18F-FMISO Uptake Research Articles

Development of 18F-Fluoromisonidazole Hypoxia PET/CT Diagnostic Interpretation Criteria and Validation of Interreader Reliability, Reproducibility, and Performance.

Tumor hypoxia, an integral biomarker to guide radiotherapy, can be imaged with 18F-fluoromisonidazole (18F-FMISO) hypoxia PET. One major obstacle to its broader application is the lack of standardized interpretation criteria. We sought to develop and validate practical interpretation criteria and a dedicated training protocol for nuclear medicine physicians to interpret 18F-FMISO hypoxia PET. Methods: We randomly selected 123 patients with human papillomavirus-positive oropharyngeal cancer enrolled in a phase II trial who underwent 123 18F-FDG PET/CT and 134 18F-FMISO PET/CT scans. Four independent nuclear medicine physicians with no 18F-FMISO experience read the scans. Interpretation by a fifth nuclear medicine physician with over 2 decades of 18F-FMISO experience was the reference standard. Performance was evaluated after initial instruction and subsequent dedicated training. Scans were considered positive for hypoxia by visual assessment if 18F-FMISO uptake was greater than floor-of-mouth uptake. Additionally, SUVmax was determined to evaluate whether quantitative assessment using tumor-to-background ratios could be helpful to define hypoxia positivity. Results: Visual assessment produced a mean sensitivity and specificity of 77.3% and 80.9%, with fair interreader agreement (κ = 0.34), after initial instruction. After dedicated training, mean sensitivity and specificity improved to 97.6% and 86.9%, with almost perfect agreement (κ = 0.86). Quantitative assessment with an estimated best SUVmax ratio threshold of more than 1.2 to define hypoxia positivity produced a mean sensitivity and specificity of 56.8% and 95.9%, respectively, with substantial interreader agreement (κ = 0.66), after initial instruction. After dedicated training, mean sensitivity improved to 89.6% whereas mean specificity remained high at 95.3%, with near-perfect interreader agreement (κ = 0.86). Conclusion: Nuclear medicine physicians without 18F-FMISO hypoxia PET reading experience demonstrate much improved interreader agreement with dedicated training using specific interpretation criteria.

Mathematical modeling of 18F-Fluoromisonidazole (18F-FMISO) radiopharmaceutical transport in vascularized solid tumors

18F-Fluoromisonidazole (18F-FMISO) is a highly promising positron emission tomography radiopharmaceutical for identifying hypoxic regions in solid tumors. This research employs spatiotemporal multi-scale mathematical modeling to explore how different levels of angiogenesis influence the transport of radiopharmaceuticals within tumors. In this study, two tumor geometries with heterogeneous and uniform distributions of capillary networks were employed to incorporate varying degrees of microvascular density. The synthetic image of the heterogeneous and vascularized tumor was generated by simulating the angiogenesis process. The proposed multi-scale spatiotemporal model accounts for intricate physiological and biochemical factors within the tumor microenvironment, such as the transvascular transport of the radiopharmaceutical agent, its movement into the interstitial space by diffusion and convection mechanisms, and ultimately its uptake by tumor cells. Results showed that both quantitative and semi-quantitative metrics of 18F-FMISO uptake differ spatially and temporally at different stages during tumor growth. The presence of a high microvascular density in uniformly vascularized tumor increases cellular uptake, as it allows for more efficient release and rapid distribution of radiopharmaceutical molecules. This results in enhanced uptake compared to the heterogeneous vascularized tumor. In both heterogeneous and uniform distribution of microvessels in tumors, the diffusion transport mechanism has a more pronounced than convection. The findings of this study shed light on the transport phenomena behind 18F-FMISO radiopharmaceutical distribution and its delivery in the tumor microenvironment, aiding oncologists in their routine decision-making processes.

Hypoxia predicts favorable response to carbon ion radiotherapy in non-small cell lung cancer (NSCLC) defined by 18F-FMISO positron emission tomography/computed tomography (PET/CT) imaging.

Hypoxia is the bottleneck that affects the response of conventional photon radiotherapy, but it does not seem to have much effect on carbon ion radiotherapy (CIRT). This study aimed to evaluate the changes of hypoxia before and after CIRT in patients with non-small cell lung cancer (NSCLC) and whether 18F-fluoromisonidazole (18F-FMISO) positron emission tomography/computed tomography (PET/CT) imaging could predict the response to CIRT in NSCLC patients. A total of 29 patients with NSCLC who received CIRT were retrospectively included. 18F-FMISO PET/CT imaging was performed before and after treatment, and chest CT was performed after radiotherapy. Radiation response within 1 week after radiotherapy and at the initial follow-up were defined as the immediate response (IR) and early response (ER), respectively. The tumor-to-muscle ratio (TMR), hypoxia volume (HV), and the ΔTMR and ΔHV values of 18F-FMISO uptake were collected. Fisher's exact test, Mann-Whitney U test, Wilcoxon signed-rank test, and binary logistic regression were used to analyze data. (I) Baseline TMR could predict the IR to CIRT with a baseline TMR cut-off value of 2.35, an area under the curve (AUC) of 0.85 [95% confidence interval (CI): 0.62-1.00], a sensitivity of 80.0%, a specificity of 87.5%, and an accuracy of 85.7%. Taking the baseline TMR =2.35 as the cut-off value of high-hypoxia and low-hypoxia group, the IR rate of the high-hypoxia group [66.7% (4/6)] and the low-hypoxia group [6.7% (1/15)] was statistically different (P=0.01). (II) ΔTMR could predict early treatment response after CIRT at initial follow-up, with a cut-off value of ΔTMR =36.6%, AUC of 0.80 (95% CI: 0.61-1.00), sensitivity of 72.7%, specificity of 90.0% and accuracy of 71.4%. A higher degree of tumor hypoxia may be associated with a better IR to CIRT. ΔTMR could predict early treatment response after CIRT.

