Use of a tetrazolium based colorimetric assay in assessing photoradiation therapy in vitro.

The suitability of a colorimetric [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)] assay to the determination of cell viability following photoradiation therapy (PRT) of human breast and melanoma cell lines has been examined. Results have been shown to correlate with those obtained using a clonogenic assay system. Using the MTT assay system it was shown that differences occur in the susceptibility of both lines to PDT. In addition it has been demonstrated that both lines differ with respect to their ability to develop photosensitivity in the presence of hematoporphyrin derivative (HpD). In the absence of serum this difference is not as obvious. This MTT assay provides a valid, simple and semi-automatable system for assessment of PRT in vitro.