Subnanomolar Cathepsin S Inhibitors with High Selectivity: Optimizing Covalent Reversible α-Fluorovinylsulfones and α-Sulfonates as Potential Immunomodulators in Cancer.

The cysteine protease cathepsin S (CatS) is overexpressed in many tumors. It is known to be involved in tumor progression as well as antigen processing in antigen-presenting cells (APC). Recent evidence suggests that silencing CatS improves the anti-tumor immune response in several cancers. Therefore, CatS is an interesting target to modulate the immune response in these diseases. Here, we present a series of covalent-reversible CatS inhibitors based on the α-fluorovinylsulfone and -sulfonate warheads. We optimized two lead structures by molecular docking approaches, resulting in 22 final compounds which were evaluated in fluorometric enzyme assays for CatS inhibition and for selectivity towards the off-targets CatB and CatL. The most potent inhibitor in the series has subnanomolar affinity (Ki =0.08 nM) and more than 100,000-fold selectivity towards cathepsins B and L. These new reversible and non-cytotoxic inhibitors could serve as interesting leads to develop new immunomodulators in cancer therapy.

Dual Stimuli-Responsive Dynamic Covalent Peptide Tags: Toward Sequence-Controlled Release in Tumor-like Microenvironments.

Dynamic covalent chemistry (DCvC) has emerged as a versatile synthetic tool for devising stable, stimuli-responsive linkers or conjugates. The interplay of binding affinity, association and dissociation constants exhibits a strong influence on the selectivity of the reaction, the conversion rate, as well as the stability in aqueous solutions. Nevertheless, dynamic covalent interactions often exhibit fast binding and fast dissociation events or vice versa, affecting their conversion rates or stabilities. To overcome the limitation in linker design, we reported herein dual responsive dynamic covalent peptide tags combining a pH responsive boronate ester with fast association and dissociation rates, and a redox-active disulfide with slow formation and dissociation rate. Precoordination by boronic acid-catechol interaction improves self-sorting and selectivity in disulfide formation into heterodimers. The resulting bis-peptide conjugate exhibited improved complex stability in aqueous solution and acidic tumor-like extracellular microenvironment. Furthermore, the conjugate responds to pH changes within the physiological range as well as to redox conditions found inside cancer cells. Such tags hold great promise, through cooperative effects, for controlling the stability of bioconjugates under dilution in aqueous media, as well as designing intelligent pharmaceutics that react to distinct biological stimuli in cells.