Hypoxia PET Research Articles

18F-FMISO PET imaging: insights over MRI in patients with glioma

Hypoxic tumors have been demonstrated to be associated with amplified resistance to radiotherapy, chemo-resistance and less favorable outcome after surgery. Non-invasive identification and quantification of hypoxia in humans affected by glioma can be achieved using PET/CT and MRI techniques, although their use is still limited to the research setting. The objective of this review is to present an update of the literature about the potential clinical utility of FMISO PET imaging for the evaluation of hypoxia in patients with glioma, in comparison with advanced MRI techniques, when available. A comprehensive search strategy was used based on SCOPUS and PubMed databases using the following terms: “FMISO”/“Fluoromisonidazole” AND “brain tumor”/“glioma” AND “PET”/“Positron Emission Tomography”. From all studies published in English, we selected—for this review—the most relevant articles of the last 20 years, evaluating the use of FMISO PET in glioma patients, and comparing PET findings with MRI imaging (when available). The use of PET/CT with hypoxia radiotracers in glioma is still limited due to fragmentary data and scarce number of clinical trials in this setting. The most used PET radiotracer for the quantification of hypoxia brain tumor is 18F-FMISO and advanced MRI techniques may provide additional value, especially to couple perfusion information to hypoxia data obtained by PET. As example, relative cerebral blood volume maps could be integrated with PET imaging results for more precise and integrated evaluation of hypoxia, neo-angiogenesis and necrotic areas. Hypoxia PET imaging has demonstrated potential benefits for grading, diagnostic and prognostic purposes, despite the lack of tangible results able to introduce such method in a wide clinical setting. MRI remains the gold standard in the morphologic evaluation of glioma, but the integration of results provided by 18F-FMISO PET imaging concerning hypoxia might provide new crucial information in patients with glioma.

Mechanism-Specific Pharmacodynamics of a Novel Complex-I Inhibitor Quantified by Imaging Reversal of Consumptive Hypoxia with [18F]FAZA PET In Vivo.

Tumors lack a well-regulated vascular supply of O2 and often fail to balance O2 supply and demand. Net O2 tension within many tumors may not only depend on O2 delivery but also depend strongly on O2 demand. Thus, tumor O2 consumption rates may influence tumor hypoxia up to true anoxia. Recent reports have shown that many human tumors in vivo depend primarily on oxidative phosphorylation (OxPhos), not glycolysis, for energy generation, providing a driver for consumptive hypoxia and an exploitable vulnerability. In this regard, IACS-010759 is a novel high affinity inhibitor of OxPhos targeting mitochondrial complex-I that has recently completed a Phase-I clinical trial in leukemia. However, in solid tumors, the effective translation of OxPhos inhibitors requires methods to monitor pharmacodynamics in vivo. Herein, 18F-fluoroazomycin arabinoside ([18F]FAZA), a 2-nitroimidazole-based hypoxia PET imaging agent, was combined with a rigorous test-retest imaging method for non-invasive quantification of the reversal of consumptive hypoxia in vivo as a mechanism-specific pharmacodynamic (PD) biomarker of target engagement for IACS-010759. Neither cell death nor loss of perfusion could account for the IACS-010759-induced decrease in [18F]FAZA retention. Notably, in an OxPhos-reliant melanoma tumor, a titration curve using [18F]FAZA PET retention in vivo yielded an IC50 for IACS-010759 (1.4 mg/kg) equivalent to analysis ex vivo. Pilot [18F]FAZA PET scans of a patient with grade IV glioblastoma yielded highly reproducible, high-contrast images of hypoxia in vivo as validated by CA-IX and GLUT-1 IHC ex vivo. Thus, [18F]FAZA PET imaging provided direct evidence for the presence of consumptive hypoxia in vivo, the capacity for targeted reversal of consumptive hypoxia through the inhibition of OxPhos, and a highly-coupled mechanism-specific PD biomarker ready for translation.

Correlative Analyses between Tissue-Based Hypoxia Biomarkers and Hypoxia PET Imaging in Head and Neck Cancer Patients during Radiochemotherapy: Results from a Prospective Trial

