Effects on intermediary metabolism in mouse tissues by Ro-03-8799

NADPH oxidase-mediated reactive oxygen species production activates hypoxia-inducible factor-1 (HIF-1) via the ERK pathway after hyperthermia treatment

Hyperthermia (HT) is a strong adjuvant treatment with radiotherapy and chemotherapy because it causes tumor reoxygenation. However, the detailed molecular mechanisms of how HT enhances tumor oxygenation have not been elucidated. Here we report that 1 h of HT activates hypoxia-inducible factor-1 (HIF-1) in tumors and its downstream targets, vascular endothelial growth factor (VEGF) and pyruvate dehydrogenase kinase 1 (PDK1). Consistent with HIF-1 activation and up-regulation of its downstream genes, HT also enhances tumor perfusion/vascularization and decreases oxygen consumption. As a result, tumor hypoxia is reduced after HT, suggesting that these physiological changes contribute to HT-induced tumor reoxygenation. Because HIF-1 is a potent regulator of tumor vascularization and metabolism, our findings suggest that HIF-1 plays a role in HT-induced tumor reoxygenation by transactivating its downstream targets. We demonstrate that NADPH oxidase-mediated reactive oxygen species production, as a mechanism, up-regulates HIF-1 after HT. Furthermore, we determine that this pathway is initiated by increased transcription of NADPH oxidase-1 through the ERK pathway. In conclusion, this study determines that, although HIF-1 is a good therapeutic target, the timing of its inhibition needs to be optimized to achieve the most beneficial outcome when it is combined with other treatments of HT, radiation, and chemotherapy.

Heterogeneity in 2-deoxy-D-glucose-induced modifications in energetics and radiation responses of human tumor cell lines

PURPOSE

The glucose analog and glycolytic inhibitor, 2-deoxy-D-glucose (2-DG), has been shown to differentially enhance the radiation damage in tumor cells by inhibiting the postirradiation repair processes. The present study was undertaken to examine the relationship between 2-DG-induced modification of energy metabolism and cellular radioresponses and to identify the most relevant parameter(s) for predicting the tumor response to the combined treatment of radiation + 2-DG.

METHODS AND MATERIALS

Six human tumor cell lines (glioma: BMG-1 and U-87, squamous cell carcinoma: 4451 and 4197, and melanoma: MeWo and Be-11) were investigated. Cells were exposed to 2 Gy of Co-60 gamma-rays or 250 kVP X-rays and maintained under liquid-holding conditions 2-4 h to facilitate repair. 2-DG (5 mM, equimolar with glucose) that was added at the time of irradiation was present during the liquid holding. Glucose utilization, lactate production (enzymatic assays), and adenine nucleotides (high performance liquid chromatography and capillary isotachophoresis) were investigated as parameters of energy metabolism. Induction and repair of DNA damage (comet assay), cytogenetic damage (micronuclei formation), and cell death (macrocolony assay) were analyzed as parameters of radiation response.

RESULTS

The glucose consumption and lactate production of glioma cell lines (BMG-1 and U-87) were nearly 2-fold higher than the squamous carcinoma cell lines (4197 and 4451). The ATP content varied from 3.0 to 6.5 femto moles/cell among these lines, whereas the energy charge (0.86-0.90) did not show much variation. Presence of 2-DG inhibited the rate of glucose usage and glycolysis by 30-40% in glioma cell lines and by 15-20% in squamous carcinoma lines, while ATP levels reduced by nearly 40% in all the four cell lines. ATP:ADP ratios decreased to a greater extent ( approximately 40%) in glioma cells than in squamous carcinoma 4451 and MeWo cells; in contrast, presence of 2-DG reduced ADP:AMP ratios by 3-fold in the squamous carcinoma 4451, whereas an increase was noted in the glioma cell line BMG-1. 2-DG significantly reduced the initial rates of DNA repair in all cells, resulting in an excess residual damage after 2 h of repair in BMG-1, U-87, and 4451 cell lines, whereas no significant differences could be observed in the other cell lines. Recovery from potentially lethal damage was also significantly inhibited in BMG-1 cells. 2-DG increased the radiation-induced micronuclei formation in the melanoma line (MeWo) by nearly 60%, while a moderate (25-40%) increase was observed in the glioma cell lines (BMG-1 and U-87). Presence of 2-DG during liquid holding (4 h) enhanced the radiation-induced cell death by nearly 40% in both the glioma cell lines, while significant effects were not observed in others.

