The effect of oxygen on cellular survival and recovery after radiation

Feasibility of omitting the clinical target volume under PET-CT guidance in unresectable stage III non-small-cell lung cancer: A phase II clinical trial

BACKGROUND

This clinical trial aims at investigate the feasibility of CTV-omitted, positron-emission tomography computed tomography (PET-CT) combined with intensity-modulated radiation therapy (IMRT) for unresectable stage III NSCLC.

METHODS AND MATERIALS

This was a single-center, phase II clinical trial initiated in July 2016. Patients with unresectable stage III NSCLC undergoing routine IMRT were randomly enrolled into the study group (CTV-omitted under PET-CT guidance) and the control group (CTV-delineated). Patients received platinum-based dual-drug concurrent chemoradio therapy. In the study group, the PGTV dose was 60 Gy given in 30 daily 2 Gy fractions; in the control group, the PCTV dose was 54 Gy given in 30 daily 1.8 Gy fractions, and the PGTV dose was 60 Gy given in 30 daily 2 Gy fractions. The primary endpoint was the incidence of radiation respiratory events or esophagitis with grade 3 or higher. The secondary endpoints included objective response rate (ORR), locate control rate, progression-free survival (PFS), failure pattern and overall survival (OS).

RESULTS

A total of 90 patients were enrolled between July 2016 and March 2019. The incidence of radiation respiratory events or esophagitis with grade 3 or higher was 11.1 % in the study group, significantly lower than the rate of 28.9 % in the control group (P = 0.035), basically due to the reduced irradiated volumes of the lungs and esophagus in the study group. The median PFS was 9.0 months versus 10.0 months (P = 0.597), and the median OS 31.0 months versus 26.0 months (P = 0.489) in the study group and the control group, respectively. The failure pattern was not significantly different between the two groups (P = 0.826).

CONCLUSION

Omitting the CTV under PET-CT guidance has high feasibility to reduce severe radiation associated toxicity in IMRT for unresectable stage III NSCLC, without compromising the efficacy.

Effects of oxygen on the response of mitochondria to X-irradiation and reactive oxygen species-mediated fibroblast activation

PURPOSE

In living organisms, sensitivity to radiation increases in the presence of oxygen (O₂) compared with that under anoxic or hypoxic conditions. Here, we investigated whether O₂ concentration affected the response of mitochondria to X-rays radiation, which is associated with tumor microenvironment formation via fibroblast activation in radiation-related tumors.

MATERIALS AND METHODS

O₂ concentrations were controlled at <5% (internal environmental oxygen condition) or anoxic levels during culture of normal human diploid lung fibroblasts TIG-3 and MRC-5. Protein expression associated with the response of mitochondria to radiation was assessed using immunostaining or western blotting.

RESULTS

Induction of DNA damage (marker: γ-H2A histone family member X) and mitochondrial signaling (AMP-activated protein kinase), suppression of mitochondrial metabolic activity, and generation of reactive oxygen species occurred with radiation in cells cultured under 5% and 20% O₂ conditions. However, reducing O₂ concentration mitigated the effects of radiation on cell growth, mitochondrial damage (parkin), induction of antioxidant responses (nuclear factor E2-related factor 2), and fibroblast activation (α-smooth muscle actin). Radiation did not affect the markers used in this study in the absence of O₂.

CONCLUSION

O₂ concentration affected the response of mitochondria to radiation and reactive oxygen species-mediated fibroblast activation. Higher O₂ concentrations enhanced the effects of radiation on mitochondria in human fibroblasts. In vitro studies may overestimate in vivo radiation effects due to high O₂ concentrations.

Simulated dose painting of hypoxic sub-volumes in pancreatic cancer stereotactic body radiotherapy

Dose painting of hypoxic tumour sub-volumes using positron-emission tomography (PET) has been shown to improve tumour controlin silicoin several sites, predominantly head and neck and lung cancers. Pancreatic cancer presents a more stringent challenge, given its proximity to critical gastro-intestinal organs-at-risk (OARs), anatomic motion, and impediments to reliable PET hypoxia quantification. A radiobiological model was developed to estimate clonogen survival fraction (SF), using¹⁸F-fluoroazomycin arabinoside PET (FAZA PET) images from ten patients with unresectable pancreatic ductal adenocarcinoma to quantify oxygen enhancement effects. For each patient, four simulated five-fraction stereotactic body radiotherapy (SBRT) plans were generated: (1) a standard SBRT plan aiming to cover the planning target volume with 40 Gy, (2) dose painting plans delivering escalated doses to a maximum of three FAZA-avid hypoxic sub-volumes, (3) dose painting plans with simulated spacer separating the duodenum and pancreatic head, and (4), plans with integrated boosts to geometric contractions of the gross tumour volume (GTV). All plans saturated at least one OAR dose limit. SF was calculated for each plan and sensitivity of SF to simulated hypoxia quantification errors was evaluated. Dose painting resulted in a 55% reduction in SF as compared to standard SBRT; 78% with spacer. Integrated boosts to hypoxia-blind geometric contractions resulted in a 41% reduction in SF. The reduction in SF for dose-painting plans persisted for all hypoxia quantification parameters studied, including registration and rigid motion errors that resulted in shifts and rotations of the GTV and hypoxic sub-volumes by as much as 1 cm and 10 degrees. Although proximity to OARs ultimately limited dose escalation, with estimated SFs (∼10^-5) well above levels required to completely ablate a ∼10 cm³tumour, dose painting robustly reduced clonogen survival when accounting for expected treatment and imaging uncertainties and thus, may improve local response and associated morbidity.

