Effect of misonidazole on radiation injury to mouse spinal cord

Cellular kinetics of murine lung: model system to determine basis for radioprotection with keratinocyte growth factor

PURPOSE

Normal tissue toxicity remains a dose limitation for cancer radiotherapy and chemoradiotherapy. Growth factors offer a novel means of mitigating normal tissue radiotoxicity. In particular, keratinocyte growth factor (rHuKGF), whose proliferative activity is restricted to epithelial cells, holds promise on the basis of the findings of preclinical models of epithelial cytoprotection and the clinical developments to date. We report the radioprotection of murine lung by an increase in tissue cellularity after rHuKGF-induced proliferation.

METHODS AND MATERIALS

Flow cytometric and image analysis techniques after bromodeoxyuridine labeling were used to estimate proliferative parameters. Our specialized analytical methods measure not only labeling indexes, but also the durations of S and G(2)+M phases, potential doubling times, and the net cell production rate. Image analysis techniques were used to identify the specific cell types that were proliferating (type II pneumocytes).

RESULTS

Lung labeling index control values (0.5%) rose to a maximum (5.5%) at 3 days after intratracheal rHuKGF, returning to normal by Day 7. The potential doubling time fell from 66 days to 4.4 days. The net cell production rate rose from a control value of 1%/d to >15%/d by Day 3. This resulted in a nearly twofold increase in alveolar epithelial cellularity, which remained significantly elevated on Day 7. Saline-treated control animals exhibited no significant changes in the proliferative parameter values or cellularity. On the basis of these data, mice were irradiated, solely to the thorax, with ranges of single doses of 250 kVp X-rays 7 days after either intratracheal administration of 5 mg/kg rHuKGF or phospate-buffered saline. This interval was chosen because the proliferative response of the type II cells was finished but the cellularity of the lung remained increased. Pretreatment with rHuKGF extended the latent period before onset of pneumonitis after all radiation doses. rHuKGF treatment 7 days before thoracic irradiation significantly protected against pneumonitis (median effective dose 13.7 Gy, 95% confidence limit 13.4-14.0) compared with the control pretreatment with phosphate-buffered saline (median effective dose 12.8 Gy, 95% confidence limit 12.6-13.1).

CONCLUSION

The data showed that an increase in tissue cellularity, caused by rHuKGF treatment before irradiation, protected the lung from damage due to pneumonitis.

Murine animal model

Experimental animal models are available for the development of new treatment. Murine animal models have particular advantages for comparative study to evaluate the efficacy and safety of different treatment modalities because many mice can be treated at the same time with easy handling. Among several experimental models, murine renal carcinoma (Renca), which arises spontaneously in Balb/c mice, is the most frequently used for the assessment of chemotherapy, immunotherapy, and radiotherapy. Renca cells readily establish tumors in isogenic mice, producing histologically proven adenocarcinoma with a predictable growth rate to mimic the clinical situation for orthotopic growth and metastasis in a reasonable time frame. Because of its poor immunogenicity and its responsiveness to immunotherapy, the number of studies using cytokine gene-modified tumor vaccines-such as interferon-alpha or interleukin-2-in the Renca system is growing. Therefore, Renca experiments greatly contribute to the analysis of the mechanisms of antitumor immune response. In this chapter, we describe several experimental systems using this Renca model.

Spatial heterogeneity of the volume effect for radiation pneumonitis in mouse lung

PURPOSE

In a previous study to determine the effect of partial volume irradiation on damage and morbidity from pneumonitis in mouse lung, a critical determinant of the volume effect was the spatial location of the irradiated subvolume within the lung. The goals of the present study were to (a) define the dose-volume effect curves for radiation pneumonitis in mouse lung, (b) define the threshold volume, and (c) further investigate the spatial heterogeneity of the radiosensitivity of mouse lung.

METHODS AND MATERIALS

Eight fractional volumes ranging from 94% to 17% of the lungs of C3Hf/Kam mice were irradiated with single doses ranging from 12 to 22 Gy, depending on the volume irradiated. The fractional volumes irradiated were determined from computed tomographic scans of mouse lung. To determine the effect of location of irradiated subvolume, equivalent volumes in the base and the apex were irradiated by shielding the prescribed adjacent volume in the apex or base respectively. Dose-response curves of breathing rate at 22 weeks and lethality at 28 weeks were constructed for each subvolume irradiated in the apex or base and fitted by logit analysis, and ED50s and LD50s with 95% confidence limits obtained, respectively. Lungs from dead mice or mice sacrificed when moribund were examined for histologic signs of pneumonitis.

RESULTS

Irradiation of any of the eight subvolumes in the base yielded a consistently lower isoeffect dose for both assays of radiation pneumonitis than if the same irradiated subvolume was located in the apex. Plots of isoeffect dose for breathing rate as a function of subvolume irradiated in the base or apex showed that these curves were not linear but exhibited a plateau between irradiated volumes of 70% and 80% in both the apex and base. A similar curve was obtained for lethality and volume irradiated in the base. A threshold volume, i.e., irradiation of that volume that should produce no changes in breathing rate or mortality, was dependent on the location of the irradiated subvolume.

