Comparative human cellular radiosensitivity: III. Gamma-radiation survival of cultured skin fibroblasts and resting T-lymphocytes from the peripheral blood of the same individual

[Mechanisms of radiation-induced lymphopenia and therapeutic impact]

Radiation induced lymphopenia is frequent and can be severe and durable. Although lymphocytes have long been known as highly radiosensitive cells, it is poorly characterized. Radiation-induced lymphopenia seems to affect lymphocyte subpopulations differently and seems to be influenced by radiation modalities. The depth and duration of lymphopenia depend on the location of the irradiation and the volumes of treatment. Importantly, radiation-induced lymphopenia has been associated with poorer prognosis in several tumor types. The knowledge about radiation-induced lymphopenia might lead to a rethinking of the modalities of radiotherapy and new approaches to restore lymphocytes counts.

Identification of a radiation sensitivity gene expression profile in primary fibroblasts derived from patients who developed radiotherapy-induced fibrosis

BACKGROUND AND PURPOSE

During radiotherapy, normal tissue is unavoidably exposed to radiation which results in severe normal tissue reactions in a small fraction of patients. Because those who are sensitive cannot be determined prior to radiotherapy, the doses are limited to all patients to avoid an unacceptable number of severe adverse normal tissue responses. This limitation restricts the optimal treatment for individuals who are more tolerant to radiation. Genetic variation is a likely source for the normal tissue radiosensitivity variation observed between individuals. Therefore, understanding the radiation response at the genomic level may provide knowledge to develop individualized treatment and improve radiotherapy outcomes.

MATERIAL AND METHODS

Exon arrays were utilized to compare the basal expression profile between cell lines derived from six cancer patients with and without severe fibrosis. These data were supported by qRT-PCR and RNA-Seq techniques.

RESULTS

A set of genes (FBN2, FST, GPRC5B, NOTCH3, PLCB1, DPT, DDIT4L and SGCG) were identified as potential predictors for radiation-induced fibrosis. Many of these genes are associated with TGFβ or retinoic acid both having known links to fibrosis.

CONCLUSION

A combinatorial gene expression approach provides a promising strategy to predict fibrosis in cancer patients prior to radiotherapy.

Biological effects of space radiation on human cells: history, advances and outcomes

Exposure to radiation is one of the main concerns for space exploration by humans. By focusing deliberately on the works performed on human cells, we endeavored to review, decade by decade, the technological developments and conceptual advances of space radiation biology. Despite considerable efforts, the cancer and the toxicity risks remain to be quantified: 1) the nature and the frequency of secondary heavy ions need to be better characterized in order to estimate their contribution to the dose and to the final biological response; 2) the diversity of radiation history of each astronaut and the impact of individual susceptibility make very difficult any epidemiological analysis for estimating hazards specifically due to space radiation exposure. 3) Cytogenetic data undoubtedly revealed that space radiation exposure produce significant damage in cells. However, our knowledge of the basic mechanisms specific to low-dose, to repeated doses and to adaptive response is still poor. The application of new radiobiological techniques, like immunofluorescence, and the use of human tissue models different from blood, like skin fibroblasts, may help in clarifying all the above items.

Downregulation of human DAB2IP gene expression in prostate cancer cells results in resistance to ionizing radiation

DAB2IP (DOC-2/DAB2 interactive protein) is a member of the RAS-GTPase-activating protein family. It is often downregulated in metastatic prostate cancer and has been reported as a possible prognostic marker to predict the risk of aggressive prostate cancer. In this study, we furnish several lines of evidence indicating that metastatic human prostate cancer PC3 cells deficient in DAB2IP (shDAB2IP) exhibit increased clonogenic survival in response to ionizing radiation (IR) compared with control cells expressing an endogenous level of DAB2IP (shVector). Radioresistance was also observed in normal prostate cells that are deficient in DAB2IP. This enhanced resistance to IR in DAB2IP-deficient prostate cancer cells is primarily due to faster DNA double-strand break (DSB) repair kinetics. More than 90% of DSBs were repaired in shDAB2IP cells by 8 hours after 2 Gy radiation, whereas only 60% of DSB repair were completed in shVector cells at the same time. Second, upon irradiation, DAB2IP-deficient cells enforced a robust G(2)-M cell cycle checkpoint compared with control cells. Finally, shDAB2IP cells showed resistance to IR-induced apoptosis that could result from a striking decrease in the expression levels of proapoptotic proteins caspase-3, caspase-8, and caspase-9, and significantly higher levels of antiapoptotic proteins Bcl-2 and STAT3 than those in shVector cells. In summary, DAB2IP plays a significant role in prostate cell survival following IR exposure due to enhanced DSB repair, robust G(2)-M checkpoint control, and resistance to IR-induced apoptosis. Therefore, it is important to identify patients with dysregulated DAB2IP for (a) assessing prostate cancer risk and (b) alternative treatment regimens.

Protection of DNA and membranes from gamma-radiation induced damages by Centella asiatica

Objectives

The objective of the present study was to examine the ability of Centella asiatica extract to offer protection to DNA and membranes against the deleterious effects of ionizing radiation exposure.

Methods

Protection of DNA under in-vitro conditions of irradiation was estimated using plasmid relaxation assay. For in-vivo studies the extract was administered orally to mice exposed to whole-body γ-radiation. The ability of the extract to offer protection against whole-body γ-radiation exposure was analysed by performing an alkaline comet assay on mouse bone marrow cells. The extent of lipid peroxidation was estimated using the TBARS (thio-barbituric acid reacting substances) method, in order to monitor membrane damage. Radiation-induced mortality of the animals following a lethal dose of γ-radiation was also examined.

Key findings

Centella asiatica extract significantly reduced radiation-induced damage to DNA. The extent of radiation-induced mortality and lipid peroxidation was also found to be considerably reduced in animals administered with the extract.

Conclusions

Centella asiatica rendered radioprotection to DNA and membranes against radiation exposure, both in vitro and in vivo. We have earlier reported that administration of the extract can prevent a radiation-induced decline in antioxidant enzyme levels. This suggests that radioprotection by Centella asiatica extract could be mediated by mechanisms that act in a synergistic manner, especially involving antioxidant activity.

Unexpectedly severe acute radiotherapy side effects are associated with single nucleotide polymorphisms of the melanocortin-1 receptor

PURPOSE

The melanocortin-1 receptor (MC1R) regulates melanin biogenesis. Deoxyribonucleic acid sequence variants in the form of single nucleotide polymorphisms (SNPs) of MC1R affect melanin expression and are linked to skin phenotype. We aimed to determine whether SNPs of MC1R were associated with unexpectedly severe ionizing radiation reactions.

METHODS AND MATERIALS

The MC1R genotype of a cohort of Australians with unexpectedly severe acute and/or late reactions (Common Terminology Criteria Version 3 (CTCv3) Grade 3 or 4) to radiotherapy (RT) for cancer (n = 30) was analyzed. The findings were compared with control data from our previous study of MC1R representative of the general Australian population (n = 1,787).

RESULTS

The difference in frequency of alleles encoding a "red hair color" phenotype in the cohort of patients with unexpectedly severe acute radiation reactions (n = 12) was significantly increased compared with the control population (p = 0.003). Acute radiosensitivity was especially associated with the R160W variant allele (odds ratio, 3.64 [95% confidence interval, 1.3-10.27]). The corresponding comparison of MC1R controls with unexpectedly severe late radiation reactions (n = 18) was not significant. It was also found that R160W as a part of the genotype in the patients with unexpectedly severe acute RT side effects as compared with the control group was also significant (p = 0.043).

