Synthesis of a lipophilic prodrug of 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and its incorporation into a hepatocyte-specific lipidic carrier

Purpose. 9-(2-Phosphonylmethoxyethyl)adenine (PMEA), a patent inhibitor of Hepatitis B virus replication, is in vivo hardly taken up by parenchymal li ver cells (the site of infection). Our aim is to examine whether lactosylat ed reconstituted HDL (LacNeoHDL), a lipidic particle that is specifically i nternalized by parenchymal liver cells, is a suitable carrier for the selec tive delivery of PMEA to this cell type. Methods. To incorporate PMEA into LacNeoHDL, we synthesized a lipophilic pr odrug (PMEA-LO) by coupling PMEA via an acid-labile phosphonamidate bond to lithocholic acid-3 alpha-oleate. Results. The yield of the synthesis was 52% ([H-3]PMEA-LO: 24%). [H-3]PMEA- LO readily incorporated into LacNeoHDL (13 molecules/ particle) without aff ecting the size and net negative charge of the carrier. Further, incubation studies at lysosomal pH showed [H-3]PMEA was completely released from the carrier whereas, at neutral pH or in plasma, appreciable release was not ob served. Conclusions. The conjugation of PMEA with lithocholic acid-3 alpha-oleate r esults in a lipophilic prodrug that readily associates with LacNeoHDL. The association of the prodrug does not affect the physicochemical properties o f the particle, and PMEA is released from the carrier at lysosomal pH. Thes e findings indicate that by using the prodrug approach, LacNeoHDL is a suit able carrier to deliver PMEA to parenchymal liver cells.