BACKGROUND: Since photodynamic treatment (PDT) induces apoptosis in individual HL-60 cells originating from early granulocytic precursors of acute myeloid leukemia, the present study was undertaken to provide information on such treatment of K562 cells, which originate from early granulocytic precursors of chronic myeloid leukemia (blastic phase) and carry the bcr/abl fusion gene with anti-apoptotic properties. MATERIAL/METHODS: PDT was based on the 5-aminolevulinic acid treatment of K562 cells, followed by blue light irradiation under conditions which in HL-60 cells induce an apoptotic process without previous terminal maturation. Nuclei and nucleoli were visualized by cytochemical procedures to demonstrate DNA, RNA and silver stained proteins of nucleolus organizer regions (AgNORs). TUNEL and propidium iodide assays were used for additional control of the incidence of apoptotic and necrotic cells. RESULTS: In contrast to HL-60 cells, PDT did not induce apoptosis in K562 cells. However, after PDT some K562 cells exhibited major alterations, expressed by nuclear and cell swelling, reflecting a necrotic process, confirmed by propidium iodide. In addition, PDT produced a reduction of AgNORs, though smaller than that previously described in apoptotic HL-60 cells. CONCLUSIONS: PDT produced only necrotic changes in some K562 cells under conditions which induced in apoptosis in HL-60 cells. Thus the induction of apoptosis, nuclear and nucleolar changes in individual cells does not depend on the inducer--PDT--but on the cell properties.

Keywords: Cell Nucleolus - drug effects, Cell Nucleolus - ultrastructure, Cell Nucleus - drug effects, Aminolevulinic Acid - pharmacology, Cell Nucleolus - ultrastructure, Cell Nucleus - ultrastructure, Chromatin - ultrastructure, HL-60 Cells, K562 Cells, Leukemia, Myelogenous, Chronic, BCR-ABL Positive - pathology, Mitosis - drug effects, Necrosis, Photosensitizing Agents - pharmacology, Stem Cells - drug effects