Radiation-induced Immune Suppression Research Articles

Predicting radiation-induced immune suppression in lung cancer patients treated with stereotactic body radiation therapy.

Stereotactic body radiation therapy (SBRT) is known to modulate the immune system and contribute to the generation of anti-tumor T cells and stimulate T cell infiltration into tumors. Radiation-induced immune suppression (RIIS) is a side effect of radiation therapy that can decrease immunological function by killing naive T cells as well as SBRT-induced newly created effector T cells, suppressing the immune response to tumors and increasing susceptibility to infections. RIIS varies substantially among patients and it is currently unclear what drives this variability. Models that can accurately predict RIIS in near real time based on treatment plan characteristics would allow treatment planners to maintain current protocol specific dosimetric criteria while minimizing immune suppression. In this paper, we present an algorithm to predict RIIS based on a model of circulating blood using early stage lung cancer patients treated with SBRT. This Python-based algorithm uses DICOM data for radiation therapy treatment plans, dose maps, patient CT data sets, and organ delineations to stochastically simulate blood flow and predict the doses absorbed by circulating lymphocytes. These absorbed doses are used to predict the fraction of lymphocytes killed by a given treatment plan. Finally, the time dependence of absolute lymphocyte count (ALC) following SBRT is modeled using longitudinal blood data up to a year after treatment. This model was developed and evaluated on a cohort of 64 patients with 10-fold cross validation. Our algorithm predicted post-treatment ALC with an average error of cells/L with 89% of the patients having a prediction error below 0.5×109 cells/L. The accuracy was consistent across a wide range of clinical and treatment variables. Our model is able to predict post-treatment ALC<0.8 (grade 2 lymphopenia), with a sensitivity of 81% and a specificity of 98%. This model has a ∼38-s end-to-end prediction time of post treatment ALC. Our model performed well in predicting RIIS in patients treated using lung SBRT. With near-real time model prediction time, it has the capability to be interfaced with treatment planning systems to prospectively reduce immune cell toxicity while maintaining national SBRT conformity and plan quality criteria.

Inhibition of UVB radiation-induced tissue swelling and immune suppression by nicotinamide riboside and pterostilbene.

Environmental ultraviolet radiation has deleterious effects on humans, including sunburn and immune perturbations. These immune changes are involved in skin carcinogenesis. To determine whether nicotinamide riboside and/or pterostilbene administered systemically inhibits inflammatory and immune effects of exposure to mid-range ultraviolet radiation. To examine UVB radiation-induced inflammatory effects, mice were fed standard chow/water, 0.04% pterostilbene in chow and 0.2% nicotinamide riboside in drinking water, diet with nicotinamide riboside alone, or diet with pterostilbene alone. After 4 weeks, mice were exposed to UVB radiation (3500 J/m2), and 24-/48-h ear swelling was assessed. We also asked if each agent or the combination inhibits UVB radiation suppression of contact hypersensitivity in two models. Mice were fed standard diet/water or chow containing 0.08% pterostilbene, water with 0.4% nicotinamide riboside, or both for 4 weeks. Low-dose: Half the mice in each group were exposed on the depilated dorsum to UVB radiation (1700 J/m2) daily for 4 days, whereas half were mock-irradiated. Mice were immunized on the exposed dorsum to dinitrofluorobenzene 4 h after the last irradiation, challenged 7 days later on the ears with dinitrofluorobenzene, and 24-h ear swelling assessed. High dose: Mice were treated similarly except that a single dose of 10,000 J/m2 of radiation was administered and immunization was performed on the unirradiated shaved abdomen 3 days later. Nicotinamide riboside and pterostilbene together inhibited UVB-induced skin swelling more than either alone. Pterostilbene alone and both given together could inhibit UVB-induced immune suppression in both the low-dose and high-dose models while nicotinamide riboside alone was more effective in the low-dose model than the high-dose model. Nicotinamide riboside and pterostilbene have protective effects against UVB radiation-induced tissue swelling and immune suppression.

