Micronucleus formation in human tumour cells: lack of correlation with radiosensitivity.

The micronucleus (MN) test has been carefully characterized in four human tumour cell lines of widely differing radiosensitivity. Two radioresistant bladder carcinoma cell lines (MGH-U1 and RT112), one sensitive medulloblastoma cell line (D283MED) and a sensitive neuroblastoma cell line (HX142) were used. The number of MN per Gy of ionising radiation was 0.13 for HX142, 0.17 for D283MED, 0.21 for RT112 and 0.26 for MGH-U1. This does not rank the cell lines in the same order of radiosensitivity as clonogenic cell survival where the surviving fraction at 2 Gy (SF2) was 0.11 for HX142, 0.2 for D283MED, 0.62 for RT112 and 0.53 for MGH-U1. This discrepancy between MN formation and cell death leaves doubt as to the potential usefulness of the MN test as a rapid assay of radiosensitivity but it has potential implications for the mechanistic basis of radiosensitivity in these cells.     

The increment of micronucleus frequency in cervical carcinoma during irradiation in vivo and its prognostic value for tumour radiocurability.

A potential usefulness of micronucleus assay for prediction of tumour radiosensitivity has been tested in 64 patients with advanced stage (II B-IV B) cervical carcinoma treated by radiotherapy. The study of cellular radiosensitivity in vitro was conducted in parallel with the study of cellular damage after tumour irradiation in vivo. Radiosensitivity of in vitro cultured primary cells isolated from tumour biopsies taken before radiotherapy was evaluated using cytokinesis-block micronucleus assay. Frequency of micronuclei per binucleated cell (MN/BNC) at 2 Gy was used as a measure of radiosensitivity. Radiation sensitivity in vivo was expressed as per cent increment of micronucleus frequency in cells isolated from biopsy taken after 20 Gy (external irradiation, 10 x 2 Gy) over the pre-treatment spontaneous micronucleus level and was called MN20. Very low correlation (r = 0.324) was observed between micronucleus frequency in vitro and in vivo. Although micronucleus frequency at 2 Gy differed widely between tumours evaluated (mean MN/BNC was 0.224; range 0.08-0.416), no significant correlation was observed between this parameter and clinical outcome. The average increment of micronucleus frequency after 20 Gy amounted to 193% of spontaneous level (range 60-610%) and was independent of spontaneous micronucleation before radiotherapy. In contrast to in vitro results, these from in vivo assay seem to have a predictive value for radiotherapy of cervix cancer. The micronucleus increment in vivo that reached at least 117.5% of pretreatment value (first quartile for MN20 data set) correlated significantly with better tumour local control (P < 0.008) and overall survival (P < 0.045). Our results suggest that evaluation of increment of micronucleus frequency during radiotherapy (after fixed tested dose of 20 Gy) offers a potentially valuable approach to predicting individual radioresponsiveness and may be helpful for individualization of treatment strategy in advanced stage cervical cancer.     

Ovarian cancer: radiation sensitivity in vitro

The radiosensitivity of four human ovarian cancer cell lines was investigated in vitro by a clonogenic assay and analyzed using the linear-quadratic model. Two cell lines were found to be highly radiosensitive (mean inactivation dose (D) 0.82-0.92 Gy; surviving fraction 2 Gy (SF2) less than or equal to 0.13). Two other cell lines were less sensitive to radiation (D 1.31-1.94 Gy; SF2 0.22-0.38). Although the use of external radiotherapy in ovarian cancer has been limited due to the pattern of metastatic spread of this cancer, the present data support the view that ovarian carcinomas are radiosensitive tumors. Investigations on the effects of new approaches, such as delivering radiation more specifically to intraperitoneal ovarian cancer cells, are warranted.     

