A NEW STRUCTURAL CLASS OF PROTEASOME INHIBITORS THAT PREVENT NF-KAPPA-B ACTIVATION

The multicatalytic proteinase or proteasome is a highly conserved cell ular structure that is responsible for the ATP-dependent proteolysis o f many proteins involved in important regulatory cellular processes. W e have identified a novel class of inhibitors of the chymotrypsin-like proteolytic activity of the 20S proteasome that exhibit IC50 values r anging from 0.1 to 0.5 mu g/mL (0.1 to 1 mu). In cell proliferation as says, these compounds inhibit growth with an IC50 ranging from 5 to 10 mu g/mL (10-20 mu M). A representative member of this class of inhibi tors was tested in other biological assays. CVT-634 hoxy-1-indanone-3- acetyl-leu-D-leu-1-indanylamide) prevented lipopolysaccharide (LPS), t umor necrosis factor (TNF)-, and phorbol ester-induced activation of n uclear factor kappa B (NF-kappa B) in vitro by preventing signal-induc ed degradation of I kappa B-alpha. In these studies, the I kappa B-alp ha that accumulated was hyperphosphorylated, indicating that CVT-634 d id not inhibit I kappa B-alpha kinase, the enzyme responsible for sign al-induced phosphorylation of I kappa B-alpha. In vivo studies indicat ed that CVT-634 prevented LPS-induced TNF synthesis in a murine macrop hage cell line. In addition, in mice pretreated with CVT-634 at 25 and 50 mg/kg and subsequently treated with LPS, serum TNF levels were sig nificantly lower (225 +/- 59 and 83 +/- 41 pg/mL, respectively) than i n those mice that were treated only with LPS (865 +/- 282 pg/mL). Thes e studies suggest that specific inhibition of the chymotrypsin-like ac tivity of the proteasome is sufficient to prevent signal-induced NF-ka ppa B activation and that the proteasome is a novel target for the ide ntification of agents that may De useful in the treatment of diseases whose etiology is dependent upon the activation of NF-kappa B. (C) 199 8 Elsevier Science Inc.