Prodrugs of HIV protease inhibitors-saquinavir, indinavir and nelfinavir-derived from diglycerides or amino acids: synthesis, stability and anti-HIV activity.

With the aim of improving the pharmacological properties of current protease inhibitors (PIs), the synthesis of various acyl and carbamate amino acid- or diglyceride-containing prodrugs derived from saquinavir, indinavir and nelfinavir, their in vitro stability with respect to hydrolysis and their anti-HIV activity in CEM-SS and MT4 cells have been investigated. l-Leucine (Leu) and l-phenylalanine (Phe) were connected through their carboxyl to the PIs while l-tyrosine (Tyr) was conjugated through its aromatic hydroxyl via various spacer units. Hydrolysis of the prodrug with liberation of the active free drug was crucial for antiviral activity. The Leu- and Phe-PI prodrugs released the active free drug very rapidly (half-lives of hydrolysis in buffer at 37 degree C of 3-4 h). The Tyr-PI conjugates with a -C(O)(CH(2))(4)- linker exhibited half-lives in the 40-70 h range and antiviral activities in the 21-325 nM range (from 2 to 22 nM for the free PIs). The chemically very stable carbamate "peptidomimetic" Tyr-PI prodrugs (no hydrolysis detected after 7 days in buffer) displayed a very low anti-HIV activity or were even inactive (EC(50) from 2300 nM to >10 microM). A very low antiviral activity was measured for the diglyceride-substituted saquinavir and for all of the disubstituted indinavir and nelfinavir prodrugs. All these prodrugs probably released the active parent PI too slowly under the antiviral assay conditions. These results combined with those from transepithelial transport studies (Rouquayrol et al., Pharm. Res., 2002, 19, 1704-1712) indicate that conjugation of amino acids (through their carboxyl) to the PIs constitutes a most appealing alternative which could improve the intestinal absorption of the PIs and reduce their recognition by efflux carriers.

Transepithelial transport of prodrugs of the HIV protease inhibitors saquinavir, indinavir, and nelfinavir across Caco-2 cell monolayers.

PURPOSE: [corrected] This study is dedicated to the permeation of various amino acid-, D-glucose-, and PEG-conjugates of indinavir, saquinavir, and nelfinavir across monolayers of Caco-2 cells as models of the intestinal barrier. This screening is aimed at detecting the most promising prodrugs for improving the intestinal absorption of these protease inhibitors. METHODS: The bidirectional transport of the prodrugs was investigated using P-gp-expressing Caco-2 monolayers grown on membrane inserts using high-performance liquid chromatography for quantitation. RESULTS: The L-valyl, L-leucyl, and L-phenylalanyl ester conjugates led to an enhancement of the absorptive flux of indinavir or saquinavir. These results are likely attributable to an active transport mechanism and/or to a decrease of their efflux by carriers such as P-gp. Connection of tyrosine through its hydroxyl, of D-glucose, or of polyethylene glycol decreased their absorptive and secretory diffusion. CONCLUSIONS: Conjugation of the protease inhibitors to amino acids constitutes a most appealing alternative that could improve their intestinal absorption and oral bioavailability. Whether it could improve their delivery into the central nervous system remains to be explored. D-Glucose conjugation will most probably not improve their intestinal absorption or their crossing of the blood-brain barrier. If some pharmacologic benefits are to be expected from PEG-protease inhibitor conjugates, they must then be administered intravenously.