Tumor hypoxia influences the response of head and neck cancer (HNSCC) patients to radiotherapy and is associated with reduced outcomes. While both tissue-based hypoxia biomarkers and hypoxia PET imaging have previously been correlated with patient outcomes, the goal of this analysis was to evaluate potential correlations between biological markers and longitudinal biological imaging in a prospective trial of HNSCC patients. Forty-nine patients with locally advanced HNSCCs scheduled for definitive chemoradiation were enrolled in this prospective trial. They underwent baseline biopsies and [18F]FMISO PET imaging at baseline and at weeks 2 and 5 during treatment as well as [18F]FDG PET imaging at baseline. Immunohistochemical analyses for p16, Ki67, CD34-dependent microvascular density, hypoxia-inducible factor 1 α (HIF1α), carbonic anhydrase 9 (CAIX), Ku80 and CD44 were performed, and HPV status was assessed from tumor biopsies. Biomarker expression was quantified by the H-score and correlated with biological imaging information (Pearson product-moment correlation coefficient) and patient outcome data (Cox regression analysis). High HIF1α H-scores in the tumor were found to significantly correlate with increased tumor hypoxia during the first weeks of treatment as assessed by the difference in the FMISO tumor-to-background ratios (TBR) between baseline and week 2 (r=0.35; p<0.05) and deferred decrease in FMISO uptake between weeks 2 and 5 (r=0.35; p<0.05). Similarly, high CAIX H-scores were associated with a delayed reduction in FMISO TBR between weeks 2 and 5 (r=-0.39; p<0.05). Clinically, patients with high expression of CAIX exhibited significantly increased loco-regional recurrence rates after chemoradiation (hazard ratio 2.80 [1.08 – 7.31]; p<0.05). Additionally, loco-regional recurrence was associated with high expression of the DNA repair factor Ku80 in the tumor, although statistical significance was not reached. HPV status did not correlate with any of the tested biomarkers, and HPV-positive patients showed lower loco-regional recurrence rates (hazard ratio 0.13 [0.02 – 0.99]; p<0.01) and overall survival (hazard ratio 0.03 [0.001 – 1.73]; p<0.01) independent of their hypoxia dynamics and expression of tissue-based hypoxia biomarkers. In this trial, high expression of the tissue-based hypoxia biomarkers HIF1α and CAIX at baseline correlated with adverse hypoxia dynamics in HNSCCs during chemoradiation as assessed by PET imaging, and high CAIX levels were associated with increased loco-regional recurrence rates. Hence, tissue-based hypoxia biomarkers may be useful as predictors of hypoxia-associated radiation resistance and response of HNSCCs and warrant further investigations.

Imaging Biomarkers Multiparametric 3 Tesla MRI and FMISO Hypoxia PET during Chemoradiotherapy in HNSCC and Their Relation to Outcome

To prospectively assess in HNSCC patients the effect of chemoradiotherapy (CRT) on tumor hypoxia and tissue properties with [18F]FMISO PET/CT (FMISO PET) and multiparametric (mp) MRI at baseline and at an early (week 2) and late (week 5) time point during treatment and to analyze whether mpMRI and PET parameters are related with outcome. Patients with stage III to IVb HNSCC undergoing definitive CRT (total dose 70 Gy, 3 cycles of cisplatin over 7 weeks) were included. Patients were prospectively imaged with [18F]FDG PET/CT at baseline and with serial FMISO PET and serial 3 Tesla mpMRI for T1w-, T2w- as well as contrast-enhanced perfusion and diffusion-weighted measurements (ktrans, ve and apparent diffusion coefficient (ADC) maps) in weeks 0, 2 and 5. Patients were identified as responders or non-responders during follow-up regarding loco-regional control (LRC) and overall survival (OS). Tumor volumes were contoured and SUVmax FMISO PET and mean values for mpMRI parameters were compared between responders and non-responders with the t-test and Log Rank test at a significance level of p≤0.05. A complete set of serial FMISO PET data and 3 T MRI was available in 21 patients. Of those, 12 patients were diagnosed with local recurrence. Baseline tumor volume and FMISO-PET-derived tumor hypoxia (SUVmax FMISO) were higher among patients with local recurrence as compared to locally controlled patients (p=n.s.). On Kaplan-Meier analysis stratified at median change in SUVmax FMISO between weeks 0 to 5 (ΔFMISOwk0-5), LRC was higher for ΔFMISOwk0-5 > median (p=n.s.). For ADC, an increase was found from week 0 to 5 (responders > non-responders). LRC was significantly higher for patients with ΔADCwk0-5 and %ΔADCwk0-5 > median (Log Rank, p=0.04 and p=0.005). In perfusion MRI, ktrans increased from week 0 to 5 for both non-responders and responders (p=n.s.). For non-responders, ktrans reached a maximum at week 2, while for responders, ktrans showed a steady increase until week 5. Interstitial space volume fraction ve did not differ significantly between responders and non-responders and increased between week 0 and 5 (p=n.s.). Baseline ADC below median was significantly (p=0.013) correlated with improved OS. ADCweek2 below median was associated with improved OS (p=n.s.). Baseline ve below median was significantly correlated with improved OS (p=0.043) and associated with increased LRC (p=n.s.). Multiparametric MRI parameters ADC and interstitial space volume fraction ve obtained at baseline were significantly correlated with improved OS and an increase of ADC between week 0 to 5 was significantly correlated with improved LRC. FMISO-PET-derived tumor hypoxia and mean values of MRI parameters ktrans and ve differed between relapsing and non-relapsing patients, however without reaching statistical significance in this cohort. The correlations found for ve and ADC may suggest predictive power for OS and LRC depending on baseline imaging and the dynamics of ADC.

2-Nitroimidazole-Furanoside Derivatives for Hypoxia Imaging-Investigation of Nucleoside Transporter Interaction, 18F-Labeling and Preclinical PET Imaging.

