Induction of apoptosis and growth inhibition in myeloid malignancies by arsenic trioxide (As203)

Abstract

Clinical efficacy of As203 has been shown in patients with relapsed acute promyelocytic leukemia (APL). There is evidence As203 effects not only events specific for APL but also may target mechanism involved in the pathogenesis of other myeloid malignancies. We assessed susceptibility of induction of apoptosis by As203 (0,01-10 μM) and other agents (e.g. etoposide) in various myeloid and non-myeloid malignant cell lines. Apoptotic cells are measured by staining with annexin-V and 7-amino-actinomycin-D (7-AAD). The cell lines displayed different kinetics of response and different sensitivities of As203. Minimum concentration of As203 for induction of apoptosis after appropriate incubation was 1 μM. High concentrations of As203 (5 μM) induced apoptosis after 72 hours. With 5 μM As203: > 75% for NB-4, CEM and MV-4-11, 50–75% for PBL-985, ML-2, MV-11, 20–50% for HL-60, HEL, Jurkat, K-562, PBL-985, U-937, KG-1, KG-1a. 1 μM As203 induced apoptosis in NB-4, HL-60, U-937, CEM, HL-60, KG-1a, PBL-985, ML-2, and MV-4-11 but not in HEL, K-562, KG-1, and Jurkat after up to 35 days of incubation. However, proliferation of HEL, K-562, and Jurkat non-apoptotic subpopulations was reduced when treated with 1 μM As203. This anti-proliferative effect seems to be independent of apoptosis induction. MDR cell lines CEM-C1 and CEM-C2 were sensitive to 1 μM As203. 50% of cells were annexin-V positive after 3 day for CEM, 6 days for CEM-C1 and 16 days for CEM-C2. MDR-cell lines HL-60-MX-1 and HL-60-MX-2 were resistant to 1 μM As203. These data reveal that As203 induced apoptosis is not restricted to cell lines with the translocation t(15;17). The molecular mechanisms involved in apoptosis induction by As203 are under investigation. Preliminary results indicate an upregulation of p53, Caspase 3 and an alteration of the Bcl-x expression in CEM after 4-6 hours of incubation with 10 μM As203. In non-APL cell lines, apoptosis was induced in vitro by concentrations of As203 that are achievable also in vivo after i.v. infusion of well-tolerated As203 doses. Thus, As203 might be a suitable therapeutic agent for myeloid malignancies other than APL and non-myeloid malignancies.