Radiosensitivity of human prostate cancer and malignant melanoma cell lines

The relative radioresponsiveness of human prostate cancer compared to malignant melanoma is well known. The effects of beta-estradiol or testosterone on the X-irradiation survival of several human cell lines were studied, including: human prostate carcinoma cell lines PC3 and DU145 and human malignant melanoma cell lines A375 and A875. Lines PC3 and DU145 demonstrated 55-61 fmol per 10(6) cells of androgen receptor with no detectable estrogen or progesterone receptor. Cells were irradiated at 120 cGy/min dose rate. There was no detectable toxicity of up to 10(-4) M testosterone or beta-estradiol on PC3 or DU145 cells in the absence of X-irradiation. At plating efficiencies from 11-13%, and plating densities of 1 x 10(4) cells per 60 cm2 flask, cell lines PC3 and DU145 demonstrated a Do of 108.5 +/- 6.5, n 2.1 +/- 0.7 cGy, and Do of 143.5 +/- 1.5 cGy, n 2.4 +/- 0.5, respectively. The addition of testosterone or beta-estradiol at 10(-4) to 10(-10) M prior to or after, X-irradiation did not alter radiosensitivity. At the same dose rate of 120 cGy/min, malignant melanoma cell lines A375 and A875 had a Do of 125 +/- 2.5 cGy, n 1.56 +/- 0.8 SF2 0.65 +/- 0.03 and line A875 demonstrated a Do of 129 +/- 4.5 cGy, n 1.58 +/- 0.4 SF2 0.55 +/- 0.04, respectively. The radiosensitivity of melanoma cell lines did not decrease at low dose rate 5 cGy/min. Thus, the in vitro radiosensitivity of androgen receptor positive prostate cancer cell lines is not necessarily altered by the presence of androgen before or after irradiation. The data support the concept that all malignant melanoma cell lines do not show a broad-shouldered cell survival curve in vitro and intrinsic cellular radioresistance.     

Inherent radiosensitivity testing of tumor biopsies obtained from patients with carcinoma of the cervix or endometrium.

The inherent radiosensitivity of tumor biopsies obtained from a series of patients with carcinoma of the uterine cervix or endometrium has been characterized. Early passage cell lines were irradiated and assayed for cell survival using a clonogenic assay system. Survival curves were generated using the alpha/beta model and the surviving fraction at 2 Gy (SF2) was estimated. A wide range of SF2 values was observed among histologically similar tumors. The mean (+/- SD) SF2 value was 0.29 +/- 0.12 (range = 0.11-0.59) for the cervical biopsies and 0.30 +/- 0.13 (range = 0.11-0.67) for the endometrial biopsies. No correlation between inherent radiosensitivity and tumor DNA index or histopathology was observed. Patient accrual continues with the expectation that these results may help to determine whether SF2 values are of clinical value in predicting the response of individual patients to treatment with radiotherapy.     

Assessment of the proliferative activity and radiosensitivity of human tumours using the cytokinesis-block micronucleus assay.

We established an in vitro cytokinesis-block micronucleus assay of human tumours for estimation of the proportion of cells undergoing mitosis (the dividing fraction, DF), the time for the number of nuclei to double and the radiosensitivity in terms of the micronucleus frequency, based on a concept described previously. Under certain conditions, the nuclear number doubling time (NNDT) was considered to represent the potential doubling time. Tumour specimens obtained at surgery were disaggregated into single-cell suspensions and were directly cultured in the presence of cytochalasin B with or without irradiation. At various intervals, the percentage of multinucleate cells (the plateau value represented the DF), the average number of nuclei per cell and the number of micronuclei in binucleate cells were determined. DF and NNDT values were obtained in 58 of the 73 tumours investigated, and the micronucleus frequency was obtained in 54 of these 58 tumours. The DF ranged from 4.1% to 71% and the NNDT ranged from 3.1 to 83 days. A DF > or = 20% was associated with a higher recurrence rate in patients undergoing curative operation. A correlation was found between the NNDT and the time to relapse in patients with recurrent disease. The average number of micronuclei per binucleate cell at 2 Gy of irradiation (after subtraction of the value at 0 Gy) ranged from 0.052 to 0.35. Tumours which produced more micronuclei after irradiation showed a better response to radiotherapy. This assay can be readily performed on human tumours and appears to have promise as a predictive assay for radiation therapy.     

