Human monocytes undergo excessive apoptosis following temozolomide activating the ATM/ATR pathway while dendritic cells and macrophages are resistant

Sex and Circadian Timing Modulate Oxaliplatin Hematological and Hematopoietic Toxicities

Oxaliplatin was nearly twice as hematotoxic, with optimal circadian timing differing by 6 h, in women as compared to men with colorectal cancers. Hence, we investigated sex- and timing-related determinants of oxaliplatin hematopoietic toxicities in mice. Body-weight loss (BWL), blood cell counts, bone marrow cellularity (BMC) and seven flow-cytometry-monitored hematopoietic progenitor populations were evaluated 72 h after oxaliplatin chronotherapy administration (5 mg/kg). In control animals, circadian rhythms of circulating white blood cells showed a peak at ZT5 in both sexes, whereas BMC was maximum at ZT20 in males and ZT13h40 in females. All BM progenitor counts presented robust rhythms with phases around ZT3h30 in females, whereas only three of them rhythmically cycled in males with a ≈ -6 h phase shift. In treated females, chronotoxicity rhythms occurred in BWL, WBC, BMC and all BM progenitors with the best timing at ZT15, ZT21, ZT15h15 and ZT14h45, respectively. In males, almost no endpoints showed circadian rhythms, BWL and WBC toxicity being minimal, albeit with a substantial drop in BM progenitors. Increasing dose (10 mg/kg) in males induced circadian rhythms in BWL and WBC but not in BM endpoints. Our results suggest complex and sex-specific clock-controlled regulation of the hematopoietic system and its response to oxaliplatin.

Pathological mechanisms and crosstalk among different forms of cell death in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disorder characterized by a profound immune dysregulation and the presence of a variety of autoantibodies. Aberrant activation of programmed cell death (PCD) signaling and accelerated cell death is critical in the immunopathogenesis of SLE. Accumulating cellular components from the dead cells and ineffective clearance of the dead cell debris, in particular the nucleic acids and nucleic acids-protein complexes, provide a stable source of self-antigens, which potently activate auto-reactive B cells and promote IFN-I responses in SLE. Different cell types display distinct susceptibility and characteristics to a certain type of cell death, while different PCDs in various cells have mutual and intricate connections to promote immune dysregulation and contribute to the development of SLE. In this review, we discuss the role of various cell death pathways and their interactions in the pathogenesis of SLE. An in depth understanding of the interconnections among various forms cell death in SLE will lead to a better understanding of disease pathogenesis, shedding light on the development of novel therapeutic targets.

GM-CSF Protects Macrophages from DNA Damage by Inducing Differentiation

At inflammatory loci, pro-inflammatory activation of macrophages produces large amounts of reactive oxygen species (ROS) that induce DNA breaks and apoptosis. Given that M-CSF and GM-CSF induce two different pathways in macrophages, one for proliferation and the other for survival, in this study we wanted to determine if these growth factors are able to protect against the DNA damage produced during macrophage activation. In macrophages treated with DNA-damaging agents we found that GM-CSF protects better against DNA damage than M-CSF. Treatment with GM-CSF resulted in faster recovery of DNA damage than treatment with M-CSF. The number of apoptotic cells induced after DNA damage was higher in the presence of M-CSF. Protection against DNA damage by GM-CSF is not related to its higher capacity to induce proliferation. GM-CSF induces differentiation markers such as CD11c and MHCII, as well as the pro-survival Bcl-2A1 protein, which make macrophages more resistant to DNA damage.

Plasmodium berghei-Released Factor, PbTIP, Modulates the Host Innate Immune Responses

The Plasmodium parasite has to cross various immunological barriers for successful infection. Parasites have evolved mechanisms to evade host immune responses, which hugely contributes to the successful infection and transmission by parasites. One way in which a parasite evades immune surveillance is by expressing molecular mimics of the host molecules in order to manipulate the host responses. In this study, we report a Plasmodium berghei hypothetical protein, PbTIP (PbANKA_124360.0), which is a Plasmodium homolog of the human T-cell immunomodulatory protein (TIP). The latter possesses immunomodulatory activities and suppressed the host immune responses in a mouse acute graft-versus-host disease (GvHD) model. The Plasmodium berghei protein, PbTIP, is expressed on the merozoite surface and exported to the host erythrocyte surface upon infection. It is shed in the blood circulation by the activity of an uncharacterized membrane protease(s). The shed PbTIP could be detected in the host serum during infection. Our results demonstrate that the shed PbTIP exhibits binding on the surface of macrophages and reduces their inflammatory cytokine response while upregulating the anti-inflammatory cytokines such as TGF-β and IL-10. Such manipulated immune responses are observed in the later stage of malaria infection. PbTIP induced Th2-type gene transcript changes in macrophages, hinting toward its potential to regulate the host immune responses against the parasite. Therefore, this study highlights the role of a Plasmodium-released protein, PbTIP, in immune evasion using macrophages, which may represent the critical strategy of the parasite to successfully survive and thrive in its host. This study also indicates the human malaria parasite TIP as a potential diagnostic molecule that could be exploited in lateral flow-based immunochromatographic tests for malaria disease diagnosis.

Abscopal Effect and Drug-Induced Xenogenization: A Strategic Alliance in Cancer Treatment?

The current state of cancer treatment is still far from being satisfactory considering the strong impairment of patients' quality of life and the high lethality of malignant diseases. Therefore, it is critical for innovative approaches to be tested in the near future. In view of the crucial role that is played by tumor immunity, the present review provides essential information on the immune-mediated effects potentially generated by the interplay between ionizing radiation and cytotoxic antitumor agents when interacting with target malignant cells. Therefore, the radiation-dependent abscopal effect (i.e., a biological effect of ionizing radiation that occurs outside the irradiated field), the influence of cancer chemotherapy on the antigenic pattern of target neoplastic cells, and the immunogenic cell death (ICD) caused by anticancer agents are the main topics of this presentation. It is widely accepted that tumor immunity plays a fundamental role in generating an abscopal effect and that anticancer drugs can profoundly influence not only the host immune responses, but also the immunogenic pattern of malignant cells. Remarkably, several anticancer drugs impact both the abscopal effect and ICD. In addition, certain classes of anticancer agents are able to amplify already expressed tumor-associated antigens (TAA). More importantly, other drugs, especially triazenes, induce the appearance of new tumor neoantigens (TNA), a phenomenon that we termed drug-induced xenogenization (DIX). The adoption of the abscopal effect is proposed as a potential therapeutic modality when properly applied concomitantly with drug-induced increase in tumor cell immunogenicity and ICD. Although little to no preclinical or clinical studies are presently available on this subject, we discuss this issue in terms of potential mechanisms and therapeutic benefits. Upcoming investigations are aimed at evaluating how chemical anticancer drugs, radiation, and immunotherapies are interacting and cooperate in evoking the abscopal effect, tumor xenogenization and ICD, paving the way for new and possibly successful approaches in cancer therapy.

Efficacy of the new therapeutic approach in curing malignant neoplasms on the model of human glioblastoma

OBJECTIVE

Glioma is a highly invasive tumor, frequently disposed in essential areas of the brain, which makes its surgical excision extremely difficult; meanwhile adjuvant therapy remains quite ineffective.

