How does radiation kill cells?

Catalyzing Synthesis of Chiral Nitrendipine

This paper describes the chiral synthesis of R-2,6-dimethyl-4-(3-nitro phenyl)-1,4- dihydro-pyridine-3,5-dicarboxylic acid 3-ethyl ester 5-methyl ester (R-Nitrendipine) using chiral phase transfer catalyst. The structure of the obtained nitrendipine crystals was determined with single crystal X-ray diffraction. The crystal is monoclinic, with the space group of P21/c and unit cell constants of a=8.8577(15), b=15.581(3), c=12.999(2)Å, β=92.458(4)°, V=1792.3(5)Å3, Z=4, Dc =1.335g/cm3, F(000)=760. X-ray analysis reveals that the product is a chiral nitrendipine with R-configuration of the dihydropyridine ring. And measurement of polarimeter reveals that the synthesized nitrendipine is a chiral molecular.

Cancer and radiation therapy: current advances and future directions

In recent years remarkable progress has been made towards the understanding of proposed hallmarks of cancer development and treatment. However with its increasing incidence, the clinical management of cancer continues to be a challenge for the 21st century. Treatment modalities comprise of radiation therapy, surgery, chemotherapy, immunotherapy and hormonal therapy. Radiation therapy remains an important component of cancer treatment with approximately 50% of all cancer patients receiving radiation therapy during their course of illness; it contributes towards 40% of curative treatment for cancer. The main goal of radiation therapy is to deprive cancer cells of their multiplication (cell division) potential. Celebrating a century of advances since Marie Curie won her second Nobel Prize for her research into radium, 2011 has been designated the Year of Radiation therapy in the UK. Over the last 100 years, ongoing advances in the techniques of radiation treatment and progress made in understanding the biology of cancer cell responses to radiation will endeavor to increase the survival and reduce treatment side effects for cancer patients. In this review, principles, application and advances in radiation therapy with their biological end points are discussed.

Delayed cell death associated with mitotic catastrophe in γ-irradiated stem-like glioma cells

Background and Purpose

Stem-like tumor cells are regarded as highly resistant to ionizing radiation (IR). Previous studies have focused on apoptosis early after irradiation, and the apoptosis resistance observed has been attributed to reduced DNA damage or enhanced DNA repair compared to non-stem tumor cells. Here, early and late radioresponse of patient-derived stem-like glioma cells (SLGCs) and differentiated cells directly derived from them were examined for cell death mode and the influence of stem cell-specific growth factors.

Materials and methods

Primary SLGCs were propagated in serum-free medium with the stem-cell mitogens epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2). Differentiation was induced by serum-containing medium without EGF and FGF. Radiation sensitivity was evaluated by assessing proliferation, clonogenic survival, apoptosis, and mitotic catastrophe. DNA damage-associated γH2AX as well as p53 and p21 expression were determined by Western blots.

Results

SLGCs failed to apoptose in the first 4 days after irradiation even at high single doses up to 10 Gy, but we observed substantial cell death later than 4 days postirradiation in 3 of 6 SLGC lines treated with 5 or 10 Gy. This delayed cell death was observed in 3 of the 4 SLGC lines with nonfunctional p53, was associated with mitotic catastrophe and occurred via apoptosis. The early apoptosis resistance of the SLGCs was associated with lower γH2AX compared to differentiated cells, but we found that the stem-cell culture cytokines EGF plus FGF-2 strongly reduce γH2AX levels. Nonetheless, in two p53-deficient SLGC lines examined γIR-induced apoptosis even correlated with EGF/FGF-induced proliferation and mitotic catastrophe. In a line containing CD133-positive and -negative stem-like cells, the CD133-positive cells proliferated faster and underwent more γIR-induced mitotic catastrophe.

Conclusions

Our results suggest the importance of delayed apoptosis, associated mitotic catastrophe, and cellular proliferation for γIR-induced death of p53-deficient SLGCs. This may have therapeutic implications. We further show that the stem-cell culture cytokines EGF plus FGF-2 activate DNA repair and thus confound in vitro comparisons of DNA damage repair between stem-like and more differentiated tumor cells.

X-irradiation reduces the proliferation of astrocytes by cell cycle arrest

Reactive astrogliosis is one of the key components of the cellular response to CNS injury and is considered a major impediment to axonal regeneration. Our previous study demonstrated that cell cycle inhibition treatment can reduce astrocyte activation and proliferation in vivo. In this study, we examined whether reactive astrogliosis can be suppressed by X-irradiation in vitro by modulating cell cycle progression. X-irradiation with low dose (4 Gy) suppressed astrocyte proliferation as demonstrated by immunofluorescence staining with BrdU and Ki67 in monolayer astrocyte cultures and those in scratch-wound model. The proportions of BrdU (+) and Ki67 (+) cells at 12, 24, and 48 h after 4 Gy irradiation were significantly lower than those in control group. FACS analysis of monolayer astrocyte cultures showed that X-irradiation decreased the proportion of astrocytes in S phase at 12 and 24h after irradiation with a dose-dependent manner. Furthermore, after X-irradiation, higher levels of p53 were observed by western blot as compared to control astrocyte cultures. Taken together, these data support that X-irradiation can decrease astrogliosis via arresting the cell cycle progression, which might constitute an effective therapeutic intervention in diseases characterized by excessive proliferation of glial cells.

A specific inhibitor of protein kinase CK2 delays gamma-H2Ax foci removal and reduces clonogenic survival of irradiated mammalian cells

Background

The protein kinase CK2 sustains multiple pro-survival functions in cellular DNA damage response and its level is tightly regulated in normal cells but elevated in cancers. Because CK2 is thus considered as potential therapeutic target, DNA double-strand break (DSB) formation and rejoining, apoptosis induction and clonogenic survival was assessed in irradiated mammalian cells upon chemical inhibition of CK2.

