Brain targeting of anti-HIV nucleosides: Synthesis and in vitro and in vivo studies of dihydropyridine derivatives of 3′-azido-2′,3′-dideoxyuridine and 3′-azido-3′-deoxythymidine

A significant number of patients with AIDS and AIDS-related complex develop neurological complications. Therefore, it is critical that anti-HIV agents penetrate the blood-brain barrier and suppress viral replication in the brain. In an effort to increase the brain delivery of anti-HIV nucleosides, in vitro and in vivo pharmacokinetics of dihydropyridine derivatives of 3′-azido-2′,3′-dideoxyuridine (AzddU, AZDU, or CS-87) and 3′-azido-3′-deoxythymidine (AZT, Zidovudine) have been studied. In vitro studies of the prodrugs (AzddU-DHP and AZT-DHP) in human serum, mouse serum, and mouse brain homogenate indicated that the rates of serum conversion from prodrugs to parent drugs are species dependent: mouse brain homogenate > mouse serum > human serum. Half-lives in human serum, mouse serum, and mouse brain homogenate are 4.33, 0.56, 0.17 h, respectively, for AzddU and 7.70, 1.40, and 0.18 h, respectively, for AZT. In vivo studies of AzddU-DHP and AZT-DHP showed that the prodrugs have areas under the serum concentration-time curves (AUC) similar to those of the parent drugs. The AUC in serum for AzddU following prodrug administration is 25.79 μg h/mL, which is similar to die value of 25.83 μg h/mL when AzddU was administered. Analogously, the serum AUCs for AZT when AZT-DHP and AZT were administered are 25.38 and 26.64 μg h/mL, respectively. However, the brain AUCs for both AzddU and AZT derived from prodrugs, being 11.43 and 11.28 μg h/mL, respectively, are greater than the brain AUCs for AzddU (2.09 μg h/mL) and AZT (1.21 μg h/mL) when the parent drugs were administered. Thus, the relative brain exposure (r_e) for AzddU (5.47) and AZT (9.32) indicate a significant increase in exposure to the anti-HIV nucleosides following prodrug administrations. The results of extended half-lives of the synthesized prodrugs in human serum along with the higher r_e values in vivo warrant studies in larger animals to determine the potential usefulness of the prodrugs in humans.