Endogenous Porphyrins from ALA

ALA also appears to have potential for clinical use as a photodiagnostic or photodetection agent. Fluorescence visualized after intravesical instillation of ALA shows some specificity for mucosal lesions including cancer and dysplasias, although false positives caused by inflammatory areas are also seen. However, it is the improvement in sensitivity rather than in specificity that suggests that ALA photodiagnosis could be a useful tool for guiding biopsies. 

It is of particular interest that such cationic dyes have preferential affinity for enzymes of mitochondria of neoplastic cells. Consequently, cationic dyes inhibit respiration and energy metabolism by inhibiting cytochrome c oxidase.However, the commonly used porphyrin-type photosensitizers are spread over several cellular compartments. In order to optimize the photodynamic effect, it seems promising to combine, on the one hand, the accumulation of the sensitizer in the very important inner mitochondrial membrane system and, on the other hand, the generation of singlet oxygen by specially designed porphyrin sensitizers. 

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