CONCLUSIONS

The modifications in energetics and radiation responses by 2-DG vary considerably among different human tumor cell lines, and the relationships between energy metabolism and various radiobiologic parameters are complex in nature. The 2-DG-induced modification of radiation response does not strictly correlate with changes in the levels of ATP. However, a significant enhancement of the radiation damage by 2-DG was observed in cells with high rates of glucose usage and glycolysis, which appear to be the two most important factors determining the tumor response to the combined treatment of 2-DG + radiation therapy.

Hematoporphyrin derivatives potentiate the radiosensitizing effects of 2-deoxy-D-glucose in cancer cells

PURPOSE

Two deoxy-D-glucose (2-DG), an inhibitor of glucose transport and glycolysis, has been shown to differentially inhibit the repair of radiation damage in cancer cells by reducing the flow of metabolic energy. Since hematoporphyrin derivatives (Hpd) inhibit certain enzymes of the respiratory metabolism, resulting in an increase in the glucose usage and glycolysis, Hpd could possibly enhance the energy-linked radiosensitizing effects of 2-DG in cancer cells. The purpose of the present work was to verify this suggestion.

METHODS AND MATERIALS

Two human tumor cell lines (cerebral glioma, BMG-1 and squamous cell carcinoma, 4197) and a murine tumor cell line (Ehrlich ascites tumor [EAT], F-15) in vitro were investigated. A commercially available preparation of Hpd, Photosan-3 (PS-3) was used in the present studies. Cells incubated with 0-10 microg/ml PS-3 for 0-24 h before irradiation were exposed to 2.5 Gy of Co-60 gamma rays and maintained under liquid holding conditions for 1-4 h to facilitate repair. 2-DG (0-5 mM) added at the time of irradiation was present during the liquid holding. Radiation-induced cytogenetic damage (micronuclei formation) and cell death (macrocolony assay) were analyzed as parameters of radiation response. Effects of these radiosensitizers on glucose usage and glycolysis were also studied by measuring the glucose consumption and lactate production using enzymatic assays.

RESULTS

The glucose consumption and lactate production of BMG-1 cells (0.83 and 1.43 pmole/cell/h) were twofold higher than in the 4197 cells (0.38 and 0.63 pmole/cell/h). Presence of PS-3 (10 microg/ml) enhanced the rate of glycolysis (glucose consumption and lactate production) in these cells by 35% to 65%, which was reduced by 20% to 40% in the presence of 5 mM 2-DG. In exponentially growing BMG-1 and EAT cells, presence of 2-DG (5 mM; equimolar with glucose) for 4 hours after irradiation increased the radiation-induced micronuclei formation and cell death by nearly 40%, whereas no significant effects could be observed in 4197 cells. In EAT cells, radiation was also observed to induce apoptotic death, which was significantly increased in the presence of the combination (PS-3 + 2-DG). The combination (PS-3 + 2-DG) enhanced the radiation damage in all three cell systems by 60-100%. Furthermore, the radiosensitizing effects of the combination (PS-3 + 2-DG) were higher at pH 6.7 as compared to pH 7. 4. In the plateau phase, presence of 2-DG alone did not significantly influence the radiation response of either BMG-1 or of 4197 cells, whereas in combination with PS-3, 2-DG enhanced the radiation damage in both these cell lines by 40% to 50%. Furthermore, in BMG-1 cells, the effects of 2-DG were observed to be reversible to a very great extent, while that of the combination were mostly irreversible.

CONCLUSION

The hematoporphyrin derivative PS-3 enhances the radiosensitizing effects of 2-DG in cancer cells, possibly by further reducing the energy supply leading to an irreversible inhibition of DNA repair, and increased cytogenetic damage and cell death. Since both these compounds have been used in clinical practice, further studies to investigate their use in improving radiotherapy of tumors are warranted.