Induction of Mitotic Catastrophe via Inhibition of Aurora B by Ionizing Radiation With Additive of Mulberry Water Extract in Human Bladder Cancer Cells

Mulberry fruit water extract (MWE) has been reported to synergistically enhance the cytotoxic effect of paclitaxel by promoting mitotic catastrophe to induce apoptosis in bladder cancer cells in our previous work. The aim of this study was to evaluate and to mechanistically explore the effects of MWE on bladder cancer responses to ionizing radiation (IR) by treating TSGH 8301 bladder carcinoma cells with MWE after exposing to IR. The results of MTT assay showed a synergistic cytotoxicity of IR with the co-treatment of MWE (IR/MWE) by inducing G2/M phase arrest as demonstrated by flow cytometry analysis in TSGH 8301, HT1367 and HT1197 bladder carcinoma cells lines. The IR/MWE-treated cells expressed increased levels of the G2/M phase arrest-related proteins cdc2/cyclin B1 and displayed giant multinucleated morphology, a typical characteristic of mitotic catastrophe. Immunofluorescent confocal microscopy revealed that the combined strategy inhibited Aurora B phosphorylation through Ras/Raf/MEK/ERK signaling cascade as demonstrated by Western blotting analysis. IR/MWE also caused an inhibitory effect on Plk1 and the subsequent downstream regulator RhoA repression and Cep55 induction, which would influence cell cycle progression in the early steps of cytokinesis. A profound tumor growth suppression and inactivation of Aurora B activity in the tumor tissues by IR/MWE treatment were confirmed in the TSGH 8301 xenograft model in vivo. These data demonstrated that MWE could be an effective auxiliary to synergize with radiation on the anticancer efficacy by promoting mitotic catastrophe through inhibition of Aurora B, providing a novel and effective therapeutic option for bladder cancer management.

Efficacy of the smaller target volume for stage III non-small cell lung cancer treated with intensity-modulated radiotherapy

The present study reports the local recurrence, distant metastasis, progression-free survival, overall survival and radiation toxicity between two arms of stage III non-small cell lung cancer (NSCLC) treated with intensity-modulated radiotherapy (IMRT); one arm with clinical target volume (CTV) and the other without CTV. The two arms of local recurrence, distant metastasis, progression-free survival, overall survival, grade 3-4 radiation esophagitis and hematological toxicity had no statistical significance. However, the grade 3-4 radiation pneumonia rate of the group without CTV was significantly decreased. This supports the concept that stage III NSCLC treated with IMRT, which omitted CTV, can reduce the occurrence of radiation pneumonia. The aim of the present study was to analyze the feasibility of the smaller target volume for stage III NSCLC treated with IMRT. Data from 105 patients with stage III NSCLC who were hospitalized and received IMRT between January 1, 2008 and November 30, 2012 were retrospectively analyzed. A total of 55 cases were irradiated with target volume without CTV and 50 cases were irradiated with CTV. Dose prescription was 100% PTV at 54-63 Gy/27-35 F/5.4-7 weeks. The two arms of the patient characteristics and treatment deliveries had no statistical significance. The two arms of the patients were compared for local recurrence, distant metastasis, progression-free survival, overall survival and radiation-related toxicity. In the arms without and with CTV, the local relapse and distant metastases rates were 32.7 and 32.0% (P=1.000) and 56.4 and 48.0% (P=0.946), respectively. The median progression-free survival time for the two arms was 9 months (P=0.619). The 1-, 2- and 3-year survival rates of the arms without and with CTV were 74.5, 43.6 and 23.6%, and 70.0, 46.0 and 20.0% (P=0.956), respectively. In the two arms, grade 3-4 radiation esophagitis and hematological toxicity had no statistical significance. However, in the arm without CTV, grade 3-4 radiation pneumonia was only 5.5%, compared with 18.0% in the arm with CTV (P=0.044). In conclusion, the smaller target volume for stage III NSCLC treated with IMRT was feasible.

Feasibility of omitting clinical target volume for limited-disease small cell lung cancer treated with chemotherapy and intensity-modulated radiotherapy

Purpose

To analyze the feasibility of omitting clinical target volume (CTV) for limited small cell lung cancer treated with chemotherapy and intensity modulated radiotherapy.

Methods and materials

89 patients were treated from January 1, 2008 to August 31, 2011, 54 cases were irradiated with target volume without CTV, and 35 cases were irradiated with CTV. Both arms were irradiated post chemotherapy tumor extent and omitted elective nodal irradiation; dose prescription was 95% PTV56-63 Gy/28-35 F/5.6-7 weeks.

Results

In the arm without CTV and arm with CTV, the local relapse rates were 16.7% and 17.1% (p = 0.586) respectively. In the arm without CTV, of the 9 patients with local relapse, 6 recurred in-field, 2 recurred in margin, 1 recurred out of field. In the arm with CTV, of the 6 patients with local relapse, 4 recurred in-field, 1 recurred in margin, 1 recurred out of field. The distant metastases rates were 42.6% and 51.4% (p = 0.274) respectively. Grade 3-4 hematological toxicity and radiation esophagitis had no statistically significant, but grade 3-4 radiation pneumonia was observed in only 7.4% in the arm without CTV, compared 22.9% in the arm with CTV (p = 0.040). The median survival in the arm without CTV had not reached, compared with 38 months in the with CTV arm. The l- years, 2- years, 3- years survival rates of the arm without CTV and the arm with CTV were 81.0%, 66.2%, 61.5% and 88.6%, 61.7%, 56.6% (p = 0.517). The multivariate analysis indicated that the distant metastases (p = 0.000) and PCI factor (p = 0.004) were significantly related to overall survival.

Conclusions

Target delineation omitting CTV for limited-disease small cell lung cancer received IMRT was feasible. The distant metastases and PCI factor were significantly related to overall survival.