CONCLUSIONS

In this small cohort of cancer patients, deoxyribonucleic acid sequence variants of the MC1R gene, especially the R160W variant, have been associated with unexpectedly severe acute reactions to RT. This result needs to be verified in a larger cohort of patients.

Variant CD44 expression by human fibroblasts

CD44 is a cell surface glycoprotein with roles in tumour invasion and metastasis. CD44 is variably spliced from ten variant exons and mis-splicing is a biomarker for detection of colon, urothelial and other carcinomas. Fibroblasts are normally considered to lack variant exons and thus should not generate false-positive signals. Transcription of variant exons by fibroblasts was investigated by exon-specific reverse transcription-polymerase chain reaction (RT-PCR) for variant exons v2-v10 using normal primary fibroblasts, immortalized and experimentally transformed fibroblasts. Flow cytometry, immunocytochemistry and Western blotting were used to determine expression. All types of fibroblasts, including normal primary culture fibroblasts, transcribed low levels of variant exon mRNA. Expression could not be detected by blotting or immunocytochemistry but flow cytometry revealed minor expression of some exons by all three types of cultured fibroblast. Fibroblasts do transcribe and express small amounts of variant exon CD44. This may need to be considered when using exon splicing as a biomarker for malignancy in clinical samples containing connective tissue.

No Different Sensitivity in Terms of Whole-Body Irradiation between Normal and Acatalasemic Mice

To elucidate the radiosensitivity of an acatalasemic mouse, we examined the time and dose-dependency in the survival rates, the lymphocytes and the intestinal epithelial cells, and the antioxidant function after 3.0 to 12.0 Gy whole body irradiation. Results showed that no significant differences between acatalasemic mice and normal mice were observed in the survival rates and the histological changes in spleens and small intestine after each irradiation. The catalase activities in livers and spleens of acatalasemic mice were significantly lower than those of normal mice and the glutathione peroxidase activity in livers of acatalasemic mice was significantly higher than that of normal mice. At 10 days after 6.0 Gy irradiation, the catalase activities in livers of acatalasemic and normal mice and that in spleens of normal mice significantly decreased compared with no-irradiation control, and there were no differences between those catalase activities. The total glutathione content in acatalasemic mice was significantly higher than that in normal mice at 10 days after 6.0 Gy irradiation. These findings suggested that the radiosensitivity of acatalasemic mice in terms of whole body irradiation doesn't significantly differ from that of normal mice, probably due to compensated sufficient contents of glutathione peroxidase and total glutathione in acatalasemic mice.

Minimal ionizing radiation sensitivity in a large cohort of xeroderma pigmentosum fibroblasts

We have examined our ionizing radiation survival data for 33 xeroderma pigmentosum (XP) primary fibroblast lines and compared the data to that of 53 normal fibroblast lines, 7 Cockayne syndrome (CS) lines, 4 combined XP/CS lines and 8 ataxia-telangiectasia fibroblast lines. Although there are differences in radiosensitivity between cell lines within each class, we have no convincing evidence that XP lines as a group are more sensitive to ionizing radiation than the general population. However, because the XP phenotype may lead to premature ageing, especially of sun-exposed tissues, we would still advocate caution when XP patients come to radiotherapy. Our results confirm the extreme ionizing radiation hypersensitivity of ataxia-telangiectasia; they are also consistent with a tendency for slight hypersensitivity in CS, but not (necessarily) in combined XP/CS.

Chromosomal radiosensitivity in two cell lineages derived from clinically radiosensitive cancer patients

PURPOSE

Despite its prominent contribution to cancer cure and palliation, around 1% to 5% of cancer patients suffer serious side effects from radiotherapy. A cardinal goal in the fields of radiobiology and oncology is to predict normal tissue radiosensitivity of a cancer patient before radiotherapy. Higher tumor control rates are likely if radiotherapy individualization could be achieved by applying predictive approaches.

EXPERIMENTAL DESIGN

Here, we make use of the cytokinesis block micronucleus assay to assess radiosensitivity in cell lines derived from two different cell lineages obtained from clinically radiosensitive patients. We determined the micronucleus frequency after graded doses of ionizing radiation to primary fibroblasts and lymphoblast cell lines derived from 36 highly radiosensitive cancer patients.

RESULTS

Many cell lines, following exposure to ionizing radiation, from patients with severe clinical reactions to radiotherapy showed statistically significantly higher frequencies of micronuclei than those from patients who had normal reactions to radiotherapy. One individual revealed significantly higher micronucleus frequencies in both cell lineages. Interestingly, lymphoblast cell lines from one patient showed micronucleus frequencies similar to ataxia telangiectasia mutated-deficient cells.

CONCLUSIONS

These results indicate that the micronucleus assay may have use for identifying predisposition to clinical radiosensitivity, at least in a subset of patients as a component of a pretreatment radiosensitivity assay for use in the clinic.

Detecting Normal Cell Radiosensitivity via Assay of DNA Damage in Lymphocytes for Individualizing Radiotherapy in Head and Neck Cancer Patients

PURPOSE

The purpose of this study was to determine whether the distribution of radiosensitivities in normal tissues of head and neck cancer patients, measured using a DNA damage assay on lymphocytes, is likely to provide sufficient discrimination to enable reliable identification of patients with abnormal sensitivities.

MATERIAL AND METHODS

Radiosensitivity was assessed in 307 lymphocyte samples from unselected head and neck cancer patients and was quantified as the initial number of DNA double-strand breaks (dsb) induced per Gray and per DNA unit (200 Mbp).

RESULTS

The existence of an inter-individual variation in the radiosensitivity parameter is described by the range (0.41--9.38 dsb/Gy/DNA unit) of the values found. We detected 37 patients who developed severe skin reactions during radiotherapy treatment and we compared their radiosensitivity values with the remaining patients treated. Radiosensitivity values of >7.20 dsb/Gy/DNA unit should theoretically correspond to highly radiosensitive patients.

CONCLUSIONS

Our results suggest that initial DNA damage measured on lymphocytes offers an approach to predict the acute response of human normal tissues prior to radiotherapy. .

DNA methylation changes at human Th2 cytokine genes coincide with DNase I hypersensitive site formation during CD4(+) T cell differentiation

The differentiation of naive CD4(+) T lymphocytes into Th1 and Th2 lineages generates either cellular or humoral immune responses. Th2 cells express the cytokines IL-4, -5, and -13, which are implicated in asthma and atopy. Much has been published about the regulation of murine Th2 cytokine expression, but studies in human primary T cells are less common. We have developed a method for differentiating human CD45RA(+) (naive) T cells into Th1 and Th2 populations that display distinct cytokine expression profiles. We examined both CpG methylation, using bisulfite DNA modification and sequencing, and chromatin structure around the IL-4 and IL-13 genes before and after human T cell differentiation and in normal human skin fibroblasts. In naive cells, the DNA was predominantly methylated. After Th2 differentiation, DNase I hypersensitive sites (DHS) appeared at IL-4 and IL-13 and CpG demethylation occurred only around the Th2-specific DHS. Both DHS and CpG demethylation coincided with consensus binding sites for the Th2-specific transcription factor GATA-3. Although fibroblasts, like naive and Th1 cells, did not express IL-4 or IL-13, DHS and unmethylated CpG sites that were distinct from the Th2-specific sites were observed, suggesting that chromatin structure in this cluster not only varies in T cells according to IL-4/IL-13 expression but is also tissue specific.

