title: Tumor cell killing enabled by listeriolysin O-liposome-mediated delivery of the protein toxin gelonin.
abstract: Gelonin is a type I plant toxin that has potential as an effective anti-tumor agent by virtue of its enzymatic capacity to inactivate ribosomes and arrest protein synthesis, thereby effectively limiting the growth of cancer cells. Being a hydrophilic macromolecule, however, gelonin has limited access to its target subcellular compartment, the cytosol; it is effectively plasma membrane-impermeant and subject to rapid degradation within endosomes and lysosomes upon cellular uptake as it lacks the membrane-translocating capability that is typically provided by a disulfide-linked B polypeptide found in the type II toxins (e.g. ricin). These inherent characteristics generate the need for the development of a specialized cytosolic delivery strategy for gelonin as an effective anti-tumor therapeutic agent. Here we describe an efficient means of delivering gelonin to the cytosol of B16 melanoma cells. Gelonin was co-encapsulated inside pH-sensitive liposomes with listeriolysin O, the pore-forming protein that mediates escape of the intracellular pathogen Listeria monocytogenes from the endosome into the cytosol. In in vitro experiments, co-encapsulated listeriolysin O enabled liposomal gelonin-mediated B16 cell killing with a gelonin IC50 of approximately 0.1 nM with an extreme efficiency requiring an incubation time of only 1 h. By contrast, cells treated with equivalent concentrations of unencapsulated gelonin or gelonin encapsulated alone in pH-sensitive liposomes exhibited no detectable cytotoxicity. Moreover, treatment by direct intratumor injection into subcutaneous solid tumors of B16 melanoma in a mouse model showed that pH-sensitive liposomes containing both listeriolysin O and gelonin were more effective than control formulations in curtailing tumor growth rates.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-1065, USA.
authors.forename: Chester J
authors.initials: CJ
authors.lastname: Provoda
authors.forename: Ethan M
authors.initials: EM
authors.lastname: Stier
authors.forename: Kyung-Dall
authors.initials: KD
authors.lastname: Lee
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000493:pharmacokinetics / Q000633:toxicity; D001427:Bacterial Toxins / Q000633:toxicity; D001692:Biological Transport; D002470:Cell Survival / Q000187:drug effects*; D004337:Drug Carriers; D006360:Heat-Shock Proteins / Q000633:toxicity*; D006460:Hemolysin Proteins; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000138:chemical synthesis; D008546:Melanoma, Experimental / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D010940:Plant Proteins / Q000493:pharmacokinetics* / Q000633:toxicity*; D054789:Ribosome Inactivating Proteins, Type 1; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D001427:Bacterial Toxins; D004337:Drug Carriers; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; D008081:Liposomes; D010940:Plant Proteins; D054789:Ribosome Inactivating Proteins, Type 1; C025674:GEL protein, Gelonium multiflorum; C038705:hlyA protein, Listeria monocytogenes