Low-dose hyperradiosensitivity of human glioblastoma cell lines in vitro does not translate into improved outcome of ultrafractionated radiotherapy in vivo

Purpose: Low dose hyperradiosensitivity (HRS) has been observed in HGL21- and T98G human glioblastoma cells in vitro. The present study investigates whether these effects translate into improved outcome of ultrafractionated irradiation (UF) in vivo.

Material and methods: T98G or HGL21 were transplanted on the hind leg of nude mice. Tumours were irradiated with UF (3 fractions of 0.4 Gy per day, interval 4 h, 7 days per week) or with conventional fractionation (CF; 1 fraction of 1.68 Gy per day, 5 days per week) over 2 or 4 weeks in HGL21 and 2,4 or 6 weeks in T98G. In HGL21, graded top-up doses under clamped hypoxia were applied after 4 weeks of fractionated irradiation. Additional groups of animals were irradiated with single doses under clamp hypoxic conditions with or without whole body irradiation (WBI) before tumour transplantation. Experimental endpoints were growth delay (time to 5-fold starting volume, GD_V5) and local tumour control.

Results: In T98G tumours median relative GD_V5 was 1.2 [95%C.I. 0.96; ∞] in the CF and 0.8 [0.7; 1.02] in the UF arm (p = 0.009) indicating that ultrafractionation is less efficient than conventional fractionation. The TCD₅₀ value of 33.5 Gy [22; 45] after UF was higher than TCD₅₀ of 23.6 Gy [16; 31] after CF (p = 0.15). In HGL21 the median relative GD_V5 was not significantly different between CF and UF. The top-up TCD₅₀ value of 16.1 Gy [95% C.I. 9; 23 Gy] after CF was significantly lower than the corresponding value of 33.2 Gy [23; 44] after UF irradiation (p = 0.007), indicating a higher efficacy of CF compared to UF.

Conclusion: The results on human T98G and HGL21 glioblastoma do not support the hypothesis that HRS in vitro translates into improved outcome of ultrafractionated irradiation in vivo.     

Ultrafractionation in A7 human malignant glioma in nude mice

PURPOSE: Low-dose hyperradiosensitivity (HRS) has been demonstrated in numerous cell lines in vitro, including a number of radioresistant human malignant glioma cell lines such as A7. The aim of our experiment was to show whether HRS can be exploited by using ultrafractionated irradiation (UF) to improve local control of A7 tumours growing in nude mice. Extrapolation of the in vitro results predict a 3.7-fold difference in the efficacy of UF compared with conventional fractionation (CF). MATERIAL AND METHODS: Subcutaneuously growing A7 tumours were irradiated either with UF (126 fractions in 6 weeks, 0.4 Gy per fraction) or CF (30 fractions in 6 weeks, 1.68 Gy per fraction). The total dose was 50.4 Gy in both experimental arms. Fractionated irradiations were given under ambient conditions and followed by graded top-up doses under clamp hypoxia. Endpoints were tumour growth delay and local tumour control 180 days after the end of treatment. RESULTS: UF resulted in a significant decrease of tumour growth delay and in a significant increase of the top-up TCD(50) compared with CF (40.0 Gy [95% CI 29; 61 Gy] versus 28.3 Gy [24; 35 Gy], p=0.047). CONCLUSIONS: Despite a pronounced HRS phenomenon in vitro, UF was significantly less effective than CF in A7 human malignant glioma in nude mice. These results neither disprove the existence of HRS nor do they exclude a possible clinical value of UF. The findings rather indicate that simplistic extrapolation from results obtained after single-dose exposure or few fractions in vitro is not sufficient to predict outcome of UF in vivo and that comprehensive evaluation of novel treatment options in animal models continues to be an essential requirement for clinical translation.     

