A key point for successful
transplantation of autologous hematopoietic stem cells in the treatment of
leukemia is the purging technique, of which
photodynamic therapy (
PDT) proved effective and promising. The aim of this study was to evaluate the purging effect of a novel amphipathic
photosensitizer, di-sulfo-di-phthalimidomethyl phthalolcyanine
zinc (ZnPcS2P2)-based
PDT (ZnPcS2P2-PDT) on murine erythroblastic leukemic EL9611 cells. Bone marrow cells (BMC), harvested from normal BALB/c mice, were contaminated with variable EL9611 cells. Cell
suspensions were incubated with 4 microg/ml
ZnPcS2P2 for 5 h and then exposed to 2.1 J/cm2 irradiation by a
semiconductor laser 670 nm. Lethally irradiated recipient BALB/c mice (7 Gy) received syngeneic
bone marrow transplantation with purged or nonpurged cell mixtures of 10(7) BMC contaminated with variable numbers (10(2)-10(5)) of EL9611 cells. All of the irradiated controls died due to
sepsis. All of the mice injected with nonpurged cell mixtures developed
leukemia and died, whereas the mice transplanted with ZnPcS2P2-PDT-treated mixtures had a longer survival time, and the fewer leukemic cells there were in the cell mixtures, the higher the
leukemia-free survival rate. We conclude that ZnPcS2P2-PDT could purge leukemic cells from bone marrow autografts but could retain sufficient progenitor cells for the hematopoietic activity.