Hypoxic stress visualized in the cervical spinal cord of ALS patients

ABSTRACT Objective: Amyotrophic lateral sclerosis (ALS) is a progressive and fatal motor neuron disease. Hypoxic stress is suspected as the pathogenesis of ALS, however, no positron emission tomography (PET) study for hypoxic stress has been conducted in the spinal cord of ALS patients. Methods: In the present study, we examined cervical spinal hypoxic stress of nineALS patients with upper extremity (U/E) atrophy by18F-fluoromisonidazole (FMISO) PET. Results: On the ipsilateral side of C1 and C5 levels, 18F-FMISO uptake increased significantly compared with the contralateral side (*p < 0.05) and the control subject (**p < 0.01). In addition, a strong correlation was found between 18F-FMISO uptake of the C5 level and the rate of progression of the ALS FRS-R score (R = 0.781, *p = 0.013). Conclusion: These results indicate that hypoxic stress increased in the spinal cord of ALS patients with a close link to ALS progression. Both hypoxic stress and a compromised response to hypoxia, which may lead to subsequent motor neuron death, could be a potential therapeutic target for ALS.

Assessment of the Prognostic Value of Radiomic Features in 18F-FMISO PET Imaging of Hypoxia in Postsurgery Brain Cancer Patients: Secondary Analysis of Imaging Data from a Single-Center Study and the Multicenter ACRIN 6684 Trial.

Hypoxia is associated with resistance to radiotherapy and chemotherapy in malignant gliomas, and it can be imaged by positron emission tomography with 18F-fluoromisonidazole (18F-FMISO). Previous results for patients with brain cancer imaged with 18F-FMISO at a single center before conventional chemoradiotherapy showed that tumor uptake via T/Bmax (tissue SUVmax/blood SUV) and hypoxic volume (HV) was associated with poor survival. However, in a multicenter clinical trial (ACRIN 6684), traditional uptake parameters were not found to be prognostically significant, but tumor SUVpeak did predict survival at 1 year. The present analysis considered both study cohorts to reconcile key differences and examine the potential utility of adding radiomic features as prognostic variables for outcome prediction on the combined cohort of 72 patients with brain cancer (30 University of Washington and 42 ACRIN 6684). We used both 18F-FMISO intensity metrics (T/Bmax, HV, SUV, SUVmax, SUVpeak) and assessed radiomic measures that determined first-order (histogram), second-order, and higher-order radiomic features of 18F-FMISO uptake distributions. A multivariate model was developed that included age, HV, and the intensity of 18F-FMISO uptake. HV and SUVpeak were both independent predictors of outcome for the combined data set (P < .001) and were also found significant in multivariate prognostic models (P < .002 and P < .001, respectively). Further model selection that included radiomic features showed the additional prognostic value for overall survival of specific higher order texture features, leading to an increase in relative risk prediction performance by a further 5%, when added to the multivariate clinical model..

Relationship among hypoxia, 18F-fluoromisonidazole positron emission tomography uptake, and tumor angiogenesis in oral squamous cell carcinoma

Objectives Hypoxia is a common feature of cancer and, thus, is a prognostic factor for many types of cancer. Clinically, the prognosis of cancer with low oxygenation level is poor, and there is strong evidence that hypoxia in the tumor microenvironment is related to tumor angiogenesis and malignant progression. 18F-fluoromisonidazole (18F-FMISO) has been used in clinical and preclinical studies to provide spatially resolved images for localizing and quantifying tissue hypoxia.18F-FMISO can detect tumor hypoxia noninvasively. Hypoxia-inducible factor (HIF-1) is a key player in the transcriptional response to low oxygen in many types of cancer. Most transcriptional responses to low oxygen (O2) are mediated by HIFs, which are highly conserved transcription factors that control the expression of various angiogenic, metabolic genes. 18F-FMISO imaging of hypoxia in head and neck cancer remains challenging. It is unclear whether 18F-FMISO positron emission tomography (PET) can identify tumor anigiogenesis and HIF-1α expression in oral squamous cell carcinoma (OSCC). We evaluated the relationship among 18F-FMISO PET uptake, HIF-1α expression, and tumor angiogenesis in OSCC. Study Design In this retrospective study, immunohistochemistry was performed for CD31 and HIF-1α on 40 OSCC specimens. Each patient was evaluated by both 18F-FMISO PET before surgery, and the tumor–muscle ratio (TMR) of 18F-FMISO PET were measured. The threshold for the hypoxic volume based on TMR was set at 1.25 (TMR ≥ 1.25: hypoxic tumor; and TMR Results 18F-FMISO uptake in the primary site of OSCC indicates a hypoxic environment with HIF-1α expression. The CD31-positive vessel area was increased in the hypoxic tumor compared with that in the nonhypoxic tumor. The tumor vessel in the hypoxic tumor was morphologically more irregular and tortuous than that in the nonhypoxic tumor. Conclusions We demonstrated a significant relationship between 18F-FMISO TMR and CD31 and HIF1α expression in OSCC. In the future, we will perform detailed research on the relationship between tumor angiogenesis and 18F-FMISO uptake.