Ultrafractionation does not Improve the Results of Radiotherapy in Radioresistant Murine DDL1 Lymphoma

Background and Purpose: Low-dose hyperradiosensitivity (HRS), i.e., a relatively higher efficacy of doses ≤ 0.5 Gy compared to doses > 1 Gy, has been shown in a number of tumor cell lines in vitro. Therefore ultrafractionated irradiation, i.e., application of very low doses per fraction, has been proposed to improve the effects of radiotherapy. The present study investigates ultrafractionation (UF) in radioresistant murine DDL1 T-cell lymphoma in mice.Material and Methods: UF was performed with 0.4 Gy per fraction, three fractions per day at 7 days per week, and conventional fractionation (CF) with 1.68 Gy per fraction, one fraction per day at 5 days per week. Tumor growth delay was evaluated for 2, 4 and 6 weeks of irradiation as time that tumors needed to reach fivefold the starting volume (GD_V5).Results: GD_V5 was not significantly different between UF and CF. The composite median relative GD_V5 calculated for all tumors irradiated in the present study was 1.00 [95% confidence interval 0.99; 1.08] in the CF and 0.99 [0.92; 1.01] in the UF arm (p = 0.24).Conclusion: UF was not more efficient than CF in DDL1 tumors. Taken together with previous experiments on human A7 glioblastoma, which showed a negative effect of UF on local tumor control, the preclinical data obtained in this laboratory so far do not support the use of ultrafractionated schedules in radiotherapy.     

Ultrafractionation in A7 human malignant glioma in nude mice

Purpose: Low‐dose hyperradiosensitivity (HRS) has been demonstrated in numerous cell lines in vitro, including a number of radioresistant human malignant glioma cell lines such as A7. The aim of our experiment was to show whether HRS can be exploited by using ultrafractionated irradiation (UF) to improve local control of A7 tumours growing in nude mice. Extrapolation of the in vitro results predict a 3.7‐fold difference in the efficacy of UF compared with conventional fractionation (CF).

Material and methods: Subcutaneuously growing A7 tumours were irradiated either with UF (126 fractions in 6 weeks, 0.4?Gy per fraction) or CF (30 fractions in 6 weeks, 1.68?Gy per fraction). The total dose was 50.4?Gy in both experimental arms. Fractionated irradiations were given under ambient conditions and followed by graded top‐up doses under clamp hypoxia. Endpoints were tumour growth delay and local tumour control 180 days after the end of treatment.

Results: UF resulted in a significant decrease of tumour growth delay and in a significant increase of the top‐up TCD₅₀ compared with CF (40.0?Gy [95% CI 29; 61?Gy] versus 28.3?Gy [24; 35?Gy], p=0.047).

Conclusions: Despite a pronounced HRS phenomenon in vitro, UF was significantly less effective than CF in A7 human malignant glioma in nude mice. These results neither disprove the existence of HRS nor do they exclude a possible clinical value of UF. The findings rather indicate that simplistic extrapolation from results obtained after single‐dose exposure or few fractions in vitro is not sufficient to predict outcome of UF in vivo and that comprehensive evaluation of novel treatment options in animal models continues to be an essential requirement for clinical translation.     

Ultrafractionation does not Improve the Results of Radiotherapy in Radioresistant Murine DDL1 Lymphoma

Background and Purpose:  

Low-dose hyperradiosensitivity (HRS), i.e., a relatively higher efficacy of doses ≤ 0.5 Gy compared to doses > 1 Gy, has been shown in a number of tumor cell lines in vitro. Therefore ultrafractionated irradiation, i.e., application of very low doses per fraction, has been proposed to improve the effects of radiotherapy. The present study investigates ultrafractionation (UF) in radioresistant murine DDL1 T-cell lymphoma in mice.     

Low-dose hypersensitivity after fractionated low-dose irradiation in vitro

Purpose : It was demonstrated previously that some radioresistant tumour cell lines respond to decreasing single, low radiation doses by becoming increasingly radiosensitive. This paper reports the response of four radioresistant human glioma cell lines to multiple low-dose radiation exposures given at various intervals. Three of the cell lines (T98G, U87, A7) were proven already to show low-dose hyper-radiosensitivity (HRS) after single low doses; the fourth, U373, does not show HRS after acute doses. Materials and methods : Clonogenic cell-survival measurements were made in vitro using the Dynamic Microscopic Image Processing Scanner (DMIPS) or Cell Sorter (CS) following exposure to 240kVp X-rays one or more times. Results : A consistent, time-dependent hypersensitive response to a second, or subsequent, dose was observed in the cell lines that demonstrated HRS. This time-dependent change in radiosensitivity did not occur in the radioresistant cell line that did not show HRS (U373). In one cell line that demonstrated strong HRS, T98G, a similar time-dependent hypersensitive response was also seen when the cells were irradiated whilst held in the G1-phase of the cell cycle. In this same cell line, significantly increased cell kill was demonstrated when three very low doses (0.4 Gy) were given per day, 4 h apart, for 5 days, compared with the same total dose given as once-daily 1.2Gy fractions. Conclusions : These data demonstrate the possibility that a multipledose per day, low-dose per fraction regimen, termed 'ultrafractionation', could produce increased tumour cell kill in radioresistant tumours compared with the same total dose given as conventional-sized 2 Gy fractions.     

