Radiation response of mouse lymphoid and myeloid cell lines. Part III. Different signals can lead to apoptosis and may influence sensitivity to killing by DNA double-strand breakage

The value of repeated CT in monitoring the disease progression in moderate COVID-19 pneumonia: A single-center, retrospective study

ABSTRACT

The role of thoracic CT (computerized tomography) in monitoring disease course of COVID-19 is controversial. The purpose of this study is to investigate the risk factors and predictive value of deterioration on repeatedly performed CT scan during hospitalization.All COVID-19 patients treated in our isolation ward, from January 22, 2020 to February 7, 2020, were reviewed. Patients included were categorized into RD (Radiological Deterioration) group or NRD (No Radiological Deterioration) group according to the manifestation on the CT routinely performed during the hospitalization. All clinical data and CT images were analyzed.Forty three patients were included in our study. All are moderate cases with at least 4 CT scans each. Eighteen (42.9%) patients had radiological deteriorations which were all identified in CT2 (the first CT after admission). Patients in RD group had lower leukocyte count (P = .003), lymphocyte count (P = .030), and higher prevalence (P = .012) of elevated C-reactive protein (CRP) at admission. NRD patients had a lower prevalence of reticulations (P = .034) on baseline CT (CT1, performed within 2 days before admission) and a longer duration between symptom onset and the time of CT2 (P < .01). There was no significant difference in hospital stay or fibrotic change on CT4 (follow-up CT scan performed 4 weeks after discharge) between 2 groups. Shorter duration between symptom onset and CT2 time (odds ratio [OR], 0.436; 95% confidence interval: 0.233-0.816; P < .01) and lower leukocyte count in baseline evaluation (OR, 0.316; 95% CI: 0.116-0.859; P < .05) were associated with increased odds of radiological deterioration on CT image during hospitalization.For moderate COVID-19 patients, the value of routinely performed CT during the treatment is limited. We recommend avoiding using CT as a routine monitor in moderate COVID-19 patients.

Dose Dependent Biological Effects of Idarubicin in HL-60 Cells: Alterations of the Cell-Cycle and Apoptosis

TP-53 deficient cells of human leukaemia HL-60 die by massive apoptosis after treatment by high (50-100 nmol/l) doses of DNA damaging agent Idarubicin, regardless of the cell-cycle phase, in which they are affected. In contrary, after relatively low dose 10 nmol/l the cells die after cell-cycle arrest in G2phase. The results show, that apoptosis induced by idarubicin could appear independently of the cell-cycle phase and that period in which apoptosis is observed is related to the dose of Idarubicin.

A Review of Radiation-Induced Lymphocyte Apoptosis as a Predictor of Late Toxicity After Breast Radiotherapy

BACKGROUND

Improved survivorship in patients with breast cancer means many are currently living with the late effects of radiotherapy, particularly fibrosis. Personalized treatment is not currently considered for patients with breast cancer. Radiation-induced lymphocyte apoptosis (RILA), a predictive assay, could offer a novel approach in predicting patients at a higher risk of developing this late toxicity and therefore improving informed decision-making.

MATERIALS AND METHODS

A systematic search of PubMed and Embase was performed and eight clinical trials were identified that investigate RILA as a predictor of late breast fibrosis after radiotherapy.

RESULTS

Median RILA scores were lower in patients who experienced ≥ grade 2 fibrosis than in patients who experienced ≥ grade 1. A clear inverse relationship between RILA scores and late toxicity was reported in the literature; however, there were several other confounding factors involved in the development of fibrosis. CD8 lymphocytes were reported to have superior sensitivity and specificity over CD4 lymphocytes.

CONCLUSION

RILA was reported to be an effective biomarker in predicting fibrosis in breast cancer but other factors also need to be considered before clinical implementation.

Mitochondrial dynamics during cell cycling

Mitochondria are the cell's power plant that must be in a proper functional state in order to produce the energy necessary for basic cellular functions, such as proliferation. Mitochondria are 'dynamic' in that they are constantly undergoing fission and fusion to remain in a functional state throughout the cell cycle, as well as during other vital processes such as energy supply, cellular respiration and programmed cell death. The mitochondrial fission/fusion machinery is involved in generating young mitochondria, while eliminating old, damaged and non-repairable ones. As a result, the organelles change in shape, size and number throughout the cell cycle. Such precise and accurate balance is maintained by the cytoskeletal transporting system via microtubules, which deliver the mitochondrion from one location to another. During the gap phases G₁ and G₂, mitochondria form an interconnected network, whereas in mitosis and S-phase fragmentation of the mitochondrial network will take place. However, such balance is lost during neoplastic transformation and autoimmune disorders. Several proteins, such as Drp1, Fis1, Kif-family proteins, Opa1, Bax and mitofusins change in activity and might link the mitochondrial fission/fusion events with processes such as alteration of mitochondrial membrane potential, apoptosis, necrosis, cell cycle arrest, and malignant growth. All this indicates how vital proper functioning of mitochondria is in maintaining cell integrity and preventing carcinogenesis.

Susceptibility of ATM-deficient pancreatic cancer cells to radiation

Ataxia telangiectasia mutated (ATM) is inactivated in a significant minority of pancreatic ductal adenocarcinomas and may be predictor of treatment response. We determined if ATM deficiency renders pancreatic cancer cells more sensitive to fractionated radiation or commonly used chemotherapeutics. ATM expression was knocked down in three pancreatic cancer cell lines using ATM-targeting shRNA. Isogenic cell lines were tested for sensitivity to several chemotherapeutic agents and radiation. DNA repair kinetics were analyzed in irradiated cells using the comet assay. We find that while rendering pancreatic cancer cells ATM-deficient did not significantly change their sensitivity to several chemotherapeutics, it did render them exquisitely sensitized to radiation. Pancreatic cancer ATM status may help predict response to radiotherapy.

Prediction of radiation-induced toxicity by in vitro radiosensitivity of lymphocytes in prostate cancer patients

Aim: To identify predictive assays for radiation-induced toxicity in prostate cancer patients. Patients & methods: Patients have been surveyed prospectively before and up to 16 months after radiotherapy using a validated questionnaire. Subgroups of 25 patients with minor and larger score changes, respectively, were selected for γ-H2AX, G2 and Annexin V assays. Results: A significantly higher spontaneous chromatid aberration yield (HR: 1.46 [95% CI: 1.02–2.09]; p = 0.04), higher levels of early apoptotic (HR: 1.12 [95% CI: 1.01–1.24]; p = 0.04) and late apoptotic and necrotic (HR: 1.10 [95% CI: 0.99–1.23]; p = 0.08) lymphocytes 24 h post-irradiation were found in patients with a bowel bother score decrease greater than 20 points more than 1 year after treatment. Conclusion: Chromatid aberration and apoptosis/necrosis assays appear to be suitable for the prediction of radiation-induced toxicity.

miR-124 radiosensitizes human glioma cells by targeting CDK4

The aberrant expression of cyclin-dependent kinase-4 (CDK4) has previously been observed in human brain glioma. Furthermore, it is observed that up-regulation of CDK4 is associated with therapy resistance and relapse. However, the mechanisms behind these phenomena remain unclear. Here, we demonstrated that elevated CDK4 expression is correlated with poor prognosis in glioma after radiotherapy and that CDK4 knockdown conferred radiosensitivity in glioma cell lines. CDK4 was identified as potential downstream target of miR-124 through bioinformatics analysis and dual-firefly luciferase reporter assay. Furthermore, restoration of miR-124 could confer radiosensitivity. Cell differentiation agent-2 (CDA-2) mimicked the effect of miR-124 restoration and CDK4 knockdown, and sensitized xenografts to radiation in an animal model. Our findings demonstrated for the first time that CDK4 was a downstream target of miR-124 and that CDA-2 could radiosensitize Glioblastoma multiforme cells through the MiR-124-CDK4 axis.

