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16th International HIV Drug Resistance Workshop12-16 June 2007, Barbados |
STRUCTURAL BASIS FOR THE RESISTANCE PROFILE OF THE HIV-1 PROTEASE INHIBITOR PL-100
Antivir Ther. 2007; 12:S17 (abstract no. 15)
JP Vacca1, MK Holloway1, TJ Allison1, CA Coburn1, JJ Wu2 and MA Wainberg3
1Merck Research Laboratories, Montreal, Canada; 2Ambrilia Biopharma Inc., Montreal, Canada; 3McGill University, Montreal, Canada
BACKGROUND: PL-100 is a novel HIV-1 protease inhibitor (PI) with a favourable cross-resistance profile that was discovered at Ambrilia Biopharma and was recently licensed to Merck Inc. for development. Its phosphorylated prodrug PPL-100 (MK-8122) is currently in Phase I human clinical trials. Serial passage of the compound in mononuclear cells infected with a laboratoryadapted HIV-1 strain resulted in the eventual isolation of several viral mutants containing substitutions in a novel region of the active site. Modelling studies in the wild-type active site and in mutant variants suggest a structural basis for the modest loss in activity.
METHODS: It has been previously reported that, after 48 weeks of passaging under increasing selective pressure of PL- 100, we observed a novel pattern of mutations (K45R, M46I, T80I and P81S) in the PR gene. T80I was observed at week 8. All other mutations did not appear until week 25. No further mutations were observed up to 48 weeks. While K45R and M46I are known mutations in the flap region, T80I and P81S are novel mutations in the substrate cleft. In order to understand this novel resistance profile, a model of PL-100 was created in the active site of the wild-type protease. Modelling of the C-terminal segment was guided by comparison to the crystal structure of amprenavir, while the N-terminal segment was generated based on conformational search and energy minimization. The T80I and/or P81S mutations were then incorporated into the WT crystal structure and the bound pose for PL-100 was re-examined in the mutant enzyme models. Subsequently, an X-ray structure of PL-100 was obtained in the wild-type protease which confirmed the initial modelling study.
RESULTS: In the model of PL-100 in the WT active site, the transition state hydroxyl group interacts with the catalytic aspartates, D25 and D225. The 4-aminophenyl sulphonamide fills the S2′ pocket and the isobutyl group occupies the S1′ pocket in a manner similar to amprenavir. The lysine backbone extends through the active site cleft and positions the diphenyl-alanine amide moiety in the S3–S4 region. The two diphenyl groups fill the P3 and P1 sites, and are arrayed on either side of P81. Mutation of this group to a serine would change the shape and character of the active site in this region, possibly creating an unfavourable hydrophilic/hydrophobic clash with the adjacent phenyl groups of PL-100.
CONCLUSION: The mutational profile of PL-100 can be deduced from a model and subsequent X-ray crystal structure of the inhibitor bound to HIV-1 protease. This information can aid in the understanding of the resistance profile of PPL-100 and the design of novel protease inhibitors.
2007-06-12
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