Identification of a human valacyclovirase: biphenyl hydrolase-like protein as valacyclovir hydrolase.
Valacyclovir is the 5'-valyl ester prodrug of acyclovir, an effective anti-herpetic drug. Systemic availability of acyclovir in humans is three to five times higher when administered orally as the prodrug. The increased bioavailability of valacyclovir is attributed to carrier-mediated intestinal absorption, via the hPEPT1 peptide transporter, followed by the rapid and complete conversion to acyclovir. The one or more human enzymes responsible for in vivo activation of the prodrug to the active drug and its conversion sites, however, have not been identified. In this report, we describe the purification, identification, and characterization of a human enzyme that activates valacyclovir to acyclovir. A protein with significant hydrolytic activity toward valacyclovir, the 5'-glycyl ester of acyclovir, and the 5'-valyl ester of zidovudine (AZT), was purified from Caco-2 cells derived from human intestine. Using a non-redundant data base search, the N-terminal 19-amino acid sequence of the purified 27-kDa, basic protein revealed a perfect match within the N terminus of a serine hydrolase, Biphenyl hydrolase-like (BPHL, gi:4757862) protein, previously cloned from human breast carcinoma. Recombinant BPHL exhibited significant hydrolytic activity for both valacyclovir and valganciclovir with specificity constants (kcat/Km), 420 and 53.2 mm-1.s-1, respectively. We conclude that BPHL may be an important enzyme activating valacyclovir and valganciclovir in humans and an important new target for prodrug design.
Department of Pharmaceutical Sciences, College of Pharmacy, The University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
Insook
I
Kim
Xiao-Yan
XY
Chu
Seonyoung
S
Kim
Chester J
CJ
Provoda
Kyung-Dall
KD
Lee
Gordon L
GL
Amidon
D000212:Acyclovir / Q000031:analogs & derivatives* / Q000737:chemistry*; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry* / Q000494:pharmacology*; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006867:Hydrolases / Q000737:chemistry*; D006868:Hydrolysis; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D000077483:Valacyclovir; D014633:Valine / Q000031:analogs & derivatives* / Q000737:chemistry*
D011994:Recombinant Proteins; D006867:Hydrolases; C093745:BPHL protein, human; D002265:Carboxylic Ester Hydrolases; D014633:Valine; D000077483:Valacyclovir; D000212:Acyclovir