18f-faza and Hypoxia

18F-FDG is a most popular radiopharmaceutical for tumor diagnosis in the world. In addition, 11C-methionine, 18F-FLT and 11C-choline have been used to compensate for drawbacks of 18F-FDG. Now, novel radiopharmaceuticals are required to estimate or predict therapeutic efficacy because we have many strategies to treat tumors. Radiotherapy which damage DNA by producing free radicals is commonly used to treat various types of tumors. Hypoxia is closely associated with resistance to chemo- and/or radiotherapy and is a common feature of solid tumors. Recently, understanding of tumor hypoxia in oncology has led to development of radiopharmaceuticals for hypoxia imaging. This review provides an overview of PET radiopharmaceuticals for hypoxia imaging and 18F-FBPA which is used for boron neutron capture therapy.

Topics: Animals; Boron Compounds; Boron Neutron Capture Therapy; Coordination Complexes; Fluorine Radioisotopes; Humans; Hypoxia; Misonidazole; Neoplasms; Nitroimidazoles; Organometallic Compounds; Phenylalanine; Positron-Emission Tomography; Radiopharmaceuticals; Thiosemicarbazones

A wide variety of imaging approaches have been developed in the past few decades for monitoring tumor oxygenation and hypoxia in vivo. In particular, nuclear medicine has seen the development of several radiolabeled hypoxia markers and is the preferred method for imaging of tumor hypoxia. Hypoxia imaging is increasingly being used in the clinical setting and is progressing from a mere detection method to application in individualization of chemoradiotherapy.

Topics: Humans; Hypoxia; Misonidazole; Neoplasms; Neovascularization, Pathologic; Nitroimidazoles; Positron-Emission Tomography; Radiography; Radiopharmaceuticals

Tumor hypoxia is associated with poor response to radiation (RT). We previously discovered a novel mechanism of metformin: enhancing tumor RT response by decreasing tumor hypoxia. We hypothesized that metformin would decrease tumor hypoxia and improve cervical cancer response to RT.. A window-of-opportunity, phase II randomized trial was performed in stage IB-IVA cervical cancer. Patients underwent screening positron emission tomography (PET) imaging with hypoxia tracer fluoroazomycin arabinoside (FAZA). Only patients with FAZA uptake (hypoxic tumor) were included and randomized 2:1 to receive metformin in combination with chemoRT or chemoRT alone. A second FAZA-PET/CT scan was performed after 1 week of metformin or no intervention (control). The primary endpoint was a change in fractional hypoxic volume (FHV) between FAZA-PET scans, compared using the Wilcoxon signed-rank test. The study was closed early due to FAZA availability and the COVID-19 pandemic.. Of the 20 consented patients, 6 were excluded due to no FAZA uptake and 1 withdrew. FHV of 10 patients in the metformin arm decreased by an average of 10.2% (44.4%-34.2%) ± SD 16.9% after 1 week of metformin, compared with an average increase of 4.7% (29.1%-33.8%) ± 11.5% for the 3 controls (P = 0.027). Those with FHV reduction after metformin had significantly lower MATE2 expression. With a median follow-up of 2.8 years, the 2-year disease-free survival was 67% for the metformin arm versus 33% for controls (P = 0.09).. Metformin decreased cervical tumor hypoxia in this trial that selected for patients with hypoxic tumor. See related commentary by Lyng et al., p. 5233.

Topics: COVID-19; Female; Humans; Hypoxia; Metformin; Nitroimidazoles; Pandemics; Positron Emission Tomography Computed Tomography; Positron-Emission Tomography; Radiopharmaceuticals; Uterine Cervical Neoplasms