Influence of the scan time point when assessing hypoxia in 18F-fluoromisonidazole PET: 2 vs. 4h.

18F-fluoromisonidazole (18F-FMISO) is the most widely used positron emission tomography (PET) tracer for imaging tumor hypoxia. Previous reports suggested that the time from injection to the scan may affect the assessment of 18F-FMISO uptake. Herein, we directly compared the images at 2h and 4h after a single injection of 18F-FMISO. Twenty-three patients with or suspected of having a brain tumor were scanned twice at 2 and 4h following an intravenous injection of 18F-FMISO. We estimated the mean standardized uptake value (SUV) of the gray matter and white matter and the gray-to-white matter ratio in the background brain tissue from the two scans. We also performed a semi-quantitative analysis using the SUVmax and maximum tumor-to-normal ratio (TNR) for the tumor. At 2h, the SUVmean of gray matter was significantly higher than that of white matter (median 1.23, interquartile range (IQR) 1.10-1.32 vs. 1.04, IQR 0.95-1.16, p < 0.0001), whereas at 4h, it significantly decreased to approach that of the white matter (1.10, IQR 1.00-1.23 vs. 1.02, IQR 0.93-1.13, p = NS). The gray-to-white matter ratio thus significantly declined from 1.17 (IQR 1.14-1.19) to 1.09 (IQR 1.07-1.10) (p < 0.0001). All 7 patients with glioblastoma showed significant increases in the SUVmax (2.20, IQR 1.67-3.32 at 2h vs. 2.65, IQR 1.74-4.41 at 4h, p = 0.016) and the TNR (1.75, IQR 1.40-2.38 at 2h vs. 2.34, IQR 1.67-3.60 at 4h, p = 0.016). In the assessment of hypoxic tumors, 18F-FMISO PET for hypoxia imaging should be obtained at 4h rather than 2h after the injection.

Long-time follow-up of radiotherapy boost in patients with lung cancer based on FMISO PET: Can we expect a better survival outcome? (RTEP5 3 years follow-up)

Background Chemoradiotherapy is the reference curative-intent treatment for nonresectable locally advanced non-small-cell lung carcinoma (NSCLC), with unsatisfying survival partially due to radiation resistance in hypoxic tissues, raising the question of targeted radiotherapy. Objective To evaluate the risk-benefit of radiotherapy boost on hypoxic tumors in NSCLC patients treated by curative-intent chemoradiotherapy in an open-label, nonrandomized, phase II clinical trial developed from 2012 to 2015 with a 3-year follow-up. Multicenter study performed in 15 French academic centers ( NCT01576796 ). Participants: eligible patients had locally advanced NSCLC and no contraindication to concomitant chemoradiotherapy. Seventy-nine patients underwent a run-in period, of which 54 were included. Twenty-four patients completed the study at 3 years. 18F-fluoromisonidazole (18F-MISO) positron emission tomography/computed tomography was performed to determine the hypoxic profile of patients (34 positive and 20 negative). Those with positive 18F-FMISO status and without organ-at-risk constraints (n = 24) received radiotherapy boost (70–84 Gy); the others received standard radiotherapy (66 Gy). Overall survival (OS), progression-free survival (PFS), and safety. Hypotheses tested were formulated before data collection. Results: fifty-four patients were evaluated, with a median age of 61 (41–76) years. OS and PFS rates at 1, 2, and 3 years were, respectively, 87%, 58.2%, and 48.5%, and 59.3%, 36.4%, and 28.8%. The median OS in the positive 18F-FMISO group was 25.8 months and was not reached at 3 years in the negative (P = 0.01). A difference was also observed for PFS (12 vs. 26.2 months, P = 0.048). By focusing on positive 18F-FMISO patients, no difference was observed in OS according to the dose, probably because of the small sample size (P = 0.30). However, the median OS seemed to be in favor of boosted patients (26.5 vs. 15.3 months, P = 0.71). In patients who underwent boost, no significant early or late toxicities were observed. Conclusions and relevance 18F-FMISO uptake in NSCLC patients is strongly associated with poor prognosis features. In the group of 18F-FMISO-positive patients, radiotherapy boost seems to improve the OS by 11.2 months. These results deserve further attention in a future clinical trial devoted to hypoxic patients to confirm boost efficacy.

