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-κB Mutations or Activation of the CD30, CD40, and RANK Receptors

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Abstract
Purpose: The malignant Hodgkin and Reed-Sternberg cells of Hodgkin disease (HD) are known to constitutively express high levels of activated nuclear factor κB (NF-κB), 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 NF-κB and modulating critical cellular regulatory proteins, but its activity in cells carrying IκBα 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-dimethylthiazol-2-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 IκBα 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 NF-κB 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 apoptosis-inducing 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.