Tumour hypoxia is thought to play a significant role in the outcome of solid tumour therapy. Positron emission tomography (PET) is the best-validated noninvasive technique able to demonstrate the presence of hypoxia in vivo. The locally developed PET tracer for imaging hypoxia, 1-alpha-D: -(5-deoxy-5-[(18)F]-fluoroarabinofuranosyl)-2-nitroimidazole ((18)F-FAZA), has been shown to accumulate in experimental models of tumour hypoxia and to clear rapidly from the circulation and nonhypoxic tissues. The safety and general biodistribution patterns of this radiopharmaceutical in patients with squamous cell carcinoma of the head and neck (HNSCC), small-cell lung cancer (SCLC) or non-small-cell lung cancer (NSCLC), malignant lymphoma, and high-grade gliomas, were demonstrated in this study.. Patients with known primary or suspected metastatic HNSCC, SCLC or NSCLC, malignant lymphoma or high-grade gliomas were dosed with 5.2 MBq/kg of (18)F-FAZA, then scanned 2-3 h after injection using a PET or PET/CT scanner. Images were interpreted by three experienced nuclear medicine physicians. The location and relative uptake scores (graded 0 to 4) of normal and abnormal (18)F-FAZA biodistribution patterns, the calculated tumour-to-background (T/B) ratio, and the maximum standardized uptake value were recorded.. Included in the study were 50 patients (32 men, 18 women). All seven patients with high-grade gliomas showed very high uptake of (18)F-FAZA in the primary tumour. In six out of nine patients with HNSCC, clear uptake of (18)F-FAZA was observed in the primary tumour and/or the lymph nodes in the neck. Of the 21 lymphoma patients (15 with non-Hodgkin's lymphoma and 6 with Hodgkin's disease), 3 demonstrated moderate lymphoma-related uptake. Of the 13 lung cancer patients (12 NSCLC, 1 SCLC), 7 had increased (18)F-FAZA uptake in the primary lung tumour. No side effects of the administration of (18)F-FAZA were observed.. This study suggests that (18)F-FAZA may be a very useful radiopharmaceutical to image hypoxia in the tumour types selected. Especially the high uptake by gliomas was encouraging. Given the good imaging properties, including acceptable T/B ratios in the tumour categories studied, (18)F-FAZA could be considered as a very promising agent for assessing the hypoxic fraction of these tumour types.

Topics: Adolescent; Adult; Aged; Aged, 80 and over; Carcinoma, Non-Small-Cell Lung; Carcinoma, Small Cell; Carcinoma, Squamous Cell; Female; Fluorine Radioisotopes; Glioma; Head and Neck Neoplasms; Humans; Hypoxia; Lung Neoplasms; Lymphoma; Male; Middle Aged; Neoplasms; Nitroimidazoles; Positron-Emission Tomography; Radiopharmaceuticals; Young Adult

(18)F-fluoroazomycin arabinoside ((18)F-FAZA) is a PET tracer of tumor hypoxia. However, as hypoxia often is associated with decreased perfusion, the delivery of (18)F-FAZA may be compromised, potentially disturbing the association between tissue hypoxia and (18)F-FAZA uptake. The aim of this study was to gain insight into the relationship between tumor perfusion and (18)F-FAZA uptake.. Ten patients diagnosed with advanced non-small cell lung cancer underwent subsequent dynamic (15)O-H2O and (18)F-FAZA PET scans with arterial sampling. Parametric images of both (15)O-H2O-derived perfusion (tumor blood flow [TBF]) and volume of distribution (V(T)) of (18)F-FAZA were generated. Next, multiparametric classification was performed using lesional and global thresholds. Voxels were classified as low or high TBF and (18)F-FAZA V(T), respectively. Finally, by combining these initial classifications, voxels were allocated to 4 categories: lowTBF-lowV(T), lowTBF-highV(T), highTBF-lowV(T), and highTBF-highV(T).. A total of 13 malignant lesions were identified in the 10 patients. The TBF and (18)F-FAZA V(T) values (average ± SD) across all lesions were 0.45 ± 0.20 mL·cm(-3)·min(-1) and 0.94 ± 0.31 mL·cm(-3), respectively. The averages of all lesional median values for TBF and (18)F-FAZA V(T) were 0.37 ± 0.15 mL·cm(-3)·min(-1) and 0.85 ± 0.18 mL·cm(-3), respectively. Multiparametric analysis showed that classified voxels were clustered rather than randomly distributed. Several intralesion areas were identified where (18)F-FAZA V(T) was inversely related to TBF. On the other hand, there were also distinct areas where TBF as well as (18)F-FAZA V(T) were decreased or increased.. The present data indicate that spatial variation of (18)F-FAZA uptake is not necessarily inversely related to TBF. This suggests that decreased TBF may result in flow-limited delivery of (18)F-FAZA. Areas with both high (18)F-FAZA uptake and high TBF values suggest that high (18)F-FAZA uptake, possibly suggesting hypoxia, may occur despite high TBF values. In conclusion, multiparametric evaluation of the spatial distributions of both TBF and (18)F-FAZA uptake may be helpful for understanding the (18)F-FAZA signal.