Influence of cellular radiation sensitivity on local tumor control of human melanoma xenografts given fractionated radiation treatment

The radiocurability of human melanoma xenografts was studied by treating tumors with multiple fractions of 2.0 Gy and using local tumor control at 180 days as end point. Three melanoma lines (E. F., G. E., M. F.) that are only weakly immunogenic in athymic nude mice (BALB/c-nu/nu/BOM) were selected for the study. The tumor radiocurability was found to differ considerably among the lines; the radiation doses required to achieve local control of 50% of the tumors irradiated (TCD50s; mean +/- SE) were 85.0 +/- 4.7 Gy (E.F.), 60.3 +/- 5.4 Gy (G.E.), and 99.3 +/- 5.7 Gy (M. F.). The radiation sensitivity in vitro of cells isolated directly from tumors also differed significantly among the lines. The TCD50 showed positive correlations with the surviving fraction after 2.0 Gy in vitro, the surviving fraction after two doses of 2.0 Gy (4-h interval) in vitro, and the surviving fraction after 4.0 Gy at a low dose rate (1.25 cGy/min) in vitro. Thus, the differences in tumor radiocurability among the lines were mainly a consequence of cellular differences in the capacity to repair radiation damage. Comparisons of measured TCD50s with theoretical TCD50s, calculated from cell-surviving fractions measured in vitro after radiation treatment in vitro or in vivo, suggested that other tumor parameters, e.g., rate of population between radiation fractions, also had a significant impact on the TCD50. However, this study strongly supports the assumptions that the surviving fraction at 2.0 Gy in vitro is a useful parameter for prediction of clinical tumor radiocurability.     

Radiation sensitivity of human ovarian carcinoma cell lines in vitro: effects of growth factors and hormones, basement membrane, and intercellular contact

The radiation sensitivity of six established human ovarian carcinoma cell lines was determined in vitro under five different experimental conditions. Cells from exponentially growing monolayer cultures were assayed under three different post-irradiation culture conditions, i.e., conventional conditions on a plastic surface, in the presence of growth factors and hormones, and on a basement membrane. Multicellular aggregates were dissociated either immediately before or immediately after irradiation and assayed under conventional conditions. The radiation sensitivity differed considerably among the cell lines; the initial slope alpha ranged from 0.05 +/- 0.03 Gy-1 to 0.36 +/- 0.07 Gy-1 and the surviving fraction at 2.0 Gy from 0.32 +/- 0.06 to 0.78 +/- 0.06 under conventional conditions. There was no significant effect of the growth factors and hormones and of the basement membrane on the survival curves for any of the cell lines. Only one of the lines showed a significant intercellular contact effect. The presence of this effect required that the cells were grown as aggregates, but was independent of whether the irradiation was performed on dissociated or intact aggregates. The present work with established cell lines indicates that the outcome of an in vitro predictive assay for clinical radioresponsiveness of ovarian carcinomas would probably not vary significantly among the five experimental conditions studied here. However, further studies using cells isolated directly from human ovarian carcinoma surgical specimens are warranted.     

Response of human tumor cells of varying radiosensitivity and radiocurability to fractionated irradiation.

The cytotoxic effects of radiation delivered in daily fractions of 2.0 Gy were examined in plateau phase cultures of human tumor cells of varying in vitro radiosensitivity, derived from tumors of varying radiocurability. Among the eight cell lines examined, three types of responses to fractionated irradiation were observed. In the group composed of tumor cell lines that were radioresistant in culture (D0 > 2 Gy) and derived from known local radiation failures or from tumor histologies associated with radiation failure, a gradual linear reduction in surviving fraction versus total dose was observed. In a second group, composed of cell lines that were radiosensitive in culture (D0 approximately 1 Gy) but derived from known radiation failures, the surviving fraction initially declined and began to plateau after 6 Gy (three fractions of 2 Gy). In the third group, composed of radiosensitive cell lines derived from tumors associated with high radiocurability, a rapid decline in surviving fraction versus total dose was observed. The in vitro response of human tumor cells to fractionated irradiation delivered at clinically relevant doses appears to be independent of in vitro X-ray sensitivity and p53 status but related to clinical radiocurability, suggesting a possible role in predicting tumor response to radiotherapy.     

