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

Clinical and experimental evidence of bcl-2 involvement in the response to photodynamic therapy

Purpose: The role of apoptosis related proteins in the response of human malignancies to photodynamic therapy (PDT) is under investigation. The aim of the study was to examine the role of p53 and of bcl-2 protein expression in the response to PDT. Materials and Methods: Paraffin-embedded material from 37 patients with early esophageal cancer treated with PDT (argon dye laser after intravenous injection of hematoporphyrine derivative) was studied immunohistochemically for p53 protein nuclear accumulation and bcl-2 cytoplasmic expression. Patients with residual disease after two rounds of PDT received definitive radiotherapy. In a subsequent in vitro study, W18 human lung fibroblasts and W138-SV-40 virus transformed were assessed for their sensitivity to PDT. The constitutive bcl-2 overexpression of the transformed cells vs. normal cells (assessed with RT-PCR) as 16-fold. Results: Positive bcl-2 and p53 expression was noted in 10 out of 36 (27%) and 14 out of 36 (39%) patients, respectively. Seven out of 11 tumors (63%) with bcl-2 expression responded completely to PDT vs. 6 out of 26 (23%) of cases with no bcl-2 expression (p=0.02). No association of p53, T-stage and of histology grade with response to PDT or PDT/RT was noted. The sensitivity to PDT of transformed human fibroblasts compared to normal ones was 4 times more at a fluence of 4.3 J/cm(2) (4% vs. 1% cell kill) as well as at a fluence of 5.4 J/cm(2) (8% vs. 2% cell kill). Conclusion: Bcl-2 protein expression is associated with favorable response to PDT and can be used as a predictor of cancer response to PDT. This finding can be explained by experimental studies showing that PDT induces selective degradation of the bcl-2 protein, leading to apoptosis by decreasing the bcl-2/bax ratio. Studies on PDT combination with agents targeting bcl-2 (i.e. taxanes) are on going to eventually assess a super-additive effect

Molecular effectors and modulators of hypericin-mediated cell death in bladder cancer cells

peer reviewedPhotodynamic therapy (PDT) is an anticancer approach utilizing a light-absorbing molecule and visible light irradiation to generate, in the presence of O(2), cytotoxic reactive oxygen species, which cause tumor ablation. Given that the photosensitizer hypericin is under consideration for PDT treatment of bladder cancer we used oligonucleotide microarrays in the T24 bladder cancer cell line to identify differentially expressed genes with therapeutic potential. This study reveals that the expression of several genes involved in various metabolic processes, stress-induced cell death, autophagy, proliferation, inflammation and carcinogenesis is strongly affected by PDT and pinpoints the coordinated induction of a cluster of genes involved in the unfolded protein response pathway after endoplasmic reticulum stress and in antioxidant response. Analysis of PDT-treated cells after p38(MAPK) inhibition or silencing unraveled that the induction of an important subset of differentially expressed genes regulating growth and invasion, as well as adaptive mechanisms against oxidative stress, is governed by this stress-activated kinase. Moreover, p38(MAPK) inhibition blocked autonomous regrowth and migration of cancer cells escaping PDT-induced cell death. This analysis identifies new molecular effectors of the cancer cell response to PDT opening attractive avenues to improve the therapeutic efficacy of hypericin-based PDT of bladder cancer