Methods

MRC5 human fibroblasts and WIDR human colon carcinoma cells were incubated with highly specific CK2 inhibitor 4,5,6,7-tetrabromobenzotriazole (TBB), or mock-treated, 2 hours prior to irradiation. DSB was measured by pulsed-field electrophoresis (PFGE) as well as gamma-H2AX foci formation and removal. Apoptosis induction was tested by DAPI staining and sub-G1 flow cytometry, survival was quantified by clonogenic assay.

Results

TBB treatment did not affect initial DNA fragmention (PFGE; up to 80 Gy) or foci formation (1 Gy). While DNA fragment rejoining (PFGE) was not inhibited by the drug, TBB clearly delayed gamma-H2AX foci disappearence during postirradiation incubation. No apoptosis induction could be detected for up to 38 hours for both cell lines and exposure conditions (monotherapies or combination), but TBB treatment at this moderately toxic concentration of 20 μM (about 40% survival) enhanced radiation-induced cell killing in the clonogenic assay.

Conclusions

The data imply a role of CK2 in gamma-H2AX dephosporylation, most likely through its known ability to stimulate PP2A phosphatase, rather than DSB rejoining. The slight but definite clonogenic radiosensitization by TBB does apparently not result from interference with an apoptosis suppression function of CK2 in these cells but could reflect inhibitor-induced uncoupling of DNA damage response decay from break ligation.

Proton inactivation of melanoma cells enhanced by fotemustine

Response of human HTB140 melanoma cells to proton irradiation in combination with fotemustine (FM) was investigated. Effects of these agents were analysed on cell proliferation and induction of apoptosis. Cells pretreated with 100- or 250-µM of FM were irradiated in the middle of the therapeutic 62-MeV proton spread-out Bragg peak, with a dose of 16 Gy. All treatments reduced proliferation and survival of melanoma cells. The most pronounced effects of the combined treatment were obtained for cell survivals. The level of apoptosis increased after all applied treatments. Particularly good pro-apoptotic effect was achieved when proton irradiation was combined with 250 μM of FM. This was followed by the increased expression of p53 gene. The obtained results have shown that combined application of FM and protons significantly reduced growth of this resistant melanoma cell line.

Hepatocyte growth factor in lung repair and pulmonary fibrosis

Pulmonary remodeling is characterized by the permanent and progressive loss of the normal alveolar architecture, especially the loss of alveolar epithelial and endothelial cells, persistent proliferation of activated fibroblasts, or myofibroblasts, and alteration of extracellular matrix. Hepatocyte growth factor (HGF) is a pleiotropic factor, which induces cellular motility, survival, proliferation, and morphogenesis, depending upon the cell type. In the adult, HGF has been demonstrated to play a critical role in tissue repair, including in the lung. Administration of HGF protein or ectopic expression of HGF has been demonstrated in animal models of pulmonary fibrosis to induce normal tissue repair and to prevent fibrotic remodeling. HGF-induced inhibition of fibrotic remodeling may occur via multiple direct and indirect mechanisms including the induction of cell survival and proliferation of pulmonary epithelial and endothelial cells, and the reduction of myofibroblast accumulation.

Secondary necrosis: the natural outcome of the complete apoptotic program

The predominant definition of apoptosis considers that the elimination of the apoptosing cell is by heterolytic degradation following phagocytosis by an assisting scavenger (efferocytosis). However, an alternative and largely underestimated outcome of apoptosis is secondary necrosis, an autolytic process of cell disintegration with release of cell components that occurs when there is no intervention of scavengers and the full apoptotic program is completed. Secondary necrosis is the typical outcome of apoptosis in unicellular eukaryotes but, importantly, it may also occur in multicellular animals and has been implicated in the genesis of important human pathologies. Secondary necrosis is a mode of cell elimination with specific molecular and morphological features and should be considered the natural outcome of the complete apoptotic program.

Different radiosensitivity of CD4(+)CD25(+) regulatory T cells and effector T cells to low dose gamma irradiation in vitro

PURPOSE

To determine the radiosensitivity difference of human Cluster of Differentiation (CD)4(+)CD25(+) regulatory T cells (Treg) and effector T cells to low dose gamma ray and elucidate the underlying mechanisms in vitro.

MATERIALS AND METHODS

Blood samples were collected from five health subjects and five patients with advanced hepatocellular carcinoma (HCC). Treg and CD4(+)CD25⁻ T cells were selected using magnetic microbeads. The proliferative profiles, cytokine secretion, and differential expressions of apoptosis-related proteins in Treg and CD4(+)CD25⁻ T cells were compared using [³H]-thymidine incorporation, Luminex assay and flow cytometry when treated with various low doses of γ-ray.

RESULTS

A dose-dependent reduction of proliferation in response to irradiation which paralleled the induction of apoptosis existed in Treg and CD4(+)CD25⁻ T cells. Treg were more radiosensitive to low-dose irradiation (0.94 Gray [Gy]) than effector T cells. The interferon-γ (IFNγ) was significantly upregulated and interleukin 10 (IL-10) was significantly downregulated in irradiated Treg. An enhanced immune response to low dose gamma ray existed in the peripheral blood in patients with advanced HCC. Higher levels of active caspase-3, CD95, B cell lymphoma 2 (Bcl-2)-associated X protein (Bax) expression were observed in Treg compared to CD4(+)CD25⁻ T cells. In addition, gamma irradiation activated CD4(+)CD25⁻ T cells to express CD25.

CONCLUSIONS

These studies revealed that Treg were more radiosensitive than CD4(+)CD25⁻ T cells to low dose irradiation. Higher expressions of apoptosis-related proteins such as caspase-3, CD95 and Bax were observed in Treg when compared to CD4(+)CD25⁻ T cells. Our results suggest that treatment with low doses of gamma irradiation may be a viable strategy to enhance immune response in patients with advanced HCC.

