Nicolas Richy

20S Proteasome Inhibition: Designing Noncovalent Linear Peptide Mimics of the Natural Product TMC-95A

The 20S proteasome maintains homeostasis and regulates important intracellular processes by subjecting most intracellular proteins to endoproteolytic cleavage. This complex hydrolysis machinery has received considerable attention for the treatment of many diseases, including cancer. We report a new set of noncovalent peptide mimics based on TMC-95A and our rational approach to inhibitor optimization using both crystallographic and kinetic studies.

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 (Ki = 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.

Noncovalent inhibition of 20S proteasome by pegylated dimerized inhibitors

We exploited the concept of polyvalent interactions to produce highly selective and efficient inhibitors of eukaryotic proteasome. This multicatalytic protease with the unique topography of its 6 active sites has emerged as a promising target to treat cancer with the use of the covalent inhibitor bortezomib. We used our reference noncovalent inhibitor, a selective TMC-95A tripeptide linear mimic, to design dimeric noncovalent proteasome inhibitors that target two active sites simultaneously. We synthesized pegylated monomer and dimers of the reference inhibitor and evaluated their capacity to inhibit a mammalian 20S proteasome. The inhibitory power of the dimers depended on the average length of their spacer. Lineweaver-Burk double-reciprocal plots indicated competitive inhibition. The best dimer inhibited CT-L activity 800-times more efficiently than the reference inhibitor.

Synthesis of lactams by isomerization of oxindoles substituted at C-3 by an ω-amino chain.

Oxindoles substituted at N-1 by electron-withdrawing groups and at C-3 by ω-amino chains of various lengths undergo mild and easy isomerization to new 5- to 12-membered lactams in good yields (30-96%). As efficient asymmetric syntheses of diversely 3,3-disubstituted oxindoles are currently developed, this isomerization provides a new and valuable access to medium-sized lactams α-substituted with a quaternary asymmetric carbon bearing a 2-aminophenyl residue.

N-silyloxaziridines: synthesis and use for electrophilic amination.

N-Silyloxaziridines were synthesized for the first time. Their tert-butyldiphenylsilyl (TBDPS) derivatives were stable reagents that were prepared on a multigram scale in three steps and in 44% overall yield from the corresponding benzylamines. They were mild electrophilic aminating reagents that reacted at room temperature with diversely substituted primary and secondary amines to produce N-monoalkyl or N,N-dialkyl benzaldehyde hydrazones in 44-87% yield.

Structure-based design of human immuno- and constitutive proteasomes inhibitors

Starting from the X-ray structure of our previous tripeptidic linear mimics of TMC-95A in complex with yeast 20S proteasome, we introduced new structural features to induce a differential inhibition between human constitutive and immunoproteasome 20S particles. Libraries of 24 tripeptidic and 6 dipeptidic derivatives were synthesized. The optimized preparation of 3-hydroxyoxindolyl alanine residues from tryptophan and their incorporation in peptides were described. Several potent inhibitors of human constitutive proteasome and immunoproteasome acting at the nanomolar level (IC50 = 7.1 nM against the chymotrypsin-like activity for the best inhibitor) were obtained. A cytotoxic effect at the submicromolar level was observed against 6 human cancer cell lines.

New Conjugated meso-Tetrafluorenylporphyrin-Cored Derivatives as Fluorescent Two-Photon Photosensitizers for Singlet Oxygen Generation

A series of three conjugated meso-porphyrin dendrimers containing conjugated dendrons featuring 2,7-fluorenyl groups, incorporating overall 8, 12, or 28 fluorenyl units have been synthesized and characterized. The photophysical properties of these new compounds were studied in the context of photodynamic therapy. The relevant linear and nonlinear optical properties were measured in organic media and useful structure-properties relationships were derived.

Diphenylamino-substituted tristyryl vs. triphenyl isocyanurates: improved conjugation has minimal impact on two-photon absorption

This contribution reports the synthesis of C87H60N6O3 (3-NPh2), the tristyryl analogue of the triphenylisocyanurate C81H54N6O3 (2-NPh2) which was previously demonstrated to be an active two-photon absorber. Contrary to expectation, planarization and extension of the central π-system does not lead to a marked improvement of the two-photon absorption cross-section.