Kinetics of mouse jejunum radiosensitization by 2',2'-difluorodeoxycytidine (gemcitabine) and its relationship with pharmacodynamics of DNA synthesis inhibition and cell cycle redistribution in crypt cells.

Gemcitabine (dFdC), a deoxycitidine nucleoside analogue, inhibits DNA synthesis and repair of radiation-induced chromosome breaks in vitro, radiosensitizes various human and mouse cells in vitro and shows clinical activity in several tumours. Limited data are however available on the effect of dFdC on normal tissue radiotolerance and on factors associated with dFdC's radiosensitization in vivo. The purpose of this study was to determine the effect of dFdC on mouse jejunum radiosensitization and to investigate the kinetics of DNA synthesis inhibition and cell cycle redistribution in the jejunal crypts as surrogates of radiosensitization in vivo. For assessment of jejunum tolerance, the mice were irradiated on the whole body with 60Co gamma rays (3.5-18 Gy single dose) with or without prior administration of dFdC (150 mg kg-1). Jejunum tolerance was evaluated by the number of regenerated crypts per circumference at 86 h after irradiation. For pharmacodynamic studies, dFdC (150 or 600 mg kg-1) was given i.p. and jejunum was harvested at various times (0-48 h), preceded by a pulse BrdUrd labelling. Labelled cells were detected by immunohistochemistry on paraffin-embedded sections. DNA synthesis was inhibited within 3 h after dFdC administration. After an early wave of apoptosis (3-6 h), DNA synthesis recovered by 6 h, and crypt cells became synchronized. At 48 h, the labelling index returned almost to background level. At a level of 40 regenerated crypts, radiosensitization was observed for a 3 h time interval (dose modification factor of 1.3) and was associated with DNA synthesis inhibition, whereas a slight radioprotection was observed for a 48-h time interval (dose modification factor of 0.9) when DNA synthesis has reinitiated. In conclusion, dFdC altered the radioresponse of the mouse jejunum in a schedule-dependent fashion. Our data tend to support the hypothesis that DNA synthesis inhibition and cell cycle redistribution are surrogates for radiosensitization. More data points are however required before a definite conclusion can be drawn

Measurements of radiobiological effectiveness in the 85 MeV proton beam produced at the cyclotron CYCLONE of Louvain-la-Neuve, Belgium.

The RBE of the 85 MeV proton beam produced at the cyclotron of Louvain-la-Neuve using 60Co gamma rays as the reference radiation was determined for survival of Chinese hamster ovary cells in vitro and for intestinal crypt regeneration in mice in vivo. Cell survival curves determined at different depths yielded, for a surviving fraction (SF) of 0.01, RBE values of 1.11 +/- 0.05 at the initial plateau of the unmodulated beam, 1.10 +/- 0.03 at the middle of a 0.5-cm spread-out Bragg peak (SOBP), 1.03 +/- 0.03 at the beginning of a 3-cm SOBP and 1.07 +/- 0.03 at the end of a 3-cm SOBP. The highest RBE values were obtained at the middle of the 0.5-cm SOBP and at the end of the 3-cm SOBP (RBE = 1.22 and 1.16, respectively, at SF = 0.5), although the variations are not statistically significant. Irradiations with 3-Gy fractions separated by an interval of 3.5 h yielded RBEs of 1.11 +/- 0.30 and 0.90 +/- 0.32 at the initial plateau and at the middle of the 0.5-cm SOBP, respectively. Irradiations of mice at the middle of the 3-cm SOBP yielded an RBE of 1.08 +/- 0.03 for 20 regenerated crypts at a proton dose of 12.3 Gy

Measurements of radiobiological effectiveness in the 85 MeV proton beam produced at the cyclotron CYCLONE of Louvain-la-Neuve, Belgium.

