Usnic Acid

This study aimed to identify plasma proteins causally associated with pulmonary arterial hypertension (PAH) by using a proteome-wide Mendelian randomization (PWMR) approach. We integrated two large proteomic genome-wide association study (GWAS) data sets with two PAH GWAS data sets and applied PWMR, Bayesian colocalization, and SMR to prioritize candidate proteins. Drug prediction, molecular docking, single-cell RNA sequencing (scRNA-seq) profiling, and a phenome-wide association study (PheWAS) were further used to assess druggability and potential phenotypic associations. PWMR identified 271 PAH-associated proteins, which were refined to the following three targets: CASP10, NOTCH3, and NCAM2. Molecular docking showed strong predicted binding between CASP10 and usnic acid and masoprocol and between NOTCH3 and 2-mercaptobenzothiazole. scRNA-seq data revealed CASP10 expression in endothelial and inflammatory cells and NOTCH3 expression in smooth muscle cells and fibroblasts. The PheWAS did not detect any adverse associations that survived the false discovery rate (FDR) correction. Overall, this integrated analysis highlights CASP10 and NOTCH3 as potential therapeutic targets for PAH. CASP10, as supported by stronger predicted druggability and multiomics evidence, warrants priority for further experimental evaluation.

The impact of the isoxazole derivative of usnic acid, ISOXUS (formerly known as 2b) on cancer and non-cancerous cell metabolism was investigated. ISOXUS significantly reduced the utilisation of most metabolic substrates that produce NADH or FADH2, mitochondrial electron flow and oxygen consumption rate (OCR) in MCF-7 breast cancer cells in contrast to HB2 normal epithelial cells. Molecular docking revealed that ISOXUS inhibits mitochondrial respiratory chain complex II, which was confirmed experimentally. Disturbance of electron flow in MCF-7 cells resulted in increased reactive oxygen species (ROS) production. They appeared crucial for ISOXUS-induced cancer cell vacuolization and a drop in survival as an antioxidant, α-tocopherol, protected against these processes. These findings indicate that ISOXUS is a metabolic inhibitor that targets mitochondrial complex II in breast cancer cells resulting in diminished ATP production and increased ROS formation which translates into reduced cell viability.