Apoptosis in radiation therapy: a double-edged sword

Radiation therapy achieves its therapeutic effects by inducing apoptosis and non-apoptotic cell death. The aim of this focused review is to highlight the aspects of the cell death pathways most relevant to conventional fractionated radiation therapy. I review reports on how our current understanding of the molecular mechanisms of cell death may enable us to revise the four radiobiological principles (reoxygenation, repair of sublethal damage, redistribution of cells in the cell cycle, and repopulation of surviving cells) for radiation treatment with fractionated dose delivery. Apoptosis and non-apoptotic forms of cell death are not represented in the linear quadratic model, which is clinically used to calculate the effects of different total doses, dose per fraction and fraction number on reproductive cell death, a mode of cell death associated with lethal chromosome aberrations. Examples are provided to justify or not a reassessment of the role of apoptosis and non-apoptotic cell death in radiosensitivity, tumor cell proliferation and tumor microenvironment. As our understanding of apoptosis developed at the molecular level, so did our understanding of other forms of cell death, particularly autophagy and to a lesser extent, senescence. The linear quadratic model remains a guide for the treatment planner. The therapeutic clinical roles of apoptosis and non-apoptotic forms of cell death remain to be defined. Their relative importance will probably lie in tumor developmental history related to its type, size and stage. Radiobiological research should focus on the quantitative effects of dose and fractionation on the radiation induction of apoptotic and non-apoptotic types of cell death and the interplay among cell death pathways. This article is part of a Special Issue entitled “Apoptosis: Four Decades Later”

Molecular markers of apoptosis in cancer patients exposed to ionizing radiation: the post-chornobyl view

During the past three decades, the deleterious consequences of Chornobyl accident including carcinogenic effects in the people who were accidentally exposed to radiation have been intensively studied. In particular, recent studies provided increased knowledge of the molecular pathogenesis of thyroid tumors in children exposed to Chornobyl fallout. The risk of several forms of leukemia including myelodysplastic syndromes is elevated in Chornobyl liquidators. Furthermore, the upward trends of increases in a variety of other tumors including breast cancer, cancers of central nervous system and renal cancer have been reported in the persons exposed to Chornobyl fallout. There is growing evidence that insufficient apoptosis allows irradiated cells to survive and thereby contributes to carcinogenesis. The purpose of the present survey is to summarize the recent findings related to apoptotic biomarkers among cancer patients from the different populations affected by the Chornobyl catastrophe. Among the particularly radiosensitive cancer sites, we focused on thyroid cancer and leukemia. Several genes and/or proteins controlling apoptosis directly or indirectly have been incorporated into the analysis. The data reviewed here provide a mechanistic link between the apoptosis alterations and development of radiation-related cancer in the 30-year post-Chornobyl period. We suggest that the type of mutations arising from misrepair of DNA double strand breaks (gene fusion and amplification) is the initial signature event in radiation-induced thyroid cancer. Much work has to be done over the next years to elucidate central questions related to the nature of human radiation carcinogenesis. This article is part of a Special Issue entitled “The Chornobyl Nuclear Accident: Thirty Years After”

The Effect of Docetaxel (Taxotere®) on Human Gastric Cancer Cells Exhibiting Low-Dose Radiation Hypersensitivity

Low-dose radiation hypersensitivity (HRS) describes a phenomenon of excessive sensitivity to X ray doses <0.5 Gy. Docetaxel is a taxane shown to arrest cells in the G2/M phase of the cell cycle. Some previous studies suggested that HRS might result from the abrogation of the early G2 checkpoint arrest. First we tested whether HRS occurs in gastric cancer—derived cells, and whether pre-treatment of cells with low docetaxel concentrations can enhance the magnitude of HRS in gastric cancer cells. The results demonstrated HRS at ~0.3 Gy and the synergy between 0.3 Gy and docetaxel (3 nM for 24 h), and the additivity of other drug/dose combinations. The synergistic effect was associated with a significant docetaxel-induced G2 accumulation. Next, we evaluated in time-course experiments ATM kinase activity and proteins associated with the induction and maintenance of the early G2 checkpoint. The results of multi-immunoblot analysis demonstrate that HRS does not correlate with the ATM-dependent early G2 checkpoint arrest. We speculate that G2 checkpoint adaptation, a phenomenon associated with a prolonged cell cycle arrest, might be involved in HRS. Our results also suggest a new approach for the improvement the effectiveness of docetaxel-based radiotherapy using low doses per fraction