PLD-repair in human melanoma xenografts following single dose and fractionated irradiation

PLD-repair following single dose and fractionated irradiation was studied in vivo using five human melanoma xenograft lines. Tumours given single graded radiation doses were excised immediately after or 24 h after the radiation exposure for assay of cell survival in vitro. All melanoma lines showed PLD-repair after single dose irradiation: the PLD-repair factors, i.e. the ratio of the Do values for tumours excised 24 h after and immediately after irradiation, ranged from 1.2 +/- 0.1 to 1.4 +/- 0.1. PLD-repair following fractionated irradiation was studied by giving tumours seven fractions of 2.0 Gy over 7 days and then, after an interval of 24 h, single graded radiation doses in the range 6-21 Gy. Cell survival was assayed in vitro immediately after or 24 h after the last radiation exposure. The Do values as well as the surviving fractions were approximately equal after immediate and delayed cell seeding, i.e. none of the melanoma lines showed significant PLD-repair after fractionated irradiation. The lack of PLD-repair after fractionated irradiation was possibly a consequence of radiation-induced recruitment of quiescent tumour cells into the cell cycle. Consequently, PLD-repair is probably not a major cause of failure in the radiation therapy of malignant melanoma when treated with 2.0 Gy fractions.     

Radiosensitivity testing of human primary brain tumor specimens.

The inherent radiosensitivity of early passage cells derived from 22 patients with tumors of glial origin has been determined using a clonogenic assay system. The mean (+/- SD) surviving fraction at 2 Gy was 0.37 +/- 0.22 (range = 0.02-0.87). No correlation between inherent radiosensitivity and tumor cell plating efficiency or intracellular glutathione was observed. Tumor cells that were both resistant to nitrosoureas and expressed the Mer+ phenotype did not differ significantly in their radiosensitivity as compared to cells that were repair deficient (Mer-) and sensitive to nitrosoureas. Initial clinical follow-up suggests that factors in addition to inherent tumor cell radiosensitivity, such as performance status and age, continue to be the most important determinants of the response of patients with primary brain tumors to radiotherapy.     

Ability to undergo apoptosis does not correlate with the intrinsic radiosensitivity (SF2) of human cervix tumor cell lines

PURPOSE: To investigate the relationship between radiation-induced apoptosis and clonogenic cell kill in 9 cervical cancer cell lines. METHODS AND MATERIALS: Cells were irradiated with 0, 2, 8, and 30 Gy. The level of apoptosis was evaluated using flow cytometry (Annexin-V binding), light microscropy (morphology), gel electrophoresis (DNA ladder formation), and TUNEL assay. Cell survival was measured using a clonogenic assay. RESULTS: Of the 9 cervical carcinoma cell lines analyzed, 3 underwent radiation-induced apoptosis: CaSki, HT3, and 778. The levels of apoptosis, obtained 72 h after a dose of 30 Gy, were 49%, 28%, and 26%, respectively. All cell lines exhibited some level of background apoptosis measured by Annexin-V binding (mean = 2.6%+/-0.8; range, 0.2-6.9%) that correlated with the level of radiation-induced apoptosis (r = 0.92, p = 0.001). In 6 of the 9 lines, necrosis was the dominant form of cell death. A significant inverse relationship was found between the level of radiation-induced apoptosis and necrosis after 30 Gy (r = -0.87, p = 0.002). No relationship was found between radiation-induced apoptosis and intrinsic radiosensitivity measured, using a clonogenic assay, as surviving fraction at 2 Gy (SF2). CONCLUSION: Cervical carcinoma cells do not readily undergo radiation-induced apoptosis in vitro. There is no relationship between ability to undergo apoptosis and intrinsic radiosensitivity measured using a clonogenic assay.     

