PHOTODYNAMIC-ACTION OF ENDOGENOUSLY SYNTHESIZED PORPHYRINS FROM AMINOLEVULINIC ACID, USING A NEW MODEL FOR ASSAYING THE EFFECTIVENESS OF TUMORAL CELL-KILLING

1. The effectiveness of the photodynamic action of porphyrins, was stu died by means of the tissue explant culture technique. A murine tumor tissue explant was incubated in a medium containing 0.6 mM of ALA for periods of 1 and 2 hr, total porphyrins synthesized under these condit ions were of the same level as those found in our previous in vivo exp eriments. The explants were then irradiated for 30 min with He-Ne lase r of 3.5 mW output power placed at a distance of 10 cm. Controls of no n-irradiated tumor tissue slices incubated with and without ALA were p erformed. Immediately after irradiation, innocula of exactly 1 mm3 of the irradiated and non-irradiated tissue were subcutaneously injected under the right and left flanks of the same animal, respectively. The growth of the tumor was measured 15, 20 and 25 days after implantation . 2. Results obtained showed that the explants that were incubated for 1 hr with ALA and irradiated, reaching a concentration of 2.8 mug por phyrins/g tissue, produced a reduction of 50-70% of tumor size as comp ared with the non-irradiated controls incubated with ALA. Explants inc ubated for 2 hr, reaching a concentration of 4.6 mug porphyrins/g tiss ue, produced from 60% to complete lack of tumor growth. The effectiven ess index (EI) of photoirradiation was calculated on the basis of the tumor growth in irradiated and non-irradiated tumors. El was nearly 10 0% showing almost complete tumor cell destruction for tumor irradiated for 2 hr with 0.6 mM ALA. 3. As indicators of cell injury and subsequ ent death and necrosis, LDH activity in the incubation medium and intr acellular potassium content were measured. Results indicated that as a consequence of irradiation of porphyrin loaded tumor explants, signif icant release of LDH to the medium and loss of intracellular potassium occurred. These findings show great to complete tumor destruction by combination of porphyrins endogenously formed from ALA and low irradia nce with laser.