Radioresponsiveness of human glioma, sarcoma, and breast cancer spheroids depends on tumor differentiation

Substrate stiffness affects the morphology, proliferation, and radiosensitivity of cervical squamous carcinoma cells

Cervical cancer is associated with the highest morbidity rate among gynecological cancers. Radiotherapy plays an important role in the treatment of cervical cancer. However, a considerable number of patients are radiation resistant, leading to a poor prognosis. Matrix stiffness is related to the occurrence, development, and chemoresistance of solid tumors. The association between matrix stiffness and radiosensitivity in cervical cancer cells remains unknown. Here, we sought to determine the effect of matrix stiffness on the phenotype and radiosensitivity of cervical cancer cells. Cervical squamous carcinoma SiHa cells were grown on substrates of different stiffnesses (0.5, 5, and 25 kPa). Cell morphology, proliferation, and radiosensitivity were examined. Cells grown on hard substrates displayed stronger proliferative activity, larger size, and higher differentiation degree, which was reflected in a more mature skeleton assembly, more abundant pseudopodia formation, and smaller nuclear/cytoplasmic ratio. In addition, SiHa cells exhibited stiffness-dependent resistance to radiation, possibly via altered apoptosis-related protein expression. Our findings demonstrate that matrix stiffness affects the morphology, proliferation, and radiosensitivity of SiHa cells. Tissue stiffness may be an indicator of the sensitivity of a patient to radiotherapy. Thus, the data provide insights into the diagnosis of cervical cancer and the design of future radiotherapies.

Hypofractionated Radiotherapy as Adjuvant Treatment in Early Breast Cancer. A Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Adjuvant radiotherapy after breast-conserving surgery is indicated in the vast majority of breast cancer patients. Conventionally fractionated radiotherapy with 50 Gy in 25 fractions was considered standard of care for several decades. The recently publishes long-term results of randomized trials that have tested different moderately hypofractionated radiotherapy schedules that may change clinical practice.

PATIENTS AND METHODS

A Pubmed search was carried out to identify the relevant publications on hypofractionated radiotherapy in breast cancer. In total, 4 randomized controlled trials representing the results of 7,095 patients with 10 years of follow-up were identified. A meta-analysis on the primary end point ipsilateral breast cancer recurrence and a review of the toxicity data were performed.

RESULTS

Moderately hypofractionated radiotherapy using schedules such as 40 Gy in 15 fractions administered within 3 weeks are as efficient and safe as conventionally fractionated radiotherapy for most breast cancer patients who need adjuvant radiotherapy after breast-conserving surgery. In patients aged < 40 years, after neoadjuvant chemotherapy, and if regional lymph node radiotherapy is indicated, further data are needed.

CONCLUSION

Moderately hypofractionated radiotherapy can be recommended as standard treatment after breast-conserving surgery in the majority of breast cancer patients.

Differential S-phase progression after irradiation of p53 functional versus non-functional tumour cells

Background

Many pathways seem to be involved in the regulation of the intra-S-phase checkpoint after exposure to ionizing radiation, but the role of p53 has proven to be rather elusive. Here we have a closer look at the progression of irradiated cells through S-phase in dependence of their p53 status.

Materials and methods.

Three pairs of tumour cell lines were used, each consisting of one p53 functional and one p53 non-functional line. Cells were labelled with bromodeoxyuridine(BrdU) immediately after irradiation, they were then incubated in label-free medium, and at different times afterwards their position within the S-phase was determined by means of flow cytometry.

Results

While in the p53 deficient cells progression through S-phase was slowed significantly over at least a few hours, it was halted for just about an hour in the p53 proficient cells and then proceeded without further delay or even at a slightly accelerated pace.

Conclusions

It is clear from the experiments presented here that p53 does play a role for the progress of cells through the S-phase after X-ray exposure, but the exact mechanisms by which replicon initiation and elongation is controlled in irradiated cells remain to be elucidated.

Boron neutron capture therapy induces cell cycle arrest and cell apoptosis of glioma stem/progenitor cells in vitro

BACKGROUND

Glioma stem cells in the quiescent state are resistant to clinical radiation therapy. An almost inevitable glioma recurrence is due to the persistence of these cells. The high linear energy transfer associated with boron neutron capture therapy (BNCT) could kill quiescent and proliferative cells.

METHODS

The present study aimed to evaluate the effects of BNCT on glioma stem/progenitor cells in vitro. The damage induced by BNCT was assessed using cell cycle progression, apoptotic cell ratio and apoptosis-associated proteins expression.