The benefits of PET imaging of tumor hypoxia in patient management has been demonstrated in many examples and with various tracers over the last years. Although, the optimal hypoxia imaging agent has yet to be found, 2-nitroimidazole (azomycin) sugar derivatives—mimicking nucleosides—have proven their potential with [18F]FAZA ([18F]fluoro-azomycin-α-arabinoside) as a prominent representative in clinical use. Still, for all of these tracers, cellular uptake by passive diffusion is postulated with the disadvantage of slow kinetics and low tumor-to-background ratios. We recently evaluated [18F]fluoro-azomycin-β-deoxyriboside (β-[18F]FAZDR), with a structure more similar to nucleosides than [18F]FAZA and possible interaction with nucleoside transporters. For a deeper insight, we comparatively studied the interaction of FAZA, β-FAZA, α-FAZDR and β-FAZDR with nucleoside transporters (SLC29A1/2 and SLC28A1/2/3) in vitro, showing variable interactions of the compounds. The highest interactions being for β-FAZDR (IC50 124 ± 33 µM for SLC28A3), but also for FAZA with the non-nucleosidic α-configuration, the interactions were remarkable (290 ± 44 µM {SLC28A1}; 640 ± 10 µM {SLC28A2}). An improved synthesis was developed for β-FAZA. For a PET study in tumor-bearing mice, α-[18F]FAZDR was synthesized (radiochemical yield: 15.9 ± 9.0% (n = 3), max. 10.3 GBq, molar activity > 50 GBq/µmol) and compared to β-[18F]FAZDR and [18F]FMISO, the hypoxia imaging gold standard. We observed highest tumor-to-muscle ratios (TMR) for β-[18F]FAZDR already at 1 h p.i. (2.52 ± 0.94, n = 4) in comparison to [18F]FMISO (1.37 ± 0.11, n = 5) and α-[18F]FAZDR (1.93 ± 0.39, n = 4), with possible mediation by the involvement of nucleoside transporters. After 3 h p.i., TMR were not significantly different for all 3 tracers (2.5–3.0). Highest clearance from tumor tissue was observed for β-[18F]FAZDR (56.6 ± 6.8%, 2 h p.i.), followed by α-[18F]FAZDR (34.2 ± 7.5%) and [18F]FMISO (11.8 ± 6.5%). In conclusion, both isomers of [18F]FAZDR showed their potential as PET hypoxia tracers. Differences in uptake behavior may be attributed to a potential variable involvement of transport mechanisms.

Molecular PET imaging in adaptive radiotherapy: brain.

Owing to their heterogeneity and radioresistance, the prognosis of primitive brain tumors, which are mainly glial tumors, remains poor. Dose escalation in radioresistant areas is a potential issue for improving local control and overall survival. This review focuses on advances in biological and metabolic imaging of brain tumors that are proving to be essential for defining tumor target volumes in radiation therapy (RT) and for increasing the use of DPRT (dose painting RT) and ART (adaptative RT), to optimize dose in radio-resistant areas. Various biological imaging modalities such as PET (hypoxia, glucidic metabolism, protidic metabolism, cellular proliferation, inflammation, cellular membrane synthesis) and MRI (spectroscopy) may be used to identify these areas of radioresistance. The integration of these biological imaging modalities improves the diagnosis, prognosis and treatment of brain tumors. Technological improvements (PET and MRI), the development of research, and intensive cooperation between different departments are necessary before using daily metabolic imaging (PET and MRI) to treat patients with brain tumors. The adaptation of treatment volumes during RT (ART) seems promising, but its development requires improvements in several areas and an interdisciplinary approach involving radiology, nuclear medicine and radiotherapy. We review the literature on biological imaging to outline the perspectives for using DPRT and ART in brain tumors.

Effect of HNSCC Radiochemotherapy on Imaging Biomarker T2* MRI and its Relation to FMISO-PET Derived Hypoxia

Previous studies using hypoxia PET have shown significant reduction of tumor hypoxia (reoxygenation) during primary radiochemotherapy (RCT) of HNSCC and a significant correlation between reoxygenation on hypoxia PET and local control. Assessment of tumor hypoxia using MRI would offer independence from hypoxia PET tracer availability. The apparent MRI transverse relaxation time T2* has been proposed as an imaging biomarker and as a potential surrogate for hypoxia PET. The aim of this study was to assess the effect of primary RCT on T2* at an early (week 2) and late (week 5) time point during RCT and to analyse the relation between T2* and established hypoxia PET tracer 18F-misonidazole PET/CT (FMISO PET) and standard 18F-FDG PET/CT (FDG PET). In 10 T2-4N+ HNSCC patients, FDG PET was obtained at baseline and repeat FMISO PET and 3 Tesla MRI T2* in weeks 0, 2 and 5. MRI gross tumor volumes for tumor and lymph nodes (GTV-T, GTV-LN) were contoured and FMISO PET derived hypoxic tumor/lymph node subvolumes (HSV-T, HSV-LN) and complementary non-hypoxic subvolumes (nonHSV-T, nonHSV-LN) were generated using a threshold level of 1.4 times the mean SUV FMISO within muscle. Volumes were contoured for all time points (week 0, 2 and 5) individually and mean values for T2* and SUVmean FDG PET were obtained. Within GTVs (T, LN), r2 (FMISO to T2*) was calculated for [FMISO SUVmax GTV/SUVmean muscle] to [T2* mean GTV] and r2 (FMISO to FDG) was calculated for [FMISO SUVmax GTV/SUVmean muscle] to [FDG SUVmax GTV/SUVmean muscle]. From week 0 to 5 GTV-T and GTV-LN decreased by -56% and -63%, respectively and HSV-T and HSV-LN nearly completely resolved (n = 10). Mean T2* signal showed no significant change for GTV-T or GTV-LN. Within HSV-T mean T2* values were smaller compared to nonHSV-T: 15.0+/-4.6 vs. 18.3+/-2.9 (p = 0.051), whereas FDG SUVmean was significantly higher within hypoxic as compared to non-hypoxic regions: HSV-T 12.1+/-5.5 vs. nonHSV-T 6.1+/-2.6 and HSV-LN 10.2+/-3.9 vs. nonHSV-LN 4.7+/-1.9 (week 0, p≤0.026 and p≤0.011). Correlation between FMISO PET and FDG PET was higher than between FMSIO PET and T2*: r2 for GTV-T (FMISO/FDG)=0.81, r2 for GTV-T (FMISO/T2*)=0.32. Marked reduction of tumor hypoxia between week 0, 2 and 5 found on FMISO PET was not accompanied by a significant T2*change within GTVs over time. At baseline, smaller T2* values and significantly larger FDG SUVmean were found within HSV-T as compared to nonHSV-T. These results suggest a relation between tumor oxygenation status and T2* at baseline, however with the correlation coefficient r2 FMISO/T2* being lower than r2 FMISO/FDG. Overall, T2* quantitation was feasible and the findings on T2* imaging warrant further investigations but do not indicate a simple surrogate role for T2* as hypoxia imaging marker due to lack of correlation to established hypoxia marker FMISO PET. Our findings on reduction of FMISO uptake during RCT were in line with previous reports.

