18F-fluoromisonidazole positron emission tomography before treatment is a predictor of radiotherapy outcome and survival prognosis in patients with head and neck squamous cell carcinoma

Ultrasound and Microbubbles Mediated Bleomycin Delivery in Feline Oral Squamous Cell Carcinoma—An In Vivo Veterinary Study

To investigate the feasibility and tolerability of ultrasound and microbubbles (USMB)-enhanced chemotherapy delivery for head and neck cancer, we performed a veterinary trial in feline companion animals with oral squamous cell carcinomas. Six cats were treated with a combination of bleomycin and USMB therapy three times, using the Pulse Wave Doppler mode on a clinical ultrasound system and EMA/FDA approved microbubbles. They were evaluated for adverse events, quality of life, tumour response and survival. Furthermore, tumour perfusion was monitored before and after USMB therapy using contrast-enhanced ultrasound (CEUS). USMB treatments were feasible and well tolerated. Among 5 cats treated with optimized US settings, 3 had stable disease at first, but showed disease progression 5 or 11 weeks after first treatment. One cat had progressive disease one week after the first treatment session, maintaining a stable disease thereafter. Eventually, all cats except one showed progressive disease, but each survived longer than the median overall survival time of 44 days reported in literature. CEUS performed immediately before and after USMB therapy suggested an increase in tumour perfusion based on an increase in median area under the curve (AUC) in 6 out of 12 evaluated treatment sessions. In this small hypothesis-generating study, USMB plus chemotherapy was feasible and well-tolerated in a feline companion animal model and showed potential for enhancing tumour perfusion in order to increase drug delivery. This could be a forward step toward clinical translation of USMB therapy to human patients with a clinical need for locally enhanced treatment.

A Phase II Randomized Trial of Chemoradiation with or without Metformin in Locally Advanced Cervical Cancer

PURPOSE

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.

PATIENTS AND METHODS

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.

RESULTS

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).

CONCLUSIONS

Metformin decreased cervical tumor hypoxia in this trial that selected for patients with hypoxic tumor. See related commentary by Lyng et al., p. 5233.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Limitations of Fluorine 18 Fluoromisonidazole in Assessing Treatment-induced Tissue Hypoxia after Transcatheter Arterial Embolization of Hepatocellular Carcinoma: A Prospective Pilot Study

Purpose To determine the variance and correlation with tumor viability of fluorine 18 (¹⁸F) fluoromisonidazole (FMISO) uptake in hepatocellular carcinoma (HCC) prior to and after embolization treatment. Materials and Methods In this single-arm, single-center, prospective pilot study between September 2016 and March 2017, participants with at least one tumor measuring 1.5 cm or larger with imaging or histologic findings diagnostic for HCC were enrolled (five men; mean age, 68 years; age range, 61-76 years). Participants underwent ¹⁸F-FMISO PET/CT before and after bland embolization of HCC. A tumor-to-liver ratio (TLR) was calculated by using standardized uptake values of tumor and liver. The difference in mean TLR before and after treatment was compared by using a Wilcoxon rank sum test, and correlation between TLR and tumor viability was assessed by using the Spearman rank correlation coefficient. Results Four participants with five tumors were included in the final analysis. The median tumor diameter was 3.2 cm (IQR, 3.0-3.9 cm). The median TLR before treatment was 0.97 (IQR, 0.88-0.98), with a variance of 0.02, and the median TLR after treatment was 0.85 (IQR, 0.79-1), with a variance of 0.01; both findings indicate a narrow range of ¹⁸F-FMISO uptake in HCC. The Spearman rank correlation coefficient was 0.87, indicating a high correlation between change in TLR and nonviable tumor. Conclusion Although there was a correlation between change in TLR and response to treatment, the low signal-to-noise ratio of ¹⁸F-FMISO in the liver limited its use in HCC. Keywords: Molecular Imaging-Clinical Translation, Embolization, Abdomen/Gastrointestinal, Liver Clinical trial registration no. NCT02695628 © RSNA, 2022.

Imaging of Tumor Hypoxia With Radionuclide-Labeled Tracers for PET

The hypoxic state in a solid tumor refers to the internal hypoxic environment that appears as the tumor volume increases (the maximum radius exceeds 180-200 microns). This state can promote angiogenesis, destroy the balance of the cell’s internal environment, and lead to resistance to radiotherapy and chemotherapy, as well as poor prognostic factors such as metastasis and recurrence. Therefore, accurate quantification, mapping, and monitoring of hypoxia, targeted therapy, and improvement of tumor hypoxia are of great significance for tumor treatment and improving patient survival. Despite many years of development, PET-based hypoxia imaging is still the most widely used evaluation method. This article provides a comprehensive overview of tumor hypoxia imaging using radionuclide-labeled PET tracers. We introduced the mechanism of tumor hypoxia and the reasons leading to the poor prognosis, and more comprehensively included the past, recent and ongoing studies of PET radiotracers for tumor hypoxia imaging. At the same time, the advantages and disadvantages of mainstream methods for detecting tumor hypoxia are summarized.