RESULTS

The surviving fraction and cell viability of glioma stem/progenitor cells were decreased compared with differentiated glioma cells using the same boronophenylalanine pretreatment and the same dose of neutron flux. BNCT induced cell cycle arrest in the G2/M phase and cell apoptosis via the mitochondrial pathway, with changes in the expression of associated proteins.

CONCLUSIONS

Glioma stem/progenitor cells, which are resistant to current clinical radiotherapy, could be effectively killed by BNCT in vitro via cell cycle arrest and apoptosis using a prolonged neutron irradiation, although radiosensitivity of glioma stem/progenitor cells was decreased compared with differentiated glioma cells when using the same dose of thermal neutron exposure and boronophenylalanine pretreatment. Thus, BNCT could offer an appreciable therapeutic advantage to prevent tumor recurrence, and may become a promising treatment in recurrent glioma.

Concurrent hypofractionated radiotherapy and 5-Fluorouracil for advanced sarcomas of the bone

Purpose. 5-Fluorouracil (5-FU) has shown radiosensitizing properties in vitro. This paper reports the effects of radiotherapy and concomitant intravenous 5-FU radiosensitization in the treatment of advanced bone sarcomas.

Subjects/methods. Four patients with large inoperable bone sarcomas (three chondrosarcomas and one fibrosarcoma) were treated with hypofractionated radiotherapy and concomitant 5-FU bolus injection (300 mg m⁻²) before each fraction of radiotherapy. A radiation fraction of 5 Gy was given twice a week to a normalized total dose (α/β=4 Gy) of 75 Gy.

Results. The regimen was well tolerated, the main toxicity being grade I/II diarrhoea in two cases with pelvic irradiation. Treatment interruption for 1 week was necessary in two cases with pelvic disease but not in two patients treated for sarcoma of the extremities. A complete symptomatic relief was obtained in all cases immediately after the third to the fifth fraction and the median duration was 10 months. Computed tomography scan documented a partial response in 2/4 cases.

Discussion. Hypofractionated radiotherapy combined with potential lethal damage inhibitors for bone sarcomas requires further investigation.

Relative biological effectiveness of 6 MeV neutrons with respect to cell inactivation and disturbances of the G1 phase

The relative biological effectiveness (RBE) of neutrons and other types of densely ionizing radiation appears to be close to 1.0 for the induction of strand breaks, but considerably higher RBEs have been found for cellular end points such as colony-forming ability. This may be due to differences in the processing of strand breaks or to the involvement of other lesions whose yields are more dependent on radiation quality. Because cell cycle delays may be of great importance in the processing of DNA damage, we determined the RBE for disturbances of the G1 phase in four different cell types (Be11 melanoma, 4197 squamous cell carcinoma, EA14 glioma, GM6419 fibroblasts) and compared them with the RBE for cell inactivation. The method we used to determine the progress from G1 into S was as follows: Cells were serum-deprived for a number of days and then stimulated to grow with culture medium containing normal amounts of serum. Immediately before the change of medium, cells were exposed to graded doses of either 240 kV X rays or 6 MeV neutrons. At different times afterward, cells were labeled with BrdU and the numbers of active S-phase cells were assessed using two-parameter flow cytometry. For all four cell types, cells started to progress from G1 into S after a few hours. Radiation suppressed this process in all cases, but there were some interesting differences. For Be11 and 4197 cells, the most obvious effect was a delay in G1; the labeling index increased a few hours later in irradiated samples than in controls, and there was no significant effect on the maximum labeling index. For EA14 and GM6419 cells, although smaller doses were used because of greater radiosensitivity, a delay of the entry into S phase was again noticeable, but the most significant effect was a reduction in the maximum percentage of active S-phase cells after stimulation, indicating a permanent or long-term arrest in G1. The RBE for the G1 delay was the same for all four cell types, about 2.8, while the RBE for the G1 arrest varied between 3.2 for the most resistant Be11 cells and 1.7 for the most sensitive GM6419 cells. This trend was similar to that observed for the RBE for cell inactivation. If, as described above, the same number of strand breaks per dose is induced by neutrons and by X rays, the signal transduction cascade translates them into a greater G1 delay in the case of higher LET. This appears to be independent of repair capacity, because it is similar in all cell types we investigated. We therefore assume that a higher lesion density or the presence of other types of lesions is important for this relatively early effect. A G1 arrest, however, is more closely related to the later events leading to cell inactivation, where strand break repair does play a major role, influencing X-ray sensitivity more strongly than sensitivity to neutrons because of a lower repairability of lesions induced by higher-LET radiation.

