PURPOSE: Darinaparsin (Zio-101) is a novel organic arsenical compound with encouraging clinical activity in relapsed/refractory T-cell lymphoma (TCL) and Hodgkin lymphoma (HL); however, little is known about its mechanism of action.

EXPERIMENTAL DESIGN: TCL cell lines (Jurkat, Hut78, and HH) and HL cell lines (L428, L540, and L1236) were examined for in vitro cell death by MTT assay and Annexin V-based flow cytometry. Jurkat and L540-derived xenografts in SCID mice were examined for in vivo tumor inhibition and survival. Biologic effects of darinaparsin on the MAPK pathway were investigated using pharmacologic inhibitors, RNAi and transient transfection for overexpression for SHP1 and MEK.

RESULTS: Darinaparsin treatment resulted in time- and dose-dependent cytotoxicity and apoptosis in all TCL and HL cell lines. In addition, darinaparsin had more rapid, higher, and sustained intracellular arsenic levels compared with arsenic trioxide via mass spectrometry. In vivo experiments with Jurkat (TCL) and L540 (HL)-derived lymphoma xenografts showed significant inhibition of tumor growth and improved survival in darinaparsin-treated SCID mice. Biologically, darinaparsin caused phosphorylation of ERK (and relevant downstream substrates) primarily by decreasing the inhibitory SHP1 phosphatase and coimmunoprecipitation showed significant ERK/SHP1 interaction. Furthermore, ERK shRNA knockdown or constitutive overexpression of SHP1 resulted in increased apoptosis, whereas cotreatment with pharmacologic MEK inhibitors resulted in synergistic cell death. Conversely, SHP1 blockade (via pharmacologic inhibition or RNAi) and MEK constitutive activation decreased darinaparsin-related cell death.

CONCLUSIONS: Altogether, these data show that darinaparsin is highly active in HL and TCL and its activity is dependent primarily on MAPK mechanisms.