RESUMEN

Indirect emissions of nitrous oxide (N2O) stemming from nitrogen (N) leaching in agricultural fields constitute a significant contributor to atmospheric N2O. Groundwater nitrate (NO3--N) pollution is severe in the Ningxia Yellow River Irrigation Area (NYRIA), coupled with high NO3--N leaching, exacerbates the risk of indirect N2O emissions from groundwater. Over two years of field observations, this study investigated the characteristics and interannual variations of dissolved N2O (dN2O) concentrations and indirect N2O emission factors (EF5g) in shallow groundwater. The research focused on three typical farmlands in the NYRIA, each subjected to six levels of N fertilizer application. The mean dN2O concentrations in the groundwater of paddy, corn and vegetable fields were 5.17, 8.40 and 16.35 µg N·L-1, respectively. Notably, the dN2O concentrations in the shallow groundwater of upland fields exceeded those in paddy fields, with maximum levels in vegetable fields nearly an order of magnitude higher. Elevated N application significantly increased dN2O concentrations across various farmlands, showing statistically significant variation. However, differences in EF5g-A and EF5g-B within the same farmland were negligible. Denitrification was the primary process contributing to N2O production in groundwater, with nitrification also played a crucial role in upland fields. Factors such as NO3--N, NH4+-N, dissolved oxygen (DO), and pH critically influenced N2O production. EF5g-B, which considers the NO3--N consumption during denitrification processes in groundwater, was deemed more appropriate than EF5g-A for assessing the indirect N2O emission in the NYRIA. The EF5g of agricultural fields exhibited minimal sensitivity to N input but was significantly affected by other factors, such as the planting pattern. The study revealed the rationality of adopting EF5g-B in assessing indirect N2O emissions, providing valuable insights for N management strategies in regions with high NO3--N leaching. Minimizing N fertilizer application while ensuring crop yield, especially in upland fields, is beneficial for reducing N2O emissions.

RESUMEN

Numerous studies have demonstrated high concentrations of dissolved N2O and indirect N2O emission factors in groundwater affected by agriculture. However, the characteristics of seasonal and vertical dimensional difference in groundwater in high nitrate leaching areas are relatively lacking. We monitored the concentrations of dissolved and wellhead N2O of 23 groundwater wells over a one year period to understand the seasonal characteristics of dissolved and wellhead N2O concentrations and indirect N2O emission factors (EF5) of the shallow and deep groundwater in a high nitrogen leaching area and analyze the reasons for their differences. The mean dissolved N2O concentration in groundwater was 9.71 (9.03) µg/L, which was 1.5-fold higher during the wet season relative to the dry season. Furthermore, the leaching of soil N2O caused by rainfall and irrigation could be a pivotal factor affecting seasonal variation in the dissolved N2O. Shallow wells were found to have higher dissolved and wellhead N2O concentrations compared with deep wells in all seasons. The low wellhead N2O concentrations during the dry season were attributed to the seasonal decrease of the groundwater table and dissolved N2O concentrations. We concluded that indirect N2O emission factors did not vary in the vertical dimension but were higher during the wet season than that during the dry season. In addition, the mean indirect N2O emission factor in the groundwater was 0.025 %, which was one order of magnitude below the current IPCC value (0.25 %). Thus, we proposed that such a low indirect N2O emissions factor could imply a low indirect N2O emission potential in groundwater with high dissolved oxygen and nitrogen loads. Our study further indicated that seasonal differences in dissolved N2O concentrations and indirect N2O emission factors should be considered when estimating the potential emissions of dissolved N2O in groundwater.

RESUMEN

Streams and rivers are important sources of nitrous oxide (N2 O), a powerful greenhouse gas. Estimating global riverine N2 O emissions is critical for the assessment of anthropogenic N2 O emission inventories. The indirect N2 O emission factor (EF5r ) model, one of the bottom-up approaches, adopts a fixed EF5r value to estimate riverine N2 O emissions based on IPCC methodology. However, the estimates have considerable uncertainty due to the large spatiotemporal variations in EF5r values. Factors regulating EF5r are poorly understood at the global scale. Here, we combine 4-year in situ observations across rivers of different land use types in China, with a global meta-analysis over six continents, to explore the spatiotemporal variations and controls on EF5r values. Our results show that the EF5r values in China and other regions with high N loads are lower than those for regions with lower N loads. Although the global mean EF5r value is comparable to the IPCC default value, the global EF5r values are highly skewed with large variations, indicating that adopting region-specific EF5r values rather than revising the fixed default value is more appropriate for the estimation of regional and global riverine N2 O emissions. The ratio of dissolved organic carbon to nitrate (DOC/NO3 - ) and NO3 - concentration are identified as the dominant predictors of region-specific EF5r values at both regional and global scales because stoichiometry and nutrients strictly regulate denitrification and N2 O production efficiency in rivers. A multiple linear regression model using DOC/NO3 - and NO3 - is proposed to predict region-specific EF5r values. The good fit of the model associated with easily obtained water quality variables allows its widespread application. This study fills a key knowledge gap in predicting region-specific EF5r values at the global scale and provides a pathway to estimate global riverine N2 O emissions more accurately based on IPCC methodology.

