Nuclear damage induced by liposomes containing FITC-labelled saporin on human melanoma cells in vitro

Ribosome-inactivating proteins are enzymes of plant origin which de-adenila te the major ribosomal RNA, making it unable to bind the elongation factor and thus arresting protein synthesis. Recently the N-glycosidase activity o f these enzymes has been extended also to deoxyribonucleotides substrates. In the present study we report the successful entrapment of the type 1 ribo some-inactivating protein saporin, covalently labelled with fluorescein iso thiocyanate (FITC) into L-alpha lecitin/cholesterol liposomes and describe its delivery to human melanoma cells in vitro. The fluorescein reacted toxi n maintained its enzymatic activity, although to a reduced extent; its inte raction with liposomes resulted in the entry of the protein through the lip id bilayers. The resulting vesicles are carriers that can deliver the toxin inside cells; as a consequence the cytotoxic effects of the encapsulated e nzyme were evident at a concentration two order of magnitude lower than tha t of the native one. In particular the nuclear damage, as revealed by micro nuclei formation, was evident within 44 hr. The intracellular dynamics of t he enzyme, as analyzed by confocal microscopy, point to an endocytic pathwa y of vesicles entry.