A 24-amino acid leader peptide of a new human recombinant manganese superoxide dismutase can
enter cells and carry molecules. Here, we demonstrated that six of the 24 amino acids penetrate cells
through a particular gate represented by a specific amino acid sequence of the oestrogen receptor
(ER). We analysed the internalization of the synthetic hexapeptide and the cytotoxic activity of the
hexapeptide conjugated to cisplatin on a cell line panel. In most cell lines, the hexapeptide delivered
an amount of cisplatin that was 2 to 8 times greater than that released by cisplatin when the drug
was used alone. This increased delivery increases the therapeutic index of cisplatin and reduces side
effects caused by a high dosage or long-term treatment times. We may consider this hexapeptide a new
molecular carrier to deliver molecules with therapeutic activity into ER+ cells for diagnostic purposes
and clinical or immune therapy