Individualization of radiotherapy in breast cancer patients: possible usefulness of a DNA damage assay to measure normal cell radiosensitivity

PURPOSE

The purpose of this study was to determine whether the distribution of sensitivities in breast cancer patients, measured using a DNA damage assay on lymphocytes, is likely to provide sufficient discrimination to enable the reliable identification of patients with abnormal sensitivities.

MATERIAL AND METHODS

Radiosensitivity (x) was assessed in 226 samples of lymphocytes from unselected women with breast cancer and was quantified as the initial number of DNA double-strand breaks (dsb) induced per Gy and per DNA unit (200 Mbp).

RESULTS

The existence of an inter-individual variation in the parameter (x) is described through the range (0.40-4.72 dsb/Gy/DNA unit) of values found, which have been fitted to the mathematical model defined by the log-normal distribution (mu = 0.42+/-0.03; sigma = 0.52+/-0.03; R(2)=0.9475). A total of 189 patients received radiotherapy after surgical treatment. Among them, we have detected 15 patients who developed severe skin reactions and we have compared their radiosensitivity values with the rest of patients treated.

CONCLUSIONS

Our results suggest that DNA initial damage measured on lymphocytes offers an approach to predict the acute response of human normal tissues prior to radiotherapy. Values of x higher than 3.20 dsb/Gy/DNA unit theoretically should correspond to the highly radio-sensitive patients. Using the experimental results, we have calculated the strength of the test by means of the area under the receiver operator characteristic curves (A(Z)) to determine whether the radiosensitivity assay can discriminate between patients according to their radiation response. The value found (A(Z)=0.675+/-0.072) is indicative of a fair-poor discriminating capacity of the test to identify the patients with higher risk of developing a severe acute reaction during the radiotherapy treatment.

Sensitization of resistant lymphoma cells to irradiation-induced apoptosis by the death ligand TRAIL

A combination of antitumor approaches acting on different death pathways seems ideal for increasing therapeutic responses, especially when defined resistance mechanisms interfere with individual cellular processes. Apoptosis pathways triggered by ionizing radiation (XRT) and the death ligand TRAIL were analysed in Jurkat lymphoma cells. Both induced the activation of caspase-8, caspase-3, BID and mitochondrial potential loss. TRAIL induced apoptosis required caspase-8, whereas it was not essential for radiation induced apoptosis. The inhibition of mitochondrial damage by Bcl-2 abrogated XRT induced apoptosis and caspase activation, but only marginally attenuated TRAIL induced cell death. The combined treatment with TRAIL and XRT exerted additive apoptotic effects in control cells, whereas highly synergistic effects occurred in cells overexpressing Bcl-2. In addition, a strong effect of TRAIL on radiation induced clonogenic cell death was found. In conclusion, TRAIL seems to be of high potential value for a combination with ionizing radiation in tumor therapy.

Four radiation hypersensitivity cases and their implications for clinical radiotherapy

BACKGROUND AND PURPOSE

Over a 20 year period, four out of 2000 paediatric radiotherapy patients, treated at St. Bartholomew's Hospital (three with lymphoma, one with angiosarcoma), have revealed extreme/fatal clinical hypersensitivity in normal tissues.

PATIENTS AND METHODS

Cellular hypersensitivity was confirmed in vitro and attributed to the ataxia-telangiectasia (A-T) gene in cases I and II, a newly described defect in the DNA ligase 4 gene in case III, and a novel and as yet incompletely defined, molecular defect in case IV who presented with xeroderma pigmentosum (XP).

RESULTS

The severe clinical hypersensitivity preceded the cellular and molecular analysis, but did not manifest as a clinically exaggerated normal tissue reaction until 3+ weeks after the start of a conventionally fractionated course of radiotherapy, by which time the latent damage had been inflicted. There were no clinical stigmata to alert the clinician to a predisposing syndrome in two patients (cases I and II). We point out that approximately 20% of A-T patients are classified as variants with delayed expression of clinical symptoms, and case II falls into this category.

CONCLUSIONS

As lymphoma (incidence, one in 100000 children) constituted the majority of the diagnoses, questions arise as to: (1), the probability of other centres having experienced and being presented in the future with similar problems (particularly bearing in mind that other oncologically predisposing radiosensitivity syndromes have not been not represented in our experience); and (2), the appropriateness, efficiency and applicability of predictive assays. Unambiguous cellular radiosensitivity would have been apparent from clonal assays on fibroblast cultures from all four cases prior to treatment, but such assays take 4-6 weeks to produce results. While estimates of chromosome damage or clonal assays on pre-treatment blood derived cells would be faster, there is a health economics issue as to the general applicability of such 'screening' assays.

Complex-type chromosomal exchanges in blood lymphocytes during radiation therapy correlate with acute toxicity

The new method of chemical-induced premature chromosome condensation combined with fluorescence in situ hybridization was used to analyze chromosomal damage in peripheral blood mononuclear lymphocytes of patients undergoing radiation treatment for esophageal cancer with high-energy X-rays or accelerated carbon ions at the National Institute of Radiological Sciences (Chiba, Japan). Total number of aberrant cells correlated with radiation field size, but no correlation was found with acute toxicity. A high frequency of complex-type exchanges were also recorded. This aberration type presented a high individual variability, and correlated well with the acute morbidity. Cytogenetic analysis by interphase chromosome painting is proposed as a useful tool for monitoring normal tissue effects during radiotherapy.

Altered apoptotic profiles in irradiated patients with increased toxicity

PURPOSE

A retrospective study of radiation-induced apoptosis in CD4 and CD8 T-lymphocytes, from 12 cancer patients who displayed enhanced toxicity to radiation therapy and 9 ataxia telangiectasia patients, was performed to test for altered response compared to healthy blood-donors and normal cancer patients.

METHODS AND MATERIALS

Three milliliters of heparinized blood from each donor was sent via express post to the Paul Scherrer Institute (PSI) for subsequent examination. The blood was diluted 1:10 in RPMI medium, irradiated with 0-, 2-, or 9-Gy X-rays, and incubated for 48 h. CD4 and CD8 T-lymphocytes were then labeled using FITC-conjugated antibodies, erythrocytes were lysed, and the DNA stained with propidium iodide. Subsequently, cells were analyzed using a Becton Dickinson FACScan flow cytometer. Radiation-induced apoptosis was recognized in leukocytes as reduced DNA content attributed to apoptosis-associated changes in chromatin structure. Apoptosis was confirmed by light microscopy, electron microscopy, and by the use of commercially available apoptosis detection kits (in situ nick translation and Annexin V). Data from hypersensitive individuals were compared to a standard database of 105 healthy blood-donors, and a database of 48 cancer patient blood donors who displayed normal toxicity to radiation therapy. To integrate radiosensitivity results from CD4 and CD8 T-lymphocytes after 2 and 9 Gy, z-score analyses were performed.