Radiosensitization in prostate cancer: mechanisms and targets

Prostate cancer is the second most commonly diagnosed cancer in American men over the age of 45 years and is the third most common cause of cancer related deaths in American men. In 2012 it is estimated that 241,740 men will be diagnosed with prostate cancer and 28,170 men will succumb to prostate cancer. Currently, radiation therapy is one of the most common definitive treatment options for localized prostate cancer. However, significant number of patients undergoing radiation therapy will develop locally persistent/recurrent tumours. The varying response rates to radiation may be due to 1) tumor microenvironment, 2) tumor stage/grade, 3) modality used to deliver radiation, and 4) dose of radiation. Higher doses of radiation has not always proved to be effective and have been associated with increased morbidity. Compounds designed to enhance the killing effects of radiation, radiosensitizers, have been extensively investigated over the past decade. The development of radiosensitizing agents could improve survival, improve quality of life and reduce costs, thus benefiting both patients and healthcare systems. Herin, we shall review the role and mechanisms of various agents that can sensitize tumours, specifically prostate cancer.

Chromosomal breaks during mitotic catastrophe trigger γH2AX-ATM-p53-mediated apoptosis

Although the cause and outcome of mitotic catastrophe (MC) has been thoroughly investigated, precisely how the ensuing lethality is regulated during or following this process and what signals are involved remain unknown. Moreover, the mechanism of the decision of cell death modalities following MC is still not well characterised. We demonstrate here a crucial role of the γH2AX-ATM-p53 pathway in the regulation of the apoptotic outcome of MC resulting from cells entering mitosis with damaged DNA. In addition to p53 deficiency, the depletion of ATM (ataxia telangiectasia mutated), but not ATR (ataxia telangiectasia and Rad3-related protein), protected against apoptosis and shifted cell death towards necrosis. Activation of this pathway is triggered by the augmented chromosomal damage acquired during anaphase in doxorubicin-treated cells lacking 14-3-3σ (also known as epithelial cell marker protein-1 or stratifin). Moreover, cells that enter mitosis with damaged DNA encounter segregation problems because of their abnormal chromosomes, leading to defects in mitotic exit, and they therefore accumulate in G1 phase. These multi- or micronucleated cells are prevented from cycling again in a p53- and p21-dependent manner, and subsequently die. Because increased chromosomal damage resulting in extensive H2AX phosphorylation appears to be a direct cause of catastrophic mitosis, our results describe a mechanism that involves generation of additional DNA damage during MC to eliminate chromosomally unstable cells.

Giant cell formation: the way to cell death or cell survival?

The study of giant cells in populations of different tumor cells and evaluation of their role in cancer development is an expanding field. The formation of giant cells has been shown to be followed by mitotic catastrophe, apoptosis, necrosis, and other types of cell elimination. Reports also demonstrate that giant cells can escape cell death and give rise to new cancer cells. However, it is not known if the programmed cell death is involved in this type of cell cycle disorders. Here we describe principal events that are observed during giant cell formation. We also consider the role of giant cells in cancer development, taking into account both published work and our own recent data in this field.

Phosphorylation and cytoplasmic localization of MAPK p38 during apoptosis signaling in bone marrow granulocytes of mice irradiated in vivo and the role of amifostine in reducing these effects

We studied p38 phosphorylation and its intracellular localization during p53 and Puma (a p53 upregulated modulator of apoptosis) apoptotic signaling pathway in bone marrow granulocytes in mice irradiated in vivo and the role of the radioprotector amifostine in ameliorating these responses. Sixty-four C57BL mice were randomly assigned in two non-irradiated (Ami-/rad- and Ami+/rad-) and two irradiated (Ami-/rad+ and Ami+/rad+) groups. Animals received 400mg/kg of amifostine i.p. 30 min prior to a single whole body radiation dose of 7Gy. The experiments were performed using immunohistochemistry for caspase-3, cleaved caspase-3, p53, p-p53 (Ser 15), Puma, p38 and p-p38 (Thr 180/Tyr 182) protein expression. In addition transmission electron microscopy was used for ultrastructural characterization of apoptosis. Data showed that: (i) amifostine significantly reduced the number of apoptotic cells, (ii) p-p53 and Puma proteins were strongly immunostained in granulocytes after irradiation (Ami-/rad+), (iii) amifostine decreased the immunostaining of the proteins (Ami+/rad+), (iv) p38 was immunolocalized in physiological conditions in the nucleus and cytoplasm of granulocytes and neither radiation nor amifostine changed the protein immunostaining or its subcellular distribution, but influenced its activation, (v) radiation-induced p38 phosphorylation and its cytoplasmic accumulation during apoptosis signaling in granulocytes after whole body high radiation dose and amifostine markedly reduced these effects.

Identifying patients at risk for late radiation-induced toxicity

The impact of curative radiotherapy depends mainly on the total dose delivered in the targeted volume. Nevertheless, the dose delivered to the surrounding healthy tissues may reduce the therapeutic ratio of many treatments. Two different side effects (acute and late) can occur during and after radiotherapy. Of particular interest are the radiation-induced late complications (LC) due to their irreversibility and the potential impact on quality of life. In one population treated with the same technique, it appears that individual radiosensitivity clearly exists. In the hypothesis that genetic is involved in this area of research, low CD4 and CD8 lymphocyte apoptosis were shown to be correlated with high grade of LC. In addition, recent data suggest that patients with severe radiation-induced LC possess 4 or more single nucleotide polymorphisms (SNPs) in candidate genes and low radiation-induced CD8 lymphocyte apoptosis in vitro. On-going studies are being analyzing the entire genome using a genome-wide association study (GWAS).

Pharmacological inhibition of DNA repair enzymes differentially modulates telomerase activity and apoptosis in two human leukaemia cell lines

PURPOSE

To investigate the effect of wortmannin and 3-aminobenzamide (3-AB) on telomerase activity and apoptosis in two human leukaemia cells.

MATERIALS AND METHODS

MOLT-4 (p53-wild type) and KG1a (p53-null) cells were irradiated with gamma-rays (3 Gy at 1.57 Gy min(-1)) and the effects of wortmannin and 3-AB were evaluated. Telomerase activity was measured by polymerase chain reaction and the expression of human telomerase reverse transcriptase, human telomerase RNA and telomerase-associated protein 1 was assessed by reverse transcriptase-polymerase chain reaction. Apoptosis was evaluated by fluorescence microscopy and flow cytometry.

RESULTS

A radiation-induced up-regulation of telomerase activity was observed from 4 h post-irradiation in both cell lines. This up-regulation was abrogated by wortmannin and 3-AB. Telomerase activity was maximal 24 h post-irradiation, coinciding with an accumulation of human telomerase reverse transcriptase mRNA. Apoptosis and G2/M arrest were evident from 4 h post-irradiation in MOLT-4 cells. KG1a cells exhibited a G2/M block at 24 h post-irradiation and apoptosis increased between 24 and 48 h post-irradiation. 3-AB abolished G2/M blockage and enhanced radiation-induced apoptosis in both cell lines, while wortmannin increased apoptosis only in MOLT-4 cells.

CONCLUSIONS

3-AB inhibits the radiation-associated telomerase activity increase and enhances apoptosis in MOLT-4 and KG1a cells. Wortmannin, which also inhibits the radiation-associated telomerase activity increase in both cell lines, does not modify radiation-induced apoptosis in KG1a cells. DNA repair enzymes might be selective targets for enhancing radiosensitivity in certain tumour cells.

