The synthesis and properties of unsymmetrical 3,7-diaminophenothiazin-5-ium iodide salts: Potential photosensitisers for photodynamic therapy

A series of unsymmetrical 3,7-(N,N-disubstituted-amino)-phenothiazin-5-ium iodides have been prepared by stepwise reaction of secondary amines with phenothiazin-5-ium tetraiodide hydrate. The singlet oxygen generating efficiencies and polarity characteristics of the dyes are compared with those of Methylene Blue, and the factors influencing the potential value of these compounds as photosensitisers for photodynamic therapy are discussed. Preliminary data for the in vivo anti-tumour efficacy of the compounds suggest that high lipophilicity is an important requirement for high activity.