RESULTS

A cohort of 12 hypersensitive patients was evaluated; 8 showed enhanced early toxicity, 3 showed enhanced late toxicity, and 1 showed both. The cohort displayed less radiation-induced apoptosis (-1.8 sigma) than average age-matched donors. A cohort of 9 ataxia telangiectasia homozygotes displayed even less apoptosis (-3.6 sigma).

CONCLUSION

The leukocyte apoptosis assay appears to be a useful predictor of individuals likely to display increased toxicity to radiation therapy; however, validation of this requires a prospective study.

DNA damage and prediction of radiation response in lymphocytes and epidermal skin human cells

The success of radiotherapy in eradicating tumours depends on the total radiation dose, but what limits this dose is the tolerance of the normal tissues within the treatment volume. Studies involving fibroblast survival have demonstrated the theoretical feasibility of a predictive assay of radiation sensitivity, but such an assay is still far from clinical application. Using pulsed-field gel electrophoresis (PFGE), we have quantified the initial "apparent" number of DNA double-strand breaks (dsb) induced by the radiation as an alternative measure of sensitivity in 2 different normal cell types from the same patients, epidermal skin cells and lymphocytes. We found significant inter-individual variation in the measured dsb (1-5 dsb/Gy/DNA unit). We also found a linear correlation between molecular damage in lymphocytes and skin samples from the same patient (slope = 0.83; r = 0.694; p = 0.0001). These results suggest that the initial number of dsb could be used as an indicator of the in vivo response to radiation.

Role of antioxidant enzymes on ionizing radiation resistance

Exposure of cells to ionizing radiation leads to formation of reactive oxygen species (ROS) that are associated with radiation-induced cytotoxicity. The antioxidant enzymes manganese superoxide dismutase (MnSOD), copper-zinc superoxide dismutase (CuZnSOD), and glutathione peroxidase (GPx), are key intracellular antioxidants in the metabolism of ROS. We investigated the potential role of the three antioxidant enzymes in radioresistance by analyzing cell morphology, cell viability, and cellular radioresistance in stably transfected CHO cell lines overexpressing MnSOD, CuZnSOD, and GPx, respectively. We found that overexpression of human MnSOD substantially protected cells from ionizing radiation injury. Relative to MnSOD, GPx could slightly reduce the radiation sensitivity while the radioresistance in CuZnSOD expressing cells did not change significantly. The results suggested that MnSOD may play a central role in protecting cells against reactive oxygen species injury during ionizing radiation exposure among MnSOD, CuZnSOD, and GPx.

Comparison between radiation-induced cell cycle delay in lymphocytes and radiotherapy response in head and neck cancer

A study was made evaluating the use of radiation-induced cell cycle delay in lymphocytes to predict tumour response to radiotherapy. Peripheral blood lymphocytes were isolated from whole blood from 49 patients with head and neck cancer before treatment with radiotherapy and from 25 healthy donors. The clinical response to radiotherapy was assessed at 0-2 months after treatment. The level of radiation-induced cell cycle delay was measured using flow cytometry after mitogen stimulation of lymphocytes. The analysis of ten normal donors gave no significant difference in variability between the intra-assay and the intra-donor samples. However, the cell cycle data for lymphocytes from these healthy donors showed significant inter-individual differences in G2 phase accumulation. Patients showing no response to radiotherapy had a high level of S-phase cells compared with partial (P < 0.001) and complete responders (P = 0.016). An inverse relationship was found when analysing the fraction of cells in G2 (P = 0.009 and 0.034 respectively). In general, healthy donors had similar cell cycle kinetics compared with the non-responders. In conclusion, the result indicates that radiation-induced cell cycle delay in lymphocytes is inversely correlated with tumour response to radiotherapy in head and neck cancer patients. However, the value of the present test for predicting individual tumour response is limited, because of assay variability and overlap between groups.

Interindividual variation in cytogenetic response to X-ray and colchicine measured with the cytokinesis-block micronucleus assay

Interindividual variation in cytogenetic response to two different types of micronucleus (MN) inducer, X-rays (a clastogen) and colchicine (a spindle poison), was investigated in the peripheral blood lymphocytes of normal healthy donors by the cytokinesis-block MN method. The data for 124 donors between the ages of 19 and 80 years showed that the histogram of individual frequency of X-ray (2 Gy)-induced micronucleated cells followed the normal distribution (Shapiro Wilks W-test) with a significant interindividual variance (ANOVA, p < 0.001). This was, however, not the case for colchicine (0.03 microgram/ml)-induced micronucleated cells. Instead, a skewed distribution illustrating interindividual variation was evident (ANOVA, p < 0.001). Statistical analysis of the effect of age and sex on MN incidence by using the Kruskal-Wallis test indicated that age affected the baseline and colchicine-induced MN incidences strongly but not the X-ray-induced MN incidence. There was no effect of sex on the incidence of micronuclei induced by either agent. In order to avoid any possible effect of age on the MN index, data for young subjects aged less than 30 years old were analyzed separately. The results of this analysis again showed significant interindividual variations in baseline, X-ray-induced, and colchicine-induced micronucleated cell rates. Results of the correlation-coefficient analysis showed that neither X-ray-induced MN incidence nor colchicine-induced MN incidence was related to baseline MN incidence. No correlation between X-ray-induced and colchicine-induced MN incidences was also found by this analysis. These results suggest that interindividual variance in chromosomal response to mutagens in normal populations may be a real phenomenon, as is interindividual variance in baseline MN frequency, and that individual susceptibilities to the two different types of micronucleus inducers (X-ray and colchicine) are unrelated, and the baseline MN level is not of predictive value for the susceptibilities.

[Genetic predisposition and radiation sensitivity of tumors]

BACKGROUND

Studies on normal tissue radiation sensitivity have demonstrated profound differences of individual sensitivities. A number of genetic syndromes associated with abnormal radiation sensitivity have been described. Significant differences have also been detected in persons without known genetic disorders. The question arises as to whether tumors originating from normal tissues with abnormal radiation sensitivity share this abnormal sensitivity and as to whether a general correlation between normal tissue sensitivity and tumor tissue sensitivity can be substantiated.

METHODS

Experimental and clinical data derived from own investigations and an extensive review of the literature was used to answer the question.

RESULTS

Experimental studies on normal and tumor tissues of SCID-and C3H-mice demonstrated that the 2.7-fold enhanced radiation sensitivity of SCID normal tissues is also found in SCID tumors. Clinical investigations on cervical carcinoma and breast cancer patients revealed higher local control rates in patients with more pronounced acute side effects. A weak trend towards the same relationship was found in head and neck cancer patients. Case reports on unusually severe acute radiation side effects or unexpected tumor remissions as well as few reports on radiotherapy in ataxia telangiectasia (AT) patients suggest a correlation between normal- and tumor-tissue radiation sensitivity. Studies on fibroblasts and tumor cells from the same patient support this hypothesis in soft tissue sarcoma patients, but do not so for head and neck cancer patients. Tumor cells exhibit a considerably higher variation of radiation sensitivities than normal tissue cells.

CONCLUSIONS

Experimental and clinical data are compatible with the hypothesis that normal tissue radiation sensitivity predicts for tumor tissue sensitivity. However, in view of the larger heterogeneity of tumor cell radiation sensitivity as compared to normal tissue radiation sensitivity, the development of a clinically useful predictive test for tumor sensitivity based on normal cell sensitivity appears to be unrealistic.