619 CP31398, which reverses UV-induced p53 mutations, does not undo ultraviolet radiation-induced immune suppression

Chronic, excessive exposure to solar ultraviolet radiation is the major causative agent for cutaneous squamous cell carcinomas. Mutations in p53 are essential for these cancers to develop. UV radiation is also immunosuppressive and is an additional requirement for UV-induced SCCs to develop. Mutations in p53 can be reversed with the compound CP31398, which results in fewer SCCs in mice exposed to a UV radiation skin carcinogenesis protocol. It is unknown whether p53 mutations contribute to photoimmunosuppression. The purpose of this study was to determine if the UV immunosuppressive effects could be reversed by pretreatment with CP31398. A local UVB regimen consisting of UVB radiation (200 mJ/cm2) for 4 days followed by sensitization with the hapten 2, 4, dinitrofluorobenzene (DNFB) was employed for photoimmunosuppression. To determine the role of CP-31398, we treated the shaved dorsal skin of C57BL/6 mice with CP-31398 (1.25 mg/mouse) or vehicle cream, 30 min before each UVB treatment. Treatment with CP-31398 did not abrogate the immunosuppressive effect of UV. These findings suggest that although p53 mutations are responsible for UV-induced SCCs, they are not necessary for UV-induced immunosuppression.

Reversing radiation-induced immunosuppression using a new therapeutic modality

Radiation-induced immune suppression poses significant health challenges for millions of patients undergoing cancer chemotherapy and radiotherapy treatment, and astronauts and space tourists travelling to outer space. While a limited number of recombinant protein therapies, such a Sargramostim, are approved for accelerating hematologic recovery, the pronounced role of granulocyte-macrophage colony-stimulating factor (GM-CSF or CSF2) as a proinflammatory cytokine poses additional challenges in creating immune dysfunction towards pathogenic autoimmune diseases. Here we present an approach to high-throughput drug-discovery, target validation, and lead molecule identification using nucleic acid-based molecules. These Nanoligomer™ molecules are rationally designed using a bioinformatics and an artificial intelligence (AI)-based ranking method and synthesized as a single-modality combining 6-different design elements to up- or downregulate gene expression of target gene, resulting in elevated or diminished protein expression of intended target. This method additionally alters related gene network targets ultimately resulting in pathway modulation. This approach was used to perturb and identify the most effective upstream regulators and canonical pathways for therapeutic intervention to reverse radiation-induced immunosuppression. The lead Nanoligomer™ identified in a screen of human donor derived peripheral blood mononuclear cells (PBMCs) upregulated Erythropoietin (EPO) and showed the greatest reversal of radiation induced cytokine changes. It was further tested in vivo in a mouse radiation-model with low-dose (3 mg/kg) intraperitoneal administration and was shown to regulate gene expression of epo in lung tissue as well as counter immune suppression. These results point to the broader applicability of our approach towards drug-discovery, and potential for further investigation of our lead molecule as reversible gene therapy to treat adverse health outcomes induced by radiation exposure.

PTEN: A novel target for vitamin D in melanoma

Melanoma is the most dangerous form of skin cancer, with poor prognosis in advanced stages. Vitamin D, also produced by ultraviolet radiation, is known for its anti-proliferative properties in some cancers including melanoma. While vitamin D deficiency has been associated with advanced melanoma stage and higher levels of vitamin D have been associated with better outcomes, the role for vitamin D in melanoma remains unclear. Vitamin D synthesis is initiated upon UVB exposure of skin cells and results in formation of the active metabolite 1,25-dihydroxyvitamin D3 (1,25D). We have previously demonstrated that 1,25D plays a role in protection against ultraviolet radiation-induced DNA damage, immune suppression, and skin carcinogenesis. In this study 1,25D significantly reduced cell viability and increased caspase levels in human melanoma cell lines. This effect was not present in cells that lacked both phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a well-known tumour suppressor, and the vitamin D receptor (VDR). PTEN is frequently lost or mutated in melanoma. Incubation of selected melanoma cell lines with 1,25D resulted in significant increases in PTEN levels and downregulation of the AKT pathway and its downstream effectors. This suggests that 1,25D may act to reduce melanoma cell viability by targeting PTEN.