CONCLUSION

The response of mouse lung to partial volume irradiation is heterogeneous and is critically dependent on the specific location of the irradiated subvolume in the lung, i.e., a given subvolume in the base is consistently more sensitive than the same subvolume in the apex using either breathing rate or lethality as assays of radiation pneumonitis. We suggest that this heterogeneity is due to the anatomy of the tracheobronchial tree, i.e., to the distribution of non-gas exchange-conducting airways in the irradiated volume. These data have implications for the modeling of dose-volume effects in the lung and the prediction of normal tissue complication probabilities for radiation pneumonitis in humans.

Damage and morbidity from pneumonitis after irradiation of partial volumes of mouse lung

PURPOSE

The aims of this study were to: (a) define the relationship of dose and volume irradiated to damage and morbidity in mouse lung, (b) determine the threshold volume for morbidity after partial lung irradiation; and (c) determine whether the response to radiation of mouse lung is independent of the region irradiated.

METHODS AND MATERIALS

C3Hf/Kam female mice were used in this study. The fractional volume of the lung to be irradiated was determined by two methods, weights and computed tomography (CT) scanning. Two experiments were performed to define the volume effect and to determine whether the response of the mouse lung to radiation was homogeneous. In the first experiment, single doses of x-rays ranging from 12 to 20 Gy were given to partial volumes of 84%, 70%, and 40% including the base, 50%, 33%, and 17% including the apex, to 43% in the middle, and to the sum of 57% as 17% in the apex and 40% in the base. In the second experiment, the same volumes of 50% and 70-75% in the apex and base of the lung were irradiated with single doses ranging from 12-19.25 Gy. Morbidity from radiation pneumonitis was quantitated by two end points, breathing rate and lethality between 12 and 32 weeks after irradiation. Damage was assessed by histopathological evidence of pneumonitis.

RESULTS

Clear well-defined dose-response curves were obtained for both breathing rate and lethality after all volumes irradiated. There was a clear volume-dependent shift of the dose-response curves for breathing rate and lethality at 28 weeks after irradiation, the end of the pneumonitis phase of damage, to higher doses compared with these data after whole-lung irradiation. In addition, the slopes of the dose-response curves for irradiation of partial lung volumes were more shallow compared to those after whole-lung irradiation. Increases in breathing rate correlated with lethality when the volume irradiated was equal to or greater than 50% of the reference volume. However, after irradiation of volumes smaller than 40%, breathing rate increases were not accompanied by death. A heterogeneous response of the mouse lung to radiation was observed in the first experiment and confirmed by the second experiment. For a given volume irradiated, the isoeffect dose was always less for the base than for the apex of the lung. The threshold volume for breathing rate changes was less than 17 and 40% when the irradiated volumes involved the apex and base, respectively. For lethality, the threshold volume was between 40 and 70% for the base and greater than 50% for the apex of the lung. Finally, damage as assessed by histological evidence of pneumonitis was observed in the irradiated area only.

CONCLUSIONS

(a) The volume effect was resolvable in mice, (b) the volume effect in mouse lung exhibits a clear threshold for morbidity, (c) the threshold volume for morbidity is dependent on the end point, (d) the response of mouse lung is heterogeneous, dependent on the site irradiated, and is always greater for the same volumes irradiated in the base than the apex, and, (e) histopathological damage does not always produce observable morbidity.

The extent, time course, and fraction size dependence of mouse spinal cord recovery from radiation injury

PURPOSE

This experiment was designed to assess: (a) the influence of fraction size and time interval between fractions on the tolerance of the spinal cord to high cumulative doses of radiation; and (b) the influence of the long-term recovery process on the tolerance of the spinal cord to reirradiation.

METHODS AND MATERIALS

The T10-L2 level of the spinal cord of C3Hf mice was irradiated using a conventionally fractionated regimen of 2.0 Gy once daily, a prolonged fractionated regimen of 1.2 Gy once daily, a hyperfractionated regimen of 1.2 Gy twice daily, or a single dose of 12 Gy followed 0-190 days later by a second dose of 5-20 Gy. Mice in the multifractionated regimen groups were given a single 15 Gy top-up dose 24 h after reaching a cumulative fractionated dose of 24-70 Gy. Hind limb strength was measured weekly for 2 years after the completion of irradiation.