Adapting radiotherapy to hypoxic tumours

In the current work, the concepts of biologically adapted radiotherapy of hypoxic tumours in a framework encompassing functional tumour imaging, tumour control predictions, inverse treatment planning and intensity modulated radiotherapy (IMRT) were presented. Dynamic contrast enhanced magnetic resonance imaging (DCEMRI) of a spontaneous sarcoma in the nasal region of a dog was employed. The tracer concentration in the tumour was assumed related to the oxygen tension and compared to Eppendorf histograph measurements. Based on the pO(2)-related images derived from the MR analysis, the tumour was divided into four compartments by a segmentation procedure. DICOM structure sets for IMRT planning could be derived thereof. In order to display the possible advantages of non-uniform tumour doses, dose redistribution among the four tumour compartments was introduced. The dose redistribution was constrained by keeping the average dose to the tumour equal to a conventional target dose. The compartmental doses yielding optimum tumour control probability (TCP) were used as input in an inverse planning system, where the planning basis was the pO(2)-related tumour images from the MR analysis. Uniform (conventional) and non-uniform IMRT plans were scored both physically and biologically. The consequences of random and systematic errors in the compartmental images were evaluated. The normalized frequency distributions of the tracer concentration and the pO(2) Eppendorf measurements were not significantly different. 28% of the tumour had, according to the MR analysis, pO(2) values of less than 5 mm Hg. The optimum TCP following a non-uniform dose prescription was about four times higher than that following a uniform dose prescription. The non-uniform IMRT dose distribution resulting from the inverse planning gave a three times higher TCP than that of the uniform distribution. The TCP and the dose-based plan quality depended on IMRT parameters defined in the inverse planning procedure (fields and step-and-shoot intensity levels). Simulated random and systematic errors in the pO(2)-related images reduced the TCP for the non-uniform dose prescription. In conclusion, improved tumour control of hypoxic tumours by dose redistribution may be expected following hypoxia imaging, tumour control predictions, inverse treatment planning and IMRT.

Relationships between radiosensitivity and microvascular density in esophageal carcinoma: significance of hypoxic fraction

PURPOSE

The prognosis and the radiosensitivity of macroscopically infiltrative type of esophageal carcinoma are worse than those of the localized type of esophageal carcinoma treated with irradiation. The aim of this study was to investigate the cause of differences in radiosensitivity and prognosis of esophageal carcinoma according to macroscopic type from the viewpoint of tumor angiogenesis.

METHODS AND MATERIALS

A total of 40 surgically resected esophageal carcinoma tissues with good material remaining were selected at random from macroscopically localized type (n = 20) and infiltrative type (n = 20) of esophageal carcinoma. The highest intratumoral microvascular density (h-MVD), average intratumoral microvascular density (a-MVD), Ki67 labeling index, and expression of vascular endothelial growth factor (VEGF) in each section were estimated.

RESULTS

h-MVD was significantly (p = 0.0006) greater in the infiltrative type than in the localized type, whereas a-MVD (p = 0.0014) and Ki67 labeling index (p = 0.022) were significantly lower in the infiltrative type than in the localized type. The expression level of VEGF was significantly (p < 0.0001) higher in the infiltrative type.

CONCLUSIONS

The generally underdeveloped vascular densities with low proliferation activities (suggesting increase of hypoxic fraction) seemed to be one of the reasons for unfavorable radiosensitivities of infiltrative type of esophageal carcinoma. The infiltrative type of esophageal carcinoma shows a high level of VEGF expression and high activity of tumor angiogenesis. The locally enhanced neovascularization, which occurs frequently in hematogenous metastasis seemed to be one of the reasons for the unfavorable prognosis of the infiltrative type of esophageal carcinoma.

Association of preoperative radiation effect with tumor angiogenesis and vascular endothelial growth factor in oral squamous cell carcinoma

This study examined the relationship between tumor angiogenesis and the radiation-induced response, evaluated based on pathological changes, in oral squamous cell carcinoma patients treated with preoperative radiation therapy. Forty-one cases of squamous cell carcinoma treated with preoperative radiation therapy were investigated. Tumor angiogenesis was assessed by scoring the intratumor microvessel density (IMVD). Expression of vascular endothelial growth factor (VEGF) was also evaluated before and after preoperative radiotherapy. There was no correlation between IMVD in the specimens before therapy and the pathological response to radiation therapy. However, radiation therapy decreased IMVD in the specimens after therapy. A significant association was observed between VEGF expression and resistance to radiation therapy: only 4 of the 21 patients whose tumors exhibited a high level (2 + or 3 + ) of VEGF staining experienced a major (3 + or 4 + ) pathological response to radiation therapy. Furthermore, an increasing level of VEGF expression after radiation therapy was observed in non-effective (0 to 2 + ) response cases. These results suggest that VEGF expression and the induction of this protein are related to radiosensitivity and could be used to predict the effects of preoperative radiation therapy on oral squamous cell carcinoma.

Effects of radiotherapy and estramustine on the microvasculature in malignant glioma

Tumour angiogenesis is essential for progression of solid tumours and constitutes an interesting target for therapy. However, impaired tumour blood supply may also be an important obstacle for treatment by radiotherapy and chemotherapy. Estramustine has been shown to increase tumour blood flow and potentiate the effect of radiotherapy in experimental glioma. This study investigated the effects of fractionated radiotherapy and estramustine on angiogenesis in malignant glioma. The intracerebral BT4C rat glioma model was used and the animals were given whole brain radiotherapy 4 Gy x 5 days alone or in combination with estramustine 20 mg kg(-1) i.p. daily. Tumour microvascular density (MVD) was assessed by manual and computerized morphometrical analysis. Expression of vascular endothelial growth factor (VEGF) was studied by in situ hybridization. Radiotherapy decreased MVD to 157 vessels per mm2 compared to 217 vessels per mm2 in controls. Estramustine counteracted this anti-angiogenic effect and potentiated the anti-tumoural effect of radiotherapy. In addition, vessel size increased after estramustine treatment. Five days after completion of radiotherapy the expression of VEGF was increased in the centre of the tumours. In conclusion, fractionated radiotherapy decreases microvascular density in experimental malignant glioma. This effect was abolished by estramustine. The anti-vascular effect of irradiation is important to recognize when combining radiotherapy with cytotoxic drugs.

Superfractionation as a potential hypoxic cell radiosensitizer: prediction of an optimum dose per fraction

PURPOSE

A dose "window of opportunity" has been identified in an earlier modeling study (1) if the inducible repair variant of the LQ model is adopted instead of the pure LQ model, and if all survival curve parameters are equally modified by the presence or absence of oxygen. In this paper we have extended the calculations to consider survival curve parameters from 15 sets of data obtained for cells tested at low doses using clonogenic assays.

METHODS AND MATERIALS

A simple computer model has been used to simulate the response of each cell line to various doses per fraction in multifraction schedules, with oxic and hypoxic cells receiving the same fractional dose. We have then used pairs of simulated survival curves to estimate the effective hypoxic protection (OER') as a function of the dose per fraction.