PET Imaging for Head and Neck Cancers

Head and neck cancers are commonly encountered cancers in clinical practice in the United States. Fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) PET/CT has been clinically applied in staging, occult primary tumor detection, treatment planning, response assessment, follow-up, recurrent disease detection, and prognosis prediction in these patients. Alternative PET tracers remain investigational and can provide additional valuable information such as radioresistant tumor hypoxia. The recent introduction of ¹⁸F-FDG PET/MR imaging has provided the advantage of combining the superior soft tissue resolution of MR imaging with the functional information provided by ¹⁸F-FDG PET. This article is a concise review of recent advances in PET imaging in head and neck cancer.

Application of Community Detection Algorithm to Investigate the Correlation between Imaging Biomarkers of Tumor Metabolism, Hypoxia, Cellularity, and Perfusion for Precision Radiotherapy in Head and Neck Squamous Cell Carcinomas

The present study aimed to investigate the correlation at pre-treatment (TX) between quantitative metrics derived from multimodality imaging (MMI), including 18F-FDG-PET/CT, 18F-FMISO-PET/CT, DW- and DCE-MRI, using a community detection algorithm (CDA) in head and neck squamous cell carcinoma (HNSCC) patients. Twenty-three HNSCC patients with 27 metastatic lymph nodes underwent a total of 69 MMI exams at pre-TX. Correlations among quantitative metrics derived from FDG-PET/CT (SUL), FMSIO-PET/CT (K1, k3, TBR, and DV), DW-MRI (ADC, IVIM [D, D*, and f]), and FXR DCE-MRI [Ktrans, ve, and τi]) were investigated using the CDA based on a "spin-glass model" coupled with the Spearman's rank, ρ, analysis. Mean MRI T2 weighted tumor volumes and SULmean values were moderately positively correlated (ρ = 0.48, p = 0.01). ADC and D exhibited a moderate negative correlation with SULmean (ρ ≤ -0.42, p < 0.03 for both). K1 and Ktrans were positively correlated (ρ = 0.48, p = 0.01). In contrast, Ktrans and k3max were negatively correlated (ρ = -0.41, p = 0.03). CDA revealed four communities for 16 metrics interconnected with 33 edges in the network. DV, Ktrans, and K1 had 8, 7, and 6 edges in the network, respectively. After validation in a larger population, the CDA approach may aid in identifying useful biomarkers for developing individual patient care in HNSCC.

18F-FMISO-PET Hypoxia Monitoring for Head-and-Neck Cancer Patients: Radiomics Analyses Predict the Outcome of Chemo-Radiotherapy

Tumor hypoxia is associated with radiation resistance and can be longitudinally monitored by 18F-fluoromisonidazole (18F-FMISO)-PET/CT. Our study aimed at evaluating radiomics dynamics of 18F-FMISO-hypoxia imaging during chemo-radiotherapy (CRT) as predictors for treatment outcome in head-and-neck squamous cell carcinoma (HNSCC) patients. We prospectively recruited 35 HNSCC patients undergoing definitive CRT and longitudinal 18F-FMISO-PET/CT scans at weeks 0, 2 and 5 (W0/W2/W5). Patients were classified based on peritherapeutic variations of the hypoxic sub-volume (HSV) size (increasing/stable/decreasing) and location (geographically-static/geographically-dynamic) by a new objective classification parameter (CP) accounting for spatial overlap. Additionally, 130 radiomic features (RF) were extracted from HSV at W0, and their variations during CRT were quantified by relative deviations (∆RF). Prediction of treatment outcome was considered statistically relevant after being corrected for multiple testing and confirmed for the two 18F-FMISO-PET/CT time-points and for a validation cohort. HSV decreased in 64% of patients at W2 and in 80% at W5. CP distinguished earlier disease progression (geographically-dynamic) from later disease progression (geographically-static) in both time-points and cohorts. The texture feature low grey-level zone emphasis predicted local recurrence with AUCW2 = 0.82 and AUCW5 = 0.81 in initial cohort (N = 25) and AUCW2 = 0.79 and AUCW5 = 0.80 in validation cohort. Radiomics analysis of 18F-FMISO-derived hypoxia dynamics was able to predict outcome of HNSCC patients after CRT.

Intrinsic radiomic expression patterns after 20 Gy demonstrate early metabolic response of oropharyngeal cancers

PURPOSE

This study investigated the prognostic potential of intra-treatment PET radiomics data in patients undergoing definitive (chemo) radiation therapy for oropharyngeal cancer (OPC) on a prospective clinical trial. We hypothesized that the radiomic expression of OPC tumors after 20 Gy is associated with recurrence-free survival (RFS).

MATERIALS AND METHODS

Sixty-four patients undergoing definitive (chemo)radiation for OPC were prospectively enrolled on an IRB-approved study. Investigational ¹⁸ F-FDG-PET/CT images were acquired prior to treatment and 2 weeks (20 Gy) into a seven-week course of therapy. Fifty-five quantitative radiomic features were extracted from the primary tumor as potential biomarkers of early metabolic response. An unsupervised data clustering algorithm was used to partition patients into clusters based only on their radiomic expression. Clustering results were naïvely compared to residual disease and/or subsequent recurrence and used to derive Kaplan-Meier estimators of RFS. To test whether radiomic expression provides prognostic value beyond conventional clinical features associated with head and neck cancer, multivariable Cox proportional hazards modeling was used to adjust radiomic clusters for T and N stage, HPV status, and change in tumor volume.