RESULTS

Paralysis occurred in a bimodal time distribution, with peaks at 5-10 months and 15-23 months after the completion of irradiation. The cumulative radiation dose was directly associated with the incidence of paralysis in each radiation schedule (p < 0.0001) and inversely associated with the time to onset of paralysis in the 1.2 Gy b.i.d. (p = 0.0001) and 2.0 Gy q.d. schedules (p = 0.03). The median latency of paralysis in each group was inversely associated with the incidence of paralysis in that group (p < 0.001). Decreasing the fraction size from 2.0 to 1.2 Gy once daily markedly increased the radiation tolerance of the spinal cord (p < 0.0001), consistent with a very small alpha-beta value of -0.30 Gy (approximately 95% confidence interval -0.72, +0.18) in the linear-quadratic model. Decreasing the time interval from 24 h to alternating 8 and 16 h periods produced an offsetting diminuation in cord tolerance (p < 0.0001). The 1.2 Gy once daily schedule resulted in ED20 and ED50 values that were approximately double those of the 2.0 Gy once daily and the 1.2 Gy twice daily schedules and a relative risk of paralysis from a given dose that was 0.03 times the risk associated with the other two regimens (p < 0.0001). There was no significant difference between the 2.0 Gy once daily and the 1.2 Gy twice daily dose-paralysis curves (p = 0.86). The residual from a single 12 Gy radiation dose was 17% after 190 days, leaving the retreatment ED50 only 10% below the ED50 of previously unirradiated spinal cord. The relative risk of paralysis after 12 Gy plus a second radiation dose decreased from 1.00 with no time interval between doses to 0.51-0.73 with a 0.25, 1 or 3 day interval, 0.32 with a 7 day interval, 0.11 with a 30 day interval, and 0.06 with a 190 day interval.

CONCLUSION

The increased radiation tolerance of the murine spinal cord produced by decreasing the fraction size from 2.0 to 1.2 Gy was offset by the diminished tolerance produced by decreasing the time interval between fractions from 24 to 8-16 h, resulting in no significant difference in the dose-paralysis curves of conventional and hyperfractionated radiation schedules. The rodent spinal cord eliminates the majority of the occult radiation injury produced by a radiation dose equal to half the ED50 during the months following irradiation. This permits retreatment of previously irradiated spinal cord to high doses without the induction of myelopathy.

Synergy of radiation therapy and immunotherapy in murine renal cell carcinoma

The treatment of metastatic renal cell carcinoma with immunotherapy has resulted in objective anti-tumor responses in 15-30% of patients. To enhance the therapeutic effects of immunotherapy, it is becoming evident that this approach should be combined with other treatment modalities. In this study, a spontaneously metastasizing murine renal adenocarcinoma (Renca), transplanted under the renal capsule, was treated with either radiation therapy, immunotherapy or a combination of both. In order to distinguish between the local and systemic effects of radiation therapy, total body irradiation was compared to irradiation of the tumor-bearing kidney only, or irradiation of the whole mouse with the tumor-bearing kidney shielded. Immunotherapy was administered with interleukin-2 (IL-2) alone or with IL-2 and lymphokine activated killer (LAK) cells. Combined radiation and immunotherapy induced a better anti-tumor response than either modality alone. The best response was obtained by local tumor irradiation and IL-2 therapy and resulted in a significant reduction in primary tumor size, elimination of lung metastases and a significant increase in survival.

Alteration in myelin-associated proteins following spinal cord irradiation in guinea pigs

The aim of this study was to investigate the pathological and cellular basis for radiation-induced myelopathy in guinea pigs by monitoring biochemical alterations in levels of myelin basic protein and 2',3'-cyclic nucleotide phosphohydrolase. Guinea pigs were irradiated to the lumbar region with various doses of neutrons or cobalt gamma irradiation. The ED50s for paralysis were 17.2 Gy and 67.5 Gy for neutron and cobalt irradiation, respectively, and was histologically associated with demyelination. In spinal cords taken from animals at the onset of paralysis myelin basic protein levels were decreased in direct relationship to the radiation dose. The lowest doses to cause paralysis led to a 25% decrease in MBP levels. In a separate experiment, alterations in MBP were measured in the spinal cords over the time period leading up to paralysis. Surprisingly, decreases in MBP were found immediately after the end of the 4 week irradiation period. These early changes in MBP were not markedly dose dependent and occurred with nonparalyzing doses. Dose-dependent decreases were found only just before the onset of paralysis. CNPase activity measured in the same specimens showed changes that were essentially similar to those for MBP. In the CSF, MBP levels were essentially constant until onset of paralysis. This study showed that demyelination, as assessed by the levels of the myelin-associated proteins MBP and CNPase, can occur soon after spinal cord irradiation but that profound dose-dependent changes are seen only immediately preceding the onset of paralysis. Although increases in MBP in the CSF were associated with the onset of radiation-induced myelopathy, its assay is unlikely to predict this complication of irradiation.