METHODS

In the current report, a new therapeutic approach in curing malignant neoplasms has been performed on the U87 human glioblastoma model. This approach, termed "Karanahan", is aimed at the eradication of cancer stem cells (CSCs), which were recently shown to be capable of internalizing fragments of extracellular double-stranded DNA. After being internalized, these fragments interfere in the process of repairing interstrand cross-links caused by exposure to appropriate cytostatics, and such an interference results either in elimination of CSCs or in the loss of their tumorigenic potency. Implementation of the approach requires a scheduled administration of cytostatic and complex composite double-stranded DNA preparation.

RESULTS

U87 cells treated in vitro in accordance with the Karanahan approach completely lost their tumorigenicity and produced no grafts upon intracerebral transplantation into immunodeficient mice. In SCID mice with developed subcutaneous grafts, the treatment resulted in reliable slowing down of tumor growth rate (P < 0.05). In the experiment with intracerebral transplantation of U87 cells followed by surgical excision of the developed graft and subsequent therapeutic treatment, the Karanahan approach was shown to reliably slow down the tumor growth rate and increase the median survival of the mice twofold relative to the control.

CONCLUSIONS

The effectiveness of the Karanahan approach has been demonstrated both in vitro and in vivo in treating developed subcutaneous grafts as well as orthotopic grafts after surgical excision of the tumor.

Melphalan flufenamide inhibits osteoclastogenesis by suppressing proliferation of monocytes

Myeloma bone disease is a major complication in multiple myeloma affecting quality of life and survival. It is characterized by increased activity of osteoclasts, bone resorbing cells. Myeloma microenvironment promotes excessive osteoclastogenesis, a process of production of osteoclasts from their precursors, monocytes. The effects of two anti-myeloma drugs, melphalan flufenamide (melflufen) and melphalan, on the activity and proliferation of osteoclasts and their progenitors, monocytes, were assessed in this study. In line with previous research, differentiation of monocytes was associated with increased expression of genes encoding DNA damage repair proteins. Hence monocytes were more sensitive to DNA damage-causing alkylating agents than their differentiated progeny, osteoclasts. In addition, differentiated progeny of monocytes showed increased gene expression of immune checkpoint ligands which may potentially create an immunosuppressive microenvironment. Melflufen was ten-fold more active than melphalan in inhibiting proliferation of osteoclast progenitors. Furthermore, melflufen was also superior to melphalan in inhibition of osteoclastogenesis and bone resorption. These results demonstrate that melflufen may exert beneficial effects in patients with multiple myeloma such as reducing bone resorption and immunosuppressive milieu by inhibiting osteoclastogenesis.

Comparison of DNA repair and radiosensitivity of different blood cell populations

Despite the frequent use of ionising radiation (IR) in therapy and diagnostics and the unavoidable exposure to external radiation sources, our knowledge regarding the radiosensitivity of human blood cell populations is limited and published data, obtained under different experimental conditions, are heterogeneous. To compare the radiosensitivity of different hematopoietic cell populations, we set out to determine the responses of cells obtained from peripheral blood of healthy volunteers under identical conditions (resting, non-stimulated cells). First, we measured the radiation response of T cells (Treg, Th, CTL), B cells, NK cells, CD34+ progenitor cells and monocytes obtained from peripheral blood and monocyte-derived macrophages (Mph) and immature dendritic cells (iDC) ex vivo and show that T and B cells are highly sensitive, starting to undergo apoptosis following IR with a dose as low as 0.125 Gy. Importantly, there was no clear threshold dose and cell death/apoptosis increased up to a saturation level with a dose of 2 Gy. The sensitivity decreased in the order of T cells > NK and B cells > monocytes > macrophages and iDC. The data confirm a previous report that Mph and iDC are radiation-resistant compared to their progenitor monocytes. Although non-stimulated T and B cells were highly radiation-sensitive compared to monocytes and macrophages, they were competent in the repair of DNA double-strand breaks, as shown by a decline in γH2AX foci in the post-exposure period. CD34+ cells obtained from peripheral blood also showed γH2AX decline post-exposure, indicating they are repair competent. Granulocytes (CD15+) did not display any γH2AX staining following IR. Although peripheral blood lymphocytes, the main fraction are T cells, were significantly more radiation-sensitive than monocytes, they displayed the expression of the repair proteins XRCC1, ligase III and PARP-1, which were nearly non-expressed in monocytes. To assess whether monocytes are depleted in vivo following IR, we measured the amount of T cells and monocytes in cancer patients who received total-body radiation (TBR, 6 × 2 Gy). We observed that the number of T cells in the peripheral blood significantly declined already after the first day of TBR and remained at a low level, which was accompanied by an increase in the number of γH2AX foci in the surviving CD3+ T cell fraction. In contrast, the number of monocytes did not decline extensively, reflecting their radiation resistance compared to T cells. Monocytes also showed an accumulation of γH2AX foci in vivo, but the levels were significantly lower than in T cells. CD56+ NK cells displayed a response similar to T cells. The data support the notion that unstimulated T cell subfractions are nearly equally radiation sensitive. There are, however, remarkable differences in the radiation sensitivity between the lymphoid and the myeloid lineage, with lymphoid cells being significantly more sensitive than cells of the myeloid lineage. In the myeloid lineage, macrophages and iDCs were the most radio-resistant cell types.

Impaired DNA repair in mouse monocytes compared to macrophages and precursors

Previously we showed that human monocytes isolated from peripheral blood display downregulation of several DNA repair proteins, including XRCC1, ligase III, PARP-1 and DNA-PK_CS, resulting in a deficiency of DNA repair, while in macrophages derived from monocytes the repair protein expression and DNA repair is restored. To see whether this is a specific phenomenon of human monocytes and macrophages, we assessed the expression of these repair genes in mice. We also addressed the question at which differentiation step in bone marrow cells downregulation of DNA repair gene expression occurs. The study revealed that mouse monocytes, similar to human, lack the expression of XRCC1, ligase III, PARP-1 and DNA-PK_CS. If mice were treated with total body irradiation, they showed significant apoptosis in bone marrow monocytes, but not in peritoneal macrophages. This was also observed after treatment with the methylating anticancer drug temozolomide, resulting in high death rate of monocytes, but not macrophages. Monocytes arise from hematopoietic stem cells. Even the early stem cell fraction (LT-HSC) expressed detectable amounts of XRCC1, which was transiently upregulated, achieving the highest expression level in CMP (common myeloid progenitor) and, during the subsequent differentiation process, downregulated up to a non-detectable level in monocytes. The immediate monocyte precursor GMP also expressed ligase III, PARP-1 and DNA-PK_CS. All these repair genes lacking in monocytes were upregulated again in macrophages. The sensitivity of monocytes, macrophages and precursor cells roughly correlated with their XRCC1 expression level. Monocytes, but not macrophages, also displayed strong γH2AX focal staining, indicating the presence of non-repaired DNA double-strand breaks following total body irradiation. Overall, the data revealed that murine monocytes exhibit the same DNA repair-impaired phenotype and high sensitivity compared to macrophages as observed in human. Therefore, the repair deficiency previously described for human monocytes appears to be a general property of this cell type.

Myeloid Cells in Glioblastoma Microenvironment

Glioblastoma (GBM) is the most aggressive, malignant primary brain tumor in adults. GBM is notoriously resistant to immunotherapy mainly due to its unique immune microenvironment. High dimensional data analysis reveals the extensive heterogeneity of immune components making up the GBM microenvironment. Myeloid cells are the most predominant contributors to the GBM microenvironment; these cells are critical regulators of immune and therapeutic responses to GBM. Here, we will review the most recent advances on the characteristics and functions of different populations of myeloid cells in GBM, including bone marrow-derived macrophages, microglia, myeloid-derived suppressor cells, dendritic cells, and neutrophils. Epigenetic, metabolic, and phenotypic peculiarities of microglia and bone marrow-derived macrophages will also be assessed. The final goal of this review will be to provide new insights into novel therapeutic approaches for specific targeting of myeloid cells to improve the efficacy of current treatments in GBM patients.

