Oxic and anoxic enhancement of radiation-mediated toxicity by horseradish peroxidase/indole-3-acetic acid gene therapy.
OBJECTIVE
To evaluate the interaction of horseradish peroxidase (HRP)/indole-3-acetic acid (IAA) gene therapy with therapeutically relevant doses of radiation.


METHODS
Human T24 bladder and FaDu nasopharyngeal carcinoma cells were transiently transfected with the HRP cDNA using a non-viral delivery method. HRP expression was confirmed by immunostain and enzyme activity assay. The cells were exposed to IAA or the analogue 1-Me-IAA in conjunction with X-rays in air or in anoxic conditions, and cytotoxicity was determined by clonogenic assay.


RESULTS
A significant and selective enhancement of radiation-mediated cytotoxicity was observed. Pre-incubation with the prodrugs induced sensitizer enhancement ratios (SER) ranging from 2.6 (0.1mM IAA) to 5.4 (0.5 mM IAA). Radiosensitization was also observed when prodrug exposure was performed immediately after irradiation (SER=2.1-5.6), or in anoxic conditions (SER=3.6).


CONCLUSIONS
The use of gene therapy protocols to enhance the effect of ionizing radiation holds promise for anticancer therapy. The data suggest that the combination of HRP/IAA gene therapy with ionizing radiation could present therapeutic advantages in the treatment of solid malignancies, in particular to target the hypoxic population, which has been shown to correlate with poor outcome after radiotherapy.
Greco
O
O
Tumour Microcirculation Group, Gray Cancer Institute, PO BOX 100, Northwood, Middlesex, HA6 2JR, UK.
Tozer
G M
GM
Dachs
G U
GU
D015687:Cell Hypoxia; D002470:Cell Survival / Q000528:radiation effects; D015316:Genetic Therapy / Q000379:methods*; D006735:Horseradish Peroxidase / Q000235:genetics*; D006801:Humans; D007210:Indoleacetic Acids / Q000494:pharmacology*; D009369:Neoplasms / Q000378:metabolism / Q000532:radiotherapy* / Q000628:therapy*; D010100:Oxygen / Q000378:metabolism; D018714:Radiotherapy, Adjuvant; D014162:Transfection; D014407:Tumor Cells, Cultured
D007210:Indoleacetic Acids; C030737:indoleacetic acid; D006735:Horseradish Peroxidase; D010100:Oxygen