Asunto(s)

Nitratos , Óxido Nitroso , Óxido Nitroso/análisis , Nitratos/análisis , Materia Orgánica Disuelta , Monitoreo del Ambiente , Ríos

RESUMEN

BACKGROUND: A common feature of solid tumours that are resistant to therapy is the presence of regions with low oxygen content (i.e., hypoxia). Oxygen electrode studies suggest that localized prostate adenocarcinoma is commonly hypoxic, although conflicting data have been reported between immunohistochemical detection of hypoxia-induced proteins in biopsy specimens and positron emission tomography (PET) imaging of 18F-labeled hypoxia reporters. Although the 2-nitroimidazole 18F-EF5 is well-established to label hypoxic tumour cells in pre-clinical tumour models and clinical trials of multiple primary tumour sites, it has yet to be tested in prostate cancer. The purpose of this study was to evaluate the feasibility of using 18F-EF5 to detect hypoxia in clinical prostate tumours. MATERIAL AND METHODS: Patients with localized adenocarcinoma of the prostate were recruited for pre-treatment 18F-EF5 PET scans. Immunohistochemistry was conducted on diagnostic biopsies to assess the expression of glucose transporter 1 (GLUT1), osteopontin (OPN), and carbonic anhydrase IX (CAIX). Immunoreactivity scores of staining intensity and frequency were used to indicate the presence of tumour hypoxia. RESULTS: We found low tumour-to-muscle ratios of 18F-EF5 uptake that were not consistent with tumour hypoxia, causing early termination of the study. However, we observed GLUT1 and OPN expression in all prostate tumour biopsies, indicating the presence of hypoxia in all tumours. CONCLUSION: Our data do not support the use of 18F-EF5 PET to detect hypoxia in prostate adenocarcinoma, and suggest the use of immunohistochemistry to quantify expression of the hypoxia-inducible proteins GLUT1 and OPN as indications of prostate tumour hypoxia.

Asunto(s)

Adenocarcinoma , Próstata , Adenocarcinoma/diagnóstico por imagen , Hipoxia de la Célula , Humanos , Hipoxia , Masculino , Tomografía de Emisión de Positrones , Próstata/diagnóstico por imagen , Hipoxia Tumoral

RESUMEN

BACKGROUND: Hypoxia dose painting is a radiotherapy technique to increase the dose to hypoxic regions of the tumour. Still, the clinical effect relies on the reproducibility of the hypoxic region shown in the medical image. 18F-EF5 is a hypoxia tracer for positron emission tomography (PET), and this study investigated the repeatability of 18F-EF5-based dose painting by numbers (DPBN) in head and neck cancer (HNC). MATERIALS AND METHODS: Eight HNC patients undergoing two 18F-EF5-PET/CT sessions (A and B) before radiotherapy were included. A linear conversion of PET signal intensity to radiotherapy dose prescription was employed and DPBN treatment plans were created using the image basis acquired at each PET/CT session. Also, plan A was recalculated on the image basis for session B. Voxel-by-voxel Pearson's correlation and quality factor were calculated to assess the DPBN plan quality and repeatability. RESULTS: The mean (SD) correlation coefficient between DPBN prescription and plan was 0.92 (0.02) and 0.93 (0.02) for sessions A and B, respectively, with corresponding quality factors of 0.02 (0.002) and 0.02 (0.003), respectively. The mean correlation between dose prescriptions at day A and B was 0.72 (0.13), and 0.77 (0.12) for the corresponding plans. A mean correlation of 0.80 (0.08) was found between plan A, recalculated on image basis B, and plan B. CONCLUSION: Hypoxia DPBN planning based on 18F-EF5-PET/CT showed high repeatability. This illustrates that 18F-EF5-PET provides a robust target for dose painting.

