The Novel Organic Arsenical, Darinaparsin (ZIO-101), Induces Apoptosis through AKT and MEK/ERK Pathways In Hodgkin Lymphoma (HL) and T-Cell Lymphoma (TCL) Cell Lines

The inorganic arsenic, arsenic trioxide (ATO), has a narrow therapeutic index, which has limited its clinical use in most malignancies. Darinaparsin (ZIO-101, S-dimethylarsino-glutathione), synthesized by conjugating dimethylarsenic to glutathione, is a novel organic arsenical that is under investigation as a novel agent for the treatment of cancer. Furthermore, early-phase clinical trials with darinaparsin have demonstrated low toxicity and encouraging clinical efficacy in relapsed/refractory hematologic malignancies.

We treated several TCL cell lines (Jurkat, C10MJ, Hut-78, and MT2) and the resistant HL cell line, L428, with increasing concentrations of darinaparsin (0.5-5μM) +/− the MEK inhibitor, U0126, or ERK siRNA (Qiagen HiPerFect transfection). Cell survival and apoptosis were measured by MTT and Annexin-V/propidium iodide staining, respectively. Further, tumor intracellular darinaparsin and ATO concentrations were assessed with mass spectrometry, while transcription pathway intermediates were analyzed by Western blotting.

Darinaparsin inhibited cell growth and induced apoptosis in all cell lines at 1–3μM. At 2μm (48 hours), darinaparsin induced approximately 80% apoptosis in each of the four TCL lines, while 3μM resulted in 65% apoptosis in L428 cells. By comparison, >10μM of ATO (48 hours) was required to induce 40% apoptosis in TCL and 25% apoptosis in L428. At 1–3μM, darinaparsin induced significant increases in caspase 3 and PARP activation in TCL, while interestingly, minimal caspase or PARP was observed in L428. Notably, in L428 cells at 1 hour, mass spectrometry showed that intracellular accumulation of darinaparsin was >10-fold higher as compared with equivalent ATO concentrations (p<0.01). We also treated L428 cells with U0126 (5μM) or ERK2 siRNA, both combined with darinaparsin. Pre-incubation with U0126 or siRNA knock down of ERK2, followed by treatment with darinaparsin, significantly enhanced darinaparsin-induced apoptosis (p<0.05). To further investigate darinaparsin-induced signaling pathways, we analyzed phospho-AKT (p-AKT), and phospho-ERK (p-ERK) in Jurkat and L428. We found down-regulation of p-AKT in Jurkat as well as L428 cells, while total AKT remained unchanged. Additionally, an increase in p-ERK was observed in L428 cells with 2–3μM darinaparsin, while p-ERK was down-regulated in Jurkat cells.

Darninaparsin induces significant cell death in HL and TCL cell lines that is mediated through AKT and MEK/ERK-based pathways. Additionally, markedly higher intracellular darinaparsin levels are achieved in lymphoma cells compared with equivalent concentrations of ATO. Continued pre-clinical and clinical trial investigation of darinaparsin in HL and TCL is warranted.

No relevant conflicts of interest to declare.