Structure–activity Relationships for Tumour Radiosensitization by Analogues of Nicotinamide and Benzamide

Summary

Nicotinamide has been shown in our laboratory and those of other investigators to be an effective radiosensitizer of a variety of mouse tumours, while producing little or no radiosensitization of normal tissues. Its mechanism of action is different from classical electron-affinic compounds and appears to be the result of improved tumour oxygenation. In this study we have synthesized 29 analogues of nicotinamide and benzamide and characterized them for their tumour radiosensitization and acute toxicity in mice. The data show that a wide range of additions to the nicotinamide and benzamide ring produce tumour radiosensitization similar to that produced by equimolar doses of misonidazole, but that substitutions of the amide tend to reduce radiosensitization. Other structure–activity relationships are evident. Although some compounds produce similar tumour radiosensitization to nicotinamide at equimolar doses, and are comparably low in acute toxicity, none appears sufficiently superior to supplant nicotinamide itself as a candidate for clinical trials. Thus these data provide evidence that nicotinamide, because of the extensive experience with its use in man, is likely to be the best drug in the benzamide–nicotinamide series for development as a radiosensitizer of human tumours.     

Differential Radiosensitization of Human Tumour Cells by 3-aminobenzamide and Benzamide: Inhibitors of Poly(ADP-ribosylation)

Summary

The effect of 3-aminobenzamide (3AB) and benzamide (BZ) (inhibitors of poly(ADP-ribose) synthetase) on radiosensitivity was investigated in normal human fibroblasts and three human cell lines established from tumours with varying degrees of clinical radiocurability. The human tumour cell lines selected were: (1) Ewing's sarcoma, a bone tumour usually considered radiocurable with moderate radiation doses; (2) lung adenocarcinoma, a tumour considered radiocurable with high doses of radiotherapy; and (3) osteosarcoma, a very resistant tumour which is rarely controlled by standard doses of radiotherapy. Poly(ADP-ribose) synthetase inhibitors were added to cultures 2h prior to irradiation and removed 24h after. Inhibitors were used at doses producing little or no toxicity in cells.

In the presence of these inhibitors, a differential radiosensitization was observed. Ewing's sarcoma cells and normal human fibroblasts were sensitized to an equal extent by either 8 mm 3AB or 4 mm BZ. However, no sensitization was observed at these concentrations in the lung adenocarcinoma cells or osteosarcoma cells. The degree of radiosensitization in vitro by 3AB and BZ correlates well with the clinical radiocurability of these tumours in vivo.     

Is sensitization with nicotinamide and carbogen dependent on nicotinamide concentration at the time of irradiation?

PURPOSE: To determine whether tumour radiosensitization and the therapeutic benefit of administering carbogen with nicotinamide depend upon irradiating at the time of peak drug concentration. MATERIALS AND METHODS: Local tumour control of CaNT tumours in CBA mice and acute skin reactions in albino WHT mice were assessed after treatment with 10 X-ray fractions in air, carbogen alone or combined with 0.1, 0.2 or 0.5 mg g(-1) nicotinamide, injected 15, 30 or 60 min before irradiation. Plasma and tumour drug pharmacokinetics were performed. RESULTS: Nicotinamide was rapidly taken up into tumours; a six- and threefold higher concentration was obtained with 0.5 mg g(-1) compared with 0.1 and 0.2 mg g(-1), respectively. Tumour, but not skin, radiosensitization increased as the dose of nicotinamide increased (p = 0.03), but at each dose level there was no significant difference in radiosensitivity when irradiations were done at or after the time of peak concentration. An almost eightfold increase in plasma levels increased tumour enhancement ratios from 1.74 to 1.92 (p < 0.0001). In tumours all schedules gave significant enhancement relative to carbogen alone (p < or = 0.04). CONCLUSIONS: Tumour and skin radiosensitivity was independent of time of nicotinamide administration. Higher drug concentrations were not mirrored by proportionally higher enhancement ratios. Lower plasma levels than previously suggested significantly enhanced tumour radiosensitivity relative to carbogen alone. The clinical implications of these findings are discussed.     

Is sensitization with nicotinamide and carbogen dependent on nicotinamide concentration at the time of irradiation?