Topics: Aged; Carcinoma, Non-Small-Cell Lung; Cluster Analysis; Female; Humans; Hypoxia; Lung Neoplasms; Male; Middle Aged; Neoplasms; Nitroimidazoles; Oxygen Radioisotopes; Positron-Emission Tomography; Radiopharmaceuticals; Regional Blood Flow; Water

Pancreatic cancers are thought to be unusually hypoxic, which might sensitize them to drugs that are activated under hypoxic conditions. In order to develop this idea in the clinic, a minimally invasive technique for measuring the oxygenation status of pancreatic cancers is needed.. We tested the potential for minimally invasive imaging of hypoxia in pancreatic cancer patients, using the 2-nitroimidazole PET tracer (18)F-fluoroazomycin arabinoside (or (18)F-1-α-D-[5-fluoro-5-deoxyarabinofuranosyl]-2-nitroimidazole [(18)F-FAZA]). Dynamic and static scans were obtained in 21 patients with either locally advanced or metastatic disease. The hypoxic fraction was determined in the 2-h static scans as the percentage of voxels with SUVs more than 3 SDs from the mean values obtained for skeletal muscle.. Hypoxia was detected in 15 of 20 evaluable patients, with the hypoxic fraction ranging from less than 5% to greater than 50%. Compartmental analysis of the dynamic scans allowed us to approximate the tumor perfusion as mL/min/g of tissue, a value that is independent of the extent of hypoxia derived from tracer uptake in the 2-h static scan. There was no significant correlation between tumor perfusion and hypoxia; nor did we see an association between tumor volume and hypoxia.. Although pancreatic cancers can be highly hypoxic, a substantial proportion appears to be well oxygenated. Therefore, we suggest that a minimally invasive technique such as the one described in this study be used for patient stratification in future clinical trials of hypoxia-targeting agents.

Topics: Aged; Aged, 80 and over; Algorithms; Female; Humans; Hypoxia; Male; Middle Aged; Models, Biological; Neoplasm Metastasis; Nitroimidazoles; Pancreatic Neoplasms; Positron-Emission Tomography; Radiopharmaceuticals; Regional Blood Flow

To investigate the effect of hypoxia tracer properties on positron emission tomography (PET) image quality for three tracers [18F]-fluoromisonidazole (FMISO), [18F]-fluoroazomycinarabinoside (FAZA) and [18F]-flortanidazole (HX4), using mathematical simulations based on microscopic tumor tissue sections.. Oxygen distribution and tracer binding was mathematically simulated on immunohistochemically stained cross-sections of tumor xenografts. Tracer diffusion properties were determined based on available literature. Blood activity and clearance over a four-hour period post-injection (p.i.) were derived from clinical dynamic PET scans of patients suffering from head and neck or bronchial cancer. Simulations were performed both for average patient blood activities and for individual patients, and image contrast between normoxic and hypoxic tissue areas was determined over this four-hour period p.i.. On average, HX4 showed a six-fold higher clearance than FMISO and an almost three-fold higher clearance than FAZA based on the clinical PET data. The absolute variation in clearance was significantly higher for HX4 than for FMISO (standard deviations of 5.75 *10-5 s-1 vs. 1.55 *10-5 s-1). The absolute tracer activity in these scans at four hours p.i. was highest for FMISO and lowest for HX4. Simulated contrast at four hours p.i. was highest for HX4 (2.39), while FMISO and FAZA were comparable (1.67 and 1.75, respectively). Variations in contrast of 7-11% were observed for each tracer depending on the vascularization patterns of the chosen tissue. Higher variations in clearance for HX4 resulted in an increased inter-patient variance in simulated contrast at four hours p.i.. In line with recent experimental and clinical data, the results suggest that HX4 is a promising new tracer that provides high image contrast four hours p.i., though inter-patient variance can be very high. Nevertheless, the widely used tracer FMISO provides a robust and reproducible signal four hours p.i., but with a lower contrast. The simulations revealed tracer clearance to be the key factor in determining image contrast.

