Comparison of different cytotoxicity assays for in vitro evaluation of mesoporous silica nanoparticles

Colorimetric or luminogenic cytotoxicity assays are typically applied for in vitro cytotoxicity evaluations due to their easy handling and low cost. However, the results may be strongly assay-dependent. Furthermore, when applied to nanoparticle toxicity screening, nanoparticle-specific interferences can occur. Therefore, it is important to evaluate the assays for different classes of nanoparticles. Mesoporous silica nanoparticles (MSNs) have emerged as a promising platform for both diagnostic and therapeutic applications but a comparison between the commonly employed colorimetric formazan-dependent MTT and WST-1 and luminescent ATP-dependent cytotoxicity assays is still missing. In this work, we evaluated the applicability of four different in vitro cell viability assays for the cytotoxicity analysis of three differently functionalized mesoporous silica nanoparticles towards TZM-bl indicator cells. The results derived from the colorimetric measurements of cell-viability were compared with results obtained by cell count experiments, flow cytometry, and optical microscopy. The correlation between the viability assay results and the viable cell count was observed to be both assay and particle dependent. The MTT assay generally overestimated the cytotoxicity of the mesoporous silica particles, while the WST-1 assay sometimes clearly underestimated their cytotoxicity and even suggested a viability exceeding 100%. Of the two ATP-based assays, the CellTiterGlo assay gave the best correlation with cell count data, although some particle-dependent effects were observed. In conclusion, ATP-based assays seem most suitable for in vitro cytotoxicity evaluation of MSNs.