Cellular uptake kinetics and photodynamic activity of meso-tetrahydroxyphenylchlorin (mTHPC)

Meso-tetrahydroxyphenylchlorin (mTHPC) was evaluated in vitro in HT29 human colon adenocarcinoma cell line and compared with hematoporphyrin derivative (HpD). The cellular distribution of mTHPC was analyzed by fluorescence microscopy and revealed that mTHPC distributed diffusively in the cytoplasm. A lower proportion of the photosensitizer (50%) was found in the nuclear area. In both areas, mTHPC fluorescence decay was monoexponential. The incorporation kinetics, evaluated by flow cytometry showed that mTHPC cellular uptake is related to the incubation time until 12 hours, then a plateau appeared. For 12 hr-incubation period, the cellular uptake of mTHPC was found to be linearly related to the extracellular concentration, suggesting passive diffusion mechanism. Cytotoxicity assays were performed using MTT assay after photoirradiation at 650 nm for mTHPC and 630 nm for HpD. The photodynamic activity of mTHPC was influenced by serum protein of the culture medium and time-delayed with a maximal activity 48 hrs after the photoirradiation. In optimized experimental conditions i.e. 2% serum protein-containing culture medium, 12 hr-incubation period, cytotoxicity measured 48 hrs after exposure to 10 J/cm2 light fluence, mTHPC appeared approximately 50-fold more active than HpD with IC50 values of 0.06 (mu) g/ml and 3.30 (mu) g/ml, respectively.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.