Interaction between Fibroblasts and Immune Cells Following DNA Damage Induced by Ionizing Radiation

Cancer-associated fibroblasts (CAF) form the basis of tumor microenvironment and possess immunomodulatory functions by interacting with other cells surrounding tumor, including T lymphocytes, macrophages, dendritic cells and natural killer cells. Ionizing radiation is a broadly-used method in radiotherapy to target tumors. In mammalian cells, ionizing radiation induces various types of DNA damages and DNA damage response. Being unspecific, radiotherapy affects all the cells in tumor microenvironment, including the tumor itself, CAFs and immune cells. CAFs are extremely radio-resistant and do not initiate apoptosis even at high doses of radiation. However, following radiation, CAFs become senescent and produce a distinct combination of immunoregulatory molecules. Radiosensitivity of immune cells varies depending on the cell type due to inefficient DNA repair in, for example, monocytes and granulocytes. In this minireview, we are summarizing recent findings on the interaction between CAF, ionizing radiation and immune cells in the tumor microenvironment.

A Dual Face of APE1 in the Maintenance of Genetic Stability in Monocytes: An Overview of the Current Status and Future Perspectives

Monocytes, which play a crucial role in the immune system, are characterized by an enormous sensitivity to oxidative stress. As they lack four key proteins responsible for DNA damage response (DDR) pathways, they are especially prone to reactive oxygen species (ROS) exposure leading to oxidative DNA lesions and, consequently, ROS-driven apoptosis. Although such a phenomenon is of important biological significance in the regulation of monocyte/macrophage/dendritic cells’ balance, it also a challenge for monocytic mechanisms that have to provide and maintain genetic stability of its own DNA. Interestingly, apurinic/apyrimidinic endonuclease 1 (APE1), which is one of the key proteins in two DDR mechanisms, base excision repair (BER) and non-homologous end joining (NHEJ) pathways, operates in monocytic cells, although both BER and NHEJ are impaired in these cells. Thus, on the one hand, APE1 endonucleolytic activity leads to enhanced levels of both single- and double-strand DNA breaks (SSDs and DSBs, respectively) in monocytic DNA that remain unrepaired because of the impaired BER and NHEJ. On the other hand, there is some experimental evidence suggesting that APE1 is a crucial player in monocytic genome maintenance and stability through different molecular mechanisms, including induction of cytoprotective and antioxidant genes. Here, the dual face of APE1 is discussed.

Persistent DNA damage triggers activation of the integrated stress response to promote cell survival under nutrient restriction

BACKGROUND

Base-excision repair (BER) is a central DNA repair mechanism responsible for the maintenance of genome integrity. Accordingly, BER defects have been implicated in cancer, presumably by precipitating cellular transformation through an increase in the occurrence of mutations. Hence, tight adaptation of BER capacity is essential for DNA stability. However, counterintuitive to this, prolonged exposure of cells to pro-inflammatory molecules or DNA-damaging agents causes a BER deficiency by downregulating the central scaffold protein XRCC1. The rationale for this XRCC1 downregulation in response to persistent DNA damage remains enigmatic. Based on our previous findings that XRCC1 downregulation causes wide-ranging anabolic changes, we hypothesised that BER depletion could enhance cellular survival under stress, such as nutrient restriction.

RESULTS

Here, we demonstrate that persistent single-strand breaks (SSBs) caused by XRCC1 downregulation trigger the integrated stress response (ISR) to promote cellular survival under nutrient-restricted conditions. ISR activation depends on DNA damage signalling via ATM, which triggers PERK-mediated eIF2α phosphorylation, increasing translation of the stress-response factor ATF4. Furthermore, we demonstrate that SSBs, induced either through depletion of the transcription factor Sp1, responsible for XRCC1 levels, or through prolonged oxidative stress, trigger ISR-mediated cell survival under nutrient restriction as well. Finally, the ISR pathway can also be initiated by persistent DNA double-strand breaks.

CONCLUSIONS

Our results uncover a previously unappreciated connection between persistent DNA damage, caused by a decrease in BER capacity or direct induction of DNA damage, and the ISR pathway that supports cell survival in response to genotoxic stress with implications for tumour biology and beyond.

Mechanism of colorectal carcinogenesis triggered by heme iron from red meat

Colorectal cancer (CRC) is one of the major tumor entities worldwide, with an increasing incidence in younger people. CRC formation is causally linked to various genetic, life-style and dietary risk factors. Among the ladder, the consumption of red meat has emerged as important risk factor contributing to CRC. A large body of evidence shows that heme iron is the critical component of red meat, which promotes colorectal carcinogenesis. In this review, we describe the uptake and cellular fate of both heme and inorganic iron in intestinal epithelial cells. Next, an overview on the DNA damaging properties of heme iron is provided, highlighting the DNA adducts relevant for CRC etiology. Moreover, heme triggered mechanisms leading to colonic hyperproliferation are presented, which are intimately linked to changes in the intestinal microbiota induced by heme. A special focus was set on the impact of heme iron on innate and adaptive immune cells, which could be relevant in the context of CRC. Finally, we recapitulate in vivo studies providing evidence for the tumor-promoting potential of dietary heme iron. Altogether, heme iron affects numerous key pathways involved in the pathogenesis of CRC.

Dendritic Cell-Based Immunotherapy in Advanced Sarcoma and Neuroblastoma Pediatric Patients: Anti-cancer Treatment Preceding Monocyte Harvest Impairs the Immunostimulatory and Antigen-Presenting Behavior of DCs and Manufacturing Process Outcome

Despite efforts to develop novel treatment strategies, refractory and relapsing sarcoma, and high-risk neuroblastoma continue to have poor prognoses and limited overall survival. Monocyte-derived dendritic cell (DC)-based anti-cancer immunotherapy represents a promising treatment modality in these neoplasias. A DC-based anti-cancer vaccine was evaluated for safety in an academic phase-I/II clinical trial for children, adolescents, and young adults with progressive, recurrent, or primarily metastatic high-risk tumors, mainly sarcomas and neuroblastomas. The DC vaccine was loaded with self-tumor antigens obtained from patient tumor tissue. DC vaccine quality was assessed in terms of DC yield, viability, immunophenotype, production of IL-12 and IL-10, and stimulation of allogenic donor T-cells and autologous T-cells in allo-MLR and auto-MLR, respectively. Here, we show that the outcome of the manufacture of DC-based vaccine is highly variable in terms of both DC yield and DC immunostimulatory properties. In 30% of cases, manufacturing resulted in a product that failed to meet medicinal product specifications and therefore was not released for administration to a patient. Focusing on the isolation of monocytes and the pharmacotherapy preceding monocyte harvest, we show that isolation of monocytes by elutriation is not superior to adherence on plastic in terms of DC yield, viability, or immunostimulatory capacity. Trial patients having undergone monocyte-interfering pharmacotherapy prior to monocyte harvest was associated with an impaired DC-based immunotherapy product outcome. Certain combinations of anti-cancer treatment resulted in a similar pattern of inadequate DC parameters, namely, a combination of temozolomide with irinotecan was associated with DCs showing poor maturation and decreased immunostimulatory features, and a combination of pazopanib, topotecan, and MTD-based cyclophosphamide was associated with poor monocyte differentiation and decreased DC immunostimulatory parameters. Searching for a surrogate marker predicting an adverse outcome of DC manufacture in the peripheral blood complete blood count prior to monocyte harvest, we observed an association between an increased number of immature granulocytes in peripheral blood and decreased potency of the DC-based product as quantified by allo-MLR. We conclude that the DC-manufacturing yield and the immunostimulatory quality of anti-cancer DC-based vaccines generated from the monocytes of patients were not influenced by the monocyte isolation modality but were detrimentally affected by the specific combination of anti-cancer agents used prior to monocyte harvest.