Cyclophosphamide 24 hours before or after total body irradiation: effects on lung and bone marrow

Preparative regimens for bone marrow transplantation (BMT) use a sequence of drugs, such as cyclophosphamide, in combination with radiation. However, the optimum sequencing of the two agents that will maximize tumor cell kill and minimize normal tissue damage is unknown and controversial. The studies presented here were done in order to determine the effect of cyclophosphamide on bone marrow and lung damage in mice when given 24 h before or after total body irradiation (TBI). A range of single doses of TBI was given before or after a single sublethal dose of 180 mg/kg of cyclophosphamide. The bone marrow of all mice intended for lung damage assessment was reconstituted with 5 x 10(6) syngeneic bone marrow cells. Lung damage was assessed by breathing rate and lethality; bone marrow damage by lethality at 30 days. LD50 values for pneumonitis were obtained between 30 and 84 days after cyclophosphamide and radiation and between 80 and 180 days after radiation alone. Dose modifying factors were obtained as the ratio of LD50s for mice given only TBI compared to those for mice given cyclophosphamide and TBI. Cyclophosphamide enhanced radiation pneumonitis when given before or after TBI, giving DMFs of 1.4 and 1.2 (1.1-1.4, 95% c.l.) respectively. The effect of cyclophosphamide on radiation pneumonitis was drug dose-dependent. The LD50 for death from bone marrow damage was reduced when cyclophosphamide was given either before or after TBI but the effect was greater, i.e. the LD50 was lower when cyclophosphamide was given after TBI. These data show that cyclophosphamide given 24 h after TBI causes less lung damage but more bone marrow damage in this mouse model.

Manipulation of the radiosensitivity of pig epidermis by changing the concentration of oxygen and halothane in the anaesthetic gas mixture

A gas mixture of halothane, oxygen and nitrous oxide has been used to anesthetize pigs for irradiation. The effects of various concentrations of halothane and oxygen on the radiosensitivity of the epidermis were examined after irradiation with single doses of beta-rays from strontium-90 plaques. The incidence of moist desquamation was used as an endpoint, and experiments were compared on the basis of the dose associated with a 50 per cent incidence of moist desquamation (ED50 +/- SE). For pigs inspiring an anaesthetic gas mixture of 2 per cent halothane, approximately 70 per cent oxygen and approximately 30 per cent nitrous oxide the ED50 for moist desquamation was 27.32 +/- 0.52 Gy. A similar ED50 value of 27.39 +/- 1.20 Gy was obtained when 4 per cent halothane was used in place of 2 per cent. When the pigs were breathing air (approximately 21 per cent oxygen) in place of oxygen and nitrous oxide the ED50 values were increased significantly to 31.25 +/- 0.94 Gy and 33.72 +/- 1.08 Gy for 2, and 4 per cent halothane, respectively. This change in the radiosensitivity of the epidermis was represented by dose modification factors of approximately 1.13 and approximately 1.23 for 2 and 4 per cent halothane, respectively. Irradiation with a high oxygen concentration in the inspired gas mixture did not result in any significant variation of the dose required to produce moist desquamation in 50 per cent of the fields irradiated for dorsal, lateral and ventral positioned skin fields on the flank. However, pigs breathing air and halothane during irradiation showed marked differences in the radiosensitivity of the various sites on the flank, with ED50 values for moist desquamation of approximately 37 Gy and 26-30 Gy for dorsal and ventral positioned fields, respectively. This marked difference in radiosensitivity suggests variations in the physiological compensation over the flank when pigs are breathing oxygen at low concentrations under anaesthesia.

The influence of bone marrow depletion on intestinal radiation damage

These experiments were designed to test the hypothesis that bone marrow damage contributes to lethality when the endpoint used is LD50 for gastrointestinal damage. Specific pathogen-free mice were irradiated to the total body, total abdomen, or to the total body followed by rescue with syngeneic bone marrow cells. The relationship between animal survival and jejunal crypt survival was also examined under these three experimental conditions. The LD50/10 after total abdominal irradiation (15.6 Gy) was higher than that for total body irradiation (11.4 Gy). Rescue with syngeneic bone marrow cells after total body irradiation also increased the LD50 10 days to 14.6 Gy. The proportion of animals surviving after total body irradiation depended on the number of bone marrow cells injected as a rescue inoculum. Hence gastrointestinal death after total body irradiation is influenced by bone marrow depletion. Crypt survival, however, was similar following all three experimental procedures. These data, therefore, demonstrate a dissociation between a clonogenic and lethality assay of intestinal damage. Furthermore, a comparison of crypt survival at the LD50 under the different conditions showed that a factor of 10 times more crypts were needed to rescue a mouse from gut lethality when the total body was irradiated than when only the total abdomen was treated. Hence, the concept of the intestinal "tissue rescuing unit" as a precise and constant number of crypts is inappropriate and will vary with the experimental conditions.