Low-dose hypersensitivity after fractionated low-dose irradiation in vitro

PURPOSE: It was demonstrated previously that some radioresistant tumour cell lines respond to decreasing single, low radiation doses by becoming increasingly radiosensitive. This paper reports the response of four radioresistant human glioma cell lines to multiple low-dose radiation exposures given at various intervals. Three of the cell lines (T98G, U87, A7) were proven already to show low-dose hyper-radiosensitivity (HRS) after single low doses; the fourth, U373, does not show HRS after acute doses. MATERIALS AND METHODS: Clonogenic cell-survival measurements were made in vitro using the Dynamic Microscopic Image Processing Scanner (DMIPS) or Cell Sorter (CS) following exposure to 240kVp X-rays one or more times. RESULTS: A consistent, time-dependent hypersensitive response to a second, or subsequent, dose was observed in the cell lines that demonstrated HRS. This time-dependent change in radiosensitivity did not occur in the radioresistant cell line that did not show HRS (U373). In one cell line that demonstrated strong HRS, T98G, a similar time-dependent hypersensitive response was also seen when the cells were irradiated whilst held in the G1-phase of the cell cycle. In this same cell line, significantly increased cell kill was demonstrated when three very low doses (0.4 Gy) were given per day, 4 h apart, for 5 days, compared with the same total dose given as once-daily 1.2Gy fractions. CONCLUSIONS: These data demonstrate the possibility that a multipledose per day, low-dose per fraction regimen, termed 'ultrafractionation', could produce increased tumour cell kill in radioresistant tumours compared with the same total dose given as conventional-sized 2 Gy fractions.     

Impact of increased cell loss on the repopulation rate during fractionated irradiation in human FaDu squamous cell carcinoma growing in nude mice

PURPOSE: To determine the impact of increased necrotic cell loss on the repopulation rate of clonogenic cells during fractionated irradiation in human FaDu squamous cell carcinoma in nude mice. MATERIALS AND METHODS: FaDu tumours were transplanted into pre-irradiated subcutaneous tissues. This manoeuvre has previously been shown to result in a clear-cut tumour bed effect, i.e. tumours grow at a slower rate compared with control tumours. This tumour bed effect was caused by an increased necrotic cell loss with a constant cell production rate. After increasing numbers of 3-Gy fractions (time intervals 24 or 48 h), graded top-up doses were given to determine the dose required to control 50% of the tumours (TCD50). All irradiations were given under clamp hypoxia. RESULTS: With increasing numbers of daily fractions, the top-up TCD50 decreased from 37.9 Gy (95% CI: 31; 45) after single dose irradiation to 14.1 Gy (8; 20) after irradiation with 15 fractions in 15 days. Irradiation with 18 daily 3-Gy fractions controlled more than 50% of the tumours without a top-up dose. After irradiation with six fractions every second day, the top-up TCD50 decreased to 26.9 Gy (22; 32). No further decrease of the TCD50 was observed after 12 and 18 irradiations every second day. Assuming a constant increase of TCD50 with time, the calculated doubling time of the clonogenic tumour cells (Tclon) was 7.8 days (4.4; 11.3). The Tclon calculated for FaDu tumours growing in pre-irradiated tissues was significantly longer (p=0.0004) than the Tclon of 5.1 days (3.7; 6.5) determined under the same assumptions in a previous study for FaDu tumours growing in normal subcutaneous tissues. CONCLUSIONS: Increased necrotic cell loss by pre-irradiation of the tumour bed resulted in longer clonogen doubling times during fractionated radiotherapy of human FaDu squamous cell carcinoma. This implies that a decreased necrotic cell loss might be the link between reoxygenation and repopulation demonstrated previously in the same tumour model.     