Effect of neutron capture therapy on the cell cycle of human squamous cell carcinoma cells

PURPOSE

The effects of boronophenylalanine (BPA)-mediated boron neutron capture therapy (BNCT) on the growth potential and cell cycle of human oral squamous cell carcinoma (SCC) cells were examined.

MATERIALS AND METHODS

SAS cells expressing a functional wild-type p53 were exposed to neutron beams in the presence of BPA and growth potential was measured by colony formation assay and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The cell cycle and cell cycle-related proteins were examined by flow cytometry and immunoblot analysis.

RESULTS

BNCT affected the colony-forming ability and viability of SAS cells. In the flow-cytometric analysis of BNCT-treated cells, the cell cycle was arrested at the G1 and G2 checkpoints, and sub-G1 cells appeared. Apoptotic cells were detected by nuclear DNA staining. Immunoblot analysis revealed the phosphorylation of p53, up-regulation of p21, and down-regulation of retinoblastoma (Rb) gene protein at 6 h after BNCT. Twelve hours after BNCT, the up-regulation of Wee1, phosphorylation of cdc2, and up-regulation of cyclin B1 were observed. Cleavage of poly (ADP-ribose) polymerase (PARP) occurred from 6 h after BNCT.

CONCLUSION

These results indicate that the early inhibitory effect of BNCT on the growth of human oral SCC cells can be ascribed to arrest at the G1 and G2 checkpoints and apoptosis associated with G1 arrest.

Death through a tragedy: mitotic catastrophe

Mitotic catastrophe (MC) has long been considered as a mode of cell death that results from premature or inappropriate entry of cells into mitosis and can be caused by chemical or physical stresses. Whereas it initially was depicted as the main form of cell death induced by ionizing radiation, it is today known to be triggered also by treatment with agents influencing the stability of microtubule, various anticancer drugs and mitotic failure caused by defective cell cycle checkpoints. Although various descriptions explaining MC exist, there is still no general accepted definition of this phenomenon. Here, we present evidences indicating that death-associated MC is not a separate mode of cell death, rather a process ('prestage') preceding cell death, which can occur through necrosis or apoptosis. The final outcome of MC depends on the molecular profile of the cell.

Intrinsic radiation sensitivity: cellular signaling is the key

The concept that the balance between DNA damage and repair determines intrinsic radiation sensitivity has dominated radiobiology for several decades. There is undeniably a cause- effect relationship between radiation-induced molecular alterations in the genomic DNA and cellular consequences. In the last decade, however, it has become obvious that the chromatin context affects the fate of damaged DNA and that cellular signaling is an important factor in defining intrinsic radiation sensitivity. Damaged DNA is the site of signal generation; however, alternative signaling at the plasma membrane is triggered: Reactive oxygen species (ROS) inactivate phosphatases and consequently cause activation of kinases localized at the plasma membrane; this includes ligand-independent activation of receptor kinases. Cells with an apparently functional DNA repair system may show increased radiation sensitivity due to deficiencies in specific kinases essential for repair activation and checkpoint control. Other signals that determine intrinsic radiosensitivity may affect proneness to apoptosis, the balance between DNA damage fixation and repair, and the translocation of proteins participating in the response to ionizing radiation. Interplay between the various signals decides the extent to which the repair of radiation-inflicted damage is supported or limited; in some cell types, this includes DNA-damage-independent processes guided by plasma membrane-generated signaling. Cellular signaling in the context of specific subcellular structures is the key to understanding how the molecular effects of radiation are expressed as biological consequences in various cell types. A systems approach should bring us closer to this end.

Free radical scavenger edaravone suppresses x-ray-induced apoptosis through p53 inhibition in MOLT-4 cells

Edaravone, a clinical drug used widely for the treatment of acute cerebral infarction, is reported to scavenge free radicals. In the present study, we investigated the radioprotective effect of edaravone on X-ray-induced apoptosis in MOLT-4 cells. Apoptosis was determined by the dye exclusion test, Annexin V binding assay, cleavage of caspase, and DNA fragmentation. We found that edaravone significantly suppressed the X-ray-induced apoptosis. The amount of intracellular ROS production was determined by the chloromethyl-2',7'-dichlorodihydro-fluorescein diacetate system. We found that the intracellular ROS production by X-irradiation was completely suppressed by the addition of edaravone. The accumulation and phosphorylation of p53 and the expression of p21(WAF1), a target protein of p53, which were induced by X-irradiation, were also suppressed by adding edaravone. We conclude that the free radical scavenger edaravone suppresses X-ray-induced apoptosis in MOLT-4 cells by inhibiting p53.

The cisplatin-irradiation combination suggests that apoptosis is not a major determinant of clonogenic death

It is commonly believed that tumor cells treated with anticancer agents, chemotherapy and/or radiation, die by apoptosis and that tumors which do not undergo apoptosis are resistant to treatment. In this study, we investigated the molecular basis underlying cisplatin cytotoxicity in the murine teratocarcinoma F9 cell line to see whether irradiation enhances cisplatin-induced cytotoxicity. We compared the apoptosis induced by chemo and/or radiotherapy with other cellular effects such as cell survival, clonogenic capability, cell cycle perturbation, expression of p53 and p53-related mRNAs, and necrosis. When combined with radiation, a clear additive cytotoxic effect of cisplatin was demonstrated. We found that both cisplatin and radiation induced cell death, but the level of induced apoptosis was low and there was no correlation with the results of the clonogenic assays: we noted a difference between cytotoxic effects in the clonogenic assay and the extent of apoptosis by fluorescence-activated cell sorter analysis, suggesting that cell killing reflected not only apoptosis but also cell cycle arrest, and that apoptosis, cell kinetics and clonogenicity suppression were independent processes.

Genotoxic effects in M5 cells and Chinese hamster V79 cells after exposure to 7Li-beam (LET=60 keV/microm) and correlation of their survival dynamics to nuclear damages and cell death

Chinese hamster V79 cell and a cell strain M5, derived from V79 cells and reported to be relatively resistant to gamma-ray, hydrogen peroxide, and N-methyl-N-nitro-N-nitrosoguanidine (MNNG; a potent human carcinogen), were exposed to high LET (7)Li-beam (LET=60 keV/microm) at approximately 90% confluent state in the dose range of 0-1 Gy. Effects of (7)Li-beam exposure on cell survival, micronuclei induction (MN), chromosomal aberrations (CA) and apoptosis were compared in both the cell lines. A dose-dependent decline in survival for both the cell lines was noted, relatively less in M5 cells (mostly p<0.01) indicating greater radio-resistance in this strain. The MN, CA and apoptosis increased in a dose-dependent manner in both V79 and M5 cells. Significant differences in various other parameters between these two cell lines were also noted. The relative intensity of DNA ladder, which is a useful marker for the determination of the extent of apoptosis induction, was much higher in V79 cells. A good correlation between the reduction of the surviving fractions and the increase in frequencies of MN or CA or apoptosis was noted for both the cell lines.

Hyperacute neuropathological findings after proton beam radiosurgery of the rat hippocampus

OBJECTIVE

To study the hyperacute histological and immunohistochemical effects of stereotactic proton beam irradiation of the rat hippocampus.

METHODS

Nine rats underwent proton beam radiosurgery of one hippocampus with nominal doses of cobalt-2, -12, and -60 Gray equivalents (n = 3 each). Control animals (n = 3) were not irradiated. Animals were killed 5 hours after irradiation and brain sections were stained for Nissl, silver degeneration, deoxyribonucleic acid (DNA) fragmentation (DNAF), and the activated form of two mitogen-activated protein kinases (MAPKs), phospho-Erk1/2 (P-Erk1/2) and p38. Stained cells in the hippocampus expressing DNAF and/or P-Erk1/2 were counted. Confocal microscopy with double immunofluorescent staining was used to examine cellular colocalization of DNAF and P-Erk1/2.

