High-Throughput Screening Reveals New Glutaminase Inhibitor Molecules.

The glutaminase (GLS) enzyme hydrolyzes glutamine into glutamate, an important anaplerotic source for the tricarboxylic acid cycle in rapidly growing cancer cells under the Warburg effect. Glutamine-derived α-ketoglutarate is also an important cofactor of chromatin-modifying enzymes, and through epigenetic changes, it keeps cancer cells in an undifferentiated state. Moreover, glutamate is an important neurotransmitter, and deregulated glutaminase activity in the nervous system underlies several neurological disorders. Given the proven importance of glutaminase for critical diseases, we describe the development of a new coupled enzyme-based fluorescent glutaminase activity assay formatted for 384-well plates for high-throughput screening (HTS) of glutaminase inhibitors. We applied the new methodology to screen a ∼30,000-compound library to search for GLS inhibitors. The HTS assay identified 11 glutaminase inhibitors as hits that were characterized by in silico, biochemical, and glutaminase-based cellular assays. A structure-activity relationship study on the most promising hit (C9) allowed the discovery of a derivative, C9.22, with enhanced in vitro and cellular glutaminase-inhibiting activity. In summary, we discovered a new glutaminase inhibitor with an innovative structural scaffold and described the molecular determinants of its activity.

Chemical Elicitors Induce Rare Bioactive Secondary Metabolites in Deep-Sea Bacteria under Laboratory Conditions.

Bacterial genome sequencing has revealed a vast number of novel biosynthetic gene clusters (BGC) with potential to produce bioactive natural products. However, the biosynthesis of secondary metabolites by bacteria is often silenced under laboratory conditions, limiting the controlled expression of natural products. Here we describe an integrated methodology for the construction and screening of an elicited and pre-fractionated library of marine bacteria. In this pilot study, chemical elicitors were evaluated to mimic the natural environment and to induce the expression of cryptic BGCs in deep-sea bacteria. By integrating high-resolution untargeted metabolomics with cheminformatics analyses, it was possible to visualize, mine, identify and map the chemical and biological space of the elicited bacterial metabolites. The results show that elicited bacterial metabolites correspond to ~45% of the compounds produced under laboratory conditions. In addition, the elicited chemical space is novel (~70% of the elicited compounds) or concentrated in the chemical space of drugs. Fractionation of the crude extracts further evidenced minor compounds (~90% of the collection) and the detection of biological activity. This pilot work pinpoints strategies for constructing and evaluating chemically diverse bacterial natural product libraries towards the identification of novel bacterial metabolites in natural product-based drug discovery pipelines.

Multiple unbiased approaches identify oxidosqualene cyclase as the molecular target of a promising anti-leishmanial.

Phenotypic screening identified a benzothiophene compound with activity against Leishmania donovani, the causative agent of visceral leishmaniasis. Using multiple orthogonal approaches, oxidosqualene cyclase (OSC), a key enzyme of sterol biosynthesis, was identified as the target of this racemic compound and its enantiomers. Whole genome sequencing and screening of a genome-wide overexpression library confirmed that OSC gene amplification is associated with resistance to compound 1. Introduction of an ectopic copy of the OSC gene into wild-type cells reduced susceptibility to these compounds confirming the role of this enzyme in resistance. Biochemical analyses demonstrated the accumulation of the substrate of OSC and depletion of its product in compound (S)-1-treated-promastigotes and cell-free membrane preparations, respectively. Thermal proteome profiling confirmed that compound (S)-1 binds directly to OSC. Finally, modeling and docking studies identified key interactions between compound (S)-1 and the LdOSC active site. Strategies to improve the potency for this promising anti-leishmanial are proposed.

Design and synthesis of cenocladamide analogues and their evaluation against breast cancer cell lines.

This work describes the total synthesis of the alkaloid cenocladamide and a concise library of nine structural analogues aiming at their evaluation against the breast cancer cell line MDA-MB-231. The most promising compound (3; IC50 = 6.6 µM) was also evaluated in a panel of seven breast cancer cell lines and two non-tumorigenic cell lines. We further conducted an initial investigation on the mechanism of action of analogue 3, which lacks the endocyclic double bond when compared to cenocladamide. The present study presents the discovery of a cenocladamide analogue with interesting cytotoxic activity, which could be useful for further optimization towards new chemotherapeutic agents for breast cancer treatment.