Asunto(s)

Neoplasias de Cabeza y Cuello , Tomografía Computarizada por Tomografía de Emisión de Positrones , Fluorodesoxiglucosa F18 , Neoplasias de Cabeza y Cuello/diagnóstico por imagen , Neoplasias de Cabeza y Cuello/radioterapia , Humanos , Hipoxia , Tomografía de Emisión de Positrones , Radiofármacos , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por Computador , Reproducibilidad de los Resultados

RESUMEN

Aquaculture ponds are important anthropogenic sources of nitrous oxide (N2O). Direct N2O emissions arising from feed application to ponds have been widely investigated, but indirect emissions from N2O production from residual feeds in pond water are much less understood and characterized to refine the IPCC emission factor. In this study, we determined the concentrations and spatiotemporal variations of dissolved N2O and NO3--N in situ in three aquaculture ponds at the Min River Estuary in southeastern China during the culture period over two years, and calculated the indirect N2O emission factor (EF5) for aquaculture ponds using the N2O-N/NO3--N mass ratio methodology. Our results indicated that the EF5 values in the ponds over the culture period ranged between 0.0007 and 0.0543, with a clear seasonal pattern which closely followed that of the DOC:NO3-N ratio. We also observed significant spatial variations in EF5 among the three ponds, which could be attributed to the difference in feed conversion rate. In addition, we assessed the EF5 values from aquaculture ponds in five regions of the Chinese coastline across the latitudinal gradient from the tropical to the temperate zones. The average EF5 value from aquaculture ponds across the five coastal regions was 0.0093±0.0024, which was approximately 3.7 times of the IPCC default value for rivers and estuaries (0.0025). Moreover, the EF5 values demonstrated considerable spatial variations across these coastal regions with a coefficient of variation of 59%, which were largely related to the difference in water salinity. Our findings filled a key knowledge gap about the indirect N2O emission factor from aquaculture ponds, and provided field evidence for the refinement of EF5 value currently adopted by IPCC in the national greenhouse gas inventory.

Asunto(s)

Acuicultura , Monitoreo del Ambiente , China , Estuarios , Óxido Nitroso/análisis , Ríos

RESUMEN

Nitrate (NO3-) and nitrous oxide (N2O) accumulate in groundwater in relation to human activities and pose multiple threats to the global environment (harming human health and atmospheric damage). This study focused on the evaluation of groundwater NO3-, N2O, and its indirect emission factor under different land use types (agricultural land, urban land, and forest) and response mechanism of major anions to dissolved N2O within groundwater in Dexing which has the largest copper mine in Asia. Specifically, this work used self-organizing maps (SOMs) to identify which anion conditions (NO3-, SO42-, F-, Cl-) and water quality parameters were suitable for the accumulation of groundwater N2O. Finally, we found that the shallow groundwater of agricultural land has a high concentration of NO3- and N2O and the agricultural activity has a significant effect on the temporal and spatial variation of N2O in groundwater. The result of SOMs combined with the positive correlation between N2O and NO3-/SO42- suggested that the electron donor required for denitrification has a significant effect on N2O accumulation. In this respect, when an increased proportion of reduced sulfur is available as an electron donor for autotrophic denitrification, this results in lower concentrations of N2O in groundwater. Through the comprehensive evaluation of the anion conditions and N2O in groundwater under different land use types, this study case can help to estimate the N2O indirect emission from groundwater, so as to constrain the global nitrogen budget.

Asunto(s)

Desnitrificación , Agua Subterránea , Asia , Electrones , Humanos , Nitratos/análisis , Óxido Nitroso/análisis

RESUMEN

An endophytic fungal antagonist Trichoderma longibrachiatum EF5 exhibited biocontrol activity against a soil-borne fungal pathogen Macrophomina phaseolina. Under dual co-culture, T. longibrachiatum EF5 showed 58% inhibition against M. phaseolina. Crude soluble metabolites (SMs) extracted from EF5 exhibited biocontrol activity (61%), which is more significant than the cell-free extract. Dual culture of both T. longibrachiatum EF5 and M. phaseolina displayed entangled mycelial structures and retarded hyphal growth. The metabolites responsible for antibiosis and pathogenic activity profiled through GC-MS revealed a total of 131 SMs from axenic culture and upon the interaction of T. longibrachiatum EF5 and M. phaseolina. Interestingly, potential plant-growth-promoting and antimicrobial compounds such as 1- pentanol, 1-hexanol, myristonyl pantothenate, bisabolol, d-Alanine, and diethyl trisulphide were unique with T. longibrachiatum EF5. Few compounds that were not observed or produced minimally under axenic culture were increased during their interaction (e.g., 1,6-anhydro-á-d-Glucopyranose and 5-heptyl dihydro-2(3H)-Furanone), suggesting antimicrobial action against the pathogen. This study also unraveled the induction of amino sugar metabolism when T. longibrachiatum EF5 interacts with M. phaseolina, which is responsible for colonization and counterfeiting the pathogen. Hence T. longibrachiatum EF5 could be a potential biocontrol agent employed for defense priming and plant growth promotion.