Neoplastic transformation of mouse C3H 10T1/2 and Syrian hamster embryo cells by heavy ions

C3H 10T1/2 mouse-embryo fibroblasts were used for transformation experiments to study the effectiveness of various heavy ions with energies up to 20 MeV/u and LET values from 170 to 16.000 keV/μm. The transformation frequency per unit absorbed dose decreased with increasing ionization density; at the highest values of LET we found a decrease even of the transformation efficiency per unit fluence. Uranium ions at energies of 5, 9, and 16.3 MeV/u did not induced any transformation. In additional studies piimary Syrian hamster embryo cells (SHE) were exposed to heavy ions in order to characterize cytological and molecular changes which may be correlated with neoplastic transformation. Growth behaviour, chromosomal status, tumorigenicity in nude mice, and expression of oncogenes of transformed cell lines were examined

Absence of a dose-rate effect in the transformation of C3H 10T1/2 cells by α-particles

The findings of Hill et al. (1984) on the greatly enhanced transformation frequencies at very low dose rates of fission neutrons induced us to perform an analogous study with -particles at comparable dose rates. Transformation frequencies were determined with γ-rays at high dose rate (0·5 Gy/min), and with -particles at high (0·2 Gy/min) and at low dose rates (0·83-2·5 mGy/min) in the C3H 10T1/2 cell system. α-particles were substantially more effective than γ-rays, both for cell inactivation and for neoplastic transformation at high and low dose rates. The relative biological effectiveness (RBE) for cell inactivation and for neoplastic transformation was of similar magnitude, and ranged from about 3 at an -particle dose of 2 Gy to values of the order of 10 at 0·25 Gy. In contrast to the experiments of Hill et al. (1984) with fission neutrons, no increased transformation frequencies were observed when the -particle dose was protracted over several hours

Syrian hamster dermal cell immortalization is not enhanced by power line frequency electromagnetic field exposure

Several epidemiological studies have suggested associations between exposure to residential power line frequency electromagnetic fields and childhood leukaemia, and between occupational exposure and adult leukaemia. A variety of in vitro studies have provided limited supporting evidence for the role of such exposures in cancer induction in the form of acknowledged cellular end points, such as enhanced mutation rate and cell proliferation, though the former is seen only with extremely high flux density exposure or with co-exposure to ionizing radiation. However, in vitro experiments on a scale large enough to detect rare cancer-initiating events, such as primary cell immortalization following residential level exposures, have not thus far been reported. In this study, large cultures of primary Syrian hamster dermal cells were continuously exposed to power line frequency electromagnetic fields of 10 100 and 1000 μT for 60 h, with and without prior exposure to a threshold (1.5 Gy), or sub-threshold (0.5 Gy), immortalizing dose of ionizing radiation. Electromagnetic field exposure alone did not immortalize these cells at a detectable frequency (≥ 1 × 10−7); furthermore, such exposure did not enhance the frequency of ionizing radiation-induced immortalization. © 1999 Cancer Research Campaig

Pharmacokinetic analysis of two different docetaxel dose levels in patients with non-small cell lung cancer treated with docetaxel as monotherapy or with concurrent radiotherapy

<p>Abstract</p> <p>Background</p> <p>Previous pharmacokinetic studies with docetaxel have mostly used 3-weekly (75 mg/m²and 100 mg/m²) or weekly regimens (35–40 mg/m²). The pharmacokinetics and radiosensitizing efficacy of weekly 20 mg/m²docetaxel, has however not been well characterized. We examined the pharmacokinetics of weekly docetaxel when administered with concurrent radiotherapy and compared the results with a 3-weekly 100 mg/m²regimen.</p> <p>Methods</p> <p>Thirty-four patients with non small cell lung cancer (NSCLC) were included in this study, 19 receiving 100 mg/m²docetaxel 3-weekly as single therapy, and 15 receiving 20 mg/m²docetaxel weekly with concurrent radiotherapy. A newly developed HPLC method was used for measuring docetaxel levels, capable of quantifying docetaxel in plasma down to the nanomolar level.</p> <p>Results</p> <p>The HPLC method showed detectable concentrations of docetaxel in plasma even after 72 hours. In the present study we have demonstrated that median docetaxel plasma levels of 3 nM can be obtained 72 hours after a dose of 20 mg/m².</p> <p>Conclusion</p> <p>The pharmacokinetics of docetaxel is characterized by great inter-individual variability and at some time points plasma concentrations for 20 mg/m²and 100 mg/m²docetaxel were overlapping. Extrapolation of these results indicates that radio sensitizing docetaxel concentrations may be present for as long as 1 week, thus supporting the use of 20 mg/m²weekly docetaxel.</p

