Targeting mitochondrial homeostasis with small molecules: from environmental contaminants to inhibitors of nucleotide re-cycling

Mitochondria constantly sustain cell energetic needs and maintain redox homeostasis. Under stress conditions mitochondria may also be the major responsible for the overproduction of reactive oxygen/nitrogen species (ROS/RNS), thus leading to a decreased antioxidant defense and promoting oxidative/nitrosative stress (OS/NS). Prostate cancer is featured by a peculiar energetic metabolism, that makes mitochondria highly susceptible to alterations caused by endogenous or exogenous factors. Environmental contaminants (EC) are responsible for detrimental effects due to their high diffusion/bioaccumulation. Agrochemicals, such as Imidacloprid (IMI) and Phenmedipham (Phen), and the plastic component Bisphenol A (BPA), are able to exert endocrine disruption activity and induce mitochondrial alterations with ROS/RNS dysregulation. Interestingly, dysregulation of ribonucleotides re­cycling, the latter exerted by the mitochondrial ribonuclease REXO2 (degrading 2­5 nucleotides RNA fragments) leads to altered mitochondrial energy profiling and genome stability. We developed specific inhibitors of this enzyme to promote mitochondrial dysfunction in prostate cancer cells (DU145/PC3, showing different level of malignancy and bioenergetics deficit). A set of dinucleotide analogues has been screened in vitro and in cells to assess REXO2 inhibition activity. The EC involvement in OS/NS has been investigated and their effect on ROS production and mitochondrial membrane potential (MMP) has been characterized by taking advantage of specific fluorescent probes (JC­1/DCF­DA/MAK145); furthermore, the oxygen consumption of cells in the presence of EC or REXO2 inhibitors has been assessed. The results will be discussed in the frame of an alteration of mitochondrial homeostasis and function highlighting a potential for REXO2 as a new biomarker for mitochondrial physiology or as a target for anticancer therapies.