Boron neutron capture therapy (BNCT) is increasingly being used in the treatment of several aggressive cancers, including cerebral glioblastoma multiforme. The main requirement for this therapy is selective targeting of tumor cells by sufficient quantities of¹⁰B atoms required for their capture/irradiation with low-energy thermal neutrons. The low content of boron targeting species in glioblastoma multiforme accounts for the difficulty in selective targeting of this very malignant cerebral tumor by this radiation modality. In the present study, we have used for the first time boron nitride nanotubes as carriers of boron atoms to overcome this problem and enhance the selective targeting and ablative efficacy of BNCT for these tumors. Following their dispersion in aqueous solution by noncovalent coating with biocompatible poly-l-lysine solutions, boron nitride nanotubes were functionalized with a fluorescent probe (quantum dots) to enable their tracking and with folic acid as selective tumor targeting ligand. Initial in vitro studies have confirmed substantive and selective uptake of these nanovectors by glioblastoma multiforme cells, an observation which confirms their potential clinical application for BNCT therapy for these malignant cerebral tumors.

Carbon nanotubes (CNTs) are widely used for biomedical applications as intracellular transporters of biomolecules owing to their ability to cross cell membranes. In this article, we survey the reported literature and results of our published work in an attempt to provide a rational view of the various CNT internalization mechanisms. Essentially three uptake mechanisms (phagocytosis, diffusion and endocytosis) have been reported in the literature. In addressing the subject of cellular internalization of CNTs, the unique physicochemical characteristics of CNTs that influence and drive the cell uptake pathway are considered. According to available evidence, the degree of dispersion, the formation of supramolecular complexes and the nanotube length are crucial factors in determining the exact mechanism of cellular uptake. In conclusion, phagocytosis appears to be the internalization pathway for CNT aggregates, bundles, cluster or single dispersed nanotubes 1 microm or more in length; endocytosis is the internalization mechanism for nanotubes forming supramolecular structures; and diffusion is the internalization mechanism for submicron CNTs that do not form supramolecular complexes. This information may be relevant to the rational design of CNT-based carriers for cell therapy.