Dispersion of cisplatin-loaded carbon nanohorns with a conjugate comprised of an artificial peptide aptamer and polyethylene glycol

Hydrophobic single-wall carbon nanohorns (SWNHs) were dispersed in aqueous media by noncovalently modifying their surfaces with conjugate molecules comprised of polyethylene glycol (PEG) and a peptide aptamer (NHBP-1) that specifically bind to the surfaces of the SWNHs. The conjugates were synthesized by coupling PEG (average molecular weights of 20,000 and 5000) to the N-terminus of NHBP-1 to produce 20PEG-NHBP and 5PEG-NHBP, respectively. Oxidized SWNHs (oxSWNHs) mixed with 20PEG-NHBP or 5PEG-NHBP were well dispersed in water and passed through a gel filtration column, whereas the oxSWNHs treated with PEG stuck to the top of the column. Although the presence of salts in the media significantly impaired the dispersibility of the oxSWNHs, the oxSWNHs/20PEG-NHBP complexes were well dispersed in both the phosphate-buffered saline (PBS) and cell culture medium. The amount of 20PEG-NHBP bound to the oxSWNHs was estimated to be 0.32 g/g of oxSWNHs, and a dynamic light scattering analysis revealed the diameter of the oxSWNHs/20PEG-NHBP complex to be approximately 210 nm. We then showed that CDDP@oxSWNHs/20PEG-NHBP, in which the cancer chemotherapy drug cisplatin (CDDP) was loaded inside the oxSWNHs, was well dispersed in both the PBS and culture medium and exerted a potent cytotoxic effect against cancer cells. The good dispersion of drug-loaded carbon nanomaterials, like that seen here, is a prerequisite for the clinical application of such materials.