Directed enzyme pro-drug gene therapy for pancreatic cancer in vivo.
BACKGROUND
Directed enzyme pro-drug therapy incorporates the delivery of a gene to a cancer cell that will be specifically expressed and will confer sensitivity to a therapeutic agent. Tumor-specific gene expression can be achieved by coupling the promoter for the carcinoembryonic antigen (CEA) to a gene such as herpes simplex virus thymidine kinase (HSV-tk), which phosphorylates ganciclovir to a potent DNA synthesis inhibitor.


METHODS
Retroviral vectors were constructed to contain the CEA promoter coupled to HSV-tk (LN-CEA-TK) and were used to transduce the CEA-expressing pancreatic carcinoma cell line BXPC3. Recombinant pancreatic carcinoma cell lines expressing HSV-tk (BXPC3CEA-TK) were then tested for sensitivity to the toxic effects on ganciclovir after engraftment into severe combined immunodeficient mice. Tumors were generated by subcutaneous inoculation of 20 x 10(6) tumor cells consisting of BXPC3 and/or BXPC3CEA-TK cells in ratios of 100:0, 90:10, 50:50, 10:90, and 0:100. After 3 days mice received daily ganciclovir (0.1 mg/kg) or phosphate-buffered saline solution by intraperitoneal injection and were monitored for tumor growth.


RESULTS
All severe combined immunodeficient mice inoculated with BXPC3 or BXPC3CEA-TK cells in any proportion developed large pancreatic tumors. As expected, a significant reduction in tumor size was seen in the BXPC3CEA-TK engrafted mice receiving ganciclovir compared with mice receiving phosphate-buffered saline solution or mice engrafted with only BXPC3. In addition, all animals with any fraction of cells expressing HSV-tk exhibited a significant reduction in tumor growth, including animals with only 10% of cells expressing HSV-tk.


CONCLUSIONS
These results suggest the potential utility of directed enzyme pro-drug therapy in patients with CEA-expressing pancreatic carcinoma.
DiMaio
J M
JM
Department of Surgery, Duke University Medical Center, Durham, NC 27710.
Clary
B M
BM
Via
D F
DF
Coveney
E
E
Pappas
T N
TN
Lyerly
H K
HK
D000818:Animals; D001483:Base Sequence; D002272:Carcinoembryonic Antigen / Q000235:genetics; D002460:Cell Line; D015774:Ganciclovir / Q000378:metabolism / Q000627:therapeutic use*; D015316:Genetic Therapy; D006801:Humans; D051379:Mice; D016513:Mice, SCID; D008969:Molecular Sequence Data; D010190:Pancreatic Neoplasms / Q000628:therapy*; D011355:Prodrugs / Q000378:metabolism / Q000627:therapeutic use*; D012190:Retroviridae / Q000235:genetics*; D018139:Simplexvirus / Q000201:enzymology; D013937:Thymidine Kinase / Q000235:genetics*
D002272:Carcinoembryonic Antigen; D011355:Prodrugs; D013937:Thymidine Kinase; D015774:Ganciclovir