Expression of the bifunctional suicide gene CDUPRT increases radiosensitization and bystander effect of 5-FC in prostate cancer cells.
OBJECTIVE
To test the hypothesis that, with 5-fluorocytosine (5-FC) treatment, the co-expression of cytosine deaminase (CD) and uracil phosphoribosyltransferase (UPRT) can lead to greater radiosensitization and bystander effect than CD-expression alone.


METHODS
R3327-AT cell lines stably expressing CD or CDUPRT were generated. The 5-FC and 5-FU cytotoxicity, and the radiosensitivity with/without 5-FC treatment, of these cells were evaluated under both aerobic and hypoxic conditions. The bystander effect was assessed by apoptosis staining and clonogenic survival. The pharmacokinetics of 5-FU and 5-FC metabolism was monitored in mice bearing CD- or CDUPRT-expressing tumors using 19F MR spectroscopy (MRS).


RESULTS
CDUPRT-expressing cells were more sensitive to 5-FC and 5-FU than CD-expressing cells. CDUPRT-expression further enhanced the radiosensitizing effect of 5-FC, relative to that achieved by CD-expression alone. A 25-fold lower dose of 5-FC resulted in the same magnitude of radiosensitization in CDUPRT-expressing cells, relative to that in CD-expressing cells. The 5-FC cytotoxicity in co-cultures of parental cells mixed with 10-20% CDUPRT cells was similar to that in 100% CDUPRT cells. 19F MRS measurements showed that expression of CDUPRT leads to enhanced accumulation of fluorine nucleotide (FNuc), relative to that associated with CD-expression alone.


CONCLUSIONS
Our study suggests that CDUPRT/5-FC strategy may be more effective than CD/5-FC, especially when used in combination with radiation.
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
Ligang
L
Xing
Xiaorong
X
Sun
Xuelong
X
Deng
Khushali
K
Kotedia
Muneyasu
M
Urano
Jason A
JA
Koutcher
C Clifton
CC
Ling
Gloria C
GC
Li
D000818:Animals; D015153:Blotting, Western; D024201:Bystander Effect / Q000235:genetics*; D045744:Cell Line, Tumor / Q000187:drug effects; D018920:Coculture Techniques; D043525:Cytosine Deaminase / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D005437:Flucytosine / Q000494:pharmacology*; D005472:Fluorouracil / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051379:Mice; D008819:Mice, Nude; D010430:Pentosyltransferases / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D011336:Probability; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D011836:Radiation Tolerance / Q000187:drug effects* / Q000235:genetics*; D012016:Reference Values; D014162:Transfection
D005437:Flucytosine; D010430:Pentosyltransferases; C023269:uracil phosphoribosyltransferase; D043525:Cytosine Deaminase; D005472:Fluorouracil