Local Interleukin-12 Treatment Enhances the Efficacy of Radiation Therapy by Overcoming Radiation-Induced Immune Suppression.

Radiation therapy (RT) recruits myeloid cells, leading to an immunosuppressive microenvironment that impedes its efficacy against tumors. Combination of immunotherapy with RT is a potential approach to reversing the immunosuppressive condition and enhancing tumor control after RT. This study aimed to assess the effects of local interleukin-12 (IL-12) therapy on improving the efficacy of RT in a murine prostate cancer model. Combined treatment effectively shrunk the radioresistant tumors by inducing a T helper-1 immune response and influx of CD8+ T cells. It also delayed the radiation-induced vascular damage accompanied by increased α-smooth muscle actin-positive pericyte coverage and blood perfusion. Moreover, RT significantly reduced the IL-12-induced levels of alanine aminotransferase in blood. However, it did not further improve the IL-12-induced anti-tumor effect on distant tumors. Upregulated expression of T-cell exhaustion-associated genes was found in tumors treated with IL-12 only and combined treatment, suggesting that T-cell exhaustion is potentially correlated with tumor relapse in combined treatment. In conclusion, this study illustrated that combination of radiation and local IL-12 therapy enhanced the host immune response and promoted vascular maturation and function. Furthermore, combination treatment was associated with less systemic toxicity than IL-12 alone, providing a potential option for tumor therapy in clinical settings.

Abstract 524: HMGB1-activated IRF3 and NF-κB contributes to UV radiation-induced immune suppression by upregulating PD-L1

Abstract Solar ultraviolet radiation (UVR) suppresses skin immunity, which facilitates skin lesion initiation and establishment by promoting immune evasion. It is unclear whether immune checkpoints are involved in the modulation of skin immunity by UVR. Here we report that the expression of immune checkpoint molecule PD-L1 was significantly increased in melanocytes and melanoma cells upon UVR exposure. The damage-associated molecular patterns molecule HMGB1 was secreted by melanocytes and keratinocytes upon UVR, which subsequently activated the RAGE (receptor for advanced glycation endproducts) receptor to promote the NF-κB and IRF3-dependent transcription of PD-L1 in melanocytes. We also found that UVR exposure significantly reduced the susceptibility of melanoma cells to CD8+ T cell-dependent cytotoxicity, which was mitigated by inhibiting the HMGB1/TBK1/IRF3/NF-κB cascade or blocking the PD-1/PD-L1 checkpoint. Taken together, our findings demonstrate that UVR-induced PD-L1 upregulation contributes to the immune suppression in the skin microenvironment, which may promote immune evasion of oncogenic cells, and melanoma initiation and progression. Citation Format: Wei Wang, Nicole Chapman, Bo Zhang, Mingqi Li, Meiyun Fan, R. Nicholas Laribee, M. Raza Zaidi, Lawrence Pfeffer, Hongbo Chi, Zhaohui Wu. HMGB1-activated IRF3 and NF-κB contributes to UV radiation-induced immune suppression by upregulating PD-L1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 524.

Upregulation of PD-L1 via HMGB1-Activated IRF3 and NF-κB Contributes to UV Radiation-Induced Immune Suppression.

Solar ultraviolet radiation (UVR) suppresses skin immunity, which facilitates initiation of skin lesions and establishment of tumors by promoting immune evasion. It is unclear whether immune checkpoints are involved in the modulation of skin immunity by UVR. Here, we report that UVR exposure significantly increased expression of immune checkpoint molecule PD-L1 in melanoma cells. The damage-associated molecular patterns molecule HMGB1 was secreted by melanocytes and keratinocytes upon UVR, which subsequently activated the receptor for advanced glycation endproducts (RAGE) receptor to promote NF-κB- and IRF3-dependent transcription of PD-L1 in melanocytes. UVR exposure significantly reduced the susceptibility of melanoma cells to CD8+ T-cell-dependent cytotoxicity, which was mitigated by inhibiting the HMGB1/TBK1/IRF3/NF-κB cascade or by blocking the PD-1/PD-L1 checkpoint. Taken together, our findings demonstrate that UVR-induced upregulation of PD-L1 contributes to immune suppression in the skin microenvironment, which may promote immune evasion of oncogenic cells and drive melanoma initiation and progression. SIGNIFICANCE: These findings identify PD-L1 as a critical component of UV-induced immune suppression in the skin, which facilitates immunoevasion of oncogenic melanocytes and development of melanoma.See related commentary by Sahu, p. 2805.

