Design of ovalbumin-loaded mesoporous silica nanoparticles as proof of concept for the development of personalized anti-cancer nanovaccines

Despite the standard treatment, the prognosis of glioblastoma multiforme patients remains dismal. New therapies, like dendritic cell immunotherapy, are emerging to overcome the limitations of the current treatment. Multiple groups already use this treatment strategy and observe long term survival in several patients. Important disadvantages of this patient customized treatment are its high cost and limited efficacy.

Based on our preliminary results from in vivo studies with polystyrene nanoparticles, the use of nanoparticles may provide a solution. We report the production of biodegradable mesoporous silica nanoparticles (MSNPs), which can be used as a vaccine carrier to stimulate the adaptive immune system. In a first stage, the nanoparticle synthesis and functionalization were optimized and the final product was fully characterized for its properties and biodegradability. The synthesis consists of a one pot wet chemistry process which can easily be manipulated in order to modify the properties of the MSNPs. The physicochemical properties of the synthesized MSNPs were investigated with transmission electron microscopy, small angle X-ray scattering, dynamic light scattering, zeta potential measurements, thermogravimetric analysis and fourier transform infrared spectroscopy. Finally, the effect of different synthesis parameters on the biodegradability of the particles was examined, using molybdenum blue chemistry and spectrophotometric analysis. In a second stage, ovalbumin was used as a model antigen and loaded on the MSNPs with optimized carbodiimide crosslinker chemistry. The nanovaccine was tested in vitro on dendritic cell cultures to examine the toxicity, uptake, maturation effect of the vaccine and the potential immunogenicity. In a third and final stage, the vaccine was administered in vivo in mice and the T-cell populations were examined from the splenocytes.

The nanoparticles were determined to be stable at physiological pH due to their negative surface charge. The nanoparticles were successfully functionalized, as confirmed by thermogravimetric measurements. The degradation behavior of the nanoparticles was shown to be strongly dependent on the synthesis parameters (such as temperature, concentration of catalyst and washing alcohol) and could be varied from several hours to 3 – 4 days. Additionally, the dendritic cells were able to take up the MSNPs, as well as the vaccine bound to the particles. This uptake was determined to be mostly an ATP-dependent process. Moreover, it was shown that the nanovaccine could induce maturation of dendritic cells, which was not observed for polystyrene nanoparticle based vaccines used in our previous experiments. Therefore, there is a strong indication that MSNP vaccines could have an adjuvant effect on the dendritic cells and perhaps the adaptive immune response. Moreover, it was found that dendritic cells treated with the nanovaccine were able to cross-present the ovalbumin antigen in significantly higher amount than control conditions (immature and mature dendritic cells and dendritic cells treated with MSNPs alone). No significant difference was found compared to dendritic cells loaded with ovalbumin alone. Finally, spleens collected from nanovaccine immunized mice had a significantly increased amount of CD8+ T-cells and a decreased amount of CD4+ T-cells, compared to mice administered with ovalbumine alone. These preliminary results show that MSNP can be studied further as carrier in the production of antitumor nanovaccines.