Radiation sterilisation of cultured human brain tumour cells for clinical immune tumour therapy

The aim is to investigate the radiosensitivity of noninfected cultured human glioma cells to ascertain that intracutaneously administered cells are viable enough to produce interferon-gamma but not able to proliferate. Cell cultures were established from five patients undergoing brain tumour surgery. By karyotyping, we found four malignant (three glioblastoma multiforme (GBM), one giant cell glioma) and one normal. The cells were irradiated with (137)Cs-gamma rays at absorbed dose levels of 0, 20, 40, 60, 80, 100 and 120 Gy. The fraction of viable cells was examined by MTT incorporation assay. The average of the data obtained from three GBM cell cultures was fitted to an exponential model. The parameters were: extrapolation number n=0.85+/-0.10, mean lethal dose D(0)=12.4+/-3.2 Gy and an additional uncertainty parameter deltaS=0.14+/-0.03. By setting deltaS=0, the corresponding values of the parameters were n=0.86+/-0.16 and D(0)=30.0+/-8.1 Gy. The rate of proliferation was examined by (3)H-thymidine incorporation. The average of the proliferation data obtained from three GBM cell cultures was fitted to an exponential model yielding n=0.943+/-0.005 and D(0)=5.8+/-0.5 Gy for deltaS=0.057+/-0.005, and by setting deltaS=0, n=1.00+/-0.02 and D(0)=8.4+/-1.6 Gy. No outgrowth of plated cells was observed after 4 weeks at an absorbed dose of 100 Gy. This absorbed dose is recommended for irradiation of 2 x 10(6) glioma cells used for clinical immunisation.     

Fractionated irradiation of five human lung cancer cell lines and prediction of survival according to a radiobiology model

BACKGROUND: This study evaluates a predictive radiobiology model by measurements of surviving fraction (SF) by the clonogenic assay or the extrapolation method and the proliferation rate in vitro. It is hypothesized that incorporating proliferation to intrinsic radiosensitivity, measured by SF, to predict radiation responsiveness after fractionated irradiation adds to the model's accuracy. Materials and Methods. Five lung cancer cell lines with known SF after 1 Gy (SF1), and also SF2 and SF5, were irradiated with three different fractionation regimes; 10 × 1 Gy, 5 × 2 Gy or 2 × 5 Gy during the same total time to achieve empirical SF. In addition, the SF1, SF2 and SF5 after fractionated irradiation was calculated for each cell line based on the already known single fraction SF and with or without a proliferation factor. The results were compared to the empirical data. Results and Discussion: By using the clonogenic assay to measure radiosensitivity, prediction of radiosensitivity was improved after fractionated radiotherapy when proliferation was used in the radiobiology model. However, this was not the case in the cell lines where the extrapolation method was used to calculate SF. Thus, a radiobiology model including intrinsic radiosensitivity, measured by the clonogenic assay, as well as proliferation, is better at predicting survival after fractionated radiotherapy, compared to the use of intrinsic radiosensitivity alone.     

A comparison of heat sensitivity, radiosensitivity and PLDR in four human melanoma cell lines.

Comparison of the heat sensitivity and radiosensitivity of four human melanoma cell lines in culture revealed a large variation in sensitivity amongst the four cell lines. Three of the four cell lines had large shoulders on the survival curves when exposed to hyperthermia (44 degrees C or 45 degrees C). These three cell lines also had demonstrable shoulders on the acute radiation dose response curves. The most radiosensitive cell line did not show a shoulder region in the heat or radiation survival curves (HT-144, Dq = 0.2 Gy). Despite this consistency in the presence or absence of shoulder, there was no correlation between heat and radiation sensitivity in the four melanoma cell lines. Furthermore, regardless of radiosensitivity, all four lines studied showed competent repair of potentially lethal damage. The recovery ratios at a surviving fraction of 0.001 ranged from 5.7 to 7.6. All four lines had a similar cell cycle distribution at the time of treatment, hence the variation observed in the response of these four lines to radiation and heat was not due to differences in cell cycle kinetics. Preliminary results of DNA polymerase-alpha and -beta activities do not demonstrate a clear correlation between cellular levels of these two enzymes and radiosensitivity.     

