Improved Method to Assess Titanate-Metal Suppression of Oral Cancer Metabolism

Micro-titanates are water soluble ceramic particles (1-20μm) that bind multivalent metal ions.  Previous studies report that titanate-metal ion complexes suppress oral cancer cell metabolism; but recent evidence suggest that the particles adhere to cells and culture plates, resulting in interference with the assessment of metabolic activity during optical density (OD) quantification.  Objectives:  The aim of the current study was to compare the NanoDrop device versus the traditional plate reader for estimating the effect of titanate metal complexes on the metabolic activity of oral cancer cells.  Methods: Oral Squamous Cell Carcinoma (OSC2) cells were plated (5000cell/cm²) in 96-well format (n=8) for 24h prior to treatment by micro-titanates with and without metals (0-200μg/mL; native-no metal, Au(III), Hg(II), cisplatin).  Succinate dehydrogenase activity (MTT method) was used to estimate cellular metabolic activity; OD (562nm) was measured with a plate reader and the NanoDrop device (analyzes 1-2μL of MTT product). Differences were determined using one-way ANOVA and Tukey post-hoc analysis (α=0.05).  Results: For native titanates, the plate reader underestimated the effect of the titanates on OSC2 metabolic activity in a concentration dependent manner by up to 40% at 200μg/mL (p<0.05) when compared with the NanoDrop method.  For titanate-metal complexes, the NanoDrop method detected 20-25% more suppression of metabolic activity at 200μg/mL (all p<0.05) than the plate reader detected.  Overall, the plate reader method was not able to accurately measure metabolic suppression above 50-100μg/mL of titanate.  Conclusions: Micro-titanate particles interfere with OD measurements by a traditional plate reader.  The NanoDrop device was more effective in detecting metabolic suppression by titanates and titanate-metal complexes, especially at concentrations >50μg/mL.  Previous reports may have underestimated the potential of micro-titanate compounds to suppress cancer cell metabolism.