Superoxide Dismutase (SOD) Activity with Fe-chlorin e6-Na and Suppression of Malignant Tumor Growth in Rats

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Abstract
Derivatives of porphyrin, specifically Fe-chlorin e6-Na (FeCNa), mimic Superoxide dismutase (SOD). This SOD activity was determined by decrease in electron spin resonance (ESR) signals and increase in hydrogen peroxide (H202) as the intermediate of O2 by the coloration using 4-aminoantipyrin. Chlorin e6-Na used for cancer photodynamic therapy (PDT)(1) does not show SOD mimicking activity. The specific activity of FeCNa, comparing with bovine RBC-SOD, was 1/7.5 as determined by ESR analysis. The iron element of Fe-chlorin e6-Na, being tightly encased in the molecule, did not participate in the Fenton reaction. The SOD mimetic activity of FeCNa was stable against physico-chemical treatment such as pH shock, heat and digestion by pronase. For cancer bearing rats with oxidative stress (OS), immediate relief of OS was possible by a single intraperitoneal injection of FeCNa and relief continued for 24 hours. The subsequent administration of FeCNa suppressed cancer growth in vivo.