Residual radiation damage in murine lung assessed by pneumonitis

The amount of radiation damage remaining in mouse lung has been assessed by retreatment from 1 to 6 months after a range of first doses. Pneumonitis at 196 days after retreatment was used as the endpoint. Lungs were first irradiated with a range of single doses (6-10 Gy). Ten Gy was the highest dose that, on its own, produced no changes in breathing rate or deaths due to pneumonitis. One to 6 months later lungs were retreated with a full range of single doses. Isoeffect doses were calculated for lethality for all retreatment times after each priming dose. The amount of residual damage remaining in the lung has been calculated as both a proportion of first doses and as the effect equivalent of remembered dose. Following a 10 Gy first dose, there was evidence of remembered irradiation injury at all retreatment intervals. After a 6 Gy priming dose, the lungs could be retreated to tolerance. The amount of residual damage was proportional to the size of first dose and was highest at 1 month (27% after 6 Gy and 70% after 10 Gy) and lowest after 3 months (0% after 6 Gy and 46% after 10 Gy). This partial recovery of lung function between 1 and 3 months was followed by an increase in amount of damage "remembered"; that is, a reduction in the retreatment dose that could be delivered. The proportion of residual damage after 10 Gy was never less than 25%. The data suggest an early target cell depletion and regeneration in the lung (within 3 months), the extent of which is dependent on the size of initial injury.

The kinetics of repair in mouse lung after fractionated irradiation

The kinetics of repair of sublethal damage in mouse lung was studied after fractionated doses of 137Cs gamma-rays. A wide range of doses per fraction (1.7-12 Gy) was given with interfraction intervals ranging from 0.5 to 24 h. The data were analysed by a direct method of analysis using the incomplete repair model. The half-time of repair (T1/2) was 0.76 h for the pneumonitis phase of damage (up to 8 months) and 0.65 h for the later phase of damage up to 12 months. The rate of repair was dependent on fraction size for both phases of lung damage and was faster after large dose fractions than after small fractions. The T1/2 was 0.6 h (95 per cent c.1. 0.53, 0.69) for doses per fraction greater than 5 Gy and 0.83 h (95 per cent c.1 0.76, 0.92) for doses per fraction of 2 Gy. Repair was nearly complete by 6 h, at least for the pneumonitis phase of damage. To the extent that extrapolation of these data to humans may be valid, these results imply that treatments with multiple fractions per day that involve the lung will not be limited by the necessity for interfraction intervals much longer than 6 h.

Effects of fractionated schedules of irradiation combined with cis-diamminedichloroplatinum II on the SCCVII/St tumor and normal tissues of the C3H/KM mouse

The interaction of cis-diamminedichloroplatinum II (c-DDP) and a course of 5 daily irradiations was investigated in the SCCVII/St tumor and normal tissues (duodenal crypt cells and lung) of the C3H mouse. Two schedules with daily doses of 2.4 mg/kg c-DDP given immediately before 4 Gy X ray on 5 consecutive days and a single 12 mg/kg c-DDP dose followed 24 hr later by the first of 5 daily 4 Gy X ray doses produced the most consistent and significant supra-additive effects on the SCCVII tumor. This supra-additive effect was also achieved with lower and much less toxic drug doses. These schedules produced high enhancement ratios (dose effect factors DEF) for mouse duodenal crypt cells, but the degree of enhancement was less than that for the SCCVII tumor. Schedules with a 72-hr interval between drug and radiation treatments, which produced low enhancement ratios for the SCCVII tumor and duodenal crypt cells, gave high enhancement ratios for the lung. It is concluded that c-DDP has the potential of enhancing the radiation effect on normal tissues, and the degree of enhancement depends upon the interval between X ray and c-DDP. The enhancement ratios for the SCCVII tumors are greater than for normal tissues, and this results in high therapeutic gain factors (TGF). Comparing the effects on tumor with those on normal tissues, it may be seen that there is clinical usefulness in simultaneous combination treatments and perhaps moreso in the administration of a single drug dose 24 hr before the first of 5 daily X ray fractions.

WR 2721 modification of type II cell and endothelial cell function in mouse lung after single doses of radiation

The ability of WR 2721 to protect endothelial cells and Type II cells in mouse lung after single doses of X rays was studied using specific assays of cell function to assess damage. The whole thorax of mice was exposed to a range of single doses of X rays either alone or 30 minutes after an i.p. injection of 400 mg/kg of WR 2721. Endothelial cell function was assayed by angiotensin converting enzyme (ACE) and Type II cell function by phosphatidylcholine and total protein present in lavage fluid 28 days after radiation. Similar protection factors (PFs) were found for the functional activity of both cell types, 1.2 and 1.24 for ACE and phosphatidylcholine respectively. These values were somewhat less than the PF of 1.37 for lethality from pneumonitis 7 to 9 months after irradiation for this mouse strain. The lack of a clear difference between the PFs for the functional activity of these two cell types suggests that neither the endothelial cell nor the Type II cell can be accepted or excluded as the target cell for radiation pneumonitis in lung.