RESULTS

Both DNAF and P-Erk1/2 showed quantitative dose-dependent increases in staining in the targeted hippocampus compared with the contralateral side and controls. This finding was restricted to the subgranular proliferative zone of the hippocampus. Both markers also were up-regulated on the contralateral side when compared with controls in a dose-dependent fashion. Simultaneous staining for DNAF and P-Erk1/2 was found in fewer than half of all cells. p38 was unchanged compared with controls. Although Nissl staining appeared normal, silver stain confirmed dose-dependent cellular degeneration.

CONCLUSION

DNAF, a marker of cell death, was present in rat hippocampi within 5 hours of delivery of cobalt-2 Gray equivalents stereotactically focused irradiation, suggesting that even low-dose radiosurgery has hyperacute neurotoxic effects. Activated mitogen-activated protein kinase was incompletely colocalized with DNAF, suggesting that activation of this cascade is neither necessary nor sufficient to initiate acute cell death after irradiation.

Vascular Endothelial Cells Produce Soluble Factors That Mediate the Recovery of Human Hematopoietic Stem Cells after Radiation Injury

The risk of terrorism with nuclear or radiologic weapons is considered to be high over the coming decade. Ionizing radiation can cause a spectrum of hematologic toxicities, from mild myelosuppression to myeloablation and death. However, the potential regenerative capacity of human hematopoietic stem cells (HSCs) after radiation injury has not been well characterized. In this study, we sought to characterize the effects of ionizing radiation on human HSCs and to determine whether signals from vascular endothelial cells could promote the repair of irradiated HSCs. Exposure of human bone marrow CD34+ cells to 400 cGy caused a precipitous decline in hematopoietic progenitor cell content and primitive cells capable of repopulating nonobese diabetic/severe combined immunodeficient mice (SCID-repopulating cells), which was not retrievable via treatment with cytokines. Conversely, culture of 400 cGy-irradiated bone marrow CD34+ cells with endothelial cells under noncontact conditions supported the differential recovery of both viable progenitor cells and primitive SCID-repopulating cells. These data illustrate that vascular endothelial cells produce soluble factors that promote the repair and functional recovery of HSCs after radiation injury and suggest that novel factors with radiotherapeutic potential can be identified within this milieu.

CD4 and CD8 T-lymphocyte apoptosis can predict radiation-induced late toxicity: a prospective study in 399 patients

PURPOSE

Predicting late effects in patients treated with radiation therapy by assessing in vitro radiation-induced CD4 and CD8 T-lymphocyte apoptosis can be useful in individualizing treatment.

EXPERIMENTAL DESIGN

In a prospective study, 399 curatively irradiated patients were tested using a rapid assay where fresh blood samples were in vitro irradiated with 8 Gy X-rays. Lymphocytes were collected and prepared for flow cytometric analysis. Apoptosis was assessed by associated condensation of DNA. The incidences of late toxicities were compared for CD4 and CD8 T-lymphocyte apoptoses using receiver-operating characteristic curves and cumulative incidence.

RESULTS

No association was found between early toxicity and T-lymphocyte apoptosis. Grade 2 and 3 late toxicities were observed in 31% and 7% of patients, respectively. More radiation-induced T-lymphocyte apoptosis was significantly associated with less grade 2 and 3 late toxicity (Gray's test, P < 0.0001). CD8 (area under the curve = 0.83) was more sensitive and specific than CD4. No grade 3 late toxicity was observed for patients with CD4 and CD8 values greater than 15% and 24%, respectively. The 2-year cumulative incidence for grade 2 or 3 late toxicity was 70%, 32%, and 12% for patients with absolute change in CD8 T-lymphocyte apoptosis of < or =16, 16 to 24, and >24, respectively.

CONCLUSIONS

Radiation-induced T-lymphocyte apoptosis can significantly predict differences in late toxicity between individuals. It could be used as a rapid screen for hypersensitive patients to radiotherapy. In future dose escalation studies, patients could be selected using the apoptosis assay.

Relationship between clonogenic radiosensitivity, radiation-induced apoptosis and DNA damage/repair in human colon cancer cells

The intrinsic radiation sensitivity of normal and tumour tissue is a major determinant of the outcome of radiotherapy. There is currently no established test that can be used routinely to measure the radiosensitivity of the cells in an individual patient's cancer in a manner that can inform treatment planning. The purpose of this study was to evaluate, in four human colorectal adenocarcinoma cell lines, two possible end points as surrogate markers of radiation response – apoptosis and induction of DNA single-strand breaks – and to compare the results with those of a conventional clonogenic assay. Cell lines (SW707 SW480, SW48 and HT29) known to differ in radiosensitivity were exposed to single doses of X-rays ranging from 0.5 to 5 Gy and cell survival was measured using the clonogenic assay. Apoptosis was determined on the basis of morphology under fluorescent microscopy and DNA damage/repair was measured, as tail moment, using an adaptation of the alkaline comet assay. The relationship between surviving fraction at 2 Gy (SF₂) and the percentage of apoptotic cells 24 h after the same dose was complex, but apoptosis accurately predicted the order of radiosensitivities as measured by SF₂. Initial damage measured after 2 Gy using the alkaline comet assay gave a close correlation with SF₂ (r²=0.95), whereas there was no correlation between initial DNA damage repair rate and SF₂.

Ex vivo culture rescues hematopoietic stem cells with long-term repopulating capacity following harvest from lethally irradiated mice

OBJECTIVE

High-dose ionizing radiation can cause lethal myeloablation in exposed individuals. We examined whether ex vivo culture could rescue hematopoietic stem cells with repopulating capacity following harvest from lethally irradiated animals.

METHODS

We exposed B6.SJL mice to 1050 cGy, harvested their irradiated bone marrow (BM), and examined whether ex vivo culture of the irradiated BM mononuclear cells (MNC) with porcine microvascular endothelial cells (PMVEC) or cytokines alone could rescue hematopoietic cells with in vitro colony-forming activity, in vivo radioprotective capacity, and long-term repopulating potential.

RESULTS

PMVEC coculture supported the recovery of fourfold and 80-fold greater numbers of total cells and colony-forming cells (CFC) compared to cyokines alone following 1050 cGy irradiation. All control mice irradiated with 1050 cGy died by day 30, as did mice transplanted with 1050 cGy-irradiated BM MNC. In contrast, transplantation of 1050 cGy-irradiated/PMVEC-cultured BM was fully radioprotective in 12 of 16 recipient mice (75%) exposed to 1050 cGy. Six of the 12 CD45.2+ mice (50%) transplanted with 1050 cGy-irradiated/PMVEC-cultured cells showed long-term (>6 months) multilineage repopulation derived from irradiated donor CD45.1+ cells. Surprisingly, transplantation of identical doses of 1050 cGy-irradiated/cytokine-cultured BM was also radioprotective in 50% of irradiated recipient mice and 50% of these mice demonstrated donor-derived repopulation.

CONCLUSIONS

Fully functional BM stem and progenitor cells can be rescued following harvest from lethally irradiated animals via ex vivo culture with PMVEC or cytokines alone. This method can serve as a model for the rapid ex vivo rescue and transplantation of autologous BM progenitors in the treatment of victims of radiation injury.

