Characterization of Liposomal Systems Entrapping Boron-Containing Compounds in Response to pH Gradients

Abstract

Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when a stable isotope, Boron-10, is irradiated with low-energy thermal neutrons to yield ionizing Helium and Lithium ions that are highly damaging and usually lethal to cells. The successful treatment of cancer by BNCT requires the selective concentration of Boron-10 within malignant tumors. Liposomes have been used as drug delivery vehicles for in vivo application, including several anticancer agents. The ability of two Boron-containing compounds, 1-p-borono-phenylalanine (BPA) HCl and o-carboranylpropylamine chloride (CPA) to accumulate within unilamellar liposomes passively and in response to a transmembrane pH gradient are compared. Characterization of the obtained systems is performed for conventional and polyethylene glycol (PEG)-modified (stealth) liposomes, in terms of lipid and drug contents, vesicle size and stability. The results indicate that BPA can be successfully encapsulated in conventional liposomes by passive loading, while the active loading approach is more suitable for the entrapment of CPA.