Asunto(s)

Trichoderma , Amino Azúcares , Ascomicetos , Hypocreales , Enfermedades de las Plantas , Suelo

RESUMEN

RATIONALE: Evaluation of the feasibility of [18F]EF5-PET/CT scan in identifying hypoxic lesions in ovarian tumors in prospective clinical setting. METHODS: Fifteen patients with a suspected malignant ovarian tumor were scanned with [18F]EF5 and [18F]FDG-PET/CT preoperatively. The distribution of [18F]EF5-uptake, total intraabdominal metabolic tumor volume (TMTV), and hypoxic subvolume (HSV) were assessed. RESULTS: [18F]EF5-PET/CT suggested hypoxia in 47% (7/15) patients. The median HSV was 87 cm3 (31% of TMTV). The [18F]EF5-uptake was detected in primary tumors and in four patients also in intra-abdominal metastases. The [18F]EF5-uptake in cancer tissue was low compared to physiological excretory pathways, complicating the interpretation of PET/CT images. CONCLUSIONS: [18F]EF5-PET/CT is not feasible in ovarian cancer imaging in clinical setting due to physiological intra-abdominal [18F]EF5-accumulation. However, it may be useful when used complementarily to FDG-PET/CT.

RESUMEN

Multi-level ditch area is a major component of the hydrographic net of plain area, China. Given the high concentration of nitrogen (N) in the surface water and vigorous biogeochemical interactions, ditch is likely to be the hot spots of N2O emission. However, N2O emission flux and emission factor (EF5r) of multi-level ditches have not been determined. To address this knowledge gap, a 1-year field work in three ditches with different levels in Chengdu Plain was conducted. It is found that the annual flux of N2O emission and EF5r was higher in the lateral (0.0020 and 83.94 µg m-2 h-1) and field ditches (0.0019 and 110.75 µg m-2 h-1) than in the branch ditch (0.0016 and 46.38 µg m-2 h-1, P < 0.05). It is found that parameters of groundwater level, discharge, precipitation, and NH4+ were the primary factors, and these parameters can model the N2O flux well. Furthermore, the content of NH4+ in the surface water of ditches presented better correlation with the emission of N2O than the content of NO3-. Therefore, controlling NH4+ emission and lessening fertilizer usage in summer may be key solutions for indirect reduction of N2O in Chengdu Plain.

Asunto(s)

Contaminantes Atmosféricos/análisis , Drenaje de Agua , Agua Dulce/química , Agua Subterránea/química , Óxido Nitroso/análisis , Contaminantes Químicos del Agua/análisis , China , Monitoreo del Ambiente , Fertilizantes/análisis , Nitrógeno/análisis , Estaciones del Año

RESUMEN

Current estimates of global indirect N2O emissions are based on a relatively small dataset and remain a major source of uncertainly in the global N2O budget. Nitrogen (N)-enriched groundwater from agricultural fields may act as an important source of indirect N2O emissions as it discharges to adjacent watershed areas. During 2015-2017, dissolved N2O concentrations in groundwater were measured and indirect N2O emission factors (EF5g) calculated under three typical high-N land-use types (vineyard, vegetable field and paddy field) in eastern China. The average dissolved N2O concentrations in groundwater were 58.1 ±â€¯40.4, 18.5 ±â€¯11.5 and 0.72 ±â€¯0.27  µg N L-1 for vineyard, vegetable field and paddy field, respectively. The dissolved N2O was over-saturated and was therefore a net source of N2O to the atmosphere. The indirect N2O emission factors (EF5g) of vineyard (0.0091) and vegetable (0.0092) fields were much higher than the current Intergovernmental Panel on Climate Change (IPCC) default value of 0.0025 which indicated that these land-uses may have led to indirect N2O emissions from the underlying groundwater. In contrast, the EF5g of the paddy field (0.0019) was slightly lower than the default EF5g proposed by IPCC (2006) and contributed minimal indirect N2O emissions to the atmosphere. However, the current IPCC method may have overestimated the contribution of groundwater N2O to the global N cycle because it took residual but not initial groundwater NO3--N concentration into account when calculating EF5g. Therefore, we proposed the adoption of an improved method for calculating the EF5g and compared it to the current IPCC (2006) method using data from the present study and other published data. The results of the comparison showed that the improved method was more scientifically appropriate measurement for calculating EF5g.