Radiation-induced cell death mechanisms

The main goal when treating malignancies with radiation therapy is to deprive tumor cells of their reproductive potential. One approach to achieve this is by inducing tumor cell apoptosis. Accumulating evidences suggest that induction of apoptosis alone is insufficient to account for the therapeutic effect of radiotherapy. It has become obvious in the last few years that inhibition of the proliferative capacity of malignant cells following irradiation, especially with solid tumors, can occur via alternative cell death modalities or permanent cell cycle arrests, i.e., senescence. In this review, apoptosis and mitotic catastrophe, the two major cell deaths induced by radiation, are described and dissected in terms of activating mechanisms. Furthermore, treatment-induced senescence and its relevance for the outcome of radiotherapy of cancer will be discussed. The importance of p53 for the induction and execution of these different types of cell deaths is highlighted. The efficiency of radiotherapy and radioimmunotherapy has much to gain by understanding the cell death mechanisms that are induced in tumor cells following irradiation. Strategies to use specific inhibitors that will manipulate key molecules in these pathways in combination with radiation might potentiate therapy and enhance tumor cell kill.

Effect of radiation treatment on newly established human breast cancer cell lines MACL-1 and MGSO-3

The characterization of new cell lines is an important tool to understand the biological processes involved in cancer treatments. In the present study, we used two newly established epithelial human breast cancer cell lines from primary sites MACL-1 and MGSO-3 and compared their susceptibility to the treatment with ionizing radiation (IR) with the commercial cell line MDA-MB-231. In the doses used (10 or 20 Gy), IR induced a reduction in cell viability and cell death, measured as DNA fragmentation, at 48 and 72 h after treatment. In addition, 48 h after treatment with IR, we observed an enhancement in the percentage of apoptotic cells. The broad-range caspases inhibitor zVAD-FMK inhibited cytotoxicity induced by IR. After 24 h, treatment with IR activated caspase-9 in MACL-1 and MDA-MB-231 but not in MGSO-3 cells. Thirty hours after treatment with IR (20 Gy), we observed an activation of caspases 8 and 3. These results suggest the involvement of caspases in the cell death induced by IR in two newly established cell lines. These cells may be useful in studies of breast cancer in defining basic mechanisms in molecular and cellular radiobiology and may contribute to the rational design of future models of cancer therapies.

ATM- and ATR-mediated response to DNA damage induced by a novel camptothecin, ST1968

DNA damage response and checkpoint activation are expected to influence the sensitivity to DNA-damaging agents. This study was designed to investigate the DNA damage response to the novel camptothecin, ST1968, in two tumor cell lines with a different biological background (A2780 and KB), which underwent distinct cell cycle perturbations and cell death modalities. Following treatment with the camptothecin or ionizing radiation, both inducing double-strand DNA breaks, the ovarian carcinoma A2780 cells exhibited activation of the ATM-Chk2 pathway and early induction of apoptosis. In contrast, the squamous carcinoma KB cells exhibited activation of ATR-Chk1 pathway, a persistent G(2)/M-phase arrest, cellular senescence, mitotic catastrophe and delayed apoptosis, suggesting a defective ATM pathway. The cellular response to UV-induced DNA damage, which activates ATR-Chk1 pathway, was similar in the two cell lines exhibiting early apoptosis induction. Inhibition of ATM in A2780 cells, resulting in reduced phosphorylation of Chk2, enhanced ST1968-induced apoptosis, but had no effect in KB cells. The susceptibility to camptothecin-induced apoptosis of A2780 cells was likely p53-dependent but not related to the activation of the ATM pathway. In contrast, the inhibition of Chk1 enhanced apoptosis response in KB cell but not in A2780. Thus, depending on the biological context, the camptothecin activated ATM-Chk2 or ATR-Chk1 pathways, both having a protective role. In conclusion, our results are consistent with the interpretation that the modality of cell death response is not the critical determinant of sensitivity to camptothecins, and support the interest of inhibition of checkpoint kinases to improve the efficacy of camptothecins.

Effect of N-acetylcysteine on (12)C(6+) ion irradiation-induced lymphocytes DNA damages and immunity changes in mice

The aims of present study are to estimate the biological risks to the immunity of mice exposed to heavy ion radiation and to investigate the effect of N-acetylcysteine (NAC) on (12)C(6+) ion irradiation-induced lymphocyte DNA damage. Results showed that in the brine group, the levels of lymphocyte DNA damage and MN, thymocytes G(2)/M phase arrest and apoptosis percentages (except for activity of NK cells) were up at each time point. A time-response curve for MN and DNA damage appeared in the NAC group. We found that whole-body (12)C(6+) ion irradiation at a dose of 4 Gy could: induce lymphocyte DNA double-strand breaks (DSBs); immunocytes DSBs may lead to acute effects on immunity; and 200 mg/kg NAC showed significant protection against radiation harm.

Cell death induced by N-methyl-N-nitrosourea, a model S(N)1 methylating agent, in two lung cancer cell lines of human origin

New therapeutic approaches are needed for lung cancer, the leading cause of cancer death. Methylating agents constitute a widely used class of anticancer drugs, the effect of which on human non small cell lung cancer (NSCLC) has not been adequately studied. N-methyl-N-nitrosourea (MNU), a model S(N)1 methylating agent, induced cell death through a distinct mechanism in two human NSCLC cell lines studied, A549(p53(wt)) and H157(p53(null)). In A549(p53(wt)), MNU induced G2/M arrest, accompanied by cdc25A degradation, hnRNP B1 induction, hnRNP C1/C2 downregulation. Non-apoptotic cell death was confirmed by the lack of increase in the sub-G1 DNA content, Poly (ADP-ribose) polymerase cleavage and caspase-3, -7 activation. In H157(p53(null)), MNU induced apoptotic cell death, confirmed by cytofluorometry of DNA content and immunodetection of apoptotic markers, accompanied by overexpression of hnRNP B1 and C1/C2. Thus, the mechanism of the cell death induced by S(N)1 methylating agents is cell type-dependent and must be assessed prior treatment.

