darinaparsin and Multiple-Myeloma

Here, we report the identification of dimethylarsinothioyl glutathione (DMMTA(V)(GS)) as a metabolite in cellular extracts of dimethyarsinous glutathione (Darinaparsin, DMA(III)(GS)) treated human multiple myeloma (MM) cell lines. Co-elution of sulfur and arsenic on the inductively coupled plasma mass spectrometer (ICP-MS) indicated the presence of sulfur along with arsenic in the newly observed unidentified molecule on the speciation chromatograms of cell lines treated with DMA(III)(GS). Liquid chromatography-electrospray ionization-mass spectrometry of the unknown peak in the MS and tandem MS modes revealed molecular ion peaks at m/z = 443.9 and 466.0, corresponding to [DMMTA(V)(GS) + H](+) and [DMMTA(V)(GS) + Na](+), as well as peaks at 314.8 for the loss of glutamic acid and 231.1 for the loss of glycine. In addition, peaks were observed at 176.9 corresponding to cysteine and glycine adducts and at 137.1 for the [C2H6AsS](+) ion. An increase in the peak area of the unidentified peak was observed upon spiking the cell extracts with a standard of DMMTA(V)(GS). Heat deactivation of MM cells prevented the formation of DMMTA(V)(GS) raising the possibility of its formation via an enzymatic reaction. Formation studies in DMA(III)(GS) treated MM cells revealed the dependence of DMMTA(V)(GS) formation on the depletion of DMA(III)(GS). The presence of 5 mM glutathione prevented its formation, indicating that DMA(III), a dissociation product of DMA(III)(GS), is likely a precursor for the formation of DMMTA(V)(GS). DMMTA(V)(GS) was observed to form under acidic and neutral pH conditions (pH 3.0-7.4). In addition, DMMTA(V)(GS) was found to be stable in cell extracts at both acidic and neutral pH conditions. When assessing the toxicity by exposing multiple myeloma cells to arsenicals externally, DMMTA(V)(GS) was found to be much less toxic than DMA(III)(GS) and DMMTA(V), potentially due to its limited uptake in the cells (10 and 16% of the uptakes of DMA(III)(GS) and DMMTA(V), respectively).

Topics: Antineoplastic Agents; Apoptosis; Arsenicals; Cell Line, Tumor; Glutathione; Humans; Multiple Myeloma

Here, we report on the organic arsenical darinaparsin (ZIO-101, S-dimethylarsino-glutathione) and its anti-myeloma activity compared with inorganic arsenic trioxide. Darinaparsin induced apoptosis in multiple myeloma cell lines in a dose-dependent manner, and the addition of N-acetylcysteine, which increases intracellular glutathione (GSH), blocked cytotoxicity of both darinaparsin and arsenic trioxide. In contrast to arsenic trioxide, intracellular GSH does not appear to be important for darinaparsin metabolism, as an inhibitor of GSH synthesis, buthionine sulfoximine, had little effect on drug activity. This discrepancy was resolved when we determined the effects of thiols on drug uptake. The addition of exogenous GSH, L-cysteine, or D-cysteine prevented darinaparsin cellular uptake and cell death but had no effect on the uptake or activity of arsenic trioxide, suggesting a difference in the transport mechanism of these two drugs. In addition, gene expression profiling revealed differences in the signaling of protective responses between darinaparsin and arsenic trioxide. Although both arsenicals induced a transient heat shock response, only arsenic trioxide treatment induced transcription of metal response genes and anti-oxidant genes related to the Nrf2-Keap1 pathway. In contrast to the protective responses, both arsenicals induced up-regulation of BH3-only proteins. Moreover, silencing of BH3-only proteins Noxa, Bim, and Bmf protected myeloma cells from darinaparsin-induced cell death. Finally, treatment of an arsenic trioxide-resistant myeloma cell line with darinaparsin resulted in dose-dependent apoptosis, indicating that cross-resistance does not necessarily develop between these two forms of arsenic in multiple myeloma cell lines. These results suggest darinaparsin may be useful as an alternative treatment in arsenic trioxide-resistant hematologic cancers.

Topics: Antineoplastic Agents; Apoptosis; Arsenic Trioxide; Arsenicals; Buthionine Sulfoximine; Cell Line, Tumor; Cell Survival; Cysteine; Drug Resistance, Neoplasm; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Glutathione; Humans; Multiple Myeloma; Oxides