Retention of cellular radiation sensitivity in cell and xenograft lines established from human melanoma surgical specimens.

Six human melanoma xenograft lines have been established in athymic mice from metastatic lesions in six different patients. Permanent cell lines in monolayer culture have been established from four of the xenograft lines. The cellular radiation sensitivity of the donor patients' tumors, the xenograft lines, and the cell lines were measured in vitro. The Courtenay soft agar colony assay was used for the donor patients' tumors, and a conventional plastic surface colony assay was used for the cell lines, whereas both assays were used for the xenograft lines. The cell survival data were analyzed using the multitarget single-hit as well as the linear-quadratic model. The donor patients' tumors differed considerably in cellular radiation sensitivity (the D0 ranged from 0.85 +/- 0.08 to 1.17 +/- 0.09 Gy, the alpha from 0.25 +/- 0.06 to 0.87 +/- 0.14 Gy-1, and the surviving fraction at 2.0 Gy from 0.15 +/- 0.04 to 0.50 +/- 0.06). The xenograft lines showed similar survival curves in soft agar and on the plastic surface, and the survival curves of a xenograft line and the corresponding cell line were not significantly different. These survival curves were not significantly different from those of the donor patients' tumors, regardless of which survival curve parameter was considered, i.e., the cellular radiation sensitivity of the donor patients' tumors was retained in the cell and xenograft lines. Moreover, the cell and xenograft lines have growth properties in vitro and in vivo that render a wide variety of experiments possible. Consequently, they show great promise for future studies of human tumor radiation biology.     

CoCl2诱导缺氧对Eca109细胞细胞周期及放射敏感性的影响

Objective:To investigate the change of the cell cycle,apoptosis and radiosensitivity effect by CoCl2 induced hypoxia in esophageal cancer line Eca109 cells in vitro.Methods:The hypoxia culture model induced by 150 microM CoCl2 was established.The cell cycle and apoptosis were measured with flow cytometry (FCM).The radiosensitivity was analysized with clonogenic assay after irradiation alone or combined with hypoxia in Eca109 cells in vitro.Results:Eca109 cells were treated with 150 microM CoCl2 for 24 h,cell cycle arrest in G0/G1 phase increase and decreasing arrest in S phase with longer of hypoxiac time (0-24 h),the other rate of cell cycle and apoptosis did not change obviously.The G2/M phase block was arrested obviously in radiation alone comparing with the hypoxia plus irradiated group,apoptosis did not occur in Eca109 cell line following irradiation.The DO value and cell surviving fraction of Eca109 cell was 2.48 Gy,2.44 Gy and 97.33%,96.33% in hypoxia and control group,respectively;the Dq value of Eca109 cell was 2.89 Gy,0.52 Gy,the cell surviving fraction after radiation with 4 Gy was 48.3%,21.7% in hypoxia and control group,respectively.The hypoxia decreased the radiosensitivity in esophageal cancer Eca109 cells with clonogenic assay.Conclusion:Hypoxia induced by CoCl2 influences radiosensitivity of Eca109 cell through regulating cellular proliferation rates.     