Prospective single-arm study of 72 Gy hyperfractionated radiation therapy and combination chemotherapy for anaplastic astrocytomas

Background

Despite intensive multimodal treatment, outcome of patients with malignant glioma remains poor, and a standard dose of radiotherapy for anaplastic astrocytoma has not been defined. In the past RTOG study (83-02), the arm of 72 Gy hyperfractionated radiotherapy (HFRT) for malignant gliomas showed better outcome than the arms of higher doses (76.8 – 81.6 Gy) and the arms of lower doses (48 – 54.4 Gy). The purpose of this study is to verify the efficacy of this protocol.

Methods

From July 1995, 44 consecutive eligible patients with histologically proven anaplastic astrocytoma were enrolled in this study (HFRT group). The standard regimen in this protocol was post-operative radiotherapy of 72 Gy in 60 fractions (1.2 Gy/fraction, 2 fractions/day) with concurrent chemotherapy (weekly ACNU). The primary endpoint was local control rate (LCR), and the secondary endpoints were overall survival (OS), progression-free survival (PFS) and late toxicity.

Results

Three-year OS of the HFRT group was 64.8% (95% confidence interval; 48.4–81.3%). Three-year PFS rate and LCR were 64.4% (95%CI: 48.4–80.3%) and 81.6% (95%CI: 69.2–94.8%), respectively.

The number of failures at 5 years in the HFRT group were 14 (32%). The number of failures inside the irradiation field was only about half (50%) of all failures. One (2%) of the patients clinically diagnosed as brain necrosis due to radiation therapy.

Conclusion

The results of this study suggested that 72 Gy HFRT seemed to show favorable outcome for patients with anaplastic astrocytoma with tolerable toxicity.

Prognostic significance of surgery and radiation therapy in cases of anaplastic astrocytoma: retrospective analysis of 170 cases

OBJECT

The purpose of this retrospective study was to estimate the prognostic impact of treatment parameters for 170 patients with anaplastic astrocytoma (AA).

METHODS

Survival outcome and prognostic factors were analyzed for 170 patients with AA. In the multivariate analysis, site of lesion (frontal or parietal lobe, p = 0.002), extent of surgery (total or subtotal resection, p = 0.001), Karnofsky Performance Scale status (0-2, p = 0.021), age (< or = 50 years, p = 0.024), and total dose of radiation therapy (> 60 Gy, p = 0.029) were significant favorable prognostic factors. In the analysis of groups according to extent of surgery, patients who underwent total or subtotal resection had a significantly more favorable prognosis than did patients who underwent partial resection or biopsy (5-year survival rate 54.0% for total or subtotal resection compared with 17.5% for partial resection or biopsy; median survival time [MST] 62.6 months compared with 22.9 months [p < 0.0001, log-rank test]; hazard ratio [HR] 0.67; and 95% confidence interval [CI] 0.52-0.85 [p = 0.001]). In the analysis of groups according to total radiation dose, the group of patients who received doses greater than 60 Gy had a significantly more favorable prognosis than did the group who received 60 Gy or less (5-year survival rate 45.0% for patients who received doses greater than 60 Gy compared with 21.1% for those receiving 60 Gy or less; MST 48.9 months compared with 21.6 months [p = 0.0006, log-rank test]; HR 0.96; 95% CI 0.93-0.99 [p = 0.029]).

CONCLUSIONS

The most important parameter in the treatment of AA was extent of surgery, and total radiation dose was the second most important factor. Resection of as much of the tumor as possible and delivery of a total radiation dose of greater than 60 Gy seem to be required for local control of AA.

Effects of irradiation and cisplatin on human glioma spheroids: inhibition of cell proliferation and cell migration

PURPOSE

Investigation of cell migration and proliferation of human glioma cell line spheroids (CLS) and evaluation of morphology, apoptosis, and immunohistochemical expression of MIB-1, p53, and p21 of organotypic muticellular spheroids (OMS) following cisplatin (CDDP) and irradiation (RT).