18F-fluoromisonidazole positron emission tomography may be applicable in the evaluation of colorectal cancer liver metastasis

BackgroundPositron emission tomography (PET) imaging is a non-invasive functional imaging method used to reflect tumor spatial information, and to provide biological characteristics of tumor progression. The aim of this study was to focus on the application of 18F-fluoromisonidazole (FMISO) PET quantitative parameter of maximum standardized uptake value (SUVmax) ratio to detect the liver metastatic potential of human colorectal cancer (CRC) in mice. MethodsColorectal liver metastases (CRLM) xenograft models were established by injecting tumor cells (LoVo, HT29 and HCT116) into spleen of mice, tumor-bearing xenograft models were established by subcutaneously injecting tumor cells in the right left flank of mice. Wound healing assays were performed to examine the ability of cell migration in vitro. 18F-FMISO uptake in CRC cell lines was measured by cellular uptake assay. 18F-FMISO-based micro-PET imaging of CRLM and tumor-bearing mice was performed and quantified by tumor-to-liver SUVmax ratio. The correlation between the 18F-FMISO SUVmax ratio, liver metastases number, hypoxia-induced factor 1α (HIF-1α) and serum starvation-induced glucose transporter 1 (GLUT-1) was evaluated using Pearson correlation analysis. ResultsCompared with HT29 and HCT116, LoVo-CRLM mice had significantly higher liver metastases ratio and shorter median survival time. LoVo cells exhibited stronger migration capacity and higher radiotracer uptake compared with HT29 and HCT116 in in vitro. Moreover, 18F-FMISO SUVmax ratio was significantly higher in both LoVo-CRLM model and LoVo-bearing tumor model compared to models established using HT29 and HCT116. In addition, Pearson correlation analysis revealed a significant correlation between 18F-FMISO SUVmax ratio of CRLM mice and number of liver metastases larger than 0.5 cm, as well as between 18F-FMISO SUVmax ratio and HIF-1α or GLUT-1 expression in tumor-bearing tissues. Conclusions18F-FMISO parameter of SUVmax ratio may provide useful tumor biological information in mice with CRLM, thus allowing for better prediction of CRLM and yielding useful radioactive markers for predicting liver metastasis potential in CRC.

Accumulation of hypoxia imaging probe "18F-FMISO" in macrophages depends on macrophage polarization in addition to hypoxic state.

Macrophages play an essential role in immune response, and are closely related to the progression of diseases such as cancer and atherosclerosis. Macrophages polarize to M1 or M2 type, which is related to the environmental hypoxic state. Previously, we found that 18F-FMISO uptake varied according to expression levels of biomolecules such as glutathione S-transferase P1 (GST-P1), which catalyzes the conjugation of glutathione to 18F-FMISO metabolites, and multidrug resistance-associated protein 1 (MRP1), which exports glutathione-18F-FMISO metabolite conjugates out of cells. However, the relationship between macrophage polarization and 18F-FMISO accumulation remains unclear. Mouse peritoneal macrophages were polarized to either the M1 or M2 type, and were treated with 18F-FMISO. Then, their radioactivity after a 4h incubation period under normoxic (21% O2) or hypoxic (1% O2) condition was measured. GST-P1 and MRP1 expression levels were measured by qRT-PCR. M2 macrophages exhibited a significantly higher uptake of 18F-FMISO than non-polarized (M0) macrophages, whereas M1 macrophages had a significantly lower uptake than M0 macrophages (M0: 1.05 ± 0.22, M1: 0.34 ± 0.02, M2: 4.17 ± 0.36 %dose/mg protein). The GST-P1 expression level in M1 macrophages was higher than that in M2 and M0 macrophages [GST-P1/β-actin normalized by M0: 9.0 ± 3.7 (M1), 1.2 ± 0.2 (M2)]. The MRP1 expression level in M1 macrophages was significantly higher than that in M2 and M0 macrophages [MRP1/β-actin normalized by M0 macrophages: 5.1 ± 2.1 (M1), 2.8 ± 1.0 (M2)]. 18F-FMISO accumulation in macrophages may depend on the polarization state in addition to hypoxic condition.

Evaluating cardiac hypoxia in hibernating myocardium: Comparison of 99mTc-MIBI/18F-fluorodeoxyglucose and 18F-fluoromisonidazole positron emission tomography-computed tomography in relation to normal, hibernating, and infarct myocardium.

The aim of this prospective study was to explore the feasibility of 18F-fluoromisonidazole (18F-FMISO) cardiac positron emission tomography/computed tomography (PET/CT) in the detection of cardiac hypoxia in patients of ischemic heart disease (IHD) and to compare the uptake pattern with that of 99mTc-MIBI and 18F-fluorodeoxyglucose (18F-FDG). Twenty-six patients suffering from IHD were evaluated in this study. The patients initially underwent 99mTc-MIBI rest/stress myocardial perfusion imaging and 18F-FDG cardiac PET/CT as a part of their routine cardiac imaging. Patients with hibernating myocardium on these scans further underwent 18F-FMISO Cardiac PET/CT. Controls were also considered in the form of patients with scarred and normal myocardium. On visual assessment, increased 18F-FMISO uptake was noted in the hibernating myocardium compared to scarred or normal myocardium. On semiquantification analysis, there was overlap in the uptake values with a range of maximum standardized uptake value (SUVmax) in hibernating, scarred, and normal myocardium being 0.8–2.2 g/dl, 0.7–1.8 g/dl, and 0.7–1.6 g/dl, respectively. On individual patient-specific comparison in subjects harboring both hibernating and scarred myocardium, it was observed that SUVmax of 18F-FMISO in hibernating myocardium was highest, followed by scarred myocardium and normal myocardium, respectively. The ratio of 18F-FMISO SUVmax of hibernating to the normal myocardium in these subjects was always more than 1, and never less than the ratio of SUVmax of scarred to normal myocardium. Thus, in this mixed population study, it was observed that on an individual patient basis, hypoxic myocardium consistently showed higher 18F-FMISO uptake than surrounding scarred and normal myocardium. The ratio of 18F-FMISO SUVmax of hibernating to normal myocardium was higher than the ratio of scarred to the normal myocardium in all patients. On overall basis, however, there was considerable overlap in the SUV values among hibernating, scarred, and normal myocardium resulting in difficulty in differentiation of these entities with FMISO cardiac PET. 18F-FDG cardiac PET/CT remains the standard and superior method to determine hibernating myocardium in patients of IHD due to its superior contrast. The limitation of FMISO is poor signal to noise ratio because of high background uptake from the blood pool. Cardiac PET/CT with superior hypoxia tracers needs to be further examined for imaging cardiac hypoxia.