Ionizing radiation induces apoptotic signal through protein kinase Cdelta (delta) and survival signal through Akt and cyclic-nucleotide response element-binding protein (CREB) in Jurkat T cells

Although ionizing radiation induces a loss of proliferative capacity as well as cell death by apoptosis and necrosis, cells can oppose the damaging effects by activating survival signal pathways. Here we report the effect of 1.5- and 6-Gy doses of ionizing radiation on apoptotic protein kinase Cdelta (PKCdelta) and survival cyclic-nucleotide response element-binding protein (CREB) signal in Jurkat T cells. Cell cycle analysis, performed by flow cytometry, showed a significant G2M arrest 24 h after exposure to 6 Gy. This arrest was accompanied by dead cells, which increased in number up to 7 days, when cell viability was further reduced. The response was apparently promoted by caspase-3-mediated PKCdelta activation, and thus apoptosis. Moreover, the presence of viable cells up to 7 days in samples exposed to 6 Gy is explained by Akt activation, which may influence the nuclear transcription factor CREB, leading to resistance to ionizing radiation. Thus, the knowledge of apoptotic and survival pathways activated in tumor cells may help in establishing specific therapies by combining selective inhibitors or stimulators of key signaling proteins with conventional chemotherapy, hormone therapy, and radiotherapy.

Effect of adiponectin deficiency on intestinal damage and hematopoietic responses of mice exposed to gamma radiation

Adiponectin (APN) is an adipose tissue-derived cytokine that regulates insulin sensitivity and inflammation. It is also involved in modulation of cell proliferation by binding to various growth factors. Based on its known effects in modulating cell proliferation and oxidative stress, APN may potentially be involved in regulating tissue damage and repair following irradiation. Adiponectin KO mice and their WT littermates were exposed to a single whole-body dose of 3 or 6Gy gamma radiation. Radiation-induced alterations were studied in jejunum, blood, bone marrow and thymus at days 1 and 5 post-irradiation and compared with sham-irradiated groups. In WT mice, irradiation did not significantly alter serum APN levels while inducing a significant decrease in serum leptin. Irradiation caused a significant reduction in thymocyte cellularity, with concomitant decrease in CD4(+), CD8(+) and CD4(+)CD8(+) T cell populations, with no significant differences between WT and APN KO mice. Irradiation resulted in a significantly higher increase in the frequency of micronucleated reticulocytes in the blood of APN KO compared with WT mice, whereas frequency of micronucleated normochromatic erythrocytes in the bone marrow at day 5 was significantly higher in WT compared with APN KO mice. Finally, irradiation induced similar alterations in villus height and crypt cell proliferation in the jejunum of WT and APN KO mice. Jejunum explants from sham-irradiated APN KO mice produced higher levels of IL-6 compared with tissue from WT animals, but the difference was no longer apparent following irradiation. Our data indicate that APN deficiency does not play a significant role in modulating radiation-induced gastrointestinal injury in mice, while it may participate in regulation of damage to the hematopoietic system.

Association of reactive oxygen species levels and radioresistance in cancer stem cells

The metabolism of oxygen, although central to life, produces reactive oxygen species (ROS) that have been implicated in processes as diverse as cancer, cardiovascular disease and ageing. It has recently been shown that central nervous system stem cells and haematopoietic stem cells and early progenitors contain lower levels of ROS than their more mature progeny, and that these differences are critical for maintaining stem cell function. We proposed that epithelial tissue stem cells and their cancer stem cell (CSC) counterparts may also share this property. Here we show that normal mammary epithelial stem cells contain lower concentrations of ROS than their more mature progeny cells. Notably, subsets of CSCs in some human and murine breast tumours contain lower ROS levels than corresponding non-tumorigenic cells (NTCs). Consistent with ROS being critical mediators of ionizing-radiation-induced cell killing, CSCs in these tumours develop less DNA damage and are preferentially spared after irradiation compared to NTCs. Lower ROS levels in CSCs are associated with increased expression of free radical scavenging systems. Pharmacological depletion of ROS scavengers in CSCs markedly decreases their clonogenicity and results in radiosensitization. These results indicate that, similar to normal tissue stem cells, subsets of CSCs in some tumours contain lower ROS levels and enhanced ROS defences compared to their non-tumorigenic progeny, which may contribute to tumour radioresistance.

The use of gamma-irradiation and ultraviolet-irradiation in the preparation of human melanoma cells for use in autologous whole-cell vaccines

Background

Human cancer vaccines incorporating autologous tumor cells carry a risk of implantation and subsequent metastasis of viable tumor cells into the patient who is being treated. Despite the fact that the melanoma cell preparations used in a recent vaccine trial (Mel37) were gamma-irradiated (200 Gy), approximately 25% of the preparations failed quality control release criteria which required that the irradiated cells incorporate ³H-thymidine at no more than 5% the level seen in the non-irradiated cells. We have, therefore, investigated ultraviolet (UV)-irradiation as a possible adjunct to, or replacement for gamma-irradiation.

Methods

Melanoma cells were gamma- and/or UV-irradiated. ³H-thymidine uptake was used to assess proliferation of the treated and untreated cells. Caspase-3 activity and DNA fragmentation were measured as indicators of apoptosis. Immunohistochemistry and Western blot analysis was used to assess antigen expression.

Results

UV-irradiation, either alone or in combination with gamma-irradiation, proved to be extremely effective in controlling the proliferation of melanoma cells. In contrast to gamma-irradiation, UV-irradiation was also capable of inducing significant levels of apoptosis. UV-irradiation, but not gamma-irradiation, was associated with the loss of tyrosinase expression. Neither form of radiation affected the expression of gp100, MART-1/MelanA, or S100.

Conclusion

These results indicate that UV-irradiation may increase the safety of autologous melanoma vaccines, although it may do so at the expense of altering the antigenic profile of the irradiated tumor cells.

