Functionalized Graphene Quantum Dots ModulateMalignancy of Glioblastoma Multiforme by Downregulating Neurospheres Formation

Glioblastoma multiforme (GBM) is the most aggressive brain cancer. We previously demon-strated the effect of biocompatible surface functionalized graphene quantum dots (GQDs) on GBMcells as chemotherapy enhancers in combination with the antitumor drug doxorubicin (Dox). How-ever, traditional two-dimensional cultures could not represent a reliable model of tumor behavior. Inthis work, we investigated the effect of carboxylated (COOH-GQDs), aminated (NH2-GQDs) andunfunctionalized GQDs on a three-dimensional model of neurospheres. Neurospheres are clusters ofGBM cells, which formation is driven by the presence of a stem subpopulation involved in cancermalignancy. Tumor recurrence after surgical resection, chemotherapy and radiotherapy indeeddepends on the presence of cancer cells with stem properties. We measured a significant reduction innumber and size of neurospheres after two weeks of monitoring in the presence of COOH-GQDsand GQDs. Previous works pointed out how variations of membrane fluidity could affect mem-brane stability and cell-to-cell interactions, thus influencing cell clustering. Therefore, we measuredchanges in membrane fluidity after administration of GQDs. We found that COOH-GQDs andGQDs significantly increased membrane fluidity with respect to the treatment with NH2-GQDs orcompared to untreated cells. Shifts in the phase of phospholipid bilayer were in accordance with thenegative surface net charge of GQDs. We depicted a strong correlation between negatively chargedGQDs-induced increase in membrane fluidity and the downregulation of neurospheres formation.Our results indicate that COOH-GQDs and GQDs significantly modulate tumor malignancy byincreasing fluidity of cell membrane, with a consequent inhibition of cell-to-cell interaction.