Purpose: To determine whether tumour radiosensitization and the therapeutic benefit of administering carbogen with nicotinamide depend upon irradiating at the time of peak drug concentration.

Materials and methods: Local tumour control of CaNT tumours in CBA mice and acute skin reactions in albino WHT mice were assessed after treatment with 10 X‐ray fractions in air, carbogen alone or combined with 0.1, 0.2 or 0.5?mg?g^?1 nicotinamide, injected 15, 30 or 60?min before irradiation. Plasma and tumour drug pharmacokinetics were performed.

Results: Nicotinamide was rapidly taken up into tumours; a six‐ and threefold higher concentration was obtained with 0.5?mg?g^?1 compared with 0.1 and 0.2?mg?g^?1, respectively. Tumour, but not skin, radiosensitization increased as the dose of nicotinamide increased (p=0.03), but at each dose level there was no significant difference in radiosensitivity when irradiations were done at or after the time of peak concentration. An almost eightfold increase in plasma levels increased tumour enhancement ratios from 1.74 to 1.92 (p<0.0001). In tumours all schedules gave significant enhancement relative to carbogen alone (p≤0.04).

Conclusions: Tumour and skin radiosensitivity was independent of time of nicotinamide administration. Higher drug concentrations were not mirrored by proportionally higher enhancement ratios. Lower plasma levels than previously suggested significantly enhanced tumour radiosensitivity relative to carbogen alone. The clinical implications of these findings are discussed.     

The potential therapeutic gain of radiation-associated gene therapy with the suicide gene cytosine deaminase

PURPOSE: To estimate the concentration of 5-fluorocytosine (5-FC), necessary for conversion to 5-fluorouracil (5-FU) in tumours transduced with the gene cytosine deaminase (CD), to achieve clinically significant radiosensitization to radiotherapy. MATERIALS AND METHODS: Starting with a tumour control probability (TCP) of 37% from radiotherapy of 66 Gy in 2 Gy fractions, estimates were made of increase in TCP expected from sensitizer enhancement ratios (SER) of 1.1, 1.2, etc. SER values for 5-FU were obtained from a literature review. Clinical toxicity of 5-FC is also reviewed. RESULTS: 5-FU has been reported to be an effective radiosensitizer if maintained for several days after each irradiation at concentrations of 0.6-0.9 microg/ml in surrounding medium. 5-FC is well tolerated by patients at concentrations of 25-100 microg/ml (average 60 microg/ml) for 6 weeks in standard antifungal treatment. Sufficient 5-FU should be available if conversion efficiency from 5-FC is 1-3%. SER values of 1.1 to 1.2 should be achievable with daily 2 Gy fractions. In vitro and xenograft experiments are reviewed and they do not contradict the conclusions. CONCLUSIONS: Increases in tumour control of 20 to 40% can be expected, which should be detectable in a 2-arm randomized trial of 260 (for 20%) or 60 (for 40%) patients.     

Radiosensitization of C3H mouse mammary tumours using fractionated doses of x rays with the drug Ro-07-0582.

Three fractionated X-ray schedules were used, with and without the electron-affinic radiosensitizer of hypoxic cells, Ro-07-0582, to determine the local control of first-generation transplants of spontaneous mammary tumours in C3H mice. Three or five fractions were given in either four or nine days overall time. The results were compared with acute skin reactions in other mice caused by the same treatment schedules. For a given skin reaction, the local control of tumours varied widely, from good to bad, when different X-ray only schedules were used. All three schedules using Ro-07-0582 however yielded good results. It appears that the use of the hypoxic-cell radiosensitizer took the unreliability out of these short fractionated treatments.     