RESULTS

The resistance of hypoxic cells is reduced by using smaller doses per fraction than 2 Gy in all these fractionated clinical simulations, whether using a simple LQ model, or the more complex LQ/IR model. If there is no inducible repair, the optimum dose is infinitely low. If there is inducible repair, there is an optimum dose per fraction at which hypoxic protection is minimized. This is usually around 0.5 Gy. It depends on the dose needed to induce repair being higher in hypoxia than in oxygen. The OER' may even go below unity, i.e. hypoxic cells may be more sensitive than oxic cells.

CONCLUSIONS

If oxic and hypoxic cells are repeatedly exposed to doses of the same magnitude, as occurs in clinical radiotherapy, the observed hypoxic protection varies with the fractional dose. The OER' is predicted to diminish at lower doses in all cell lines. The loss of hypoxic resistance with superfractionation is predicted to be proportional to the capacity of the cells to induce repair, i.e. their intrinsic radioresistance at a dose of 2 Gy.

New insights into factors influencing the clinically relevant oxygen enhancement ratio

BACKGROUND AND PURPOSE

This paper deals with the variations in the oxygen enhancement ratios that could be observed (OER') when comparing oxic and hypoxic cells in different types of fractionated experiments as a consequence of the non-linearity of the underlying cell survival curves. Calculations have been made of the OER' that would be obtained for fractionated irradiations with a series of small doses to allow the comparison of isoeffective doses in oxic and hypoxic conditions. Two styles of fractionated experiment were modelled. In one, the dose per fraction was kept constant in the oxic and hypoxic arms of the experiment, necessitating more fractions in hypoxia to achieve the same level of cell kill. In the other the number of fractions was kept constant and the fraction size was varied to obtain equal levels of damage. The first is the relevant design for the clinic, whereas the second is the design most commonly used in animal studies.

MATERIALS AND METHODS

Three models of the survival curve were used to simulate the response of cells to radiation injury, all based on the linear quadratic model, but with various added assumptions. A simple classical LQ model is compared with two models in which the concept of inducible repair is added. In one of these the induction dose for 'switching on' the more resistant response is assumed to be increased in hypoxia and in the other it is assumed to be independent of the oxygen tension.

RESULTS

These calculations show a clear and previously unsuspected dependence of the measured OER' on the design of the fractionated experiment. The values obtained in the clinical and animal types of study differ considerably with all three models. The direction and magnitude of that difference depends critically on the assumptions about the fine structure of the survival curve shape. The authors suggest that the inducible repair version with an oxygen-dependent induction dose is probably the most relevant model. Using this, the measured OER' is reduced at doses around 2 Gy for the clinically relevant design of constant sized fractions to the oxic and hypoxic cells. It may even, in certain model assumptions, fall below unity resulting in an increased sensitivity, not resistance, from the hypoxia.

CONCLUSIONS

These calculations indicate the urgent need for more knowledge about the fine structure of the low dose region of the survival curves for human tumour cells and especially for comparisons in the presence and absence of oxygen. The extent of the hypersensitivity at very low doses, the trigger dose needed to induce the repair and its oxygen modification may be dominant factors in determining the response of tumour cells to clinically relevant fractionation schedules.

Tumor blood flow and the cytotoxic effects of estramustine and its constituents in a rat glioma model

OBJECTIVE

Estramustine (EaM) is a conjugate of nor-nitrogen mustard (NNM) and 17 beta-estradiol (E2) that has cytotoxic and radiosensitizing effects on experimental malignant glioma. Its mechanism of action is only partly understood. To further investigate the mechanism in vivo, the effects on tumor blood flow (TBF) and tumor growth were analyzed.

METHODS

TBF was measured by radioactive microspheres, and tumor growth was measured by weight. Apoptosis was evaluated by in situ end labeling and gel electrophoresis. The effects of the constituents NNM and E2 were also evaluated.

RESULTS

EaM increased TBF to 153.8 ml/100 g/min after 3 days and to 153.9 ml/100 g/min after 10 days of treatment, compared with 94.0 ml/100 g/min in untreated controls. Cerebral blood flow did not change after EaM treatment. NNM increased TBF but also showed a tendency to increase cerebral blood flow. E2 increased TBF, whereas cerebral blood flow was unchanged. EaM resulted in a rapid reduction in tumor weight from 230 mg in untreated animals to 146 mg after 3 days of treatment. EaM induced an early transient fragmentation of deoxyribonucleic acid in glioma but not in the normal brain. Neither NNM nor E2 affected tumor weight.

CONCLUSION

EaM increases TBF in the BT4C rat glioma model with a concomitant rapid antitumoral effect. The increase in TBF could partially be induced by an estrogen-like action of EaM, but the rapid cytotoxic effect of the drug is obviously attributed to the intact EaM compound. This cytotoxic effect might be attributable to the induction of programmed cell death.

Hypoxic cell sensitization: low-dose intrinsic radiosensitivity is predictive for etanidazole efficacy in a panel of human tumour cell lines

We used a cell sorter assay to evaluate the efficacy of the hypoxic cell sensitizer etanidazole over 3-4 logs of cell inactivation, with particular attention to the clinically relevant low-dose survival region. Analysis of the radiation responses in a panel of six human tumour cell lines under conditions of hypoxia and hypoxia with etanidazole revealed both a cell-line and radiation dose-dependence in the sensitizing ability of this drug. Fits of the linear-quadratic (LQ) model to the low-dose region of cell survival indicate that sensitization of hypoxic cells by etanidazole results primarily from a modification of the beta parameter. This results in selective sensitization of cell lines in which this parameter contributes significantly to cell kill (i.e. a low alpha/beta ratio) and implies that the efficacy of this drug may be tumour specific. Selective modification of beta also leads to a radiation dose-dependence of the sensitizing enhancement ratio (SER). Analysis of the alpha and beta parameters derived from fist to data at low doses of radiation, suggests that the dose-dependence of this sensitizer, and possibly others including oxygen, is cell-line dependent; cell lines exhibiting a low alpha/beta ratio (i.e. with a large shoulder) exhibit little or no SER dose dependence, while those with a high alpha/beta ratio (i.e. small shoulder) exhibit a reduced SER at low doses as compared to high doses. Furthermore, this analysis suggests that modelling of the low-dose radiation survival data under conditions of hypoxia, can be predictive for both the absolute sensitizing ability of etanidazole, and its dose dependence. Our results also indicate that measurement of the in vitro low-dose radiation survival response in a panel of human cell lines is a more effective assay for evaluating agents like etanidazole than simply high-dose measurements in rodent cell lines which have, in general, demonstrated more congruent survival responses.