Susceptibility of Mouse Splenic Cells to Oxidative DNA Damage by X-Ray Irradiation

Susceptibility to oxidative stress by X-ray irradiation was examined in splenic cells of BDF1 mouse and fetal human lung fibroblasts, TIG-7. Survival rates of splenic cells irradiated with X-rays were lower than those of TIG-7 cells irradiated similarly. The content of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) immediately after X-ray irradiation in the DNA of splenic cells increased until 2 Gy irradiation, but remained constant above 2 Gy. The 8-oxodG contents rose in proportion to the dose of X-rays in TIG-7 cells. Although the survival rate of splenic cells exposed to 1 Gy irradiation decreased with time, the survival rate of TIG-7 cells remained unchanged. The 8-oxodG content in splenic cells irradiated with X-rays did not decrease even 48 h after irradiation, while that in TIG-7 cells decreased with time, and recovered to the pre-irradiation level after 48 h. A DNA ladder was observed in splenic cells 2 h after X-ray irradiation, but the ladder was not found in fibroblasts. Furthermore, caspase-3 activity increased after X-ray irradiation of splenic cells. These results indicate that splenic cells are sensitive to oxidative stress induced by X-ray irradiation and that splenic cells damaged by even low doses of X-rays are removed through apoptosis rather than by a repair pathway.

Gamma radiation-induced apoptosis, G2 delay, and the risk of salivary and thyroid carcinomas?a preliminary report

BACKGROUND

While radiation has been the only well-established risk factor for salivary and thyroid cancers, the exact mechanisms remain unknown. We hypothesized that individuals with altered apoptotic response to gamma irradiation may be susceptible to salivary and thyroid cancers.

METHODS

We tested our hypothesis in a pilot case-control study of 29 patients with neoplasms of the salivary and thyroid glands and 29 cancer-free control subjects. Patients and control subjects were matched on age, sex, and ethnicity. In vitro gamma radiation-induced apoptosis in lymphocytes was quantified utilizing the TUNEL assay and flow cytometry.

RESULTS

The mean apoptotic capacity was 13.55 +/- 10.54 for control subjects, 5.75 +/- 4.96 for patients with salivary gland carcinomas (p =.003), and 6.87 +/- 4.45 for patients with thyroid carcinomas (p =.006). These differences were associated with a 10-fold increased risk of salivary gland carcinoma (odds ratio [OR] = 10.71; 95% confidence interval [CI], 1.21-94.86) and a four-fold increased risk of thyroid carcinoma (OR = 3.93; 95% CI, 0.90-17.08).

CONCLUSIONS

Our data suggests that gamma radiation-induced apoptosis may serve as a biomarker of genetic susceptibility to salivary and thyroid carcinoma, and further confirmatory studies with larger sample size are warranted.

Suppression of apoptosis and clonogenic survival in irradiated human lymphoblasts with different TP53 status

The influence of radiation-induced apoptosis on radiosensitivity was studied in a set of closely related human lymphoblastoid cell lines differing in TP53 status. The clonogenic survival of irradiated TK6 cells (expressing wild-type TP53), WTK1 cells (overexpressing mutant TP53), and TK6E6 cells (negative for TP53 owing to transfection with HPV16 E6) was assessed in relation to the induction of apoptosis and its suppression by caspase inhibition or treatment with PMA as well as after treatment with caffeine. Measurements using the alkaline comet assay and pulsed-field electrophoresis of the induction and repair of DNA strand breaks showed similar kinetics of the processing of early DNA damage in these cell lines. The cytochalasin B micronucleus assay revealed identical levels of residual damage in the first postirradiation mitosis of these cells. Abrogation of TP53-dependent apoptosis in TK6E6 cells resulted in a distinct increase in radioresistance. Further suppression of apoptosis as observed in WTK1 cells overexpressing mutant TP53 apparently was not responsible for the high radioresistance of WTK1 cells, since other means of highly efficient suppression of apoptosis (caspase inhibition or PMA treatment) increased the clonogenic survival of irradiated TK6 cells only to levels similar to those of TK6E6 cells with abrogated TP53-dependent apoptosis. Considering the similar levels of residual chromosomal damage in TK6E6 cells and WTK1 cells, a hitherto unknown mechanism of tolerance needs to be inferred for these TP53 mutant cells. This residual damage tolerance, however, appears to require an intact G2/M-phase checkpoint function since the relative radioresistance of the WTK1 cells was completely lost upon caffeine treatment, which also resulted in a failure of the TK6 and TK6E6 cells to execute apoptosis. In this situation, the cellular response seems to be dominated entirely by TP53-independent mitotic failure.

Comparative analysis of DNA breakage, chromosomal aberrations and apoptosis induced by the anti-herpes purine nucleoside analogues aciclovir, ganciclovir and penciclovir

Nucleoside analogues have been used in antiviral therapy and suicide cancer gene therapy. Therefore, it is of importance to compare their potential cytotoxic and genotoxic action. Using metabolically competent CHO cells expressing the thymidine kinase gene of herpes simplex virus type 1 (CHO-HSVtk cells) as a model system, the induction of DNA breaks was compared with the induction of structural chromosomal aberrations and apoptosis/necrosis after exposure to the anti-herpes nucleoside analogues aciclovir (ACV), ganciclovir (GCV) and penciclovir (PCV). After continuous treatment of CHO-HSVtk cells with the drugs, LD(10) in a colony-forming assay was 50, 0.5 and 1 microM for ACV, GCV and PCV, respectively, with GCV to be the most potent agent as determined at a given dose level. There was a remarkable difference in the activity of the agents to kill HSVtk expressing and non-expressing cells: the difference in cellular sensitivity of HSVtk(+) versus HSVtk(-) cells at LD(10) level was 7-fold for ACV, 60-fold for GCV and 400-fold for PCV. The drugs were shown to be strong inducers of apoptosis that was analysed as to concentration- and time-dependence; they induced to only very low extent necrosis. The agents were also highly potent in the induction of DNA single-strand breaks (SSBs) and double-strand breaks (DSBs) (as measured by single cell gel electrophoresis (SCGE)) and chromosomal aberrations. Although PCV induced DNA DSBs with a kinetics and frequency similar to that of GCV, it caused mostly condensation defects instead of "typical" structural chromosomal aberrations. For the drugs used, the frequency of apoptotic cells and the induction of abnormal mitoses appear to be related indicating genotoxic effects induced by the agents to be involved in cell killing due to apoptosis.

[The effects of ionizing radiation on stem cells and hematopoietic progenitors: the place of apoptosis and the therapeutic potential of anti-apoptosis treatments]

Abstract: Bone marrow aplasia observed following ionizing radiation exposure (Total Body Irradiation; gamma dose range: 2-10 Gy) is a result, in particular, of the radiation-induced (RI) apoptosis in hematopoietic stem and progenitor cells (HSPC). We have previously shown in a baboon model of mobilized peripheral blood CD34+ cell irradiation in vitro that RI apoptosis in HSPC was an early event, mostly occurring within the first 24 hours, which involves the CD95 Fas pathway. Apoptosis may be significantly reduced with a combination of 4 cytokines (4F): Stem Cell Factor (SCF), FLT-3 Ligand (FL), thrombopoietin (TPO), and interleukin-3 (IL-3), each at 50 ng x mL(-1) (15% survival versus <3% untreated cells, 24 h post-irradiation at 2.5 Gy). In this study we show that addition of TNF-alpha(800 IU/ml) induces an increase in 4F efficacy in terms of cell survival 24 h after incubation (26% survival after 24 h irradiation exposure at 2.5 Gy) and amplification (k) of CD34+ cells after 6 days in a serum free culture medium (SFM) (kCD34+ = 4.3 and 6.3 respectively for 4F and successive 4F + TNF-a/ 4F treatments). In addition, the 4F combination allows culture on pre-established allogenic irradiated stromal cells in vitro at 4 Gy (kCD34+ = 4.5). Overall this study suggests (i) the potential therapeutic interest for an early administration of anti-apoptotic cytokines with or without hematopoiesis inhibitors (emergency cytokine therapy) and (ii) the feasibility in the accidentally irradiated individual, of autologous cell therapy based on ex vivo expansion in order to perform autograft of residual HSPC collected after the accident.