Rapid assay of intrinsic radiosensitivity based on apoptosis in human CD4 and CD8 T-lymphocytes

PURPOSE

An assay for radiosensitivity has numerous applications in the clinic. Avoidance of acute responses, prediction of normal tissue toxicity, and individualization of patient radiotherapy are included among these. We have developed a rapid assay (about 24 h) able to predict intrinsic radiosensitivity of CD4 and CD8 T-lymphocytes based on radiation-induced apoptosis.

METHODS AND MATERIALS

Fresh blood samples (1-2 ml in heparinized tubes) were irradiated with 0-, 2-, and 8-Gy X rays at a dose rate of approximately 3 Gy/min. Following irradiation, the cells were collected and prepared for flow-cytometric analysis and cell sorting. In conjunction with the CellQuest software available with the FACSVantage cell sorter (Becton-Dickinson), two T-lymphocyte types were analyzed on the basis of their cell-specific antigens (CD4 and CD8), and DNA was stained with DAPI. Following the separation of these cell types, radiation-induced cell death was assessed. Cytotoxicity was characterized by gradual degradation of internucleosomal DNA which results in a sub-G1 peak on the DNA histogram, and by the associated loss of surface antigens causing an intermediate positive peak in the antibody histogram. Using the assay, we investigated the interdonor variation in a cohort of 45 healthy adult blood donors and 5 children [one had immunodeficiency, centromeric instability, and facial anomalies syndrome (ICF), and one had ataxia telangiectasia (AT)]. Intradonor variation was assessed with 10 different experiments from a single donor.

RESULTS

CD4 and CD8 T-lymphocyte radiosensitivities were correlated (r = 0.63 and 0.65 for 2 and 8 Gy, respectively) in 45 adult donors. Both for CD4 and CD8 cells, 2 and 8 Gy irradiation responses showed a good correlation (r = 0.77 for both). Interdonor variation was significantly higher than intradonor variation (p < 0.0005) for all CD4 and CD8 data. We observed a decrease in the antigen fluorescence of dying cells, a phenomenon referred to as antigen-ebb. Antigen-ebb was clearly observed in both cell types, and correlated significantly with cytotoxicity. A trend was observed between radiosensitivity and donor age, but there was no correlation for gender. Blood from a 4-year-old girl presenting with ICF demonstrated compromised radiation-induced cytotoxicity in her CD4 T-lymphocytes, and an 11-year-old boy presenting with AT demonstrated compromised radiation-induced cytotoxicity in both his CD4 and CD8 T-lymphocytes.

CONCLUSION

We conclude that the assay provides a rapid means of determining radiosensitivity, can discriminate differences in radiation-induced cytotoxicity between individuals, and can be used as a rapid screen for genetically hypersensitive patients. Antigen-ebb offers interesting possibilities for molecular biological investigations, permitting characterization and isolation of abnormal but vital cells in the absence of clastogenic agents.

Hypersensitivity of ataxia-telangiectasia fibroblasts to a nitric oxide donor

Ataxia-telangiectasia (A-T) is a human autosomal recessive disease characterised by immunodeficiency, extreme sensitivity to ionising radiation and progressive cerebellar ataxia. The defective gene has recently been cloned and is a member of the phosphatidylinositol 3-kinase family. We have investigated the possibility that the neurodegeneration in A-T might be induced by an endogenously formed mutagen causing radiation-like damage. Nitric oxide is known to be formed in the cerebellum and we present evidence that A-T fibroblasts are hypersensitive to killing by the nitric oxide donor S-nitrosoglutathione (GSNO), as are fibroblasts from a radiosensitive individual without ataxia. Killing was determined as loss of colony forming ability. GSNO induces dose-dependent DNA strand breakage, but to no greater extent in A-T fibroblasts. Breakdown of GSNO to nitrite and nitrate appears to occur to the same extent in both normal and A-T fibroblasts. Cell killing by GSNO appears to be associated in both types of cell with formation of nitrite, rather than nitrate, as the ultimate oxidation product of nitric oxide.

Influence of environmental and genetic factors on variation in human response to DNA damaging agents

Exogenous DNA damaging agents must be considered in the context of endogenous reactive species which have the potential to damage DNA. Although a no-effect level for a DNA-damaging compound may not exist, it may be feasible to define a level where reducing exposure to the compound is no longer the most effective way of reducing human risk. Modifying environmental factors which affect human response to damage may be the better strategy. Although a number of rare human syndromes are associated with a reduced ability to repair DNA damage, it is not clear how wide is the range of genetic variation in repair capacity among normal individuals. Studies with DNA repair-deficient human syndromes indicate that processes other than mutation and DNA repair must be involved in the development of cancer, and these processes may represent new sources of variation in human response to genotoxic agents.

Comparison between normal tissue reactions and local tumor control in head and neck cancer patients treated by definitive radiotherapy

PURPOSE

This study was conducted to test for the relationship between tumor and normal tissue radiosensitivity, by comparing local tumor control to the severity of acute and late normal tissue reactions in head and neck cancer patients treated by definitive radiotherapy.

METHODS AND MATERIALS

Two hundred eighty-six patients with head and neck cancer who were treated at the University of Texas M. D. Anderson Cancer Center between 1983 and 1993 were selected for the study. Of these, 124 (43%) were treated by a concomitant boost regimen and 162 (57%) by hyperfractionation. All patients had at least 1 year of follow-up. The tumor stage distribution according to the 1992 American Joint Committee on Cancer (AJCC) staging system was as follows: T1, 3%; T2, 53%; T3, 40%; T4, 4%. The average doses delivered were 71.2 Gy and 76.2 Gy for the concomitant boost and hyperfractionation regimens, respectively, with no significant variation between patients. Acute and late reactions were recorded using the Radiation Therapy Oncology Group (RTOG)/European Organization for Research on Treatment of Cancer (EORTC) grading system (0 to 4). The median follow-up period was 38 months (range: 12-107 months). The time to local tumor recurrence was analyzed in relation to the severity of acute and late reactions expressed as the maximum recorded grades, and to the time intensity of acute mucositis, expressed as the area under the curve of mucositis grade vs. time. Univariate and multivariate analyses also included T stage, N stage, and site of origin as other prognostic variables, and were carried out using a proportional hazards model.

RESULTS

Fifty-four patients (19%) suffered local failure. T stage was found to significantly influence local control (p = 0.009). There was a nonsignificant trend for higher failure rates in patients with maximum Grade 1 or 2 vs. those with Grade 3 or 4 acute mucositis (28 and 18%, respectively; p = 0.17). No correlation was found between the severity of late reactions and local tumor control after radiotherapy. Analysis by time intensity of mucositis revealed a wide variation between individuals with a nonsignificant trend for higher local failure rates in patients with low mucositis time intensity scores.

CONCLUSIONS

These clinical results suggest a possible relationship between normal tissue and tumor radiosensitivity. However, additional studies with a larger numbers of patients, and using refined normal tissue endpoints that incorporate a time function are needed to fully elucidate this question.