Mechanisms involved in radiation enhancement of intratumoral dendritic cell therapy

We have previously reported that local tumor irradiation, without inducing cell death, can augment the therapeutic efficacy of intratumoral (IT) dendritic cell (DC) vaccination. This study examined potential mechanisms underlying radiation enhancement of IT DC therapy in this setting. Even though ionizing radiation did not mediate tumor cell killing, bone marrow-derived DCs acquired in vitro tumor antigens from irradiated D5 murine melanoma cells more efficiently than from untreated cells. This radiation-enhanced loading of DCs did not induce DC maturation, but was associated with improved cross-priming of T cells both in vitro and in vivo. Furthermore, in vivo pulsing of DCs with irradiated versus untreated tumor cells resulted in superior presentation of tumor antigens to T cells. In addition, tumor irradiation facilitated homing of IT administered DCs to the draining lymph node, possibly by down-regulating CCL21 expression within the tumor mass. Studies of the tumor microenvironment in irradiated versus untreated tumors did not reveal significant inflammatory changes. Moreover, radiation did not promote accumulation of CD4 or CD8 effector T cells within solid tumors. Our results indicate that, without inducing cytotoxicity, tumor irradiation can enhance the ability of DCs to capture tumor antigens, migrate to the draining lymph node, and present processed antigens to T cells. These findings may prove useful in designing future strategies for human cancer immunotherapy.

3-Ethyl 5-methyl 2-hydr-oxy-6-methyl-4-(4-nitro-phen-yl)-2-trifluoro-methyl-1,2,3,4-tetra-hydro-pyridine-3,5-dicarboxyl-ate

In the title compound, C₁₈H₁₉F₃N₂O₇, the tetrahydropyridine ring adopts a half-chair conformation. The nitro group is disordered over two sites with occupancies of 0.780 (15) and 0.220 (15). An intra­molecular N—H⋯F hydrogen bond is observed in the mol­ecular structure. The mol­ecules are linked into a two-dimensional network parallel to (100) by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds.

The mechanism of killing of B-lymphoma cells by 111In-conjugated antibodies

PURPOSE

To determine the mode of killing of B-lymphoma cell lines by 111In-conjugated antibodies (Ab).

MATERIALS AND METHODS

Cells were treated with a range of radiolabeled Ab concentrations to produce a level of killing from 80 - 99.9%, as determined by a long-term proliferation assay. On days 1, 2, 3 and 4, apoptosis was evaluated in individual cells by two assays: (i) Mitochondrial function by JC-1 staining; and (ii) presence of cleaved PARP (poly-ADP-ribose-polymerase) by immunofluorescence. Five cell lines were tested, including two non-Burkitt lines, RL and FSCCL.

RESULTS

In preliminary experiments, it was realized that the standard JC-1 assay, which is widely used, does not distinguish between apoptotic and necrotic cells. The JC-1 assay becomes useful if it is combined with a stain for lysed cells, Sytox green, and then is able to distinguish between viable, apoptotic and necrotic cells. Of the 5 cell lines tested, only Ramos had a large population of apoptotic cells detected by the modified JC-1 assay, but all four of the other cell lines showed evidence of cleaved PARP, albeit to markedly different degrees. The caspase inhibitor, Z-VAD (N-benzyloxycarbonyl-Val-Ala-Asp(O-Me) fluoromethyl ketone), significantly inhibited the killing of Daudi cells.

CONCLUSIONS

Apoptosis was activated in at least four of the five cell lines tested, and participated in the killing of the cells. Staining for cleaved PARP was much more sensitive than the modified JC-1 assay, for most cell lines, probably because it can detect cells that have already lysed, but which died via apoptosis. In addition, the methodological issues discussed may lead to a better understanding of the role of apoptosis in tumor cell cytotoxicity.

Gamma-radiation induces apoptosis via sarcoplasmatic reticulum in guinea pig ileum smooth muscle cells

We investigated the effects of gamma-radiation on cells isolated from the longitudinal smooth muscle layer of the guinea pig ileum, a relatively radioresistant tissue. Single doses (up to 50 Gy) reduced the amount of sarcoplasmatic reticulum and condensed the myofibrils, as shown by electron microscopy 3 days post-irradiation. After that, contractility of smooth muscle strips was reduced. Ca(2+) handling was altered after irradiation, as shown in fura-2 loaded cells, with elevated basal intracellular Ca(2+), reduced amount of intrareticular Ca(2+), and reduced capacitive Ca(2+) entry. Radiation also induced apoptosis, judged from flow cytometry of cells loaded with proprium iodide. Electron microscopy showed that radiation caused condensation of chromatin in dense masses around the nuclear envelope, the presence of apoptotic bodies, fragmentation of the nucleus, detachment of cells from their neighbors, and reductions in cell volume. Radiation also caused activation of caspase 12. Apoptosis was reduced by the administration of the caspase inhibitor Z-Val-Ala-Asp-fluoromethyl-ketone methyl ester (Z-VAD-FMK) during the 3 day period after irradiation, and by the chelator of intracellular Ca(2+), 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), from 1 h before until 2 h after irradiation. BAPTA also reduced the effects of radiation on contractility, basal intracellular Ca(2+), amount of intrareticular Ca(2+), capacitative Ca(2+) entry, and apoptosis. In conclusion, the effects of gamma radiation on contractility, Ca(2+) handling, and apoptosis appear due to a toxic action of intracellular Ca(2+). Ca(2+)-induced damage to the sarcoplasmatic reticulum seems a key event in impaired Ca(2+) handling and apoptosis induced by gamma-radiation.

Antiangiogenic therapy with mammalian target of rapamycin inhibitor RAD001 (Everolimus) increases radiosensitivity in solid cancer

PURPOSE

Radiotherapy exerts direct antivascular effects in tumors and also induces a proangiogenic stress response in tumor cells via the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (mTOR) pathway. Therefore, the combination of radiotherapy and antiangiogenic therapy with mTOR inhibitor RAD001 (Everolimus) might exert additive/synergistic effects on tumor growth.

EXPERIMENTAL DESIGN

Effects of radiation combined with mTOR inhibitor RAD001 were studied on proliferation of murine colon cancer CT-26, human pancreatic cancer L3.6pl, and human umbilical vascular endothelial cells in vitro. In vivo tumor growth of subcutaneous colon cancer CT 26 and orthotopic pancreatic cancer L3.6pl was assessed after fractionated radiotherapy (5 x 2 or 5 x 4 Gy) with or without the addition of the mTOR inhibitor RAD001. RAD001 (1.5 mg/kg/d) was administered until the end of experiments beginning before or after radiotherapy.