Effect of radiochemotherapy on T2* MRI in HNSCC and its relation to FMISO PET derived hypoxia and FDG PET

BackgroundTo assess the effect of radiochemotherapy (RCT) on proposed tumour hypoxia marker transverse relaxation time (T2*) and to analyse the relation between T2* and 18F-misonidazole PET/CT (FMISO-PET) and 18F-fluorodeoxyglucose PET/CT (FDG-PET).MethodsTen patients undergoing definitive RCT for squamous cell head-and-neck cancer (HNSCC) received repeat FMISO- and 3 Tesla T2*-weighted MRI at weeks 0, 2 and 5 during treatment and FDG-PET at baseline. Gross tumour volumes (GTV) of tumour (T), lymph nodes (LN) and hypoxic subvolumes (HSV, based on FMISO-PET) and complementary non-hypoxic subvolumes (nonHSV) were generated. Mean values for T2* and SUVmean FDG were determined.ResultsDuring RCT, marked reduction of tumour hypoxia on FMISO-PET was observed (T, LN), while mean T2* did not change significantly. At baseline, mean T2* values within HSV-T (15 ± 5 ms) were smaller compared to nonHSV-T (18 ± 3 ms; p = 0.051), whereas FDG SUVmean (12 ± 6) was significantly higher for HSV-T (12 ± 6) than for nonHSV-T (6 ± 3; p = 0.026) and higher for HSV-LN (10 ± 4) than for nonHSV-LN (5 ± 2; p ≤ 0.011). Correlation between FMISO PET and FDG PET was higher than between FMSIO PET and T2* (R2 for GTV-T (FMISO/FDG) = 0.81, R2 for GTV-T (FMISO/T2*) = 0.32).ConclusionsMarked reduction of tumour hypoxia between week 0, 2 and 5 found on FMISO PET was not accompanied by a significant T2*change within GTVs over time. These results suggest a relation between tumour oxygenation status and T2* at baseline, but no simple correlation over time. Therefore, caution is warranted when using T2* as a substitute for FMISO-PET to monitor tumour hypoxia during RCT in HNSCC patients.Trial registrationDRKS,DRKS00003830. Registered 23.04.2012.

18F-Flortanidazole Hypoxia PET Holds Promise as a Prognostic and Predictive Imaging Biomarker in a Lung Cancer Xenograft Model Treated with Metformin and Radiotherapy.

Metformin may improve tumor oxygenation and thus radiotherapy response, but imaging biomarkers for selection of suitable patients are still under investigation. First, we assessed the effect of acute metformin administration on non-small cell lung cancer xenograft tumor hypoxia using PET imaging with the hypoxia tracer 18F-flortanidazole. Second, we verified the effect of a single dose of metformin before radiotherapy on long-term treatment outcome. Third, we examined the potential of baseline 18F-flortanidazole as a prognostic or predictive biomarker for treatment response. Methods: A549 tumor-bearing mice underwent a 18F-flortanidazole PET/CT scan to determine baseline tumor hypoxia. The next day, mice received a 100 mg/kg intravenous injection of metformin. 18F-flortanidazole was administered intravenously 30 min later, and a second PET/CT scan was performed to assess changes in tumor hypoxia. Two days later, the mice were divided into 3 therapy groups: controls (group 1), radiotherapy (group 2), and metformin + radiotherapy (group 3). Animals received saline (groups 1-2) or metformin (100 mg/kg; group 3) intravenously, followed by a single radiotherapy dose of 10 Gy (groups 2-3) or sham irradiation (group 1) 30 min later. Tumor growth was monitored triweekly by caliper measurement, and tumor volume relative to baseline was calculated. The tumor doubling time (TDT), that is, the time to reach twice the preirradiation tumor volume, was defined as the endpoint. Results: Thirty minutes after metformin treatment, 18F-flortanidazole demonstrated a significant change in tumor hypoxia, with a mean intratumoral reduction in 18F-flortanidazole tumor-to-background ratio (TBR) from 3.21 ± 0.13 to 2.87 ± 0.13 (P = 0.0001). Overall, relative tumor volume over time differed across treatment groups (P < 0.0001). Similarly, the median TDT was 19, 34, and 52 d in controls, the radiotherapy group, and the metformin + radiotherapy group, respectively (log-rank P < 0.0001). Both baseline 18F-flortanidazole TBR (hazard ratio, 2.0; P = 0.0004) and change from baseline TBR (hazard ratio, 0.39; P = 0.04) were prognostic biomarkers for TDT irrespective of treatment, and baseline TBR predicted metformin-specific treatment effects that were dependent on baseline tumor hypoxia. Conclusion: Using 18F-flortanidazole PET imaging in a non-small cell lung cancer xenograft model, we showed that metformin may act as a radiosensitizer by increasing tumor oxygenation and that baseline 18F-flortanidazole shows promise as an imaging biomarker.