RESULTS

While pre-treatment radiomics were not prognostic, intra-treatment radiomic expression was intrinsically associated with both residual/recurrent disease (P = 0.0256, χ 2 test) and RFS (HR = 7.53, 95% CI = 2.54-22.3; P = 0.0201). On univariate Cox analysis, radiomic cluster was associated with RFS (unadjusted HR = 2.70; 95% CI = 1.26-5.76; P = 0.0104) and maintained significance after adjustment for T, N staging, HPV status, and change in tumor volume after 20 Gy (adjusted HR = 2.69; 95% CI = 1.03-7.04; P = 0.0442). The particular radiomic characteristics associated with outcomes suggest that metabolic spatial heterogeneity after 20 Gy portends complete and durable therapeutic response. This finding is independent of baseline metabolic imaging characteristics and clinical features of head and neck cancer, thus providing prognostic advantages over existing approaches.

CONCLUSIONS

Our data illustrate the prognostic value of intra-treatment metabolic image interrogation, which may potentially guide adaptive therapy strategies for OPC patients and serve as a blueprint for other disease sites. The quality of our study was strengthened by its prospective image acquisition protocol, homogenous patient cohort, relatively long patient follow-up times, and unsupervised clustering formalism that is less prone to hyper-parameter tuning and over-fitting compared to supervised learning.

Evolution of the hypoxic compartment on sequential oxygen partial pressure maps during radiochemotherapy in advanced head and neck cancer

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Repeated PET imaging of hypoxia may be pivotal in radiotherapy outcome prediction.

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Oxygen partial pressure maps can be non-linearly derived from radiotracer uptake.

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The hypoxic target volume evolution in extension and severity can be determined.

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The first two treatment week parameters have potential for outcome prediction.

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Information may be used for treatment adaptation personalised strategies.

Background and purpose

Longitudinal Positron Emission Tomography (PET) with hypoxia-specific radiotracers allows monitoring the time evolution of regions of increased radioresistance and may become fundamental in determining the radiochemotherapy outcome in Head-and-Neck Squamous Cell Carcinoma (HNSCC). The aim of this study was to investigate the evolution of the hypoxic target volume on oxygen partial pressure maps (pO₂-HTV) derived from ¹⁸FMISO-PET images acquired before and during radiochemotherapy and to uncover correlations between extent and severity of hypoxia and treatment outcome.

Material and methods

¹⁸FMISO-PET/CT images were acquired at three time points (before treatment start, in weeks two and five) for twenty-eight HNSCC patients treated with radiochemotherapy. The images were converted into pO₂ maps and corresponding pO₂-HTVs (pO₂-HTV₁, pO₂-HTV₂, pO₂-HTV₃) were contoured at 10 mmHg. Different parameters describing the pO₂-HTV time evolution were considered, such as the percent and absolute difference between the pO₂-HTVs (%HTV_i,j and HTV_i-HTV_j with i,j = 1, 2, 3, respectively) and the slope of the linear regression curve fitting the pO₂-HTVs in time. Correlations were sought between the pO₂-HTV evolution parameters and loco-regional recurrence (LRR) using the Receiver Operating Characteristic method.

Results

The Area Under the Curve values for %HTV_1,2, HTV₁-HTV₂, HTV₁-HTV₃ and the slope of the pO₂-HTV linear regression curve were 0.75 (p = 0.04), 0.73 (p = 0.02), 0.73 (p = 0.02) and 0.75 (p = 0.007), respectively. Other parameter combinations were not statistically significant.

Conclusions

The pO₂-HTV evolution during radiochemotherapy showed predictive value for LRR. The changes in the tumour hypoxia during the first two treatment weeks may be used for adaptive personalized treatment approaches.

In vivo evaluation of percutaneous carbon dioxide treatment for improving intratumoral hypoxia using 18F-fluoromisonidazole PET-CT

Carbon dioxide (CO₂) treatment is reported to have an antitumor effect owing to the improvement in intratumoral hypoxia. Previous studies were based on histological analysis alone. In the present study, the improvement in intratumoral hypoxia by percutaneous CO₂ treatment in vivo was determined using ¹⁸F-fluoromisonidazole positron emission tomography-computed tomography (¹⁸F-FMISO PET-CT) images. Twelve Japanese nude mice underwent implantation of LM8 tumor cells in the dorsal subcutaneous area 2 weeks before percutaneous CO₂ treatment and ¹⁸F-FMISO PET-CT scans. Immediately after intravenous injection of ¹⁸F-FMISO, CO₂ and room air were administered transcutaneously in the CO₂-treated group (n=6) and a control group (n=6), respectively; each treatment was performed for 10 minutes. PET-CT was performed 2 h after administration of ¹⁸F-FMISO. ¹⁸F-FMISO tumor uptake was quantitatively evaluated using the maximum standardized uptake value (SUV_max), tumor-to-liver ratio (TLR), tumor-to-muscle ratio (TMR), metabolic tumor volume (MTV) and total lesion glycolysis (TLG). Mean ± standard error of the mean (SEM) of the tumor volume was not significantly different between the two groups (CO₂-treated group, 1.178±0.450 cm³; control group, 1.368±0.295 cm3; P=0.485). Mean ± SEM of SUV_max, TLR, MTV (cm3) and TLG were significantly lower in the CO₂-treated group compared with the control group (0.880±0.095 vs. 1.253±0.071, P=0.015; 1.063±0.147361 vs. 1.455±0.078, P=0.041; 0.353±0.139 vs. 1.569±0.438, P=0.015; 0.182±0.070 vs. 1.028±0.338, P=0.015), respectively. TMR was not significantly different between the two groups (4.520±0.503 vs. 5.504±0.310; P=0.240). In conclusion, ¹⁸F-FMISO PET revealed that percutaneous CO₂ treatment improved intratumoral hypoxia in vivo. This technique enables assessment of the therapeutic effect in CO₂ treatment by imaging, and may contribute to its clinical application.