Chemical agents that promote chromatin compaction radiosensitize tumour cells

Purpose : Previous studies indicated that cells whose chromatin is naturally compacted at the time of radiation are hypersensitive to radiation-induced killing, primarily by single-hit inactivation. Some chemicals that are known to promote chromatin compaction in interphase cells are here investigated for their radiosensitizing potential. Materials and methods : Okadaic acid (OA), a protein phosphatase inhibitor, fostriecin (FC), a topoisomerase II inhibitor and trichostatin A (TSA), a histone deacetylase inhibitor, were reported to promote chromatin compaction in mammalian cells. Asynchronous populations of HT-29 (human colon carcinoma) cells were exposed to various concentrations of OA, FC and TSA for various times before irradiation with various doses of Cs-137 n -rays and toxicity and radiosensitization were measured. Induced chromatin compaction was visualized by electron microscopy (EM). Histone 1 (H1) and histone 3 (H3) phosphorylation was measured by Western blotting, whole-cell fluorescence microscopy and confocal microscopy. Results : OA and FC produced significant radiosensitization at 2 Gy after short (2 h) exposures. These chemical treatments also produced increased phosphorylation of H3 and increased chromatin compaction as measured by EM. A 2-h exposure of cells to TSA had no effect on cell radiosensitivity, histone phosphorylation or chromatin condensation. However, a 16-h exposure to TSA produced significant radiosensitization, histone phosphorylation and chromatin condensation, presumably by secondary mechanisms. Conclusions : These data are consistent with the hypothesis that compacted chromatin is a hypersensitive target for radiation killing. Furthermore, the modulation of chromatin conformation by drugs selectively in tumour cells might radiosensitize tumours whose cells are intrinsically radioresistant.     

Chemical agents that promote chromatin compaction radiosensitize tumour cells.

PURPOSE: Previous studies indicated that cells whose chromatin is naturally compacted at the time of radiation are hypersensitive to radiation-induced killing, primarily by single-hit inactivation. Some chemicals that are known to promote chromatin compaction in interphase cells are here investigated for their radiosensitizing potential. MATERIALS AND METHODS: Okadaic acid (OA), a protein phosphatase inhibitor, fostriecin (FC), a topoisomerase II inhibitor and trichostatin A (TSA), a histone deacetylase inhibitor, were reported to promote chromatin compaction in mammalian cells. Asynchronous populations of HT-29 (human colon carcinoma) cells were exposed to various concentrations of OA, FC and TSA for various times before irradiation with various doses of Cs-137 gamma-rays and toxicity and radiosensitization were measured. Induced chromatin compaction was visualized by electron microscopy (EM). Histone 1 (H1) and histone 3 (H3) phosphorylation was measured by Western blotting, whole-cell fluorescence microscopy and confocal microscopy. RESULTS: OA and FC produced significant radiosensitization at 2 Gy after short (2 h) exposures. These chemical treatments also produced increased phosphorylation of H3 and increased chromatin compaction as measured by EM. A 2-h exposure of cells to TSA had no effect on cell radiosensitivity, histone phosphorylation or chromatin condensation. However, a 16-h exposure to TSA produced significant radiosensitization, histone phosphorylation and chromatin condensation, presumably by secondary mechanisms. CONCLUSIONS: These data are consistent with the hypothesis that compacted chromatin is a hypersensitive target for radiation killing. Furthermore, the modulation of chromatin conformation by drugs selectively in tumour cells might radiosensitize tumours whose cells are intrinsically radioresistant.     

Radiosensitization by misonidazole, pimonidazole and azomycin and intracellular uptake in human tumour cell lines

The radiosensitization of two human tumour in vitro cell lines, HT-1080 and LoVo, has been compared with that of the Chinese hamster cell line V79-379A. Although the two human tumour cell lines were more radiosensitive than the V79 cell line sensitizer, enhancement ratios for misonidazole, pimonidazole and azomycin were similar (relative to extracellular concentration) for all three cell lines. Average intracellular concentrations of radiosensitizer were measured by high-performance liquid chromatography. In all three cell lines the uptake of misonidazole and azomycin was extremely rapid whereas that of pimonidazole was initially much slower before reaching a plateau. The ratios of intracellular concentration of radiosensitizer to extracellular concentration (Ci to Ce) for misonidazole were 0.8 (HT-1080) and 0.7 (LoVo and V79); for azomycin 0.9 (HT-1080 and LoVo) and 0.8 (V79). In contrast Ci/Ce for pimonidazole varied with cell line, the values being 1.8 (LoVo), 2.6 (HT-1080) and 3.3 (V79). Intracellular amounts of non-protein sulphydryl (NPSH) varied between cell lines by about a factor of three. However, when the average cell volume was taken into consideration the concentrations of NPSH were very similar, being 4.2 (HT-1080), 5.6 (LoVo) and 5.7 (V79) mmol dm-3. NPSH levels expressed as nmol per mg protein were also similar.     