Ganciclovir-induced apoptosis in HSV-1 thymidine kinase expressing cells: critical role of DNA breaks, Bcl-2 decline and caspase-9 activation

Although ganciclovir (GCV) is most often used in suicide anticancer gene therapy, the mechanism of GCV-induced cell killing and apoptosis is not fully understood. We analysed the mechanism of apoptosis triggered by GCV using a model system of CHO cells stably transfected with HSV-1 thymidine kinase (HSVtk). GCV-induced apoptosis is due to incorporation of the drug into DNA resulting in replication-dependent formation of DNA double-strand breaks and, at later stages, S and G2/M arrest. GCV-provoked DNA instability was likely to be responsible for the observed initial decline in Bcl-2 level and caspase-9/-3 activation. Further decline in the Bcl-2 level was due to cleavage of the protein by caspase-9, as demonstrated by use of caspase inhibitors and transfection with trans-dominant negative caspase expression vectors. Bcl-2 cleavage resulted in the appearance of a pro-apoptotic 23 kDa Bcl-2 fragment and in excessive cytochrome c release, dephosphorylation of BAD, cleavage of PARP and finally DNA degradation. Since Fas/CD95 and caspase-8 were only slightly activated we conclude GCV-induced apoptosis to occur in this cell system mainly by activating the mitochondrial damage pathway. This process is independent of p53 for which the cells are mutated. Caspase-9 mediated cleavage of Bcl-2 accelerates the apoptotic process and may explain the high potential of GCV to induce apoptosis. Data are also discussed as to implications for HSVtk gene therapy utilizing GCV.

Kinetics of apoptotic markers in exogeneously induced apoptosis of EL4 cells

We investigated the time-dependence of apoptotic events in EL4 cells by monitoring plasma membrane changes in correlation to DNA fragmentation and cell shrinkage. We applied three apoptosis inducers (staurosporine, tubericidine and X-rays) and we looked at various markers to follow the early-to-late apoptotic events: phospholipid translocation (identified through annexin V-fluorescein assay and propidium iodide), lipid package (via merocyanine assay), membrane fluidity and anisotropy (via fluorescent measurements), DNA fragmentation by the fluorescence-labeling test and cell size measurements. The different apoptotic inducers caused different reactions of the cells: staurosporine induced apoptosis most rapidly in a high number of cells, tubercidine triggered apoptosis only in the S phase cells, while X-rays caused a G2/M arrest and subsequently apoptosis. Loss of lipid asymmetry is promptly detectable after one hour of incubation time. The phosphatidylserine translocation, decrease of lipid package and anisotropy, and the increase of membrane fluidity appeared to be based on the same process of lipid asymmetry loss. Therefore, the DNA fragmentation and the cell shrinkage appear to be parallel and independent processes running on different time scales but which are kinetically inter-related. The results indicate different signal steps to apoptosis dependent on inducer characteristics but the kinetics of "early-to-late" apoptosis appears to be a fixed program.

Mitotic death: a mechanism of survival? A review

Mitotic death is a delayed response of p53 mutant tumours that are resistant to genotoxic damage. Questions surround why this response is so delayed and how its mechanisms serve a survival function. After uncoupling apoptosis from G1 and S phase arrests and adapting these checkpoints, p53 mutated tumour cells arrive at the G2 compartment where decisions regarding survival and death are made. Missed or insufficient DNA repair in G1 and S phases after severe genotoxic damage results in cells arriving in G2 with an accumulation of point mutations and chromosome breaks. Double strand breaks can be repaired by homologous recombination during G2 arrest. However, cells with excessive chromosome lesions either directly bypass the G2/M checkpoint, starting endocycles from G2 arrest, or are subsequently detected by the spindle checkpoint and present with the features of mitotic death. These complex features include apoptosis from metaphase and mitosis restitution, the latter of which can also facilitate transient endocycles, producing endopolyploid cells. The ability of cells to initiate endocycles during G2 arrest and mitosis restitution most likely reflects their similar molecular environments, with down-regulated mitosis promoting factor activity. Resulting endocycling cells have the ability to repair damaged DNA, and although mostly reproductively dead, in some cases give rise to mitotic progeny. We conclude that the features of mitotic death do not simply represent aberrations of dying cells but are indicative of a switch to amitotic modes of cell survival that may provide additional mechanisms of genotoxic resistance.

New concepts in radiation-induced apoptosis: 'premitotic apoptosis' and 'postmitotic apoptosis'

Formerly, the mechanisms responsible for the killing of cells by ionizing radiation were regarded as being divided into two distinct forms, interphase death and reproductive death. Since they were defined based on the classical radiobiological concepts using a clonogenic cell survival assay, biochemical and molecular biological mechanisms involved in the induction of radiation-induced cell death were not fully understood in relation to the modes of cell death. Recent multidisciplinary approaches to cell death mechanism have revealed that radiation-induced cell death is divided into several distinct pathways by the time course and cell-cycle position, and that apoptotic cell death plays a key role in almost every mode of cell death. This review discusses the mechanisms of radiation-induced apoptosis in relation to cell-cycle progression and highlights a new concept of the mode of cell death: 'premitotic apoptosis' and 'postmitotic apoptosis'. The former is a rapid apoptotic cell death associated with a prompt activation of caspase-3, a key enzyme of intracellular signaling of apoptosis. A rapid execution of cell killing in premitotic apoptosis is presumably due to the prompt activation of a set of pre-existed molecules following DNA damages. In contrast, the latter is a delayed apoptotic cell death after cell division, and unlike premitotic apoptosis, it neither requires a rapid activation of caspase-3 nor is inhibited by a specific inhibitor, Ac-DEVD-CHO. A downregulation of anti-apoptotic genes such as MAPK and Bcl-2 may play a key role in this mode of cell death. Characterization of these two types of apoptotic cell death regarding the cell cycle regulation and intracellular signaling will greatly help to understand the mechanisms of radiation-induced apoptosis.

Wortmannin selectively enhances radiation-induced apoptosis in proliferative but not quiescent cells

PURPOSE

To examine whether wortmannin enhances radiation-induced apoptosis in human lymphoid cells.

METHODS AND MATERIALS

Different concentrations of wortmannin (0-40 micrOM) were added to TK6 lymphoblastoid cell and whole blood cell cultures 15 min before irradiation (0-6-Gy X-rays). After irradiation, medium was changed and cells were left to incubate for 48 h. In blood samples, CD4, CD8, and CD20 lymphocytes were labeled using FITC-conjugated antibodies. All cell types were fixed in a diethyleneglycol-formaldehyde solution. DNA was stained with propidium iodide. Apoptosis was quantified using flow cytometry and confirmed using fluorescence microscopy.

RESULTS

Wortmannin significantly enhances radiation-induced apoptosis in lymphoblastoid cells. Compared to the controls, wortmannin treatment only slightly enhanced radiation-induced apoptosis in quiescent T-lymphocytes and had no effect in quiescent B-lymphocytes.

CONCLUSION

Wortmannin enhances radiation-induced apoptosis in a cell-type dependent manner. If the selective effect of wortmannin on proliferative tissues also exists in nonlymphoid tissues, it should enhance the therapeutic ratio of treatments for tumors located in poorly proliferative healthy tissues. Further studies are needed to compare the effects of wortmannin in human tumor cells and various normal cells including proliferative and quiescent cells.

