New 26S Proteasome Inhibitors with High Selectivity for Chymotrypsin-Like Activity and p53-Dependent Cytotoxicity

Abstract

The 26S proteasome has emerged over the past decade as an attractive therapeutic target in the treatment of cancers. Here, we report new tripeptide aldehydes that are highly specific for the chymotrypsin-like catalytic activity of the proteasome. These new specific proteasome inhibitors demonstrated high potency and specificity for sarcoma cells, with therapeutic windows superior to those observed for benchmark proteasome inhibitors, MG132 and Bortezomib. Constraining the peptide backbone into the β-strand geometry, known to favor binding to a protease, resulted in decreased activity in vitro and reduced anticancer activity. Using these new proteasome inhibitors, we show that the presence of an intact p53 pathway significantly enhances cytotoxic activity, thus suggesting that this tumor suppressor is a critical downstream mediator of cell death following proteasomal inhibition.

Selective depletion of tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin by environmental and endogenous serine proteases: linking diet and cancer

“…7f ). Selective inhibitors of proteasomal chymotryptic activity – carfilzomib [ 86 – 88 ], epoxomicin (epox, 1 μM) [ 89 , 90 ] and carbobenzoxy-Leu-Leu-leucinal (MG132, 10 μM) [ 91 ] - did not affect DCC or neogenin expression (Fig. 7g-j ) although carfilzomib did reduce significantly the effect of chymotrypsin.…”

Apigenin manipulates the ubiquitin–proteasome system to rescue estrogen receptor-β from degradation and induce apoptosis in prostate cancer cells

“…Ac-Ala-Pro-Nle-Asp-CHO, inhibitor of caspase-like activity [20]; Ada-(Ahx)3-(Leu)3-vinyl sulfone, inhibitor of all the three activities; Clasto-Lactacystin β-lactone, inhibitor of chymotrypsin and trypsin-like activities; and MG-132 inhibitor of all the three activities [10] did not significantly accumulate ubiquitinated ER-β as compared to epoxomicin. This clearly suggests that specific inhibition of chymotrypsin-like activity is needed for the accumulation of ubiquitinated ER-β.…”

“…7b). Ac-Ala-Pro-Nle-Asp-CHO (a specific inhibitor of caspaselike activity) [20], Clasto-Lactacystin β-lactone-(inhibitor of chymotrypsin and trypsin-like activities), Ada-(Ahx)3-(Leu)3-vinyl sulfone (inhibitor of all the three enzyme activities) and MG132 (inhibitor of all the three activities) [10] failed to accumulate significant amount of ubiquitinated ER-β. However, Epoxomicin (a potent inhibitor of chymotrypsin-like activity) [21] accumulated ubiquitinated ER-β significantly like apigenin (Fig.…”

“…Bortezomib has been approved by the FDA as a frontline treatment for multiple myeloma, providing the proof that targeting the ubiquitin-proteasome pathway is a viable route for the treatment of human cancers [7,8]. However, potent inhibition of all three catalytic subunits of the proteasome results in profound non-specific cytotoxicity to non-transformed cells [9] as seen in case of synthetic proteasome inhibitors like bortezomib and MG132 [10]. Moreover, their lower efficacy as stand-alone drugs and resistance in solid tumors are added drawbacks.…”

Cyclisation To Form Small, Medium and Large Rings by Use of Catalysed and Uncatalysed Azide–Alkyne Cycloadditions (AACs)

“…After synthesis of their precursor tripeptides 84 – 86 (Scheme ), copper(I) bromide and DBU were applied in dichloromethane to achieve cyclisation. These conditions were shown to be high‐yielding, mild and devoid of competing dimerisation, thus avoiding the problems associated with the use of copper(I) iodide or Cu(MeCN) 4 PF 6 , which had previously been reported to give competing dimer and trimer formation, necessitating purification by HPLC. The authors were able to purify their macrocycles 87 – 89 by simple flash chromatography.…”