Development of phosphonate-terminated magnetic mesoporous silica nanoparticles for pH-controlled release of doxorubicin and improved tumor accumulation

In this study, phosphonate-terminated magnetic mesoporous nanoparticles (pMMSNs) was designed by incorporation of MNPs in the center of mesoporous silica nanoparticles (MSNs) and followed by grafting phosphonate group on to the surface of MMSNs. The carrier exhibited a typical superparamagnetic feature and the saturation magnetization was 4.89 emu/g measured by vibrating sample magnetometer (VSM). pMMSNs had a spherical morphology and a pore size of 2.2 nm. From N2 adsorption-desorption analysis, pMMSNs had a surface area of 613.4 m2/g and a pore volume of 0.78 cm3/g. Phosphonate modification improved the colloidal stability of MMSNs, and the hydrodynamic diameter of pMMSNs was around 175 nm. The hydrophilic phosphonate group significantly enhanced the negative surface charge of MMSNs from −19.3 mV to −28.8 mV pMMSNs with more negative surface charge had a 2.3-fold higher drug loading capacity than that of MMSNs. In addition, the rate and amount of release of doxorubicin (DOX) from DOX/pMMSNs was pH-dependent and increased with the decrease of pH. At pH 7.4, the release amount was quite low and only approximately 17 wt% of DOX was released in 48 h. At pH 5.0 and 3.0, the release rate increased significantly and the release amount achieved 31 wt% and 60 wt% in 48 h, respectively. To evaluate the magnetic targeting performance of pMMSNs, FITC labeled pMMSNs was injected into mice bearing S180 solid tumor. FITC labeled pMMSNs controlled by an external magnetic field showed higher tumor accumulation and lower normal tissue distribution