Isomer-dependent adsorption and release of cis- and trans-platin anticancer drugs by mesoporous silica nanoparticles.

We report on adsorption and release of the anticancer drugs cisplatin and transplatin from mesoporous silica nanomaterials, emphasizing the differences between cisplatin and its much less toxic isomer. Two types of particles, MCM-41 and SBA-15, were used, either as just synthesized or after calcination to remove the templates. The particles were characterized by TEM, nitrogen physisorption, and elemental analysis. The UV-vis spectra of cisplatin and transplatin were obtained and the intensities of several bands (205-210 nm, 210-220 nm, 220-235 nm, and 300-330 nm) were found proportional to drug concentrations, allowing their use for measuring drug concentration. To evaluate drug adsorption by nanoparticles, nanoparticles were incubated in drug solutions and removed by centrifugation, after which the supernatants were scanned by spectrometer to determine drug remaining. It was found that calcined MCM adsorbed less cisplatin or transplatin per particle than as-synthesized MCM. SBA nanoparticles adsorbed slightly more cisplatin than MCM, and slightly less transplatin. Measurements of drug adsorption as a function of time show that drug is rapidly adsorbed by all particles studied. This rapid adsorption is probably associated with adsorption of drug on the external surfaces of the particles as well as the possible physisorption within the surfactant assemblies or by replacing the surfactant molecules or ions in the case of the as-synthesized materials. For calcined SBA particles, it is followed by a slow take-up of drug, perhaps due to the internal pores. There is no slow take-up by as-synthesized SBA particles or by either as-synthesized or calcined MCM particles. Measurement of the release of platinum drugs from nanoparticles previously soaked in drug solutions showed a substantial quick release for all particles and both drugs. This was followed by a slow release of Pt species in the case of transplatin in calcined SBA.