Noncovalent Fluorescent Probes of Human Immuno- and Constitutive Proteasomes

We report here the synthesis and biological evaluation of fluorescent probes functioning as inhibitors that noncovalently block human immuno- and constitutive proteasomes. These cell-penetrating linear analogues of the natural cyclopeptide TMC-95A were efficient on cells at the nanomolar level and assessed by confocal microscopy and flow cytometry. They may constitute an alternative to previously reported fluorescent probes that all bind covalently to proteasomes

Dimerized Linear Mimics of a Natural Cyclopeptide (TMC-95A) Are Potent Noncovalent Inhibitors of the Eukaryotic 20S Proteasome

Noncovalent proteasome inhibitors introduce an alternative mechanism of inhibition to that of covalent inhibitors used in cancer therapy. Starting from a noncovalent linear mimic of TMC-95A, a series of dimerized inhibitors using polyaminohexanoic acid spacers has been designed and optimized to target simultaneously two of the six active sites of the eukaryotic 20S proteasome. The homodimerized compounds actively inhibited chymotrypsin-like (<i>K</i>_i = 6–11 nM) and trypsin-like activities, whereas postacid activity was poorly modified. The noncovalent binding mode was ascertained by X-ray crystallography of the inhibitors complexed with the yeast 20S proteasome. The inhibition of proteasomal activities in human cells was evaluated. The use of the multivalency inhibitor concept has produced highly efficient and selective noncovalent compounds (no inhibition of calpain and cathepsin) that have potential therapeutic advantages compared to covalent binders such as bortezomib and carfilzomib