The RBE of the 85 MeV proton beam produced at the cyclotron of Louvain-la-Neuve using 60Co gamma rays as the reference radiation was determined for survival of Chinese hamster ovary cells in vitro and for intestinal crypt regeneration in mice in vivo. Cell survival curves determined at different depths yielded, for a surviving fraction (SF) of 0.01, RBE values of 1.11 +/- 0.05 at the initial plateau of the unmodulated beam, 1.10 +/- 0.03 at the middle of a 0.5-cm spread-out Bragg peak (SOBP), 1.03 +/- 0.03 at the beginning of a 3-cm SOBP and 1.07 +/- 0.03 at the end of a 3-cm SOBP. The highest RBE values were obtained at the middle of the 0.5-cm SOBP and at the end of the 3-cm SOBP (RBE = 1.22 and 1.16, respectively, at SF = 0.5), although the variations are not statistically significant. Irradiations with 3-Gy fractions separated by an interval of 3.5 h yielded RBEs of 1.11 +/- 0.30 and 0.90 +/- 0.32 at the initial plateau and at the middle of the 0.5-cm SOBP, respectively. Irradiations of mice at the middle of the 3-cm SOBP yielded an RBE of 1.08 +/- 0.03 for 20 regenerated crypts at a proton dose of 12.3 Gy

Variation of RBE between p(75) + Be and d(50) + Be neutrons determined for chromosome aberrations in Allium cepa.

The RBE of p(75) + Be neutrons relative to d(50) + Be neutrons has been determined for chromosome aberrations induced in Allium cepa (onion) roots. Two biological criteria were selected: the average number of aberrations (mainly fragments) per cell in anaphase and telophase, and the percentage of aberration-free cells. The influence of sampling time (3 to 7 h incubation) between irradiation and fixation was investigated systematically. This factor did not significantly influence the results. The RBE values of p(75) + Be neutrons compared to those of d(50) + Be neutrons were 0.85 (0.79-0.91) and 0.87 (0.80-0.95) for the first and the second criteria, respectively. In previous experiments for the same beams, we found an RBE of 0.90 (0.86-0.94) for survival of V79 cells (D0 ratio), 0.96 (0.93-0.99) for the intestinal crypt cell system, and 0.83 (0.70-0.96) for Vicia faba growth delay

Réparation cellulaire précoce du poumon et de l'intestin, chez la souris, après irradiation par neutrons rapides et rayons gamma

Lung tolerance is assessed from LD50 at 180 days after thoracic irradiation, in mice, with d(50) + Be neutrons and 60Co gamma rays. Early intestinal tolerance is assessed from LD50 at 7 days after abdominal irradiation. Additional dose (Dr) to reach LD50 when a single dose Ds is split into 2 equal fractions Di separated by different time intervals "i", is determined (Dr = 2Di - Ds), Dr is larger after gamma than after neutron irradiation, for lung and intestine. After thoracic irradiation with gamma rays, Dr reaches 3.36, 4.38, 5.12 and 5.37 Gy for "i" = 2, 6, 12 and 24 hours respectively; after neutron irradiation, Dr reaches 0.66, 0.9, 1.29, 1.95 and 1.50 Gy for "i" = 1, 2, 4, 12 and 24 hours. Dr is smaller for intestine; after abdominal irradiation with gamma rays, it reaches 1.99, 2.59, 2.74, 3.11, 3.34, 4.44 and 4.56 Gy for "i" = 1, 2, 3.5, 8, 12, 18 and 24 hours; after neutron irradiation, it reaches 0.13, 0.45, 0.42 and 1.33 Gy for "i" = 1.5, 3.5, 5.5 and 24 hours. After gamma irradiation, early repair is complete after 3.5 hours for intestine and needs 12 hours for lung

Early repair kinetics of intestine and lung in mice, after fast neutron and photon irradiation.

