Toward targeted "oxidation therapy" of cancer: peroxidase-catalysed cytotoxicity of indole-3-acetic acids.
OBJECTIVE
The study aimed to identify suitable prodrugs that could be used to test the hypothesis that peroxidase activity in cells, either endogenous or enhanced by immunological targeting, can activate prodrugs to cytotoxins. We hypothesized that prototype prodrugs based on derivatives of indole-3-acetic acid (IAA), when activated by peroxidase enzymes (e.g., from horseradish, HRP) should produce peroxyl radicals, with deleterious biological consequences.


METHODS
V79 hamster cells were incubated with IAA or derivatives +/- HRP and cytotoxicity assessed by a clonogenic assay. To assess the toxicity of stable oxidation products, prodrugs were also oxidized by HRP without cells, and the products then added to cells.


RESULTS
The combination of prodrug and enzyme resulted in cytotoxicity, but neither indole nor enzyme in isolation was toxic under the conditions used. Although lipid peroxidation was stimulated in liposomes by the prodrug/enzyme treatment, it could not be measured in mammalian cells. Adding oxidized prodrugs to cells resulted in cytotoxicity.


CONCLUSIONS
Although the hypothesis that prodrugs of this type could enhance oxidative stress via lipid peroxidation was not established, the results nonetheless demonstrated oxidatively-activated cytotoxicity via indole acetic acid prodrugs, and suggested these as a new type of substrate for antibody-directed enzyme-prodrug therapy (ADEPT). The hypothesized free-radical fragmentation intermediates were demonstrated, but lipid peroxidation associated with peroxyl radical formation was unlikely to be the major route to cytotoxicity.
Folkes
L K
LK
Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, Northwood, Middlesex, UK.
Candeias
L P
LP
Wardman
P
P
D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism; D002460:Cell Line / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D018922:HL-60 Cells / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000378:metabolism; D006801:Humans; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000627:therapeutic use; D010084:Oxidation-Reduction; D010544:Peroxidases / Q000378:metabolism*; D011355:Prodrugs / Q000378:metabolism* / Q000627:therapeutic use
D000970:Antineoplastic Agents; D007210:Indoleacetic Acids; D011355:Prodrugs; D006735:Horseradish Peroxidase; D010544:Peroxidases