Breaking the DNA Damage Response via Serine/Threonine Kinase Inhibitors to Improve Cancer Treatment

Multiple, both endogenous and exogenous, sources may induce DNA damage and DNA replication stress. Cells have developed DNA damage response (DDR) signaling pathways to maintain genomic stability and effectively detect and repair DNA lesions. Serine/ threonine kinases such as Ataxia-telangiectasia mutated (ATM) and Ataxia-telangiectasia and Rad3-Related (ATR) are the major regulators of DDR, since after sensing stalled DNA replication forks, DNA double- or single-strand breaks, may directly phosphorylate and activate their downstream targets, that play a key role in DNA repair, cell cycle arrest and apoptotic cell death. Interestingly, key components of DDR signaling networks may constitute an attractive target for anti-cancer therapy through two distinct potential approaches: as chemoand radiosensitizers to enhance the effectiveness of currently used genotoxic treatment or as single agents to exploit defects in DDR in cancer cells via synthetic lethal approach. Moreover, the newest data reported that serine/threonine protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is also closely associated with cancer development and progression. Thereby, utilization of small-molecule, serine/threonine kinase inhibitors may provide a novel, groundbreaking, anti-cancer treatment strategy. Currently, a range of potent, highlyselective toward ATM, ATR and PERK inhibitors has been discovered, but after foregoing study, additional investigations are necessary for their future clinical use.

PARP-1 Is Critical for Recruitment of Dendritic Cells to the Lung in a Mouse Model of Asthma but Dispensable for Their Differentiation and Function

Dendritic cells (DCs) are critical in asthma and many other immune diseases. We previously demonstrated a role for PARP-1 in asthma. Evidence on PARP-1 playing a role in Th2-associated DC function is not clear. In this study, we examined whether PARP-1 is critical for DC differentiation and function using bone marrow progenitors and their migration to the lung in an ovalbumin-based mouse model of asthma. Results show that changes in PARP-1 levels during GM-CSF-induced DC differentiation from bone marrow progenitors were cyclic and appear to be part of an array of changes that included STAT3/STAT5/STAT6/GRAIL/RAD51. Interestingly, PARP-1 gene deletion affected primarily STAT6 and γH2AX. PARP-1 inhibition significantly reduced the migration of DCs to the lungs of ovalbumin-challenged mice, which was associated with a concomitant reduction in lung levels of the adhesion molecule VCAM-1. The requirement of PARP-1 for VCAM-1 expression was confirmed using endothelial and lung smooth muscle cells. PARP-1 expression and activity were also required for VCAM-1 in differentiated DCs. An assessment of CD11b⁺/CD11c⁺/MHCII^high DCs in spleens and lymph nodes of OVA-sensitized mice revealed that PARP-1 inhibition genetically or by olaparib exerted little to no effect on DC differentiation, percentage of CD80⁺/CD86⁺/CD40⁺-expressing cells, or their capacity to promote proliferation of ovalbumin-primed (OTII) CD4⁺ T cells. These findings were corroborated using GM-CSF-induced differentiation of DCs from the bone marrow. Surprisingly, the PARP-1^−/− DCs exhibited a higher intrinsic capacity to induce OTII CD4⁺ T cell proliferation in the absence of ovalbumin. Overall, our results show that PARP-1 plays little to no role in DC differentiation and function and that the protective effect of PARP-1 inhibition against asthma is associated with a prevention of DC migration to the lung through a reduction in VCAM-1 expression. Given the current use of PARP inhibitors (e.g., olaparib) in the clinic, the present results may be of interest for the relevant therapies.

Genome-wide DNA copy number analysis and targeted transcriptional analysis of canine histiocytic malignancies identifies diagnostic signatures and highlights disruption of spindle assembly complex

Canine histiocytic malignancies (HM) are rare across the general dog population, but overrepresented in certain breeds, such as Bernese mountain dog and flat-coated retriever. Accurate diagnosis relies on immunohistochemical staining to rule out histologically similar cancers with different prognoses and treatment strategies (e.g., lymphoma and hemangiosarcoma). HM are generally treatment refractory with overall survival of less than 6 months. A lack of understanding regarding the mechanisms of disease development and progression hinders development of novel therapeutics. While the study of human tumors can benefit veterinary medicine, the rarity of the suggested orthologous disease (dendritic cell sarcoma) precludes this. This study aims to improve the understanding of underlying disease mechanisms using genome-wide DNA copy number and gene expression analysis of spontaneous HM across several dog breeds. Extensive DNA copy number disruption was evident, with losses of segments of chromosomes 16 and 31 detected in 93% and 72% of tumors, respectively. Droplet digital PCR (ddPCR) evaluation of these regions in numerous cancer specimens effectively discriminated HM from other common round cell tumors, including lymphoma and hemangiosarcoma, resulting in a novel, rapid diagnostic aid for veterinary medicine. Transcriptional analysis demonstrated disruption of the spindle assembly complex, which is linked to genomic instability and reduced therapeutic impact in humans. A key signature detected was up-regulation of Matrix Metalloproteinase 9 (MMP9), supported by an immunohistochemistry-based assessment of MMP9 protein levels. Since MMP9 has been linked with rapid metastasis and tumor aggression in humans, the data in this study offer a possible mechanism of aggression in HM.

Targeting the lysosome by an aminomethylated Riccardin D triggers DNA damage through cathepsin B-mediated degradation of BRCA1

RD-N, an aminomethylated derivative of riccardin D, is a lysosomotropic agent that can trigger lysosomal membrane permeabilization followed by cathepsin B (CTSB)-dependent apoptosis in prostate cancer (PCa) cells, but the underlying mechanisms remain unknown. Here we show that RD-N treatment drives CTSB translocation from the lysosomes to the nucleus where it promotes DNA damage by suppression of the breast cancer 1 protein (BRCA1). Inhibition of CTSB activity with its specific inhibitors, or by CTSB-targeting siRNA or CTSB with enzyme-negative domain attenuated activation of BRCA1 and DNA damage induced by RD-N. Conversely, CTSB overexpression resulted in inhibition of BRCA1 and sensitized PCa cells to RD-N-induced cell death. Furthermore, RD-N-induced cell death was exacerbated in BRCA1-deficient cancer cells. We also demonstrated that CTSB/BRCA1-dependent DNA damage was critical for RD-N, but not for etoposide, reinforcing the importance of CTSB/BRCA1 in RD-N-mediated cell death. In addition, RD-N synergistically increased cell sensitivity to cisplatin, and this effect was more evidenced in BRCA1-deficient cancer cells. This study reveals a novel molecular mechanism that RD-N promotes CTSB-dependent DNA damage by the suppression of BRCA1 in PCa cells, leading to the identification of a potential compound that target lysosomes for cancer treatment.

