Plasma membrane-associated graphene oxide as aplatform for modulating signalling through cell-surfacereceptors: an integrin-focused proof-of-concept study

Graphene oxide (GO) has primarily been studied for delivering therapeutic molecules into cells. In earlier research, the authors discovered that GO tends to stick to cancer cell membranes but is absorbed by non-cancerous epithelial cells. Now, they investigate if GO stuck to the cancer cell membrane can be used to display bioactive ligands and affect the signaling of cell-surface receptors in cancer cells.

To test this idea, they attached an RGD-containing peptide to GO using a non-covalent bond at the cancer cell membrane. They examined how well GO and the peptide interact, how cells interacted/absorbed GO, cell movement, and changes in focal adhesion signaling. The interaction was measured using a TNBSA assay, and GO's properties were determined through atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and colloidal measurements.

Right after forming the complex, about 70% of the RGD was found near GO. This bond made the nitrogen signal stronger and changed the main XRD peak of GO, but it kept its sheet-like structure. They looked at how U87 and U251 glioblastoma cells (with different amounts of integrin) and non-cancerous BEAS-2B bronchial epithelial cells responded.

Confocal microscopy showed GO and GO:RGD mostly stayed on the plasma membrane of U87 and U251 cells, while BEAS-2B cells had more internalization. Most importantly, GO:RGD significantly decreased key signs of cell movement, like speed and direction in U87 and U251 cells, showing they moved less. Free RGD didn't have a big effect, and GO alone only reduced movement in U251 cells slightly.

None of the treatments changed BEAS-2B cell movement. Flow cytometry also showed a lower pFAK-associated signal in GO:RGD-treated U87 cells. These results show that the cell type-specific way GO stays on the membrane can be used as a platform to show bioactive ligands that influence cell-surface receptor signaling, which could lead to new GO-based ways to modify signaling and cell behavior.