Estramustine in malignant glioma

Estramustine, a carbamate ester combining 17 beta-estradiol and nornitrogen mustard, has primarily been employed in the treatment of advanced prostatic carcinoma. However, a significant amount of preclinical investigation has been directed toward estramustine's activity against human malignant glioma. These studies have demonstrated that estramustine has potent antiproliferative effects against malignant glioma both in vitro and in vivo. Similar antimitotic effects also have been demonstrated for other carbamate esters. Estramustine does not impair proliferation of nonneoplastic astrocytes at concentrations that inhibit glioma cells. Although the reasons for this selective activity remain to be determined, it has been shown that malignant gliomas expresses an estramustine-specific binding site, estramustine-binding protein, more than brain tissue. In the clinical situation, an uptake and accumulation of estramustine in human glioma tissue have been demonstrated. Estramustine has been shown to enhance the cytotoxic effects of irradiation in relatively radioresistant glioma cells both in cell culture and in a rat glioma model. Estramustine has been regarded as mainly an anti-mitotic drug but recently other effects such as inhibition of DNA synthesis, induction of apoptosis, and membrane alterations have been shown. This report summarizes the preclinical observations concerning the effects of estramustine and related compounds on human malignant gliomas. These findings form the basis for proposing further laboratory and clinical investigation regarding estramustine and human malignant gliomas.

Radiosensitizing effect of estramustine in malignant glioma in vitro and in vivo

Estramustine-phosphate (EMP), a combination of nornitrogen mustard and 17 beta-estradiol, has been demonstrated to exert specific antiproliferative effects on human glioma cells in vitro. The cytotoxic effect is, at least partially, mediated by inhibiting microtubule function. In this study the combined effect of EMP and radiation was evaluated in the human glioma cell-lines, 251-MG and 105-MG, in vitro, and in the rat glioma BT4C in vitro and in vivo. In all cell-lines an additive effect of EMP and radiation was obtained in vitro. Assuming equal effect of EMP is obtained in subsequent radiation fractions, the cell kill will be increased from 2-3 to 5-10 logs if delivering 30 fractions of 2 Gy combined with EMP. In the BT4C rat model the combined effect was found to be synergistic. Flow cytometry demonstrated an arrest in G2/M phase in all cell-lines after EMP treatment. This block in G2/M phase in addition to the previously demonstrated induction of free oxygen radicals, and the increase of blood flow with an assumed subsequent increase of oxygenation, might provide an explanation for the observed radiosensitizing effect of estramustine.

Relative biological effectiveness of intermediate energy protons. Comparisons with 60Co gamma-radiation using two cell lines

Range modulated proton beams are used for radiotherapy of malignant tumours at several accelerator laboratories with the aim of introducing proton therapy as a clinical hospital-based therapy modality. Due to the finite range and the sharpness of the dose gradients, the dose to well defined target volumes can be raised without excessive irradiation of non-target tissue. The prescribed proton doses are determined in part on the basis of the relative biological effectiveness (RBE) of the particular radiation quality. In this study, RBE values were determined for a proton beam with a maximal range of 33 mm, which corresponds to an energy of approximately 67 MeV. The range modulated depth-dose distribution, with a 20 mm extended Bragg peak, was mainly designed for high precision treatment of small targets such as uveal melanomas. The tested cell lines, LS-174T and V79-379A, were chosen because of their suitability for clonogenic assays. The cells were irradiated with single doses in the range 2-10 Gy at different depths in the extended peak region of the range modulated proton beam. RBE values were determined by comparing the doses needed to obtain the same reduction in colony formation (0.5, 0.1 and 0.01) as with the reference 60Co gamma source. The mean RBE value was 1.22 with a standard deviation of 0.08. The variations depended on both cell type and on the survival levels considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Backscatter radiation at tissue-titanium interfaces. Biological effects from diagnostic 65 kVp x-rays

The induced secondary electrons from a metal surface by diagnostic x-rays are thought to contribute to cell damage near the tissue-metal boundaries of metal implants. Titanium implants are becoming increasingly more popular for tissue reconstructions and it is rather often desirable to take radiographs of the operated area. In this study we compared the biological effects of radiation on cultured mammalian test cells grown on titanium plates with the radiation effects on cells that were grown on plastic control plates. In order to study the acute radiation effects on cell growth it was necessary to work with rather high radiation doses (0.7-5 Gy). Photon energies, suitable for diagnostic radiography in odontology, 65 kV, were applied. We found that the cells grown on titanium plates were, in terms of the applied dose in the surrounding culture medium, more sensitive to the irradiations than the cells growing on plastic plates. The survival curve for the cells on titanium had a steeper slope, showed no shoulder in the low-dose region and looked like curves normally obtained for high LET radiation. It was not possible to resolve to what degree the titanium-dependent changes were due to an increased dose near the titanium surface or to a change in the radiobiological effectiveness. Although there was a significant decrease in cellular survival near the metal, postoperative intraoral radiography after titanium implantations need not be excluded. The maximal doses given in odontological x-ray examinations are less than 1 mGy and, if the results in this study are applied, the biological effects near the titanium implant will correspond to biological effects in soft tissue of doses less than 20 mGy which is lower than the doses that give acute effects. The risk of acute healing disturbances are significant only at much higher radiation doses.

