[Effect of zinc phthalocyanine-mediated photodynamic therapy on bone marrow purging, an experimental study].

OBJECTIVE

To probe into the purging effects of zinc phthalocyanine-mediated photodynamic therapy (PDT) on simulated remission bone marrow grafts of chronic granulocytic leukemia.

METHODS

(1) K562 cells, aline chronic granulocytic leukemia cells, and normal mononuclear cells (MNC) were cultured. Zinc phthalocyanine (ZnPcS(2)P(2)), a photosensitizer, with the terminal concentration of 1.0 micro g/ml was added into the cultures. The K562 cells and normal MNCs in the suspensions were broken. Fluorescence spectrophotometry was used to determine the concentration of zinc phthalocyanine in cells at different time points so as to find the optimal time for photodynamic purging process. (2) Suspensions of K562 cells and MNCs were made and incubated with zinc phthalocyanine of different concentrations (0.062 5, 0.125, 0.25, 0.5, and 1.0 micro g/ml) for 5 hours. A blank control group (sodium chloride of the same volume was added), a PDT control group (without photosensitizer), and a photosensitizer control group (zinc phthalocyanine was added without PDT) were established. Then the suspensions were irradiated with 670 nm laser. Trypan blue dye exclusion technique was used to calculate the number of live cells for a period of 5 days. The proliferative potency of K562 cells was detected by MTT colorimetric assay. The OD value was detected with ELISA apparatus to calculate the inhibition rate. Colony formation of K562 cells and MNCs was determined. (3) K562 cells were mixed into normal MNCs at the ratios of 1:100 and 1:1,000 so as to create the model of simulated remission bone marrow. After PDT treatment, colony formation test was done and nested-PCR was used to detect the bcr-abl mRNA expression in K562 cells. Colony formation test was made on the MNCs treated with PDT. The antiproliferative effects of PDT on normal hematopoietic progenitors were evaluated by CFU-Mix, CFU-GM and CFU-E assays.

RESULTS

(1) The zinc phthalocyanine content in the MNCs reached its peak within the first hour of incubation and then rapidly decreased to the lowest value in 4 hours. However, the zinc phthalocyanine content in the K562 cells gradually increased within the first 4 hours of incubation and reached its peak by the fifth hour with a ratio of zinc phthalocyanine content in K562 cells to that in MNCs of 4.59. Therefore, the fifth hour after incubation was selected as the optimal time to irradiate the suspensions using the laser with a wavelength of 670 nm. (2) The inhibitory rate of laser on the colony information rate was 91.1% for the K562 cells, 18.0% for the MNCs in CFU-Mix methyl cellulose culture system, 18.6% for the MNCs in CFU-GM methyl cellulose culture system, and 17.8% for the MNCs in CFU-E methyl cellulose culture system At the concentration of 0.25 micro g/ml, K562 cells were inhibited by 91.1%, however, CFU-Mix, CFU-GM and CFU-E were relatively spared, inhibitory rate being 18.0%, 18.6% and 17.8% respectively. (3) At the concentration of 0.25 micro g/ml, residual K562 cells in the simulated remission bone marrow were completely photoinactivated.

CONCLUSION

Zinc phthalocyanine -based PDT selectively kills K562 cells. It would be a promising purging technique for chronic granulocytic leukemia.