Glucose is a key driver for GLUT1-mediated nanoparticles internalization in breast cancer cells

Around 1930, Otto Heinrich Warburg discovered that, even in the presence of oxygen, tumor cells undergo aerobic glycolysis rather than a normal oxidative phosphorylation1. Aerobic glycolysis produces just 2 molecules of ATP per molecule of glucose, while up to 36 ATP molecules are produced by oxidative phosphorylation, thus cancer metabolism and oncogenes have been investigated to better understand the reason why tumor cells, that require high ATP levels to supply their energy needs, take this pathway2. Nowadays it is clear that both normal and tumor cells are capable to switch oxidative pathway to overcome their energetic drawbacks, the former process by a finely regulated way whereas the second is allowed by a deregulated gene expression3,4. Although it is not clear whether the Warburg effect is the cause or the consequence of the genetic dysregulation5, the increased glucose metabolism of cancer cells has been used for diagnostics purposes, such as for the Positron Emission Tomography with the [18F]-Fluorodeoxyglucose ([18F]FDG)6,7. In a recent paper, Alvarez and co-workers demonstrated a high [18F]FDG uptake, by glucose specific transporter 1 (GLUT1), in aggressive Her2-positive mammary tumors8. Moreover, in this high grade cancer, it has been demonstrated that the aerobic glycolytic metabolism correlates with tumor aggressiveness9. GLUT1 protein is member of a family of glucose transporter molecules belonging to solute carrier 2A (SLC2A)10 and it is over-expressed in cell lines derived from highly aggressive tumors, both as mRNA11 and protein12. These and other works13,14 outlined the particular metabolic process characterizing the high aggressive cancer cells. Specifically targeting these cells by exploiting their metabolic pathways15,16, rather than using membrane receptors, represents one of the most interesting and promising approaches in cancer research, that could, for instance, help to overcome drug resistance12,17. In this work we proposed a metabolic-based method to detect breast cancer cells with a basal phenotype (basal cells with mesenchymal features)18 and discriminate them, in a co-culture environment, from those with a luminal phenotype. MCF7 and MDA-MB-231 have been chosen as breast cancer cell lines representative of luminal and basal cells, respectively. MCF7 cells, bearing a CD44neg/Ep-CAMpos/E-cadherinpos phenotype, have been classified as luminal-epithelial and weakly metastatic19. Despite of their epithelial origin, MDA-MB-231 cells, presenting a 85 ± 5% of CD44 + /CD24− population, positive to CD105 and negative for both Ep-CAM and E-cadherin staining, are classified as mesenchymal-like phenotype with tendency to metastasize19. This cell line over-expresses GLUT1 and typically exhibits Warburg effect characteristics as demonstrated in a xenograft mouse model, by correlating the acidification of the external tumor microenvironment to the lactic acid production20. Moreover, this occurrence was proved to be the key driver for local invasion from both primary and metastatic tumor masses, with consequent enhanced growth conditions21,22. Combining the knowledge on GLUT1 expression patterns with the Warburg effect, our goal was to investigate on the differences between mesenchymal- and epithelial like cancer cells. Due to their large application in cancer diagnosis and treatment, we used glucose-coated MNPs as vectors introduced in the culture medium. Regarding MNP uptake, we proved a distinctive behavior between epithelial- and mesenchymal-like cells, thus allowing us to discriminate them in co-culture. Interestingly, tuning the glucose concentration in the medium could further enhance this difference.