Role of Non-FDG-PET/CT in Head and Neck Cancer

Head and neck cancers are commonly encountered malignancies in the United States, of which the majority are attributed to squamous cell carcinoma. ¹⁸F-FDG-PET/CT has been well established in the evaluation, treatment planning, prognostic implications of these tumors and is routinely applied for the management of patients with these cancers. Many alternative investigational PET radiotracers have been extensively studied in the evaluation of these tumors. Although these radiotracers have not been able to replace ¹⁸F-FDG-PET/CT in routine clinical practice currently, they may provide important additional information about the biological mechanisms of these tumors, such as foci of tumor hypoxia as seen on hypoxia specific PET radiotracers such as ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO), which could be useful in targeting radioresistant hypoxic tumor foci when treatment planning. There are multiple other hypoxia-specific PET radiotracers such as ¹⁸F-Fluoroazomycinarabinoside (FAZA), ¹⁸F-Flortanidazole (HX4), which have been evaluated similarly, of which ¹⁸F-Fluoromisonidazole (¹⁸F-FMISO) has been the most investigated. Other radiotracers frequently studied in the evaluation of these tumors include radiolabeled amino acid PET radiotracers, which show increased uptake in tumor cells with limited uptake in inflammatory tissue, which can be useful especially in differentiating postradiation inflammation from residual and/or recurrent disease. ¹⁸F-Fluorothymidine (FLT) is localized intracellularly by nucleoside transport and undergoes phosphorylation thereby being retained within tumor cells and can serve as an indicator of tumor proliferation. Decrease in radiotracer activity following treatment can be an early indicator of treatment response. This review aims at synthesizing the available literature on the most studied non-FDG-PET/CT in head and neck cancer.

YC-1 sensitizes the antitumor effects of boron neutron capture therapy in hypoxic tumor cells

The uptake of boron into tumor cells is a key factor in the biological effects of boron neutron capture therapy (BNCT). The uptake of boron agents is suppressed in hypoxic conditions, but the mechanism of hypoxia-induced modulation of suppression of boron uptake is not clear. Therefore, we evaluated whether hypoxia-inducible factor 1α (HIF-1α) contributes to attenuation of the antitumor effects of BNCT in hypoxic tumor cells. We also tested whether YC-1, a HIF-1α-targeting inhibitor, has therapeutic potential with BNCT. To elucidate the mechanism of attenuation of the effects of BNCT caused by hypoxia, deferoxamine (DFO) was used in experiments. Cells were incubated in normal oxygen, hypoxic conditions (1% O2) or 5 μM DFO for 24 h. Then, cells were treated with 10B-boronophenylalanine (BPA) for 2 h and boron accumulation in cells was evaluated. To clarify the relationship between HIF-1α and L-type amino acid transporter 1 (LAT1), gene expression was evaluated by a using HIF-1α gene knockdown technique. Finally, to improve attenuation of the effects of BNCT in hypoxic cells, BNCT was combined with YC-1. Boron uptake was continuously suppressed up to 2 h after administration of BPA by 5 μM DFO treatment. In cells treated with 5 μM DFO, LAT1 expression was restored in HIF-1α-knocked down samples in all cell lines, revealing that HIF-1α suppresses LAT1 expression in hypoxic cells. From the results of the surviving fraction after BNCT combined with YC-1, treatment with YC-1 sensitized the antitumor effects of BNCT in cells cultured in hypoxia.

Assessment of tumour hypoxia, proliferation and glucose metabolism in head and neck cancer before and during treatment

OBJECTIVE

The aim of the study was to assess the feasibility of multitracer positron emission tomography (PET) imaging before and during chemoradiation and to evaluate the predictive value of image-based factors for outcome in locally advanced head and neck cancers treated with chemoradiation.

METHODS

In the week prior to the treatment [¹⁸F]-2-flu-2-deoxy-D-glucose (FDG), [¹⁸F]-3'-flu-3'deoxythymidine (FLT) and [¹⁸F]-flumisonidazole (FMISO) imaging was performed. FLT scans were repeated at 14 and 28 Gy and FMISO at 36 Gy. Overall survival, disease-free survival and local control were correlated with subvolume parameters, and with tumour-to-muscle ratio for FMISO. For every tracer, total metabolic tumour volume was calculated.

