestine by both passive and active mechanisms via the monocarboxylate type 1 transporter. Arbaclofen placarbil is rapidly converted to R-baclofen in human and animal tissues in vitro. This conversion seems to be primarily catalyzed in human tissues by human carboxylesterase-2, a major carboxylesterase expressed at high levels in various tissues including human intestinal cells. Arbaclofen placarbil was efficiently absorbed and rapidly converted to R-baclofen after oral dosing in rats, dogs, and monkeys. Exposure to R-baclofen was proportional to arbaclofen placarbil dose, whereas exposure to intact prodrug was low. Arbaclofen placarbil demonstrated enhanced colonic absorption, i.e., 5-fold higher R-baclofen exposure in rats and 12-fold higher in monkeys compared with intracolonic administration of R-baclofen. Sustained release formulations of arbaclofen placarbil demonstrated sustained R-baclofen exposure in dogs with bioavailability up to 68%. In clinical use, arbaclofen placarbil may improve the treatment of patients with gastroesophageal reflux disease, spasticity, and numerous other conditions by prolonging exposure and decreasing the fluctuations in plasma levels of R-baclofen.

Discovery of a novel potent GABAB receptor agonist

Structure-activity studies have led to a discovery of 3-(4-pyridyl)methyl ether derivative 9d that has 25- to 50-fold greater functional potency than R-baclofen at human and rodent GABA(B) receptors in vitro. Mouse hypothermia studies confirm that this compound crosses the blood-brain barrier and is approximately 50-fold more potent after systemic administration.