Abstract 2763: Tryptophan metabolism contributes to radiation-induced immune checkpoint reactivation in glioblastoma

Abstract Glioblastoma (GBM) is an aggressive brain tumor with limited treatment options. Immune checkpoint inhibitors designed to revert tumor-induced immune suppression have emerged as potent anti-cancer therapies. We performed cross-platform analyses coupling global metabolomic and gene-expression profiling in patient-derived gliomas. We identified aberrant tryptophan metabolism as a metabolic node in glioblastoma, which represents an emerging immune checkpoint. Specifically, GBM demonstrated an accumulation of tryptophan and kynurenine when compared to low-grade glioma (LGG), while kynurenate, a metabolite immediately downstream of kynurenine, was significantly lower in glioblastoma, resulting kynurenine/kynurenate ratio demonstrating &amp;gt;90% accuracy in discriminating between GBM and LGG. These metabolic findings were corroborated by increased expression of indoleamine-2,3-dioxygenase-1 (IDO1) in GBM, a key enzyme involved in tryptophan metabolism and kynurenine production. Cross-platform analysis using gene expression arrays allowed for molecular subtyping of GBM, demonstrated that aberrant tryptophan metabolism was specific to classical and mesenchymal subtypes, while kynurenate accumulation, the metabolite elevated in LGG, was only evident in the proneural subtype. This metabolic phenotype was recapitulated in GBM preclinical models, which demonstrated robust IFNγ-induced IDO1 pathway activation and kynurenine production. The novel IDO1 inhibitor GDC-0919 demonstrated potent inhibition of tryptophan metabolism in our model and importantly, effectively crossed the blood-brain barrier. To explore the immune consequence of aberrant tryptophan metabolism in GBM, we extended investigations to an adult astrocytic, genetically engineered mouse (GEM) cell line to allow for in vivo studies using immune competent mice. Using this orthotopic mouse model, we demonstrated that although GDC-0919 as a single agent did not have anti-tumor activity, it had strong potential for enhancing radiation response in glioblastoma, which was further augmented when using a hypofractionated regimen. The immunological evaluation demonstrated that radiation response in glioblastoma involves immune stimulation, reflected by an increase in activated and cytotoxic T-cells, which is balanced by immune checkpoint reactivation, reflected by an increase in IDO1 expression and immunosuppressive regulatory T cells. GDC-0919 mitigated radiation-induced immune suppression and enhanced immune activation. These findings support clinical efforts designed to combine IDO1 inhibition with hypofractionated radiation in glioblastoma, offering the promise of harnessing a patient's immune system to attack these otherwise recalcitrant tumors. Citation Format: Pravin Kesawani, Antony Prabhu, Shiva Kant, Praveen Kumar, Stewart F. Graham, Katie Buelow, George Wilson, C Ryan Miller, Prakash Chinnaiyan. Tryptophan metabolism contributes to radiation-induced immune checkpoint reactivation in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2763.

Immune modulatory properties of radiotherapy

Radiotherapy (RT) is a common treatment for cancer and about 60% of all cancer patients will receive it during their course of illness. RT primarily aims to achieve local tumor control. The induction of DNA damage by reactive oxygen species (ROS), tumor cell death and the modulation of the tumor microenvironment are the main effects of ionizing irradiation to reduce tumor masses, but also to modulate the immune system. RT might thereby act as an in situ cancer vaccine under certain microenvironmental conditions. However, RT also fosters the upregulation of immune suppressive molecules such as immune checkpoint molecules. The presentation will focus on how local irradiation changes the tumor cell phenotype and the tumor microenvironment and consecutively does impact on local and systemic changes in immune cell compositions. In particular the impact of ROS, danger signals and cytokines on it will be outlined. The dynamics of immune changes, the radiosensitivity of distinct immune cells as well as biological basis for reasonable combination of RT with immune stimulation will be discussed in detail, as well as how radiation-induced immune suppression can be overcome. Based on the pre-clinical knowledge, innovative clinical study concepts of radio-immune treatments will be presented.