OC-0268: FAZA PET hypoxia as a marker of loco-regional recurrence in HNSCC? Results from the DAHANCA 24 trial

OC-0268: FAZA PET hypoxia as a marker of loco-regional recurrence in HNSCC? Results from the DAHANCA 24 trial

Impact of tissue transport on PET hypoxia quantification in pancreatic tumours

BackgroundThe clinical impact of hypoxia in solid tumours is indisputable and yet questions about the sensitivity of hypoxia-PET imaging have impeded its uptake into routine clinical practice. Notably, the binding rate of hypoxia-sensitive PET tracers is slow, comparable to the rate of diffusive equilibration in some tissue types, including mucinous and necrotic tissue. This means that tracer uptake on the scale of a PET imaging voxel—large enough to include such tissue and hypoxic cells—can be as much determined by tissue transport properties as it is by hypoxia. Dynamic PET imaging of 20 patients with pancreatic ductal adenocarcinoma was used to assess the impact of transport on surrogate metrics of hypoxia: the tumour-to-blood ratio [TBR(t)] at time t post-tracer injection and the trapping rate k3 inferred from a two-tissue compartment model. Transport quantities obtained from this model included the vascular influx and efflux rate coefficients, k1 and k2, and the distribution volume vd≡k1/(k2+k3).ResultsCorrelations between voxel- and whole tumour-scale k3 and TBR values were weak to modest: the population average of the Pearson correlation coefficients (r) between voxel-scale k3 and TBR (1 h) [TBR(2 h)] values was 0.10 [0.01] in the 20 patients, while the correlation between tumour-scale k3 and TBR(2 h) values was 0.58. Using Patlak’s formula to correct uptake for the distribution volume, correlations became strong (r=0.80[0.52] and r=0.93, respectively). The distribution volume was substantially below unity for a large fraction of tumours studied, with vd ranging from 0.68 to 1 (population average, 0.85). Surprisingly, k3 values were strongly correlated with vd in all patients. A model was proposed to explain this in which k3 is a combination of the hypoxia-sensitive tracer binding rate kb and the rate keq of equilibration in slow-equilibrating regions occupying a volume fraction 1−vd of the imaged tissue. This model was used to calculate the proposed hypoxia surrogate marker kb.ConclusionsHypoxia-sensitive PET tracers are slow to reach diffusive equilibrium in a substantial fraction of pancreatic tumours, confounding quantification of hypoxia using both static (TBR) and dynamic (k3) PET imaging. TBR is reduced by distribution volume effects and k3 is enhanced by slow equilibration. We proposed a novel model to quantify tissue transport properties and hypoxia-sensitive tracer binding in order to improve the sensitivity of hypoxia-PET imaging.

Combined FDG and CT Radiomics Features Predict FMISO Uptake in Head and Neck Cancer

18F-fluoromisonidazole (FMISO) is a hypoxia PET imaging agent that has been used in head and neck to alter management. However, FMISO is still an investigational agent that requires an institutional review board with an IND and therefore is not widely available. Having a surrogate biomarker based on an approved imaging technique that could indirectly identify hypoxia would enable hypoxia-based treatment modulation in a routine clinical setting. In this work we assessed whether a radiomics biomarker built from FDG PET and CT features could predict FMISO uptake on a per-lesion basis. One hundred head and neck cancer patients undergoing chemoradiotherapy treatment at a single institution between 2011 and 2016 received pre-treatment FDG and FMISO PET/CT. A total of 134 lesions delineated by physicians on the treatment planning CT and with a volume larger than 10 cc were analyzed. Forty-six lesions were held out as a validation set. The level of hypoxia was defined as the maximum tumor-to-blood ratio (TBRmax) of FMISO uptake measured at ∼150 minutes post injection. Approximately 200 radiomics features were extracted from FDG PET (first order and run length features only) and treatment planning CT (all orders, including run length), and used to produce a prediction of FMISO TBRmax. The most frequent features were selected by lasso using 100×10-fold cross validation (CV). The resulting features and their bilinear interaction terms were used again in a lasso regression model. The final combination of predictors was found by minimizing the mean square error on nested 10-fold CV. Performance was assessed by means of (i) R2, (ii) F-test P-value for a constant-model null hypothesis, and (iii) area under the curve (AUC) analysis, assuming a hypoxia threshold of TBRmaxthresh = 1.4. The mean FMISO TBRmax of the population was 1.82 (SD = 0.65). The resulting model contained two individual FDG PET features (median SUV and low gray-level run emphasis) and three interaction terms with other PET run-length and CT Haralick correlation features. In the training dataset (n = 88) the resulting prediction had an adjusted R2 = 0.42. For a hypoxia threshold of TBRmaxthresh = 1.4, the AUC was 0.86. In the validation dataset the prediction had an adjusted R2 of 0.17, with F-test P = 0.002. Assuming TBRmaxthresh = 1.4, the AUC for the validation dataset was 0.79, with an optimal operating point of FPR = 0.21 and TPR = 0.78. We found that FDG PET and CT provide complementary information that can be used to form a radiomics biomarker that correlates with tumor hypoxia as evaluated by FMISO PET. Further validation using multi-institutional datasets is required. Clinically, this is a promising approach to identify a subset of head and neck radiotherapy patients who may benefit from hypoxia-based dose modification.

