In order to define the rate of PpIX formation, we investigated the
effect of concentration and duration of exposure of ALA and its derivatives,
using different cell lines and direct fluorescence measurements.
Once inside the cell, ALA esters are rapidly hydrolysed by cellular esterases into free ALA acid which can then enter the metabolic pathway leading to the production of PpIX [4]. As displayed on figures 1 and 2, ALA hexylester resulted in the highest relatives fluorescence values whereas ALA-PEG-esters 4 and 5 are less efficient for the production of PpIX.
However, we carried out a premilary study of the ALA-PEG-esters toxicity
and first results demonstrated that these derivatives seem to be less cytotoxic
at high concentrations than corresponding alkyl esters.
9N-termnial protected peptide derivatives 8 was first studied and
directly used as a precursor of PPIX. However, we did not observe any formation
of PpIX. Using N-terminal deprotected peptide 9, the production of PPIX
was observed (Figure 3).
Figure 3
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