Comparison of the Cytotoxic Effects of Merocyanine-540 on Leukemic Cells and Normal Human Bone Marrow1

Various chemical compounds have been described to induce photosensitization of tumor cells resulting in cell death. We studied the effect of merocyanine-540 (MC-540) on both leukemic and normal bone marrow (BM) cells. Acute promyelocytic leukemia (HL-60) and common acute lymphoblastic leukemia antigen-positive nun-1, non-B acute lymphoblastic leukemia (Reh) cell lines were incubated with MC-540 and simulta neously exposed to white light. Normal human BM and mixtures of leukemic cells with BM cells were treated under similar conditions. At constant illumination rates of 50,000 Ix, significant (at least 4 to 5 logs) tumor cell destruction was obtained with MC-540 concentrations of 20 «ig/mlor more for HL-60, and 10 MÕ/nil or more for Reh cells. Incubation of BM under equivalent conditions preserved 18.0% of granulocytemacrophage colony-forming units and 14.2% of erythroid burst-forming units. Similar results were obtained when tumor cells were mixed with irradiated BM and then treated with MC-540. In summary, cell photosensitization with MC-540 has a selective cytotoxic effect towards leu kemic cells and therefore may be useful for purging tumor cells from