The distribution of the anti-HIV drug, 2′3′-dideoxycytidine (ddC), across the blood-brain and blood-cerebrospinal fluid barriers and the influence of organic anion transport inhibitors

The brain and CSF distribution of the HIV reverse transcriptase inhibitor, 2'3'-dideoxycytidine (ddC), was investigated by the in situ brain perfusion and isolated incubated choroid plexus methods in the guinea pig. Multiple-time brain perfusions indicated that the distribution of [H-3]ddC to the brain and CSF was low and the unidirectional rate constant (Kin) for the brain uptake of this nucleoside analogue (0.52 +/- 0.10 muL/min/g) was not significantly different to that for the vascular marker, [C-14]mannitol (0.44 +/- 0.09 muL/min/g). The influence of unlabelled ddC, six organic anion transport inhibitors and 3'-azido 3'-deoxythymidine (AZT) on the CNS uptake of (H-3]ddC was examined in situ and in vitro. ddC, probenecid and 2,4-clichlorophenoxyacetic acid altered the distribution of [H-3]ddC into the brain and choroid plexuses, indicating that the limited distribution of [H-3]ddC was a result of an organic anion efflux transporter, in addition to the low lipophilicity of this drug ;(octanol-saline partition coefficient, 0.047 +/- 0.001). The CNS distribution was also sensitive to p-aminohippurate and deltorphin II, but not digoxin, suggesting the involvement of organic anion transporters (OAT1/OAT3-like) and organic anion transporting polypeptides (OATP1/OATPA-like). AZT did not effect the accumulation of [H-3]ddC, indicating that when these nucleoside analogues are used in anti-HIV combination therapy, the CNS distribution of ddC is unchanged.