Induction of Cell Cycle Arrest and Apoptosis by the Proteasome Inhibitor PS-341 in Hodgkin Disease Cell Lines Is Independent of Inhibitor of Nuclear Factor- B Mutations or Activation of the CD30, CD40, and RANK Receptors

Purpose: The malignant Hodgkin and Reed-Sternberg cells of Hodgkin disease (HD) are known to constitutively express high levels of activated nuclear factor B (NFB), which plays an important role in their survival. The proteasome inhibitor PS-341 has been recently shown to modulate tumor cell proliferation and survival by inhibiting NFB and modulating critical cellular regulatory proteins, but its activity in cells carrying I B gene mutations has not been reported previously. Experimental Design: The activity of PS-341 in four well-characterized, HD-derived cell lines. Cell proliferation and apoptosis were determined by the 3-(4,5-dimethylthiazol2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfonyl)-2H-tetrazolium (MTS) and Annexin-V binding methods, respectively. Cell cycle analysis was determined by flow cytometry. Intracellular protein levels were determined by Western blot. Results: PS-341 demonstrated a strong antiproliferative activity, which was irrespective of the status of mutations in I B and even the presence of CD30, CD40, or RANK receptor activation. This effect was attributable to the induction of apoptosis and cell cycle arrest at the G2-M phase. PS-341 not only inhibited nuclear localization of NFB but also activated the caspase cascade, increased p21 and Bax levels, and decreased Bcl-2 levels. Furthermore, PS-341 enhanced the effect of gemcitabine chemotherapy and potentiated the effect of tumor necrosis factor-related apoptosisinducing ligand/APO2L and two agonistic antibodies to tumor necrosis factor-related apoptosis-inducing ligand death receptors R1 and R2. Conclusions: The in vitro activity of PS-341 against HD-derived cell lines suggests that PS-341 may have a therapeutic value for the treatment of HD.