The influence of overall treatment time on renal injury after multifraction irradiation

The influence of overall treatment time on the radiation response of the mouse kidney was studied in an experiment in which 16 fractions were administered either evenly distributed over 20, 40 or 80 days, or as a split course (8 F/3 days; 74 days rest; 8 F/3 days). Urine output and an isotope assay of glomerular filtration were used to test the mice sequentially. The data were used both to obtain dose-response curves and also to determine the latent period before a chosen level of injury was expressed functionally. Prolonging the overall time from 20 to 80 days increased the isoeffect dose by 2-5 Gy (4-9%) for the isotope assay, and by 4-9 Gy (7-18%) for the urine output assay. This additional recovery as the interval between fractions was prolonged from 1 to 5 days is consistent with slow repair and can be expressed as a small "T" exponent of 0.02-0.12. (One analysis gave a result consistent with negative repair, but the errors on this result were unusually wide.) When the radiation was given as a split course, at the rate of 2 fractions per day, with a large gap of 10.5 weeks between courses, there was no additional sparing compared with 16 fractions over 20 days. This indicates that any sparing that might have resulted from slow repair or stimulated repopulation in the gap has been counterbalanced by having less time for repair of sublethal injury when intervals of 6-12 h are used instead of 24-48 h. Clearly no great increase in the tolerance dose for mouse kidney resulted from the split course.

Protection of mouse lung by WR-2721 after fractionated doses of irradiation

The radioprotective effect of WR-2721 on mouse lung has been studied after single doses, 4 or 7 equal fractions of X rays. Using breathing rate and lethality to measure lung injury up to 1 year after radiation, significant protection against both pneumonitis at 7 months and fibrosis at 12 months was observed using 300 mg/kg of WR-2721. The degree of radioprotection was similar for pneumonitis and fibrosis and was not less after doses per fraction of 4.0 Gy. These data indicate that protection of mouse lung by WR-2721 will not be less in a multifractionated schedule of radiation, at least for doses per fraction greater than 4.0 Gy.

The effect of breathing 100% oxygen on lung response to radiation in mice

The response of the lung after single doses of radiation was measured in mice breathing air, or 100% oxygen, or in air-breathing mice given the hypoxic cell sensitizer misonidazole 30 min before irradiation. There was a clear enhancement of only the pneumonitis response in the mice breathing oxygen when breathing rate or lethality was used to assess injury. Less enhancement of the late fibrotic reaction was observed in these animals. No enhancement of either phase of lung response was observed in the misonidazole-treated mice. Dose reduction factors (DRF) were estimated from these data and used to calculate oxygen concentration in the lung, giving values ranging between 187 and 250 micron oxygen.

Scanning electron microscopy and transmission electron microscopy of the ciliated cells of the trachea of the rabbit treated with misonidazole alone and in combination with ionizing radiation

The trachea is often located in the treatment volume when irradiating malignant tumours in the thorax. In order to evaluate possible synergism between misonidazole and irradiation on this tissue, the following studies were made. Fifty rabbits were treated with daily injections of 100 mg misonidazole given i.p. on consecutive days from 1 to 10 days. Morphological investigations of the trachea were made with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and light microscopy (LM). Physiological examinations were performed with recording of the ciliary beat frequency. The results were compared with those from a group of 100 rabbits given misonidazole in a similar manner and exposed to irradiation (2 Gy) 15-30 min after each injection. Ten rabbits were used as controls. The results are compared to the effect of fractionated irradiation alone with 2 Gy/day. Fractionated irradiation of the ciliary epithelium in the trachea of the rabbit has shown dose-dependent physiological and morphological effects. Misonidazole potentiates these effects of radiation with a more pronounced change of the ciliary beat frequency and an increased metabolic activity as could be visualized on TEM. The combination of drug and irradiation also induced a hyperplasia of the ciliary epithelium. Misonidazole itself had no effect on the ciliary beat frequency, but caused a hypoplasia of the ciliary epithelium.

Late effects of irradiation in mouse jejunum

The response of mouse jejunum at intervals up to 1 year after single 'priming' doses of X-rays has been assessed by crypt survival after retreatment with single doses of X-rays and morphometric analysis of changes in the intestinal submucosa. The first 'priming' dose was given as a single dose to the whole abdomen. To assess crypt survival, groups of mice were retreated to the whole body with a range of test doses 2, 6 or 12 months later, while other groups of mice were given only the priming doses. These data were compared to crypt survival in mice not previously irradiated. The crypt dose-survival curves in mice re-irradiated at all three intervals after priming irradiation were displaced to higher doses in pre-treated than in non-pre-treated mice and were characterized by higher D0 values. Misonidazole given before the test exposure reversed this effect so that the dose survival curve for crypts in pre-treated mice were superimposed on that for mice not previously irradiated, suggesting that the increase in isoeffect dose and the change in the D0 in previously exposed mice was due to crypt hypoxia. Quantification of the area of the submucosa showed that its area was increased at all three times after the priming doses and was a result of collagen deposition and oedema. Thus, the hypoxia in the crypts was probably secondary to these changes. Deaths began at 6-7 months after priming irradiation and were due to intestinal obstruction and stenosis. Thus, as in other tissues, two phases of injury can be assayed in the intestine of experimental animals.

