Targeting Notch signaling by design. (a) Upon binding to Jagged or Delta ligands, the Notch receptor is subjected to proteolytic processing that releases the Notch intracellular domain (NICD), which translocates to the nucleus where it regulates Notch-dependent gene expression. The cleavage event is mediated by the γ-secretase (GS) complex rendering Notch sensitive to GS-inhibitors (GSIs). (b) For targeted Notch therapy, the following particle design was chosen: mesoporous silica nanoparticle (MSNP) matrix for loading of GSI; surface functionalization of a PEI-layer for facilitated further modifications such as coupling of targeting ligands, suspension stabilization, and possible molecular gate properties; labeling with fluorophore for easy visualization and conjugation of folate (FA) to the PEI-layer on the particle surface for cellular targeting. FITC, fluorescein isothiocyanate

Cell-specific block of Notch signaling by γ-secretase inhibitor-mesoporous silica nanoparticles (GSI-MSNPs) conjugated to folate (FA). (a) Luciferase reporter assays for Notch activity demonstrate cell-specific inhibition of Notch in high- folate receptor (FR) HeLa cells as compared to low-FR 293 cells at 24 hours of incubation with MSNPs loaded with 1 weight% and 2.5 weight% GSI, respectively. Notch was activated by transfection of ΔE Notch1 in both cell lines. Control MSNPs (Ctrl-MSNPs) denote drug free control particles; GSI-MSNPs denote GSI-containing particles. Both particles were FA-conjugated. X-axis denotes particle concentration (n ≥ 3; mean ± SD). (b) Luciferase reporter assay demonstrates dose-dependent inhibition of Notch signaling by free GSI in 293 and HeLa cells (n ≥ 3; mean ± SD). The boxes in a and b denote GSI concentration at 0.1 µg/ml (***P < 0.0001). (c) Immunoblot of HeLa cells transfected with GS-cleavable active form of Notch, ΔENotch1, and treated with GSI-loaded (GSI-MSNPs) and drug free particles (Ctrl-MSNPs) using an antibody against the GS-cleaved active form of Notch, Notch intracellular domain (NICD). Hsc-70 is used as a loading control. RLU, relative luciferase units.

Internalization of folate (FA)-conjugated mesoporous silica nanoparticles (MSNPs) in MCF7 (FA high), MDA-MB-231, T47D, SK-BR-3 and MDA-MB-468 breast cancer cells. (a) Folate receptor (FR) surface expression in breast cancer cells. Cells were labeled with anti-FR antibody followed by Alexa 488-conjugated secondary antibody (black line) and analyzed by flow cytometry. Nonspecific fluorescence was measured using the secondary antibody only (shaded area). The results are representative of two independent experiments. (b) The endocytosed particles were detected by flow cytometry and mean fluorescence intensity (MFI) was measured after 4 hours and normalized to background fluorescence of each cell line in the absence of particles (n = 3, mean ± SD). (c) FA-mediated uptake of MSNPs. Uptake of PEI-MSNPs and FA-MSNPs was measured at 4 hours of particle incubation and normalized to background fluorescence. The graph shows the FA-mediated uptake as a function of the unspecific uptake of FA-MSNPs (n = 3, mean ± SD).

Tumor accumulation and retention of mesoporous silica nanoparticles (MSNPs) through folate (FA)-functionalization. (a) FA-conjugated and nonconjugated particles (PEI) were injected peritumorally and followed by the IVIS Lumina II imaging system for 72 hours. Scale bars range from 300 to 8000 counts for images 30 minutes to 72 hours, whereas scale bar is 200 to 4500 counts for control image (before injection). (b) Graph shows the quantification of the fluorescence intensity in tumors injected with FA-MSNPs and PEI-MSNPs over time as related to the initial intensity within each tumor (n = 6, two tumors per animal). (*P < 0.05). (c) Ex vivo imaging of internal organs and tumors 72 hours after injection of MSNPs. The tumors were cut in half to visualize particles within the tumor tissue.

γ-Secretase inhibitor (GSI)-loaded mesoporous silica nanoparticles (MSNPs) block Notch activity, inhibit tumor growth, and control stem cell functions in vivo. (a) MDA-MB-231 tumor-bearing mice were injected peritumorally up to day 12 (arrowheads) with FA-conjugated GSI-loaded (GSI-MSNP, 20 mg/kg, 2.5 weight% GSI) and empty MSNPs [control MSNPs (Ctrl-MSNP), 20 mg/kg] (tumor size was followed for 3 weeks (n = 6, mean ± SD). (**P < 0.011). (b) MDA-MB-231 tumor-bearing mice were injected peritumorally up to day 12 (arrowheads) with 1 mg/kg free DAPT {N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester} (GSI) or the DMSO aqueous vehicle solution (Vehicle). Tumor size was followed until day 22 (n = 4, mean ± SD). (c) GSI-MSNP-treatment leads to reduction in the levels of active Notch in the tumors, as demonstrated by western blot using an antibody against Notch intracellular domain (NICD), the active form of Notch. (d,e) Oral delivery of GSI-MSNP induces goblet cell differentiation and diarrhea. (d) Stool from mice fed by gavage with DMSO-vehicle solutions, free DAPT (500 mg/kg), control particles (Ctrl-MSNP) and DAPT particles (GSI-MSNP, 250 mg/kg DAPT) (2–4 mice per treatment) was collected. The % water content (stool hydration) was determined from stool wet and dry weights. Statistics; Students t-test, unpaired, normal distribution. (e) Duodenum from mice fed control particles (Ctrl-MSNP) or GSI particles (GSI-MSNP) by gavage (2 mice per treatment) was excised, fixed in 4% paraformaldehyde and processed for paraffin embedding. 6 µm sections were stained for Goblet cells by Periodic-Shiff (PAS)-staining, and the number of goblet cells in intact crypts and villi displaying clear cross sections were counted in 6–10 sections per mice. Statistics; Students t-test.

Mesoporous silica nanoparticles (MSNPs) accumulate in the tumors, are biocompatible biodegradable and eliminated through renal excretion. (a) In vivo imaging of mice injected peritumoral with PEI-MSNPs or folate (FA)-MSNPs. Images of the abdominal area demonstrate accumulation of fluorescence in the bladder, and imaging of the dorsal area show accumulation of fluorescence in the tumors. Time lapse imaging of the abdominal area shows elimination of fluorescence within 48 hours after injections (number of animals per group, n = 4, two tumors per animal). (b) Ex vivo analyses (left) and quantification of fluorescence intensity (right) in organs from mice injected intravenous (i.v.) with FA-MSNPs. Mice were killed 196 hours after injection (n = 4). Please note the occasional signal from brain tissue which most likely represents background fluorescence as it is present also in untreated control animals. (c) Histological analysis of brain, kidney, spleen, liver, and lungs of untreated mice and FA-MSNPs-treated mice showed no morphological changes. Mice were killed 192 hours after i.v. injection.