Induction of Immune Mediators in Glioma and Prostate Cancer Cells by Non-Lethal Photodynamic Therapy

BACKGROUND: Photodynamic therapy (PDT) uses the combination of photosensitizing drugs and harmless light to cause selective damage to tumor cells. PDT is therefore an option for focal therapy of localized disease or for otherwise unresectable tumors. In addition, there is increasing evidence that PDT can induce systemic anti-tumor immunity, supporting control of tumor cells, which were not eliminated by the primary treatment. However, the effect of non-lethal PDT on the behavior and malignant potential of tumor cells surviving PDT is molecularly not well defined. METHODOLOGY/PRINCIPAL FINDINGS: Here we have evaluated changes in the transcriptome of human glioblastoma (U87, U373) and human (PC-3, DU145) and murine prostate cancer cells (TRAMP-C1, TRAMP-C2) after non-lethal PDT in vitro and in vivo using oligonucleotide microarray analyses. We found that the overall response was similar between the different cell lines and photosensitizers both in vitro and in vivo. The most prominently upregulated genes encoded proteins that belong to pathways activated by cellular stress or are involved in cell cycle arrest. This response was similar to the rescue response of tumor cells following high-dose PDT. In contrast, tumor cells dealing with non-lethal PDT were found to significantly upregulate a number of immune genes, which included the chemokine genes CXCL2, CXCL3 and IL8/CXCL8 as well as the genes for IL6 and its receptor IL6R, which can stimulate proinflammatory reactions, while IL6 and IL6R can also enhance tumor growth. CONCLUSIONS: Our results indicate that PDT can support anti-tumor immune responses and is, therefore, a rational therapy even if tumor cells cannot be completely eliminated by primary phototoxic mechanisms alone. However, non-lethal PDT can also stimulate tumor growth-promoting autocrine loops, as seen by the upregulation of IL6 and its receptor. Thus the efficacy of PDT to treat tumors may be improved by controlling unwanted and potentially deleterious growth-stimulatory pathways

Molecular architecture of potassium chloride co-transporter KCC2

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Dynamic ABCG2 expression in human embryonic stem cells provides the basis for stress response

ABCG2 is a plasmamembrane multidrug transporter with an established role in the cancer drug resistance phenotype. This protein is expressed in various tissues, including several types of stem cells. Although ABCG2 is not essential for life, knock-out mice were found to be hypersensitive to xenobiotics and had reduced levels of the side population of hematopoietic stem cells. Previously we have shown that ABCG2 is present in human embryonic stem cell (hESC) lines while exhibiting a heterogeneous expression pattern. In the present study we examined the role and function of this heterogeneity, and investigated whether it is related to stress responses in hESCs. We did not find any difference between the expression of pluripotency markers in ABCG2 positive and negative hESCs, however, ABCG2 expressing cells had a higher growth rate following cell separation. We found that certain harmful conditions (physical stress, drugs and UV light exposure) are tolerated much better in the presence of ABCG2 protein. This property can be explained by the transporter function which eliminates potential toxic metabolites accumulated during stress conditions. In contrast, mild oxidative stress in hESCs caused a rapid internalization of ABCG2, indicating that certain environmental factors may induce the removal of this transporter from the plasmamembrane. In the light of these results we suggest that a dynamic balance of ABCG2 expression at the population level has an advantage to promptly respond to changes in the cellular environment. Such an actively maintained heterogeneity might be evolutionarily favorable to protect special cell types, including pluripotent stem cells