title: Oncolytic herpes simplex virus expressing yeast cytosine deaminase: relationship between viral replication, transgene expression, prodrug bioactivation.
abstract: Yeast cytosine deaminase (yCD) is a well-characterized prodrug/enzyme system that converts 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU), and has been combined with oncolytic viruses. However, in vivo studies of the interactions between 5-FC bioactivation and viral replication have not been previously reported, nor have the kinetics of transgene expression and the pharmacokinetics of 5-FC and 5-FU. We constructed a replication-conditional Herpes simplex virus 1 (HSV-1) expressing yCD and examined cytotoxicity when 5-FC was initiated at different times after viral infection, and observed that earlier 5-FC administration led to greater cytotoxicity than later 5-FC administration in vitro and in vivo. In animal models, 12 days of 5-FC administration was superior to 6 days, but dosing beyond 12 days did not further enhance efficacy. Consistent with the dosing-schedule results, both viral genomic DNA copy number and viral titers were observed to peak on Day 3 after viral injection and gradually decrease thereafter. The virus is replication-conditional and was detected in tumors for as long as 2 weeks after viral injection. The maximum relative extent of yCD conversion of 5-FC to 5-FU in tumors was observed on Day 6 after viral injection and it decreased progressively thereafter. The observation that 5-FU generation within tumors did not lead to appreciable levels of systemic 5-FU (<10 ng ml⁻¹) is important and has not been previously reported. The approaches used in these studies of the relationship between the viral replication kinetics, transgene expression, prodrug administration and anti-tumor efficacy are useful in the design of clinical trials of armed, oncolytic viruses.
authors.affiliation: Division of Surgical Oncology, Massachusetts General Hospital Cancer Center and Harvard Medical School, Boston, MA, USA.
authors.forename: S
authors.initials: S
authors.lastname: Yamada
authors.forename: T
authors.initials: T
authors.lastname: Kuroda
authors.forename: B C
authors.initials: BC
authors.lastname: Fuchs
authors.forename: X
authors.initials: X
authors.lastname: He
authors.forename: J G
authors.initials: JG
authors.lastname: Supko
authors.forename: A
authors.initials: A
authors.lastname: Schmitt
authors.forename: C M
authors.initials: CM
authors.lastname: McGinn
authors.forename: M
authors.initials: M
authors.lastname: Lanuti
authors.forename: K K
authors.initials: KK
authors.lastname: Tanabe
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000493:pharmacokinetics; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000628:therapy* / Q000821:virology; D043525:Cytosine Deaminase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D004334:Drug Administration Schedule; D005437:Flucytosine / Q000493:pharmacokinetics*; D005472:Fluorouracil / Q000493:pharmacokinetics*; D015316:Genetic Therapy / Q000379:methods; D005822:Genetic Vectors; D019073:HT29 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D050130:Oncolytic Virotherapy / Q000379:methods*; D011355:Prodrugs / Q000493:pharmacokinetics*; D018139:Simplexvirus / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D019076:Transgenes; D014779:Virus Replication; D023041:Xenograft Model Antitumor Assays; D015003:Yeasts / Q000201:enzymology / Q000235:genetics
chemical_list: D000964:Antimetabolites, Antineoplastic; D011355:Prodrugs; D005437:Flucytosine; D043525:Cytosine Deaminase; D005472:Fluorouracil
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