Topics: Humans; Hypoxia; Imidazoles; Misonidazole; Models, Theoretical; Nitroimidazoles; Positron-Emission Tomography; Radiopharmaceuticals; Triazoles

(18)F-fluoroazomycinarabinoside ((18)F-FAZA) is a promising hypoxia radiopharmaceutical agent with outstanding biokinetic parameters. We aimed to determine the accuracy of (18)F-FAZA-PET/CT scan in detecting hypoxic regions within the tumor using immunohistochemical markers in a pilot study.. Eleven patients with primary or recurrent laryngeal squamous cell carcinoma were indicated for total laryngectomy (TLE). Patients underwent (18)F-FAZA-PET/CT scan before TLE. Hypoxic regions inside the laryngeal tumor were determined. After TLE, regions with high uptake on (18)F-FAZA-PET scan were selected for immunohistochemical examination for exogenous (pimonidazole) and endogenous (HIF1α, CA-IX and GLUT-1) hypoxia markers. To assess the accuracy of (18)F-FAZA-PET scanning, radiopharmacon accumulation was related with immunohistochemical expression of hypoxia markers.. Inter- and intratumoral heterogeneity of tumor hypoxia was observed on (18)F-FAZA-PET scan. Nine of the eleven tumors were hypoxic with (18)F-FAZA-PET. Hypoxia could also be detected with pimonidazole, HIF1α, CA-IX and GLUT-1 expression in some tumors. No clear association was observed between (18)F-FAZA uptake and hypoxia markers.. This pilot study could not prove the accuracy of (18)F-FAZA-PET in determining hypoxic subvolumes in laryngeal cancer. Further study is required to investigate the benefit of (18)F-FAZA-PET imaging in radiotherapy planning.

Topics: Aged; Aged, 80 and over; Biomarkers; Carcinoma, Squamous Cell; Female; Head and Neck Neoplasms; Humans; Hypoxia; Laryngeal Neoplasms; Laryngectomy; Male; Middle Aged; Multimodal Imaging; Neoplasm Recurrence, Local; Nitroimidazoles; Pilot Projects; Positron-Emission Tomography; Prospective Studies; Radiopharmaceuticals; Squamous Cell Carcinoma of Head and Neck; Tomography, X-Ray Computed

The routine manufacture of most short-lived positron-emitting radiopharmaceuticals (PERs) involves conventional heating to accelerate the radiolabeling process. Nucleophilic radiofluorination reactions are generally slow at lower temperatures, and are accompanied by thermal decomposition of both precursor and product at higher temperatures. This necessitates HPLC purification and results in lower recovered radiochemical yields (rRCYs). [(18)F]FAZA, a PER for clinical imaging of focal tissue hypoxia, is routinely manufactured in-house in 3-12% rRCY using a Health Canada approved conventional heating procedure. The microwave-assisted (MW) radiosynthesis of [(18)F]FAZA is now reported.. Manual (MRDS) and automated (ASU) reagent delivery systems coupled to a commercial MW unit were built in-house. The MW unit controlled power, irradiation time and monitored reaction temperature (Tmax control), while the acetylAZA tosylate precursor and QMA Accel(TM) cartridge eluent reagents (K2CO3, K2.2.2) were dispensed by the MRDS or ASU. The radiofluorination yields (RFYs) and the chemical and radiochemical TLC profiles of the post-labeling reaction mixtures were compared to those obtained using the conventional heating production method and to those reported for optimized literature methods.. MW RFYs for [(18)F]FAZA reached >76% (n=3) in 3 min. Post-labeling analysis of the MW-assisted reaction mixtures demonstrated cleaner UV and radiochemical TLC profiles than those obtained from conventional heating in routine production runs; the relatively clean MW reactions allowed rapid HPLC isolation of [(18)F]FAZA in overall rRCYs of 55±4%.. In practical terms, the MW process provided only small gains in reaction time and RFY, but produced only a few secondary impurities, thereby improving the rRCY in comparison to conventional heating methods. These findings provide a rationale for adaptation of the MW-assisted method for the routine production of clinical [(18)F]FAZA.

Topics: Chromatography, High Pressure Liquid; Chromatography, Thin Layer; Fluorine Radioisotopes; Hot Temperature; Humans; Hypoxia; Kinetics; Microwaves; Nitroimidazoles; Radiochemistry; Radiopharmaceuticals

