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The conversion of primary structures of novel, highly selective and sensitive, internally quenched peptide substrates of the human 20S proteasome into peptide aldehydes is presented. Such covalent and reversible inhibitors differ in their primary structures and chemical moieties attached to their N‐terminal amino group. Inhibitory potency is primarily tested against proteolytic subunits of human constitutive 20S proteasome (β1c, β2c, and β5c subunits), but in some cases, also against 20S immunoproteasome β5i. Most of the peptide aldehydes act nonspecifically and bind equipotently to the corresponding proteolytic subunits of both forms of proteasome (β5c and β5i). Two inhibitors are 2.7‐times more specific for immunoproteasome over its constitutive counterpart. The antitumor activity of the selected inhibitors and MG132 (used here as the reference) is analyzed using MTT assay against nonmalignant human fetal osteoblastic hFOB 1.19, malignant human osteosarcoma MG‐63, human pancreatic cancer MiaPaCa‐2, and human acute leukemia Jurkat T cell lines. All inhibitors tested are able to decrease cell viability in a concentration‐dependent manner. One of the peptide aldehydes exerted stronger, as compared to the MG132, activity against human glioblastoma cell line U87‐MG. Moreover, its combination with dinaciclib, which is a novel, potent inhibitor of cyclin‐dependent kinases, reduces cellular metabolic activity more potently as compared to either proteasome inhibitor or dinaciclib alone. [ABSTRACT FROM AUTHOR]

Isothermal titration calorimetry (ITC) technique was used to study the interactions of trypsin with bicyclic sunflower-derived trypsin inhibitor (SFTI-1) as well as with its new monocyclic (with disulphide bridge only) analogues (CHO)-SFTI-1 and (CHO)-SFTI-1. ITC measurements were run in 50 mM buffer solution of HEPES or Tricine of pH 8, containing 20 mM CaCl at 298.15 K. Based on calorimetric data, the equilibrium constants for the inhibitor-enzyme-binding processes, K, the binding stoichiometry, N (inhibitor-to-enzyme molar ratio), as well as thermodynamic parameters (Δ G, Δ H, Δ S) for the reactions were determined. The study revealed that the stoichiometry of the resulting complexes equals 1:1. The negative binding enthalpy (Δ H) and favourable entropy factor ( TΔ S) suggest an important contribution of hydrogen bonding as well as hydrophobic interactions to the inhibitor-enzyme affinity. Furthermore, the relationship between the modification of the peptide structure, the experimental conditions and the thermodynamic parameters has been discussed. [ABSTRACT FROM AUTHOR]

Starting from the primary structure of sunflower trypsin inhibitor SFTI-1, we designed novel non-covalent inhibitors of human and yeast 20S proteasomes. Peptides with Arg residue in P1 position and two basic amino acid residues (Lys or/and Arg) in P2′ and P3′ positions strongly inhibited chymotrypsin-like and caspase-like activities, while trypsin-like activity was poorly modified. We found that some SFTI-1 analogues up-regulated exclusively the chymotrypsin-like activity of latent yeast 20S proteasome. [ABSTRACT FROM AUTHOR]

• Insulin mimetics could represent an alternative strategy for treatment of diabetes. • Multipodal compounds based on adamantane or proline scaffolds were synthesized. • Adamantane-based compound displaced insulin from insulin receptor with K d of 500 nM. • Molecular modeling showed possible binding modes of mimetics to the insulin receptor. Multi-orthogonal molecular scaffolds can be applied as core structures of bioactive compounds. Here, we prepared four tri-orthogonal scaffolds based on adamantane or proline skeletons. The scaffolds were used for the solid-phase synthesis of model insulin mimetics bearing two different peptides on the scaffolds. We found that adamantane-derived compounds bind to the insulin receptor more effectively (K d value of 0.5 μM) than proline-derived compounds (K d values of 15–38 μM) bearing the same peptides. Molecular dynamics simulations suggest that spacers between peptides and central scaffolds can provide greater flexibility that can contribute to increased binding affinity. Molecular modeling showed possible binding modes of mimetics to the insulin receptor. Our data show that the structure of the central scaffold and flexibility of attached peptides in this type of compound are important and that different scaffolds should be considered when designing peptide hormone mimetics. [ABSTRACT FROM AUTHOR]