Lung tumour growth delay and normal tissue toxicity induced by three cytotoxic platinum drugs.

Single doses of the drug cisplatin and its analogues carboplatin and iproplatin were administered to tumour-bearing rats. The tumours used were two bronchial squamous cell carcinomas, that are part of a panel of experimental lung tumours developed at this institute. Cisplatin resulted in severe nephrotoxicity. Carboplatin and iproplatin were less nephrotoxic, but resulted in acute gastrointestinal and (probably) hematological toxicity. Carboplatin also caused late occurring liver damage. The responses of the tumours were compared at the level of maximum tolerated drug doses for early toxicity. The level of response was different for the two tumours. One was more sensitive to the drugs than the other. The effects of cisplatin and carboplatin were approximately similar. Iproplatin was less effective. Because cisplatin caused more severe late toxicity, it is concluded that carboplatin has the best therapeutic index for these two lung tumours.     

Threshold dose–response in radiation carcinogenesis: an approach from chronic β-irradiation experiments and a review of non-tumour doses

Purpose : To discuss the threshold dose problem in radiation carcinogenesis after a review of the present author's experimental data on mouse tumour induction by chronic β -irradiation and other relevant data. Conclusions : A threshold dose-response in radiation carcinogenesis appears in certain tissues and under certain conditions. The optimum condition for demonstrating an apparent threshold is with partial-body chronic or repeated radiation rather than with acute whole-body radiation. Its possible mechanism is host tolerance, involving DNA repair, apoptosis and an immune response activated by low radiation doses. This tolerance level was examined by a survey in the literature of non-tumour-inducing doses, D nt, the highest dose at which no significant increase of tumours was observed above the control level.     

Threshold dose-response in radiation carcinogenesis: an approach from chronic beta-irradiation experiments and a review of non-tumour doses

PURPOSE: To discuss the threshold dose problem in radiation carcinogenesis after a review of the present author's experimental data on mouse tumour induction by chronic beta-irradiation and other relevant data. CONCLUSIONS: A threshold dose-response in radiation carcinogenesis appears in certain tissues and under certain conditions. The optimum condition for demonstrating an apparent threshold is with partial-body chronic or repeated radiation rather than with acute whole-body radiation. Its possible mechanism is host tolerance, involving DNA repair, apoptosis and an immune response activated by low radiation doses. This tolerance level was examined by a survey in the literature of non-tumour-inducing doses, D(nt), the highest dose at which no significant increase of tumours was observed above the control level.     

Evaluation of risk factors for lung tumour induction in rats exposed to either NpO 2 or PuO 2 aerosols

Purpose : To compare the incidence of each lung tumour type after inhalation exposure of rats to either NpO 2 or industrial PuO 2 aerosols, which have a similar size. Materials and methods : Male Sprague-Dawley rats were exposed once and followed during their whole life span. At the end of their life, the whole lungs were fixed, embedded and cut into thin sections for histological analysis. The presence of tumours was evaluated on three distinct levels of the lobes for phenotype determination to establish dose-effect relationships. Results : In the range of lung doses studied (0.05 to more than 50 Gy), the general trend was an increased frequency of all types of tumours after inhalation exposure to neptunium compared with plutonium. The linearity of the lower part of the dose-effect relationships for all malignant lung tumours leads to the conclusion that NpO 2 is 3.3-fold more carcinogenic than PuO 2. Conclusions : According to a linear extrapolation of the data on malignant lung tumour incidence collected among all studies reported on actinide oxide carcinogenesis, the risk of lung tumour appears to vary over a factor of about 10 depending on the nature and/or size of the aerosol. This variation has to be taken into account for a realistic assessment of tumour risk.     

