Receptor Ligand-Free Mesoporous Silica Nanoparticles: A Streamlined Strategy for Targeted Drug Delivery across the Blood–Brain Barrier

Mesoporous silica nanoparticles (MSNs) represent a promising avenue for targeted brain tumor therapy. However, the blood–brain barrier (BBB) often presents a formidable obstacle to efficient drug delivery. This study introduces a ligand-free PEGylated MSN variant (RMSN25-PEG-TA) with a 25 nm size and a slight positive charge, which exhibits superior BBB penetration. Utilizing two-photon imaging, RMSN25-PEG-TA particles remained in circulation for over 24 h, indicating significant traversal beyond the cerebrovascular realm. Importantly, DOX@RMSN25-PEG-TA, our MSN loaded with doxorubicin (DOX), harnessed the enhanced permeability and retention (EPR) effect to achieve a 6-fold increase in brain accumulation compared to free DOX. In vivo evaluations confirmed the potent inhibition of orthotopic glioma growth by DOX@RMSN25-PEG-TA, extending survival rates in spontaneous brain tumor models by over 28% and offering an improved biosafety profile. Advanced LC-MS/MS investigations unveiled a distinctive protein corona surrounding RMSN25-PEG-TA, suggesting proteins such as apolipoprotein E and albumin could play pivotal roles in enabling its BBB penetration. Our results underscore the potential of ligand-free MSNs in treating brain tumors, which supports the development of future drug–nanoparticle design paradigms.


Experimental Section:
The calculation formula of the transport efficiency across the BBB: Transport efficiency (%) ; =   -    -  × 100% where C upper is the concentration of silica in the apical side, C bottom is the silica concentration of a transported sample, and C blank is the silica concentration of the medium.

Figure S2 .
Figure S2.Quantitative fluorescence image analysis based on intensities of regions of interest (ROIs) at three different regions from IF imaging.Scale bar=40 μm.

Figure S3 .
Figure S3.IF-stained images of U87 orthotopic mouse brains.At 48 h post-injection with RMSN 25 -PEG-TA(2:1) at a dose of 200 mg/kg body weight, mice were sacrificed, and frozen sections of the brain were stained with Fluor 488-labeled CD-31 (blood vessels), CD-140b (pericytes), and ZO-1 (tight junctions).Images were captured using confocal microscopy.Red and blue signals represent RITC-conjugated MSNs and DAPI-stained cell nuclei, respectively.Yellow arrowhead: colocalization of red and green signals.White arrowhead: no colocalization of red and green signals.Scale bar=25 μm.

Figure S5 .
Figure S5.In vitro degradation of MSN 25 -PEG-TA and DOX@MSN 25 -PEG-TA, incubated in PBS at 37°C for seven days.(a) The morphology of MSNs in PBS observed by TEM images.(b-c) The size and count rate of MSNs detected by DLS measurement at various time points.

Table S1 . Total surface area, interplanar spacing, and pore size of mesoporous silica nanoparticles (MSNs)
Z-average, harmonic intensity averaged particle diameter; TEM, transmission electron microscopy; DLS, dynamic light scattering; PDI, polydispersity index; d 100 , interplanar spacing calculated from the Bragg formulation; S BET , surface area calculated from data using the BET equation; D BJH , pore diameter assigned from the maximum on the BJH pore size distribution.

Table S2 . Thermogravimetric analytical (TGA) results for MSNs with various modifications
wt%, normalized weight loss from the TGA.

Table S5 . Elemental analysis of MSNs with various modifications
Percentages of carbon, hydrogen, and nitrogen contents for MSNs were obtained from an elemental analysis.PEG, polyethylene glycol; TA, TA-silane.

Table S6 . Characteristics of MSN 25 -PEG-TA and DOX@MSN 25 -PEG-TA
DOX. doxorubicin.LC (%), ratio of the mass of the drug divided by the mass of the nanoparticle; EE (%), mass of the drug encapsulated in nanoparticles divided by the mass of the drug initially present in the solvent mixture.