Synthesis, characterisation and in vitro investigation of photodynamic activity of 5-(4-octadecanamidophenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin trichloride on HeLa cells using low light fluence rate.

Photodynamic therapy (PDT) is a treatment that aims to kill cancer cells by reactive oxygen species, mainly singlet oxygen, produced through light activation of a photosensitiser (PS). Amongst photosensitisers that attracted the most attention in the last decade are cationic and amphiphilic molecules based on porphyrin, chlorin and phthalocyanine structures. Our aim was to join this search for more optimal balance of the lipophilic and hydrophilic moieties in a PS. A new amphiphilic porphyrin, 5-(4-octadecanamidophenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin trichloride (5) was synthesised and characterised by (1)H NMR, UV-vis and fluorescence spectroscopy, and by MALDI-TOF/TOF spectrometry. In vitro photodynamic activity of 5 was evaluated on HeLa cell lines and compared to the activity of the hydrophilic 5-(4-acetamidophenyl)-10,15,20-tris(N-methylpyridinium-3-yl)porphyrin trichloride (7). Low fluence rate (2mWcm(-2)) of red light (643nm) was used for the activation, and both porphyrins showed a drug dose-response as well as a light dose-response relationship, but the amphiphilic porphyrin was presented with significantly lower IC50 values. The obtained IC50 values for 5 were 1.4µM at 15min irradiation time and 0.7µM when the time of irradiation was 30min, while for 7 these values were 37 and 6 times higher, respectively. These results confirm the importance of the lipophilic component in a PS and show a potential for 5 to be used as a PS in PDT applications.