Intrinsic Proteolytic\nActivities from Cancer Cells\nAre Sufficient to Activate Alkoxyamine Prodrugs and Induce Cell Death

In search of better specificity and lower chances of\nresistance,\nprotease-activatable alkoxyamine prodrugs to fight cancer have been\nproposed. These molecules are made of a peptide linked to an alkoxyamine.\nProteolysis of the peptide converts the stable prodrug at 37 °C\nto a metastable alkoxyamine that spontaneously homolyzes into two\nfree radicals: a stable nitroxide and a very reactive alkyl radical.\nThe alkyl radical induces apoptosis in the surrounding cells by inducing\nrandom chemical alterations. Here, we show that varying the peptide\nmoiety from succinyl-Ala-Ala-Pro-Val- to PyroGlu-Gly-Arg- or PyroGlu-Gly-Lys-\nis effective in switching the activating enzyme from elastase to urokinase.\nFurthermore, these prodrugs induce the death of HT-1080 cells, a cell\nline that secretes several active proteases in culture. This cytotoxic\nactivity can be suppressed by protease inhibitors and does not affect\ncell lines devoid of active urokinase. We thus provide examples of\nalkoxyamine prodrugs that are efficiently activated by the limited\nintrinsic protease activity and that succeed in the destruction of\ncancer cell lines and cancer cells from tumor explants.