Radiation induced renal damage in mice: influence of fraction size

Two functional assays (urine output and isotope clearance) have been used to assess the response of mouse kidneys to localized irradiation. The influence of the size of each X ray dose has been investigated by using single doses and two to 16 equal fractions. The X ray dose in each treatment ranged from 16 Gy as a single dose to 3.5 Gy (X 16 fractions). Three separate experiments were performed, one with and two without anesthetic for the irradiation. Sequential testing of the mice was used to determine the latent period before radiation damage became manifest. Latency was found to be dose dependent; functional defects appeared earlier after higher doses but there was a minimum period of 14-19 weeks before the onset of damage. The repair capacity of the kidney was assessed by comparing isoeffective doses from the dose-response curves. Within 24 hours a recovered dose of 5 Gy was obtained if 2 doses were used instead of one. The isoeffective dose increased with fractionation and a fraction number exponent of 0.42 was obtained. Analysis of the data using a linear quadratic model yielded a low alpha/beta ratio of 0-3.5 Gy. This is similar to values obtained for other late responding normal tissues and implies that the use of small dose fractions will spare the kidney relative to tumors and acutely reacting normal tissues. In conventional radiotherapy more effective sparing of the kidney should be achieved by using thin shielding with each fraction than by completely shielding the kidney for the latter part of the treatment course.

Radiation induced renal damage in mice: influence of overall treatment time

The influence of overall treatment time on the radiation response of the mouse kidney was studied by varying the time over which 2 or 5 fractions of X-rays were administered. Two functional assays (urine output and 51Cr-EDTA excretion), and renal weight at sacrifice were used to obtain dose-response curves and estimate isoeffective doses. Split dose experiments showed Elkind recovery of about 5 Gy in 24 h. With a 7-day interval between fractions a transitory increase in isoeffect dose was observed in the first experiment. In the second, more extensive, experiment the recovered dose did not increase significantly even if the interval between two fractions was prolonged up to 25 days. Therefore, if slow repair occurred it was not worth more than 1 Gy because this was the limit of resolution of the assays used. As overall time was prolonged to 60 days an additional 1-2 Gy were recovered: it is difficult to explain this delayed sparing effect on the basis of a compensatory proliferative response, because the labelling indices of the likely target cells in the kidney are so low. Whatever the mechanisms involved, an increase in overall time had only a slight effect on isoeffect dose in these experiments and values for the "T" exponent were low (0.0-0.09). Recovery from sublethal injury between fractions has a much larger effect.

WR-2721 protection of pneumonitis and fibrosis in mouse lung after single doses of x rays

The radioprotective effect of WR-2721 has been studied in mouse lung after single doses of radiation. Using the breathing rate assay and lethality, radioprotection was assessed at monthly intervals between 3 and 18 months after irradiation during both pneumonitis and chronic fibrosis. The degree of radioprotection was greater for fibrosis than for pneumonitis using both assays. In replicate experiments, dose modifying factors (DMF's) ranging from 1.2 to 1.4 were obtained for pneumonitis and 1.5 and 1.6 for fibrosis. The differences in DMF's for the two phases of lung damage were significant. A difference in the time course of expression of damage was seen in both the breathing rate and lethality assays between mice irradiated with and without WR-2721: the damage ended sooner in the drug-treated mice. This difference is best explained by protection of all damage after 5 months by WR-2721. No evidence of drug toxicity was found. We conclude that WR-2721 protects against chronic lung fibrosis caused by radiation at least as well as against the earlier appearing pneumonitis after single doses of radiation. Thus, if WR-2721 is dose modifying and if late tissue complications are dose limiting in clinical radiotherapy, then a therapeutic benefit would be obtained by the use of this drug in clinical radiotherapy, provided that the radioprotection of tumors did not exceed a factor of 1.5-1.6.

A murine model of lip epidermal/mucosal reactions to X-irradiation

A new radiobiological test system has been developed for lip epidermal/mucosal reactions in mice. This is intended for use in investigations of the effect of non-standard fractionation and of modifying drugs on oral radiation reactions in human cancer patients. An arbitrary scale of scores was devised, with separate scores for oedema of the lips and for erythema or exudation. After single doses of 13-20 Gy, the mouse lip epidermal reactions began at 5 days, reached a peak about 10-13 days, and had fallen to low values, but not to zero, by 21 days. Several different periods for averaging the reaction scores were tested for relative steepness and variability, the most useful being 10-12 days inclusive or the 12th day score alone. The use of longer periods of averaging led to apparent saturation of the scores. It was found that large doses of X-rays repeated at 21-23 day intervals did not lead to escalating waves of reactions unless each dose was greater than 17 Gy. With these larger doses, escalation of reactions occurred even if the intervals were extended.