Predicting tumor hypoxia in non-small cell lung cancer by combining CT, FDG PET and dynamic contrast-enhanced CT

Background: Most solid tumors contain inadequately oxygenated (i.e., hypoxic) regions, which tend to be more aggressive and treatment resistant. Hypoxia PET allows visualization of hypoxia and may enable treatment adaptation. However, hypoxia PET imaging is expensive, time-consuming and not widely available. We aimed to predict hypoxia levels in non-small cell lung cancer (NSCLC) using more easily available imaging modalities: FDG-PET/CT and dynamic contrast-enhanced CT (DCE-CT).Material and methods: For 34 NSCLC patients, included in two clinical trials, hypoxia HX4-PET/CT, planning FDG-PET/CT and DCE-CT scans were acquired before radiotherapy. Scans were non-rigidly registered to the planning CT. Tumor blood flow (BF) and blood volume (BV) were calculated by kinetic analysis of DCE-CT images. Within the gross tumor volume, independent clusters, i.e., supervoxels, were created based on FDG-PET/CT. For each supervoxel, tumor-to-background ratios (TBR) were calculated (median SUV/aorta SUVmean) for HX4-PET/CT and supervoxel features (median, SD, entropy) for the other modalities. Two random forest models (cross-validated: 10 folds, five repeats) were trained to predict the hypoxia TBR; one based on CT, FDG, BF and BV, and one with only CT and FDG features. Patients were split in a training (trial NCT01024829) and independent test set (trial NCT01210378). For each patient, predicted, and observed hypoxic volumes (HV) (TBR > 1.2) were compared.Results: Fifteen patients (3291 supervoxels) were used for training and 19 patients (1502 supervoxels) for testing. The model with all features (RMSE training: 0.19 ± 0.01, test: 0.27) outperformed the model with only CT and FDG-PET features (RMSE training: 0.20 ± 0.01, test: 0.29). All tumors of the test set were correctly classified as normoxic or hypoxic (HV > 1 cm3) by the best performing model.Conclusions: We created a data-driven methodology to predict hypoxia levels and hypoxia spatial patterns using CT, FDG-PET and DCE-CT features in NSCLC. The model correctly classifies all tumors, and could therefore, aid tumor hypoxia classification and patient stratification.

Characterizing hypoxia in human glioma: A simultaneous multimodal MRI and PET study.

Hypoxia plays an important role for the prognosis and therapy response of cancer. Thus, hypoxia imaging would be a valuable tool for pre-therapeutic assessment of tumor malignancy. However, there is no standard validated technique for clinical application available yet. Therefore, we performed a study in 12 patients with high-grade glioma, where we directly compared the two currently most promising techniques, namely the MR-based relative oxygen extraction fraction (MR-rOEF) and the PET hypoxia marker H-1-(3-[18 F]-fluoro-2-hydroxypropyl)-2-nitroimidazole ([18 F]-FMISO). MR-rOEF was determined from separate measurements of T2 , T2 * and relative cerebral blood volume (rCBV) employing a multi-parametric approach for quantification of the blood-oxygenation-level-dependent (BOLD) effect. With respect to [18 F]-FMISO-PET, besides the commonly used late uptake between 120 and 130min ([18 F]-FMISO120-130 min ), we also analyzed the hypoxia specific uptake rate [18 F]-FMISO-k3 , as obtained by pharmacokinetic modeling of dynamic uptake data. Since pharmacokinetic modeling of partially acquired dynamic [18 F]-FMISO data was sensitive to a low signal-to-noise-ratio, analysis was restricted to high-uptake tumor regions. Individual spatial analyses of deoxygenation and hypoxia-related parameter maps revealed that high MR-rOEF values clustered in (edematous) peritumoral tissue, while areas with high [18 F]-FMISO120-130 min concentrated in and around active tumor with disrupted blood-brain barrier, i.e. contrast enhancement in T1 -weighted MRI. Volume-of-interest-based correlations between MR-rOEF and [18 F]-FMISO120-130 min as well as [18 F]-FMISO-k3 , and voxel-wise analyses in individual patients, yielded limited correlations, supporting the notion that [18 F]-FMISO uptake, even after 2h, might still be influenced by perfusion while [18 F]-FMISO-k3 was severely hampered by noise. According to these results, vascular deoxygenation, as measured by MR-rOEF, and severe tissue hypoxia, as measured by [18 F]-FMISO, show a poor spatial correspondence. Overall, the two methods appear to rather provide complementary than redundant information about high-grade glioma biology.