Tumour hypoxia is linked to treatment resistance. Positron emission tomography (PET) using hypoxia tracers such as fluoroazomycin arabinoside (FAZA) may allow identification of patients with hypoxic tumours and the monitoring of the efficacy of hypoxia-targeting treatment. Since hypoxia PET is characterized by poor image contrast, and tumour hypoxia undergoes spontaneous changes and is affected by therapy, it remains unclear to what extent PET scans are reproducible. Tumour-bearing mice are valuable in the validation of hypoxia PET, but identification of a reliable reference tissue value (blood sample or image-derived muscle value) for repeated scans may be difficult due to the small size of the animal or absence of anatomical information (pure PET). Here tumour hypoxia was monitored over time using repeated PET scans in individual tumour-bearing mice before and during fractionated radiotherapy.. Mice bearing human SiHa cervix tumour xenografts underwent a PET scan 3 h following injection of FAZA on two consecutive days before initiation of treatment (baseline) and again following irradiation with four and ten fractions of 2.5 Gy. On the last scan day, mice were given an intraperitoneal injection of pimonidazole (hypoxia marker), tumours were collected and the intratumoral distribution of FAZA (autoradiography) and hypoxia (pimonidazole immunohistology) were determined in cryosections.. Tissue section analysis revealed that the intratumoral distribution of FAZA was strongly correlated with the regional density of hypoxic (pimonidazole-positive) cells, even when necrosis was present, suggesting that FAZA PET provides a reliable measure of tumour hypoxia at the time of the scan. PET-based quantification of tumour tracer uptake relative to injected dose showed excellent reproducibility at baseline, whereas normalization using an image-derived nonhypoxic reference tissue (muscle) proved highly unreliable since a valid and reliable reference value could not be determined. The intratumoral distribution of tracer was stable at baseline as shown by a voxel-by-voxel comparison of the two scans (R = 0.82, range 0.72-0.90). During treatment, overall tracer retention changed in individual mice, but there was no evidence of general reoxygenation.. Hypoxia PET scans are quantitatively correct and highly reproducible in tumour-bearing mice. Preclinical hypoxia PET is therefore a valuable and reliable tool for the development of strategies that target or modify hypoxia.

Topics: Animals; Body Weight; Cell Line, Tumor; Collagen; Dose Fractionation, Radiation; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; Drug Combinations; Female; Fluorine Radioisotopes; Humans; Hypoxia; Image Processing, Computer-Assisted; Laminin; Mice; Mice, Nude; Neoplasm Transplantation; Nitroimidazoles; Positron-Emission Tomography; Proteoglycans; Radiotherapy; Uterine Cervical Neoplasms

Tumor hypoxia is linked to poor prognosis, but identification and quantification of tissue hypoxia remains a challenge. The hypoxia-specificity of HIF-1α target genes in vivo has been questioned due to the confounding influence of other microenvironmental abnormalities known to affect gene expression (e.g., low pH). Here we describe a new technique that by exploiting intratumoral oxygenation heterogeneity allows us to identify and objectively rank the most robust mRNA hypoxia biomarkers.. Mice carrying human (FaDudd) or murine (SCCVII) tumors were injected with the PET hypoxia tracer FAZA. Four hours post-injection tumors were removed, frozen, and crushed into milligram-sized fragments, which were transferred individually to pre-weighed tubes containing RNAlater and then weighed. For each fragment radioactivity per tissue mass and expression patterns of selected mRNA biomarkers were analyzed and compared.. In both tumour models, fragmentation into pieces weighing 10 to 60 mg resulted in tissue fragments with highly variable relative content of hypoxic cells as evidenced by an up to 13-fold variation in FAZA radioactivity per mass of tissue. Linear regression analysis comparing FAZA retention with patterns of gene expression in individual tissue fragments revealed that CA9, GLUT1 and LOX mRNA levels were equally and strongly correlated to hypoxic extent in FaDudd. The same link between hypoxia and gene expression profile was observed for CA9 and GLUT1, but not LOX, in SCCVII tumors. Apparent in vivo hypoxia-specificity for other putative molecular markers of tissue hypoxia was considerably weaker.. The portrayed technique allows multiple pairwise measurements of mRNA transcript levels and extent of hypoxia in individual tumors at a smallest possible volumetric scale which (by limiting averaging effects inherent to whole-tumor analysis) strengthen the conclusiveness on true hypoxia-specificity of candidate genes while limiting the required number of tumors. Among tested genes, our study identified CA9, GLUT1 and possibly LOX as highly specific biomarkers of tumor hypoxia in vivo.