Effect of subsequent acute-dose irradiation on cell survival in vitro following low dose-rate exposures

Purpose : Following acute irradiation, excess radiosensitivity is generally seen at doses <1 Gy, a phenomenon termed 'low-dose hyper-radiosensitivity' (HRS). A very strong, HRS-like inverse dose-rate effect has also been described following continuous low dose-rate (LDR) irradiation at <30 cGy h -1. We report on the sequential irradiation of a cell line by such LDR exposures followed by low acute doses, where either treatment individually would elicit a hypersensitive response. The aim was to determine if a prior LDR exposure would remove the HRS normally seen in response to very small acute radiation doses. Materials and methods : T98G human glioma cells were given single continuous LDR exposures of 5-60 cGy h -1 using a 60 Co γ-source. At intervals of 0 or 4 h following LDR irradiation, cells were further irradiated with a range of acute doses using 240-kVp X-rays. The response to the combined treatment was assessed using high-precision clonogenic cell survival assays, and the amount of HRS at acute doses <1 Gy was determined. Results : LDR at ≥60 cGy h -1 to total doses up to 5 Gy in asynchronously growing cells did not remove HRS in the subsequent acute-dose survival curve. In confluent cultures, subsequent acute-dose HRS was not present after an LDR dose of 5 Gy at either 60 or 30 cGy h -1, but returned if a 4-h interval was left between LDR and acute-dose irradiation. In confluent cultures, acute-dose HRS remained for LDR treatments at 5 or 10 cGy h -1 or if the total dose was 2 Gy. Taking all cultures and dose-rates together, the 'degree' of acute-dose HRS, as measured by α s, was significantly greater in cells irradiated at LDR to a total dose of 2 than of 5Gy. Conclusions : Initial LDR exposure can affect a subsequent HRS response. HRS is reduced after LDR exposures at greater dose intensity, but can recover again within 4 h of completion of LDR exposure. This suggests that processes determining increased resistance to small acute doses (removal of HRS) might be governed by the level of repairable DNA lesions.     

Effect of subsequent acute-dose irradiation on cell survival in vitro following low dose-rate exposures

PURPOSE: Following acute irradiation, excess radiosensitivity is generally seen at doses <1 Gy, a phenomenon termed "low-dose hyper-radiosensitivity" (HRS). A very strong, HRS-like inverse dose-rate effect has also been described following continuous low dose-rate (LDR) irradiation at <30 cGy h(-1). We report on the sequential irradiation of a cell line by such LDR exposures followed by low acute doses, where either treatment individually would elicit a hypersensitive response. The aim was to determine if a prior LDR exposure would remove the HRS normally seen in response to very small acute radiation doses. MATERIALS AND METHODS: T98G human glioma cells were given single continuous LDR exposures of 5-60 cGy h(-1) using a (60)Co gamma-source. At intervals of 0 or 4 h following LDR irradiation, cells were further irradiated with a range of acute doses using 240-kVp X-rays. The response to the combined treatment was assessed using high-precision clonogenic cell survival assays, and the amount of HRS at acute doses <1 Gy was determined. RESULTS: LDR at > or = 60 cGy h(-1) to total doses up to 5 Gy in asynchronously growing cells did not remove HRS in the subsequent acute-dose survival curve. In confluent cultures, subsequent acute-dose HRS was not present after an LDR dose of 5 Gy at either 60 or 30 cGy h(-1), but returned if a 4-h interval was left between LDR and acute-dose irradiation. In confluent cultures, acute-dose HRS remained for LDR treatments at 5 or 10 cGy h(-1) or if the total dose was 2 Gy. Taking all cultures and dose-rates together, the "degree" of acute-dose HRS, as measured by alpha(s), was significantly greater in cells irradiated at LDR to a total dose of 2 than of 5Gy. CONCLUSIONS: Initial LDR exposure can affect a subsequent HRS response. HRS is reduced after LDR exposures at greater dose intensity, but can recover again within 4 h of completion of LDR exposure. This suggests that processes determining increased resistance to small acute doses (removal of HRS) might be governed by the level of repairable DNA lesions.     

The roles of TGF-β3 and peroxynitrite in removal of hyper-radiosensitivity by priming irradiation

Abstract

Purpose: To investigate the mechanisms inducing and maintaining the permanent elimination of low dose hyper-radiosensitivity (HRS) in cells given a dose of 0.3 Gy at low dose-rate (LDR) (0.3 Gy/h).

Materials and methods: Two human HRS-positive cell lines (T-47D, T98G) were used. The effects of pretreatments with transforming growth factor beta (TGF-β) neutralizers, TGF-β3 or peroxynitrite scavenger on HRS were investigated using the colony assay. Cytoplasmic levels of TGF-β3 were measured using post-embedding immunogold electron microscopic analysis.

