Does Hypericum perforatum L. extract show any specificity as photosensitizer for HL-60 leukemic cells and cord blood hemopoietic progenitors during photodynamic therapy?
Autologous bone marrow transplantation is a therapeutic modality that increases the survival rates for children with malignancies with poor prognosis but relapse rates are high and attributed partially to the existence of residual malignant cells. Photodynamic treatment (PDT) has been developed among purging strategies. We investigated the effect of the methanolic extract (ME) and its polar methanolic fraction (PMF) of Hypericum perforatum L., as a new photosensitizer for the leukemic cell line HL-60 and cord blood (CB) hemopoietic progenitors as well as the subcellular localization of the photosensitizer.


METHODS
ME and PMF were prepared after extraction of the dry herb with methanol (ME), followed by liquid-liquid extraction with petroleum ether (PMF). Cells were incubated with the extracts before irradiation with Nd-Yvo Laser. Various concentrations of PMF or ME as well as irradiation doses were tested. Following irradiation, cell viability was determined by trypan blue in continuous liquid cultures for HL-60 cells and in clonogenic assays for CB cells. The subcellular localization of the photosensitizer was determined by confocal microscopy.


RESULTS
Laser photoirradiation in the presence of both PMF and ME induces the killing of HL-60 cells. This effect is dose dependent. No CFU-GM and BFU-E growth was observed from CB mononuclear cells under the tested experimental conditions. Confocal microscopy revealed that the extracts localize mainly in the cytoplasm of the cells.


CONCLUSIONS
PDT with both PMF and ME induces the killing of HL-60 leukemic cells and the optimal conditions of treatment were determined. This effect of PDT/PMF was also exerted on CB progenitor cells indicative of the non-selective uptake of the photosensitizer by malignant cells. Though this suggests that PDT/PMF cannot be helpful in autologous bone marrow purging, these novel extracts can however be beneficial in the PDT treatment of tumors given their photostability, low toxicity and low cost.
Department of Pediatric Hematology/Oncology, University of Crete, Medical School, P.O. Box 2208, 71003 Heraklion Crete, Greece. dikapso@yahoo.com
D
D
Kapsokalyvas
H
H
Dimitriou
D
D
Skalkos
G
G
Konstantoudakis
G
G
Filippidis
E
E
Stiakaki
Th
T
Papazoglou
M
M
Kalmanti
D018922:HL-60 Cells / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000187:drug effects; D006801:Humans; D020902:Hypericum; D010778:Photochemotherapy; D008517:Phytotherapy; D010936:Plant Extracts / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
D010936:Plant Extracts; D011838:Radiation-Sensitizing Agents