High levels of delayed radiation-induced apoptosis observed in lymphoblastoid cell lines from ataxia-telangiectasia patients

PURPOSE

Cells from ataxia-telangiectasia (A-T) patients are extremely sensitive to radiation but display decreased apoptosis, as measured during the first 3 days following radiation. To explain this apparent contradiction, we examined apoptosis in normal and A-T cells at late time points following radiation, under the assumption that radiation-induced apoptosis is delayed in the A-T cells.

METHODS AND MATERIALS

Blood cells and lymphoblastoid cell lines from A-T patients, as well as healthy donors, were irradiated with X-rays. Apoptosis was measured at different time points (up to 7 and 30 days for lymphocytes and lymphoblastoid cells, respectively) using a flow cytometric method based on the reduction of intracellular DNA content (sub-G1 population).

RESULTS

Compared to normal cells, CD4 and CD8 A-T lymphocytes displayed constantly reduced levels of radiation-induced apoptosis for up to 7 days after treatment. A-T lymphoblastoid cells, however, displayed a delayed and prolonged apoptosis.

CONCLUSION

A-T lymphoblastoid cells show high levels of delayed radiation-induced apoptosis, which may contribute to the high cellular radiosensitivity displayed by the A-T phenotype. ATM (the gene mutated in A-T) plays different roles in the apoptotic response to ionizing radiation in quiescent lymphocytes and proliferative lymphoblastoid cells.

Computerized video time-lapse analysis of apoptosis of REC:Myc cells X-irradiated in different phases of the cell cycle

Asynchronous rat embryo cells expressing Myc were followed in 50 fields by computerized video time lapse (CVTL) for three to four cycles before irradiation (4 Gy) and then for 6-7 days thereafter. Pedigrees were constructed for single cells that had been irradiated in different parts of the cycle, i.e. at different times after they were born. Over 95% of the cell death occurred by postmitotic apoptosis after the cells and their progeny had divided from one to six times. The duration of the process of apoptosis once it was initiated was independent of the phase in which the cell was irradiated. Cell death was defined as cessation of movement, typically 20-60 min after the cell rounded with membrane blebbing, but membrane rupture did not occur until 5 to 40 h later. The times to apoptosis and the number of divisions after irradiation were less for cells irradiated late in the cycle. Cells irradiated in G(1) phase divided one to six times and survived 40-120 h before undergoing apoptosis compared to only one to two times and 5-40 h for cells irradiated in G(2) phase. The only cells that died without dividing after irradiation were irradiated in mid to late S phase. Essentially the same results were observed for a dose of 9.5 Gy, although the progeny died sooner and after fewer divisions than after 4 Gy. Regardless of the phase in which they were irradiated, the cells underwent apoptosis from 2 to 150 h after their last division. Therefore, the postmitotic apoptosis did not occur in a predictable or programmed manner, although apoptosis was associated with lengthening of both the generation time and the duration of mitosis immediately prior to the death of the daughter cells. After the non-clonogenic cells divided and yielded progeny entering the first generation after irradiation with 4 Gy, 60% of the progeny either had micronuclei or were sisters of cells that had micronuclei, compared to none of the progeny of clonogenic cells having micronuclei in generation 1. However, another 20% of the non-clonogenic cells had progeny with micronuclei appearing first in generation 2 or 3. As a result, 80% of the non-clonogenic cells had progeny with micronuclei. Furthermore, cells with micronuclei were more likely to die during the generation in which the micronuclei were observed than cells not having micronuclei. Also, micronuclei were occasionally observed in the progeny from clonogenic cells in later generations at about the same time that lethal sectoring was observed. Thus cell death was associated with formation of micronuclei. Most importantly, cells irradiated in late S or G(2) phase were more radiosensitive than cells irradiated in G(1) phase for both loss of clonogenic survival and the time of death and number of divisions completed after irradiation. Finally, the cumulative percentage of apoptosis scored in whole populations of asynchronous or synchronous populations, without distinguishing between the progeny of individually irradiated cells, underestimates the true amount of apoptosis that occurs in cells that undergo postmitotic apoptosis after irradiation. Scoring cell death in whole populations of cells gives erroneous results since both clonogenic and non-clonogenic cells are dividing as non-clonogenic cells are undergoing apoptosis over a period of many days.

[Regulation of cell cycle and radiation-induced cell death]

Tight control of cell proliferation is mandatory to prevent cancer formation as well as to normal organ development and homeostasis. This occurs through checkpoints that operate in both time and space and are involved in the control of numerous pathways including DNA replication and transcription, cell cycle progression, signal transduction and differentiation. Moreover, evidence has accumulated to show that apoptosis is tightly connected with the regulation of cell cycle progression. In this paper we describe the main pathways that determine checkpoints in the cell cycle and apoptosis. It is also recalled that in solid tumors radiation-induced cell death occurs most frequently through non-apoptotic mechanisms involving oncosis, and mitotic or delayed cell death.

Involvement of SAPK/JNK pathway in X-ray-induced rapid cell death of human T-cell leukemia cell line MOLT-4

We found that SAPK/JNK was phosphorylated during X-ray-induced rapid cell death of MOLT-4 cells and that acid Sphingomyelinase inhibitor D609 suppressed the rapid cell death as well as phosphorylation of SAPK/JNK. Also C2-ceramide caused phosphorylation of SAPK/JNK, followed by rapid cell death. Further we isolated X-ray-resistant radiation-hybrid clones from MOLT-4 and 50 Gy irradiated mouse FM3A cells by repeated selections with 3 Gy irradiation. One of them named Rh-1a was found resistant to X-ray- as well as C2-ceramide-induced rapid cell death. Rh-1a cells had mouse DNA but no increase in either mouse or human Bcl-2 determined by Western blotting. Accumulation of p53 after X-irradiation was similarly observed in both parental MOLT-4 and Rh-1a cells. However, contrasting to prolonged and prominent phosphorylated status of SAPK/JNK in MOLT-4 cells, Rh-1a cells exhibited short transient increase and FM3A cells showed no increase of phosphorylated status SAPK/JNK after X-irradiation. Therefore, SAPK/JNK activation is considered important in X-ray-induced rapid cell death or apoptosis of MOLT-4 cells.

Postnatal mammary gland development requires macrophages and eosinophils

Interactions between mammary epithelial and mesenchymal cells including fibroblasts and adipocytes are crucial for the proper postnatal development of the mammary ductal tree. Often overlooked, however, are the migrant cells that enter tissues at different stages of development. In this paper we identify two such cell types, macrophages and eosinophils, that are recruited around the growing terminal end buds (TEBs) during postnatal development. An important role for leukocytes in mammary gland ductal outgrowth is first demonstrated by depleting mice of leukocytes using sub-lethal (gamma)-irradiation. This treatment results in a curtailment of mammary gland epithelial development that is completely rescued by bone-marrow transplantation, concurrent with a restoration of macrophage and eosinophil recruitment around the growing ducts. Using mice homozygous for a null mutation in the gene for CSF1 (Csfm(op)/Csfm(op)), the major growth factor for macrophages, we show that in the absence of CSF1, the population of macrophages in mammary glands is depleted. In this mutant, the formation of TEBs, their outgrowth into the fat pad and the branching of the resultant ducts are all impaired. Similarly, by using mice homozygous for a null mutation in the gene for eotaxin, a major chemokine for local recruitment of eosinophils in tissue, we identify eotaxin as the necessary and sufficient chemokine responsible for eosinophil recruitment around TEBs. In the absence of eosinophils, mammary gland branch formation and to a lesser extent TEB formation are reduced. Our data show that CSF1-regulated macrophages, in collaboration with eotaxin-regulated eosinophils, have essential and complementary functions in regulating the branching morphogenesis of the mammary gland.