Asunto(s)

Agricultura , Contaminantes Atmosféricos/análisis , Monitoreo del Ambiente , Agua Subterránea/análisis , Dióxido de Nitrógeno/análisis , China , Granjas , Nitrógeno/análisis , Óxido Nitroso/análisis

RESUMEN

Nitrogen (N)-enriched leaching water may act as a source of indirect N2O emission when it is discharged to agricultural drainage ditches. In this study, indirect N2O emissions from an agricultural drainage ditch mainly receiving interflow water were measured using the static chamber-gas chromatography technique during 2012-2015 in the central Sichuan Basin in southwestern China. We found the drainage ditch was a source of indirect N2O emissions contributing an inter-annual mean flux of 6.56 ±â€¯1.12 µg N m-2 h-1 and a mean indirect N2O emission factor (EF5g) value of 0.03 ±â€¯0.003%. The mean EF5g value from literature review was 0.51%, which was higher than the default EF5g value (0.25%) proposed by the Intergovernmental Panel on Climate Change (IPCC) in 2006. Our study demonstrated that, more in situ observations of N2O emissions as regards N leaching are required, to account for the large variation in EF5g values and to improve the accuracy and confidence of the default EF5g value. Indirect N2O emissions varied with season, higher emissions occurred in summer and autumn. These seasonal variations were related to drainage water NO3--N concentration, temperature, and precipitation. Our results showed that intensive precipitation increased NO3--N concentrations and N2O emissions, and when combined with warmer water temperatures, these may have increased the denitrification rate that led to the higher summer and autumn N2O emissions in the studied agricultural drainage ditch.

Asunto(s)

Agricultura , Monitoreo del Ambiente , Dióxido de Nitrógeno/análisis , Aguas Residuales/química , Contaminantes Químicos del Agua/análisis , China , Desnitrificación , Nitrógeno/análisis , Óxido Nitroso/análisis , Agua/análisis

RESUMEN

Agricultural headwater streams have a close hydrologic connection with adjacent farmland ecosystems. Based on the aggravation of agricultural nonpoint source of nitrogen (N) pollution, these streams can become an important sink of N and source of indirect nitrous oxide (N2O) emission. In this study, indirect N2O emissions from an agricultural headwater stream in the hilly area of purple soil in the upper reach of the Yangtze River were measured in situ using the closed static chamber-GC technique during the rainy season (June to September 2015). The results show that the headwater stream is a source of indirect N2O emissions, with a mean emission rate of 12.8 µg·(m2·h)-1, which is close to the direct N2O emission level from local farmland during the same season. The indirect N2O emission factor (EF5r=0.01%) determined in this study is much lower than the default value proposed by the Intergovernmental Panel on Climate Change (0.25%; IPCC, 2006) for the estimation of indirect agricultural N2O emissions and far lower than the recalculated mean value (0.20%) based on available global data. However, based on the limited number of studies on EF5r and the high spatial variations among them, more in situ observations are needed and vital to generate more accurate EF5r values and reduce the uncertainty of indirect N2O estimations calculated based on the EF5r. The indirect N2O fluxes are positively correlated with the NO3--N concentrations of the stream. Thus, denitrification is the main process of N2O production. Moreover, the indirect N2O fluxes could be notably promoted by the rapid increase of the NO3--N concentrations that were driven by rainfall>9 mm during days with continuous rain.

RESUMEN

PURPOSE: Hypoxia contributes to radiotherapy resistance and more aggressive behaviour of several types of cancer. This study was designed to evaluate the repeatability of intratumour uptake of the hypoxia tracer [18F]EF5 in paired PET/CT scans. METHODS: Ten patients with newly diagnosed head and neck cancer (HNC) received three static PET/CT scans before chemoradiotherapy: two with [18F]EF5 a median of 7 days apart and one with [18F]FDG. Metabolically active primary tumour volumes were defined in [18F]FDG images and transferred to co-registered [18F]EF5 images for repeatability analysis. A tumour-to-muscle uptake ratio (TMR) of 1.5 at 3 h from injection of [18F]EF5 was used as a threshold representing hypoxic tissue. RESULTS: In 10 paired [18F]EF5 PET/CT image sets, SUVmean, SUVmax, and TMR showed a good correlation with the intraclass correlation coefficients of 0.81, 0.85, and 0.87, respectively. The relative coefficients of repeatability for these parameters were 15%, 17%, and 10%, respectively. Fractional hypoxic volumes of the tumours in the repeated scans had a high correlation using the Spearman rank correlation test (r = 0.94). In a voxel-by-voxel TMR analysis between the repeated scans, the mean of Pearson correlation coefficients of individual patients was 0.65. The mean (± SD) difference of TMR in the pooled data set was 0.03 ± 0.20. CONCLUSION: Pretreatment [18F]EF5 PET/CT within one week shows high repeatability and is feasible for the guiding of hypoxia-targeted treatment interventions in HNC.

