Graphene is an attractive choice for the development of an effective drug carrier in cancer treatment due to its high adsorption area and pH-responsive drug affinity. In combination with the highly potent metabolic drug phenformin, increased doses could be efficiently delivered to cancer cells. This study compares the use of graphene oxide (GO) and polyethylene glycol stabilized (PEGylated) pristine graphene nanosheets (PGNSs) for drug delivery applications with phenformin. The cytotoxicity and mitotoxicity of the graphene-based systems were assessed in human cells and zebrafish larvae. Targeted drug release from GO and PGNSs was evaluated at different pH levels known to arise in proliferating tumor microenvironments. PGNSs were less cytotoxic and mitotoxic than GO, and showed an increased release of phenformin at lower pH in cells, compared to GO. In addition, the systemic phenformin effect was mitigated in zebrafish larvae when bound to GO and PGNSs compared to free phenformin, as measured by flavin metabolic lifetime imaging. These results pave the way for improved phenformin-based cancer therapy using graphene nano-sheets, where PGNSs were superior to GO.
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