Relationship between the Regulation of Caspase-8-Mediated Apoptosis and Radioresistance in Human THP-1-Derived Macrophages

Radiosensitivity varies depending on the cell type; highly differentiated cells typically exhibit greater radioresistance. We recently demonstrated that human macrophages derived from THP-1 monocytic cells, which lack TP53, are highly resistant to radiation-induced apoptosis compared with undifferentiated THP-1 cells. However, the mechanisms by which THP-1 cells acquire radioresistance during differentiation remain unknown. Herein, we investigated the mechanisms by which THP-1-derived macrophages develop p53-independent radioresistance by analyzing DNA damage responses and apoptotic pathways. Analysis of γ-H2AX foci, which indicates the formation of DNA double-strand breaks (DSB), suggested that a capacity to repair DSB of macrophages is comparable to that of radiosensitive THP-1 cells. Furthermore, treatment with inhibitors against DSB repair-related proteins failed to enhance radiation-induced apoptosis in THP-1-derrived macrophages. Analysis of the apoptotic pathways showed that radiosensitive THP-1 cells undergo apoptosis through the caspase-8/caspase-3 cascade after irradiation, whereas this was not observed in the macrophages. Caspase-8 protein expression was lower in macrophages than in THP-1 cells, whereas mRNA expressions were comparable between both cell types. Co-treatment with a proteasome inhibitor and ionizing radiation effectively induced apoptosis in macrophages in a caspase-8-dependent manner. Results suggest that the regulation of caspase-8-mediated apoptosis during differentiation plays a role in the p53-independent radioresistance of THP-1-derived macrophages.

Compromised DNA Repair and Signalling in Human Granulocytes

In previous studies, we showed impaired DNA repair in human monocytes. Here, we addressed the question of whether human neutrophilic granulocytes that arise from the same precursor as monocytes exhibit a similar phenotype and are impaired in repairing their DNA. We show that neutrophilic granulocytes isolated from peripheral blood display a lack of the same repair proteins that are missing in monocytes and do not show repair of their DNA when damaged by ionising radiation (IR) or chemical ROS. Contrary to T cells, we observed no decline in the number of single-strand breaks following γ-radiation. Also, granulocytes did not show γH2AX foci formation while T cells and peripheral blood lymphocytes (PBL) responded. In comparison to PBL, XRCC1, PARP-1 and ligase III were not expressed and there was also no discernible signal for key damage response proteins ATM, ATR and DNA-PKCS as well as γH2AX in neutrophils. Time course and dose-response experiments confirmed the absence of H2AX phosphorylation after radiation treatment although an accumulation of double-strand breaks was detected in the neutral Comet assay. Overall, the data indicate that terminally differentiated neutrophilic granulocytes in the peripheral blood display strong downregulation of DNA repair and DNA damage response factors, which should be taken into account if studies with whole peripheral blood containing granulocytes are performed, causing a significant intra-experimental variation in the cellular repair capacity.

Assessment of Poly(ADP-ribose) Polymerase1 (PARP1) expression and activity in cells purified from blood and milk of dairy cattle

Poly(ADP-ribosyl)ation (PAR) is a post-translational protein modification catalysed by enzyme member of the poly(ADP-ribose) polymerases (PARPs) family. The activation of several PARPs is triggered by DNA strand breakage and the main PARP enzyme involved in this process is PARP1. Besides its involvement in DNA repair, PARP1 is involved in several cellular processes including transcription, epigenetics, chromatin re-modelling as well as in the maintenance of genomic stability. Moreover, several studies in human and animal models showed PARP1 activation in various inflammatory disorders. The aims of the study were (1) to characterize PARP1 expression in bovine peripheral blood mononuclear cells (PBMC) and (2) to evaluate PAR levels as a potential inflammatory marker in cells isolated from blood and milk samples following different types of infection, including mastitis. Our results show that (i) bovine PBMC express PARP1; (ii) lymphocytes exhibit higher expression of PARP1 than monocytes; (iii) PARP1 and PAR levels were higher in circulating PBMCs of infected cows; (iv) PAR levels were higher in cells isolated from milk with higher Somatic Cell Counts (SCC > 100,000 cells/mL) than in cells from milk with low SCCs. In conclusion, these findings suggest that PARP1 is activated during mastitis, which may prove to be a useful biomarker of mastitis.

Immunotherapies for malignant glioma

Glioblastoma multiforme (GBM) is a highly malignant primary brain cancer with a dreadful overall survival and for which treatment options are limited. Recent breakthroughs in novel immune-related treatment strategies for cancer have spurred interests in usurping the power of the patient's immune system to recognize and eliminate GBM. Here, we discuss the unique properties of GBM's tumor microenvironment, the effects of GBM standard on care therapy on tumor-associated immune cells, and review several approaches aimed at therapeutically targeting the immune system for GBM treatment. We believe that a comprehensive understanding of the intricate micro-environmental landscape of GBM will abound into the development of novel immunotherapy strategies for GBM patients.

Conditional Knockdown of Gene Expression in Cancer Cell Lines to Study the Recruitment of Monocytes/Macrophages to the Tumor Microenvironment

siRNA and shRNA-mediated knock down (KD) methods of regulating gene expression are invaluable tools for understanding gene and protein function. However, in the case that the KD of the protein of interest has a lethal effect on cells or the anticipated effect of the KD is time-dependent, unconditional KD methods are not appropriate. Conditional systems are more suitable in these cases and have been the subject of much interest. These include Ecdysone-inducible overexpression systems, Cytochrome P-450 induction system¹, and the tetracycline regulated gene expression systems. The tetracycline regulated gene expression system enables reversible control over protein expression by induction of shRNA expression in the presence of tetracycline. In this protocol, we present an experimental design using functional Tet-ON system in human cancer cell lines for conditional regulation of gene expression. We then demonstrate the use of this system in the study of tumor cell-monocyte interaction.

In-depth immunophenotyping of patients with glioblastoma multiforme: Impact of steroid treatment

Despite aggressive treatment regimens based on surgery and radiochemotherapy, the prognosis of patients with grade IV glioblastoma multiforme (GBM) remains extremely poor, calling for alternative options such as immunotherapy. Immunological mechanisms including the Natural Killer Group 2 member D (NKG2D) receptor-ligand system play an important role in tumor immune surveillance and targeting the NKG2D system might be beneficial. However, before considering any kind of immunotherapy, a precise characterization of the immune system is important, particularly in GBM patients where conventional therapies with impact on the immune system are frequently co-administered. Here we performed an in-depth immunophenotyping of GBM patients and age-matched healthy controls and analyzed NKG2D ligand expression on primary GBM cells ex vivo. We report that GBM patients have a compromised innate immune system irrespective of steroid (dexamethasone) medication. However, dexamethasone drastically reduced the number of immune cells in the blood of GBM patients. Moreover, higher counts of immune cells influenced by dexamethasone like CD45⁺ lymphocytes and non-Vδ2 γδ T cells were associated with better overall survival. Higher levels of NKG2D ligands on primary GBM tumor cells were observed in patients who received radiochemotherapy, pointing towards increased immunogenic potential of GBM cells following standard radiochemotherapy. This study sheds light on how steroids and radiochemotherapy affect immune cell parameters of GBM patients, a pre-requisite for the development of new therapeutic strategies targeting the immune system in these patients.