RESULTS

33 patients were included. No correlation was found between pre-treatment maximum standardised uptake value for FDG, FLT, FMISO and outcomes. Tumour volume measured on initial CT scans and initial FLT volume correlated with disease-free survivall (p = 0.007 and 0.04 respectively). FDG and FLT metabolic tumour volumes correlated significantly with local control (p = 0.005 and 0.02 respectively). In multivariate Cox analysis only individual initial TMRmax correlated with overall survival.

CONCLUSION

PET/CT imaging is a promising tool. However, various aspects of image analysis need further clinical validation in larger multicentre study employing uniform imaging protocol and standardisation, especially for hypoxia tracer.

ADVANCES IN KNOWLEDGE

Monitoring of biological features of the tumour using multitracer PET modality seems to be a feasible option in daily clinical practice.Evaluation of hypoxic subvolumes is more patient dependent; thus, exploration of individual parameters of hypoxia is needed. tumour-to-muscle ratio seems to be the most promising so far.

Integrating molecular nuclear imaging in clinical research to improve anticancer therapy

Effective patient selection before or early during treatment is important to increasing the therapeutic benefits of anticancer treatments. This selection process is often predicated on biomarkers, predominantly biospecimen biomarkers derived from blood or tumour tissue; however, such biomarkers provide limited information about the true extent of disease or about the characteristics of different, potentially heterogeneous tumours present in an individual patient. Molecular imaging can also produce quantitative outputs; such imaging biomarkers can help to fill these knowledge gaps by providing complementary information on tumour characteristics, including heterogeneity and the microenvironment, as well as on pharmacokinetic parameters, drug-target engagement and responses to treatment. This integrative approach could therefore streamline biomarker and drug development, although a range of issues need to be overcome in order to enable a broader use of molecular imaging in clinical trials. In this Perspective article, we outline the multistage process of developing novel molecular imaging biomarkers. We discuss the challenges that have restricted the use of molecular imaging in clinical oncology research to date and outline future opportunities in this area.

[18F]FMISO PET/CT as a preoperative prognostic factor in patients with pancreatic cancer

Background

While [¹⁸F]fluoromisonidazole (FMISO), a representative PET tracer to detect hypoxia, is reported to be able to prospect the prognosis after treatment for various types of cancers, the relation is unclear for pancreatic cancer. The aim of this study is to assess the feasibility of [¹⁸F]FMISO PET/CT as a preoperative prognostic factor in patients with pancreatic cancer.

Methods

Patients with pancreatic cancer who had been initially planned for surgery received [¹⁸F]FMISO PET/CT. Peak standardized uptake value (SUV) of the pancreatic tumor was divided by SUVpeak of the aorta, and tumor blood ratio using SUVpeak (TBRpeak) was calculated. After preoperative examination, surgeons finally decided the operability of the patients. TBRpeak was compared with hypoxia-inducible factor (HIF)-1α immunohistochemistry when the tissues were available. Furthermore, correlation of TBRpeak with the recurrence-free survival and the overall survival were evaluated by Kaplan-Meyer methods.

Results

We analyzed 25 patients with pancreatic adenocarcinoma (11 women and 14 men, median age, 73 years; range, 58–81 years), and observed for 39–1101 days (median, 369 days). Nine cases (36.0%) were identified as visually positive of pancreatic cancer on [¹⁸F]FMISO PET/CT images. TBRpeak of the negative cases was significantly lower than that of the positive cases (median 1.08, interquartile range (IQR) 1.02–1.15 vs median 1.50, IQR 1.25–1.73, p < 0.001), and the cutoff TBRpeak was calculated as 1.24. Five patients were finally considered inoperable. There was no significant difference in TBRpeak of inoperable and operable patients (median 1.48, IQR 1.06–1.98 vs median 1.12, IQR 1.05–1.21, p = 0.10). There was no significant difference between TBRpeak and HIF-1α expression (p = 0.22). The patients were dichotomized by the TBRpeak cutoff, and the higher group showed significantly shorter recurrence-free survival than the other (median 218 vs 441 days, p = 0.002). As for overall survival of 20 cases of operated patients, the higher TBRpeak group showed significantly shorter overall survival than the other (median survival, 415 vs > 1000 days, p = 0.04).

Conclusions

[¹⁸F]FMISO PET/CT has the possibility to be a preoperative prognostic factor in patients with pancreatic cancer.

Electronic supplementary material

The online version of this article (10.1186/s13550-019-0507-8) contains supplementary material, which is available to authorized users.

Repeat FMISO-PET imaging weakly correlates with hypoxia-associated gene expressions for locally advanced HNSCC treated by primary radiochemotherapy

BACKGROUND

Hypoxia is an important factor of tumour resistance to radiotherapy, chemotherapy and potentially immunotherapy. It can be measured e.g. by positron emission tomography (PET) imaging or hypoxia-associated gene expressions from tumour biopsies. Here we correlate [¹⁸F]fluoromisonidazole (FMISO)-PET/CT imaging with hypoxia-associated gene expressions on a cohort of 50 head and neck squamous cell carcinoma (HNSCC) patients and compare their prognostic value for response to radiochemotherapy (RCTx).

