A low-pH culture condition enhances the radiosensitizing effect of wortmannin

Uncertainties Associated with Clonogenic Assays using a Cs-137 Irradiator and Ir-192 Afterloader: A Comprehensive Compilation for Radiation Researchers

Clonogenic assays are the gold standard for measuring cell clonogenic survival and enable quantification of a cell line's radiosensitivity through the calculation of the surviving fraction, the ratio of cell clusters (colonies) formed after radiation exposure compared to the number formed without exposure. Such studies regularly utilize Cs-137 irradiators. While uncertainties for specific procedural aspects have been described previously, a comprehensive review has not been completed. We therefore quantified uncertainties associated with clonogenic assays performed using a Cs-137 Shepherd irradiator, and a recently established brachytherapy afterloader in vitro radiation delivery apparatus (BAIRDA), through a series of experiments and a literature review. The clonogenic assay is subject to uncertainties that affect the determination of the surviving fraction (e.g., accuracy of the number of cells seeded, potential effects of hypothermia, and the threshold number of cells for a cluster to be identified as a colony). Furthermore, dose delivery uncertainties related to both the Cs-137 irradiator and BAIRDA were also quantified. The combined standard (k = 1) uncertainty was ± 6.0% in the surviving fraction for the Cs-137 irradiator (±6.3% for BAIRDA), up to ± 1.3% in the dose delivered by the Cs-137 irradiator, and up to ± 2.2% in the dose delivered by BAIRDA. The largest individual uncertainties were associated with the number of cells seeded on a plate (3.4%) and inter-observer variability in counting (4.1%), suggesting that effective reduction of uncertainties in the conduct of the clonogenic assay proper may provide the greatest relief on the uncertainty budget. Finally, measurable impact on experimental findings was assessed by applying this uncertainty to clonogenic assays of SW756 cells using either a Cs-137 irradiator or BAIRDA, introducing a maximum shift in the reported radiobiological parameters a/b and T1/2 of 0.3 Gy and 0.4 h, respectively, while the 95% confidence interval increased by 0.5 Gy and decreased by 0.4 h, respectively. Though the overall impact on radiobiological parameter estimation was small, the individual uncertainties could have a significant influence in other applications of in vitro experiments in radiation biology. Hence, better understanding of the uncertainties associated with both clonogenic assays and the radiation source used can improve the accuracy of experimental analysis and reproducibility of the results.

Unusual prolongation of radiation-induced G2 arrest in tumor xenografts derived from HeLa cells

The effect of ionizing radiation on cell cycle kinetics in solid tumors remains largely unknown because of technical limitations and these tumors’ complicated structures. In this study, we analyzed intratumoral cell cycle kinetics after X-irradiation of tumor xenografts derived from HeLa cells expressing the fluorescent ubiquitination-based cell cycle indicator (Fucci), a novel system to visualize cell cycle kinetics in vivo. Cell cycle kinetics after X-irradiation was examined by using tumor sections and in vivo real-time imaging system in tumor xenografts derived from HeLa cells expressing Fucci. We found that G2 arrest was remarkably prolonged, up to 5 days after 10-Gy irradiation, in contrast to monolayer cultures where G2 arrest returned within 24 h. Cells isolated from tumors 5 days after irradiation exhibited a higher surviving fraction than those isolated immediately or one day after irradiation. In this study, we clearly demonstrated unusual post-irradiation cell cycle kinetics in tumor xenografts derived from HeLa-Fucci cells. Our findings imply that prolonged G2 arrest occurring in tumor microenvironments following irradiation may function as a radioresistance mechanism.

Emerging issues in radiogenic cataracts and cardiovascular disease

In 2011, the International Commission on Radiological Protection issued a statement on tissue reactions (formerly termed non-stochastic or deterministic effects) to recommend lowering the threshold for cataracts and the occupational equivalent dose limit for the crystalline lens of the eye. Furthermore, this statement was the first to list circulatory disease (cardiovascular and cerebrovascular disease) as a health hazard of radiation exposure and to assign its threshold for the heart and brain. These changes have stimulated various discussions and may have impacts on some radiation workers, such as those in the medical sector. This paper considers emerging issues associated with cataracts and cardiovascular disease. For cataracts, topics dealt with herein include (i) the progressive nature, stochastic nature, target cells and trigger events of lens opacification, (ii) roles of lens protein denaturation, oxidative stress, calcium ions, tumor suppressors and DNA repair factors in cataractogenesis, (iii) dose rate effect, radiation weighting factor, and classification systems for cataracts, and (iv) estimation of the lens dose in clinical settings. Topics for cardiovascular disease include experimental animal models, relevant surrogate markers, latency period, target tissues, and roles of inflammation and cellular senescence. Future research needs are also discussed.

In vitro chemo- and radio-resistance in small cell lung cancer correlates with cell adhesion and constitutive activation of AKT and MAP kinase pathways

Most small cell lung cancer (SCLC) patients relapse within 12 months of starting combination chemotherapy plus radio-therapy, due to the development of acquired chemo- and radio-resistance. This phenomenon relates to the induction of tumour differentiation, resulting in apoptosis-resistant, morphologically variant (v-SCLC) cells, which lack the neuroendocrine expression of classic (c-) SCLC cells. In this study spontaneously adherent SCLC sublines were shown by differential gene expression analysis to provide an in vitro model of variant differentiation in SCLC, with down-regulation of neuroendocrine markers and up-regulation of epithelial differentiation markers cyclin D1, endothelin, the cell adhesion molecules CD 44 and integrin subunits alpha2, beta3 and beta4. The sensitivity of adherent SCLC sublines to etoposide, cyclophosphamide and gamma radiation was significantly diminished relative to parent suspension cell lines. Western blot analysis using phosphorylation-specific antibodies to Akt and MAP kinase revealed markedly elevated activation in adherent SCLC sublines, paralleled by increased levels of phosphorylated Bad protein and activated NF-kappaB. Subcultivation of the adherent sublines on uncoated surfaces reversed their adherent phenotype immediately and under these conditions Akt activity reverted to low levels. These results suggest that c-SCLC cells can differentiate spontaneously to v-SCLC and that the associated cellular adhesion may trigger Akt-dependent inhibition of apoptosis in SCLC cells, thus leading to acquired chemo- and radio-resistance.