PHOSPHOLIPID PRODRUG INHIBITORS OF THE HIV PROTEASE - ANTIVIRAL ACTIVITY AND PHARMACOKINETICS IN RATS

The aspartyl protease of the human immunodeficiency virus (HIV) is an important target for chemotherapeutic intervention because of its key role in cleaving the HIV gag-pol polyprotein during viral assembly and budding. Short peptides and peptidomimetics, which bind to the active site of the HIV aspartyl protease and inhibit processing of the polyp rotein, have been synthesized. These compounds are active against HIV in vitro, but many face substantial development problems because of th eir rapid elimination from the body in bile and urine. Refinement of t hese agents appears to be necessary if they are to become useful clini cally. Recently, we developed a novel chemical strategy for increasing plasma levels of HIV protease inhibitory peptides, which involves the attachment of a biodegradable phospholipid group to the C-terminus of a pentapeptide, iBOC-[L-Phe]-[D-beta-Nal]-Pip[alpha-(OH)-Leu]-Val (71 94). We coupled phosphatidylethanolamine to the C-terminal valine of 7 194 to make a phospholipid prodrug (7196). In vitro assays in HT4-6C c ells infected with HIV-1 showed that the antiviral activity of the C-t erminal phospholipid prodrug, 7196, was equal to that of the free pept ide, 7194. Similar results were obtained in vitro when a related penta peptide (7140) was derivatized at the N-terminal with dipalmitoylphosp hatidylethanolamine-succinic acid (7172). Tritium-labeled 7194 and 719 6 were prepared and injected intravenously into rats at 3 mu mol/kg; t hen the plasma was assayed for native compound and metabolites by HPLC radioactivity flow detection. The peak plasma level of the tritium-la beled lipid prodrug (7196) was 36 mu M versus 1.6 mu M for the free pr otease inhibitor pentapeptide (7194). The area under the curve of the phospholipid prodrug (7196) was 48-fold greater and its mean residence time was increased 43-fold versus the free peptide (7193). Phospholip id prodrugs appear to offer an alternative approach to optimizing in v ivo performance of HIV protease inhibitors and other small peptides.