Asunto(s)

Etanidazol/análogos & derivados , Radioisótopos de Flúor , Neoplasias de Cabeza y Cuello/diagnóstico por imagen , Neoplasias de Cabeza y Cuello/patología , Hidrocarburos Fluorados , Tomografía Computarizada por Tomografía de Emisión de Positrones , Hipoxia Tumoral , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estadificación de Neoplasias , Estudios Prospectivos

RESUMEN

BACKGROUND AND PURPOSE: Pre-clinical data have shown that PARP inhibitors (PARPi) may increase the efficacy of radiotherapy in prostate cancer. However, it is uncertain as to whether PARPi lead to clonogenic kill when combined with radiotherapy (RT). MATERIAL AND METHODS: We tested the PARP inhibitor AZD-2281 as a radiosensitizing agent under oxic and hypoxic conditions for clonogenic survival in vitro and in vivo using the human prostate cancer cell line, 22Rv1. In addition, the effects of PARPi+RT on normal tissue were investigated using a crypt clonogenic assay. RESULTS: AZD-2281 inhibited cellular PARP activity under both oxic and hypoxic conditions. The addition of AZD-2281 radiosensitized 22Rv1 cells under oxia, acute hypoxia and chronic hypoxia in vitro. The combination of AZD-2281 with fractionated radiotherapy resulted in a significant growth delay and clonogenic kill in vivo. No increased gut toxicity was observed using this combined PARPi+radiotherapy regimen. CONCLUSIONS: This is the first preclinical study to demonstrate direct clonogenic kill in vivo by the addition of AZD-2281 to radiotherapy. As we did not observe gut toxicity, the use of PARPi in the context of prostate cancer radiotherapy warrants further investigation in clinical trials.

Asunto(s)

Antineoplásicos/farmacología , Quimioradioterapia/métodos , Ftalazinas/farmacología , Piperazinas/farmacología , Inhibidores de Poli(ADP-Ribosa) Polimerasas/farmacología , Neoplasias de la Próstata/terapia , Fármacos Sensibilizantes a Radiaciones/farmacología , Animales , Antineoplásicos/farmacocinética , Línea Celular Tumoral , Fraccionamiento de la Dosis de Radiación , Evaluación Preclínica de Medicamentos , Humanos , Masculino , Ratones Desnudos , Ftalazinas/farmacocinética , Piperazinas/farmacocinética , Inhibidores de Poli(ADP-Ribosa) Polimerasas/farmacocinética , Neoplasias de la Próstata/patología , Carga Tumoral

RESUMEN

SN30000 is a second-generation benzotriazine-N-oxide hypoxia-activated prodrug scheduled for clinical trial. Previously we showed that covalent binding of the hypoxia probe EF5 predicts metabolic activation of SN30000 in a panel of cancer cell lines under anoxia, suggesting that they are activated by the same reductases. However the identity of these reductases is unknown. Here, we test whether forced expression of nine oxidoreductases with known or suspected roles in bioreductive prodrug metabolism (AKR1C3, CYB5R3, FDXR, MTRR, NDOR1, NOS2A, NQO1, NQO2 and POR) enhances oxic or anoxic reduction of SN30000 and EF5 by HCT116 cells. Covalent binding of (14)C-EF5 and reduction of SN30000 to its 1-oxide and nor-oxide metabolites was highly selective for anoxia in all lines, with significantly elevated anoxic metabolism of both compounds in lines over-expressing POR, MTRR, NOS2A or NDOR1. There was a strong correlation between EF5 binding and SN30000 metabolism under anoxia across the cell lines (R(2)=0.84, p=0.0001). Antiproliferative potency of SN30000 under anoxia was increased most strongly by overexpression of MTRR and POR. Transcript abundance in human tumours, evaluated using public domain mRNA expression data, was highest for MTRR, followed by POR, NOS2A and NDOR1, with little variation between tumour types. Immunostaining of tissue microarrays demonstrated variable MTRR protein expression across 517 human cancers with most displaying low expression. In conclusion, we have identified four diflavin reductases (POR, MTRR, NOS2A and NDOR1) capable of reducing both SN30000 and EF5, further supporting use of 2-nitroimidazole probes to predict the ability of hypoxic cells to activate SN30000.