Death of Monocytes through Oxidative Burst of Macrophages and Neutrophils: Killing in Trans

Monocytes and their descendants, macrophages, play a key role in the defence against pathogens. They also contribute to the pathogenesis of inflammatory diseases. Therefore, a mechanism maintaining a balance in the monocyte/macrophage population must be postulated. Our previous studies have shown that monocytes are impaired in DNA repair, rendering them vulnerable to genotoxic stress while monocyte-derived macrophages are DNA repair competent and genotoxic stress-resistant. Based on these findings, we hypothesized that monocytes can be selectively killed by reactive oxygen species (ROS) produced by activated macrophages. We also wished to know whether monocytes and macrophages are protected against their own ROS produced following activation. To this end, we studied the effect of the ROS burst on DNA integrity, cell death and differentiation potential of monocytes. We show that monocytes, but not macrophages, stimulated for ROS production by phorbol-12-myristate-13-acetate (PMA) undergo apoptosis, despite similar levels of initial DNA damage. Following co-cultivation with ROS producing macrophages, monocytes displayed oxidative DNA damage, accumulating DNA single-strand breaks and a high incidence of apoptosis, reducing their ability to give rise to new macrophages. Killing of monocytes by activated macrophages, termed killing in trans, was abolished by ROS scavenging and was also observed in monocytes co-cultivated with ROS producing activated granulocytes. The data revealed that monocytes, which are impaired in the repair of oxidised DNA lesions, are vulnerable to their own ROS and ROS produced by macrophages and granulocytes and support the hypothesis that this is a mechanism regulating the amount of monocytes and macrophages in a ROS-enriched inflammatory environment.

Evaluation of [18F]-ATRi as PET tracer for in vivo imaging of ATR in mouse models of brain cancer

RATIONALE

Ataxia telangiectasia and Rad3-related (ATR) threonine serine kinase is one of the key elements in orchestrating the DNA damage response (DDR). As such, inhibition of ATR can amplify the effects of chemo- and radiation-therapy, and several ATR inhibitors (ATRi) have already undergone clinical testing in cancer. For more accurate patient selection, monitoring and staging, real-time in vivo imaging of ATR could be invaluable; the development of appropriate imaging agents has remained a major challenge.

METHODS

3-amino-N-(4-[¹⁸F]phenyl)-6-(4-(methylsulfonyl)phenyl)pyrazine-2-carboxamide ([¹⁸F]-ATRi), a close analogue of Ve-821, (a clinical ATRi candidate), was readily accomplished similarly to already established synthetic procedures. Structurally, ¹⁸F was introduced at the 4-position of the aromatic ring of Ve-821 for generating a labeled ATR inhibitor. In vitro experiments were conducted in U251 MG glioblastoma cell lines and ex vivo biodistribution were performed in subcutaneous U251 MG xenograft bearing athymic nude mice following microPET imaging.

RESULTS

[¹⁸F]-ATRi has a similar pharmacokinetic profile to that of Ve-821. Using an U251 MG glioblastoma mouse model, we evaluated the in vivo binding efficiency of [¹⁸F]-ATRi. Blood and tumor showed a statistically significant difference between mice injected with only the probe or following blocking experiment with Ve-821 (1.48±0.40%ID/g vs. 0.46±0.12%ID/g in tumor and 1.85±0.47%ID/g vs. 0.84±0.3%ID/g in blood respectively).

CONCLUSIONS

[¹⁸F]-ATRi represents the first ¹⁸F positron emission tomography (PET) ATR imaging agent, and is designed on a low nanomolar and clinically relevant ATR inhibitor.

TRPM2 regulates TXNIP-mediated NLRP3 inflammasome activation via interaction with p47 phox under high glucose in human monocytic cells

Excessive production of reactive oxygen species (ROS) induced by hyperglycemia increased the secretion of interleukin-1β (IL-1β), which contributes to the pathogenesis of diabetes and its complications. Although high glucose (HG)-induced oxidative stress and aberrant Ca²⁺ channels activity causes an increase in transmembrane Ca²⁺ influx, however the relative contribution of Transient receptor potential (TRP) channels is not well studied. Here, we identified that HG (30 mM glucose for 48 h) induced the activation of the NLRP3-ASC inflammasome, leading to caspase-1 activation, and IL-1β and IL-18 secretion in human monocytic cell lines. Moreover, we used a hyperglycemia model in U937 monocytes, showing that the activation of TRPM2 was augmented, and TRPM2-mediated Ca²⁺ influx was critical for NLRP3 inflammasome activation. This pathway involved NADPH oxidase-dependent ROS production and TXNIP-NLRP3 inflammasome pathway. Furthermore, the inhibition of TRPM2 reduced ROS production and lowered NADPH oxidase activity via cooperatively interaction with p47 phox in response to HG. These results provided a mechanistic linking between TRPM2-mediated Ca²⁺ influx and p47 phox signaling to induce excess ROS production and TXNIP-mediated NLRP3 inflammasome activation under HG, and suggested that TRPM2 represented a potential target for alleviating NLRP3 inflammasome activation related to hyperglycemia-induced oxidative stress in Type 2 diabetes Mellitus (T2DM).

Immunological effects of chemotherapy and radiotherapy against brain tumors

INTRODUCTION

The mainstays of brain tumor therapy are surgery, radiotherapy and chemotherapy. Cancer immunotherapy is explored as an additional treatment modality. However, emerging evidence indicates that also radio- and chemotherapy have immunological effects in addition to their cytotoxic and cytostatic activities.

AREA COVERED

We summarize the literature on radio- and chemotherapy-mediated immunological effects in primary and secondary brain tumors and outline open questions within the field. To this end, a literature search was performed using the terms 'brain tumor', 'immune system', 'immunogenic cell death', 'vaccination', 'checkpoint inhibition', 'radiotherapy', 'chemotherapy' and derivations thereof. Expert commentary: Immunological effects of chemo- and radiotherapy in brain tumors involve direct immunogenic modulations of tumor cells, changes of the microenvironment and functional alterations of innate and adaptive immune cells. Each treatment modality can exert various effects that comprise both immune-stimulatory and immunosuppressive mechanisms. A detailed knowledge of these mechanisms is indispensable for an optimal combination of conventional anti-tumor treatments and novel immunotherapeutic approaches.

Temozolomide induces the expression of the glioma Big Potassium (gBK) ion channel, while inhibiting fascin-1 expression: possible targets for glioma therapy

OBJECTIVE

Temozolomide (TMZ) improves Glioblastoma Multiforme (GBM) patient survival. The invasive behavior of the glioma cells is the cause of GBM relapse. The glioma BK ion channel (gBK) may provide glioma cells with a mechanism to invade surrounding tissue. gBK contains epitopes that cytolytic T lymphocytes (CTLs) can recognize and kill glioma cells. Fascin-1 is an actin crosslinking molecule that supports microvilli; these membrane protrusions provide a physical defense against CTLs. TMZ was investigated to determine its effect on gBK and fascin-1 expression.

RESEARCH DESIGN AND METHODS

Human glioma cells cultured in TMZ were analyzed for their altered mRNA and gBK protein levels by using quantitative real time PCR, immunostaining and cellular functional assays.

RESULTS

TMZ slowed glioma cell growth and inhibited their transmigratory properties due to loss of fascin-1. TMZ induced increased gBK and HLA expression and allowed these TMZ-treated cells to become better targets for gBK-specific CTLs.

CONCLUSIONS

Besides its traditional chemotherapeutic effect, TMZ can have four other targeted pathways: 1) slowed glioma cell growth; 2) inhibited glioma cell transmigration; 3) increased HLA-A2 and gBK tumor antigen production; 4) increased CTL-mediated cytolysis of the TMZ treated glioma cells due to the loss of their defensive membrane protrusions supported by fascin-1.