Bioluminescence imaging of metabolites in a human tumour xenograft after treatment with hyperthermia and/or the radiosensitizer pimonidazole

The levels and distribution of ATP, glucose and lactate in human tumour xenografts following either single or combined treatment with hyperthermia (43 degrees C for 30 min) and/or pimonidazole (1 mg/g b.w) were determined by bioluminescence and compared with the mean 'global' levels obtained from the same tumours using conventional biochemical analysis. In general, the levels of ATP, glucose and lactate measured with both methods were in good agreement although the latter was consistently lower after bioluminescence determination. Compared with controls, neither the levels of ATP nor glucose were greatly affected in this tumour following treatment with the various modalities, whereas those of lactate were considerably increased as determined by both methods. The spatial distribution of ATP and glucose from controls and treated tumours was largely confined to the periphery and generally remained unchanged irrespective of treatment without any apparent alterations in the shape of the distribution curve. However, the increased lactate levels tended to accumulate towards the central region of the tumour after hyperthermia and/or sensitizer, showing an almost Gaussian-like distribution compared with controls. These results are in agreement with previous studies of global tumour metabolism showing an enhanced glycolytic activity with increased lactate levels after single or combined modality treatment.

A comparison of the physiological effects of RSU1069 and RB6145 in the SCCVII murine tumour

The physiological and therapeutic effects of the bioreductive agent RSU1069 (80 mg/kg i.p.) and its prodrug RB6145 (240 mg/kg i.p.) were investigated in the SCCVII tumour. Using laser Doppler flowmetry it was found that RSU1069 produced a significant 30% reduction in tumour blood flow 30 min after administration, while RB6145 had no effect. Tumour oxygenation, measured with an Eppendorf oxygen electrode, was unchanged by either agent except for a reduction in values less than 2.5 mmHg at 30 min after injection. Neither agent significantly altered tumour energy metabolism, assessed by 31P magnetic resonance spectroscopy. Both agents significantly increased tumour glucose content by a factor of 1.6-1.7 at 30 min after injection, but had no effect on glucose-6-phosphate or lactate levels. Tumour growth was significantly delayed by heating (42.5 degrees C, 60 min), and although neither RSU1069 nor RB6145 alone had any effect on tumour growth they produced a similar enhancement of the tumour response to heat. The therapeutic effects are consistent with the known conversion in vivo of one third of the pro-drug RB6145 to its active product RSU1069, however the physiological effects of the two agents in the SCCVII tumour are not identical.

Metabolic imaging in tumours by means of bioluminescence

A bioluminescence technique involving single photon imaging was used to quantify the spatial distribution of the metabolites ATP, glucose and lactate in cryosections of various solid tumours and normal tissue. Each section was covered with an enzyme cocktail linking the metabolite in question to luciferase with light emission proportional to the metabolite concentration. The photons emitted are imaged directly through a microscope and an imaging photon counting system. In some cases, good agreement was observed between the distribution of relatively high concentrations of ATP and glucose in viable cell regions of the periphery, while the reverse was seen in more necrotic tumour centres with comparatively high lactate levels. In general, lactate was distributed more diffusely over the sections while ATP was more highly localised and glucose assumed an intermediate pattern. In contrast to the large degree of heterogeneity seen in tumours, distribution patterns of metabolites were much more homogeneous in normal tissue, such as heart muscle. Mean values for metabolite levels in cryosections using bioluminescence are in good agreement with those obtained from the same tumour by conventional methods.

Metabolic studies and neurotoxicity in tumors and brain of mice after hypoxic cell sensitizers

PURPOSE

The effects of the radiosensitizers RK-28 and RP-170, both 2-nitroimidazole nucleoside analogues, and KU-2285, a fluorinated 2-nitroimidazole, as well as etanidazole (ETA) on glucose metabolism in mouse tumors and brain were studied to assess their degree of neurotoxicity.

METHODS AND MATERIALS

Adult male C57Bl mice received differing doses of the above sensitizers IP. Blood, brain, and tumor samples were removed at various times and the levels of glycolytic metabolites determined. Glucose uptake and phosphorylation in brain was measured by the 2-deoxyglucose method of Sokoloff et al. (6).

RESULTS

RP-170 showed neither signs of toxicity nor significant alterations in glucose metabolism in brain or tumor at doses up to 4 g/kg b.w. up to 4 h. By contrast, RK-28 was extremely neurotoxic at a dose of 1 g/kg b.w. with a high degree of lethality, resulting in a highly significant increase in the brain glucose level from 0.38 mumol/g to 2.20 mumol/g (p < 0.001) 2 h after administration, whereas that in the tumor was decreased. KU-2285 and ETA were significantly (p < 0.01) less toxic than RK-28 at this dose, as reflected in a lower increase in the brain glucose level (0.60 mumol/g), although KU-2285 approached that of RK-28 (1.43 mumol/g; p < 0.01) after 2 h following a dose of 2 g/kg b.w. However, in contrast to the other sensitizers, KU-2285 concomitantly also resulted in a highly significant continuous increase (p < 0.01) in tumor glucose levels. Labeled 3H-2-deoxyglucose studies showed that RP-170 neither markedly affected the uptake of total radioactivity into the brain nor its degree of phosphorylation whereas, KU-2285 (2 g/kg) and RK-28 (1 g/kg) decreased uptake by approximately 50% and phosphorylation approximately 3 and 4-fold, respectively. At doses of 1 g/kg, ETA and KU-2285 showed no significant changes in these parameters. This indicates a decreased level of neurotoxicity.

