Inhibition of mitochondrial translation as a novel strategy to eradicate glioblastoma stem cells

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor in adults. The search for new effective chemotherapeutic agents to treat GBM has proven challenging throughout the last few decades. As a result, very limited pharmacological treatment is currently available. GBM aggressiveness is associated with its glioblastoma stem cells (GSCs) component, which is responsible for resistance to therapy. Therefore, new specific pharmacological approaches directed to eradicate GSCs are endowed with a great therapeutic potential. GSCs have been shown to rely on mitochondrial respiration for their high energy demand. In order to have a functional mitochondrial respiration process, the five complexes forming the oxidative phosphorylation (OXPHOS) chain have to be built by the coordinate assembly of proteins translated by either the cytosolic or the mitochondrial ribosomes. Given their endosymbiotic origin and despite the evolutionary changes occurred the mitochondrial ribosomes (mitoribosomes) still share structural and functional similarities with the bacterial ones, particularly considering the functional ribosomal core. In the light of these similarities, we hypothesized that antibiotics targeting bacterial ribosomes could be exploited to inhibit mitoribosomes, affecting mitochondrial translation and OXPHOS assembly, and hence leading to detrimental effect on GSCs viability. We performed a high-content imaging driven screening of several bacterial ribosome targeting antibiotics and identified Drug A as the most promising compound due to its cytotoxic and mitotoxic effects on GSCs. We demonstrated that Drug A effectively prevents GSCs expansion, resulting to be over an order of magnitude more effective in GSCs growth inhibition than temozolomide, the only drug used in first line GBM therapy. We then investigated the mechanism of action of Drug A, proving that it inhibits mitochondrial translation and, as a consequence, it decreases the functionality of the OXPHOS complexes reducing mitochondrial respiration capacity. Moreover, we obtained the structure of this compound bound to the human mitoribosome using cryo-electron microscopy, which provides the basis for further development of more potent analogs. Finally we proved the efficacy of Drug A in vivo using a xenograft mouse model of GBM. Our results suggest that mitochondrial translation represents a therapeutic target for GBM and show that Drug A, acting via inhibition of mitochondrial translation, is extremely effective against GSCs. Given the urgent medical need for novel therapeutic approaches in GBM treatment, Drug A represents a promising therapeutic solution that is worth further preclinical and clinical investigations.