Arsenic-induced apoptosis in malignant cells in vitro

Arsenic trioxide-induced apoptosis was identified by morphological change a nd nucleosomal DNA fragmentation in hematopoietic malignant cells and neuro blastoma cells. Arsenic trioxide directly induced apoptosis in the acute pr omyelocytic cell line NB4 cells at a low dose of 1 mu M, whereas all-trans- retinoic acid caused the cells to differentiate and finally induced apoptos is, In addition to the involvement of caspase 3 in arsenic trioxide-induced apoptosis of NB4 cells, the activation of caspase 8 was also shown to be i nvolved by Western blot analysis or by apoptosis inhibition assay using cas pase 8 inhibitor Ac-IETD-CHO, The down-regulation of Bcl-2 protein was show n in arsenic trioxide-treated pre-apoptotic and early apoptotic mouse B-cel l line LyH7 cells, which overexpress Bcl-2 protein, by the studies of Weste rn blot and immunoelectron microscopy, Arsenic trioxide also induced apopto sis in the majority of neuroblastomas cell lines, The arsenic-induced apopt osis in neuroblastoma cell lines was mediated by the activation of caspase 3 in all cases tested. In regard to the intracellular content of reduced gl utathione in various neuroblastoma cell Lines, the level in the cells sensi tive to arsenic trioxide was under 40 nmol/mg protein, but the cells having more than 40 nmol/mg protein did not undergo apoptosis. N-acetylcysteine p rotected neuroblastoma cells from arsenic-induced apoptosis. Therefore, the intracellular glulathione content may be a good indicator of application o f arsenic trioxide for various kinds of cancer cells. Our results raise the possibility that arsenic trioxide will be effective even against a solid t umor such as neuroblastoma and warrants clinical trials for patients with o ther kinds of tumors not only by systemic therapy but also using local ther apy.