Arsenic metabolism in multiple myeloma and astrocytoma cells

Abstract

Arsenic trioxide (As2O3, Trisenox) is used to treat patients with refractory or relapsed acute promyelocytic leukemia (APL). Its ability to induce apoptosis in various malignant cell lines has made it a potential treatment agent for other malignancies and many clinical trials are currently in progress to evaluate its clinical usefulness for multiple myeloma and glioblastoma cancer. In the present study, we investigated the metabolism of As2O3 regarding its cellular biotransformation and interaction with metallothionein (MT) as a possible protective responses of cells to arsenic-induced cytotoxicity. The study was performed on two types of cell treated with As2O3: (1) human astrocytoma (glioblastoma) cell line U87MG treated with 0.6 microM arsenic for 0, 3, 12, 24, and 48 h or 12 microM arsenic for 3, 6, 12, 24, and 48 h and (2) bone marrow cells (BM) from two patients with multiple myeloma (MM) treated with 7 microM arsenic for 0, 43, and 67 h. Cotreatment with vitamin C (1 mg/mL) was tested in longer exposure of MM BM cells. Traces of methylation products (mainly monomethylarsenic acid) were detected in cell lysates of both cell types and in pellets of U87 MG cells, although we found problems with column-sample interactions in cases where methanol pretreatment of the sample was not used. Pentavalent inorganic arsenic (AsV) was identified in both cell types, and up to 80% of total As in MM bone marrow cell lysates was present as AsV. Such an occurrence (generation) of pentavalent arsenic after As2O3 treatment demonstrates the presence of biological oxidation of trivalent arsenic, which could represent an additional protective mechanism of the cell. Vitamin C decreased As cell content and increased the percentage of pentavalent inorganic arsenic (in the growth medium and cells). The presence of metallothionein (MT) and its response to arsenic treatment was checked in all U87 MG cells, in the control, and in one exposed sample of MM BM cells. During 48 h exposure to 0.6 or 12 muM arsenic MTI/II levels increased in U87 MG cells, but with variable Zn levels, increased Cu levels, and As binding observed in traces only. Involvement of the MT-III isoform was negligible. In contrast, 43 h exposure to 7 microMarsenic did not increase MT content in multiple myeloma cells, and the levels even decreased with respect to the control. To evaluate the importance of the observed processes, MTs in U87 and AsIII-AsV conversion in MM BM cells, which could represent a resistance response of cancer cells treated by As2O3, longer-term observation with different arsenic concentrations should be performed.