MATERIAL AND METHODS

Spheroids of the GaMg glioma cell line and OMS prepared from biopsy tissue of six glioblastoma patients were used. Radiochemosensitvity (5 microg/ml CDDP followed by RT) was determined using migration and proliferation assays on CLS. In OMS, histology and immunohistochemical studies of MIB-1, p53, and p21 expression were examined 24 and 48 h following treatment.

RESULTS

Combination treatment led to a migration inhibition of 38% (CDDP 13%; RT 27%) and specific growth delay of 2.6 (CDDP 1.3; RT 2.1) in CLS. Cell cycle analysis after combination treatment showed an accumulation of cells in the G2/M phase. In OMS, apoptosis increased, cell proliferation decreased, and p53/p21 expression increased more pronounced following CDDP+RT. No morphological damage was observed.

CONCLUSION

CDDP can lead to enhancement of the RT effect in spheroids of both human glioma cell line spheroids and biopsy spheroids from glioblastoma specimens. The exerted effect is additive rather than synergistic.

Stereotactic radiosurgery in the management of intracranial gliomas

Glial neoplasms are the most common primary intracranial malignancies. Treatment of high-grade gliomas has been frustrating, with less than 5% of patients surviving 5 years after a diagnosis of glioblastoma multiforme (GBM). Stereotactic radiosurgery (SRS) and fractionated strereotactic radiotherapy (F-SRT) provide means to either escalate the dose in primary treatment or to palliate recurrences. Because of their lower alpha/beta ratios and more focal nature, low-grade gliomas (LGG) are more attractive targets for stereotactically focused radiation. Results of available phase I-II data are reviewed for both low and high-grade gliomas. In the case of high-grade gliomas disappointing preliminary phase III data from RTOG 93-05 are discussed. Toxicity of SRS is discussed. Acute treatment toxicity of significance is unusual and generally self-limited. Occasionally an exacerbation of existing symptoms occurs. Late complications attributable to SRS are usually defined as necrosis within the treatment volume. The rate of necrosis can be hard to define in high-grade gliomas as tumor cells are often present in surgical specimens. New strategies in the application of stereotactic radiation are touched upon, these include: changes in planning and fractionation, concurrent use of chemotherapy, use of radiation modifiers and biologic agents. After reviewing the current data for high-grade gliomas, it appears that any apparent improvement in outcome seen in phase I-II trials is attributable to patient selection. The best evidence available does not support the use of SRS for primary high-grade gliomas. The somewhat limited experience in LGG also indicates a lack of benefit for patients treated with stereotactic radiosurgery or F-SRT. For a very select group of patients with small recurrent lesions, F-SRT may represent a safe, reasonable treatment.

Response of thyroid follicular cells to gamma irradiation compared to proton irradiation: II. The role of connexin 32

The objective of this study was to determine whether connexin 32-type gap junctions contribute to the "contact effect" in follicular thyrocytes and whether the response is influenced by radiation quality. Our previous studies demonstrated that early-passage follicular cultures of Fischer rat thyroid cells express functional connexin 32 gap junctions, with later-passage cultures expressing a truncated nonfunctional form of the protein. This model allowed us to assess the role of connexin 32 in radiation responsiveness without relying solely on chemical manipulation of gap junctions. The survival curves generated after gamma irradiation revealed that early-passage follicular cultures had significantly lower values of alpha (0.04 Gy(-1)) than later-passage cultures (0.11 Gy(-1)) (P < 0.0001, n = 12). As an additional way to determine whether connexin 32 was contributing to the difference in survival, cultures were treated with heptanol, resulting in higher alpha values, with early-passage cultures (0.10 Gy(-1)) nearly equivalent to untreated late-passage cultures (0.11 Gy(-1)) (P > 0.1, n = 9). This strongly suggests that the presence of functional connexin 32-type gap junctions was contributing to radiation resistance in gamma-irradiated thyroid follicles. Survival curves from proton-irradiated cultures had alpha values that were not significantly different whether cells expressed functional connexin 32 (0.10 Gy(-1)), did not express connexin 32 (0.09 Gy(-1)), or were down-regulated (early-passage plus heptanol, 0.09 Gy(-1); late-passage plus heptanol, 0.12 Gy(-1)) (P > 0.1, n = 19). Thus, for proton irradiation, the presence of connexin 32-type gap junctional channels did not influence their radiosensitivity. Collectively, the data support the following conclusions. (1) The lower alpha values from the gamma-ray survival curves of the early-passage cultures suggest greater repair efficiency and/or enhanced resistance to radiation-induced damage, coincident with the expression of connexin 32-type gap junctions. (2) The increased sensitivity of FRTL-5 cells to proton irradiation was independent of their ability to communicate through connexin 32 gap junctions. (3) The fact that the beta components of the survival curves from both gamma rays and proton beams were similar (average 0.022 +/- 0.008 Gy(-2), P > 0.1, n = 39) suggests that at higher doses the loss of viability occurs at a relatively constant rate and is independent of radiation quality and the presence of functional gap junctions.