Asunto(s)

Hipoxia de la Célula , Óxidos N-Cíclicos/farmacología , Oxidorreductasas/metabolismo , Profármacos/farmacología , Triazinas/farmacología , Electrones , Ferredoxina-NADP Reductasa/metabolismo , Citometría de Flujo , Células HCT116 , Humanos

RESUMEN

UNLABELLED: The availability of (18)F-labeled and unlabeled 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) allows for a comparative assessment of tumor hypoxia by PET and immunohistochemistry; however, the combined use of these 2 approaches has not been fully assessed in vivo. The aim of this study was to evaluate (18)F-EF5 tumor uptake versus EF5 binding and hypoxia as determined from immunohistochemistry at both macroscopic and microregional levels. METHODS: Three tumor models-PC3, HCT116, and H460-were evaluated. Tumor-bearing animals were coinjected with (18)F-EF5 and EF5 (30 mg/kg), and PET imaging was performed at 2.5 h after injection. After PET imaging and 2 min after Hoechst 33342 injection, the tumors were excised and evaluated for (18)F-EF5 distribution by autoradiography and EF5 binding by immunohistochemistry. Additionally, the effects of nonradioactive EF5 (30 mg/kg) on the hypoxia-imaging characteristics of (18)F-EF5 were evaluated by comparing the PET data for H460 tumors with those from animals injected with (18)F-EF5 alone. RESULTS: The uptake of (18)F-EF5 in hypoxic tumor regions and the spatial relationship between (18)F-EF5 uptake and EF5 binding varied among tumors. H460 tumors showed higher tumor-to-muscle contrast in PET imaging; however, the distribution and uptake of the tracer was less specific for hypoxia in H460 than in HCT116 and PC3 tumors. Correlation analyses revealed that the highest spatial correlation between (18)F-EF5 uptake and EF5 binding was in PC3 tumors (r = 0.73 ± 0.02) followed by HCT116 (r = 0.60 ± 0.06) and H460 (r = 0.53 ± 0.10). Uptake and binding of (18)F-EF5 and EF5 correlated negatively with Hoechst 33342 perfusion marker distribution in the 3 tumor models. Image contrast and heterogeneous uptake of (18)F-EF5 in H460 tumors was significantly higher when the radiotracer was used alone versus in combination with unlabeled EF5 (tumor-to-muscle ratio of 2.51 ± 0.33 vs. 1.71 ± 0.17, P < 0.001). CONCLUSION: The uptake and hypoxia selectivity of (18)F-EF5 varied among tumor models when animals also received nonradioactive EF5. Combined use of radioactive and nonradioactive EF5 for independent assessment of tumor hypoxia by PET and immunohistochemistry methods is promising; however, the EF5 drug concentrations that are required for immunohistochemistry assays may affect the uptake of (18)F-EF5 in hypoxic cells in certain tumor types as observed in H460 in this study.

Asunto(s)

Transformación Celular Neoplásica , Etanidazol/análogos & derivados , Radioisótopos de Flúor , Hidrocarburos Fluorados/metabolismo , Neoplasias/metabolismo , Neoplasias/patología , Tomografía de Emisión de Positrones , Animales , Bencimidazoles/metabolismo , Transporte Biológico , Hipoxia de la Célula , Línea Celular Tumoral , Etanidazol/metabolismo , Humanos , Inmunohistoquímica , Ratones , Neoplasias/diagnóstico por imagen , Ratas

RESUMEN

BACKGROUND: Tumor hypoxia is linked to invasion and metastasis but whether this associates with tumor growth rate is not well understood. We aimed to study the relationship between hypoxia evaluated with the positron emission tomography (PET) tracer [(18)F]EF5 and tumor growth. Our second goal was to assess the variability in the uptake of [(18)F]EF5 in tumor between two scans. METHODS: Four human head and neck squamous cell carcinoma (UT-SCC) cell lines were xenografted in flank or neck of nude mice, and tumor size was closely monitored over the study period. The tumors were clearly visible when the first [(18)F]EF5 scan was acquired. After an exponential growth phase, the tumors were imaged again with [(18)F]EF5 and also with (18)F-fluorodeoxyglucose ([(18)F]FDG). RESULTS: There was a clear correlation between the percentage of tumor growth rate per day and the [(18)F]EF5 uptake in the latter scan (r = 0.766, p = 0.01). The uptake of [(18)F]EF5 in the first scan and the uptake of [(18)F]FDG did not significantly correlate with the tumor growth rate. We also observed considerable variations in the uptake of [(18)F]EF5 between the two scans. CONCLUSIONS: The uptake of [(18)F]EF5 in the late phase of exponential tumor growth is associated with the tumor growth rate in mice bearing HNC xenografts.