Stromal fibroblasts support dendritic cells to maintain IL-23/Th17 responses after exposure to ionizing radiation

Cross talk between DCs and FBs in understanding the effects of IR in DC function.

Dendritic cell function is modulated by stromal cells, including fibroblasts. Although poorly understood, the signals delivered through this crosstalk substantially alter dendritic cell biology. This is well illustrated with release of TNF-α/IL-1β from activated dendritic cells, promoting PGE₂ secretion from stromal fibroblasts. This instructs dendritic cells to up-regulate IL-23, a key Th17-polarizing cytokine. We previously showed that ionizing radiation inhibited IL-23 production by human dendritic cells in vitro. In the present study, we investigated the hypothesis that dendritic cell-fibroblast crosstalk overcomes the suppressive effect of ionizing radiation to support appropriately polarized Th17 responses. Radiation (1–6 Gy) markedly suppressed IL-23 secretion by activated dendritic cells (P < 0.0001) without adversely impacting their viability and consequently, inhibited the generation of Th17 responses. Cytokine suppression by ionizing radiation was selective, as there was no effect on IL-1β, -6, -10, and -27 or TNF-α and only a modest (11%) decrease in IL-12p70 secretion. Coculture with fibroblasts augmented IL-23 secretion by irradiated dendritic cells and increased Th17 responses. Importantly, in contrast to dendritic cells, irradiated fibroblasts maintained their capacity to respond to TNF-α/IL-1β and produce PGE₂, thus providing the key intermediary signals for successful dendritic cell-fibroblasts crosstalk. In summary, stromal fibroblasts support Th17-polarizing cytokine production by dendritic cells that would otherwise be suppressed in an irradiated microenvironment. This has potential ramifications for understanding the immune response to local radiotherapy. These findings underscore the need to account for the impact of microenvironmental factors, including stromal cells, in understanding the control of immunity.

Early intranuclear replication of African swine fever virus genome modifies the landscape of the host cell nucleus

Although African swine fever virus (ASFV) replicates in viral cytoplasmic factories, the presence of viral DNA within the host cell nucleus has been previously reported to be essential for productive infection. Herein, we described, for the first time, the intranuclear distribution patterns of viral DNA replication events, preceding those that occur in the cytoplasmic compartment. Using BrdU pulse-labelling experiments, newly synthesized ASFV genomes were exclusively detected inside the host cell nucleus at the early phase of infection, both in swine monocyte-derived macrophages (MDMs) and Vero cells. From 8hpi onwards, BrdU labelling was only observed in ASFV cytoplasmic factories. Our results also show that ASFV specifically activates the Ataxia Telangiectasia Mutated Rad-3 related (ATR) pathway in ASFV-infected swine MDMs from the early phase of infection, most probably because ASFV genome is recognized as foreign DNA. Morphological changes of promyelocytic leukaemia nuclear bodies (PML-NBs), nuclear speckles and Cajal bodies were also found in ASFV-infected swine MDMs, strongly suggesting the viral modulation of cellular antiviral responses and cellular transcription, respectively. As described for other viral infections, the nuclear reorganization that takes place during ASFV infection may also provide an environment that favours its intranuclear replication events. Altogether, our results contribute for a better understanding of ASFV replication strategies, starting with an essential intranuclear DNA replication phase which induces host nucleus changes towards a successful viral infection.

Glutathione reaction products with a chemical allergen, methylene-diphenyl diisocyanate, stimulate alternative macrophage activation and eosinophilic airway inflammation

Isocyanates have been a leading chemical cause of occupational asthma since their utility for generating polyurethane was first recognized over 60 years ago, yet the mechanisms of isocyanate asthma pathogenesis remain unclear. The present study provides in vivo evidence that a GSH mediated pathway underlies asthma-like eosinophilic inflammatory responses to respiratory tract isocyanate exposure. In naïve mice, a mixture of GSH reaction products with the chemical allergen, methylene-diphenyl diisocyanate (MDI), induced innate immune responses, characterized by significantly increased airway levels of Chitinase YM-1 and IL-12/IL-23β (but not α) subunit. However, in mice immunologically sensitized to MDI via prior skin exposure, identical GSH-MDI doses induced substantially greater inflammatory responses, including significantly increased airway eosinophil numbers and mucus production, along with IL-12/IL-23β, chitinases, and other indicators of alternative macrophage activation. The "self"-protein albumin in mouse airway fluid was uniquely modified by GSH-MDI at position (414)K, a preferred site of MDI reactivity on human albumin. The (414)K-MDI conjugation appears to covalently cross-link GSH to albumin via GSH's NH2-terminus, a unique conformation possibly resulting from cyclized mono(GSH)-MDI or asymmetric (S,N'-linked) bis(GSH)-MDI conjugates. Together, the data support a possible thiol mediated transcarbamoylating mechanism linking MDI exposure to pathogenic eosinophilic inflammatory responses.

Tumor suppressor Ing1b facilitates DNA repair and prevents oxidative stress induced cell death

Inhibitor of growth (ING) family of proteins are known to coordinate with histone acetyltransferases and regulate the key events of cell cycle and DNA repair. Previous work from our lab showed that Ing1b regulated the nucleotide excision repair by facilitating histone acetylation and subsequent chromatin relaxation. Further, it was also shown that Ing1b protected the cells from genomic instability induced cell death by promoting ubiquitination of proliferating cell nuclear antigen (PCNA). In the present study we explored the role of Ing1b in the repair of oxidized DNA and prevention of oxidative stress induced genotoxic cell death. Using HCT116 cells we show that Ing1b protein expression is induced by treatment with H2O2. Ing1b lacking cells showed decreased ability to repair the oxidized DNA. PCNA monoubiquitination, a critical event of DNA repair was blunted in Ing1b knock down cells and augmented in Ing1b over expressing cells. Moreover, oxidative stress induced cell death was higher in cells lacking Ing1b whereas it was lower in Ing1b over expressing cells. Finally we show that inhibition of histone deacetylases, rescued the Ing1b knock down cells from cytotoxic effects of H2O2 treatment.

Interactions between polycyclic aromatic hydrocarbons in complex mixtures and implications for cancer risk assessment

In this review we discuss the effects of exposure to complex PAH mixtures in vitro and in vivo on mechanisms related to carcinogenesis. Of particular concern regarding exposure to complex PAH mixtures is how interactions between different constituents can affect the carcinogenic response and how these might be included in risk assessment. Overall the findings suggest that the responses resulting from exposure to complex PAH mixtures is varied and complicated. More- and less-than additive effects on bioactivation and DNA damage formation have been observed depending on the various mixtures studied, and equally dependent on the different test systems that are used. Furthermore, the findings show that the commonly used biological end-point of DNA damage formation is insufficient for studying mixture effects. At present the assessment of the risk of exposure to complex PAH mixtures involves comparison to individual compounds using either a surrogate or a component-based potency approach. We discuss how future risk assessment strategies for complex PAH mixtures should be based around whole mixture assessment in order to account for interaction effects. Inherent to this is the need to incorporate different experimental approaches using robust and sensitive biological endpoints. Furthermore, the emphasis on future research should be placed on studying real life mixtures that better represent the complex PAH mixtures that humans are exposed to.