METHODS

FMISO-PET/CT images of 50 HNSCC patients were acquired at four time-points before and during RCTx. For 42 of these patients, hypoxia-associated gene expressions were evaluated by nanoString technology based on a biopsy obtained before any treatment. The FMISO-PET parameters tumour-to-background ratio and hypoxic volume were correlated to the expressions of 58 hypoxia-associated genes using the Spearman correlation coefficient ρ. Three hypoxia-associated gene signatures were compared regarding their correlation with the FMISO-PET parameters using their median expression. In addition, the correlation with tumour volume was analysed. The impact of both hypoxia measurement methods on loco-regional tumour control (LRC) and overall survival (OS) was assessed by Cox regression.

RESULTS

The median expression of hypoxia-associated genes was weakly correlated to hypoxia measured by FMISO-PET imaging (ρ ≤ 0.43), with higher correlations to imaging after weeks 1 and 2 of treatment (p < 0.001). Moderate correlations were obtained between FMISO-PET imaging and tumour volume (ρ ≤ 0.69). Prognostic models for LRC and OS based on the FMISO-PET parameters could not be improved by including hypoxia classifiers.

CONCLUSION

We observed low correlations between hypoxia FMISO-PET parameters and expressions of hypoxia-associated genes. Since FMISO-PET showed a superior patient stratification, it may be the preferred biomarker over hypoxia-associated genes for stratifying patients with locally advanced HNSCC treated by primary RCTx.

Correlation between FMISO-PET based hypoxia in the primary tumour and in lymph node metastases in locally advanced HNSCC patients

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We investigated correlation between hypoxia in the primary tumour and LN before and during RCTx.

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The Correlation between primary tumour and LN hypoxia is stronger in patients with large LN compared to the entire cohort.

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We advise to perform a comprehensive evaluation of hypoxia in the primary tumour and LN.

Purpose

This secondary analysis of the prospective study on repeat [¹⁸F]fluoromisonidazole (FMISO)-PET in patients with locally advanced head and neck squamous cell carcinoma (HNSCC) assessed the correlation of hypoxia in the primary tumour and lymph node metastases (LN) prior to and during primary radiochemotherapy.

Methods

This analysis included forty-five LN-positive HNSCC patients having undergone FMISO-PET/CTs at baseline, and at week 1, 2 and 5 of radiochemotherapy. The quantitative FMISO-PET/CT parameters maximum standardised uptake value (SUV_max, corrected for partial volume effect) and peak tumour-to-background ratio (TBR_peak) were estimated in the primary tumour as well as in index and large LN, respectively. Statistical analysis was performed using the Spearman correlation coefficient ρ.

Results

In 15 patients with large LN (FDG-PET positive volume >5 ml), there was a significant correlation between the hypoxia measured in the primary tumour and the large LN at three out of four time-points using the TBR_peak (baseline: ρ = 0.57, p = 0.006; week 2: ρ = 0.64, p = 0.003 and week 5: ρ = 0.68, p = 0.001). For the entire cohort (N = 45) only assessed prior to the treatment, there was a statistically significant, though weak correlation between FMISO-SUV_max of the primary tumour and the index LN (ρ = 0.36, p = 0.015).

Conclusions

We observed a significant correlation between FMISO-based hypoxia in the primary tumour and large lymph node(s) in advanced stage HNSCC patients. However, since most patients only had relatively small hypoxic lymph node metastases, a comprehensive assessment of the primary tumour and lymph node hypoxia is essential.

FMISO-PET-based lymph node hypoxia adds to the prognostic value of tumor only hypoxia in HNSCC patients

PURPOSE

This secondary analysis of the prospective study on repeat [¹⁸F]fluoromisonidazole (FMISO)-PET in patients with locally advanced head and neck squamous cell carcinomas (HNSCC) assessed the prognostic value of synchronous hypoxia in primary tumor (Tu) and lymph node metastases (LN), and evaluated whether the combined reading was of higher prognostic value than that of primary tumor hypoxia only.

METHODS

This analysis included forty-five LN-positive HNSCC patients. FMISO-PET/CTs were performed at baseline, weeks 1, 2 and 5 of radiochemotherapy. Based on a binary scale, Tu and LN were categorized as hypoxic or normoxic, and two prognostic parameters were defined: Tu-hypoxia (independent of the LN oxygenation status) and synchronous Tu-and-LN-hypoxia. In fifteen patients with large LN (N = 21), additional quantitative analyses of FMISO-PET/CTs were performed. Imaging parameters at different time-points were correlated to the endpoints, i.e., locoregional control (LRC), local control (LC), regional control (RC) and time to progression (TTP). Survival curves were estimated using the cumulative incidence function. Univariable and multivariable Cox regression was used to evaluate the prognostic impact of hypoxia on the endpoints.

RESULTS

Synchronous Tu-and-LN-hypoxia was a strong adverse prognostic factor for LC, LRC and TTP at any of the four time-points (p ≤ 0.004), whereas Tu-hypoxia only was significantly associated with poor LC and LRC in weeks 2 and 5 (p ≤ 0.047), and with TTP in week 1 (p = 0.046). The multivariable analysis confirmed the prognostic value of synchronous Tu-and-LN-hypoxia regarding LRC (HR = 14.8, p = 0.017). The quantitative FMISO-PET/CT parameters correlated with qualitative hypoxia scale and RC (p < 0.001, p ≤ 0.033 at week 2, respectively).