Topics: Animals; Biomarkers, Tumor; Carbonic Anhydrases; Cell Line, Tumor; Female; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Glucose Transporter Type 1; Humans; Hypoxia; Mice; Mice, Inbred C3H; Mice, Inbred Strains; Mice, Nude; Neoplasms, Experimental; Nitroimidazoles; Positron-Emission Tomography; Protein-Lysine 6-Oxidase; Reproducibility of Results; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Transplantation, Heterologous

[18F]FAZA is a PET biomarker with great potential for imaging tumor hypoxia. Aim of our study was to compare [18F]FAZA uptake in mice with subcutaneous exogenous CT26 colon carcinomas and endogenous polyoma middle-T (PyV-mT) mammary carcinomas and to analyze the influence of different breathing protocols in CT26 colon carcinomas as well as the reversibility or irreversibility of [18F]FAZA uptake.. We injected subcutaneous CT26 colon carcinoma or polyomavirus middle-T (PyV-mT) mammary carcinoma-bearing mice intravenously with18F-FAZA and performed PET scans 1-3 h post injection (p.i.). To analyze the impact of oxygen supply in CT26 carcinomas we used three different breathing protocols: (P0) air; (P1) 100% oxygen 1 h prior injection until 3 h p.i.; (P2) 100% oxygen breathing starting 2 min prior tracer injection until 1 h p.i. and during the PET scans; mice were breathing air between the 2 h and 3 h 10 min static scans. Normalized PET images were analyzed by using defined regions of interest. Finally, some mice were dissected for pimonidazole immunohistochemistry.. There was no difference in18F-FAZA uptake 1-3 h p.i. between the two carcinoma types (CT26: 1.58 ± 0.45%ID/cc; PyV-mT: 1.47 ± 0.89%ID/cc, 1 h p.i., tumor size < 0.5 cm3). We measured a significant tracer clearance, which was more pronounced in muscle tissue (P0). The [18F]FAZA tumor-to-muscle-ratios in CT26 colon carcinoma-bearing mice 2 h and 3 h, but not 1 h p.i. were significantly higher when the mice breathed air (P0: 3.56 ± 0.55, 3 h) compared to the oxygen breathing protocols (P1: 2.45 ± 0.58; P2: 2.77 ± 0.42, 3 h). Surprisingly, the breathing protocols P1 and P2 showed no significant differences in T/M ratios, thus indicating that the crucial [18F]FAZA uptake phase is during the first hour after [18F]FAZA injection. Importantly, the muscle clearance was not affected by the different oxygen breathing conditions while the tumor clearance was lower when mice were breathing air.. Exogenous CT26 colon carcinomas and endogenous polyoma middle-T (PyV-mT) mammary carcinomas showed no differences in [18F]FAZA uptake 1-3 h p.i. Our analysis using various breathing protocols with air (P0) and with pure oxygen (P1, P2) clearly indicate that [18F]FAZA is an appropriate PET biomarker for in vivo analysis of hypoxia revealing an enhanced tracer uptake in tumors with reduced oxygen supply. [18F]FAZA uptake was independent of tumor-type.

Topics: Animals; Cell Hypoxia; Diagnostic Imaging; Fluorine Radioisotopes; Hypoxia; Image Processing, Computer-Assisted; Immunohistochemistry; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Neoplasms, Experimental; Nitroimidazoles; Oxygen; Positron-Emission Tomography; Radiopharmaceuticals; Respiration; Ribose

The current work evaluates 1-alpha-d-(2-deoxy-2-fluororibofuranosyl)-2-nitroimidazole (FRAZ), a novel azomycin nucleoside that is a potential radiosensitizer of tumor hypoxia. FRAZ is a ribose analogue of 1-alpha-d-(2-deoxy-2-fluoroarabinofuranosyl)-2-nitroimidazole ([(18)F]-FAZA), a clinically used hypoxia marker. Preliminary assessment of the cytotoxicity and hypoxia-specific in vitro binding in HCT-110 colorectal cancer cells indicate that the radiosensitization properties of FRAZ are similar to that of FAZA, with a sensitizer enhancement ratio (SER) of approximately 1.8. An automated radiosynthesis of [(18)F]-FRAZ using a commercial automated synthesis unit (ASU) was established (synthesis time approximately 32 min; radiochemical yield (decay uncorrecetd) approximately 22%) to facilitate its application in PET-based diagnosis of hypoxic tumors.