Results: TGF-β3 neutralizer inhibited the removal of HRS by LDR irradiation. Adding 0.001 ng/ml TGF-β3 to cells removed HRS in T98G cells while 0.01 ng/ml additionally induced resistance to higher doses. Cytoplasmic levels of TGF-β3 were higher in LDR-primed cells than in unirradiated cells. The presence of the peroxynitrite scavenger uric acid inhibited the effect of LDR irradiation. Furthermore, the permanent elimination of HRS in LDR-primed cells was reversed by treatment with uric acid. The removal of HRS by medium from hypoxic cells was inhibited by adding TGF-β3 neutralizer to the medium before transfer or by adding hypoxia inducible factor 1 (HIF-1) inhibitor chetomin to the cell medium during hypoxia.

Conclusions: TGF-β3 is involved in the regulation of cellular responses to small doses of acute irradiation. TGF-β3 activation seems to be induced by low dose-rate irradiation by a mechanism involving inducible nitric oxide (iNOS) and peroxynitrite, or during cycling hypoxia by a mechanism most likely involving HIF-1. The study suggests methods to turn resistance to doses in the HRS-range on (by TGF-β3) or off (by TGF-β3 neutralizer or by peroxynitrite inhibition).     

Effects of cell cycle phase on low-dose hyper-radiosensitivity

PURPOSE: To examine the low-dose radiation response of human glioma cell lines separated into different cell-cycle phases and to determine if low-dose hyper-radiosensitivity (HRS) differs in populations defined by cell-cycle position. To assess whether predictions of the outcome of multiple low-dose regimens should take account of cell-cycle effects. MATERIALS AND METHODS: The clonogenic survival of G1, G2 and S phase cells was measured after exposure to single doses of X-rays in two human glioma cell lines. One cell line (T98G) showed marked HRS when asynchronous cells were irradiated, while the other (U373) did not. Separation of populations and high-resolution cell counting was achieved using a fluorescence activated cell sorter. Sorted cell populations were irradiated with 240 kVp X-rays to doses between 0.05 and 5Gy. The resulting cell-survival versus dose data were comparatively fitted using the linear-quadratic and induced-repair models in order to assess the degree of HRS. RESULTS: In both cell lines the low-dose response was altered when different populations were irradiated. In T98G cells, all populations showed HRS, but this was most marked in G2 phase cells. In U373 cells, no HRS was found in G1 or S phase cells, but HRS was demonstrable in G2 phase cells. CONCLUSIONS: HRS was expressed by the whole cell population of T98G cells but the size of the effect varied with cell-cycle phase and was most marked in the G2 population. In U373 cells, the effect could only be demonstrated in G2 cells. This implies that HRS is primarily a response of G2 phase cells and that this response dominates that seen in asynchronous populations. Actively proliferating cell populations may therefore demonstrate a greater increase in radiosensitivity to very low radiation doses compared with quiescent populations.     

Effects of cell cycle phase on low-dose hyper-radiosensitivity

Purpose : To examine the low-dose radiation response of human glioma cell lines separated into different cell-cycle phases and to determine if low-dose hyper-radiosensitivity (HRS) differs in populations defined by cell-cycle position. To assess whether predictions of the outcome of multiple low-dose regimens should take account of cell-cycle effects. Materials and methods : The clonogenic survival of G1, G2 and S phase cells was measured after exposure to single doses of X-rays in two human glioma cell lines. One cell line (T98G) showed marked HRS when asynchronous cells were irradiated, while the other (U373) did not. Separation of populations and high-resolution cell counting was achieved using a fluorescence activated cell sorter. Sorted cell populations were irradiated with 240 kVp X-rays to doses between 0.05 and 5Gy. The resulting cell-survival versus dose data were comparatively fitted using the linear-quadratic and induced-repair models in order to assess the degree of HRS. Results : In both cell lines the low-dose response was altered when different populations were irradiated. In T98G cells, all populations showed HRS, but this was most marked in G2 phase cells. In U373 cells, no HRS was found in G1 or S phase cells, but HRS was demonstrable in G2 phase cells. Conclusions : HRS was expressed by the whole cell population of T98G cells but the size of the effect varied with cell-cycle phase and was most marked in the G2 population. In U373 cells, the effect could only be demonstrated in G2 cells. This implies that HRS is primarily a response of G2 phase cells and that this response dominates that seen in asynchronous populations. Actively proliferating cell populations may therefore demonstrate a greater increase in radiosensitivity to very low radiation doses compared with quiescent populations.     

