Gallate-induced nanoparticle uptake by tumor cells: Structure-activity relationships

How nanoparticles interact with biological systems determines whether they can be used in theranostic applications. It has been demonstrated that tea catechins, may enhance interactions of magnetic nanoparticles (MNPs) with tumor cells and the subsequent cellular internalization of MNPs. As part of the chemical structure of the major tea catechins, gallates are found in a variety of plants and thus food components. We asked whether the structure of gallate might act as a pharmacophore in the enhancement of the effects of MNP-cell interactions. Uptake of dextran-coated MNPs by glioma cells and cell-associated MNPs (MNP_cell) were respectively analyzed by confocal microscopy and a colorimetric iron assay. Co-incubation of MNPs and gallates, such as gallic acid and methyl gallate, induced a concentration-dependent increase in MNP_cell, which was associated with co-localization of internalized MNPs and lysosomes. An analysis of the structure-activity relationship (SAR) revealed that the galloyl moiety exerted the most prominent enhancement effects on MNP_cell which was further potentiated by the application of magnetic force; catechol coupled with a conjugated carboxylic acid side chain displayed comparable effects to gallate. Blockade or reduction in the number of hydroxyl groups rendered these compounds less effective, but without inducing cytotoxicity. The SAR results suggest that neighboring hydroxyl groups on the aromatic ring form an essential scaffold for the uptake effects; a similar SAR on antioxidant activities was also observed using a free radical-scavenging method. The results provide pivotal information for theranostic applications of gallates by facilitating nanoparticle-cell interactions and nanoparticle internalization by tumor cells.