CONCLUSION

Since the adult brain relies solely on glucose metabolism for its energy supply, interference to this pathway may be instrumental in the development of neurotoxicity, thus, underlining the need for such metabolic studies to assess the level of toxicity by radiosensitizers.

Effects of local hyperthermia on the tissue levels and toxicity of three radiosensitizers in mice

The toxicity of the radiosensitizers misonidazole (MISO), demethylmisonidazole (DEMISO) and pimonidazole (PIM) in mice can be affected differently when combined with local hyperthermia at 43 degrees C for 30 min. At a dose of 1 mg/g, only MISO plus heat resulted in 50% lethality in animals over a period of 7 days post-treatment, whereas 100% survival was observed in the case of DEMISO and PIM. The enhanced lethality may be associated with the production of toxic intermediates of MISO. Heat did not affect the levels of DEMISO in the tissues studied (plasma, brain and tumour), whereas those of PIM were markedly lowered in tumour but not affected in brain for up to 4 h after combined treatment. MISO was found to be decreased in the tumour at all times but affected differently in brain after 1 and 2 h, initially decreasing and then increasing significantly. In all cases the treatment sequence, i.e. sensitizer plus heat or vice-versa, did not affect the rate of survival. At a dose of 2 mg/g, DEMISO plus heat was found to be more toxic when DEMISO was given first (25% survival) compared to 58% on reversal. However, the levels of DEMISO in the tissues were not affected by heat. Thus, it would appear that there is no correlation between parent drug levels measured in plasma, tumour or brain and hyperthermia-induced drug lethality.

Evaluation of a new 2-nitroimidazole nucleoside analogue, RK-28 as a radiosensitizer for clinical use

The experimental data previously reported on RK-28, a hypoxic cell sensitizer which is now being tested in a phase I clinical trial, are confusing. Some data indicate superiority of RK-28 over misonidazole (MISO), whereas others do not. This paper presents our experimental data on the efficacy, toxicity, and pharmacokinetics of RK-28, in comparison with those of MISO, and also summarizes the data of other investigators. In our experiments, RK-28 had a 1.5-2.5 times higher sensitizing activity in vitro on EMT6 and SCCVII cells than MISO, and the difference was larger when the pre-irradiation incubation time was longer. The latter was considered to be due to the time-dependent cellular uptake and reactivity of RK-28 with non-protein sulphydryls. In vivo, RK-28 was almost as efficient as or slightly inferior to MISO against SCCVII and EMT6 tumours when assayed with an in vivo/in vitro assay and a growth delay time assay. The LD50/7 by a single injection of RK-28 was half that of MISO, but when 60% of LD50/7 was injected into mice every day, the total dose that could be given was higher for RK-28 than for MISO. Pharmacokinetic studies using mice, rats, rabbits, and a dog showed that RK-28 was rapidly eliminated from the blood and various tissues. From our results it was concluded that the possible success of the clinical trial of RK-28 depends on its low cumulative toxicity.

Misonidazole reduces blood flow in two experimental murine tumours

The effects of single doses of misonidazole (MISO) on blood flow and vascular volume in the SaFA and CaNT tumours and normal tissues of the mouse have been studied. MISO was administered in the dose range 250-1,000 mg kg-1 and blood flow measured at different times after MISO by the 86RbCl extraction technique. Vascular volume was assessed by the distribution of 51Cr-labelled red blood cells. MISO at doses of 500 mg kg-1 or greater decreased flow in both tumours by up to 60% within 2 h. Flow remained reduced for up to 24 h. Similar but less profound changes were seen in the skin, although flow had recovered by 24 h. Only slight changes were seen in muscle, and none in kidney. The apparent loss of flow in tumours seen after large single doses of MISO may have important implications for its use as a chemosensitizer.