CONCLUSIONS

This secondary analysis suggests that combined reading of primary tumor and LN hypoxia adds to the prognostic information of FMSIO-PET in comparison to primary tumor assessment alone in particular prior and early during radiochemotherapy. Confirmation in ongoing trials is needed before using this marker for personalized radiation oncology.

Clinical imaging of hypoxia: Current status and future directions

Tissue hypoxia is a key feature of many important causes of morbidity and mortality. In pathologies such as stroke, peripheral vascular disease and ischaemic heart disease, hypoxia is largely a consequence of low blood flow induced ischaemia, hence perfusion imaging is often used as a surrogate for hypoxia to guide clinical diagnosis and treatment. Importantly, ischaemia and hypoxia are not synonymous conditions as it is not universally true that well perfused tissues are normoxic or that poorly perfused tissues are hypoxic. In pathologies such as cancer, for instance, perfusion imaging and oxygen concentration are less well correlated, and oxygen concentration is independently correlated to radiotherapy response and overall treatment outcomes. In addition, the progression of many diseases is intricately related to maladaptive responses to the hypoxia itself. Thus there is potentially great clinical and scientific utility in direct measurements of tissue oxygenation. Despite this, imaging assessment of hypoxia in patients is rarely performed in clinical settings. This review summarises some of the current methods used to clinically evaluate hypoxia, the barriers to the routine use of these methods and the newer agents and techniques being explored for the assessment of hypoxia in pathological processes.

Intracellular hypoxia measured by 18F-fluoromisonidazole positron emission tomography has prognostic impact in patients with estrogen receptor-positive breast cancer

Background

Hypoxia is a key driver of cancer progression. We evaluated the prognostic impact of ¹⁸F-fluoromisonidazole (FMISO) prior to treatment in patients with breast cancer.

Methods

Forty-four patients with stage II/III primary breast cancer underwent positron emission tomography/computed with ¹⁸F-fluorodeoxyglucose (FDG-PET/CT) and FMISO. After measurement by FDG-PET/CT, the tissue-to-blood ratio (TBR) was obtained using FMISO-PET/CT. FMISO-TBR was compared for correlation with clinicopathological factors, disease-free survival (DFS), and overall survival (OS). Multiplex cytokines were analyzed for the correlation of FMISO-TBR.

Results

Tumors with higher nuclear grade and negativities of estrogen receptor (ER) and progesterone receptor had significantly higher FMISO-TBR than other tumors. Kaplan-Meier survival curves showed that patients with a higher FMISO-TBR (cutoff, 1.48) had a poorer prognosis of DFS (p = 0.0007) and OS (p = 0.04) than those with a lower FMISO-TBR. Multivariate analysis indicated that higher FMISO-TBR and ER negativity were independent predictors of shorter DFS (p = 0.01 and 0.03). Higher FMISO-TBR was associated with higher plasma levels of angiogenic hypoxic markers such as vascular endothelial growth factor, transforming growth factor-α, and interleukin 8.

Conclusions

FMISO-PET/CT is useful for assessing the prognosis of patients with breast cancer, but it should be stratified by ER status.

Trial registration

UMIN Clinical Trials Registry, UMIN000006802. Registered on 1 December 2011.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-0970-6) contains supplementary material, which is available to authorized users.

Quantification of Tumor Hypoxic Fractions Using Positron Emission Tomography with [18F]Fluoromisonidazole ([18F]FMISO) Kinetic Analysis and Invasive Oxygen Measurements

PURPOSE

The purpose of this study is to use dynamic [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO) positron emission tomography (PET) to compare estimates of tumor hypoxic fractions (HFs) derived by tracer kinetic modeling, tissue-to-blood ratios (TBR), and independent oxygen (pO₂) measurements.

PROCEDURES

BALB/c mice with EMT6 subcutaneous tumors were selected for PET imaging and invasive pO₂ measurements. Data from 120-min dynamic [¹⁸F]FMISO scans were fit to two-compartment irreversible three rate constant (K ₁, k ₂, k ₃) and Patlak models (K _i). Tumor HFs were calculated and compared using K _i, k ₃, TBR, and pO₂ values. The clinical impact of each method was evaluated on [¹⁸F]FMISO scans for three non-small cell lung cancer (NSCLC) radiotherapy patients.

RESULTS

HFs defined by TBR (≥1.2, ≥1.3, and ≥1.4) ranged from 2 to 85 % of absolute tumor volume. HFs defined by K _i (>0.004 ml min cm^-3) and k ₃ (>0.008 min^-1) varied from 9 to 85 %. HF quantification was highly dependent on metric (TBR, k ₃, or K _i) and threshold. HFs quantified on human [¹⁸F]FMISO scans varied from 38 to 67, 0 to 14, and 0.1 to 27 %, for each patient, respectively, using TBR, k ₃, and K _i metrics.

