Proteasome activities, inhibition

In the NF-kB pathway with celastrol 76, the inhibition of the iKBa degradation is due to the upstream blockage of the kinase activity and not by the direct inhibition of proteasome activity. On the contrary, direct inhibition of proteasome activity was observed with celastrol 76 and pristimerin 2 in prostate cancer cells.90-92 Both triterpene QMs directly inhibited the activity of the 20S subunits of proteasome at 2.5 iM and induced the accumulation of ubiquitinated proteins over time in cells,... 

Fenteany, G. et al. Inhibition of proteasome activities and subunit-specific amino-terminal threonine modification by lactacystin. Science 1995, 268, 726-731. 

Meinees, S. et al. Inhibition of proteasome activity induces concerted expression of proteasome genes and de novo formation of Mammalian proteasomes. J Biol Chem 2003, 278, 21517-25. 

Fenteany, G., Standaert, R. F., Lane, W. S., Choi, S., Corey, E. J., and Schreiber, S. L. Inhibition of proteasome activities and subunit-spedfic amino-terminal threonine modification by lactacystin. Science 1995, 268, 726-731. 

In conjunction with studies performed by van Leeuwen et al. (135-138), Layfield et al. (263) proposed a novel mechanism that could account for an inhibition of 26S proteasome activity in cases of nonfamilial AD. Mutant forms of ubiquitin may inhibit proteolysis within neurons, predisposing these cells to inclusion formation. Molecular misreading of the UBB gene results in a dinucleotide deletion in UBB mRNA (135-138,264). In AD, an age-related posttranscriptional defect in primary transcript RNA processing may occur, leading to dinucleotide deletions within open reading frames that result in frameshifts and produce abnormal extension proteins, as demonstrated by van Leeuwen and coworkers (138). 

Therefore, in addition to decreasing the formation of glycated and cross-linked protein which can inhibit proteasomal activity, carnosine may actually stimulate proteasomal function to improve the elimination altered protein forms. This proposal should be easy to test using cell culture and in tissues of aging animals fed a camosine-enriched diet. 

The structurally-related 7-lactams salinosporamide A 1, omuralide 2 and lactacystin 3, of bacterial origin, inhibit proteasome activity, and so are of interest as lead compounds for the development of anticancer agents. Barbara . M. Potts of Nereus Pharmaceuticals in San Diego has reported (J. Med. Chem. 2005,48,3684) a detailed structure-activity studies in this series, and E.J. Corey of Harvard University has prepared (J. Am. Chem. Soc. 2005,127, 8974, 15386) several interesting structural analogues. Susumi Hatakeyama of Nagasaki University, building on previous work in this area, has reported (J. Org. Chem. 2004, 69,7765) a synthesis of 2 and 3 from Tris. 

As mentioned on p. 1854, an important function of proteasomes is formation of short antigenic peptides for use by the immune system.664 Inhibition of proteasome activity reduces or prevents antigen presentation (Chapter 31).665 666 In this immune surveillance system mature proteins of host cells are cut up and checked for self-identity. The checking also includes the rapidly degraded imperfect proteins and foreign proteins from invading organisms or viruses.667 6673... 

Nam S, Smith DM, Dou QP. 2001. Ester bond-containing tea polyphenols potently inhibit proteasome activity in vitro and in vivo. J Biol Chem 276 13322-13330. 

Figure 12.2 Pharmacodynamic profiles of NPI-0052 and bortezomib after a single IV administration in mice or rats. (A) Inhibition of CT-L, T-L and C-L 205 proteasome activities in packed whole blood (PWB) lysates after a single IV administration of NPI-0052 (0.15 mg/kg) or bortezomib (1 mg/kg) in mice. NPI-0052 exhibits a broader and longer 20>S proteasome inhibition profile than bortezomib.14 (B) CT-L 205 proteasome activity recovers more quickly in peripheral blood mononuclear cell (PBMQ lysates compared with PWB lysates after NPI-0052 administration to rats at 0.05 mg/kg or 0.1 mg/kg.

The pharmacodynamic profile of NPI-0052 is different from other proteasome inhibitors (bortezomib and carfilzomib) in that upon a single IV administration to mice, a sustained inhibition ( > 72 hours) of the main three 20.S proteolytic activities is observed in packed whole blood lysates (Figure 12.2A). Bortezomib has been reported to either have no effect on or to enhance the T-L activity, while carfilzomib specifically inhibits the CT-L 20V proteasome activity.14,31 Repeated NPI-0052 administration to rodents and monkeys leads to sustained dose-dependent inhibition of whole blood 20V proteasome activity, with higher inhibition observed after subsequent administrations and with partial recovery between consecutive NPI-0052 treatments. 

In the ongoing Phase I clinical trials, the effects of NPI-0052 on proteasome activities in both packed whole blood and peripheral blood mononuclear cells are being monitored. In approximately 80 patients treated to date with NPI-0052, a dose-dependent inhibition of the whole blood 20V proteasome activity is observed, with increasing inhibition upon multiple administrations and partial recovery between consecutive doses (Figure 12.4). Nicely paralleling the pre-clinical studies, a more pronounced recovery of 20V proteasome CT-L activity is observed between consecutive NPI-0052 administrations in the peripheral mononuclear cell population of patients compared to packed whole blood. 

Figure 12.4 Inhibition of the packed whole blood (PWB) CT-L 20.S proteasome activity in patient samples increases with dose and is more pronounced after the third NPI-0052 administration. NPI-0052 is administered IV on Days 1, 8 and 15 at the doses indicated. Proteasome activity does not restore to baseline levels as indicated by the inhibition observed on Day 15 before the third NPI-0052 administration. Results are the average of three or more patients per cohort, except where indicated ( ), the average results of two patients is shown.

Stehlik C, de Martin R, Kumabashiri I, Schmid JA, Binder BR, Lipp J (1998) Nuclear factor (NF)-kappaB-regulated X-chromosome-linked iap gene expression protects endothelial cells from tumor necrosis factor alpha-induced apoptosis. J Exp Med 188 211-216 Stennicke HR, Deveraux QL, Humke EW, Reed JC, Dixit VM, Salvesen GS (1999) Caspase-9 ctin be activated without proteolytic processing. J Biol Chem 274 8359-8362 Sun XM, Butterworth M, MacFarlane M, Dubiel W, Ciechanover A, Cohen GM (2004) Caspase activation inhibits proteasome function during apoptosis. Mol Cell 14 81-93 Suzuki Y, Imai Y, Nakayama H, Takahashi K, Takio K, Takahashi R (2001) A serine protease, HtrA2, is released from the mitochondria and interacts with XIAP, inducing cell death. Mol Cell 8 613-621... 

Kumar, B., Andreatta, C., Koustas, W.T., Cole, W.C., Edwards-Prasad, J., and Prasad, K.N. (2002). Mevastatin induces degeneration and decreases viability of cAMP-induced differentiated neuroblastoma cells in culture by inhibiting proteasome activity, and mevalonic acid lactone prevents these effects. JNeurosci Res 68 627-635. 

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