Radioprotective effect of green tea and grape seed extracts mixture on gamma irradiation induced immune suppression in male albino rats

Purpose: Green tea extract (GTE) and grape seed extract (GSE) have antioxidant and radioprotective effects. The current study aimed to investigate the radioprotective effect of GTE and GSE mixture on radiation-induced immune suppression in rats.Method: A total of 35 male albino rats were divided into five groups: group 1 (control rats). The 2nd and 3rd groups rats were exposed to a single dose of gamma radiation (5 and 10 Gy), respectively. The 4th and 5th groups of rats were gamma-irradiated with 5 and 10 Gy, respectively, then administrated by gavage with GTE and GSE mixture (100 mg: 200 mg/kg BW), respectively, for 14 consecutive days.Results: Gamma irradiation induced hematological, immunological and biochemical effects in rats. Treated rats with GTE and GSE mixture (1:2) showed an increase in concentrations of immune cells including CD4 and CD8. The level of pro-inflammatory cytokines Tumor necrosis factor-α and C-reactive protein elevated after γ-irradiation and significantly decreased by mixture administration. Moreover, groups treated with antioxidant mixture showed a significant increase in all hematological parameters and a significant decrease in cholesterol and triglyceride levels.Conclusion: GTE and GSE mixture is a good radioprotector and immune modulator compound, indicating its possible use as an adjuvant during radiotherapy.

Abstract 2607: Honokiol, a phytochemical from magnolia plant, prevents UV radiation-induced immune suppression in mice through inhibition of PGE2 and DNA methylation

Abstract The exposure of ultraviolet radiation (UVR) to murine skin suppresses the development of allergic contact hypersensitivity (CHS) response which is considered to be a prototypic T-cell mediated immune response. UVR-induced suppression of immune system has been implicated in skin cancer risk. Honokiol has been shown to have anti-skin carcinogenic activity, and here we have assessed the effect of honokiol on UVR-induced immunosuppression and its possible mechanism of action. Our CHS experiments revealed that exposure of C3H/HeN mouse skin with UVB radiation (150 mJ/cm2) for 4 consecutive days resulted in significant suppression of CHS response (75%, P&amp;lt;0.001) to the skin contact sensitizer, 2,4-dinitrofluorobenzene (DNFB), which was associated with the enhancement in the levels of cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE2) production. Topical treatment of mice with honokiol (0.5 and 1.0 mg/cm2 skin area) in hydrophilic-cream based topical formulation or indomethacin (50 μg/mouse), a COX-2 inhibitor, significantly inhibits UV radiation-induced suppression of CHS response (P&amp;lt;0.01-0.005). The exposure of mice with UVB resulted in DNA hypermethylation, increase in DNA methyltransferase (Dnmt) activity, and elevated levels of Dnmt proteins in mouse skin, while treatment of mice with honokiol before each UVB exposure reduced the levels of DNA methylation as well as Dnmt activity compared with non-honokiol-treated control mice. The COX-2 deficient mice are resistant to UV-induced suppression of CHS response. Treatment of UVB exposed COX-2-deficient mice with PGE2 (50 μg/mouse/day) results in UV-induced suppression of CHS, increase in DNA methylation and Dnmt activity in the skin. Further, treatment of honokiol reversed the effect of PGE2 on UV-induced suppression of CHS response in COX-2-deficient mice. Treatment of C3H/HeN mice with 5-aza-2’-deoxycytidine (5-Aza-dc, 1.0 mg/kg body weight, i.p.), a DNA demethylating agent, after each UVB exposure restored the CHS response which was associated with a reduction in Dnmt activity and global DNA methylation levels compared to the UV-exposed mice which were not treated with 5-Aza-dc. We also compared the effect of honokiol with commercially available anti-cancer drugs, such as imiquimod and 5-fluorouracil, on CHS response in UV-exposed mice. Topical treatment of mice with equi-molar concentrations of honokiol and cancer drugs did not show significant difference in terms of inhibition of UVB induced immune suppression and thus suggests honokiol as a substitute for these drugs. These findings provide evidence that honokiol acts through inhibition of inflammatory mediators and subsequently DNA demethylation in UVR-exposed mouse skin. Citation Format: Santosh K. Katiyar, Tripti Singh, Ram Prasad. Honokiol, a phytochemical from magnolia plant, prevents UV radiation-induced immune suppression in mice through inhibition of PGE2 and DNA methylation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2607.

