| Bovine lactoferricin (LfcinB) is a 25 amino acid peptide released from the N-terminal portion of its parent protein, lactoferrin by acid-pepsin hydrolysis. Lactoferrin is found in the intracellular granules of neutrophils and in biological fluids, including saliva and milk. There is abundant evidence that lactoferrin is a major component in antimicrobial host defense. Most of the antimicrobial activity of lactoferrin has been attributed to LfcinB, which kills a wide variety of bacteria, viruses and fungi through a mechanism involving membrane destabilization. LfcinB also displays potent anticancer activity; however the extent of this activity and the mechanism(s) by which it occurs has not been investigated. In this study, I found that LfcinB killed a wide variety of human cancer cell lines, with no apparent cytotoxic effect on normal human cells. LfcinB triggered the mitochondria-dependent pathway of apoptosis, through a reactive oxygen species (ROS)-, and caspase-2-dependent loss of mitochondrial transmembrane potential, release of mitochondrial cytochrome c, and sequential caspase-9 and caspase-3 activation. LfcinB interacted with Jurkat T leukemia cells, most likely through initial electrostatic interactions, followed by formation of membrane-spanning pores that allowed LfcinB to enter the cell. In addition, immune-deficient SCID/beige mice bearing disseminated Ramos B-lymphoma cells showed a 1.9-fold increase in median survival, as well as an increased proportion (60%) of long-term survivors after treatment with LfcinB on days 1 and 3 post lymphoma cell injection. LfcinB also inhibited blood vessel development, which is required for tumour growth beyond 1-2 mm in diameter. LfcinB bound to the surface of human umbilical vein endothelial cells (HUVECs) through an interaction with heparin-like proteoglycans, thereby inhibiting heparin-binding growth factors from interacting with their cell-surface receptors. LfcinB blocked bFGF- and VEGF165-induced HUVEC proliferation and migration in vitro, and bFGF- and VEGF165-induced angiogenesis in vivo using the Matrigel model. This study has allowed me to understand the multifunctional anticancer activity of LfcinB. I have determined that LfcinB kills human tumour cells both in vitro and in vivo, through a mechanism involving membrane binding and destabilization, and the induction of apoptosis. I have also found that LfcinB displays potent antiangiogenic activity. |
