A novel form of Manganese Superoxide Dismutase: its Role as anti-Cancer, anti-Necrotic and Tumor Marker for Imaging Analysis

The manganese superoxide dismutase from lyposarcoma (LSA-MnSOD) is a tumor protein isolated and sequenced, for the first time, in human lyposarcoma cells (LSA) in the Laboratory of Experimental Oncology, Cancer Institute of Naples, G. Pascale, by Dr. Aldo Mancini. This protein showed a rapid and effective anti-cancer activity consisting of a selective cytotoxicity on certain human breast cancer cells (MCF-7), and no cytotoxic effect on normal cells, such as normal human mammary epithelium (MCF-10) and fibroblasts (MRC-5). This protein was sequenced and produced as recombinant form (rMnSOD). The rMnSOD demonstrated the ability to enter both normal and cancer cells and to perform antioxidant activity by neutralizing free radicals, turning them into hydrogen peroxide that only normal cells are able to transform into molecular oxygen and water, due to their normal levels of catalase. In cancer cells – by their well known catalase underproduction, up to 10-100 times, as compared to normal cells – the peroxide can not be converted in oxygen, so that only cancer cells will reach the threshold of toxicity that will cause apoptotic death. The surprising effect of this molecule is, however, due to its ability, following injection in vivo, to penetrate all cells giving off its antioxidant potential, through its enzymatic activity. Both LSA-MnSOD and the rMnSOD were sequenced and compared to the common mitochondrial form. The difference lies in the presence of a leader peptide detected only in LSA–MnSOD, thus explaining the unusual characteristic of the protein of entering cells, while the native protein remains confined to the mitochondrial compartment. So the leader peptide has been synthesized (rMnSOD-LP) and injected in vitro and in vivo, thus demonstrating its ability to enter cells. These experiments highlighted its role as a molecular carrier. Further studies about its carrier function were performed by conjugation of this peptide to radioactive 68Ga and its subsequent injection into animals affected by mammary tumors. PET analysis, performed two hours after injection in animals (dogs and cats), demonstrated internalization of the synthetic construct in the tumor and in its metastasis, thus allowing a more accurate identification in the body. Experiments in progress are demonstrating the ability of the leader peptide to deliver a conjugated cysplatin directly inside the tumor cells (as quantitatively demonstrated by atomic absorption spectrophotometry) and delivering cisplatin toxic load . This internalization rapidly leads to cell death in vitro and in vivo . As a further demonstration of the ability of rMnSOD to repair the damage caused by radical excess, its topical formulation has been used to treat animals affected by extended necrotic lesions, which quickly returned to the structural and functional integrity of all tissues affected by necrosis. More recently, a significant reduction of tissue injury from X ray damage was demonstrated by using MnSOD-plasmid/liposome treatments in the protection of murine lung. The latter studies demonstrated that rMnSOD not only exerts radioprotective effect on normal cells, but it is also radiosensitizing for tumor cells