Abstract A60: Targeting brain tumor stem cells

Abstract

The brain tumor stem-cell (BTSC) hypothesis proposes with acquired self-renewal properties establish a brain tumorigenic-behavior (1). Thus, failure to cure brain cancer has been attributed to the fact that typical cytotoxic therapies target rapidly proliferating brain tumor cells, while sparing the BTSC compartment, which has a low proliferation rate and high tumorigenic potential. Taking advantage of the recent development of nanotechnologies that may offer innovative drug-delivery systems for improved efficacy, specificity and biological safety (2), the aim of our work is to develop nanoparticle-based treatments targeting BTSCs. The first part of our work represents a comprehensive study of the aggressiveness of the BTSC was shown to be associated with the expression of the neural precursor cell marker AC133. Hence, the percentage of AC133 expressing glioma cells is increased after maintenance or exposure to moderately low oxygen levels (3). Our data indicate that cells maintained at 3% oxygen express more AC133 and are more aggressive after in vivo xenograft than cells cultured at 21% oxygen. Thus, oxygen pressure represents a major parameter in the expression of the AC133 molecule but is also important in aggressiveness of glioma cells. The mechanism that links hypoxia, AC133 expression and the tumorigenic behavior of BTSC has been studied. Our results, including CoCl2 induction and shRNA knockdown, suggest a role for HIF-1α in the regulation of AC133 in glioblastoma cells. The second part of our work, immunonanoparticules (ILNC) that target AC133 were synthesized by conjugation of thiolated AC133 or IgG1 isotype control immunoglobulins to lipid nanocapsules (LNC) (4) by linkage through incorporation of lipid PEG(2000) functionalized with reactive-sulfhydryl maleimide groups (DSPE-PEG(2000)-maleimide) on the surface of LNC by using a post-insertion procedure (5). Our results indicate a fixation yield of antibodies on LNC varying from 6 to 60% representing 70 antibodies per LNC. To evaluate the selectivity of immunonanoparticles binding and resulting uptake by cells a second in vitro model has been developed. Human Caco-2 cells, previously described to express AC133, were used and exposed to siRNA targeting the CD133 gene to dispose of two types of Caco-2 cells: Caco-2-AC133high and Caco-2-AC133low. We are now testing ILNC uptake in our Caco-2 cell model. We will test if ILNC are able to bind to AC133 epitope on Caco-2 cells and if they are able to be internalized in cells. Accumulated results must allow us to extend our knowledge on glioma aggressiveness and to adapt our vectors to resolve the BTSC targeting problem and their death. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A60.