Nanodiamond as the pH-responsive vehicle for an anticancer drug.

Cis-dichlorodiammineplatinum(II) (CDDP, cisplatin), a widely used anticancer drug, is successfully loaded onto nanodiamond (ND) by adsorption and complexation. The CDDP-ND composite is characterized by IR spectroscopy, atomic absorption spectroscopy, thermogravimetric analysis, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. CDDP is released from the composite in phosphate-buffered saline (PBS) of pH 6.0 at a rate higher than in PBS of pH 7.4. Therefore, it is predicted that the ND vehicle would deliver low concentrations of CDDP in the blood, but release much more drug after integration into the acidic cytoplasm, thereby reducing toxic side effects. The complexation between CDDP and the carboxyl groups on the ND surface is responsible for the pH-responsive release property. The drug released from the composite retains the same cytotoxicity as free CDDP against human cervical cancer cells.