  It is known that many potent, often aromatic drugs are water insoluble, which
has hampered their use for disease treatment. In this work, we functionalized
nano-graphene oxide (NGO), a novel graphitic material, with branched
polyethylene glycol (PEG) to obtain a biocompatible NGO-PEG conjugate stable in
various biological solutions, and used them for attaching hydrophobic aromatic
molecules including a camptothecin (CPT) analog, SN38 non-covalently via pi-pi
stacking. The resulting NGO-PEG-SN38 complex exhibited excellent water
solubility while maintaining its high cancer cell killing potency similar to
that of the free SN38 molecules in organic solvents. The efficacy of
NGO-PEG-SN38 was far higher than that of irinotecan (CPT-11), a FDA approved
water soluble SN38 prodrug used for the treatment of colon cancer. Our results
showed that graphene is a novel class of material promising for biological
applications including future in vivo cancer treatment with various aromatic,
low-solubility drugs.
