Apoptosis and growth inhibition in malignant lymphocytes after treatment with arsenic trioxide at clinically achievable concentrations

Background: Arsenic trioxide (As2O3) can induce clinical remission in patie nts with acute promyelocytic leukemia via induction of differentiation and programmed cell death (apoptosis), We investigated the effects of As2O3 on a panel of malignant lymphocytes to determine whether growth-inhibitory and apoptotic effects of As2O3 can be observed in these cells at clinically ac hievable concentrations. Methods: Eight malignant lymphocytic cell lines an d primary cultures of lymphocytic leukemia and lymphoma cells were treated with As2O3, with or without dithiothreitol (DTT) or buthionine sulfoximine (BSO) (an inhibitor of glutathione synthesis). Apoptosis was assessed by ce ll morphology, flow cytometry, annexin V protein level, and terminal deoxyn ucleotidyl transferase labeling of DNA fragments. Cellular proliferation wa s determined by 5-bromo-2'-deoxyuridine incorporation into DNA and flow cyt ometry and by use of a mitotic arrest assay. Mitochondrial transmembrane po tential (Delta Psi(m)) was measured by means of rhodamine 123 staining and flow cytometry, Protein expression was assessed by western blot analysis or immunofluorescence. Results: Therapeutic concentrations of As2O3 (1-2 mu M ) had dual effects on malignant lymphocytes: 1) inhibition of growth throug h adenosine triphosphate (ATP) depletion and prolongation of cell cycle tim e and 2) induction of apoptosis, As2O3-induced apoptosis was preceded by De lta Psi(m) collapse, DTT antagonized and BSO enhanced As2O3-induced ATP dep letion, Delta Psi(m) collapse, and apoptosis, Caspase-3 activation, usually resulting from Delta Psi(m) collapse, was not always associated with As2O3 -induced apoptosis. As2O3 induced PML (promyelocytic leukemia) protein degr adation but did not modulate expression of cell cycle-related proteins, inc luding c-myc, retinoblastoma protein, cyclin-dependent kinase 4, cyclin D1, and p53, or expression of differentiation-related antigens. Conclusions: S ubstantial growth inhibition and apoptosis without evidence of differentiat ion were induced in most malignant lymphocytic cells treated with 1-2 mu M As2O3. As2O3 may prove useful in the treatment of malignant lymphoprolifera tive disorders.