Topics: Antineoplastic Agents; Binding Sites; Biomarkers, Tumor; Cell Line, Tumor; Cell Proliferation; Colorectal Neoplasms; Drug Screening Assays, Antitumor; Fluorine Radioisotopes; Humans; Hypoxia; Isotope Labeling; Nitroimidazoles; Positron-Emission Tomography; Ribose

Positron emission tomography (PET) allows non-invasive detection and mapping of tumor hypoxia. However, slow tracer kinetics and low resolution, results in limited tumor-to-normal tissue contrast and the risk of missing areas where hypoxic cells are intermixed with necrosis. The shape of tumor time activity curves (TACs), as deduced from dynamic scans, may allow further separation of tumors/tumor sub-volumes that are inseparable based on static scans. This study was designed to define the added value of dynamic scans.. Three squamous cell carcinoma tumor models were grown in mice. Mice were injected with the (18)F-labeled PET hypoxia-tracer fluoroazomycin arabinoside (FAZA) and the immunologically-detectable hypoxia-marker pimonidazole, and PET scanned dynamically for three to six hours. Subsequently, microregional tracer retention (autoradiography) and the distribution of pimonidazole-retaining cells (immunohistology) and necrosis were analyzed in tumor tissue sections. Dynamic PET data were analysed based on a two-compartment model with irreversible tracer binding generating estimates of the putative hypoxia surrogate markers k(3) (tracer trapping rate constant) and K(i) (influx rate constant from plasma into irreversible bound tracer).. High tumor-to-reference tissue ratios and a strong linear correlation (R∼0.7 to 0.95) between density of hypoxic cells and FAZA concentration was observed three hours after tracer administration, suggesting that late time PET images provides an accurate measure of hypoxia against which kinetic model estimates can be validated. Tumor TACs varied widely (ranging from distinctly wash-out to accumulative type) among tumor types although pimonidazole-stainings revealed extensive hypoxia in all models. Kinetic analysis of tumor sub-volumes showed that k(3) correlated poorly with late time FAZA retention regionally in two of the three tumor models. The influx rate constant K(i) displayed far less variability and correlated strongly with late time FAZA retention (hypoxia) in two of three tumor models, whereas a non-consistent relationship was observed in the last tumor model. Our study demonstrates the potential usefulness of dynamic PET, but also that a simple two-compartment model may be inappropriate in some tumor models.

Topics: Animals; Carcinoma, Squamous Cell; Female; Gingival Neoplasms; Humans; Hypoxia; Mice; Mice, Inbred C3H; Neoplasm Transplantation; Neoplasms; Nitroimidazoles; Positron-Emission Tomography; Transplantation, Heterologous; Tumor Cells, Cultured; Uterine Cervical Neoplasms

PET allows non-invasive mapping of tumor hypoxia, but the combination of low resolution, slow tracer adduct-formation and slow clearance of unbound tracer remains problematic. Using a murine tumor with a hypoxic fraction within the clinical range and a tracer post-injection sampling time that results in clinically obtainable tumor-to-reference tissue activity ratios, we have analyzed to what extent inherent limitations actually compromise the validity of PET-generated hypoxia maps.. Mice bearing SCCVII tumors were injected with the PET hypoxia-marker fluoroazomycin arabinoside (FAZA), and the immunologically detectable hypoxia marker, pimonidazole. Tumors and reference tissue (muscle, blood) were harvested 0.5, 2 and 4h after FAZA administration. Tumors were analyzed for global (well counter) and regional (autoradiography) tracer distribution and compared to pimonidazole as visualized using immunofluorescence microscopy.. Hypoxic fraction as measured by pimonidazole staining ranged from 0.09 to 0.32. FAZA tumor to reference tissue ratios were close to unity 0.5h post-injection but reached values of 2 and 6 when tracer distribution time was prolonged to 2 and 4h, respectively. A fine-scale pixel-by-pixel comparison of autoradiograms and immunofluorescence images revealed a clear spatial link between FAZA and pimonidazole-adduct signal intensities at 2h and later. Furthermore, when using a pixel size that mimics the resolution in PET, an excellent correlation between pixel FAZA mean intensity and density of hypoxic cells was observed already at 2h post-injection.. Despite inherent weaknesses, PET-hypoxia imaging is able to generate quantitative tumor maps that accurately reflect the underlying microscopic reality (i.e., hypoxic cell density) in an animal model with a clinical realistic image contrast.