Evaluation of risk factors for lung tumour induction in rats exposed to either NpO(2) or PuO(2) aerosols

PURPOSE: To compare the incidence of each lung tumour type after inhalation exposure of rats to either NpO(2) or industrial PuO(2) aerosols, which have a similar size. MATERIALS AND METHODS: Male Sprague-Dawley rats were exposed once and followed during their whole life span. At the end of their life, the whole lungs were fixed, embedded and cut into thin sections for histological analysis. The presence of tumours was evaluated on three distinct levels of the lobes for phenotype determination to establish dose-effect relationships. RESULTS: In the range of lung doses studied (0.05 to more than 50 Gy), the general trend was an increased frequency of all types of tumours after inhalation exposure to neptunium compared with plutonium. The linearity of the lower part of the dose-effect relationships for all malignant lung tumours leads to the conclusion that NpO(2) is 3.3-fold more carcinogenic than PuO(2). CONCLUSIONS: According to a linear extrapolation of the data on malignant lung tumour incidence collected among all studies reported on actinide oxide carcinogenesis, the risk of lung tumour appears to vary over a factor of about 10 depending on the nature and/or size of the aerosol. This variation has to be taken into account for a realistic assessment of tumour risk.     

Radiosensitization of tumour cells by cantharidin and some analogues

PURPOSE: Mammalian cells at mitosis contain chromatin in compacted form and are hypersensitive to ionizing radiation. Previous research had shown some chemicals that induce chromatin compaction within interphase cells act as radiosensitizers. Of these agents, cantharidin (LS-1), which is an inhibitor of protein phosphatases 1 (PP1) and 2A (PP2A), showed good radiosensitizing activity at non-toxic doses. Cantharidin and 13 additional structural analogues (LS-2-14) were tested for their radiosensitizing activity on tumour cells in vitro. MATERIALS AND METHODS: Twelve of the 14 cantharidin analogues were synthesized in the authors' laboratory. Various concentrations of the drugs were screened for toxicity and radiosensitizing effectiveness with asynchronous DU-145 (human prostate carcinoma) cells. More detailed radiobiological studies of the more potent agents were performed with HT-29 (human colon carcinoma) cells since they could be readily synchronized. The radiosensitization of G1 phase HT-29 cells was measured after a 2-h exposure to the more potent drugs and reductions of the surviving fraction after an acute dose of 2 Gy (SF2Gy) served to estimate their relative effectiveness. The increase in phosphorylation of histone 1 (H1) and histone 3 (H3) induced by these drug exposures was measured by Western blotting of protein extracts. Drug-induced change in chromatin morphology was visualized by electron microscopy, and the alkaline comet assay (which measures DNA single-strand breaks) was employed to measure the radiation sensitivity of cellular chromatin in the drug-treated cells. RESULTS: Of the 14 cantharidin analogues tested, LS-1, LS-2 and LS-5 at concentrations of 3-20 microM showed little or no toxicity, produced elevated levels of H1 and H3 phosphorylation, and effected significant radiosensitization at low radiation dose. The chromatin in tumour cells treated with LS-5 became visibly compacted and its DNA was about 1.6 times more sensitive to radiation-induced strand breakage relative to that of control cells. CONCLUSIONS: The results confirm the authors' earlier studies that showed an increase in tumour cell intrinsic radiosensitivity by exposure to agents that promote chromatin compaction. LS-5 was identified as the optimal radiosensitizing agent of this class of compounds. Radiosensitization was correlated with chromatin compaction and elevated phosphorylation of H1 and H3. The DNA in drug-treated cells exhibited an enhanced sensitivity to radiation-induced single-strand breakage.     

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.     

The response of six mouse tumours to combined heat and X rays: implications for therapy.

The response of six types of mouse tumour to single doses of X rays alone or to X rays in combination with moderate hyperthermia (42.5 degrees C/60 min) has been assessed using delay in tumour regrowth. Thermal sensitization was observed in five of the six tumours. The degree of sensitization varied with the size of the X-ray dose, being larger at higher doses. The degree of sensitization also depended on the sequence and separation of the heat and irradiation. The thermal sensitization has been measured in terms of the X-ray doses to produce the same level of tumour damage with or without heat, i.e. thermal enhancement ratios. These TER values, measured for X-ray doses in excess of 20 Gy, are not greater in any of the tumours than in a range of normal tissues, if the X rays and heat are given in close succession. Separation of the heat and X rays reduces the TER values slightly, but some effect is still apparent at 3--24 hours. In normal tissues the effect of heat is totally lost within four hours. Comparison of these tumour data with published normal tissue data indicates a therapeutic advantage if the heat and X rays are separated by more than one hour. This therapeutic gain is most reliably achieved and heat given after irradiation.     