Platelet-Activating Factor Induces Epigenetic Modifications in Human Mast Cells

Ultraviolet (UV) radiation-induced systemic immune suppression is a major risk factor for skin cancer induction. The migration of dermal mast cells from the skin to the draining lymph nodes plays a prominent role in activating systemic immune suppression. UV-induced keratinocyte-derived platelet-activating factor (PAF) activates mast cell migration, in part by up regulating the expression of CXCR4 on the surface of mast cells. Others have indicated that epigenetic mechanisms regulate CXCR4 expression, so we asked whether PAF activates epigenetic mechanisms in mast cells. Human mast cells were treated with PAF and the effect on DNA methylation and/or acetylation was measured. PAF suppressed the expression of DNA methyltransferase (DNMT) 1 and 3b. On the other hand, PAF increased p300 histone acetyltransferase expression, and the acetylation of histone H3, which coincided with a decreased expression of the histone deacetylase HDAC2. Chromatin immunoprecipitation assays indicated that PAF-treatment activated the acetylation of the CXCR4 promoter. Finally, inhibiting histone acetylation blocked p300 up-regulation and suppressed PAF-induced surface expression of CXCR4. Our findings suggest a novel molecular mechanism for PAF, activation of epigenetic modifications. We suggest that PAF may serve as an endogenous molecular mediator that links the environment (UV radiation) with the epigenome.

Interleukin-17 mediated inflammatory responses are required for ultraviolet radiation-induced immune suppression.

Ultraviolet radiation (UVR) induces immunosuppression and is a major factor for development of skin cancer. Numerous efforts have been made to determine mechanisms for UVR-induced immunosuppression and to develop strategies for prevention and treatment of UVR-induced cancers. In the current study, we use IL-17 receptor (IL-17R) deficient mice to examine whether IL-17 mediated responses have a role in UVB (290-320)-induced immunosuppression of contact hypersensitivity responses. Results demonstrate that IL-17 mediated responses are required for UVB-induced immunosuppression of contact hypersensitivity responses. The systemic immune suppression and development of regulatory T cells are inhibited in UVB-treated IL-17R deficient mice compared to wild-type animals. The deficiency in IL-17R inhibits the infiltration and development of a tolerogenic myeloid cell population in UVB-treated skin, which expresses CD11b and Gr-1 and produces reactive oxygen species. We speculate that the development of the tolerogenic myeloid cells is dependent on IL-17-induced chemokines and inflammatory mediators in UVB-treated skin. The inhibition of the tolerogenic myeloid cells may be attributed to the suppression of regulatory T cells in UVR-treated IL-17R(-/-) mice. The findings may be exploited to new strategies for prevention and treatment of UVR-induced skin diseases and cancers.

Pharmacologically Antagonizing the CXCR4-CXCL12 Chemokine Pathway with AMD3100 Inhibits Sunlight-Induced Skin Cancer

One way sunlight causes skin cancer is by suppressing anti-tumor immunity. A major mechanism involves altering mast cell migration via the C-X-C motif chemokine receptor 4-C-X-C motif chemokine ligand 12 (CXCR4-CXCL12) chemokine pathway. We have discovered that pharmacologically blocking this pathway with the CXCR4 antagonist AMD3100 prevents both UV radiation-induced immune suppression and skin cancer. The majority of control mice receiving UV-only developed histopathologically confirmed squamous cell carcinomas. In contrast, skin tumor incidence and burden was significantly lower in AMD3100-treated mice. Perhaps most striking was that AMD3100 completely prevented the outgrowth of latent tumors that occurred once UV irradiation ceased. AMD3100 protection from UV immunosuppression and skin cancer was associated with reduced mast cell infiltration into the skin, draining lymph nodes, and the tumor itself. Thus a major target of CXCR4 antagonism was the mast cell. Our results indicate that interfering with UV-induced CXCL12 by antagonizing CXCR4 significantly inhibits skin tumor development by blocking UV-induced effects on mast cells. Hence, the CXCR4-CXCL12 chemokine pathway is a novel therapeutic target in the prevention of UV-induced skin cancer.