Protective effect of deoxyribonucleosides on UV-irradiated human peripheral blood T-lymphocytes: possibilities for the selective killing of either cycling or non-cycling cells

Non-cycling human T-lymphocytes from normal subjects show a 10-fold greater sensitivity than fibroblasts to UV-B (280-315 nm) irradiation from a Westinghouse FS20 lamp, but only a 2.7-fold greater sensitivity to UV-C (254 nm) irradiation. Hypersensitivity is associated with a deficiency in the rejoining of excision breaks. Non-cycling T-lymphocytes have extremely low deoxyribonucleotide pools. Addition to the medium of the four deoxyribonucleosides, each at a concentration of 10(-5) M, substantially increases survival and reduces the persistence of excision-related strand breaks following UV-B or UV-C irradiation (Yew and Johnson (1979) Biochim. Biophys. Acta 562, 240-241; Green et al. (1994) Mutation Res., 315, 25-32). UV-resistance of T-lymphocytes is also increased by stimulating the cells into cycle. The addition of deoxyribonucleosides does not further enhance survival of cycling cells and they do not reach the level of resistance achieved by non-cycling cells in the presence of deoxyribonucleosides. We suggest that two opposing effects are in operation. Cells out of cycle can show increased resistance to DNA damage in the absence of division but they also have reduced deoxyribonucleotide pools, which may limit DNA repair. With UV-B irradiation, the exceptionally low dNTP pools in non-cycling T-lymphocytes cause this second effect to predominate. In contrast, with ionising radiation, which forms highly cytotoxic double-strand breaks, non-cycling human T-lymphocytes are slightly more resistant than fibroblasts. Non-cycling cells such as T-lymphocytes should be especially sensitive to agents which produce a high proportion of read excisable damage, but should show normal resistance to agents which highly toxic lesions. It may be possible by choice of DNA damaging agent and manipulation of cellular deoxyribonucleotide pools, to choose regimes which will selectively kill either cycling or non-cycling cells and to improve the efficacy of standard therapeutic procedures. Conditions favouring selective killing of non-dividing T-lymphocytes but sparing stem cells may be of value in bone marrow transplantation. Conditions favouring selective killing of dividing cancer cells but sparing non-dividing normal tissue may be of value in cancer therapy.

A review of human cell radiosensitivity in vitro

The survival curves of 694 human cell lines irradiated in exponentially growing phase in vitro were collected from the literature. Among them, 271 were derived from tumors, 423 were nontransformed fibroblasts and other normal cell strains from healthy people or people with some genetic disorders. Seventy-six different cell types are identified, and a specific radiosensitivity could be associated with each, using D and surviving fraction at 2 Gy. Technical factors such as culture medium, feeder cells, and scoring method were found to affect intrinsic radiosensitivity. In particular, the cell type is not a discriminating factor when cells are studied in agar. Results obtained with cells irradiated in agar must be used cautiously, depending on how the cells were prepared for the experiments. The use of feeder cells narrows the range of radiosensitivity of human cells. For cells irradiated as monolayer, it was possible to build a scale of radiosensitivity according to cell type, ranging, in terms of D from 0.6 Gy for the most sensitive cell lines to more than 4 Gy for the most resistant. Considering that, in most cases, we could estimate the variation of radiosensitivity within each cell type, our classification among cell types can be used by researchers to place their results in the context of the literature.

Use of fluorescence in situ hybridization to determine the relationship between chromosome aberrations and cell survival in eight human fibroblast strains

A predictive assay of normal tissue radiosensitivity could benefit 'treatment tailoring' of radiotherapy for certain categories of tumour. The use of present clonogenic cell survival assays for this purpose would be impractical in routine clinical practice because of the lengthy assay time. Fluorescence in situ hybridization (FISH) using whole chromosome probes on metaphases was investigated as a potential substitute. Eight human fibroblast cell strains with a range of radiosensitivities were tested. For each strain, cell survival curves were determined and correlated with chromosome aberrations detected by FISH performed on metaphase cells collected 52 h after irradiation. A whole chromosome probe for chromosome 4 was used for all cell strains. The results revealed an increase in the percentage of metaphases with aberrant chromosomes (translocations and/or breaks) with increasing radiation dose for all strains. For the more radiosensitive cell strains there were relatively more aberrant metaphases for a given radiation dose when compared with fibroblasts from a normal donor. The relationship between surviving fraction and chromosome aberrations showed some variation between strains, but a linear regression for all data showed a highly statistically significant correlation (r = 0.89, p < 0.0005). These results suggest that an assay of chromosome damage using FISH could substitute for the clonogenic assay to predict the radiation sensitivity of human fibroblasts.

Effect of gamma-irradiation on the effector function of T lymphocytes in microbial control

A chlamydial-specific T cell clone, capable of inhibiting the growth of infectious Chlamydia in vivo and in vitro, was employed to investigate the effect of gamma-irradiation on the ability of effector T cells to control infections. Clone 2.14-0 (CD4+), specific for the Chlamydia trachomatis biovar agent of mouse pneumonitis (MoPn), was irradiated with varying doses (0, 2.5, 5.0, 10.0, 20.0 and 40.0 Gy) and its biological functions and ability to inhibit the intraepithelial growth of MoPn were assessed. The results revealed that although gamma-irradiation drastically reduced the proliferative response of the clone to antigen, it did not affect the phenotype and the effector function of inhibiting chlamydial growth. The preservation of anti-chlamydial function after gamma-irradiation correlated with the retention of IFN-gamma and TNF-alpha secretion in response to antigenic stimulation. We conclude that the biologic functions of T cells requiring proliferation and differentiation are more likely to be adversely affected by gamma-irradiation on the short-term, but the effector functions, possibly associated with cytokines and cytolysis, may be preserved among persisting effector T cells in an irradiated individual.

Normal tissue radiosensitivity in breast cancer patients

PURPOSE

To investigate whether in vitro radiosensitivity of lymphocytes derived from a blood sample will predict late effects from radiotherapy in breast cancer patients.

METHODS AND MATERIALS

Blood samples were collected from consenting patients who had received radiotherapy for breast cancer. Lymphocytes were extracted and transformed by the Epstein-Barr virus. The resulting lymphoblastoid cell lines (LCLs) were assessed for in vitro radiosensitivity using a tetrazolium-based colorimetric assay (MTT). Survival curves were generated using doses of 0.5 to 2 Gy. For each analysis an LCL derived from an individual with the radiosensitive condition ataxia-telangiectasia (AT) was run as control. Some patients also consented to give skin biopsies from which fibroblast cultures were derived. Clonogenic assays were performed to generate survival curves using doses in the range of 0.5 to 4 Gy. Comparison was made with the data obtained from LCLs. Late effects of radiotherapy were assessed using the Radiation Therapy Oncology Group (RTOG) scoring scheme and compared with the in vitro radiosensitivity data.

RESULTS

LCLs from 56 breast cancer patients were assessed for in vitro radiosensitivity. Surviving fraction to 2 Gy (SF2) generated from survival curves ranged from 0.04-0.35 with coefficient of variation for the whole group of 41%. None of the LCLs equalled the sensitivity of the AT line, but 16% showed equal or greater sensitivity to a line derived from an AT heterozygote. Comparison of LCL and fibroblast radiosensitivity showed reasonable correlation for 12 paired samples (r = 0.64). The majority of patients showed no or minimal effects after radiotherapy (Grade 0, 1 effects) but seven developed a Grade 2 reaction and four a Grade 3 or 4 reaction. Patients with a Grade 2-4 reaction were found to be more sensitive in vitro than those with a Grade 0-1 reaction (p < 0.02).

CONCLUSIONS

The use of the MTT assay to assess LCL radiosensitivity has demonstrated considerable heterogeneity amongst the breast cancer population. The presence of a proportion of patients showing in vitro sensitivity but normal clinical response to radiotherapy would limit the usefulness of the assay for predictive purposes.