Reducing intratumour acute hypoxia through bevacizumab treatment, referring to the response of quiescent tumour cells and metastatic potential

Objectives

The aim was to evaluate the influence of bevacizumab on intratumour oxygenation status and lung metastasis following radiotherapy, with specific reference to the response of quiescent (Q) cell populations within irradiated tumours.

Methods

B16-BL6 melanoma tumour-bearing C57BL/6 mice were continuously given 5-bromo-2-deoxyuridine (BrdU) to label all proliferating (P) cells. They received γ-ray irradiation following treatment with the acute hypoxia-releasing agent nicotinamide or local mild temperature hyperthermia (MTH) with or without the administration of bevacizumab under aerobic conditions or totally hypoxic conditions, achieved by clamping the proximal end of the tumours. Immediately after the irradiation, cells from some tumours were isolated and incubated with a cytokinesis blocker. The responses of the Q and total (P + Q) cell populations were assessed based on the frequency of micronuclei using immunofluorescence staining for BrdU. In the other tumour-bearing mice, macroscopic lung metastases were enumerated 17 days after irradiation.

Results

3 days after bevacizumab administration, acute hypoxia-rich total cell population in the tumour showed a remarkably enhanced radiosensitivity to γ-rays, and the hypoxic fraction (HF) was reduced, even after MTH treatment. However, the hypoxic fraction was not reduced after nicotinamide treatment. With or without γ-ray irradiation, bevacizumab administration showed some potential to reduce the number of lung metastases as well as nicotinamide treatment.

Conclusion

Bevacizumab has the potential to reduce perfusion-limited acute hypoxia and some potential to cause a decrease in the number of lung metastases as well as nicotinamide.It was believed that antiangiogenic therapy prevents tumour vascular growth and proliferation and deprives the tumour of oxygen and nutrients necessary for survival [1]. However, subsequent study has suggested that antiangiogenic therapy may also “normalise” the tumour vasculature for a short period of time, thereby providing a window of opportunity for improved drug delivery and enhanced sensitivity to radiation [1,2]. Tumour hypoxia results from either limited oxygen diffusion (chronic hypoxia) or limited perfusion (acute hypoxia) [3]. Furthermore, it has been reported that acute and cyclic, but not chronic, hypoxia significantly increases the number of spontaneous lung metastases, and that this effect is due to the influence of acute hypoxia treatment on the primary tumour [4,5].In this study, we attempted to analyse hypoxia in solid tumours after the administration of the vascular endothelial growth factor (VEGF) inhibitor, bevacizumab, using the acute hypoxia-releasing agent nicotinamide combined with γ-ray irradiation in terms of both local tumour response and lung metastasis compared with irradiation combined with mild temperature hyperthermia (MTH), which has already been shown to have the potential to release tumour cells from diffusion-limited chronic hypoxia [6,7]. In addition, for the local tumour response, the effect on the total (proliferating (P)+quiescent (Q)) tumour cell population and on the Q cell population was evaluated using our original method for detecting the response of Q cells in solid tumours [8].     

Radiosensitization of Chinese Hamster Cells by Oxygen and Misonidazole at Low X-ray Doses

Summary

The radiosensitization of Chinese hamster V79 cells in vitro by air and misonidazole at low X-ray doses (0·2–6·0 Gy) had been studied. These survival data, together with high-dose data, were fitted to the linear quadratic model ln S = ?(αD + βD²), deriving estimates of α and β by six different methods to illustrate the influence of the statistical treatment on the values so derived. This in vitro study clearly demonstrated that the survival parameters α and β are dependent to some degree on the method of analysis of the raw survival data; however, their ratios, the values of oxygen enhancement ratios (OERs) and radiosensitizer enhancement ratios (SERs) derived from the different methods, are similar. All methods of analysis give reduced OERs at low radiation doses for combined low- and high-dose X-ray data. However, the OERs are still appreciably high, ranging from 2·45 to 2·50 for an oxic dose of 2 Gy. All methods of analysis gave reduced SERs at low doses for combined low and high X-ray dose data for hypoxic cells irradiated in 1 mmol dm^?3 misonidazole. At survival levels corresponding to doses of 2 Gy in the presence of 1 mmol dm^?3 misonidazole and SERs ranged from 1·2 to 1·5.