B10 is a glycosylated derivative of
betulinic acid with promising activity against
glioma cells. Lysosomal cell death pathways appear to be essential for its cytotoxicity. We investigated the influence of
hypoxia, nutrient deprivation and current standard
therapies on B10 cytotoxicity. The human
glioma cell lines LN-308 and LNT-229 were exposed to B10 alone or together with irradiation,
temozolomide, nutrient deprivation or
hypoxia. Cell growth and viability were evaluated by
crystal violet staining, clonogenicity assays,
propidium iodide uptake and LDH release assays. Cell death was examined using an inhibitor of lysosomal acidification (
bafilomycin A1), a
cathepsin inhibitor (CA074-Me) and a
short-hairpin RNA targeting
cathepsin B.
Hypoxia substantially enhanced B10-induced cell death. This effect was sensitive to
bafilomycin A1 and thus dependent on
hypoxia-induced lysosomal acidification.
Cathepsin B appeared to mediate cell death because either the inhibitor CA074-Me or
cathepsin B gene silencing rescued
glioma cells from B10 toxicity under
hypoxia. B10 is a novel
antitumor agent with substantially enhanced cytotoxicity under
hypoxia conferred by increased lysosomal cell death pathway activation. Given the importance of
hypoxia for
therapy resistance, malignant progression, and as a result of antiangiogenic
therapies, B10 might be a promising strategy for hypoxic
tumors like
malignant glioma.