The CSN5 enzyme appears to be an excellent target for biological drugs because an increase in the deneddylating enzyme Csn5 is reported in many types of tumors. Unfortunately, the study of the CSN5 gene is complicated by the fact that its deletion is lethal in mammal embryos. Previously using the yeast Saccharomyces cerevisiae as a model for the selection of inhibitors of the deneddylating Csn5 enzyme, using a library of FDA approved natural compounds, we selected a set of molecules which inhibited the Csn5 activity. The deletion of the CSN5 gene in yeast is not lethal and it is therefore possible to study the phenotype that derives from the absence of this enzyme. In yeast, the CSN complex (Csn5 is its catalytic enzyme) is required for the transition between the exponential phase growth and the stationary phase, in which the lack of nutrients induces a relevant changes in transcription, activating, among other pathways, the autophagy. In particular, the deletion of the CSN5 gene in yeast cells causes the activation of the transcription of two autophagic genes (ATG16 and ATG33) and an increase of the vacuolar size, suggesting the autophagy activation in growth phase in which autophagy is usually not required. In cancer cells, autophagy has been recognized as an adaptive response to starvation or stress conditions. However prolonged autophagy leads to a high turnover rate of proteins and organelles above the survival threshold resulting in cancer cells death. This adaptation can be utilized as a therapeutic tool for the cancer treatment (alone or in combination with other drugs) because the use of molecules promoting autophagy could significantly increase the cell death in the tumors. In this project we propose to test the inhibitors of CSN5 activity in human glioblastoma, that results one of the most aggressive brain tumor in human with high resistance to apoptosis and to conventional chemiotherapic drug treatments.
In recent years the interest on the neddylation pathway as an antitumor target is significantly increasing since the inhibitor of the activating enzyme Nedd8 (MLN4924) has reached phase 1 and 2 in some clinical trials. In addition, a new molecule, CSN5i-3 was recently described as a CSN5 inhibitor with anticancer activity. Indeed, since that an up regulation of the human CSN5 enzyme is present in many tumors, its inibitors may be considered a promising tool for cancer therapy in the future. In this project we propose to test on glioblastoma cell lines (U251 and U87) two inhibitors of Csn5 previously selected from a screening performed in yeast.
Taking advantage of the phenotypes observed in yeast using the Csn5 inhibitors, we will be able to address our experiments to the autophagic pathway and the mitochondrial function, a field still unexplored in a glioblastoma model.