Background  Photodynamic therapy (PDT) is a non-surgical method for treating non-melanoma skin cancer and precancerous lesions which involves the activation of a photosensitizer by visible light to produce activated oxygen species within target cells, resulting in the destruction of the latter. The present study evaluates the effect of PDT on primary normal and basal cell carcinoma cultures in vitro.

Methods  Primary human keratinocytes and carcinoma cell cultures were exposed to various concentrations of 5,10,15,20-tetra-(para-methoxyphenyl) porphyrin (TMP) and its zinc compound (Zn-TMP) for 24 hours, with or without chitosan, and then irradiated using a PDT lamp (630 nm, 6 J/cm2). The effects of PDT were assessed using a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay and an immunocytochemical method with Annexin V-FITC for detecting apoptosis.

Results  Both tested substances, TMP and Zn-TMP, had a phototoxic effect on primary human carcinoma cell cultures in concentrations of 1–100 μg/ml, which positively correlated with the concentration of the photosensitizer. There was no phototoxic effect on primary keratinocytes, probably because of the preferential accumulation of photosensitizing substances in tumoral cells. Administration of chitosan in association with photosensitizing substances increased cell viability compared with photosensitizers alone, exerting a cytoprotective effect.

Conclusions  The study demonstrates that the photodynamic activity of TMP and its metalloporphyrin derivative is limited to primary human carcinoma cells and suggests that these porphyrins could be efficiently used in PDT in vivo.