Inhibition of pH regulation as a therapeutic strategy in hypoxic human breast cancer cells

The following organizations are gratefully acknowledged: University of Edinburgh (JM), Medical Research Council (EJJ), EPSRC IMPACT (CW), Medical Research Scotland (CX) and Scottish Universities Life Sciences Alliance (CMP). This research was financed in part by a Grant of the 7th Framework Program of the European Union (METOXIA project; HEALTH-F2-2009-222741), along with the Breast Cancer Institute (BCI) and Aitken Breast Cancer Research Fund.Hypoxic cancer cells exhibit resistance to many therapies. This study compared the therapeutic effect of targeting the pH regulatory proteins (CAIX, NHE1 and V-ATPase) that permit cancer cells to adapt to hypoxic conditions, using both 2D and 3D culture models. Drugs targeting CAIX, NHE1 and V-ATPase exhibited anti-proliferative effects in MCF-7, MDA-MB-231 and HBL-100 breast cancer cell lines in 2D. Protein and gene expression analysis in 2D showed that CAIX was the most hypoxia-inducible protein of the 3 targets. However, the expression of CAIX differed between the 3 cell lines. This difference in CAIX expression in hypoxia was consistent with a varying activity of FIH-1 between the cell lines. 3D expression analysis demonstrated that both CAIX and NHE1 were up-regulated in the hypoxic areas of multicellular tumor spheroids. However, the induction of CAIX expression in hypoxia was again cell line dependent. 3D invasion assays conducted with spheroids showed that CAIX inhibition significantly reduced the invasion of cells. Finally, the capability of both NHE1 and CAIX inhibitors to combine effectively with irradiation was exhibited in clonogenic assays. Proteomic-mass-spectrometric analysis indicated that CAIX inhibition might be combining with irradiation through stimulating apoptotic cell death. Of the three proteins, CAIX represents the target with the most promise for the treatment of breast cancer.Publisher PDFPeer reviewe

Dominant negative knockout of p53 abolishes ErbB2-dependent apoptosis and permits growth acceleration in human breast cancer cells

We previously reported that the ErbB2 oncoprotein prolongs and amplifies growth factor signalling by impairing ligand-dependent downregulation of hetero-oligomerised epidermal growth factor receptors. Here we show that treatment of A431 cells with different epidermal growth factor receptor ligands can cause growth inhibition to an extent paralleling ErbB2 tyrosine phosphorylation. To determine whether such growth inhibition signifies an interaction between the cell cycle machinery and ErbB2-dependent alterations of cell signalling kinetics, we used MCF7 breast cancer cells (which express wild-type p53) to create transient and stable ErbB2 transfectants (MCF7-B2). Compared with parental cells, MCF7-B2 cells are characterised by upregulation of p53, p21WAF and Myc, downregulation of Bcl2, and apoptosis. In contrast, MCF7-B2 cells co-transfected with dominant negative p53 (MCF7-B2/Δp53) exhibit reduced apoptosis and enhanced growth relative to both parental MCF7-B2 and control cells. These data imply that wild-type p53 limits survival of ErbB2-overexpressing breast cancer cells, and suggest that signals of varying length and/or intensity may evoke different cell outcomes depending upon the integrity of cell cycle control genes. We submit that acquisition of cell cycle control defects may play a permissive role in ErbB2 upregulation, and that the ErbB2 overexpression phenotype may in turn select for the survival of cells with p53 mutations or other tumour suppressor gene defects