Backscatter radiation at tissue-titanium interfaces. Analyses of biological effects from 60Co and protons

It has been claimed that implanted metals can cause backscatter radiation in radiation therapy with a dose enhancement at the bone-metal and tissue-metal interfaces on the beam entrance side. Theoretical calculations and experimental measurements with ionization chambers have indicated that such effects might be significant. Titanium implants are increasingly used in oral and maxillo-facial surgery for reconstruction purposes. A more detailed knowledge of backscatter-induced effects is therefore desired when head and neck cancers in patients with implants are treated with radiotherapy. We have made comparisons of cell survival after irradiation of two types of cultured cells grown directly on titanium metal and on plastic control supports. The cell cultures were irradiated with either 60Co photons or range modulated protons. No significant differences in the colony-forming capacity were found between the irradiated cells grown on titanium and those grown on plastic control supports. This was the case for both radiation types and the results were also observed to be dose-independent. The only observed phenomena were that the two cell-lines differed in radiosensitivity and that protons gave higher biological effects than gamma radiation. The results show that there were no significant changes in cell survival at the interface between the tissue equivalent medium and titanium support indicating that a dose increase induced by backscatter radiation, which possibly could demolish the osseointegration or induce osteoradionecrosis, are minimal when high energy photons or range modulated protons are applied.

Radiobiological aspects of continuous low dose-rate irradiation and fractionated high dose-rate irradiation

The biological effects of continuous low dose-rate irradiation and fractionated high dose-rate irradiation in interstitial and intracavitary radiotherapy and total body irradiation are discussed in terms of dose-rate fractionation sensitivity for various tissues. A scaling between dose rate and fraction size was established for acute and late normal-tissue effects which can serve as a guideline for local treatment in the range of dose rates between 0.02 and 0.005 Gy/min and fraction sizes between 8.5 and 2.5 Gy. This is valid provided cell-cycle progression and proliferation can be ignored. Assuming that the acute and late tissue responses are characterised by alpha/beta values of about 10 and 3 Gy and a mono-exponential repair half-time of about 3 h, the same total doses given with either of the two methods are approximately equivalent. The equivalence for acute and late non-hemopoietic normal tissue damage is 0.02 Gy/min and 8.5 Gy per fraction; 0.01 Gy/min and 5.5 Gy per fraction; and 0.005 Gy/min and 2.5 Gy per fraction. A very low dose rate, below 0.005 Gy/min, is thus necessary to simulate high dose-rate radiotherapy with fraction sizes of about 2 Gy. The scaling factor is, however, dependent on the repair half-time of the tissue. A review of published data on dose-rate effects for normal-tissue response showed a significantly stronger dose-rate dependence for late than for acute effects below 0.02 Gy/min. There was no significant difference in dose-rate dependence between various acute non-hemopoietic effects or between various late effects. The consistent dose-rate dependence, which justifies the use of a general scaling factor between fraction size and dose rate, contrasts with the wide range of values for repair half-time calculated for various normal-tissue effects. This indicates that the model currently used for repair kinetics is not satisfactory. There are also few experimental data in the clinical dose-rate range, below 0.02 Gy/min. It is therefore necessary to verify further the presented scaling between fraction size and dose rate.

Accelerated fractionation in advanced head and neck cancer: results and analysis of late sequelae

From 1975 to 1985, 161 patients affected by head and neck cancer (58 oropharynx, 67 oral cavity, 36 paranasal sinuses) were treated with radiotherapy using an accelerated fractionation (AF) schedule at the University and Hospital Radiotherapy Departments of Florence. Most cases, classified with U.I.C.C. and A.J.C. TNM (1978) were advanced (137/161 = 85%). Five-year actuarial local control and survival was 38% for the oropharynx, 18% and 20% for the oral cavity, and 38% and 31% for the paranasal sinuses. Results were analysed according to T and N stage as well. Severe late sequelae were evaluated in 53 patients without local disease and with a minimum follow-up of one year: 8 patients developed osteonecrosis; there were 3 cases of trismus, 2 cases of laryngeal oedema, one case of blindness and one case of ophthalmitis.

Repair of radiation induced damage--dependence on oxygen and energy status

Repair of radiation-induced sublethal damage by Chinese hamster V-79 cells is studied under conditions of different pO2 (15 ppm to 21%) and cellular energy status. Cellular ATP content and energy charge are drastically reduced when cells are deprived of both oxygen and nutrient. Both indices are within normal range when cells are provided with nutrients or trace levels of oxygen (300 ppm). When deprived of nutrient, hypoxic (15 ppm O2) cells do not repair SLD, while cells in 300 ppm O2 do. Thus, cellular SLD repair appears to be dependent on cellular energy status which in turn is sensitive to oxygen concentration. Relatedly, nutrient deprived hypoxic cells are sensitized to radiation with storage under 23 degrees C, a phenomenon which may stem from a decrease of endogenous glutathione content.

Radiation-induced outgrowth inhibition in explant cultures from surgical specimens of five human organs

An explant outgrowth technique to determine the radiation response of five different human organs (bladder, oesophagus, colon, breast and thyroid) is described. In each case except thyroid, where malignancies are rare, data are presented for normal and malignant tissue. Results show that variations in response, consistent with those observed in vivo, can be measured. Tumours were in all cases highly resistant to radiation relative to their corresponding normal tissue. Possible reasons for this are discussed. The method may prove useful in the prediction of the radiobiological response for tumour and surrounding normal tissue where post-operative therapy is planned.

Tumor hypoxia: its impact on cancer therapy

The presence of radiation resistant cells in solid human tumors is believed to be a major reason why radiotherapy fails to eradicate some such neoplasms. The presence of unperfused regions containing hypoxic cells may also contribute to resistance to some chemotherapeutic agents. This paper reviews the evidence that radiation resistant hypoxic cells exist in solid tumors, the assumptions and results of the methods used to detect hypoxic cells, and the causes and nature of tumor hypoxia. Evidence that radiation resistant hypoxic cells exist in the vast majority of transplanted rodent tumors and xenografted human tumors is direct and convincing, but problems with the current methodology make quantitative statements about the magnitude of the hypoxic fractions problematic. Evidence that radiation resistant hypoxic cells exist in human tumors is considerably more indirect than the evidence for their existence in transplanted tumors, but it is convincing. However, evidence that hypoxic cells are a significant cause of local failure after optimal clinical radiotherapy or chemotherapy regimens is limited and less definitive. The nature and causes of tumor hypoxia are not definitively known. In particular, it is not certain whether hypoxia is a chronic or a transient state, whether hypoxic cells are proliferating or quiescent, or whether hypoxic cells have the same repair capacity as aerobic cells. A number of new methods for assessing hypoxia are reviewed. While there are still problems with all of the new techniques, some of them have the potential of allowing the assessment of hypoxia in individual human tumors.

