Inhibition of Nitric Oxide Synthase Through Depletion of Its Cofactor Tetrahydrobiopterin as a Novel Strategy for Breast Cancer Anti-Angiogenic Therapy.

摘要

We showed previously that low molecular weight water-soluble antioxidant, manganese (III) tetrakis (N- ethylpyridinium-2-yl) porphyrin (Mn(exp) III)TE-2-PyP(exp 5+) is effective catalyst for the elimination of reactive oxygen and nitrogen species in different rodent models of oxidative stress injuries. We further showed that this porphyrin can oxidize cellular reductants, among them redox cofactor of nitric oxide synthase (NOS), tetrahydrobiopterin, BR(sub 4). It has been well- established that nitric oxide is essential for angiogenesis, stimulating endothelial cell proliferation in vitro. Tumors, being under oxidative stress, express iNOS, which leads to greatly increased levels of NO up to muM levels. Increased levels of BH(SUB 4)(sub 4) were thus required, and, reportedly, parallel increased NO production. When tetrahydrobiopterin is depleted NOS is inhibited and synthesizes superoxide rather than nitric oxide. We are testing here the hypothesis that depletion of BH(SUB 4) by MnTE-2-PyP(exp 5+) would inhibit NOS, decrease NO levels and thus inhibit angiogenesis. Within a scope of the project (Specific Aim 1), we showed that MnTE-2-PyP(exp 5+), when given to mice caused drastic decrease in tumor vasculature density of 4Tl mammary carcinoma. We also defined the thermodynamics and kinetics of BR(SUB 4) reaction with MnTE-2- PyP(exp 5+) (Batinic-Haberle et al, 20024), and adopted the HPLC method for measuring BR(SUB 4) and its oxidation product, 7,8-dihydrobiopterin in tumors.