Tissue distribution and plasma pharmacokinetics of UCN-01 at steady-state and following bolus administration in rats: influence of human alpha1-acid glycoprotein binding.

The primary focus of this study was to investigate the role of human a 1 -acid glycoprotein (hAGP) on the pharmacokinetics and tissue distribution of the antitumor drug UCN-01 (7-hydroxystaurosporine) in rats, following bolus administration and at steady-state blood concentration. To evaluate plasma pharmacokinetics, the rats received UCN-01 alone, UCN-01 + hAGP (87: 1 ratio), or UCN-01 + hAGP (26: 1 ratio) i.v. Additional rats were studied after i.m. administration of UCN-01 and i.v. administration of human AGP (87: 1 ratio). For tissue distribution, rats received UCN-01 alone, UCN-01 + hAGP (87: 1 ratio). One hour after drug administration, blood samples as well as various tissues and organs were collected. Plasma concentrations of UCN-01 as well as tissue accumulation were measured by HPLC using a fluorescence detector. Following i.v. bolus administration, the UCN-01 concentration-time profile declined bi-exponentially. The distribution half-life was 0.2 hours, while the elimination half-life was 6.65 hours. The volume of distribution of the central compartment (Vc) was 1000 ml/kg and the volume of distribution during the elimination phase (Vdb) was 2551 ml/kg. The total body clearance (TBC) was 4.4 ml/min/kg. Co-administration of hAGP with UCN-01 at 1: 87 ratio did not affect the elimination half-life of UCN-01 during our sampling period, however the distribution half-life was delayed by approximately 2.7- fold. Furthermore, the Vc, Vd β and TBC were significantly reduced to 395 ml/kg, 735 ml/kg and 1.34 ml/min/kg, respectively. UCN-01 Vd's and TBC were reduced further by increasing human hAGP; UCN-01 ratio to 26: 1. Also, hAGP administration did not significantly affect the pharmacokinetic profile of UCN-01 after i.m. administration, which was similar to that measured after i.v. administration. One hour after i.v. bolus administration, UCN-01 was distributed extensively to all tissues with a tissue/plasma ratio ranging from 10-times in the brain to more than 1000-times in the lungs. The presence of hAGP drastically reduced tissue accumulation of UCN-01, although the tissue to plasma ratio remained > 1.0 except for the brain. At steady-state blood concentration following the infusion of UCN-01 over 180 minutes, the ratio of the drug concentration to the concomitant plasma concentration remained > 1.0, even in the presence of hAGP. The data showed that the binding of UCN-01 to hAGP drastically altered its pharmacokinetics and tissue distribution, even at the plasma steady-state concentration.