Survival curves of glutathione synthetase deficient human fibroblasts: correlation between radiosensitivity in hypoxia and glutathione synthetase activity

The role of intracellular non-protein bound sulphydryl compounds (NPSH), and in particular that of glutathione (GSH), in the response of cells to ionizing radiation under different O2 concentrations has been assessed using cell strains deficient in glutathione synthetase and exhibiting different NPSH levels. The cell strains used originated from patients with 5-oxoprolinuria and from their relatives (heterozygotes and proficient homozygotes). No correlation has been found between NPSH and GSH concentrations and radiosensitivity under oxic, aerobic and hypoxic conditions. However, a highly significant correlation has been observed between radiosensitivity under hypoxic conditions (and therefore the oxygen enhancement ratio) and the glutathione synthetase activity, suggesting that synthesis of GSH is required after irradiation. In order to explain our results we postulated, beside radical processes, the existence of a GSH-dependent enzymatic repair mechanism for N2 type damage. Hypoxic radio-sensitivity measured with survival curves would result from the interaction of both competition and biochemical repair processes.

Radiation dose dependence of the sensitization by oxygen and oxygen mimic sensitizers

New and old evidence is discussed which suggests that the oxygen enhancement ratio (OER) is decreased at lower radiation doses as compared with that of higher radiation doses. In addition, there is evidence that cells irradiated in severe hypoxia have an impaired ability to recover from sublethal damage. However, there is also contrary evidence to these observations. Thus the suggestions that oxygen is not strictly a dose modifying agent have been controversial from the very beginning. It is hoped that new experimental undertakings currently performed in many different laboratories will resolve these issues as well as explain the controversy which has lasted more than 25 years in this field of radiobiologic research.

Oxygen radiosensitisation at low dose rate

Oxygen radiosensitisation has been studied at dose rates of 600, 3.37 and 0.89 Gy/h at pO2 levels of 0.001, 0.03, 0.1, 0.3, 1, 3, 10 and 21% in the gas phase. The oxygen enhancement ratio (OER), evaluated at 2% cellular survival, exhibited a decrease with dose rate from a value of 3.2 at the acute dose rate, to 2.4 at the lowest dose rate. This observation results from a decreased dose-rate effect on hypoxic cells, which is attributed to the partial suppression of sublethal damage (SLD) repair under hypoxic conditions. Oxygen radiosensitisation at the acute dose rate agrees with the calculated values based on the oxygen fixation hypothesis. Direct application of the Howard-Flanders and Moore equation to results obtained at low dose rate is not appropriate due to the influence of pO2 on SLD repair which affects radiosensitivity at low dose rate. When cells are irradiated at 3.37 Gy/h under nutrient-deprived condition (i.e. in Hanks balanced salt solution without glucose), low levels of oxygen appear to be more radioprotective than extreme hypoxia. Specifically, cells irradiated with 0.03% and 0.1% O2 are more radioresistant than cells under N2, with enhancement factors of 0.7 and 0.8, respectively. This phenomenon can be understood in terms of the ability of moderately hypoxic cells (0.03%-0.1% O2), and inability of anoxic cells, to repair SLD under nutrient deprived conditions. Radiosensitisation by these low levels of oxygen is insufficient to offset the difference caused by the disparate SLD repair capabilities.

Hypoxic fractions of solid tumors: experimental techniques, methods of analysis, and a survey of existing data

Hypoxic fractions are measured by indirect techniques, which compare the response of tumors to large single doses of radiation given under normal aeration and artificial hypoxia. This paper reviews hypoxic fraction measurements and measurement techniques, giving particular attention to the biological, technical, and statistical aspects of the assays; the implicit assumptions underlying the analyses; and the dependence of the determinations on the assay conditions and the tumor and host characteristics. The three major hypoxic fraction assay techniques (paired survival curve, clamped tumor control, and clamped growth delay) share common biological assumptions. They require that the survival curves of naturally and artificially hypoxic cells have the same slope and intercept. They assume that the majority of the cells are either fully oxic or fully hypoxic. They assume that the methods used to induce artificial hypoxia leave no oxygenated regions and that tumor cells rendered artificially hypoxic are no less viable than cells in normally-aerated tumors. The universal validity of these assumptions is questionable. Each technique uses additional special assumptions and each may measure a different population of hypoxic cells. This paper reviews 92 hypoxic fraction determinations in 42 tumor systems. Radiobiologically hypoxic cells appear to be present in the majority of macroscopic solid rodent tumors. The hypoxic fraction was found to increase as the tumor size increased from microscopic to macroscopic; the dependence of hypoxic fraction on tumor size at macroscopic sizes was less clear. The site of tumor implantation, the use of anesthesia, and certain host characteristics may influence the hypoxic fraction. The hypoxic fraction generally did not depend on the tumor growth rate, transplantation history, or histology. These findings indicate that hypoxic cells are a common feature of solid tumors in rodents and provide no evidence that hypoxic cells should not be present in human tumors.

Electro-physiological measurements in cultured cellular spheroids

Human Glioma U-118 MG and hamster V-79-379A spheroids were used as models of the nodular structure often seen in poorly vascularized regions of solid tumours. K+, Ca2+ activities and membrane potentials were measured in the spheroids, using microelectrodes. Both stable and peak values were obtained. All values were included in the analysis to allow an accurate estimate of the relative number of electro-physiologically active cells at different depths in the spheroids. The relative number of active cells decreased drastically with depth although most cells in the corresponding regions looked morphologically viable. The amplitude values of potentials and K+ activities showed, however, no significant variations with depth. The Ca2+ activity varied largely between individual cells. The relative number of proliferative cells decreased with depth in the spheroids, in parallel to the decrease in the number of electro-physiologically active cells. The results indicate that the fraction of cells, in poorly vascularized regions, having normal metabolism might be fewer than what can be estimated only on a morphological basis. Thus, the amount of cells with the capacity to contribute to growth might be overestimated when inspecting histological sections.