RESULTS

A single dose of 2 Gy reduced in vitro proliferation of L3.6pl (-16%), CT-26 (-70%), and human umbilical vascular endothelial cells (HUVEC; -72%). The mTOR inhibitor RAD001 (10 ng/mL) suppressed proliferation of HUVEC (-83%), L3.6pl (-8%), and CT-26 (-82%). Combination of even low concentrations of 0.01 ng/mL RAD001 and 0.25 Gy radiation significantly reduced proliferation of HUVECs (-57%), whereas additive effects of RAD001 and radiation on tumor cells were seen only at the highest concentrations tested. In vivo, RAD001 introduced before radiotherapy (5 x 2 Gy) improved tumor growth control in mice (L3.6pl: 326 mm(3) versus 1144 mm(3); CT-26: 210 mm(3) versus 636 mm(3); P < 0.05 versus control). RAD001 turned out to possess a dose-modifying effect on radiotherapy.

CONCLUSION

Endothelial cells seem to be most sensitive to combination of mTOR inhibition and radiotherapy. Additive tumor growth delay using the mTOR inhibitor RAD001 and radiotherapy in vivo therefore might rely on combined antiangiogenic and antivascular effects.

Alphavbeta3 and alphavbeta5 integrins control glioma cell response to ionising radiation through ILK and RhoB

Integrins are extracellular matrix receptors involved in tumour invasion and angiogenesis. Although there is evidence that inhibiting integrins might enhance the efficiency of radiotherapy, little is known about the exact mechanisms involved in the integrin-dependent modulation of tumor radiosensitivity. The purpose of this study was to investigate the role of alphavbeta3 and alphavbeta5 integrins in glioblastoma cell radioresistance and overall to decipher the downstream biological pathways. We first demonstrated that silencing alphavbeta3 and alphavbeta5 integrins with specific siRNAs significantly reduced the survival after irradiation of 2 glioblastoma cell lines: U87 and SF763. We then showed that integrin activity and integrin signalling pathways controlled the glioma cell radiosensitivity. This regulation of glioma cell response to ionising radiation was mediated through the integrin-linked kinase, ILK, and the small GTPase, RhoB, by two mechanisms. The first one, independent of ILK, consists in the regulation of the intracellular level of RhoB by alphavbeta3 or alphavbeta5 integrin. The second pathway involved in cell radiosensitivity consists in RhoB activation by ionising radiation through ILK. Furthermore, we demonstrated that the alphavbeta3/alphavbeta5 integrins/ILK/RhoB pathway controlled the glioma cells radiosensitivity by regulating radiation-induced mitotic cell death. This work identifies a new biological pathway controlling glioblastoma cells radioresistance, activated from the membrane through alphavbeta3 and/or alphavbeta5 integrins via ILK and RhoB. Our results are clues that downstream effectors of alphavbeta3 and alphavbeta5 integrins as ILK and RhoB might also be promising candidate targets for improving the efficiency of radiotherapy and thus the clinical outcome of patients with glioblastoma.

Geldanamycin promotes premature mitotic entry and micronucleation in irradiated p53/p21 deficient colon carcinoma cells

P53 wild-type and p53-null or mutant cells undergo a G(2)-phase cell-cycle arrest in response to ionizing radiation (IR). In this study we examined the effect of heat-shock protein 90 (HSP90) inhibitor, geldanamycin (GA), on IR-induced G(2) arrest in human colon adenocarcinoma cells with different p53 status. We show that GA treatment abrogates IR-induced G(2)-phase arrest in cells null or mutant for p53. Specifically, GA treatment pushed irradiated p53 signaling-defective cells into a premature mitosis characterized by aberrant mitotic figures, increased gammaH2AX expression and formation of micronucleated cells. Cells expressing wild-type p53 were resistant to GA-induced G(2) checkpoint abrogation. Notably, GA treatment decreased levels of G(2) regulatory proteins Wee1 and Chk1, and inhibitory phosphorylation of Cdc2, independent of p53 status. Further investigation identified p21 as the potential downstream effector of p53 that mediates resistance to G(2) checkpoint abrogation. Clonogenic survival studies demonstrated higher sensitivity to GA alone or combination IR plus GA treatment in p53 and p21-null cells. Collectively, these data demonstrate potential mechanisms through which HSP90 inhibition can enhance the effects of ionizing radiation in p53-compromised cancer cells. Combination IR plus HSP90 inhibitor therapies may be particularly useful in treating cancers that lack wild-type p53.

Low-dose local kidney irradiation inhibits progression of experimental crescentic nephritis by promoting apoptosis

BACKGROUND

Crescentic glomerulonephritis is a rapidly progressive form of nephritis and is usually resistant to therapeutic intervention. Apoptosis plays a role in the resolution of glomerulonephritis. We investigated the effects of local kidney irradiation on the progression of experimental crescentic glomerulonephritis.

METHODS

The following three experimental rat groups were generated: (1) Group I, sham-operated control (n = 12); (2) Group II, rats injected intravenously with rabbit anti-rat GBM antibody (nephrotoxic serum, NTS) (n = 23), and (3) Group III, a single low-dose irradiation of 0.5 Gy X-ray to both kidneys at days 6, 13, 20, and 27 after NTS injection (n = 55). Renal function and blood leukocyte count were examined in different groups of rats at various time points. Kidneys obtained at various time points were analyzed to determine the effects of radiation in experimental nephritis.