A study of the effect of misonidazole in conjunction with radiotherapy for the treatment of grades 3 and 4 astrocytomas. A report from the MRC Working Party on misonidazole in gliomas

Four hundred and thirty-six patients were treated between January 1979 and November 1981 in a double-blind randomised study of the effect of the hypoxic cell sensitiser misonidazole (Ro 07-0582, MISO) in conjunction with radiotherapy on grades 3 and 4 astrocytoma. Radiotherapy was given in 20 fractions over 4 weeks to a minimum tumour dose of 4500 cGy. Misonidazole or placebo capsules were taken four to five hours before each radiotherapy treatment to a total dose of 11-13 g m-2. Survival rates at 12 months, among the 384 eligible patients, were similar in the misonidazole treated patients (25%) and those receiving placebo (28%). The estimated hazard ratio was 1.05, indicating a slight disadvantage to misonidazole which was not statistically significant (logrank test: chi 2 = 0.18 on 1 d.f., p = 0.7). Peripheral neuropathy was noted in 11% of the misonidazole group and was mostly mild. Possible reasons for the failure to demonstrate any therapeutic gain from misonidazole are discussed.

Is there a loss of repair capacity in mouse lungs with increasing numbers of dose fractions?

The capability of mouse lung to repair sublethal damage after up to 10 fractions of X rays was assessed by an in situ breathing rate assay and lethality. The whole thorax of mice was irradiated "daily" with 4, 7 or 10 fractions of 2.75 or 3.0 Gy of X rays followed at 24 hours by graded "test" doses of X rays or neutrons. Repair capability was measured by determining the difference in test dose between 4 and 7 fractions or 7 and 10 fractions at a given isoeffect. Damage was assessed monthly up to 76 weeks after irradiation, during pneumonitis and chronic fibrosis. The data from both assays for the pneumonitis phase suggested that there may be some loss of repair between 7 and 10 fractions, although it was not large enough in only 10 fractions to be clearly demonstrated. In contrast, there was no suggestion of loss of repair for late damage after up to 10 fractions of X rays using either assay.

The effects of anesthetics and misonidazole on the development of radiation-induced lung damage in mice

The measurement of breathing frequency as a functional end-point of radiation-induced lung injury in mice allowed two phases of damage to be discerned; the first was manifest at 12-20 weeks after irradiation, the second beyond 28 weeks. Anesthesia by pentobarbitone sodium or steroids gave significant radioprotection of the lung during the early pneumonitic phase. Addition of the hypoxic cell sensitizer misonidazole removed the protective influence of the anesthetics but did not sensitize the lungs of unanesthetized mice. No anesthetic protection was detected for the late response, showing evidence for dissociation between early and late lung damage. The degree of epilation was measured on the dorsal thoracic region of the same mice. Protection by anesthetics and its reversal by misonidazole was also demonstrated. These results provide a warning of potential hazards in the laboratory evaluation of chemical radiosensitizers. The use of anesthetics at the time of irradiation could lead to an exaggerated enhancement of normal tissue damage.

Effect of misonidazole on the tolerance of the rat spinal cord to daily and multiple fractions per day of X rays

The effect of misonidazole on the induction of early and late delayed radiation damage in the rat cervical spinal cord has been determined for single doses, daily, and multiple fractions per day of X rays. Paralysis occurred in two separate waves, which could be attributed to histologically different types of damage. Administration of misonidazole before irradiation did not modify the early and late delayed radiation response of the spinal cord. This suggested that the targets for misonidazole and radiation toxicity in the central nervous system are different. Comparison of different types of anaesthesia, Nembutal and Ethrane, with or without breathing oxygen, indicated that hypoxia was not induced in the spinal cord by the experimental conditions. Irradiation with two or three fractions a day showed a reduction in spinal cord tolerance, but this reduction became less with decreasing doses per fraction.

Skin sensitization by misonidazole: a demonstration of uniform mild hypoxia

Skin reactions on irradiated mouse feet were used to measure the radiosensitization of normal tissues by misonidazole (MISO). Fractionation schedules of 1, 2, 5 and 10 daily doses of X-rays were combined with either 100 mg/kg or 670 mg/kg MISO. When unanaesthetized mice were irradiated in air, significant sensitization was observed with both the high and low drug doses, in all fractionation schedules. There was no decrease in sensitization with fractionation, even using fractions as small as 5 Gy. This indicates that many of the cells in mouse skin may be marginally hypoxic, and that sensitization at low doses is possible. Irradiation in O2 without MISO rendered the skin more sensitive to X-rays than in air. MISO given 30 min before single doses of radiation further sensitized the skin, but for 10 fractions in O2 no MISO sensitization was detected. There was little evidence for cytotoxic killing in skin by MISO. Repair of radiation damage was slightly reduced when MISO was present, during or after irradiation.