The leader peptide of a human rec. MnSOD as molecular carrier which delivers high amounts of cisplatin into tumor cells inducing a fast apoptosis in vitro

The leader peptide of a recombinant MnSOD (rMnSOD-Lp) constitutes the carrier that allows rMnSOD to penetrate tumor cells. A synthetic preparation of rMnSOD-Lp was ⁶⁸Ga labeled (rMnSOD-Lp-⁶⁸Ga) and injected into animals bearing spontaneous mammary cancers, followed by PET examinations, which demonstrated unambiguously the tumor sites in all the animals, suggesting that if rMnSOD-Lp was able to transport the radioisotope into tumor cells, it would also be able to deliver cytotoxic molecules. The rMnSOD-Lp was, therefore, conjugated to cisplatin (rMnSOD-Lp-CC) and added to cultured tumor cells. Equal concentrations of cisplatin were used for the tests. After treating the ovarian cancer cells with 11.1 μg of cisplatin alone, analysis by atomic absorbance spectrophotometry was able to detect only 6 ng of platinum, whereas when the same cells were treated with the same amount of cisplatin conjugated to leader peptide rMnSOD, 387 ng of platinum were detected, i.e., an amount 80 times greater. Only the tumor cells died following treatment with rMnSOD-Lp-CC; molecular analysis revealed that its addition generated an increasing expression of Erk-2 and Bax products, which could be inhibited only by a selective MAP/ERK kinase inhibitor (PD98059), revealing that rMnSOD-Lp-CC has an apoptotic function, exactly as occurs when using the cisplatin alone. Data are statistically significant and indicate that by using rMnSOD-Lp-CC, the cisplatin can be transformed from an agent with antireplicative activity into a specific and selective antitumor molecule, increasing its therapeutic index. We think that rMnSOD-Lp-CC deserves to be considered as a new antitumor agent.