Glioblastoma multiforme: induction of mitochondria-mediated apoptotic pathway by simultaneous pharmacological activation of TSPO (18KDa) and p53.

The resistance of Glioblastoma Multiforme (GBM) to conventional genotoxic modalities suggests to act on intracellular targets that can bypass DNA repair systems and revert the oncogenic blocks commonly found in GBM. One of the main blocks is explicated through the overexpression of the p53 natural inhibitor MDM2 [1]. The oncoprotein MDM2 binds to p53 and mediates its degradation via proteasome [Chromosomes Cancer 1994;11 91-6.]. In the present work, we chose to induce mitochondria-mediated apoptotic pathway by pharmacological activation of the Traslocator Protein (TSPO, 18KDa), which is a crucial component of the mitochondrial multiprotein complex pore [Curr Med Chem. 2003;10:1563-72.], and p53, which can induce formation of mitochondrial membrane pores following oligomerization of pro-apoptotic members of Bcl2 family [Cell Cycle. 2008;7 1949-55]. To activate simultaneously these two targets we used a single molecule, belonging to the new synthetic compound class EB. Such molecules have an indolyl-glyoxyl scaffold decorated with substituents capable of mimicking the interaction site between p53 and MDM2. Furthermore, EB molecules have the structural requirements to interact with TSPO binding site. Competitive binding assays using the TSPO selective [3H]PK11195 radioligand showed that EB bound to TSPO with nanomolar affinity. In isolated mitochondria, EB, following interaction with TSPO, induced prolonged opening of the mitochondrial pore with consequent collapse of mitochondrial membrane potential (Δψm). EB dissociated the complex p53/MDM2 reconstructed in vitro by the use of recombinant proteins and the native p53/MDM2 complex obtained from the GBM U87MG cells. Treatment of U87MG cells with EB effectively induced Δψm dissipation and activation of the mitochondria-mediated apoptotic pathway