Attenuated Salmonella targets prodrug activating enzyme carboxypeptidase G2 to mouse melanoma and human breast and colon carcinomas for effective suicide gene therapy.
OBJECTIVE
We engineered the oncolytic Salmonella typhimurium-derived bacterium VNP20009 as a vector to target delivery to tumors of the prodrug-activating enzyme carboxypeptidase G2 (CPG2) and to show enhanced antitumor efficacy on administration of different prodrugs.


METHODS
We characterized CPG2 expression in vectors by immunoblotting, immunofluorescence, and enzyme activity. We assessed prodrug activation by high-performance liquid chromatography. Target human tumor cell and bacterial vector cell cytotoxicity was measured by flow cytometry and colony-forming assays. Therapy was shown in two human tumor xenografts and one mouse allograft with postmortem analysis of bacterial and CPG2 concentration in the tumors.


RESULTS
CPG2 is expressed within the bacterial periplasm. It activates prodrugs and induces cytotoxicity in human tumor cells but not in host bacteria. Following systemic administration, bacteria multiply within xenografts reaching 2 x 10(7)/g to 2 x 10(8)/g at 40 days postinoculation. The concentration of CPG2 in these tumors increases steadily to therapeutic levels of 1 to 6 units/g. The bacteria alone reduce the growth of the tumors. Subsequent administration of prodrugs further reduces significantly the growth of the xenografts.


CONCLUSIONS
The bacteria multiply within tumors, resulting in a selective expression of CPG2. The CPG2-expressing bacteria alone reduce the growth of tumors. However, in the presence of prodrugs activated by CPG2, this oncolytic effect is greatly increased. We conclude that bacterial oncolytic therapy, combined with CPG2-mediated prodrug activation, has great potential in the treatment of a range of cancers.
Friedlos
Frank
F
Cancer Research UK Centre for Cancer Therapeutics at The Institute of Cancer Research, Sutton, Surrey, United Kingdom.
Lehouritis
Panos
P
Ogilvie
Lesley
L
Hedley
Douglas
D
Davies
Lawrence
L
Bermudes
David
D
King
Ivan
I
Martin
Jan
J
Marais
Richard
R
Springer
Caroline J
CJ
D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000628:therapy*; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D003110:Colonic Neoplasms / Q000235:genetics* / Q000628:therapy*; D005434:Flow Cytometry; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D006801:Humans; D008545:Melanoma / Q000188:drug therapy* / Q000235:genetics*; D051379:Mice; D009368:Neoplasm Transplantation; D011355:Prodrugs / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000378:metabolism*; D011623:gamma-Glutamyl Hydrolase / Q000235:genetics*
D011355:Prodrugs; D011623:gamma-Glutamyl Hydrolase