Synthesis, Racemic X-ray Crystallographic, and Permeability Studies of Bioactive Orbitides from Jatropha Species.

Orbitides are small cyclic peptides with a diverse range of therapeutic bioactivities. They are produced by many plant species, including those of the Jatropha genus. Here, the objective was to provide new structural information on orbitides to complement the growing knowledge base on orbitide sequences and activities by focusing on three Jatropha orbitides: ribifolin (1), pohlianin C (7), and jatrophidin (12). To determine three-dimensional structures, racemic crystallography, an emerging structural technique that enables rapid crystallization of biomolecules by combining equal amounts of the two enantiomers, was used. The high-resolution structure of ribifolin (0.99 Å) was elucidated from its racemate and showed it was identical to the structure crystallized from its l-enantiomer only (1.35 Å). Racemic crystallography was also used to elucidate high-resolution structures of pohlianin C (1.20 Å) and jatrophidin (1.03 Å), for which there was difficulty forming crystals without using racemic mixtures. The structures were used to interpret membrane permeability data in PAMPA and a Caco-2 cell assay, showing they had poor permeability. Overall, the results show racemic crystallography can be used to obtain high-resolution structures of orbitides and is useful when enantiopure samples are difficult to crystallize or solution structures from NMR are of low resolution.

Biologically Active Orbitides from the Euphorbiaceae Family.

A comprehensive overview of natural orbitides isolated from Euphorbiaceae species and their most relevant biological activities are presented. Euphorbiaceae is a large and diverse family, which comprises about 300 genera, and is known as an important source of medicines and toxins. Several classes of secondary metabolites have been described for this taxon, however, orbitides have been broadly reported in Jatropha and Croton genera. Additionally, the latex is documented as the main source of orbitides in this family. Based on their structural and functional diversity, orbitides present a large variety of biological activities described as cytotoxicity, antimalarial, antibacterial, antifungal, enzymatic inhibition, and immunosuppressive, although the mechanism of action still needs to be further investigated. In recent years, the discovery of bioactive cyclic peptides from different sources has grown exponentially, making them promising molecules in the search for new drug leads. This review also highlights the attempts made by many researchers to organize the orbitides nomenclature and amino acid numbering, as well the important progress recently achieved in the biosynthetic study area.

Triterpenoids as novel natural inhibitors of human cathepsin L.

Cathepsins L (catL) and B play an important role in tumor progression and have been considered promising therapeutic targets in the development of novel anticancer agents. Using a bioactivity-guided fractionation, a series of triterpenoids was identified as a new class of competitive inhibitors towards cathepsin L with affinity values in micromolar range. Among the 14 compounds evaluated, the most promising were 3-epiursolic acid (3), 3-(hydroxyimino)oleanolic acid (9), and 3-(hydroxyimino)masticadienoic acid (13) with IC50 values of 6.5, 2.4, and 2.6 µM on catL, respectively. Most of the evaluated triterpenoids do not inhibit cathepsin B. Thus, the evaluated compounds exhibit a great potential to help in the design of new inhibitors with enhanced potency and affinity towards catL. Docking studies were performed in order to gain insight on the binding mode and SAR of these compounds.

Imaging Sites of Inhibition of Proteolysis in Pathomimetic Human Breast Cancer Cultures by Light-Activated Ruthenium Compound.

The cysteine protease cathepsin B has been causally linked to progression and metastasis of breast cancers. We demonstrate inhibition by a dipeptidyl nitrile inhibitor (compound 1) of cathepsin B activity and also of pericellular degradation of dye-quenched collagen IV by living breast cancer cells. To image, localize and quantify collagen IV degradation in real-time we used 3D pathomimetic breast cancer models designed to mimic the in vivo microenvironment of breast cancers. We further report the synthesis and characterization of a caged version of compound 1, [Ru(bpy)2(1)2](BF4)2 (compound 2), which can be photoactivated with visible light. Upon light activation, compound 2, like compound 1, inhibited cathepsin B activity and pericellular collagen IV degradation by the 3D pathomimetic models of living breast cancer cells, without causing toxicity. We suggest that caged inhibitor 2 is a prototype for cathepsin B inhibitors that can control both the site and timing of inhibition in cancer.

Evaluation of flavonols and derivatives as human cathepsin B inhibitor.

Cathepsin B (catB) is a cysteine protease involved in tumour progression and represents a potential therapeutic target in cancer. Among the 15 evaluated extracts from cerrado biome, Myrcia lingua Berg. (Myrtaceae) extract demonstrated to be a source of compounds with potential to inhibit catB. Using bioactivity-guided fractionation, we have found flavonols as inhibitors and also some other derivatives were obtained. From the evaluated compounds, myricetin (5) and quercetin (6) showed the most promising results with IC50 of 4.9 and 8.2 µM, respectively, and mode of inhibition as uncompetitive on catB. The results demonstrated polyhydroxylated flavonols as promising inhibitors of catB.