Extracellular matrix proteins and chemoradiotherapy: alpha5beta1 integrin as a predictive marker in rectal cancer

AIMS

To investigate the effects of extracellular matrix (ECM) protein expression on the rates of apoptosis and proliferation in rectal cancers and subsequent response to chemoradiotherapy (CRT).

METHODS

The expression of fibronectin, collagen IV, laminin and the fibronectin receptor (FnR, alpha5beta1 integrin) were analysed in 32 pre-treatment rectal cancer biopsies by immunohistochemistry. ECM expression was correlated with tumour mitotic index (MI), apoptotic index (AI) and histopathological response to CRT.

RESULTS

18/32 cancers showed a poor response and 14/32 a good response (5/14 with complete pathological response) to CRT. Moderate to strong staining was seen in 22/32 cancers for fibronectin, 5/32 for collagen IV and 18/32 for laminin. Tumour FnR was related to stromal fibronectin content, and was significantly associated with CRT response; good responders having higher FnR expression compared to poor responders. No association was found between FnR expression and either MI or AI in pre-treatment biopsies, nor between MI or AI and CRT response.

CONCLUSIONS

Tumour FnR expression is independent of MI and AI, and may serve as a useful marker for CRT response in rectal cancer.

Tumor biology and experimental therapeutics

Recent research using multicellular tumor spheroids has resulted in new insights in the regulation of invasion and metastasis, angiogenesis and cell cycle kinetics. The onset and expansion of central necrosis in tumor spheroids has been characterized to be a complex interaction of several mechanisms; in a number of cases, necrosis is not a consequence of hypoxia or anoxia, but emerges as secondary necrosis following an accumulation of apoptosis in spheroids. Recent therapeutically oriented studies have been directed towards novel hypoxic markers, targeted therapy, multicellular-mediated drug resistance, and heavy ion irradiation of spheroids. Research efforts should be enhanced mainly in the fields of tumor tissue modeling by heterotypic three-dimensional (3D) cultures and of apoptotic versus necrotic cell death. Based on the fundamental differences between monolayer and 3D cultures, spheroids should become mandatory test systems in therapeutic screening programs.

Quiescence in S-phase and G1 arrest induced by irradiation and/or hyperthermia in six human tumour cell lines of different p53 status

PURPOSE

Quiescent S-phase cells, i.e. cells with a DNA content intermediate between G1 and G2 that nevertheless do not synthesize DNA have been previously observed in human melanoma cells exposed to radiation and/or hyperthermia. This phenomenon has now been studied in more detail comparing six human tumour cell lines of different p53 status and thus different cell-cycle checkpoint control.

MATERIALS AND METHODS

Two melanoma (Be11, MeWo), two squamous carcinoma (4197, 4451) and two glioma (EA14, U87) cell lines were used. Changes in the cell-cycle distribution after treatment were studied using two-parameter flow cytometry in order to measure DNA content and BrdU incorporation simultaneously.

RESULTS

The fraction of unlabelled cells in the S-phase compartment was determined at daily intervals after treatment. Only background levels of such cells were seen in three of the cell lines (Be11, 4197, EA14). With the other three cell lines (MeWo, 4451, U87) we observed a time- and dose-dependent increase: a few days after treatment up to 20% of all cells did not incorporate BrdU. It is interesting to note that Bell, 4197 and EA14 are p53 wild-types and show a G1 block of several hours after irradiation and/or hyperthermia, while MeWo and 4451 are p53 mutants unable to exhibit such a delay, and U87 in spite of being a p53 wild-type has a reduced ability to do so.

CONCLUSIONS

The MeWo, 4451 and U87 cell lines have less time available for the repair of DNA damage before entering into the S-phase, which leads to problems during replication and causes some kind of interphase death. Radiation-induced apoptosis does not seem to be involved here, as it is not unequivocally correlated with the induction of a G1 block or with p53 status.

