Brain Targeting of anti-HIV Nucleosides: in vitro and in vivo Evaluation of 6-chloro-2′,3′-dideoxypurine, a Lipophilic Prodrug of 2′,3′-dideoxyinosine

Abstract

Lipophilic 6-halo-2′,3′-dideoxypurine nucleosides may be useful prodrugs for the targeting of 2′,3′-dideoxyinosine (ddl) to the central nervous system. The purpose of this study was to evaluate the potential effectiveness of 6-chloro-2′,3′-dideoxypurine (6-CI-ddP) for the targeting of ddl to the brain. In vitro studies indicated that the adenosine deaminase-mediated biotransformation of 6-CI-ddP to ddl was more rapid in mouse brain homogenate than in mouse serum. The brain distribution of 6-CI-ddP and ddl was assessed in vivo in mice following intravenous and oral administration of the prodrug or parent drug. Brain concentrations of ddl were similar after intravenous administration of 6-CI-ddP or ddl. However, after oral administration of the 6-CI-ddP prodrug, significantly greater concentrations of ddl were seen in the brain compared to those found after oral administration of ddl. The brain:serum AUG ratio (expressed as a percentage) of ddl after intravenous administration of 50 mg kg−1 of the active nucleoside was 3%. Following oral administration of 250 mg kg−1 ddl, low concentrations of ddl were detected in the brain. Brain:serum AUC ratios following intravenous and oral administration of the prodrug 6-CI-ddP were 19–25%. Thus, brain:serum AUC ratios were 6- to 8-fold higher after prodrug administration than those obtained after administration of the parent nucleoside. Oral administration of 6-CI-ddP yielded concentrations of ddl in the brain similar to those obtained following intravenous administration. The results of this study provide further evidence that 6-CI-ddP may be a useful prodrug for delivering ddl to the central nervous system, particularly after oral administration.