Experimental studies of the effects of ZnPcS2P2-based-photodynamic therapy on bone marrow purging

An effective purging technique plays an important role in autologous hematopoietic stem cells transplantation. Photodynamic therapy (PDT) provides a novel approach for this purpose. This study dealt with the purging effects of di-sulfo-di-phthalimidomethyl phthalolcyanine zinc (ZnPcS2P2)-based photodynamic therapy (ZnPc-PDT).

Fluorescence intensity of cell extracts was measured using a fluorescence spectrophotometry. The proliferative potency of K562 cells and HL60 cells was detected using MTT colorimetric assay, Typan blue dye exclusion method, colony formation test. The proliferative potency of normal hematopoietic cells was evaluated using mixture colony-forming unit (CFU-Mix), granulocyte-macrophage colony-forming unit (CFU-GM), and erythrocyte colony-forming unit (CFU-E) assays. K562 cells were mixed with normal mononuclear cells (MNCs) at ratios of 1:100 and 1:1000 for creating the model of simulated remission bone marrow. Colony formation test and nested-RT-PCR were carried out to detect the residual K562 cells in cell mixture.

After a 5-hour incubation with ZnPcS2P2, the content of ZnPcS2P2 in normal MNCs was the lowest value. At the same time, the content in K562 cells and HL60 cells was very high. Therefore, the time point was selected as the optimal one for irradiating the cell suspensions. ZnPc-PDT could significantly kill proliferative K562 cells and HL60 cells in a dose-dependent manner. At the concentration of 1.0 microg/ml, the inhibitory rate of ZnPc-PDT on the colony formation was 100% for K562 cells, 89.7% for HL60 cells. 0.25 microg/ml ZnPc-PDT could completely photoinactivate residual K562 cells in the simulated remission bone marrow. Under an identical condition, the inhibitory rates of CFU-Mix, CFU-GM, CFU-E were 18.0%, 18.6%, and 17.8% respectively.

ZnPc-PDT appears to be a promising approach for bone marrow purging.