Dose-rate effect on induction and repair rate of radiation-induced DNA double-strand breaks in a normal and an ataxia telangiectasia human fibroblast cell line

Using pulsed-field gel electrophoresis (PGFE), we measured DNA double-strand breaks (DSB) in a normal human fibroblast and in a cell line derived from a patient suffering from ataxia telangiectasia (AT), a syndrome associated with a hypersensitivity to ionizing radiation. Initial DSB levels assessed after irradiation at 4 degrees C are similar in both cell lines. The DSB repair rate was measured after 30 Gy delivered at 4 degrees C and followed by an incubation at 37 degrees C for 24 h. In AT cells, the DSB repair rate is faster between 0.5 and 9 h and slower between 9 and 24 h. In addition, the DSB levels were measured after irradiation at 37 degrees C at 0.01 Gy min-1 (5-40 Gy). The shape of the curves was curvilinear and a plateau was reached at 10 Gy in the control. After an irradiation at 37 degrees C, DSB levels were significantly higher in AT cells than in the normal fibroblast cells. A model was developed assuming that DSB induction is independent of temperature and that DSB repair rate is independent of dose-rate and dose. This model was used to predict the 37 degrees C DSB data on the basis of the 4 degrees C data. Experimental data and predictions are in agreement, thus validating the above assumptions. It is suggested that, even for extreme situations such as 30 Gy delivered at 4 degrees C or 30 Gy delivered at 37 degrees C at 0.01 Gy min-1, DSB induction and repair are identical. Our results could be interpreted assuming an heterogeneity of DSB. A small fraction of DSB is slowly repaired. This fraction is lower in control than in AT cells. By protracting repair time, the 37 degrees C low-dose rate experiments permit a cleaner distinction between AT and control cells.

In vitro parameters and treatment outcome in head and neck cancers treated with surgery and/or radiation: cell characterization and correlations with local control and overall survival

PURPOSE

To determine whether in vivo parameters (surviving fraction at 2 Gy, alpha values, and calculated cell growth fraction) were predictive of the treatment outcome.

METHODS AND MATERIALS

Biopsies were obtained from patients with a head and neck tumor. In vitro parameters were determined using the CAM plate assay. Cell characterization by cytogenetic analysis was performed on 19 different cell cultures. In 25 additional cell cultures, cell clonogenicity was tested using the Courtenay Mills assay.

RESULTS

Biopsies were obtained from 156 patients with a head and neck tumor and the oropharynx was the predominant primary site. In vitro parameters were obtained in 113 cases (72%) (SF2 in 93 cases and calculated cell growth fraction in 103 cases). Cell characterization showed that cells in CAM plates were diploid with no clonal chromosome abnormalities and gave colonies in soft agar with a mean cloning efficiency of 1.610(-3). Only patients treated with surgery and/or radiation (76), were considered eligible for in vitro parameters and treatment outcome correlation studies. The mean follow-up is over 2 years (range 9-47 months). The local control rate was significantly higher (p = 0.04) for patients with alpha values above the cut-off point of 0.07 Gy-1 (69% vs. 38% at 2 years). The local control rate was also significantly higher (p = 0.04) for patients with calculated cell growth fraction values about the cut-off point of 0.06% (70% vs. 48% at 2 years). Moreover for these latter patients the overall survival rate was also significantly higher (p = 0.004) (54% vs. 26% at 2 years). It is worth noting that alpha and calculated cell growth fraction values below the cut-off points identified a small group of patients (about 20%) who were at a significantly high risk of local failure. From a pragmatic point of view, as only radiosensitivity or calculated cell growth fraction values could be obtained in a certain number of experiments due to technical reasons, the treatment outcome of patients who had either alpha and/or calculated cell growth fraction values below the cut-off levels (about 30% of all patients) was analyzed. This group of patients fared significantly worse (p = 0.02) in terms of local control (50% vs. 68% at 2 years) and (p = 0.04) overall survival (36% vs. 50% at 2 years).

CONCLUSION

These results suggest that in vitro parameters using the CAM plate assay, might be useful in predicting the treatment outcome of patients with a head and neck tumor treated with surgery and postoperative radiation, or radiation alone. However, they must be considered as preliminary because the cut offs used in the study were chosen for exploratory purposes. Only a multivariate analysis including all clinical and biologic factors will allow us to draw any firm conclusions.

Role of intracellular SOD in protecting human leukemic and cancer cells against superoxide and radiation

Many anticancer drugs have been shown to produce superoxide anion (O2.-) and seem to involve O2.- in their mode of action. Ionizing radiation provokes the decomposition reaction of water, producing a variety of reactive oxygen species, including O2.-. The finding that cancer cells are generally low in SOD activity may offer a theoretical base for radiation therapy and chemotherapy. The purpose of this study was to examine the protective effect of intracellular SOD against cytotoxicity induced by O2.- or radiation and to investigate whether exogenous SOD can protect cells from O2.-(-) and radiation-induced cytotoxicity. For this purpose, xanthine (X) and xanthine oxidase (XOD) were employed as an O2.- (-)generating system, and a linear accelerator was used for ionizing radiation. Cytotoxicity against monolayer cancer cell lines and leukemic cell lines was estimated by measuring the release of lactate dehydrogenase from these cells. The results revealed that the resistibilites to X- and XOD-generated O2.- and radiation correlated with intracellular Cu. Zn-SOD levels and that exogenous SOD could only slightly reduce X- and XOD-induced cytotoxicity while having no influence on radiation-induced cytotoxicity. Thus, intracellular SOD may play a central role in protecting cancer cells against reactive oxygen species generated by anticancer drugs and radiation.

DNA Supercoiling and Repair in Peripheral Lymphocytes as a Measure of Acute Radiation Response After Radiotherapy

DNA supercoiling density and incision kinetics during ultraviolet (UV) excision repair hav been measured in lymphocytes from 20 cancer patients and 17 healthy donors. Nucleoid sedimentation was used, which allows the sensitive detection of both DNA damage and alterations in chromatin structure. The release of DNA supercoiling after ethidium bromide intercalation and the kinetics of the incision step following UV irradiation were compared in lymphocytes derived from cancer patients and those from normal donors. The classification into lymphocytes with normal or reduced repair and normal or altered supercoiling, respectively, revealed that reduced repair as well as altered chromatin structure occurred more frequently in lymphocytes derived from patients (40% and 85%, respectively) than in those from healthy donors (35% and 23%, respectively). Even more striking was the simultaneous occurrence of both characteristics in tumor patients: in 34% of all cases reduced repair was associated with altered supercoiling density, whereas among healthy donors this association occurred in only 18% of all cases. Supercoiling density may be related to functional integrity of lymphocytes and repair capacity to recovery after radiation damage. Since both parameters are important for the radiation response of normal tissue, we consider these measurements a potential prognostic assay aimed at reducing acute reaction of the normal tissue.

