PHARMACOKINETICS AND BIODISTRIBUTION OF A NUCLEOTIDE-BASED THROMBIN INHIBITOR IN RATS

Purpose, To characterize the pharmacokinetic and tissue distribution p rofiles of a nucleotide-based thrombin inhibitor (GS522, phosphodieste r oligonucleotide, GGTTGGTGTGGTTGG) following intravenous administrati on to rats. Methods. Pharmacokinetic study: 10 mg/kg, 20 mg/kg, 30 mg/ kg (6 animals/dose) were administered to rats by rapid injection into the femoral vein. Blood samples were collected over a 45 minute period . Plasma concentrations of GS522 were determined using capillary gel e lectrophoresis with laser-induced fluorescence detection. Biodistribut ion Study: 10mg/kg (400 mu l, 31.46 mu Ci/ml) of H-3-GS522 was adminis tered to rats by rapid injection into the femoral vein. The animals we re sacrificed by decapitation at 1, 5, 10, 30, 60, 360 minutes post-do se (3 rats/point), Brain, blood, duodenum, eyes, heart, kidney, liver, lungs, muscle, pancreas, skin, spleen and vein samples were collected , processed and quantitated using liquid scintillation counting. Resul ts. The pharmacokinetic profile declines in multiexponential manner, e xhibiting extremely fast distribution and elimination (t(1/2) = 7.6-9. 0 min, Cl = 22.0-28.0 ml/min, V = 83.9-132.4 ml/kg). GS522 follows lin ear pharmacokinetics, with the area under the curve being proportional to the dose (Rsq = 0.9744). Highest radioactivity levels were detecte d in kidney, liver and blood (39.7, 15.7 and 15.3% dose/ respective or gan). Less than 1% of the dose was detected in the heart, spleen and l ungs, and >0.3% of the dose was found in the brain and eyes. The oligo nucleotide associated radioactivity was uniformly distributed between the brain regions (left and right lobe and cerebellum). Six hours foll owing the dose administration a statistically significant increase (p < 0.05)in radioactivity levels was observed in the brain, eyes, skin, liver, pancreas and vein. Conclusions. The pharmacokinetic and biodist ribution profiles of GS522 following intravenous administration to rat s at three doses were characterized. The oligonucleotide associated ra dioactivity was widely distributed in tissues. The amount of radioacti vity sharply decreased with time in most tissues. Kidney, liver and mu scle were the main sites of accumulation. The oligonucleotide associat ed radioactivity did not cross the blood brain barrier to an appreciab le extent. In addition, a statistically significant increase (p < 0.05 ) in the radioactivity levels observed in select tissues suggested a r e-uptake mechanism for intact oligonucleotide or its degradation produ cts.