Synthesis of Poly(ethylene glycol)-Based Saquinavir Prodrug Conjugates and Assessment of Release and Anti-HIV-1 Bioactivity Using a Novel Protease Inhibition Assay

• Published in: Bioconjugate chemistry 2004-11, Vol.15 (6), p.1322-1333
• Main Authors: Gunaseelan, Simi, Debrah, Olivia, Wan, Li, Leibowitz, Michael J, Rabson, Arnold B, Stein, Stanley, Sinko, Patrick J
• Format: Article
• Language: English
• Subjects: Anti-HIV Agents - administration & dosage; Anti-HIV Agents - chemical synthesis; Anti-HIV Agents - metabolism; Cell Line, Tumor; Chemistry; Enzymes; HIV Protease Inhibitors - administration & dosage; HIV Protease Inhibitors - chemical synthesis; HIV Protease Inhibitors - metabolism; HIV-1 - drug effects; HIV-1 - metabolism; Human immunodeficiency virus 1; Humans; Pharmacology; Polyethylene glycol; Polyethylene Glycols - administration & dosage; Polyethylene Glycols - chemical synthesis; Polyethylene Glycols - metabolism; Prodrugs - administration & dosage; Prodrugs - chemical synthesis; Prodrugs - metabolism; Saquinavir - administration & dosage; Saquinavir - chemical synthesis; Saquinavir - metabolism
• ISSN: 1043-1802; 1520-4812
• DOI: 10.1021/bc0498875

Various poly(ethylene glycol)(PEG)-based prodrug conjugates of the HIV-1 protease inhibitor (PI) saquinavir (SQV) were prepared using several types of chemical groups potentially capable of modifying its pharmacokinetic properties. These prodrug conjugates included SQV−cysteine-PEG3400, SQV−cysteine-PEG3400-biotin, SQV−cysteine(R.I.CK-Tat9) [a cationic retro-inverso-cysteine-lysine-Tat nonapeptide]-PEG3400, and SQV−cysteine(R.I.CK(stearate)-Tat9)-PEG3400. SQV was linked to cysteine to form a releasable SQV−cysteine ester bond in all of the conjugates. The amino group of the cysteine moiety provided an attachment site for a slower-degrading amide bond with N-hydroxysuccinimide-activated forms of PEG- and PEG-biotin. Disulfide bonds were used to attach the cationic peptides, R.I.CK-Tat9 and R.I.CK(stearate)-Tat9 to the cysteine moiety in order to provide cell-specific release. An assay was established and validated for measuring the activity of SQV and other protease inhibitors in biological samples. In this assay, cleavage of an internally quenched fluorescent substrate, Arg-Glu(EDANS)-Ser-Gln-Asn-Tyr-Pro-Ile-Val-Gly-Lys(DABCYL)-Arg by HIV-1 protease was inhibited by SQV in a dose-dependent manner at concentrations of 0.05−0.5 μM. All prodrug conjugates were shown to be inactive in this assay until the ester bond was cleaved and active SQV was released. The prodrug reconversion half-lives in 0.1 N HCl, phosphate-buffered saline (PBS) at pH 7.4 and in spiked plasma at 37 °C were 9, 14, and 0.9 h, respectively. The anti-HIV-1 activity (ED50) of the PEG-based SQV prodrug conjugates was evaluated in MT-2 cells using an MTT assay. The activity of conjugated SQV was reduced (ED50 = 900 nM) for the PEG only conjugate, but restored with the addition of biotin (ED50 = 125 nM), R.I.CK-Tat9 (ED50 = 15 nM), and R.I.CK(stearate)-Tat9 (ED50 = 62 nM) as compared to maximum achievable anti-HIV-1 activity (unconjugated SQV, control, ED50 = 15 nM), suggesting enhanced cellular uptake of conjugates. Cytotoxicity (LD50) was assessed for all prodrug conjugates using non-HIV-1 infected cells and was found to be in the micromolar range. The difference between the LD50 and ED50 suggests a favorable therapeutic index for the prodrug conjugates. In conclusion, these promising initial results demonstrate that the reconversion of the conjugate prodrugs was complete and that active SQV was released. Since the major delivery advantages of PEG prodrug conjugates can only be observed in v