Arsenic trioxide induces apoptosis of cutaneous T cell lymphoma cells: Evidence for a partially caspase-independent pathway and potentiation by ascorbic acid (vitamin C)

Arsenic trioxide (As2O3) displays apoptogenic properties against various types of hematopoietic malignancies. We investigated the effects of As2O3 on the viability of the cutaneous T cell lymphoma cell lines HuT-78, SeAx, and Myla, and of peripheral blood mononuclear cells from patients with Sezary syndrome, by using propidium iodide and annexin-V staining, terminal deoxyuridine triphosphate nick end labeling (TUNEL), cell cycle analysis, mitochondrial transmembrane potential (DeltaPsi(m)) alterations, cytochrome c release, and detection of processed caspase-3. We also report in vivo effects of As2O3 in two patients with cutaneous T cell lymphoma. The results show that As2O3 induces apoptosis of cutaneous T cell lymphoma lines and of Sezary cells from patients in a time- and concentration-dependent manner in vitro, as demonstrated by annexin-V staining, mitochondrial depolarization, and DNA fragmentation. Ascorbic acid 100 muM potentiated As2O3-induced Sezary cell death, whereas interferon-a had no synergistic effect. As2O3-induced Sezary cell death involves activation of caspase-3, cleavage of poly (ADP-ribose) polymerase, and cytochrome c release, but was only partially inhibited by the pan-caspase inhibitor Z-VAD.fluoromethylketone. Finally, As2O3 was administered to two patients with cutaneous T cell lymphoma, allowing us to obtain a partial response in one case, whereas stability was observed in the second patient. These results demonstrate that As2O3 synergizes with ascorbic acid to induce Sezary cell death at clinically achievable concentrations, through a caspase-partially independent pathway, and provide a rationale for further in vivo studies addressing the therapeutic efficacy of As2O3 in cutaneous T cell lymphoma patients.