Radiolabelling of Ascorbic Acid: A New Clue to Clarify its Action as an Anticancer Agent?

A.      C. Mamede; A.      M. Abrantes; A.      S. Pires; S.      D. Tavares; M.      E. Serra; J.      M. Maia; M.      F. Botelho

Abstract

Vitamin C exists in two forms: the reduced (ascorbic acid - AA) and oxidized form (dehydroascorbic acid - DHA). This is a nutrient whose benefits are long known and widely publicized, being most of them related to its antioxidant action. As an antioxidant, the main role of vitamin C is to neutralize free radicals, reducing oxidative stress. However, some controversial studies suggest that this nutrient may have a preventive and therapeutic role in cancer disease due to their possible pro-oxidant activity, promoting the formation of reactive oxygen species that can induce cell death in cancer cells. This factor, coupled with the decrease of antioxidant enzymes and increase of decompartmentalized transition metals in tumor cells may result in the selective cytotoxicity of vitamin C and the subsequent revelation of its therapeutic potential.

In this way the first purpose of this work was radioactively label the reduced form of vitamin C with Tc-99m, its quality control by HPLC and the time stability. The second purpose was to use the radioactive complex 99mTc-AA in in vitro and in vivo studies in order to evaluate its uptake by colorectal cancer cells and biodistribution in mices, respectively. The results suggest that the pharmaceutical formulation developed, which was reproducible and stable over time, was residually taken up by colorectal cancer cells. Future studies are needed to deepen our understanding about the radioactive complex 99mTc-AA and clarify the mechanisms of action of vitamin C in oncologic disease.

Keywords: Vitamin C, nuclear medicine, biodistribution, radiotracer, cancer, ascorbic acid, Radiolabelling