Purpurins are modified chlorins with photodynamic properties. Their strong absorption in the red region of the visible spectrum makes them candidates for use in photodynamic
cancer therapy. A series of
metal derivatives of the free base purpurins have been synthesized and shown to cause
tumor necrosis in transplantable
tumors when exposed to visible light. In the following set of experiments, the effects of two metallo-derivatives (
tin and
zinc) of two purpurins, octaethylpurpurin (NT2) and etiopurpurin (ET2), and light on the N-[4-(5-nitro-2-furyl)-2-thiazolyl]
formamide transplantable
tumors in Fischer CDF(F344)/CrlBr rats were studied. The photodynamic activity was assessed by a short term assay using
tumor dry weight 12 days after purpurin-
PDT as a criterion of response. From these experiments it appears that
SnET2 greater than SnNT2 greater than
ZnET2 greater than ZnNT2 in photodynamic activity.
SnET2 was further characterized by attempting to determine the time interval after systemic injection at which maximum
therapeutic effect occurred. These studies shown that 24 h after metallopurpurin injection was the optimum time for treatment of
tumors with visible light. In a final set of experiments, the effect of solar light on the skin of hairless mice injected with
SnET2 was found to be much less injurious than with
hematoporphyrin derivative.