Noninvasive evaluation of 18F-FDG/18F-FMISO-based Micro PET in monitoring hepatic metastasis of colorectal cancer

This study aimed to explore the application of two radiotracers (18F-fluorodeoxyglucose (FDG) and 18F-fluoromisonidazole (FMISO)) in monitoring hepatic metastases of human colorectal cancer (CRC). Mouse models of CRC hepatic metastases were established by implantation of the human CRC cell lines LoVo and HT29 by intrasplenic injection. Wound healing and Transwell assays were performed to examine cell migration and invasion abilities. Radiotracer-based cellular uptake in vitro and micro-positron emission tomography imaging of liver metastases in vivo were performed. The incidence of liver metastases in LoVo-xenografted mice was significantly higher than that in HT29-xenografted ones. The SUVmax/mean values of 18F-FMISO, but not 18F-FDG, in LoVo xenografts were significantly greater than in HT29 xenografts. In vitro, LoVo cells exhibited stronger metastatic potential and higher radiotracer uptake than HT29 cells. Mechanistically, the expression of HIF-1α and GLUT-1 in LoVo cells and LoVo tumor tissues was remarkably higher than in HT29 cells and tissues. Linear regression analysis demonstrated correlations between cellular 18F-FDG/18F-FMISO uptake and HIF-1α/GLUT-1 expression in vitro, as well as between 18F-FMISO SUVmax and GLUT-1 expression in vivo. 18F-FMISO uptake may serve as a potential biomarker for the detection of liver metastases in CRC, whereas its clinical use warrants validation.

Hypoxia Imaging and Biological Evaluation of the Radiosensitizing Effect of Oleanolic Acid.

Background and Purpose The aim of this study was to evaluate the radiosensitizing effect of oleanolic acid (OA) on C6 rat glioma and the changes in tumor biology during radiosensitization therapy on 18F-fluoromisonidazole (18F-FMISO) positron emission tomography/computed tomography (PET/CT). Methods The radiosensitizing effect of OA on C6 tumors was assessed in vivo by measuring the tumor inhibitory rate and rat survival time. Meanwhile, rats with C6 tumors were imaged with 18F-FMISO PET/CT during radiosensitization therapy. Tumor-to-muscle ratio (TMR) of 18F-FMISO maximum uptake was calculated by region of interest analysis. Changes in tumor biology after therapy were assessed with immunohistochemical staining. 18F-FMISO uptake was analyzed in relation to expression of tumor biomarkers including hypoxia-inducible factor (HIF)-1α, glucose transporter (Glut-1), the proliferation antigen Ki67, tumor suppressor P53, and microvessel density (MVD). Results The results showed that OA combined with radiation inhibited the growth rates of tumors and prolonged the survival period of tumor-bearing rats effectively (χ2 = 12.5, p < 0.01). 18F-FMISO PET/CT indicated decreases in hypoxia after radiosensitization therapy. Statistical differences were observed in TMR of the irradiation group and OA combined with irradiation group (t = 3.32, p < 0.05). HIF-1α, Glut-1, Ki67, P53, and MVD expressions in tumors were downregulated by OA combined with radiation as well as with radiation alone. Additionally, there was a significant positive linear correlation between TMR and HIF-1α, Glut-1, Ki67, P53, and MVD. Conclusions These results suggest that OA has a radiosensitizing effect on C6 tumors in terms of tumor volume inhibition, survival extension, and multiple poor prognosis biological markers downregulation. 18F-FMISO PET/CT can be of value for tumor biology noninvasive capture and radiosensitization response evaluation.

In Vivo Relationship Between Hypoxia and Angiogenesis in Human Glioblastoma: A Multimodal Imaging Study.

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor. This aggressiveness is in part attributed to the closely interrelated phenomena tumor hypoxia and angiogenesis, although few in vivo data exist in human brain tumors. This work aimed to study hypoxia and angiogenesis, in vivo and in situ, in patients admitted with GBM using multimodal imaging. Methods: Twenty-three GBM patients were assessed by 18F-fluoromisonidazole (18F-FMISO) PET and conventional and perfusion MRI before surgery. The level and location of hypoxia (18F-FMISO uptake, evaluated by tumor-to-blood [T/B] ratio), vascularization (cerebral blood volume [CBV]), and vascular permeability (contrast enhancement after gadolinium injection) were analyzed. The spatial relationship between tumor hypoxia and angiogenesis was assessed by an overlap analysis of the volume of 18F-FMISO uptake and the volumes of the high CBV regions and the contrast-enhancement regions. Results: A significant correlation was found between hypoxia and hypervascularization, especially for their maximum values (volume of maximal tumor hypoxia vs. relative CBV: r = 0.61, P = 0.002) and their volumes (hypoxia vs. hypervascularization: r = 0.91, P < 0.001). A large proportion of the high CBVs collocated with hypoxia (81.3%) and with contrast enhancement (46.5%). Conclusion: These results support the hypothesis of a tight association between hypoxia and angiogenesis. Our results suggest that there is insufficient tumor oxygenation in human GBM, despite increased tumor vascularization.

