Activation of polyamine catabolism by N¹,N¹¹- diethylnorspermine leads to cell death in glioblastoma

Glioblastoma multiforme (GBM) is one of the most therapeutically refractory human cancers. Elevated cellular polyamine levels are a common feature of cancer cells, including GBM cells, and the polyamine pathway has been explored as a potential therapeutic target to inhibit polyamine biosynthesis or activate polyamine catabolism. In this study, we investigated the effect of N ¹,N¹¹-diethylnorspermine (DENSPM), a spermine analog that activates polyamine catabolism, in GBM cells. The in vitro cell culture experiments showed that DENSPM increased the sub-G₁ apoptotic cell population in GBM cell lines but caused minimal cytotoxicity in normal astrocytes. Prior to apoptosis induction, DENSPM caused the elevation of spermidine/spermine N¹-acetyltransferase (SSAT) expression accompanied by a decrease in polyamine levels and an increase of acetylated polyamine levels, which temporally coincided with the onset of hydrogen peroxide (H₂O₂) induction in the cells. The cytotoxic effects of DENSPM in the GBM cells could be partially attenuated by either turning down SSAT mRNA with small interference RNA or inhibiting H₂O₂ production with N¹-acetylpolymine oxidase (APAO)/spermine oxidase (SMO) inhibitor. Though mitochondrial damage was induced, neither activation of the caspase cascade nor cytochrome c redistribution between the mitochondria and cytoplasm was observed. Systemic DENSPM treatment of mice with intracerebral GBM led to longer survival. Taken together, our studies indicate that DENSPM kills GBM cells through induction of SSAT coupled with H₂O ₂ production, which is a potential target for GBM therapy.