The in vivo biodistribution and urinary excretion of spherical mesoporous silica nanoparticles (MSNs) are evaluated by tail-vein injection in ICR mice, and the effects of the particle size and PEGylation are investigated. The results indicate that both MSNs and PEGylated MSNs of different particle sizes (80-360 nm) distribute mainly in the liver and spleen, a minority of them in the lungs, and a few in the kidney and heart. The PEGylated MSNs of smaller particle size escape more easily from capture by liver, spleen, and lung tissues, possess longer blood-circulation lifetime, and are more slowly biodegraded and correspondingly have a lower excreted amount of degradation products in the urine. Neither MSNs nor PEGylated MSNs cause tissue toxicity after 1 month in vivo.

The biomedical applications of mesoporous silica nanoparticles (MSNs) as efficient drug delivery carriers have attracted great attention in the last decade. The structure, morphology, size, and surface properties of MSNs have been found to be facilely tunable for the purposes of drug loading, controlled drug release and delivery, and multifuctionalization. Meanwhile, the biosafety and in vivo drug efficiency of MSN-based nano drug delivery systems (nano-DDSs), involving biocompatibility (including cytotoxicity, blood and tissue compatibility) and pharmacokinetics (including biodistribution, biodegradation, retention, excretion, blood circulation) are also drawing increasing attention because of their clinical application prospects. Herein, we review the most recent research progresses on the synthesis, controlled drug release and delivery, pharmacokinetics and biocompatibility of MSNs.

In the anti-cancer war, there are three main obstacles resulting in high mortality and recurrence rate of cancers: the severe toxic side effect of anti-cancer drugs to normal tissues due to the lack of tumor-selectivity, the multi-drug resistance (MDR) to free chemotherapeutic drugs and the deadly metastases of cancer cells. The development of state-of-art nanomedicines based on mesoporous silica nanoparticles (MSNs) is expected to overcome the above three main obstacles. In the view of the fast development of anti-cancer strategy, this review highlights the most recent advances of MSN anti-cancer nanomedicines in enhancing chemotherapeutic efficacy, overcoming the MDR and inhibiting metastasis. Furthermore, we give an outlook of the future development of MSNs-based anti-cancer nanomedicines, and propose several innovative and forward-looking anti-cancer strategies, including tumor tissue-cell-nuclear successionally targeted drug delivery strategy, tumor cell-selective nuclear-targeted drug delivery strategy, multi-targeting and multi-drug strategy, chemo-/radio-/photodynamic-/ultrasound-/thermo-combined multi-modal therapy by virtue of functionalized hollow/rattle-structured MSNs.