Rapid caspase‐dependent cell death in cultured human breast cancer cells induced by the polyamine analogue N1,N11‐diethylnorspermine

Abstract

The spermine analogue N¹,N¹¹‐diethylnorspermine (DENSPM) efficiently depletes the cellular pools of putrescine, spermidine and spermine by down‐regulating the activity of the polyamine biosynthetic enzymes and␣up‐regulating the activity of the catabolic enzyme spermidine/ spermine N¹‐acetyltransferase (SSAT). In the breast cancer cell line L56Br‐C1, treatment with 10 µm DENSPM induced SSAT activity 60 and 240‐fold at 24 and 48 h after seeding, respectively, which resulted in polyamine depletion. Cell proliferation appeared to be totally inhibited and within 48 h of treatment, there was an extensive apoptotic response. Fifty percent of the cells were found in the sub‐G₁ region, as determined by flow cytometry, and the presence of apoptotic nuclei was morphologically assessed by fluorescence microscopy. Caspase‐3 and caspase‐9 activities were significantly elevated 24 h after seeding. At 48 h after seeding, caspase‐3 and caspase‐9 activities were further elevated and at this time point a significant activation of caspase‐8 was also found. The DENSPM‐induced cell death was dependent on the activation of the caspases as it was inhibited by the general caspase inhibitor Z‐Val‐Ala‐Asp fluoromethyl ketone. The results are discussed in the light of the L56Br‐C1 cells containing mutated BRCA1 and p53, two genes involved in DNA repair.