Chromosomal radiosensitivity in breast cancer patients with a known or putative genetic predisposition

The chromosomal radiosensitivity of breast cancer patients with a known or putative genetic predisposition was investigated and compared to a group of healthy women. The chromosomal radiosensitivity was assessed with the G2 and the G0-micronucleus assay. For the G2 assay lymphocytes were irradiated in vitro with a dose of 0.4 Gy (60)Co gamma-rays after 71 h incubation, and chromatid breaks were scored in 50 metaphases. For the micronucleus assay lymphocytes were exposed in vitro to 3.5 Gy (60)Co gamma-rays at a high dose rate or low dose rate. 70 h post-irradiation cultures were arrested and micronuclei were scored in 1000 binucleate cells. The results demonstrated that the group of breast cancer patients with a known or putative genetic predisposition was on the average more radiosensitive than a population of healthy women, and this with the G2 as well as with the high dose rate and low dose rate micronucleus assay. With the G2 assay 43% of the patients were found to be radiosensitive. A higher proportion of the patients were radiosensitive with the micronucleus assay (45% with high dose rate and 61% with low dose rate). No correlation was found between the G2 and the G0-micronucleus chromosomal radiosensitivity. Out of the different subgroups considered, the group of the young breast cancer patients without family history showed the highest percentage of radiosensitive cases in the G2 (50%) as well as in the micronucleus assay (75-78%).     

Response of xenografts of human malignant gliomas and squamous cell carcinomas to fractionated irradiation.

The response of xenografts of five human malignant glioma cell lines and two human squamous cell carcinomas to fractionated irradiation was studied. For this, the tumors were transplanted into nude mice which had been further immunosuppressed by 6 Gy whole-body irradiation. Radiation was given as 30 fractions applied under normal blood flow conditions in two sessions per day over 15 days. Absolute and specific tumor growth delay after 48 Gy, and tumor control dose 50% (TCD50) were evaluated. Using local tumor control as experimental endpoint, four out of five malignant gliomas were more resistant to fractionated radiation therapy than the two squamous cell carcinomas. The TCD50s of these four gliomas ranged from 73 Gy to more than 120 Gy, whereas the TCD50s of the squamous cell carcinomas were 51 and 60 Gy. Absolute tumor growth delay correlated well with TCD50, but no correlation was obtained between specific growth delay and TCD50. The response of the human tumor xenografts in vivo did not correlate with the surviving fractions at 2 Gy of the same cell lines in vitro which have been previously obtained in our laboratory. The results suggest that the unique radioresistance observed in malignant gliomas in patients is at least in part reflected in human tumor xenografts. The lack of correlation between the surviving fraction at 2 Gy in vitro and the tumor response in vivo could be a consequence of an immune response by the host, a difference in cell radiation sensitivity between cell lines and xenografted tumors, or of differences of parameters such as hypoxic fraction, rate of repopulation, and cell cycle effects between the different tumor lines studied. It illustrates the difficulties which might be involved in the prediction of the response of individual tumors to radiation therapy based solely on the intrinsic radiosensitivity of the tumor cells as assayed by in vitro assays of colony formation.     

Response to pulsed dose rate irradiation with and without mild hyperthermia using tumour and normal cell lines.

To determine whether pulsed dose rate irradiation in combination with mild hyperthermia could radiosensitize cells in comparison to pulsed dose rate irradiation alone, human ovarian carcinoma (A2780s, cisplatin- and radiation-sensitive, and A2780cp, cisplatin- and radiation-resistant) and human fibroblast (AG1522) cell lines were used. Cells were irradiated in vitro using two fraction sizes, 0.53 Gy given every hour and 1.6 Gy given every 3h, with an overall average dose rate of 0.53 Gy/h. The data showed that 40 degrees C hyperthermia did not radiosensitize any of the cell lines for the 0.53 Gy every 1 h fractionation scheme. In addition, mild hyperthermia radiosensitized both carcinoma cell lines when using the 1.6 Gy fraction size for all doses tested in the A2780s and at higher doses in the A2780cp, but not the normal cell line. These results suggest a potential clinical advantage when using the 1.6 Gy fraction size with 40 degrees C mild hyperthermia, since hyperthermia radiosensitized the carcinoma cells but not the normal cells.