Use of an internal standard in comparative measurements of the intrinsic radiosensitivities of human T-lymphocytes

A study has been made of the intrinsic radiosensitivity of peripheral blood lymphocytes from normal individuals. Cell survival following in vitro high (1.55 Gy min-1) and low (0.0098 Gy min-1) dose-rate irradiation was obtained for single lymphocyte samples from three individuals in six experiments. Despite wide interexperimental variability the ranking of intrinsic radiosensitivity for these individuals was reproducible. Further studies were carried out using low dose-rate irradiation only, on: (1) single lymphocyte samples from 18 people; (2) 14 samples taken on different occasions from one of these donors over a period of 5 months; and (3) a large store of lymphocytes from another individual. The latter was assayed in every experiment and served as an internal standard to which results could be normalized. In comparison with uncorrected values, the normalized results for the 14 samples from the single individual showed a reduction in the spread of data while those for the 18 different donors were unchanged. An analysis of variance was carried out on a larger data set of 38 measurements which included repeat assays on several of the samples (two samples from the multiply-sampled individual and five samples from other donors were assayed twice). In comparison with the uncorrected values, the normalized results showed a reduction in experimental variability such that the coefficient of variation (CV) for surviving fraction at 4 Gy for the multiple samples from a single individual decreased from 41 to 19%. In contrast, there was little change in the variation between 18 individuals with CVs of 56 and 62%, respectively, for uncorrected and normalized results. These data suggest that the use of an internal standard for the determination of the intrinsic radiosensitivity of individuals using peripheral blood lymphocytes should aid the development and evaluation of predictive tests for the radiotherapy of cancer.

Use of low-dose rate irradiation to measure the intrinsic radiosensitivity of human T-lymphocytes

A comparison has been made of high (1.55 Gy min-1) and low dose-rate (0.0098 Gy min-1) irradiation in determining the intrinsic radiosensitivity of peripheral blood lymphocytes from normal individuals. Samples from 19 people were assessed using a limiting dilution assay and used to investigate the variability associated with evaluation of lymphocyte radiosensitivity after both high and low dose-rate irradiation. Repeat experiments on a single sample from one donor stored over a period of 6 months have been used to compare assay variability using the different dose-rates. Multiple samples taken from a single person over a period of 5 months were assayed at low dose-rate to assess intraindividual variation in measured in vitro radiosensitivity. At high dose-rate significant interexperimental variation in the measured parameters was demonstrated and, after allowing for this variability, no significant interindividual differences were found. At low dose-rate, sparing of cell kill was seen for all lymphocytes and led to an increase in the spread of data between individuals such that interindividual differences reached statistical significance for surviving fraction at 4 Gy, alpha (linear fit) and D with p < 0.004 for all parameters.

Determination of cell dose-survival relationships from endpoint dilution assays

Methods for fitting radiation survival curves to data obtained from endpoint-dilution assays are described. It is shown that for functional forms such as the linear-quadratic model the problem can be recast as a generalized linear model (GLM) and the data fitted using standard software. For functional forms which are not capable of being linearized, such as the multitarget model, the direct maximum likelihood (DML) techniques of Thames et al. (1986) can be used. Both these techniques produce exact maximum likelihood parameter estimates. Compared with the weighted least-squares (WLS) approach traditionally employed, these approaches avoid the need to approximate the binomial distribution of the number of negative wells by a normal distribution, and avoid the biases introduced by the need for arbitrary treatment of data points with 0 or 100% negative wells. The results of fittings using the novel GLM and DML approaches are compared with those obtained using the WLS method on a large series of datasets. For most datasets the WLS method performs well, compared with the exact method, but in a small number of cases the WLS predicted parameter estimates can be in error by as much as their estimated standard errors. A method for the use of a concurrent control to correct for interexperimental variation is outlined. The methods have been implemented in a Fortran computer program using the NAG subroutine library.

Radiosensitivity in vitro of human soft tissue sarcoma cell lines and skin fibroblasts derived from the same patients

Skin fibroblast cell strains and tumour cell lines were established from 12 patients with various types of soft tissue neoplasms, and radiation survival curve parameters were measured in vitro. Soft tissue sarcoma cells were consistently more sensitive to X-irradiation than fibroblasts isolated from the same patient, and were also more sensitive as a group than cell lines derived from 34 other human tumours. There was a general correlation in radiosensitivity between fibroblasts and tumour cells derived from the same patient, indicating that some component of tumour cell sensitivity may relate to genetic factors in the host. Such genetic factors, however, do not explain all of the heterogeneity in tumour cell response. The response of soft tissue sarcoma in vivo may be dependent on complex radiomodifying factors other than inherent radiation sensitivity, thus making it difficult to predict clinical outcome by use of assays which use survival of irradiated tumour cell lines in vitro as an endpoint.

Clinical correlations between late normal tissue endpoints after radiotherapy: implications for predictive assays of radiosensitivity

The discovery that certain genetic syndromes are associated with a high cellular radiosensitivity has stirred interest in the concept that radiosensitivity of persons in general should have a genetic component. This has motivated research into assays for prediction of cellular normal tissue radiosensitivity. If such an intrinsic factor were a major factor in the development of late normal tissue injury, this should be detectable as a correlation between the probability of developing injury in different tissues. This hypothesis is tested in a series of 229 patients treated with postmastectomy radiotherapy and evaluated with respect to a number of late endpoints 16 to 71 months after the end of treatment. In each patient, the presence of marked subcutaneous fibrosis and telangiectasia were evaluated in two different treatment areas: in a photon field underneath a 5-mm wax bolus and in an abutted electron field used for treating the chest wall. The use of two different doses per fraction and the fact that a single anterior photon field was used with the dose prescribed at the level of the mid-axilla, led to a substantial variation in total dose and dose per fraction in these patients. A non-tissue-specific patient-to-patient difference in radiosensitivity would cause higher than expected reactions in one treatment area to be correlated with higher than expected reactions in the other area. For each of the two endpoints, telangiectasia or subcutaneous fibrosis, patients experiencing stronger than expected reactions in one treatment area tended to do so in the other area as well. Thus, a strong host factor appears to exist for a specific endpoint. It is an open question whether this is explained by individual variability in intrinsic radiosensitivity, progression rate of injury or other. Contrary to this, no significant correlation was seen when pairing the two late end-points, fibrosis and telangiectasia. Thus, patients showing stronger than expected fibrosis developed on average marked telangiectasia with a probability well predicted from their total dose and dose per fraction. These findings suggest that an assay for clinical expression of late injury would have to be specific for that type of injury.

Radiosensitivity measurement of keratinocytes and fibroblasts from radiotherapy patients

Genetic diversity is believed to influence cellular radiosensitivity and individual variability in normal tissue reactions to radiotherapy. To measure normal cell radiosensitivity in vitro, we investigated a culture technique that yields keratinocyte and fibroblast cell cultures from small skin biopsy samples (average weight 32 mg). This technique uses 3T3 NIH cells as feeder cells, culture medium containing dialyzed fetal calf serum, low calcium, and various growth factors for keratinocyte growth. A calcium concentration of 4 x 10(-3) M and the use of lethally irradiated NIH 3T3 feeder cells were critical to the success of this method. Primary keratinocyte cultures were successfully obtained from nine biopsy specimens, and radiosensitivity measurements were obtained in six of the resulting strains. Keratinocytes were, in general, more radioresistant than fibroblasts derived from the same specimen. We conclude that radiosensitivity assessment of keratinocyte and fibroblast cultures derived from small punch biopsy specimens is feasible. Further studies can now be carried out to determine the degree of variability between individuals and the relationship between in vitro keratinocyte and fibroblast radiosensitivity and their value in predicting normal tissue responses to radiotherapy.