Methodological aspects of microelectrode measurements in cellular spheroids

Different types of oxygen microelectrodes have been tested in measurements on cellular spheroids. The shape of the oxygen gradients varied strongly depending on size and type of the spheroids. No significant differences in the results were obtained when different types of electrodes were applied. All measurements were made in a perfusion chamber. The shape of the gradients did not vary with time in the perfusion chamber. The reproducibility was found good in repeated measurements using the same spheroid. No mechanical or chemical disturbances were seen during the penetration of the spheroids. Changes in the medium flow rate through the chamber did not drastically change the shape of the oxygen gradients. Almost no convection could be seen at the bottom of the chamber close to the spheroids. The composition of the medium was found to be of importance. Lock's solution containing glucose was found to be satisfactory. The potential signals in the double barrel electrodes allowed an accurate determination of the position when the electrode hit the spheroid surface. The information gained from microelectrode measurements in spheroids might be valuable for the understanding of effects of new tumor treatment modalities in which hypoxic cell sensitizers or high LET radiation are utilized.

The potential benefit from a perfect radiosensitizer and its dependence on reoxygenation

The potential benefit of a perfect radiosensitizer has been assessed by computing the sensitization ratios that would be observed in a mixed population of oxic and hypoxic cells if different reoxygenation rates existed. The sensitizer has been assumed to be as effective as oxygen, completely non-toxic and freely diffusible to all hypoxic cells within the tumour. The calculations have been made for several different clinical fractionation regimes, namely 30, 20, 9 or 6 fractions, all with the same ret dose (NSD = 1700 rets). These calculations have allowed us to deduce how large the observed sensitization would be for differing rates of reoxygenation and for the different fractionation schemes. The size of the extrapolation number is seen to be an important parameter in these calculations. They have allowed us to indicate how much reoxygenation would be needed to abolish the benefit from (and hence the need for) a perfect radiosensitizer.

Radiation-dose dependence of the formation of micronuclei in misonidazole treated cell cultures

The effect of misonidazole at different concentrations on the anoxic radiation sensitivity of Chinese hamster cells was investigated using the frequency of radiation induced micronuclei as criterion. The result indicates that, in a high radiation dose region, sensitization with a dose modifying factor of about 1.9 and 1.3 occurs after treatment with the substance at a concentration of 8 and 0.2 mmol/l, respectively. In a low dose region the corresponding values were 1.7 and 0.8. It was concluded that high concentration of the substance in combination with high radiation doses are most beneficial.

Lack of oxygen effect in glutathione-deficient human cells in culture

The frequency of X-ray-induced DNA breaks was determined in human cell lines which are deficient in glutathione synthetase and have a greatly reduced glutathione content. Hydroxyapatite chromatography was used for the estimation of the DNA breaks in cell cultures, which were derived either from lymphoblasts transformed by infection with EB virus or from fibroblasts. The dose-effect relationship for the induction of breaks when radiation exposure was made in argon, was similar to that found when exposure was made in air. In control cultures with normal glutathione content, the induction of breaks was enhanced when irradiation was made under aerobic, instead of anaerobic, conditions. Treatment of the glutathione-deficient cells with the hypoxic radiosensitizer misonidazole did not enhance the induction of breaks by radiation delivered either in air or in argon. In control cultures, radiation induction of breaks was enhanced by misonidazole under anaerobic but not under aerobic conditions. When the glutathione-deficient cells were pretreated with cysteamine however, irradiation in the absence of oxygen resulted in a decreased frequency of DNA breaks.

Recovery from sublethal damage by acutely hypoxic tumour cells in vivo and in vitro

The ability of acutely hypoxic tumour cells to recover from sublethal damage following irradiation in vivo and in vitro has been measured using a single tumour system. The methods of assay were tumour growth delay, local tumour control and tumour cell survival in vitro following treatment in vivo or in vitro. Tumours in vivo or cells in vitro rendered acutely hypoxic during irradiation were irradiated with either single doses or two doses 24 hours apart. Cells left in situ had a greater capacity for recovery than those treated either in vivo or in vitro and then assayed in vitro. It is suggested that tumours may not show a systematically reduced capacity for recovery relative to normal tissues, unless chronically hypoxic tumour cells have a reduced capacity for recovery and determine the response. However, the results imply that deductions as to the ability of tumour cells to recover from sublethal damage (whether chronically hypoxic or not), which rely on in vitro assays, may underestimate the extent of recovery.

The effect of oxygen concentration on the X-ray induction of chromosome aberrations in human lymphocytes

In vitro dose--response curves, for unstable chromosome aberration induction in human lymphocytes under conditions of full oxygenation or of anoxia, have been obtained using 250 kVp X-rays. Dicentric yields have been fitted to the quadratic function Y = alpha D + beta D2. An Oxygen Enhancement Ratio (OER) ranging from 7.2 to 2.7 was calculated from the coefficients of these curves possibly indicating that the data do not fit to the dose-modifying model of the oxygen effect although the differences are not statistically significant. A similar analysis of total aberration data yields an OER of 3.6 to 2.7 fitting much more satisfactorily to the dose-modifying model. Variations in dicentric yield induced by 3.0 Gy and 0.75 Gy of X-rays with increasing oxygen concentration were plotted and for each dose a constant dicentric yield was observed at oxygen levels of 2 and 250 ppm. Above 250 ppm yields increased steeply up to about 1% oxygen and then more gradually to a maximum at 100% oxygen.

Alterations in the survival of X-irradiated cells by 2,4-dinitrophenol depending on ATP deprivation

The dose-survival curve of cultured melanoma cells was changed by post-irradiation treatment with 2,4-dinitrophenol (DNP). The parameters of the curves were Do = 147 R and n = 5 . 6 for untreated cells and Do = 143 R, n = 7 . 9 and Do = 142 R, n = 2 . 0 for the cells treated with 10(-5) M DNP and 5 x 10(-5) M DNP in phosphate-buffered saline, respectively. The content of ATP in the cell decreased to 5% of the control level after treatment with either concentration of DNP. The recovery of ATP content was rapid and complete after 2 hours' incubation in culture medium after the removal of 10(-5) M DNP, but was retarded and incomplete after 4 hours with 5 x 10(-5) M DNP. Thus prolonged ATP deprivation with a high concentration of DNP results in an inhibition of recovery and a reduction in the n-value.