Topics: Animals; Carcinoma, Squamous Cell; Cell Count; Cell Hypoxia; Disease Models, Animal; Female; Hypoxia; Mice; Mice, Inbred C3H; Nitroimidazoles; Oxygen; Positron-Emission Tomography; Radiopharmaceuticals; Random Allocation; Sensitivity and Specificity; Tissue Distribution

Tumour hypoxia and elevated glycolysis (Warburg effect) predict poor prognosis. Each parameter is assessable separately with positron emission tomography, but they are linked through anaerobic glycolysis (Pasteur effect). Here, we compare the oxygenation-dependent retention of fluoroazomycin arabinoside ([(18)F]FAZA), a promising but not well-characterised hypoxia-specific tracer, and fluorodeoxyglucose ([(18)F]FDG) in four carcinoma cell lines.. Cells seeded on coverslips were positioned in modified Petri dishes that allow physically separated cells to share the same tracer-containing medium pool. Following oxic, hypoxic or anoxic tracer incubation, coverslips were analysed for radioactivity ([(18)F]FDG + [(18)F]FAZA) or re-incubated in tracer-free oxygenated medium and then measured ([(18)F]FAZA). Next, we tested the reliability of [(18)F]FDG as a relative measure of glucose metabolic rate. Finally, from two cell lines, xenografts were established in mice, and the tracer distribution between hypoxic and well-oxygenated areas were deduced from tissue sections.. Three hours of anoxia strongly stimulated [(18)F]FAZA retention with anoxic-to-oxic uptake ratios typically above 30. Three out of four cell lines displayed similar selectivity of [(18)F]FDG versus glucose, but oxic uptake and anoxic-to-oxic uptake ratio of [(18)F]FDG varied considerably. Although less pronounced, [(18)F]FAZA also showed superior in vivo hypoxia specificity compared with [(18)F]FDG.. [(18)F]FAZA displays excellent in vitro characteristics for hypoxia imaging including modest cell-to-cell line variability and no binding in oxic cells. In contrast, the usability of [(18)F]FDG as a surrogate marker for hypoxia is questionable due to large variations in baseline (oxic) glucose metabolism and magnitudes of the Pasteur effects.

Topics: Animals; Binding, Competitive; Biological Transport; Cell Count; Cell Line, Tumor; Female; Fluorodeoxyglucose F18; Glucose; Humans; Hypoxia; Mice; Neoplasms; Nitroimidazoles; Oxygen; Positron-Emission Tomography; Time Factors

Topics: Animals; Diagnostic Imaging; Glucosides; Humans; Hypoxia; Hypoxia-Inducible Factor 1, alpha Subunit; Iodine Radioisotopes; Mice; Neoplasm Transplantation; Neovascularization, Pathologic; Nitroimidazoles; Oligopeptides; Radiopharmaceuticals; Research Design

Blockade of signaling through the epidermal growth factor receptor (EGFR) tyrosine kinase by inhibitors such as gefitinib (Iressa) can inhibit tumor angiogenesis and enhance responses to ionizing radiation. In this study, the ability of gefitinib to modulate intratumoral oxygenation was evaluated in human EGFR-expressing A431 squamous cell carcinoma xenografts using in vivo small animal positron emission tomography (PET) imaging with the hypoxia marker [(18)F]fluoroazomycin arabinoside (FAZA) and by the immunohistochemical detection of hypoxia-induced adducts of the 2-nitroimidazole, pimonidazole. Serial noninvasive PET imaging of A431 xenografts showed a significant reduction in FAZA uptake following treatment with 75 mg/kg/d of gefitinib [tumor to background ratio, 6.1 +/- 1.0 (pretreatment) versus 2.3 +/- 0.6 (posttreatment); P = 0.0004]. Similarly, ex vivo quantitation of FAZA uptake showed significantly reduced FAZA uptake in established A431 xenografts treated with gefitinib compared with vehicle control (tumor to blood ratio for controls versus gefitinib, 8.0 +/- 3.0 versus 2.7 +/- 0.8; P = 0.007; or tumor to muscle ratio controls versus gefitinib, 8.6 +/- 2.8 versus 2.6 +/- 1.0; P = 0.002). The effect of gefitinib treatment seemed to be independent of tumor size. In addition, gefitinib treatment reduced pimonidazole-binding in A431 xenografts measured after 5 and 8 days of gefitinib treatment compared with baseline and with tumors treated with vehicle alone. A strong correlation was observed between pimonidazole binding and FAZA uptake. Together, these findings show that gefitinib reduces intratumoral hypoxia.

Topics: Animals; Antineoplastic Agents; Carcinoma, Non-Small-Cell Lung; ErbB Receptors; Fluorine Radioisotopes; Gefitinib; Humans; Hypoxia; Lung Neoplasms; Mice; Mice, Inbred BALB C; Mice, Nude; Nitroimidazoles; Oxidation-Reduction; Oxygen; Positron-Emission Tomography; Quinazolines; Tissue Distribution