Combined fractionated external beam radiotherapy and low-dose-rate iodine-125 seeds in an experimental tumor system.

BACKGROUND: To quantify the effect of implanted low-dose-rate iodine seeds combined with fractionated external beam radiation on local control rates in an experimental tumor system. MATERIALS AND METHODS: Experiments were done on the rhabdomyosarcoma R1H of the rat transplanted s.c. into the back of male WAG/Raj albino rats. Tumors were irradiated with 200 kVp X-rays with 2 Gy/fraction 5 times weekly. The total dose of the external beam irradiation varied between 60 and 98 Gy for external beam radiotherapy alone and 10 Gy to 82 Gy for combined external beam radiotherapy and iodine seeds. One to 4 iodine seeds with a median activity of 21.05 MBq were permanently implanted 3 days before the start of external radiotherapy or 6 and 7 iodine seeds alone were used. The median tumor volume at the start of treatment was 0.12 cm3. Local tumor control rates were determined and TCD37% values were calculated applying the maximum likelihood method. RESULTS: With increasing number of implanted iodine seeds the TCD37% (of external beam irradiation) decreased. With external beam radiotherapy alone the TCD37% amounted to 103.2 Gy (95% CI, 101.3 to 105.1 Gy) decreasing to (externally applied doses) 69.7 Gy (63.7 to 74.7 Gy) after 1 implanted iodine seed and further to 31.6 Gy (25.6 to 37.6 Gy) after 4 implanted iodine seeds. The effective dose (equivalent to external dose) per iodine seed decreased with increasing number of implanted iodine seeds. One iodine seed gave an effective dose of 33.5 Gy (28.5 to 39.5 Gy) decreasing to 17.9 Gy (16.4 to 19.4 Gy) after 4 iodine seeds. CONCLUSIONS: The combined treatment of tumors with implanted low-dose-rate iodine seeds and external beam irradiation can decrease the total dose of the external beam irradiation and, hence, offer the possibility of considerable dose sparing of normal tissues without compromising local tumor control rates.     

Low-dose hyper-radiosensitivity in human hepatocellular HepG2 cells is associated with Cdc25C-mediated G2/M cell cycle checkpoint control

Purpose: Although the significance of cell cycle checkpoints in overcoming low-dose hyper-radiosensitivity (HRS) has been proposed, the underlying mechanism of HRS in human hepatocellular cells remains unclear. Therefore, the aim of this study was to characterize HRS inhuman hepatocellular HepG2 cells and to explore the molecular mechanism(s) mediating this response.

Materials and methods: HepG2 cells were exposed to various single doses of γ radiation (from 0?Gy to 4?Gy), and then were assayed at subsequent time-points. Survival curves were then generated using a linear-quadratic (LQ) equation and a modified induced repair model (MIRM). The percentage of cells in the G1, G2/M, and S phases of the cell cycle were also examined using propidium iodide (PI) staining and flow cytometry. Levels of total cell division cyclin 25C (Cdc25C) and phosphorylated Cdc25C were examined by Western blotting.

Results: Low-dose γ radiation (<0.3?Gy) induced HRS in HepG2 cells, while doses of 0.3, 0.5, and 2.0?Gy γ radiation significantly arrested HepG2 cells in the G2/M phase. While total Cdc25C levels remained unchanged after irradiation, levels of phosphorylated Cdc25C markedly increased 6, 16, and 24?h after treatment with 0.5 or 2.0?Gy radiation, and they peaked after 16?h. The latter observation is consistent with the G2/M arrest that was detected following irradiation.

Conclusions: These findings indicate that low-dose HRS in HepG2 cells may be associated with Cdc25C-mediated G2/M cell cycle checkpoint control.     