RESUMEN

UNLABELLED: Hypoxia is a significant therapeutic problem for solid tumors because hypoxic cells are treatment-resistant and more aggressive. Hypoxia-activated prodrugs such as SN30000 use a mechanism of activation in hypoxic cells similar to that of 2-nitroimidazole hypoxia PET tracers. Therefore, we have evaluated the usefulness of 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-(18)F-pentafluoropropyl)-acetamide ((18)F-EF5) PET to monitor and predict tumor response to SN30000 plus radiation treatment (RT). METHODS: Human non-small cell lung cancer xenografts (H460) in athymic rats were imaged with (18)F-EF5 PET before and after treatment with SN30000 (90 mg/kg), with or without 15-Gy RT. The feasibility of imaging early changes in hypoxia in response to SN30000 was examined 24 h after treatment, followed by ex vivo γ-counting and immunohistochemical examination to study drug-induced apoptosis. Subsequently, the therapeutic effects of SN30000 with or without RT were evaluated in tumor growth delay studies and compared with early treatment-induced changes observed by (18)F-EF5 PET. Changes in tumor hemoglobin oxygen saturation as a function of time after treatment measured by optical spectroscopy were compared with PET data. RESULTS: The uptake of (18)F-EF5 was significantly lower in SN30000-treated tumors than in saline controls 24 h after treatment (mean standardized uptake value, 0.44 ± 0.08 vs. 0.56 ± 0.08 for control group; P < 0.05). Apoptosis was significantly higher in SN30000-treated tumors than in controls. Early treatment-induced changes in (18)F-EF5 uptake were indicative of tumor response in growth delay studies at the group level. SN30000 plus RT significantly decreased (18)F-EF5 uptake relative to baseline and resulted in complete tumor remission in 5 of 7 animals. SN30000 alone decreased (18)F-EF5 uptake, generally in tumors with high initial standardized uptake values, and showed a minor tumor growth delay effect. The changes induced by SN30000 with or without RT in (18)F-EF5 uptake correlated with baseline hypoxia levels. RT caused significant increases in tumor oxygen concentration and hemoglobin oxygen saturation. CONCLUSION: A hypoxia PET imaging agent can measure changes in tumor hypoxic fraction in response to SN30000. These results suggest the utility of (18)F-EF5 PET for monitoring early response to tumor treatment with SN30000 plus RT in the clinical development of this novel hypoxia-activated prodrug.

Asunto(s)

Carcinoma de Pulmón de Células no Pequeñas/diagnóstico por imagen , Transformación Celular Neoplásica , Óxidos N-Cíclicos/uso terapéutico , Etanidazol/análogos & derivados , Radioisótopos de Flúor , Hidrocarburos Fluorados , Neoplasias Pulmonares/diagnóstico por imagen , Tomografía de Emisión de Positrones , Triazinas/uso terapéutico , Animales , Carcinoma de Pulmón de Células no Pequeñas/tratamiento farmacológico , Carcinoma de Pulmón de Células no Pequeñas/patología , Carcinoma de Pulmón de Células no Pequeñas/radioterapia , Hipoxia de la Célula/efectos de los fármacos , Hipoxia de la Célula/efectos de la radiación , Proliferación Celular/efectos de los fármacos , Proliferación Celular/efectos de la radiación , Óxidos N-Cíclicos/farmacología , Femenino , Humanos , Neoplasias Pulmonares/tratamiento farmacológico , Neoplasias Pulmonares/patología , Neoplasias Pulmonares/radioterapia , Profármacos/farmacología , Profármacos/uso terapéutico , Ratas , Resultado del Tratamiento , Triazinas/farmacología

RESUMEN

Classical descriptions of tumor physiology suggest two origins for tumor hypoxia; steady-state (diffusion-limited) hypoxia and cycling (perfusion-modulated) hypoxia. Both origins, primarily studied and characterized in murine models, predict relatively small, isolated foci or thin shells of hypoxic tissue interspersed with contrasting oxic tissue. These foci or shells would not be expected to scale with overall tumor size since the oxygen diffusion distance (determined by oxygen permeability and tissue oxygen consumption rate) is not known to vary dramatically from tumor to tumor. We have identified much larger (macroscopic) regions of hypoxia in rat gliosarcoma tumors and in larger human tumors (notably sarcomas and high-grade glial tumors), as indicated by biochemical binding of the hypoxia marker, EF5. Thus, we considered an alternative cause of tumor hypoxia related to a phenomenon first observed in window-chamber tumor models: namely longitudinal arteriole gradients. Although longitudinal arteriole gradients, as originally described, are also microscopic in nature, it is possible for them to scale with tumor size if tumor blood flow is organized in an appropriate manner. In this organization, inflowing blood would arise from relatively well-oxygenated sources and would branch and then coalesce to poorly-oxygenated outflowing blood over distances much larger than the length of conventional arterioles (multi-millimeter scale). This novel concept differs from the common characterization of tumor blood flow as disorganized and/or chaotic. The organization of blood flow to produce extended longitudinal gradients and macroscopic regional hypoxia has many important implications for the imaging, therapy and biological properties of tumors. Herein, we report the first experimental evidence for such blood flow, using rat 9L gliosarcoma tumors grown on the epigastric artery/vein pair.