Action spectrum for tumour response induced by the bis(dimethylthexylsiloxy) silicon 2,3-naphtalocyanine in mice

Photodynamic therapy (PDT) of cancer relies upon the treatment of tumour tissues with visible light after systemic administration of porphyrin-based photosensitisers. We have recently demonstrated the potentiel of bis(alkylsiloxy) silicon 2,3-naphthalocyanine derivatives as photosensitisers for PDT, using far-red light providing optimal tissue penetration. In the series, the bis(dimethylthexylsiloxy) SiNc derivative (0.1 mu mol/Kg 24 h before PDT) was the most active, inducing EMT-6 tumour regression in more than 80% of BALB/c mice. These results were obtained with an excitation wavelength fixed at 780 nm, i.e. the absorption maximum of the monomeric dye. We now report on the effect of varying the excitation wavelength from 770 to 790 nm on PDT efficiency. The action spectrum for the bis(dimethylthexylsiloxy) SiNc-induced tumor response was shown to correlate well with the fluorescence excitation spectrum of the dye.