Extracellular expression of cytosine deaminase results in increased 5-FU production for enhanced enzyme/prodrug therapy.
BACKGROUND
The cytosine deaminase/5-fluorocytosine (CD/5-FC), strategy for cancer gene therapy shows considerable promise in experimental models but, because CD is a cytosolic enzyme, intracellular production of 5-fluorouracil (5-FU) causes the demise of the transduced cells before cytotoxic concentrations of' 5-FU can be achieved within the extracellular milieu.


METHODS
A soluble secreted form of CD was constructed and evaluated compared to intracellular CD in vitro and in vivo.


RESULTS
The secreted form of CD temporarily spared transduced cells and enhanced accumulation of extracellular 5-FU. Cytosolic CD produced rapid inhibition of thymidylate synthase and cell death before significant extracellular concentrations of 5-FU developed. Finally, tumors expressing the secreted form of CD had an improved response to 5-FC treatment compared to tumors expressing intracellular CD.


CONCLUSIONS
Further evaluation of extracellular expression of CD for enzyme/prodrug therapy may provide improvements in this commonly studied gene therapy strategy.
Rehemtulla
Alnawaz
A
The Department of Radiation Oncology, The University of Michigan Medical Center, Ann Arbor, MI 48109-0582, USA. alnawaz@umich.edu
Hamstra
Daniel A
DA
Kievit
Els
E
Davis
Mary A
MA
Ng
Emily Y
EY
Dornfeld
Kenneth
K
Lawrence
Theodore S
TS
D000818:Animals; D018920:Coculture Techniques; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics; D043525:Cytosine Deaminase / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D029968:Escherichia coli Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D045604:Extracellular Fluid / Q000201:enzymology; D005260:Female; D005472:Fluorouracil / Q000493:pharmacokinetics*; D015316:Genetic Therapy / Q000379:methods*; D051379:Mice; D008819:Mice, Nude; D010957:Plasmids / Q000235:genetics; D011355:Prodrugs / Q000493:pharmacokinetics*; D051381:Rats; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors; D023041:Xenograft Model Antitumor Assays
D029968:Escherichia coli Proteins; D011355:Prodrugs; D013940:Thymidylate Synthase; D043525:Cytosine Deaminase; C468827:codA protein, E coli; D005472:Fluorouracil