Removal of anti-Galalpha1,3Gal xenoantibodies with an injectable polymer.

Preformed and elicited Ab's against the Galalpha1,3Gal terminating carbohydrate chains (alphaGal Ab's) are the primary cause of hyperacute and acute vascular xenograft rejection in pig-to-primate transplantation. alphaGal Ab's are produced by long-lived Ab-producing cells that are not susceptible to pharmacological immunosuppression. We reasoned that antigen-specific elimination of alphaGal Ab's might be achieved in vivo by systemic administration of nonimmunogenic polyvalent alphaGal structures with high avidity for alphaGal Ab's. We devised GAS914, a soluble trisaccharide-polylysine conjugate of approximately 500 kDa that effectively competes for alphaGal binding by alphaGal IgM (IC(50), 43 nM) and IgG (IC(50), 28 nM) in vitro. Injections of GAS914 in cynomolgus monkeys, at the dose of 1 mg/kg, resulted in the immediate decrease of more than 90% of circulating alphaGal Ab's and serum anti-pig cytotoxicity. In baboons, repeated injections of GAS914 effectively reduced both circulating alphaGal Ab's and cytotoxicity over several months. Studies with [(14)C]GAS914 in rhesus monkeys and Gal(-/-) mice indicate that GAS914 binds to circulating alphaGal Ab's and that the complex is quickly metabolized by the liver and excreted by the kidney. Remarkably, posttreatment alphaGal Ab titers never exceeded pretreatment levels and no sensitization to either alphaGal or the polylysine backbone has been observed. Furthermore there was no apparent acute or chronic toxicity associated with GAS914 treatment in primates. We conclude that GAS914 may be used therapeutically for the specific removal of alphaGal Ab's.

Brain pharmacokinetics of a nonpeptidic corticotropin-releasing factor receptor antagonist.

Corticotropin-releasing factor (CRF) is known to play an important role in the body response to stress. Butyl-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-yl]-ethylamine (CP-154,526) is a CRF(1) antagonist showing anxiolytic activities in rats in behavioral models, suggesting that CP-154,526 crosses the blood-brain barrier. However, there is no direct evidence for this. This study determined the pharmacokinetic profile of CP-154,526 in rats after i.v. and p.o. application. After i.v. bolus, the concentration declined in a biphasic manner, the first half-life being 0.9 h and the terminal one being 51 h. Systemic clearance was 36 ml/min/kg, and the volume of distribution was 105 l/kg. Oral bioavailability reached 27%. To study brain pharmacokinetics, rats were given a single dose of CP-154,526 p.o. or i.v. and sacrificed after different post-treatment times. Plasma, cortex, striatum, hypothalamus, hippocampus, and cerebellum concentrations were measured. After i.v. bolus, maximal brain concentration was reached after 20 min. The hypothalamus displayed significantly lower concentrations compared with the other brain tissues. In the p.o. study, the maximal plasma concentration was reached after 30 min, whereas the maximal brain concentration was observed after 1 h and remained stable until 2 h post-treatment, without significant differences between the brain tissues. The unidirectional brain extraction ratio was 27 and 9% at vascular concentrations of 0.08 and 16 nmol/ml, respectively. These results demonstrate a large brain penetration of CP-154,526 after i.v. and p.o. applications and a comparable distribution among the brain regions, except for the hypothalamus, which displayed lower concentrations after i.v. bolus.