Prostaglandin E2 Promotes UV Radiation-Induced Immune Suppression through DNA Hypermethylation

Exposure of mice to UV radiation results in suppression of the contact hypersensitivity (CHS) response. Here, we report that the UV-induced suppression of CHS is associated with increases in the levels of cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), and PGE2 receptors in the exposed skin. UV radiation.induced suppression of CHS was inhibited by topical treatment of the skin with celecoxib or indomethacin (inhibitors of COX-2) or AH6809 (an EP2 antagonist). Moreover, mice deficient in COX-2 were found to be resistant to UV-induced suppression of CHS. The exposure of wild-typemice to UVB radiation resulted in DNA hypermethylation, increased DNA methyltransferase (Dnmt) activity, and elevated levels of Dnmt1, Dnmt3a, and Dnmt3b proteins in the skin, and these responses were downregulated on topical treatment of the site of exposure after irradiation with indomethacin or EP2 antagonist. Topical treatment of UVB-exposed COX-2.deficient mice with PGE2 enhanced the UVB-induced suppression of CHS as well as global DNA methylation and elevated the levels of Dnmt activity and Dnmt proteins in the skin. Intraperitoneal injection of 5-aza-2′-deoxycytidine (5-Aza-dc), a DNA demethylating agent, restored the CHS response to 2,4-dinitrofluorobenzene in UVB-exposed skin and this was associated with the reduction in global DNA methylation and Dnmt activity and reduced levels of Dnmt proteins. Furthermore, treatment with 5-Aza-dc reversed the effect of PGE2 on UV-induced suppression of CHS in COX-2.deficient mice. These findings reveal a previously unrecognized role for PGE2 in the promotion of UVB-induced immunosuppression and indicate that it is mediated through PGE2 regulation of DNA methylation.

Silymarin inhibits ultraviolet radiation-induced immune suppression through DNA repair-dependent activation of dendritic cells and stimulation of effector T cells

Silymarin inhibits UVB-induced immunosuppression in mouse skin. To identify the molecular mechanisms underlying this effect, we used an adoptive transfer approach in which dendritic cells (DCs) from the draining lymph nodes of donor mice that had been UVB-exposed and sensitized to 2,4,-dinitrofluorobenzene (DNFB) were transferred into naïve recipient mice. The contact hypersensitivity (CHS) response of the recipient mice to DNFB was then measured. When DCs were obtained from UVB-exposed donor mice that were not treated with silymarin, the CHS response was suppressed confirming the role of DCs in the UVB-induced immunosuppression. Silymarin treatment of UVB-exposed donor mice relieved this suppression of the CHS response in the recipients. Silymarin treatment was associated with rapid repair of UVB-induced cyclobutane pyrimidine dimers (CPDs) in DCs and silymarin treatment did not prevent UV-induced immunosuppression in XPA-deficient mice which are unable to repair UV-induced DNA damage. The CHS response in mice receiving DCs from silymarin-treated UV-exposed donor mice also was associated with enhanced secretion of Th1-type cytokines and stimulation of T cells. Adoptive transfer of T cells revealed that transfer of either CD8+ or CD4+ cells from silymarin-treated, UVB-exposed donors resulted in enhancement of the CHS response. Cell culture study showed enhanced secretion of IL-2 and IFNγ by CD8+ T cells, and reduced secretion of Th2 cytokines by CD4+ T cells, obtained from silymarin-treated UVB-exposed mice. These data suggest that DNA repair-dependent functional activation of DCs, a reduction in CD4+ regulatory T-cell activity, and stimulation of CD8+ effector T cells contribute to silymarin-mediated inhibition of UVB-induced immunosuppression.

