The low curative response to current treatment regimens for most soft tissue sarcomas indicates a strong need for alternative treatment strategies and predictive markers for treatment outcome. PCI (photochemical internalization) is a novel treatment strategy to translocate drugs into cytosol that otherwise would have been degraded in lysosomes. Two highly geno-and phenotypically different uterine and vulvar leiomyosarcoma cell lines, MES-SA and SK-LMS-1, were treated with bleomycin (BLM) activated by PCI (PCIBLM). The MES-SA cells were much more sensitive to PCIBLM than the SK-LMS-1 cells and the treatment induced a 7-8 fold higher increase in DNA double-strand breaks at the same dose of light as measure by γH2AX staining. A 3-fold higher induction of apoptosis and stronger activation of Bax and p21 was also measured in the P53WT MES-SA cells, compared to the P53mut SK-LMS-1 cells. The basal formation of reactive oxygen species (ROS) was 3-fold higher in SK-LMS-1 cells than in the MES-SA cells and SK-LMS-1 cells expressed glutathione peroxidase 1 (GPx1) and more superoxide dismutase 2 (SOD2) than the MES-SA cells. Glutathione depletion with the glutathione synthetase inhibitor buthionine sulfoximine increased the cytotoxic effect of the photochemical treatment (PDT) most strongly in the SK-LMS-1 cells, and reduced PCIBLM-induced H2AX activation in the MES-SA cells, but not in the SK-LMS-1 cells. The results indicate PCIBLM as a potential novel treatment strategy for soft tissue sarcomas, with antioxidant enzymes, in particular GPx1, and the P53 status as potential predictive markers for response to PCIBLM.
Keywords: Bleomycin; Glutathione; Photochemical internalization; Photodynamic; Reactive oxygen species; Resistance; Sarcoma; γH2AX.
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