Abstract 1875: [18F]HX4 shows potential as a predictive biomarker for the radiosensitizing capacities of metformin in a NSCLC xenograft model

Abstract Introduction Metformin (MET) may improve tumor oxygenation and thus radiotherapy (RT) response. However, appropriate imaging biomarkers for patient stratification, critically needed to be able to advance to clinical trials with MET as a radiosensitizer, are still lacking. In this proof-of-concept (POC) study, we first assessed the effect of acute MET administration on NSCLC xenograft tumor hypoxia with PET using the novel hypoxia PET tracer [18F]HX4. Second, we verified the influence of a single dose of MET prior to RT on treatment outcome. Experimental procedures A549 tumor-bearing mice (n=9; animals were inoculated in both hind legs) underwent a [18F]HX4 PET/CT scan to determine baseline tumor hypoxia. The next day, mice were administered 100 mg/kg MET IV. [18F]HX4 was administered IV 30 min. later, whereupon a second PET/CT scan was performed to assess changes in tumor hypoxia. Two days after this second scan, mice were randomized into three groups (n=3/group): a control group (1), a RT group (2), and a MET+RT group (3) with comparable tumor volumes (259±103; 218±81 and 247±121 mm3, resp.). Animals were administered 0.9% saline (groups 1-2) or 100 mg/kg MET (group 3) IV, followed by a single dose of 10 Gy 30 min. after administration (groups 2-3). Control animals of group 1 underwent sham RT. During the entire study, tumor growth was monitored triweekly by caliper measurements. Calculation of the relative tumor volumes (RTV) was initiated when tumors reached a mean baseline volume of 100 mm3 with the formula RTV=Vtime x/Vbaseline. Tumor growth inhibition (TGI) was calculated for each tumor in both treatment groups with the formula TGI=1-(RTVtreated/RTVcontrol). Results MET significantly altered A549 tumor hypoxia, as the mean [18F]HX4 tumor-to-blood ratio (TBR) was reduced from 3.03±0.27 to 2.82±0.25 (p=0.040) after MET administration. The tempering influence of MET on tumor hypoxia improved RT response, as fifteen days after irradiation TGI was 63±7% in the MET+RT group as compared to only 36±9% in the RT group, however significance was not reached. To date, tumors are still being measured triweekly and this will be continued until a volume of 1500 mm3 is reached. Then, animals will be sacrificed for histological validations on tumor tissue to assess differences in a.o. proliferation and hypoxia. Conclusions Using non-invasive imaging, we showed in A549 xenograft tumors that MET acts as a radiosensitizer possibly by decreasing tumor hypoxia. Our results imply that [18F]HX4 PET imaging holds potential as a predictive biomarker for the beneficial effect of MET in the treatment of NSCLC; however, the small group sizes in this POC study did not allow us to draw sound conclusions. These promising findings will be validated in a larger follow-up study in order to validate [18F]HX4 PET as a predictive biomarker for MET and RT response. Citation Format: Sven De Bruycker, Christel Vangestel, Tim Van den Wyngaert, Steven Deleye, Dominique Vanderghinste, Steven Staelens, Sigrid Stroobants. [18F]HX4 shows potential as a predictive biomarker for the radiosensitizing capacities of metformin in a NSCLC xenograft model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1875. doi:10.1158/1538-7445.AM2017-1875

Prognostic value of dynamic hypoxia PET in head and neck cancer: Results from a planned interim analysis of a randomized phase II hypoxia-image guided dose escalation trial

Background and purposeTo prospectively assess the prognostic value of tumour hypoxia determined by dynamic [18F]Fluoromisonidazole (dynFMISO) PET/CT, and to evaluate both feasibility and toxicity in patients with locally advanced squamous cell carcinomas of the head and neck (LASCCHN) treated with dynFMISO image-guided dose escalation (DE) using dose-painting by contours. Patients and methodsWe present a planned interim analysis of a randomized phase II trial. N=25 patients with LASCCHN received baseline dynFMISO PET/CT to derive hypoxic volumes (HV). Patients with tumour hypoxia were randomized into standard radiochemotherapy (stdRT) (70Gy/35 fractions) or DE (77Gy/35 fractions) to the HV. Patients with non-hypoxic tumours were treated with stdRT. Loco-regional control (LRC) in hypoxic patients randomized to stdRT was compared to non-hypoxic patients. Feasibility and toxicity were analysed for patients in the DE arm and compared to stdRT. ResultsWith a mean follow-up of 27months, LRC in hypoxic patients receiving stdRT (n=10) was significantly worse compared to the non-hypoxic group (n=5) (2y-LRC 44.4% versus 100%, p=0.048). The respective LRC for the DE group (n=10) was 70.0%. Treatment compliance as well as acute and late toxicity did not show significant differences between the DE and the standard dose arms. ConclusionTumour hypoxia determined by baseline dynFMISO PET/CT is associated with a high risk of local failure in patients with LASCCHN. First data suggest that DE to HV is feasible without excess toxicity.

In Vivo Hypoxia PET Imaging Quantifies the Severity of Arthritic Joint Inflammation in Line with Overexpression of Hypoxia-Inducible Factor and Enhanced Reactive Oxygen Species Generation.

