Piericidin A (also named piericidin A1 in some references) was reported as a new insecticidal metabolite, produced by cultures of the soil-derived actinomycete Streptomyces mobaraensis. Piericidin A resembles coenzyme Q in its overall structure containing a pyridine ring with two adjacent methoxy groups. The most widely recognized biological target of Piericidin A is the mitochondrial electron transport chain protein NADH-ubiquinone reductase (Complex I). Respiratory inhibition by piericidin A can be reversed by the addition of vitamin-K3 (menadione) to the inhibited respiratory chain in mammalian mitochondria. Piericidin A increases ROS production. Piericidin A showed significant cytotoxic activities against several tumor cells, such as mouse leukemia cell line, human colon carcinoma cells and was selectively cytotoxic toward human multiple myeloma cells. Moreover, it was identified as a highly selective antitumor agent with greater selectivity and potency than the comparison standard mitomycin C. Piericidin A aggravates the course of genetically determined tau pathology.