WAF1 accumulation by carbon-ion beam and alpha-particle irradiation in human glioblastoma cultured cells

PURPOSE: There have been no reports about the effects of heavy-ion beams on the expression of the WAF1 gene, although ionizing radiation such as y-rays and X-rays is well known to induce WAF1 (p21/CIP1/sdi1) gene expression in a p53-dependent manner. In the present study, it was examined whether WAF1 accumulation was induced after carbon-ion (C-) beam or alpha-particle irradiation in four glioblastoma cell lines. MATERIALS AND METHODS: A colony assay for radiosensitivity and Western blot analysis of WAF1 were applied to two human glioblastoma cell lines, A-172 bearing wild-type p53 (wtp53) and T98G bearing mutated p53 (mp53). A-172/neo and A-172/mp53 were transfected with a control vector (containing only a neo selection marker) and a mp53 expression vector respectively. RESULTS: The amount of WAF1 increased markedly after X-ray irradiation in A-172 and A-172/neo cells but not in T98G and A-172/mp53 cells. The level of WAF1 reached a plateau at 3-10 h after X-ray irradiation at 5 Gy in A-172 and A-172/neo cells. Likewise, the levels of WAF1 in A-172 and A-172/neo cells reached a plateau at 3-10 h and 6-24 h after C-beam (3.0 Gy) and alpha-particle (4.5 Gy) irradiation respectively. The amount of WAF1 increased markedly in a dose-dependent manner 10 h after X-ray, C-beam or alpha-particle irradiation in A-172 and A-172/neo cells but not in T98G or A-172/mp53 cells. In addition, cell survival assay showed that these cell lines were most sensitive to C-beams, less sensitive to alpha-particles and least sensitive to X-rays at 10% survival. There was no difference in sensitivity among these cell lines against C-beam and alpha-particle irradiation whereas wtp53 cells (A-172 and A-172/neo) were more sensitive to X-rays than mp53 cells (A-172/mp53 and T98G). CONCLUSIONS: These results indicate that C-beams and alpha-particles induce p53-dependent WAF1 accumulation as well as is the case with X-rays, suggesting that WAF1 protein accumulation may not contribute to cell killing.     

Initially Accelerated Fractionation of the R1H Tumor of the Rat Increases Local Tumor Control and Might Reduce Impact of Overall Treatment Time

PURPOSE: To study the effect of treatment time prolongation following initial dose acceleration on the response of subcutaneously growing R1H tumor. MATERIAL AND METHODS: Continuous standard fractionation (30 fractions/40 days) was compared to initially accelerated treatment (30 fractions/21 days) followed by five to two fractions per week yielding total treatment times from 40 to 72 days. Local tumor control was assessed as endpoint. RESULTS: Radiation dose to control 50% of the tumors (TCD50%) decreased statistically significant from 83.5 Gy (95% confidence interval [CI]: 78.6 .. 88.4) for standard fractionation to 74.1 Gy (95% CI: 72.7 .. 75.5) determined for all accelerated treatment arms (p = 0.003). Prolongation of treatment time after initial acceleration from 40 to 72 days led to a small but statistically not significant increase in TCD50% from 72.0 Gy (95% CI: 71.0 .. 72.9) to 76.2 Gy (95% CI: 69.9 .. 82.4) corresponding to a repopulated dose of 0.9 Gy per week. This time factor is considerably smaller than for conventional radiation treatment as determined in previous experiments. CONCLUSION: The results indicate that initially accelerated irradiation not only improves local tumor control but also minimizes the negative effect of treatment time prolongation. This might be due to changes in tumor cell repopulation kinetics.     

WAF1 accumulation by carbon-ion beam and alpha-particle irradiation in human glioblastoma cultured cells

Purpose : There have been no reports about the effects of heavy-ion beams on the expression of the WAF1 gene, although ionizing radiation such as gamma-rays and X-rays is well known to induce WAF1 (p21/CIP1/sdi1) gene expression in a p53 -dependent manner. In the present study, it was examined whether WAF1 accumulation was induced after carbon-ion (C-) beam or alpha-particle irradiation in four glioblastoma cell lines. Materials and methods : A colony assay for radiosensitivity and Western blot analysis of WAF1 were applied to two human glioblastoma cell lines, A-172 bearing wild-type p53 (wt p53) and T98G bearing mutated p53 (m p53) . A-172/neo and A-172/mp53 were transfected with a control vector (containing only a neo selection marker) and a m p53 expression vector respectively. Results : The amount of WAF1 increased markedly after X-ray irradiation in A-172 and A-172/neo cells but not in T98G and A-172/mp53 cells. The level of WAF1 reached a plateau at 3-10 h after X-ray irradiation at 5 Gy in A-172 and A-172/neo cells. Likewise, the levels of WAF1 in A-172 and A-172/neo cells reached a plateau at 3-10 h and 6-24 h after C-beam (3.0Gy) and alpha-particle (4.5 Gy) irradiation respectively. The amount of WAF1 increased markedly in a dose-dependent manner 10 h after X-ray, C-beam or alpha-particle irradiation in A-172 and A172/neo cells but not in T98G or A-172/mp53 cells. In addition, cell survival assay showed that these cell lines were most sensitive to C-beams, less sensitive to alpha-particles and least sensitive to X-rays at 10% survival. There was no difference in sensitivity among these cell lines against C-beam and alpha-particle irradiation whereas wt p53 cells (A-172 and A-172/neo) were more sensitive to X-rays than m p53 cells (A-172/mp53 and T98G). Conclusions : These results indicate that C-beams and alpha-particles induce p53 -dependent WAF1 accumulation as well as is the case with X-rays, suggesting that WAF1 protein accumulation may not contribute to cell killing.     

