Teleocidin A2 inhibits human proteinase-activated receptor 2 signaling in tumor cells

N-Heterocyclic Carbene-Catalyzed Regio- and Enantioselective C7-Alkylation of 4-Aminoindoles with α-Bromoenals

The first carbene-catalyzed regio- and enantioselective indole C7-alkylation reaction between 4-aminoindoles and α-bromoenals is disclosed. The corresponding indole products could be obtained in moderate to good yields with good to excellent enantioselectivities. The evaluation of antibacterial activity against Psa revealed that nine of the C7-functionalized indoles exhibited superior inhibitory activities compared to the positive controls TC and BT. Our approach provides an efficient strategy to introduce a chiral chain into the C7 position of indole compounds, with potential applications evaluated in pesticide development.

Bacterial terpenome

Covering: up to mid-2020 Terpenoids, also called isoprenoids, are the largest and most structurally diverse family of natural products. Found in all domains of life, there are over 80 000 known compounds. The majority of characterized terpenoids, which include some of the most well known, pharmaceutically relevant, and commercially valuable natural products, are produced by plants and fungi. Comparatively, terpenoids of bacterial origin are rare. This is counter-intuitive to the fact that recent microbial genomics revealed that almost all bacteria have the biosynthetic potential to create the C5 building blocks necessary for terpenoid biosynthesis. In this review, we catalogue terpenoids produced by bacteria. We collected 1062 natural products, consisting of both primary and secondary metabolites, and classified them into two major families and 55 distinct subfamilies. To highlight the structural and chemical space of bacterial terpenoids, we discuss their structures, biosynthesis, and biological activities. Although the bacterial terpenome is relatively small, it presents a fascinating dichotomy for future research. Similarities between bacterial and non-bacterial terpenoids and their biosynthetic pathways provides alternative model systems for detailed characterization while the abundance of novel skeletons, biosynthetic pathways, and bioactivies presents new opportunities for drug discovery, genome mining, and enzymology.

Melanin processing by keratinocytes: A non-microbial type of host-pathogen interaction?

The mechanisms that regulate skin pigmentation have been the subject of intense research in recent decades. In contrast with melanin biogenesis and transport within melanocytes, little is known about how melanin is transferred and processed within keratinocytes. Several models have been proposed for how melanin is transferred, with strong evidence supporting coupled exo/endocytosis. Recently, two reports suggest that upon internalization, melanin is stored within keratinocytes in an arrested compartment, allowing the pigment to persist for long periods. In this commentary, we identify a striking parallelism between melanin processing within keratinocytes and the host-pathogen interaction with Plasmodium, opening new avenues to understand the complex molecular mechanisms that ensure skin pigmentation and photoprotection.

Synthetic Indolactam V Analogues as Inhibitors of PAR2-Induced Calcium Mobilization in Triple-Negative Breast Cancer Cells

Human proteinase-activated receptor 2 (PAR2), a transmembrane G-protein-coupled receptor (GPCR), is an attractive target for a novel anticancer therapy, as it plays a critical role in cell migration and invasion. Selective PAR2 inhibitors therefore have potential as anti-metastatic drugs. Knowing that the natural product teleocidin A2 is able to inhibit PAR2 in tumor cells, the goal of the present study was to elaborate structure-activity relationships and to identify potent PAR2 inhibitors with lower activity against the adverse target, protein kinase C (PKC). For this purpose, an efficient gram-scale total synthesis of indolactam V (i.e., the parent structure of all teleocidins) was developed, and a library of derivatives was prepared. Some compounds were indeed found to exhibit high potency as PAR2 inhibitors at low nanomolar concentrations with improved selectivity (relative to teleocidin A2). The pseudopeptidic fragment bridging the C3 and C4 positions of the indole core proved to be essential for target binding, whereas activity and target selectivity depends on the substituents at N1 or C7. This study revealed novel derivatives that show high efficacy in PAR2 antagonism combined with increased selectivity.

Teleocidin A2 inhibits human proteinase-activated receptor 2 signaling in tumor cells

Enhanced expression of the proteinase‐activated receptor 2 (PAR2) is linked to cell proliferation and migration in many cancer cell types. The role of PAR2 in cancer progression strongly illustrates the need for PAR2‐inhibiting compounds. However, to date, potent and selective PAR2 antagonists have not been reported. The natural product teleocidin A2 was characterized against PAR2‐activating peptide SLIGKV‐NH₂, and trypsin‐induced PAR2‐dependent intracellular Ca²⁺ mobilization in tumor and in primary endothelial or epithelial cells. Further biochemical and cell‐based studies were conducted to evaluate teleocidin specificity. The antagonizing effect of teleocidin A2 was confirmed in PAR2‐dependent cell migration and rearrangement of actin cytoskeleton of human breast adenocarcinoma cell line (MDA‐MB 231) breast cancer cells. Teleocidin A2 antagonizes PAR2‐dependent intracellular Ca²⁺ mobilization induced by either SLIGKV‐NH₂ or trypsin with IC₅₀ values from 15 to 25 nmol/L in MDA‐MB 231, lung carcinoma cell line, and human umbilical vein endothelial cell. Half maximal inhibition of either PAR1 or P2Y receptor‐dependent Ca²⁺ release is only achieved with 10‐ to 20‐fold higher concentrations of teleocidin A2. In low nanomolar concentrations, teleocidin A2 reverses both SLIGKV‐NH₂ and trypsin‐mediated PAR2‐dependent migration of MDA‐MB 231 cells, and has no effect itself on cell migration and no effect on cell viability. Teleocidin A2 further controls PAR2‐induced actin cytoskeleton rearrangement of MDA‐MB 231 cells. Thus, for the first time, the small molecule natural product teleocidin A2 exhibiting PAR2 antagonism in the low nanomolar range with potent antimigratory activity is described.