18F-Fluoromisonidazole Kinetic Modeling for Characterization of Tumor Perfusion and Hypoxia in Response to Antiangiogenic Therapy.

Multiparametric imaging of tumor perfusion and hypoxia with dynamic 18F-fluoromisonidazole (18F-FMISO) PET may allow for an improved response assessment to antiangiogenic therapies. Cediranib (AZD2171) is a potent inhibitor of tyrosine kinase activity associated with vascular endothelial growth factor receptors 1, 2, and 3, currently in phase II/III clinical trials. Serial dynamic 18F-FMISO PET was performed to investigate changes in tumor biomarkers of perfusion and hypoxia after cediranib treatment. Methods: Twenty-one rats bearing HT29 colorectal xenograft tumors were randomized into a vehicle-treated control group (0.5% methylcellulose daily for 2 d [5 rats] or 7 d [4 rats]) and a cediranib-treated test group (3 mg/kg daily for 2 or 7 d; 6 rats in both groups). All rats were imaged before and after treatment, using a 90-min dynamic PET acquisition after administration of 42.1 ± 3.9 MBq of 18F-FMISO by tail vein injection. Tumor volumes were delineated manually, and the input function was image-derived (abdominal aorta). Kinetic modeling was performed using an irreversible 1-plasma 2-tissue compartmental model to estimate the kinetic rate constants K1, K1/k2, and k3-surrogates for perfusion, 18F-FMISO distribution volume, and hypoxia-mediated entrapment, respectively. Tumor-to-blood ratios (TBRs) were calculated on the last dynamic frame (80-90 min). Tumors were assessed ex vivo by digital autoradiography and immunofluorescence for microscopic visualization of perfusion (pimonidazole) and hypoxia (Hoechst 33342). Results: Cediranib treatment resulted in significant reduction of mean voxelwise 18F-FMISO TBR, K1, and K1/k2 in both the 2-d and the 7-d groups (P < 0.05). The k3 parameter was increased in both groups but reached significance only in the 2-d group. In the vehicle-treated groups, no significant change in TBR, K1, K1/k2, or k3 was observed (P > 0.2). Ex vivo tumor analysis confirmed the presence of hypoxic tumor regions that nevertheless exhibited relatively lower 18F-FMISO uptake. Conclusion:18F-FMISO kinetic modeling reveals a more detailed response to antiangiogenic treatment than a single static image is able to reveal. The reduced mean K1 reflects a reduction in tumor vascular perfusion, whereas the increased k3 reflects a rise in hypoxia-mediated entrapment of the radiotracer. However, if only late static images are analyzed, the observed reduction in 18F-FMISO uptake after treatment with cediranib may be mistakenly interpreted as a global decrease, rather than an increase, in tumor hypoxia. These findings support the use of 18F-FMISO kinetic modeling to more accurately characterize the response to treatments that have a direct effect on tumor vascularization and perfusion.

Quantitative evaluation of oxygen metabolism in the intratumoral hypoxia: 18F-fluoromisonidazole and 15O-labelled gases inhalation PET

BackgroundIntratumoral hypoxia is one of the resistant factors in radiotherapy and chemotherapy for cancer. Although it is detected by 18F-fluoromisonidazole (FMISO) PET, the relationship between intratumoral hypoxia and oxygen metabolism has not been studied. The purpose of this study was to evaluate the intratumoral perfusion and oxygen metabolism in hypoxic regions using the rat xenograft model. Ten male Fischer rats with C6 glioma (body weight = 220 ± 15 g) were investigated with 18F-FMISO PET and steady-state inhalation method of 15O-labelled gases PET. The tumoral blood flow (TBF), tumoral metabolic rate of oxygen (TMRO2), oxygen extraction fraction (OEF), and tumoral blood volume (TBV) were measured under artificial ventilation with 15O–CO2, 15O–O2, and 15O–CO gases. Multiple volumes of interest (1-mm diameter sphere) were placed on the co-registered 18F-FMISO (3 h post injection) and functional 15O-labelled gases PET images. The TBF, TMRO2, OEF, and TBV values were compared among the three groups classified by the 18F-FMISO uptake as follows: group Low (L), less than 1.0; group Medium (M), between 1.0 and 2.0; and group High (H), more than 2.0 in the 18F-FMISO standardized uptake value (SUV).ResultsThere were moderate negative correlations between 18F-FMISO SUV and TBF (r = −0.56 and p < 0.01), and weak negative correlations between 18F-FMISO SUV and TMRO2 (r = −0.38 and p < 0.01) and 18F-FMISO SUV and TBV (r = −0.38 and p < 0.01). Quantitative values were as follows: TBF, (L) 55 ± 30, (M) 32 ± 17, and (H) 30 ± 15 mL/100 mL/min; OEF, (L) 33 ± 14, (M) 36 ± 17, and (H) 41 ± 16%; TMRO2, (L) 2.8 ± 1.3, (M) 1.9 ± 1.0, and (H) 2.1 ± 1.1 mL/100 mL/min; and TBV, (L) 5.7 ± 2.1, (M) 4.3 ± 1.9, and (H) 3.9 ± 1.2 mL/100 mL, respectively. Intratumoral hypoxic regions (M and H) showed significantly lower TBF, TMRO2, and TBV values than non-hypoxic regions (L). OEF showed significant increase in the severe hypoxic region compared to non-hypoxic and mild hypoxic regions.ConclusionsThis study demonstrated that intratumoral hypoxic regions showed decreased blood flow with increased oxygen extraction, suggesting the need for a treatment strategy to normalize the blood flow for oxygen-avid active tumor cells in hypoxic regions.

