Tumor-localizing properties of porphyrins. In vitro studies using the porphyrin precursor, aminolevulinic acid, in free and liposome encapsulated forms.

Tumor, liver, skin and brain explants from tumor-bearing mice were cultured for 6, 12 and 22 hours in the presence of 0.06, 0.1 and 0.2 mM aminolevulinic acid (ALA). It was found that in all organs, synthesis of porphyrins increased with time and ALA concentration. The synthesising activity of tumor was high, of the same order as that of liver, and nearly twice that of skin and brain. The tissue/tumor porphyrin concentration ratios were lower than 0.5 at longer times and higher ALA concentration. In the case of skin/tumor the lowest ratio was about 0.2 and was obtained with 0.2 mM ALA. Chromatographic analysis of individual porphyrins showed that the whole heme pathway was functional in all organs studied, including tumor. Porphyrin synthesis by different organs from tumor bearing and normal mice was comparatively investigated using free and liposome encapsulated ALA. After 22 hours of incubation with 0.4 mM ALA, porphyrin formation was greater when encapsulated ALA was used. Accumulation of porphyrins in tumor was very high. The levels of activity were the same in each pair of organs in either the tumor-bearing mice or the control. These results indicate that free or encapsulated ALA may be used for the detection of tumors and in photodynamic therapy.