Hypoxia is essential for the development of autoimmune diseases such as rheumatoid arthritis (RA) and is associated with the expression of reactive oxygen species (ROS), because of the enhanced infiltration of immune cells. The aim of this study was to demonstrate the feasibility of measuring hypoxia noninvasively in vivo in arthritic ankles with PET/MRI using the hypoxia tracers 18F-fluoromisonidazole (18F-FMISO) and 18F-fluoroazomycinarabinoside (18F-FAZA). Additionally, we quantified the temporal dynamics of hypoxia and ROS stress using L-012, an ROS-sensitive chemiluminescence optical imaging probe, and analyzed the expression of hypoxia-inducible factors (HIFs). Methods: Mice underwent noninvasive in vivo PET/MRI to measure hypoxia or optical imaging to analyze ROS expression. Additionally, we performed ex vivo pimonidazole-/HIF-1α immunohistochemistry and HIF-1α/2α Western blot/messenger RNA analysis of inflamed and healthy ankles to confirm our in vivo results. Results: Mice diseased from experimental RA exhibited a 3-fold enhancement in hypoxia tracer uptake, even in the early disease stages, and a 45-fold elevation in ROS expression in inflamed ankles compared with the ankles of healthy controls. We further found strong correlations of our noninvasive in vivo hypoxia PET data with pimonidazole and expression of HIF-1α in arthritic ankles. The strongest hypoxia tracer uptake was observed as soon as day 3, whereas the most pronounced ROS stress was evident on day 6 after the onset of experimental RA, indicating that tissue hypoxia can precede ROS stress in RA. Conclusion: Collectively, for the first time to our knowledge, we have demonstrated that the noninvasive measurement of hypoxia in inflammation using 18F-FAZA and 18F-FMISO PET imaging represents a promising new tool for uncovering and monitoring rheumatic inflammation in vivo. Further, because hypoxic inflamed tissues are associated with the overexpression of HIFs, specific inhibition of HIFs might represent a new powerful treatment strategy.

Automated PET Radiotracer Manufacture on the BG75 System and Imaging Validation Studies of [18F]fluoromisonidazole ([18F]FMISO).

The hypoxia PET tracer, 1-[18F]fluoro-3-(2-nitro-1Himidazol- 1-yl)-propan-2-ol ([18F]FMISO) is the first radiotracer developed for hypoxia PET imaging and has shown promising for cancer diagnosis and prognosis. However, access to [18F]FMISO radiotracer is limited due to the needed cyclotron and radiochemistry expertise. The study aimed to develop the automated production method on the [18F]FMISO radiotracer with the novel fully automated platform of the BG75 system and validate its usage on animal tumor models. [18F]FMISO was produced with the dose synthesis cartridge automatically on the BG75 system. Validation of [18F]FMISO hypoxia imaging functionality was conducted on two tumor mouse models (FaDu/U87 tumor). The distribution of [18F]FMISO within tumor was further validated by the standard hypoxia marker EF5. The average radiochemical purity was (99±1) % and the average pH was 5.5±0.2 with other quality attributes passing standard criteria (n=12). Overall biodistribution for [18F]FMISO in both tumor models was consistent with reported studies where bladder and large intestines presented highest activity at 90 min post injection. High spatial correlation was found between [18F]FMISO autoradiography and EF5 hypoxia staining, indicating high hypoxia specificity of [18MF]FMISO. This study shows that qualified [18F]FMISO can be efficiently produced on the BG75 system in an automated "dose-on-demand" mode using single dose disposable cards. The possibilities of having a low-cost, automated system manufacturing ([18F]Fluoride production + synthesis + QC) different radiotracers will greatly enhance the potential for PET technology to reach new geographical areas and underserved patient populations.

Efficient preparation of 2-nitroimidazole nucleosides as precursors for hypoxia PET tracers

2-Deoxy-D-ribose was converted to α/β-mixtures of methyl 3-O-acetyl- and methyl 3-O-benzoyl-2-deoxy-5-(p-toluenesulfonyl)-D-ribofuranosides. These were reacted with boron trichloride to generate ribofuranosyl chlorides, which afforded precursors for tracers to image tumor hypoxia on substitution with salts of 2-nitroimidazole. The anomeric ratio of the nucleosides was delicately influenced by the reaction conditions.Graphical abstract

Pharmacokinetic modeling of a novel hypoxia PET tracer [18F]HX4 in patients with non-small cell lung cancer.

Background[18F]HX4 is a promising new PET tracer developed to identify hypoxic areas in tumor tissue. This study analyzes [18F]HX4 kinetics and assesses the performance of simplified methods for quantification of [18F]HX4 uptake.To this end, eight patients with non-small cell lung cancer received dynamic PET scans at three different time points (0, 120, and 240 min) after injection of 426 ± 72 MBq [18F]HX4, each lasting 30 min. Several compartment models were fitted to time activity curves (TAC) derived from various areas within tumor tissue using image-derived input functions.ResultsBest fits were obtained using the reversible two-tissue compartment model with blood volume parameter (2T4k+VB). Simplified measures correlated well with VT estimates (tumor-to-blood ratio (TBr) R 2 = 0.96, tumor-to-muscle ratio R 2 = 0.94, standardized uptake value R 2 = 0.89).Conclusions[18F]HX4 shows reversible kinetics in tumor tissue: 2T4k+VB. TBr based on static imaging at 2 or 4 h can be used for quantification of [18F]HX4 uptake.Electronic supplementary materialThe online version of this article (doi:10.1186/s40658-016-0167-y) contains supplementary material, which is available to authorized users.