Antitumor immune responses induced by ionizing irradiation and further immune stimulation

The therapy of cancer emerged as multimodal treatment strategy. The major mode of action of locally applied radiotherapy (RT) is the induction of DNA damage that triggers a network of events that finally leads to tumor cell cycle arrest and cell death. Along with this, RT modifies the phenotype of the tumor cells and their microenvironment. Either may contribute to the induction of specific and systemic antitumor immune responses. The latter are boosted when additional immune therapy (IT) is applied at distinct time points during RT. We will focus on therapy-induced necrotic tumor cell death that is immunogenic due to the release of damage-associated molecular patterns. Immune-mediated distant bystander (abscopal) effects of RT when combined with dendritic cell-based IT and the role of fractionation of radiation in the induction of immunogenic tumor cell death will be discussed. Autologous whole-tumor-cell-based vaccines generated by high hydrostatic pressure technology will be introduced and the influence of cytokines and the immune modulator AnnexinA5 on the ex vivo generated or in situ therapy-induced vaccine efficacy will be outlined. RT should be regarded as immune adjuvant for metastatic disease and as a tool for the generation of an in situ vaccine when applied at distinct fractionation doses or especially in combination with IT to generate immune memory against the tumor. To identify the most beneficial combination and chronology of RT with IT is presumably one of the biggest challenges of innovative tumor research and therapies.

Human CD4+CD25+ regulatory T cells are sensitive to low dose cyclophosphamide: implications for the immune response

Regulatory T cells (Treg) play a pivotal role in the immune system since they inhibit the T cell response. It is well known that cyclophosphamide applied at low dose is able to stimulate the immune response while high dose cyclophosphamide exerts inhibitory activity. Data obtained in mice indicate that cyclophosphamide provokes a reduction in the number of Treg and impairs their suppressive activity, resulting in immune stimulation. Here, we addressed the question of the sensitivity of human Treg to cyclophosphamide, comparing Treg with cytotoxic T cells (CTL) and T helper cells (Th). We show that Treg are more sensitive than CTL and Th to mafosfamide, which is an active derivative of cyclophosphamide, which does not need metabolic activation. The high sensitivity of Treg was due to the induction of apoptosis. Treg compared to CTL and Th were not more sensitive to the alkylating drugs temozolomide and nimustine and also not to mitomycin C, indicating a specific Treg response to mafosfamide. The high sensitivity of Treg to mafosfamide resulted not only in enhanced cell death, but also in impaired Treg function as demonstrated by a decline in the suppressor activity of Treg in a co-culture model with Th and Helios positive Treg. Treatment of Treg with mafosfamide gave rise to a high level of DNA crosslinks, which were not repaired to the same extent as observed in Th and CTL. Also, Treg showed a low level of γH2AX foci up to 6 h and a high level 24 h after treatment, indicating alterations in the DNA damage response. Overall, this is the first demonstration that human Treg are, in comparison with Th and CTL, hypersensitive to cyclophosphamide, which is presumably due to a DNA repair defect.

Temozolomide-mediated DNA methylation in human myeloid precursor cells: differential involvement of intrinsic and extrinsic apoptotic pathways

PURPOSE

An understanding of how hematopoietic cells respond to therapy that causes myelosuppression will help develop approaches to prevent this potentially life-threatening toxicity. The goal of this study was to determine how human myeloid precursor cells respond to temozolomide (TMZ)-induced DNA damage.

EXPERIMENTAL DESIGN

We developed an ex vivo primary human myeloid precursor cells model system to investigate the involvement of cell-death pathways using a known myelosuppressive regimen of O(6)-benzylguanine (6BG) and TMZ.

RESULTS

Exposure to 6BG/TMZ led to increases in p53, p21, γ-H2AX, and mitochondrial DNA damage. Increases in mitochondrial membrane depolarization correlated with increased caspase-9 and -3 activities following 6BG/TMZ treatment. These events correlated with decreases in activated AKT, downregulation of the DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT), and increased cell death. During myeloid precursor cell expansion, FAS/CD95/APO1(FAS) expression increased over time and was present on approximately 100% of the cells following exposure to 6BG/TMZ. Although c-flipshort, an endogenous inhibitor of FAS-mediated signaling, was decreased in 6BG/TMZ-treated versus control, 6BG-, or TMZ alone-treated cells, there were no changes in caspase-8 activity. In addition, there were no changes in the extent of cell death in myeloid precursor cells exposed to 6BG/TMZ in the presence of neutralizing or agonistic anti-FAS antibodies, indicating that FAS-mediated signaling was not operative.

CONCLUSIONS

In human myeloid precursor cells, 6BG/TMZ-initiated apoptosis occurred by intrinsic, mitochondrial-mediated and not extrinsic, FAS-mediated apoptosis. Human myeloid precursor cells represent a clinically relevant model system for gaining insight into how hematopoietic cells respond to chemotherapeutics and offer an approach for selecting effective chemotherapeutic regimens with limited hematopoietic toxicity.

Impact of temozolomide on immune response during malignant glioma chemotherapy

Malignant glioma, or glioblastoma, is the most common and lethal form of brain tumor with a median survival time of 15 months. The established therapeutic regimen includes a tripartite therapy of surgical resection followed by radiation and temozolomide (TMZ) chemotherapy, concurrently with radiation and then as an adjuvant. TMZ, a DNA alkylating agent, is the most successful antiglioma drug and has added several months to the life expectancy of malignant glioma patients. However, TMZ is also responsible for inducing lymphopenia and myelosuppression in malignant glioma patients undergoing chemotherapy. Although TMZ-induced lymphopenia has been attributed to facilitate antitumor vaccination studies by inducing passive immune response, in general lymphopenic conditions have been associated with poor immune surveillance leading to opportunistic infections in glioma patients, as well as disrupting active antiglioma immune response by depleting both T and NK cells. Deletion of O6-methylguanine-DNA-methyltransferase (MGMT) activity, a DNA repair enzyme, by temozolomide has been determined to be the cause of lymphopenia. Drug-resistant mutation of the MGMT protein has been shown to render chemoprotection against TMZ. The immune modulating role of TMZ during glioma chemotherapy and possible mechanisms to establish a strong TMZ-resistant immune response have been discussed.

Chemotherapy disrupts learning, neurogenesis and theta activity in the adult brain

Chemotherapy, especially if prolonged, disrupts attention, working memory and speed of processing in humans. Most cancer drugs that cross the blood-brain barrier also decrease adult neurogenesis. Because new neurons are generated in the hippocampus, this decrease may contribute to the deficits in working memory and related thought processes. The neurophysiological mechanisms that underlie these deficits are generally unknown. A possible mediator is hippocampal oscillatory activity within the theta range (3-12 Hz). Theta activity predicts and promotes efficient learning in healthy animals and humans. Here, we hypothesised that chemotherapy disrupts learning via decreases in hippocampal adult neurogenesis and theta activity. Temozolomide was administered to adult male Sprague-Dawley rats in a cyclic manner for several weeks. Treatment was followed by training with different types of eyeblink classical conditioning, a form of associative learning. Chemotherapy reduced both neurogenesis and endogenous theta activity, as well as disrupted learning and related theta-band responses to the conditioned stimulus. The detrimental effects of temozolomide only occurred after several weeks of treatment, and only on a task that requires the association of events across a temporal gap and not during training with temporally overlapping stimuli. Chemotherapy did not disrupt the memory for previously learned associations, a memory independent of (new neurons in) the hippocampus. In conclusion, prolonged systemic chemotherapy is associated with a decrease in hippocampal adult neurogenesis and theta activity that may explain the selective deficits in processes of learning that describe the 'chemobrain'.