TY - JOUR
T1 - Specificity of a prodrug-activating enzyme hVACVase
T2 - The leaving group effect
AU - Sun, Jing
AU - Dahan, Arik
AU - Walls, Zachary F.
AU - Lai, Longsheng
AU - Lee, Kyung Dall
AU - Amidon, Gordon L.
PY - 2010/12/6
Y1 - 2010/12/6
N2 - Human valacyclovirase (hVACVase) is a prodrug-activating enzyme for amino acid prodrugs including the antiviral drugs valacyclovir and valganciclovir. In hVACVase-catalyzed reactions, the leaving group of the substrate corresponds to the drug moiety of the prodrug, making the leaving group effect essential for the rational design of new prodrugs targeting hVACVase activation. In this study, a series of valine esters, phenylalanine esters, and a valine amide were characterized for the effect of the leaving group on the efficiency of hVACVase-mediated prodrug activation. Except for phenylalanine methyl and ethyl esters, all of the ester substrates exhibited a relatively high specificity constant (kcat/Km), ranging from 850 to 9490 mM -1•s-1. The valine amide Val-3-APG exhibited significantly higher Km and lower kcat values compared to the corresponding ester Val-3-HPG, indicating poor specificity for hVACVase. In conclusion, the substrate leaving group has been shown to affect both binding and specific activity of hVACVase-catalyzed activation. It is proposed that hVACVase is an ideal target for α-amino acid ester prodrugs with relatively labile leaving groups while it is relatively inactivate toward amide prodrugs.
AB - Human valacyclovirase (hVACVase) is a prodrug-activating enzyme for amino acid prodrugs including the antiviral drugs valacyclovir and valganciclovir. In hVACVase-catalyzed reactions, the leaving group of the substrate corresponds to the drug moiety of the prodrug, making the leaving group effect essential for the rational design of new prodrugs targeting hVACVase activation. In this study, a series of valine esters, phenylalanine esters, and a valine amide were characterized for the effect of the leaving group on the efficiency of hVACVase-mediated prodrug activation. Except for phenylalanine methyl and ethyl esters, all of the ester substrates exhibited a relatively high specificity constant (kcat/Km), ranging from 850 to 9490 mM -1•s-1. The valine amide Val-3-APG exhibited significantly higher Km and lower kcat values compared to the corresponding ester Val-3-HPG, indicating poor specificity for hVACVase. In conclusion, the substrate leaving group has been shown to affect both binding and specific activity of hVACVase-catalyzed activation. It is proposed that hVACVase is an ideal target for α-amino acid ester prodrugs with relatively labile leaving groups while it is relatively inactivate toward amide prodrugs.
UR - http://www.scopus.com/inward/record.url?scp=78649913370&partnerID=8YFLogxK
U2 - 10.1021/mp100300k
DO - 10.1021/mp100300k
M3 - Article
C2 - 21028903
AN - SCOPUS:78649913370
SN - 1543-8384
VL - 7
SP - 2362
EP - 2368
JO - Molecular Pharmaceutics
JF - Molecular Pharmaceutics
IS - 6
ER -