Multicellular spheroids: a three-dimensional in vitro culture system to study tumour biology

The growth of tumour cells as three-dimensional multicellular spheroids in vitro has led to important insights in tumour biology, since properties of the in vivo-tumour such as proliferation or nutrient gradients, can be studied under controlled conditions. While this review starts with an update of recent data on spheroid monocultures, especially concerning tumour microenvironment and therapeutic modalities, the main emphasis is put on the spectrum of heterologous cultures which have evolved in previous years. This type of culture includes tumour cell interaction with endothelial, fibroblast or immunocompetent cells. The relation of the spheroid culture model to other types of three-dimensional culture and our critical evaluation and presentation of the technical aspects of growing and analysing spheroids are included in the text. These topics are chosen to help the experimental pathologist design experiments with tumour spheroids and to stimulate discussion.

Hypofractionated radiation induces a decrease in cell proliferation but no histological damage to organotypic multicellular spheroids of human glioblastomas

The aim of this study was to examine the effect of radiation on glioblastoma, using an organotypic multicellular spheroid (OMS) model. Most glioblastoma cell lines are, in contrast to glioblastomas in vivo, relatively radiosensitive. This limits the value of using cell lines for studying the radiation effect of glioblastomas. The advantage of OMS is maintenance of the characteristics of the original tumour, which is lost in conventional cell cultures. OMS prepared from four glioblastomas were treated with hypofractionated radiation with a radiobiologically equivalent dose to standard radiation treatment for glioblastoma patients. After treatment, the histology as well as the cell proliferation of the OMS was examined. After radiation, a significant decrease in cell proliferation was found, although no histological damage to the OMS was observed. The modest effects of radiation on the OMS are in agreement with the limited therapeutic value of radiotherapy for glioblastoma patients. Therefore, OMS seems to be a good alternative for cell lines to study the radiobiological effect on glioblastomas.

DC electrical field-induced c-fos expression and growth stimulation in multicellular prostate cancer spheroids

The effects of electrical direct current (DC) field pulses on c-fos expression, growth kinetics and vitality patterns of multicellular tumour spheroids (MCSs) were studied. Monitoring the membrane potential of MCSs by di-8-ANNEPS staining and confocal microscopy during DC electrical field treatment revealed a hyperpolarization at the anode-facing side and a depolarization at the cathode-facing side. When a single 500 V m(-1) electrical field pulse with a duration of 60 s was applied to MCSs (150-350 microm in diameter) an enhancement of the growth kinetics within a period of 6 days post pulse was observed. Whereas the volume doubling time amounted to 4-5 days in control samples, it was reduced to 1-2 days in electropulsed MCSs. At day 6 post pulse the diameter of the necrotic core was significantly smaller than the control. The critical diameter for the first appearance of central necrosis amounted to 350 +/- 50 microm in the control and 450 +/- 50 microm in the electropulsed MCSs. Coincidentally, the proliferating rim was increased to 107 +/- 11 microm in electropulsed MCSs as compared with 60 +/- 6 microm in the control. The growth stimulation may be mediated by the proto-oncogene c-fos as its expression increased by a factor of 2.5 within 2 h post pulse. c-fos expression declined towards control values within 8 h post pulse.

Improved models of tumour cure

The standard mechanistic model for the probability of tumour cure (the "Poisson model') is based on the assumption that the number of surviving clonogens at the end of treatment follows a Poisson distribution from tumour to tumour. This assumption is not correct, however, if proliferation of tumour clonogens occurs during treatment, as would be expected in general during a fractionated course of radiotherapy. In the present study, the possible magnitude of the error in the Poisson model was investigated for tumours treated with either conventional fractionation or split-course therapy. An example is presented in which the Poisson model has an absolute error of nearly 100%, predicting a cure rate of 0% when in fact the cure rate was close to 100%. The largest errors in the Poisson model found in this study were for very small tumours (approximately 100 clonogens), but for larger tumours (> or = 10(6) clonogens), the Poisson model may still be highly inaccurate, predicting a cure rate that differs from the actual cure rate by as much as 40%. Three new tumour-cure models are proposed (the GS, PS, and GS+ models), and their accuracy is also investigated. Two of these (the GS and PS models) are better than the Poisson model for the clinically relevant cases tested here. The third model, the GS+ model, consistently produced the most accurate estimate of the tumour cure rate, but has more limited use than the GS and PS models because it is more highly parametrized. It is demonstrated here that no tumour-cure model based on the effective clonogen doubling time will be perfectly accurate in all cases, since the cure rate depends on the details of the cell kinetics contributing to the effective doubling time.

