Objectives: (1) Determine the fluorescence intensity of mouse squamous cell carcinoma (SCCa) exposed to 5-aminolevulinic acid (5-ALA) in vitro. (1) Determine the threshold of cancer detection using fluorescence in SCCa treated with 5-ALA in vitro.
Methods: A mouse oral SCCa cell line was cultured in 96-well plates in different amounts and exposed to 5-ALA at different concentrations and durations. A Schwann cell line was tested in parallel to serve as a control group. The cells were excited with 405 nm wavelength of light and the fluorescent intensities were measured at an emission of 620 nm. The threshold of detecting fluorescent carcinoma cells with the naked eye was determined using a pre-defined visual analog scale.
Results: SCCa had significantly more uptake of 5-ALA than Schwann cells, as determined by the level of relative fluorescence units (RFU). The mean fluorescent intensity increased proportionately to the number of cultured SCCa. Schwann cells have negligible uptake of 5-ALA, compared to cultured SCCa. Higher concentrations of 5-ALA resulted in higher levels of RFU. Fluorescence from SCCa is detected as early as 1 hour after 5-ALA exposure in vitro. Fluorescent SCCa can be detected with the naked eye in a dose-dependent manner.
Conclusion: 5-ALA is a novel drug that has fluorescent properties and selective uptake in SCCa. These findings support further testing of 5-ALA in the detection of residual cancer and perineural invasion in a pre-clinical animal model of SCCa.