Destruction of erythroleukemia, myelocytic leukemia and Burkitt lymphoma cells by photoactivated protoporphyrin.

The effect of protoporphyrin on erythroid, myeloid and lymphoid leukemic cells and their destruction induced by the photoactivated porphyrin was studied. Friend erythroleukemic cells (FL) and myelocytic leukemic cells (ML) accumulated protoporphyrin in a cap or patch-like pattern observed by fluorescence microscopy. Photoactivated protoporphyrin induced the appearance of "holes" on the cell membrane demonstrated by scanning electron microscopy. On the other hand, Burkitt lymphoma (BL) and mastocytoma (MS) cells accumulated porphyrin intracellularly around the nuclear envelope and as circular profiles, respectively. Photoactivated protoporphyrin induced development of multiple blebs on the cell membrane, and even complete cell destruction. Cytotoxicity of protoporphyrin at short-term incubation periods was determined by [3H]thymidine and [3H]uridine incorporation. Protoporphyrin, unexposed to light, reduced the incorporation of both precursors only to a moderate extent. On the other hand, porphyrin-treated cells exposed to light showed complete inhibition of RNA and DNA synthesis. Long-term exposure of ML and BL cells to porphyrin in the dark induced a nearly 50% inhibition of RNA and DNA synthesis. Although the cytotoxic effect of protoporphyrin in the dark was lower than that of photoactivated porphyrin, this may possess a potential activity in vivo even without illumination.