Radiosurgery and fractionated radiation therapy: comparison of different techniques in an in vivo rat glioma model

To identify histological changes and effects on survival in rats harboring C6 gliomas, the authors compared radiosurgery to different fractionated radiation therapy regimens including doses of calculated biological equivalence. Rats were randomized to control (54 animals) or treatment groups after implantation of C6 glioma cells into the right frontal brain region. At 14 days, treated rats underwent stereotactic radiosurgery (35 Gy to tumor margin; 22 animals), whole-brain radiation therapy (WBRT) (20 Gy in five fractions; 18 animals), radiosurgery plus WBRT (13 animals), hemibrain radiation therapy (85 Gy in 10 fractions; 16 animals) or single-fraction hemibrain irradiation (35 Gy; 10 animals). When compared to the control group (median survival 22 days), prolonged survival was identified after radiosurgery (p < 0.0001), radiosurgery plus WBRT (p < 0.0001), WBRT alone (p = 0.0002), hemibrain radiation therapy to 85 Gy (p < 0.0001), and 35-Gy hemibrain single-fraction irradiation (p = 0.004). Compared to the control group (mean tumor diameter, 6.8 mm), the tumor size was reduced in all treatment groups except WBRT alone. Reduced tumor cell density was exhibited in rats that underwent radiosurgery (p = 0.006) and radiosurgery plus WBRT (p = 0.009) when compared with rats in the control group, a finding not observed after any fractionated regimen. Increased intratumoral edema was identified after radiosurgery (p = 0.03) and combined treatment (p = 0.05), but not after fractionated radiation therapy or 35-Gy single-fraction hemibrain irradiation. In this animal model, the addition of radiosurgery significantly increased tumor cytotoxicity, potentially at the expense of radiation effects to regional brain. We found no difference in survival benefit or tumor diameter in animals that underwent radiosurgery compared to the calculated biologically equivalent regimen of 10-fraction radiation therapy to 85 Gy. The histological responses after radiosurgery were generally greater than those achieved with biologically equivalent doses of fractionated radiation therapy.

Effects of sex- and glucocorticoid steroids on breast cancer cells grown as either multicellular tumor spheroids or monolayers

The effects of estradiol, medroxyprogesterone acetate (MPA) dexamethasone, dihydrotestosterone and the antihormones 4-OH tamoxifen and RU 38486 were studied in two established breast carcinoma cell lines, the estrogen-sensitive ZR-75-1 and the estrogen-independent BT 20 cells applying two different in vitro systems, spheroid and monolayer cell culture in steroid deprived medium. Growth of ZR-75-1 spheroids was dramatically stimulated by the addition of estradiol, an effect which was neutralized by the simultaneous addition of 4-OH tamoxifen. The antiestrogen alone as well as dihydrotestosterone and MPA reduced ZR-75-1 spheroid growth significantly. While growth of BT 20 spheroids was only transiently inhibited by tamoxifen and dihydrotestosterone, a persistent increase in BT 20 spheroid growth was observed under MPA treatment in a concentration of 1 microM. This effect, although statistically significant, was very moderate. With the exception of this finding, growth effects of the different test compounds were similar in both in vitro systems, tumor spheroids and monolayer cell cultures.

Radiation-induced apoptosis in human sarcoma and glioma cell lines

Six human soft-tissue sarcoma and 14 glioma cell lines, exhibiting considerable differences in radioresponsiveness and histological grade of differentiation of the parental tumour, were examined with respect to apoptosis development after irradiation with 60Co gamma-rays. After test doses of 6 and 25 Gy, significant changes characteristic of apoptosis occurring within 6 to 30 hr were exhibited by only 2 differentiated sarcoma cell lines, EL7 and ESS2. The characteristic internucleosomal fragmentation of DNA was detected as early as 6 hr after exposure of subconfluent monolayer cultures to 6 Gy. It was limited to cells that had detached from the culture plate, whereas adherent cells showed random degradation of DNA, namely after higher doses (25Gy) or longer incubation times (30 hr). As assessed by fluorescence microscopy of unfixed cultures stained with Hoechst 33342 and propidium iodide, the proportion of cells showing apoptotic bodies in non-irradiated controls was < 0.1% and 0.3% for EL7 and ESS2, respectively. The dose-response relationship for apoptosis was determined at 9 hr post-irradiation. After 2 Gy, the percentage of apoptotic cells was elevated to 3.4% in EL7 and 4.5% in ESS2 cultures. Saturation was obtained above 6 Gy, with 8.4% apoptosis in EL7 and 15% in ESS2 after 25 Gy. Taken together, rapid ionizing-radiation-induced apoptosis seems to be limited to a subgroup of sarcomas and is unlikely to occur in gliomas.

