Potential treatment of herpes simplex virus encephalitis by brain-specific delivery of trifluorothymidine using a dihydropyridine in equilibrium pyridinium salt type redox delivery system.

A newly described, drug-carrier delivery system in which a lipophilic derivative is enzymatically converted to a hydrophilic compound was used to treat experimental herpes simplex virus (HSV) encephalitis. Because trifluorothymidine (TFT) does not cross the blood brain barrier, the lipophilic dihydropyridine derivative 3'-(N-methyl-1, 4-dihydronicotinoyl)-5-'pivaloyltrifluorothymidine (DHTFT) was synthesized and characterized by HPLC. After intravenous administration of 20 mg/kg of DHTFT to rats, the quaternary, intermediate compound 3'-N-methyl-1,4-nicotinoyltrifluorothymidine was measured at levels of 7-8 micrograms/g brain at 1 hour and 13.5 +/- 0.8 micrograms/g brain at 4 hours. This compound had antiviral activity equivalent to that of TFT against HSV-1 in a plaque reduction assay (ID 50 = 0.5-1.0 microgram/ml), either directly or by conversion to TFT. Although survival was not prolonged in a rat model of HSV encephalitis, a statistically significant reduction in titer of HSV/g brain was achieved with daily intravenous treatment with DHTFT. TFT was not detected in brains of rats at 1 and 4 hours after intravenous DHTFT, but a low level was observed at 18 hours, 0.3 +/- 0.05 microgram/g brain. These data suggest that the lipophilic compound DHTFT or a lipophilic metabolite crossed the blood brain barrier and was converted to a quaternary compound, which accumulated in the brain and which was either active directly or was converted to TFT. The drug-carrier delivery system described here can potentially be used in the treatment of HSV or other viral encephalitides.