Photoimmune protective effect of the phytoestrogenic isoflavonoid equol is partially due to its antioxidant activities

Topical application of lotions containing the phytoestrogenic isoflavonoid equol have been reported to protect mice against UV radiation-induced inflammation, immune suppression and photocarcinogenesis. The photoimmune protective property was shown to depend on equol's activation of oestrogen receptor signalling in the skin. However, isoflavones are also recognised for their antioxidant properties in biological systems. As endogenous cutaneous antioxidant enzymes including the inducible stress protein haem oxygenase (HO)-1, have photoprotective efficacy, this study in the Skh:hr-1 hairless mouse seeks evidence for an antioxidant role for equol in contributing to its photoimmune protection. Oxidative stress has been measured as UVA-induced lipid peroxidation in the mouse skin, and was dose-dependently inhibited by topical equol. Inhibition of the UVA (320-400 nm)-inducible HO activity significantly reduced the level of equol protection against lipid peroxidation, thereby attributing a component of equol's lipid protection capacity to this stress enzyme. It was consistent that topical equol enhanced the level of HO induction by UVA irradiation in both skin and liver. Subsequently, the dose-dependent protection by topical equol lotions against solar simulated UV radiation induced immunosuppression, measured by the contact hypersensitivity reaction, was found also to be partially reduced by the inhibition of HO activity. Therefore, in addition to the activation by equol of oestrogenic signalling pathways for photoprotection, this isoflavonoid also provides UV-protective antioxidant effects that depend partially on HO-1 induction.

How Does Ionizing Irradiation Contribute to the Induction of Anti-Tumor Immunity?

Radiotherapy (RT) with ionizing irradiation is commonly used to locally attack tumors. It induces a stop of cancer cell proliferation and finally leads to tumor cell death. During the last years it has become more and more evident that besides a timely and locally restricted radiation-induced immune suppression, a specific immune activation against the tumor and its metastases is achievable by rendering the tumor cells visible for immune attack. The immune system is involved in tumor control and we here outline how RT induces anti-inflammation when applied in low doses and contributes in higher doses to the induction of anti-tumor immunity. We especially focus on how local irradiation induces abscopal effects. The latter are partly mediated by a systemic activation of the immune system against the individual tumor cells. Dendritic cells are the key players in the initiation and regulation of adaptive anti-tumor immune responses. They have to take up tumor antigens and consecutively present tumor peptides in the presence of appropriate co-stimulation. We review how combinations of RT with further immune stimulators such as AnnexinA5 and hyperthermia foster the dendritic cell-mediated induction of anti-tumor immune responses and present reasonable combination schemes of standard tumor therapies with immune therapies. It can be concluded that RT leads to targeted killing of the tumor cells and additionally induces non-targeted systemic immune effects. Multimodal tumor treatments should therefore tend to induce immunogenic tumor cell death forms within a tumor microenvironment that stimulates immune cells.

Protective effect of a marine oligopeptide preparation from Chum Salmon (Oncorhynchus keta) on radiation‐induced immune suppression in mice

A marine oligopeptide preparation (MOP) obtained from Chum Salmon (Oncorhynchus keta) by the method of enzymatic hydrolysis, has been found to enhance the innate and adaptive immunities through stimulation of the secretion of cytokines in mice. The current study aimed to further investigate the protective effect of MOP on radiation-induced immune suppression in mice. Female ICR mice (6-8 weeks old) were randomly divided into three groups, i.e. blank control, irradiation control and MOP (1.350 g kg(-1) body weight) plus irradiation-treated group. MOP significantly increased the survival rate and prolonged the survival times for 30 days after irradiation, and lessened the radiation-induced suppression of T- or B-lymphocyte proliferation, resulting in the recovery of cell-mediated and humoral immune functions. This effect may be produced by augmentation of the relative numbers of radioresistant CD(4) (+) T cells, enhancement of the level of immunostimulatory cytokine, IL-12, reduction of the level of total cellular NF-κB through the induction of IκB in spleen and inhibition of the apoptosis of splenocytes. We propose that MOP be used as an ideal adjuvant therapy to alleviate radiation-induced injuries in cancer patients.