Multiparametric Imaging of Tumor Hypoxia and Perfusion with 18F-Fluoromisonidazole Dynamic PET in Head and Neck Cancer.

Tumor hypoxia and perfusion are independent prognostic indicators of patient outcome. We developed the methodology for and investigated the utility of multiparametric imaging of tumor hypoxia and perfusion with 18F-fluoromisonidazole (18F-FMISO) dynamic PET (dPET) in head and neck cancer. Methods: One hundred twenty head and neck cancer patients underwent 0- to 30-min 18F-FMISO dPET in a customized immobilization mask, followed by 10-min static acquisitions starting at 93 ± 6 and 160 ± 13 min after injection. A total of 248 lesions (≥2 cm3) were analyzed. Voxelwise pharmacokinetic modeling was conducted using an irreversible 1-plasma 2-tissue-compartment model to calculate surrogate biomarkers of tumor hypoxia (k3), perfusion (K1), and 18F-FMISO distribution volume. The analysis was repeated with truncated dPET datasets. Results: Substantial inter- and intratumor heterogeneity was observed for all investigated metrics. Equilibration between the blood and unbound 18F-FMISO was rapid in all tumors. 18F-FMISO distribution volume deviated from the expected value of unity, causing discrepancy between k3 maps and total 18F-FMISO uptake and reducing the dynamic range of total 18F-FMISO uptake for quantifying the degree of hypoxia. Both positive and negative trends between hypoxia and perfusion were observed in individual lesions. All investigated metrics were reproducible when calculated from a truncated 20-min dataset. Conclusion:18F-FMISO dPET provides the data necessary to generate parametric maps of tumor hypoxia, perfusion, and radiotracer distribution volume. These data clarify the ambiguity in interpreting 18F-FMISO uptake and improve the characterization of lesions. We show total acquisition times can be reduced to 20 min, facilitating the translation of 18F-FMISO dPET into the clinic.

18F-Fluoromisonidazole PET/CT: A Potential Tool for Predicting Primary Endocrine Therapy Resistance in Breast Cancer

Although endocrine therapy is an effective method to treat estrogen receptor (ER)-positive breast cancer, approximately 30%-40% of all hormone receptor-positive tumors display de novo resistance. The aim of our current study was to analyze whether (18)F-labeled fluoromisonidazole (1-(2-nitro-1-imidazolyl)-2-hydroxy-3-fluoropropane [(18)F-FMISO]) PET/CT could predict primary resistance to hormonal therapy in ER-positive breast cancer. Postmenopausal women who had ER-α-positive breast cancer, stages II-IV, and had never received prior endocrine therapy were prospectively enrolled in this study. Patients underwent both (18)F-FDG and (18)F-FMISO PET/CT scans before and after treatment. The hottest (18)F-FDG standardized uptake value (SUV) in the tumor foci, the SUVs at 2 and 4 h, and the TBR2 h and TBR4 h for the target lesions were calculated (TBR2 h = SUV2 hT/SUV2 hB and TBR4 h = SUV4 hT/SUV4 hB [TBR is the tumor-to-background ratio]). Clinical outcomes of primary endocrine therapy with letrozole were evaluated according to the criteria of the World Health Organization after at least 3 mo of treatment. Immunohistochemistry for markers of proliferation (Ki67) and hypoxia-induced factor 1α was performed on a subset of tumors that had undergone biopsy or surgery. Pearson and Spearman analysis was used to determine the correlation between the parameters of (18)F-FDG and (18)F-FMISO uptake and clinical or immunohistochemistry outcomes with a 0.01 threshold for statistical significance. A total of 45 lesions (13 primary, 32 metastatic) from 20 patients met the inclusion criteria in this study. Baseline (18)F-FDG and (18)F-FMISO PET/CT scans were obtained for 33 lesions from 16 patients. The correlation between baseline (18)F-FDG uptake and clinical outcome was weak and did not reach statistical significance (r = 0.37, P = 0.031). However, there was a significantly positive correlation between baseline (18)F-FMISO uptake (SUV2 hT, TBR2 h, SUV4 hT, and TBR4 h) and clinical outcomes after ≥3 mo of primary endocrine therapy with letrozole (r = 0.77, 0.76, 0.71, and 0.78, respectively; P < 0.0001). The application of a TBR4 h cutoff of ≥1.2 allowed the prediction of 88% of the cases of progressive disease (15/17). Despite poor correlation between (18)F-FMISO uptake and hypoxia-induced factor 1α expression, a marginal positive correlation between TBR4 h and Ki67 expression was measured (r = 0.51, P = 0.011) in a subset of malignant lesions acquired by biopsy or surgery. (18)F-FMISO PET/CT can be used to predict primary endocrine resistance in ER-positive breast cancer.

