New sensitisers for photodynamic therapy : a photophysical study.
The photophysical properties of porphyrin and phthalocyanine photosensitisers for
the photodynamic therapy of cancer (PDT), sterically hindered porphyrins and a novel
chemotherapeutic agent (Mitoxantrone), have been investigated using the time resolved
techniques of laser flash photolysis, pulse radiolysis, fluorescence and near infrared
Current topics of interest in PDT and phototherapy of neonatal jaundice are the use.
of 5-aminolaevulinic acid to stimulate the formation of protoporphyrin IX for treatment of
tumour and skin lesion, and the formation of the potentially cytotoxic species, lumirubin,
by green light irradiation of infants with hyperbilirubinemia. Continuous irradiation, and
steady state techniques have been used to study the photoproduct, and singlet oxygen
formation, by these systems.
The effect of environment on the photophysical properties of haematoporphyrin has
been studied. It was found that under certain conditions the triplet state lifetime and
relative quantum yield are enhanced. The results of this have been used to suggest an
explanation for enhanced singlet oxygen yields in such environments.
A novel water soluble phthalocyanine with no peripheral substitution, but the axial
ligands conferring the desired property, has been studied and found to have a triplet state
lifetime in aqueous solution of approximately O.7J.1s, and a singlet oxygen yield of zero.
Yet this phthalocyanine has been reported to be efficient sensitizer for the photodynamic
therapy of cancer. This supports current discussions that mechanisms other than type II
(singlet oxygen) could be of significance in the destruction of tumours.