Heterogeneity in the fractionation sensitivities of human tumor cell lines: studies in a three-dimensional model system

PURPOSE

Current concepts to optimize the therapeutic gain of radiotherapy by hyperfractionation assume that human tumors are less sensitive to fractionation than late reacting normal tissues. The aim of this study was to investigate the extent of the intercell line heterogeneity of fractionation sensitivity of a wide variety of human tumor cell lines in a three-dimensional model system under fully oxic conditions using schedules with one to eight fractions. Biological characteristics of the tumors that correlate with fractionation sensitivity should be identified.

METHODS AND MATERIALS

A total of 21 cell lines from human tumors maintained as multicellular spheroids consisting of 1000-1500 cells were given fractionated irradiation within a total treatment time of maximally 50 h. Complete dose-spheroid control curves were determined for each fractionation scheme. The spheroid control data were adequately described by the linear quadratic model assuming Poisson statistics. In addition, the induction of a G2 block by a fractionated test dose of seven 3 Gy fractions given at 6-h intervals was determined in spheroid cells using flow cytometry of propidium bromide stained cell nuclei.

RESULTS

The fractionation sensitivities of human tumor cells in multicellular spheroids could be characterized by alpha/beta values, ranging from 2.8-37 Gy in dependence on the cell line. The log normally distributed alpha/beta values were positively correlated with the percentage increase in G2/M phase after the fractionated test dose compared to the controls (r = 0.72, p < 0.01), and were associated with the degree of tumor differentiation (p = 0.01, ANOVA F-test). No significant correlation between the log (alpha/beta) values and the surviving fractions at 2 Gy (SF2) or the total doses with 2 Gy per fraction necessary to control 50% of the spheroids (SCD50) was observed. Despite the intercell line variability of the alpha/beta values, the SCD50 values of the different cell lines, given with one and eight fractions or one fraction and 2 Gy per fraction, were closely associated (Spearman rank correlation coefficients: r = 0.89 or r = 0.90, p < 0.0001).

CONCLUSION

Human tumor cell lines showed a marked heterogeneity in the fractionation sensitivity when irradiated as multicellular spheroids and assayed in situ using the spheroid control end point. Therefore, the therapeutic gain of altered fractionation also depends on those biological characteristics of each individual tumor that affects its fractionation sensitivity. Parameters that correlate with fractionation sensitivity of the tumor lines in the spheroid system were identified as grade of tumor differentiation and percentage increase in G2/M cells at the end of an eight-fraction schedule.

Interaction between ionizing radiation, estrogens and antiestrogens in the modification of tumor microenvironment in estrogen dependent multicellular spheroids

MCF7 human breast cancer cells growing as multicellular spheroids were examined as a model of three-dimensional cellular organization. Estrogen-free medium inhibited spheroid formation. In medium containing estrogens, the antiestrogen hydroxytamoxifen decreased the spheroid growth rate. Analyses with the recursion formula after Gompertz fitting showed that the rate of exponential decrease in growth rate (alpha) was alpha 0.099 +/- 0.013 d-1, and the decrease in alpha' was 0.061 +/- 0.015 d-1 for 0.1 microM hydroxytamoxifen and control spheroids respectively. MCF7 cells which had been growth arrested in an estrogen-free medium showed a significant decrease in radiosensitivity (surviving fraction at 2 Gy, SF2 = 63%) when compared with 0.1 nM 17 beta-estradiol-treated cells (SF2 = 38%). No differences in radiosensitivity were seen in MCF7 spheroids in estrogen-supplemented medium (radiation dose necessary to control 50% of spheroids (SCD50) was 5.51 Gy; derived alpha, beta and SF2 were 0.301 +/- 0.110 Gy-1, 0.018 +/- 0.005 Gy-2, and 51% respectively) when compared with monolayer cultures in the same medium (alpha = 0.316 +/- 0.059 Gy-1, beta = 0.023 +/- 0.006 Gy-2 and SF2 = 50%). In the spheroid model, manipulating the cellular environment, i.e., with estrogen treatment, modulates sensitivity to ionizing radiation.