No Effect of the Hemoglobin Solution HBOC-201 on the Response of the Rat R1H Tumor to Fractionated Irradiation

BACKGROUND AND PURPOSE: Tumor hypoxia is regarded as one important underlying feature of radioresistance. The authors report on an experimental approach to improve tumor response to radiation by combining fractionated irradiation with HBOC-201, an ultrapurified polymerized hemoglobin solution, which is currently used in clinical phase II/III trials as alternative oxygen carrier and proved to be highly effective in tissue oxygenation (tpO(2)). MATERIAL AND METHODS: Subcutaneously growing rhabdomyosarcoma R1H tumors of the rat were treated with either 40 Gy (2 Gy/fraction, 20 fractions in 2 weeks, ambient) followed by graded top-up doses (clamped) alone, or in combination with HBOC-201, or with HBOC-201 plus carbogen (95% O(2) + 5% CO(2)). Local tumor control (TCD50%) and growth delay were used as endpoints. In addition, the effect of HBOC-201 alone or in combination with carbogen on the tpO(2) of tumor and muscle was determined using a flexible stationary probe (Licox, GMS). RESULTS: TCD50% values of 119 Gy (95% confidence interval 103;135), 111 Gy (84;138), and 102 Gy (83;120) were determined for tumors irradiated alone, in combination with HBOC-201, and with HBOC-201 plus carbogen, respectively. Although the dose-response curves showed a slight shift to lower doses when HBOC-201 or HBOC-201 plus carbogen was added, the differences in TCD50% were not statistically significant. No effect was seen on the growth delay of recurrent tumors. HBOC-201 alone did not effect tumor or muscle tpO(2). In combination with carbogen the mean tpO(2) of muscle raised from 23.9 mmHg to 59.3 mmHg (p < 0.05), but this effect was less pronounced than the increase in tpO(2) by carbogen alone. CONCLUSION: Low-dose application of HBOC-201 does not improve the response of the rhabdomyosarcoma R1H of the rat to fractionated irradiation.     

Effect of changing the weekly dose intensity of fractionated irradiation on local control of two human squamous cell carcinomas in nude mice

Purpose : To compare the effect of fractionated irradiation with increasing, constant or decreasing weekly dose intensity on local tumour control. Materials and methods : Human squamous cell carcinomas, FaDu and GL, were grown in nude mice. Thirty fractions were applied under ambient conditions with increasing, constant or decreasing weekly dose intensity within a constant overall treatment time of 6 weeks. Dose intensity was changed every 2 weeks. Irradiations were terminated in some groups of animals after 20 fractions in 4 weeks. Endpoint was the tumour control dose 50% (TCD 50) at day 120 (FaDu) or day 180 (GL) after end of treatment. Results : In FaDu tumours the TCD 50 value of 60 Gy (95% CI 56; 63) for fractionated irradiation with decreasing dose intensity, i.e. high initial doses, was slightly but significantly lower than the TCD50 of 68 Gy (60; 81) after low initial doses (p =0.03). The TCD50 value of 62Gy (57; 68) after constant doses was intermediate (constant vs increasing p =0.30; constant vs decreasing p =0.15). The higher effecacy of high initial doses in FaDu tumours was explained by local control occurring already during the course of irradiation. In GL tumours the TCD50 values were 52Gy (43; 62) after high initial dose intensity, 50 Gy (43; 66) after constant doses, and 55 Gy (42; 89) after low initial dose intensity. These values were not statistically different (p -values 0.20-0.75). Conclusions : The data support the view that initial dose concentration during fractionated irradiation does not enhance radioresistance of FaDu and GL tumours, for instance by an earlier onset of clonogen repopulation.