RESULTS

Radiation of the kidneys reduced the levels of blood urea nitrogen and serum creatinine compared with Group II nephritic rats of similar age (p < 0.05 or 0.001). No apparent changes in blood leukocyte counts were noted in various experimental groups. Glomerular hypercellularity, crescents, global sclerosis and tubulointerstitial damage developed gradually in Group II rats, but were decreased (p < 0.05 or 0.001) after radiation treatment. The extent of tubulointerstitial damage was also reduced, and radiation-associated histological improvements were accompanied by reduced infiltration of macrophages in the glomeruli and interstitium. The numbers of PCNA- and ED1-positive cells were reduced in the kidneys at 1 day post-irradiation, of rats irradiated at 6 and 13 days after NTS injection, compared with Group II at similar time intervals (p < 0.05). A larger numbers of TUNEL-positive cells were noted at 1 day post-irradiation in rats irradiated at 6 and 13 days after NTS injection, compared with Group II at similar time intervals (p < 0.05). Immunostaining for macrophages ED1 and TUNEL staining of serial sections of irradiated nephritic kidneys showed few ED1-positive macrophages stained for TUNEL. Overexpression of active caspases 3 and 7 was noted in irradiated kidneys, compared with the corresponding Group II rats at similar time intervals. Western blot analysis showed marked increase in active caspase 3 and active caspase 7 expression in irradiated kidneys compared with NTS injection only. A marked increase in the expression of p53 protein, which is closely related to radiation-induced apoptosis, was also observed in irradiated kidneys compared with NTS injection only.

CONCLUSION

Our study showed that renal radiation can alter acute glomerular inflammation by inducing apoptosis of intrinsic and infiltrating cells in the kidney in a rat model of crescentic glomerulonephritis. Low-dose kidney irradiation can inhibit the progression of experimental nephritis through inducing apoptosis.

DNA damage induces two distinct modes of cell death in ovarian carcinomas

Activation of p53 by cellular stress may lead to either cell cycle arrest or apoptotic cell death. Restrictions in a cell's ability to halt the cell cycle might, in turn, cause mitotic catastrophe, a delayed type of cell death with distinct morphological features. Here, we have investigated the contribution of p53 and caspase-2 to apoptotic cell death and mitotic catastrophe in cisplatin-treated ovarian carcinoma cell lines. We report that both functional p53 and caspase-2 were required for the apoptotic response, which was preceded by translocation of nuclear caspase-2 to the cytoplasm. In the absence of functional p53, cisplatin treatment resulted in caspase-2-independent mitotic catastrophe followed by necrosis. In these cells, apoptotic functions could be restored by transient expression of wt p53. Hence, p53 appeared to act as a switch between apoptosis and mitotic catastrophe followed by necrosis-like lysis in this experimental model. Further, we show that inhibition of Chk2, and/or 14-3-3sigma deficiency, sensitized cells to undergo mitotic catastrophe upon treatment with DNA-damaging agents. However, apoptotic cell death seemed to be the final outcome of this process. Thus, we hypothesize that the final mode of cell death triggered by DNA damage in ovarian carcinoma cells is determined by the profile of proteins involved in the regulation of the cell cycle, such as p53- and Chk2-related proteins.

Colocalisation of CD9 and mortalin in CD9-induced mitotic catastrophe in human prostate cancer cells

CD9, a member of the tetraspanin family of proteins, is involved in a variety of cellular interactions with many other proteins and molecules. Although CD9 has been implicated in cell fusion, migration and cancer progression, the detailed function of this protein is not completely understood and likely depends on interactions with different protein partners, which are not yet all known. Using co-immunoprecipitation and mass-spectrometric protein sequencing, we have identified in prostate cancer cells, a novel CD9 partner, the 75-kDa protein HSPA9B, also known as mortalin. We further show that introduction and overexpression of wild-type CD9 into human PC-3 prostate cancer cells induces mitotic catastrophe. We also demonstrate, by immunocolocalisation studies, the interaction of CD9 and mortalin in PC-3 cells undergoing mitotic catastrophe. Our results not only identified mortalin as a new CD9 partner, but also clarify the mechanisms by which CD9 may control prostate cancer progression.

Radiobiology of systemic radiation therapy

Although systemic radionuclide therapy (SRT) is effective as a palliative therapy in patients with metastatic cancer, there has been limited success in expanding patterns of utilization and in bringing novel systemic radiotherapeutic agents to routine clinical use. Although there are many factors that contribute to this situation, we hypothesize that a better understanding of the radiobiology and mechanism of action of SRT will facilitate the development of future compounds and the future designs of prospective clinical trials. If these trials can be rationalized to the biological basis of the therapy, it is likely that the long-term outcome would be enhanced therapeutic efficacy. In this review, we provide perspectives of the current state of low-dose-rate (LDR) radiation research and offer linkages where appropriate with current clinical knowledge. These include the recently described phenomena of low-dose hyper-radiosensitivity-increased radioresistance (LDH-IRR), adaptive responses, and biological bystander effects. Each of these areas require a major reconsideration of existing models for radiation action and an understanding of how this knowledge will integrate into the evolution of clinical SRT practice. Validation of a role in vivo for both LDH-IRR and biological bystander effects in SRT would greatly impact the way we would assess therapeutic response to SRT, the design of clinical trials of novel SRT radiopharmaceuticals, and risk estimates for both therapeutic and diagnostic radiopharmaceuticals. We believe that the current state of research in LDR effects offers a major opportunity to the nuclear medicine community to address the basic science of clinical SRT practice, to use this new knowledge to expand the use and roles of SRT, and to facilitate the introduction of new therapeutic radiopharmaceuticals.

α- and ϵ-Protein Kinase C Activity during Smooth Muscle Cell Apoptosis in Response to γ-Radiation

