Report Photodamaging effects of porphyrins and chitosan on primary human keratinocytes and carcinoma cell cultures Mirela Susan 1 , MD, Ioana Baldea 1 , MD, Simona Senila 1 , MD, Victorina Macovei 1 , MD, Simina Dreve 2 , PhD, and Rodica Mariana Ion 3 , PhD, Rodica Cosgarea 1 , MD, PhD 1 Department of Dermatology, University of Medicine and Pharmacy, Cluj-Napoca, Romania, 2 Physics of Multifunctional Nanostructured Systems, National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca, Romania, and 3 Department of Analysis, National Institute of Research and Development for Chemistry and Petrochemistry, Bucharest, Romania Correspondence Rodica Cosgarea, MD, PhD Department of Dermatology University of Medicine and Pharmacy Str. Clinicilor nr. 3–5 400006, Cluj-Napoca Romania E-mail: cosgarear@yahoo.com Conflicts of interest: None. Abstract 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 com- pound (Zn-TMP) for 24 hours, with or without chitosan, and then irradiated using a PDT lamp (630 nm, 6 J/cm 2 ). 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 lg/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. Introduction Photodynamic therapy (PDT) is a modality of treatment for skin cancer and precancerous skin lesions based on the activation of light-sensitive molecules (photosensitiz- ers), which form cytotoxic oxygen radicals, causing tissue injury and cell death. 1 To produce cytotoxic effects, PDT requires three components to be present simultaneously: light, oxygen, and a photosensitizer. 2 After the adminis- tration of a photosensitizer, which is selectively retained by tumor cells, subsequent irradiation with visible light in the presence of oxygen specifically inactivates neoplastic cells. 3 Two basic types of reaction can occur after photo- activation of the photosensitizer. One mechanism involves free-radical generation and tumoral destruction through the direct oxidation of cell structures (type I photochemi- cal reaction). The other mechanism provokes singlet oxy- gen production through energy transference from excited triplet species to molecular oxygen species, which medi- ates oxidation processes (type II photochemical reaction). The type II mechanism is commonly considered as the main process responsible for cell damage. 4 Photosensitizers are deemed to have specific chemical and biological properties. Two photochemical requisites are a high absorption coefficient in the visible region of the spectrum, mainly in the phototherapeutic window (600–1000 nm), and a sufficiently long lifespan in the excited triplet state to efficiently produce singlet oxygen. 5 Most common photosensitizers are porphyrins and por- phyrin-related macrocycles that are lipophilic and have a high propensity to accumulate in the membranes of intracellular organelles such as lysosomes and mitochon- dria. 6 Photodynamic therapy may cause cell death by necrosis or apoptosis, 7 both in vitro and in vivo. 8 Apoptosis, also known as ‘‘programmed cell death’’, involves a series of 280 International Journal of Dermatology 2011, 50, 280–286 ª 2011 The International Society of Dermatology