A simple method for accurate estimation of apoptotic cells

A simple, sensitive, and reliable "DNA diffusion" assay for the quantification of apoptosis is described. Human lymphocytes and human lymphoblastoid cells, MOLT-4, were exposed to 0, 12.5, 25, 50, or 100 rad of X-rays. After 24 h of incubation, cells were mixed with agarose, microgels were made, and cells were lysed in high salt and detergents. DNA was precipitated in microgels by ethanol. Staining of DNA was done with an intense fluorescent dye, YOYO-1. Apoptotic cells show a halo of granular DNA with a hazy outer boundary. Necrotic cells, resulting from hyperthermia treatment, on the other hand, show an unusually large homogeneous nucleus with a clearly defined boundary. The number of cells with apoptotic and necrotic appearance can be scored and quantified by using a fluorescent microscope. Results were compared with other methods of apoptosis measurement: morphological estimations of apoptosis and DNA ladder pattern formation in regular agarose gel electrophoresis. Validation of the technique was done using some known inducers of apoptosis and necrosis (hyperthermia, hydrogen peroxide, mitoxantrone, novobiocin, and sodium ascorbate).

Computerized video time-lapse microscopy studies of ionizing radiation-induced rapid-interphase and mitosis-related apoptosis in lymphoid cells

Computerized video time-lapse (CVTL) microscopy of X-irradiated cultures of cells of the murine lymphoma cell lines ST4 and L5178Y-S and the human lymphoid cell line MOLT-4 demonstrated that these cells exhibit a wide disparity in the timing of induction and execution of radiation-induced cell death that included rapid-interphase apoptosis, delayed apoptosis, and postmitotic apoptosis. ST4 cells that received 2.5 or 4 Gy of X radiation underwent rapid-interphase apoptosis within 2 h. Apoptosis commenced with a 10-20-min burst of membrane blebbing followed by swelling for 2-4 h and cell collapse. No apoptotic bodies were formed. After a dose of 1 Gy, approximately 90% of ST4 cells died by rapid-interphase apoptosis, while the remainder completed several rounds of cell division prior to cell death. Postmitotic death of ST4 cells occurred with the same morphological sequence of events as during rapid-interphase apoptosis induced by doses of 1-4 Gy. In contrast, L5178Y-S and MOLT-4 cells that received 4 Gy underwent apoptosis more slowly, with a complex series of events occurring over 30-60 h. Only 3% of L5178Y-S cells and 24% of MOLT-4 cells underwent apoptosis without attempting cell division. The cells became abnormally large during a long G(2)-phase delay, and then most of the cells (76-97%) attempted to divide for the first or second time at approximately 18-30 h postirradiation. However, either mitosis failed or division was aberrant; i.e., the large cells divided into three or four fragments which eventually fused together. This process was followed by several rounds of complex and unpredictable membrane blebbing, gross distortions of shape, fragmentation-refusion events, and formation of apoptotic bodies, after which the cells collapsed at 36-60 h postirradiation.

Detection of apoptosis and expression of apoptosis-associated proteins as early predictors of prognosis after irradiation therapy in stage IIIb uterine cervical cancer

We investigated the proportion of apoptotic cells and the expression of apoptosis-associated proteins after the delivery of the first week of irradiation for stage IIIb uterine cervical cancer. Thirty patients with stage IIIb squamous cell carcinoma of the uterine cervix who received only irradiation therapy were registered in this study. Specimens were obtained before irradiation therapy and at the end of the first week of irradiation. The apoptotic index (AI) of each tissue specimen was calculated by counting the apoptotic cells and expressed as a percentage. Immunohistochemical evaluation for apoptosis-related proteins, p53, Bcl-2, Bax, caspase-1 and caspase-3 was also performed. The AI was 0.8+/-0.9% (mean+/-SD) before irradiation and 1.7+/-1.3% at the end of the first week of irradiation. We observed that the patients who survived more than 5 years had AI levels of 2.1+/-1.3% at the end of their first week of therapy. This rate was significantly higher than the rate of 1.1+/-0.8% (P=0.02) of the patients who died within 5 years. When the cut-off value of the AI was set at 1.7%, the sensitivity, specificity, positive predictive value, and negative predictive value for the prediction of patients' prognosis after irradiation therapy were 73.4%, 72.4%, 82.4%, and 61.5%, respectively. In 17 of the AI-positive cases, expressions of Bax (P=0.006), caspase-1 (P=0.045), and caspase-3 (P=0.013) at the end of the first week were significantly higher than before irradiation. The proportion of apoptotic cells and the expression of apoptosis-associated proteins, Bax, caspase-1, and caspase-3, at the end of the first week of irradiation could be useful predictors of the prognosis in stage IIIb squamous cell carcinoma of the uterine cervix treated by irradiation therapy.

Gamma-irradiation does not impair ATRA-induced maturation of myeloid leukaemic cells: implication for combined radiation and differentiation therapy

In the present study we investigated the effects of various doses of gamma-irradiation, followed by induction of granulocytic differentiation with all-trans-retinoic acid (ATRA), on proliferative rate, differentiation capability and oxidative metabolism of leukaemic cells from two different myeloid leukaemia cell lines, HL-60 and PLB-985. Regarding the effects of such combined treatment on the proliferative capabilities of HL-60 and PLB-985 cell lines, we showed that their growth kinetics were similar after 2 Gy gamma-irradiation combined with ATRA. However, with doses >2 Gy, the behaviour of the cell lines differed largely. Indeed, HL-60 appeared to be more radiosensitive than PLB-985 regarding cell viability and proliferation. Besides, whatever dose of irradiation (2, 5 or 10 Gy) was applied, ATRA was still able to induce differentiation of HL-60 and PLB-985 into granulocytes that retained the capacity to produce superoxide anion. The results of these in vitro studies suggest that leukaemia cell lines retain their ability to respond to ATRA, a granulocytic-differentiating inducer following high doses of irradiation. This may have implications for the use of radiation therapy in combination with ATRA for the treatment of extramedullary infiltrations of myeloid leukaemias in humans.

Radio-sensitive murine thymoma cell line 3SB: characterization of its apoptosis-resistant variants induced by repeated X-irradiation

3SB, a mouse thymoma cell line, is one of the most radio-sensitive cells (D0 = 0.3 Gy), and its rapid apoptosis (4 h after 5 Gy irradiation, 90% apoptosis) seems to play a decisive role in enhancing the radiosensitivity. To understand the molecular mechanisms underlying extremely high radiosensitivity and rapid apoptosis, we attempted to isolate X-ray-resistant (XR) variants from 3SBH5, a stable subclone of 3SB, by repeating exposure of the cells to 2-5 Gy X-rays. Four independent stable XR variants, R111, R223, R316 and R429, were isolated by the repeated irradiation protocols. All XR cells possessed about 3 times higher D10 values than that of their parental 3SBH5. They were also resistant to apoptosis; only 10% cells underwent apoptosis 4 h after 5 Gy irradiation. The p53 protein was induced in all the cell lines after 5 Gy X-irradiation. These variants showed a cross resistance to a chemical reagent daunorubicin (DNR) that is known to be involved in the ceramide-mediated apoptosis. DNR, as well as C2-ceramide (5 muM) induced apoptosis in parental 3SBH5 cell, but not in two XR variants, R233 and R316 cells. Present result suggests that the induction of X-ray resistance by repeated X-irradiation might be achieved, at least partly, by the enhanced resistance to the ceramide-mediated apoptosis.