Mechanism of Action
A Unique Pro-Drug Activated by Light
A proven photochemical effect
- The photofrin pro-drug is a mixture of porphyrin oligmers.
Relatively Selective Retention in Tumor Cells
- Following administration, Photofrin clears from a variety of tissues in 40 to 72 hours
- Photofrin remains longer in tumor tissue
- Skin and organs of the reticuloendothelial system(including the liver and spleen) also retain Photofrin for longer than 40 to 72 hours after administration
Several Mechanisms of Tumor Cell Destruction
- Direct cytotoxicity via intracellular damage
- type I mechanism: highly reactive free radicals are generated that can damage intracellular membranes and mitochondria
- type II mechanism: excitation to reactive singlet oxygen species leads to oxidation of membranous cell structures
- Ischemic necrosis
- Vascular occlusion occurs secondary to vasoconstriction, platelet activation/aggregation, and clotting
- this may be partly mediated by local release of thromboxane A2
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