Abstract 5273: Multiplexed PET probes for imaging breast cancer early response to VEGF121/rGel treatment

Abstract Purpose: Monitoring of tumor early response to therapy is important in clinical oncology to reduce side effects and save costs, especially with the growing number of alternative treatment regimens that are only effective in select subgroups of patients. VEGF121/rGel fusion protein has been shown to completely suppress ocular neovascularization and inhibit the growth of melanoma and glioblastoma, as well as prostate, breast, and bladder tumor models with low systemic toxicity. The aim of this study was to apply multiplexed positron emission tomography (PET) probes to monitor glucose metabolism, cellular proliferation, tumor hypoxia and angiogenesis during VEGF121/rGel therapy of breast cancer. Methods: Orthotopic MDA-MB-435 breast cancer tumor-bearing mice were treated with 2 doses of VEGF121/rGel at days 1 and 3. Tumor growth was monitored by caliper measurement. During the therapeutic process, longitudinal PET scans were performed using 18F-FDG, 18F-FLT, 18F-FMISO, and 18F-FPPRGD2 as imaging tracers to evaluate tumor glucose metabolism, cellular proliferation, tumor hypoxia, and angiogenesis, respectively. Imaging metrics were validated by immunohistochemical analysis of the corresponding biomarkers. Results: Two doses of 12 mg/kg VEGF121/rGel, administered intraperitoneally, resulted in initial delay of tumor growth, but the growth resumed 4 days after tumor treatment was stopped. VEGF121/rGel treatment led to significantly decreased uptake of 18F-FPPRGD2 at day 1 (24.0 ± 8.8%, p &amp;lt; 0.05) and day 3 (36.3 ± 9.2%, p &amp;lt; 0.01), relative to the baseline, which slowly recovered to the baseline at day 14. 18F-FMISO uptake was increased in the treated tumors at day 1 (23.9 ± 15.7%, p &amp;lt; 0.05) and day 3 (51.4 ± 29.4%, p &amp;lt; 0.01), as compared to the control group. At day 7 and 14, 18F-FMISO uptake restored to the baseline level. The relative reductions in FLT uptake in treated tumors were approximately 13.0 ± 4.5% at day 1 and 25.0 ± 4.4% (p &amp;lt; 0.01) at day 3. No significant change of 18F-FDG uptake was observed in VEGF121/rGel treated tumors, compared with the control group. The imaging findings were supported by ex vivo analysis of related biomarkers. Conclusions: Longitudinal imaging studies with 4 PET tracers demonstrated the feasibility and usefulness of multiplexed probes for quantitative measurement of anti-tumor effects of VEGF121/rGel at the early stage of treatment. 18F-FLT, 18F-FMISO and 18F-FPPRGD2 are superior to 18F-FDG in monitoring therapy response, as supported by ex vivo analyses of related biomarkers. This pre-clinical study should be helpful in accelerating anti-cancer drug development and promoting the clinical translation of molecular imaging in tumor therapy response monitoring. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5273. doi:10.1158/1538-7445.AM2011-5273

Multiplexed PET Probes for Imaging Breast Cancer Early Response to VEGF121/rGel Treatment

In this study, we applied multiplexed positron emission tomography (PET) probes to monitor glucose metabolism, cellular proliferation, tumor hypoxia and angiogenesis during VEGF₁₂₁/rGel therapy of breast cancer. Two doses of 12 mg/kg VEGF₁₂₁/rGel, administered intraperitoneally, resulted in initial delay of tumor growth, but the growth resumed 4 days after tumor treatment was stopped. The average tumor growth rate expressed as V/V(0), were 1.11 ± 0.07, 1.21 ± 0.10, 1.58 ± 0.36 and 2.64 ± 0.72 at days 1, 3, 7 and 14, respectively. Meanwhile, the VEGF₁₂₁/rGel treatment group showed V/V₀ ratios of 1.04 ± 0.06, 1.05 ± 0.11, 1.09 ± 0.17 and 1.86 ± 0.36 at days 1, 3, 7 and 14, respectively. VEGF₁₂₁/rGel treatment led to significantly decreased uptake of ¹⁸F-FPPRGD2 at day 1 (24.0 ± 8.8%, p < 0.05) and day 3 (36.3 ± 9.2%, p < 0.01), relative to the baseline, which slowly recovered to the baseline at day 14. ¹⁸F-FMISO uptake was increased in the treated tumors at day 1 (23.9 ± 15.7%, p < 0.05) and day 3 (51.4 ± 29.4%, p < 0.01), as compared to the control group. At days 7 and 14, ¹⁸F-FMISO uptake restored to the baseline level. The relative reductions in FLT uptake in treated tumors were approximately 13.0 ± 4.5% at day 1 and 25.0 ± 4.4% (p < 0.01) at day 3. No significant change of ¹⁸F-FDG uptake was observed in VEGF₁₂₁/rGel treated tumors, compared with the control group. The imaging findings were supported by ex vivo analysis of related biomarkers. Overall, longitudinal imaging studies with 4 PET tracers demonstrated the feasibility and usefulness of multiplexed probes for quantitative measurement of antitumor effects of VEGF₁₂₁/rGel at the early stage of treatment. This preclinical study should be helpful in accelerating anticancer drug development and promoting the clinical translation of molecular imaging.