TNF and cancer: The mechanisms of the antitumor activity of PIs are inhibition of proteasome activity, down-regulation of nuclear factor κB (NF-κB) signaling through blocking inhibitory factor κB (IκB) degradation, induction of cancer cell apoptosis through production of the pro-apoptotic factor tumor necrosis factor alpha (TNF-α), stabilization of p53, and interference with a number of different cell cycle signaling pathways, e.g. AKT, MAPK, and c-Jun [4, 5].