The use of gamma-radiation in treatment of pelvic cancer is associated with injury of healthy surrounding tissues and disorders of intestinal motility; however, the cellular mechanisms involved are unclear. We tested the hypothesis that exposure of visceral smooth muscle cells (SMCs) to gamma-radiation induces apoptosis via activation of specific protein kinase C (PKC) isoforms. Cultured SMCs and slices from guinea pig ileum smooth muscle longitudinal layer (GPISMLL) were exposed to 10 to 50 Gy. Flow cytometry in gamma-radiated SMCs showed increased percentage of cells in the sub-G(0)/G(1) phase, a hallmark of apoptosis. gamma-Radiation-induced reduction in cell survival was partially but significantly alleviated with the PKC inhibitors. Sections of gamma-irradiated GPISMLL showed DNA fragmentation and apoptotic bodies analyzed by the terminal deoxynucleotidyl transferase dUTP nick-end labeling method, whereas the plasma and nuclear membranes were preserved. Confocal microscopy in gamma-radiated SMCs labeled with annexin V-fluorescein showed an increase in apoptotic cells and phosphatidylserine externalization. Contraction of GPISMLL strips in response to KCl and acetylcholine was reduced in tissues exposed to 30 and 50 Gy. gamma-Radiation of GPISMLL caused an increase in PKC activity in the particulate fraction, a decrease in the cytosolic fraction, and increased particulate/cytosolic PKC activity ratio. Western blot analysis revealed significant amounts of alpha- and epsilon-PKC in the cytosolic fraction of control GPISMLL. gamma-Radiation caused an increase in the amount of alpha- and epsilon-PKC in the particulate fraction and a decrease in the cytosolic fraction. Data suggest that gamma-radiation induces apoptosis, growth arrest, and contractile dysfunction in visceral SMCs of GPISMLL via activation and translocation of alpha- and epsilon-PKC isoforms.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

Radiation-induced apoptosis along with local and systemic cytokine elaboration is associated with DC plus radiotherapy-mediated renal cell tumor regression

Utilizing melanoma and sarcoma tumor models syngeneic to C57BL/6 mice, we previously reported the antitumor effects of intratumoral (i.t.) administration of dendritic cells (DC) combined with localized radiotherapy (RT). However, the mechanisms underlying the augmented therapeutic effects have yet to be fully defined. Using the BALB/c host, we explored in this study the capacity of RT to augment the therapeutic efficacy of DC in the syngeneic renal cell cancer, Renca. I.t. DC administration combined with RT inhibited tumor growth in a synergistic manner. This extends our previous findings using a different host strain and two histologically distinct tumor models. More importantly, we provide evidence in this report that RT induced significant apoptosis and necrosis in Renca tumor cells, which involved down-regulated expression of Bcl-2 and a concurrent up-regulated expression of Bax. We also found significantly elevated expression of TNFalpha in RT plus DC-treated Renca tumors. Furthermore, splenocytes isolated from DC plus RT-treated mice elaborated higher levels of IL-2, IL-4, IFNgamma and IgG, IgM in response to tumor cells compared with splenocytes from monotherapy-treated hosts. These data support the conclusion that radiotherapy enhanced DC vaccination by inducing tumor cell apoptosis in BABL/c host, and the significantly augmented therapeutic efficacy by RT+DC treatment was associated with an increased local production of TNFalpha as well as an amplified systemic antitumor responses conferred by the combined therapy. I.t. DC administration in concert with localized RT may represent a promising novel regimen for human cancer therapy.

Cell killing, nuclear damage and apoptosis in Chinese hamster V79 cells after irradiation with heavy-ion beams of (16)O, (12)C and (7)Li

Chinese hamster V79 cells were exposed to high LET (linear energy transfer) (16)O-beam (625keV/mum) radiation in the dose range of 0-9.83Gy. Cell survival, micronuclei (MN), chromosomal aberrations (CA) and induction of apoptosis were studied as a follow up of our earlier study on high LET radiations ((7)Li-beam of 60keV/mum and (12)C-beam of 295keV/mum) as well as (60)Co gamma-rays. Dose dependent decline in surviving fraction was noticed along with the increase of MN frequency, CA frequency as well as percentage of apoptosis as detected by nuclear fragmentation assay. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was also increased in a dose dependent manner. Additionally, expression of tyrosine kinase lck-1 gene, which plays an important role in response to ionizing radiation induced apoptosis, was increased with the increase of radiation doses and also with incubation time. The present study showed that all the high LET radiations were generally more effective in cell killing and inflicting other cytogenetic damages than that of low LET gamma-rays. The dose response curves revealed that (7)Li-beam was most effective in cell killing as well as inducing other nuclear damages followed by (12)C, (16)O and (60)Co gamma-rays, in that order. The result of this study may have some application in biological dosimetry for assessment of genotoxicity in heavy ion exposed subjects and in determining suitable doses for radiotherapy in cancer patients where various species of heavy ions are now being generally used.

Checkpoint adaptation in human cells

Checkpoint adaptation was originally described in Saccharomyces cerevisiae as the ability to divide following a sustained checkpoint arrest in the presence of unrepairable DNA breaks. A process of checkpoint adaptation was also reported in Xenopus in response to the replication inhibitor aphidicolin. Recently, we showed that checkpoint adaptation also occurs in human cells. Although cells undergoing checkpoint adaptation will frequently die in subsequent cell cycles owing to excessive DNA damage, some of the cells may be able to survive and proliferate with damaged DNA. Thus, checkpoint adaptation in human cells may potentially promote genomic instability and lead to cancer. Here, I discuss the current evidence for checkpoint adaptation in human cells and possible mechanisms and implications of this phenomenon.

Cyclic nucleotide response element binding (CREB) protein activation is involved in K562 erythroleukemia cells differentiation

K562 are human erythroleukemia cells inducible to differentiate into megakaryocytic or erythroid lineage by different agents. Cyclic nucleotide Response Element Binding (CREB) protein, a nuclear transcription factor which mediates c-AMP signaling, is a potential candidate involved in the occurrence of erythroid differentiation and adaptive response. Here we investigated signaling events in K562 cells induced with 30 microM hemin to undergo erythroid differentiation. CREB activation was detected early 1 h after hemin treatment and up to 4 and 6 days of treatment, when K562 terminal differentiation occurs together with caspase-3 maximal activation and PARP degradation. It was interesting to note that after hemin treatment in the presence of SB203580, p38 MAP kinase specific inhibitor, a reduced rate of CREB phosphorylation as well as a lower percentage of CD71/Gly+ (Glycophorin A) cells were detectable, demonstrating the p38 MAP kinase dependency of these phenomena. All in all these results document a novel relationship between CREB activation and differentiation-related apoptotic cell death and assign a role to p38 MAP kinase pathway in determining these events in K562 erythroleukemia cells.