Early repair (Elkind repair) kinetics of an early and a late responding tissue after gamma and d(50) + Be neutron irradiation were compared in mice. LD50 at five days after abdominal irradiation and LD50 at 180 days after thoracic irradiation were chosen as biological endpoints to study intestinal and lung tolerance, respectively. Elkind repair is assessed from the additional dose Dr to reach LD50 when a single dose Ds is split into two equal fractions Di separated by time intervals "i" ranging from 0 to 24 hours (Dr = 2Di-Ds). Dr is greater for lung than for intestine after both gamma and neutron irradiations. Our data are consistent with an exponential early repair with an half-life (T 1/2) of 0.5 h for intestine and 1.5 to 2 h for lung

Efficacité biologique relative (EBR) des neutrons produits à partir de deutons de 50 MeV et de protons de 34, 45, 65 et 75 MeV

RBE of p(34) + Be, p(45) + Be, p(65), + Be, p(75) + Be and d(50) + Be neutron beams produced at the cyclotron "Cyclone" of Louvain-la-Neuve were measured. The biological criterion was the regeneration of the crypts of the intestinal mucosa (50 regenerated crypts per circumference) after abdominal irradiation in mice. Taking the p(65) + Be neutrons as reference, RBE values were found equal to 1.12, 1.07, 1.00 (Ref.), 0.96 and 1.02 respectively. These results are consistent with those published for cell lethality in vitro. However, the RBE variation is smaller than this previously obtained in the laboratory for growth inhibition in Vicia faba

Radiosensitization of mouse sarcoma cells by fludarabine (F-ara-A) or gemcitabine (dFdC), two nucleoside analogues, is not mediated by an increased induction or a repair inhibition of DNA double-strand breaks as measured by pulsed-field gel electrophoresis.

PURPOSE: To investigate the effect of fludarabine (F-ara-A) and gemcitabine (dFdC), two radiosensitizing nucleoside analogues, on the induction and repair of DNA dsb after ionizing radiation. MATERIALS AND METHODS: Radiosensitization of mouse sarcoma SA-NH and FSA cells was studied using a clonogenic assay. Cell survival curves were fitted with the linear-quadratic model. DNA dsbs were detected by pulsed-field gel electrophoresis under neutral conditions. RESULTS: F-ara-A (100 micromol dm(-3) for 1 h prior to irradiation) induced a substantial radiosensitization in SA-NH cells with a dose modification factor of 2.0 for a surviving fraction of 0.5. In a FSA mouse sarcoma cell line, dFdC (5 micromol dm(-3) for 3 h prior to irradiation) induced a modest radiosensitization with a DMF of 1.2 for a surviving fraction of 0.5. Under similar experimental conditions, neither F-ara-A nor dFdC altered the yield of radiation-induced DNA dsbs in the dose range of 0-40 Gy. After a single dose of 25 Gy (SA-NH cells) or 40 Gy (FSA cells), neither the kinetics of repair nor the amount of residual damage was affected by F-ara-A or dFdC. CONCLUSIONS: For experimental conditions under which radiosensitization was observed, neither the induction nor the repair of DNA dsbs after ionizing radiation were affected by F-ara-A or dFdC

Protocol for X-ray dosimetry in radiobiology

Purpose: To harmonize X-ray dosimetry in radiobiology to allow a direct comparison of radiobiological studies performed at institutes cooperation within the framework of the European Late Effects Project Group (EULEP). Materials and methods: The 1985 EULEP protocol for X-ray dosimetry and exposure arrangements employed for studies of late somatic effects in mammals required serious revision, e.g. due to the replacement of calibration of dosemeters in terms of exposure by calibration in terms of air kerma free-in-air. An action group established by EULEP and the European Radiation Dosimetry Group (EURADOS) updated the 1985 protocol. Results: The new EULEP EURADOS protocol for X-ray dosimetry in radiobiology including the code of practice for irradiation of small animals and related dosimetry. The present protocol includes the changes in calibration procedures and dosimetric concepts for irradiation with medium energy X-rays since 1985. Accuracy and precision are replaced by the concept of combined (standard) uncertainty. The revised supplements provide more detailed background information. New appendices contain definitions of general terms used for measurements and mathematical expressions of the relative variances. Conclusion: Adherence to the present protocol will result in improved dosimetry and facilitates the comparison of results of radiobiological experiments obtained at different institutes