CONCLUSIONS

[¹⁸F]FMISO PET imaging metric choice and threshold impacts hypoxia quantification reliability. Our results suggest that tracer kinetic modeling has the potential to improve hypoxia quantification clinically as it may provide a stronger correlation with direct pO₂ measurements.

Molecular mechanisms of hypoxia in cancer

PURPOSE

Hypoxia is a condition of insufficient oxygen to support metabolism which occurs when the vascular supply is interrupted, or when a tumour outgrows its vascular supply. It is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. This review provides an overview of hypoxia imaging with Positron emission tomography (PET), with an emphasis on the biological relevance, mechanism of action, highlighting advantages, and limitations of the currently available hypoxia radiotracers.

METHODS

A comprehensive PubMed literature search was performed, identifying articles relating to biological significance and measurement of hypoxia, MRI methods, and PET imaging of hypoxia in preclinical and clinical settings, up to December 2016.

RESULTS

A variety of approaches have been explored over the years for detecting and monitoring changes in tumour hypoxia, including regional measurements with oxygen electrodes placed under CT guidance, MRI methods that measure either oxygenation or lactate production consequent to hypoxia, different nuclear medicine approaches that utilise imaging agents the accumulation of which is inversely related to oxygen tension, and optical methods. The advantages and disadvantages of these approaches are reviewed, along with individual strategies for validating different imaging methods. PET is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels.

CONCLUSION

Even though hypoxia could have significant prognostic and predictive value in the clinic, the best method for hypoxia assessment has in our opinion not been realised.

The role of necrosis, acute hypoxia and chronic hypoxia in 18F-FMISO PET image contrast: a computational modelling study

Positron emission tomography (PET) using 18F-fluoromisonidazole (FMISO) is a promising technique for imaging tumour hypoxia, and a potential target for radiotherapy dose-painting. However, the relationship between FMISO uptake and oxygen partial pressure ([Formula: see text]) is yet to be quantified fully. Tissue oxygenation varies over distances much smaller than clinical PET resolution (<100 μm versus  ∼4 mm), and cyclic variations in tumour perfusion have been observed on timescales shorter than typical FMISO PET studies (∼20 min versus a few hours). Furthermore, tracer uptake may be decreased in voxels containing some degree of necrosis. This work develops a computational model of FMISO uptake in millimetre-scale tumour regions. Coupled partial differential equations govern the evolution of oxygen and FMISO distributions, and a dynamic vascular source map represents temporal variations in perfusion. Local FMISO binding capacity is modulated by the necrotic fraction. Outputs include spatiotemporal maps of [Formula: see text] and tracer accumulation, enabling calculation of tissue-to-blood ratios (TBRs) and time-activity curves (TACs) as a function of mean tissue oxygenation. The model is characterised using experimental data, finding half-maximal FMISO binding at local [Formula: see text] of 1.4 mmHg (95% CI: 0.3-2.6 mmHg) and half-maximal necrosis at 1.2 mmHg (0.1-4.9 mmHg). Simulations predict a non-linear non-monotonic relationship between FMISO activity (4 hr post-injection) and mean tissue [Formula: see text] : tracer uptake rises sharply from negligible levels in avascular tissue, peaking at  ∼5 mmHg and declining towards blood activity in well-oxygenated conditions. Greater temporal variation in perfusion increases peak TBRs (range 2.20-5.27) as a result of smaller predicted necrotic fraction, rather than fundamental differences in FMISO accumulation under acute hypoxia. Identical late FMISO uptake can occur in regions with differing [Formula: see text] and necrotic fraction, but simulated TACs indicate that additional early-phase information may allow discrimination of hypoxic and necrotic signals. We conclude that a robust approach to FMISO interpretation (and dose-painting prescription) is likely to be based on dynamic PET analysis.

Dynamic contrast-enhanced MR imaging in predicting progression of enhancing lesions persisting after standard treatment in glioblastoma patients: a prospective study

OBJECTIVES

To prospectively explore the value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in predicting the progression of enhancing lesions persisting after standard treatment in patients with surgically resected glioblastoma (GBM).

METHODS

Forty-seven GBM patients, who underwent near-total tumorectomy followed by concurrent chemoradiation therapy (CCRT) with temozolomide (TMZ) between May 2014 and February 2016, were enrolled. Twenty-four patients were finally analyzed for measurable enhancing lesions persisting after standard treatment. DCE-MRI parameters were calculated at enhancing lesions. Mann-Whitney U tests and multivariable stepwise logistic regression were used to compare parameters between progression (n = 16) and non-progression (n = 8) groups.

RESULTS

Mean K^trans and v_e were significantly lower in progression than in non-progression (P = 0.037 and P = 0.037, respectively). The 5th percentile of the cumulative K^trans histogram was also significantly lower in the progression than in non-progression group (P = 0.017). Mean v_e was the only independent predictor of progression (P = 0.007), with a sensitivity of 100%, specificity of 63%, and an overall accuracy of 88% at a cut-off value of 0.873.

CONCLUSIONS

DCE-MRI may help predict the progression of enhancing lesions persisting after the completion of standard treatment in patients with surgically resected GBM, with mean v_e serving as an independent predictor of progression.

KEY POINTS

• Enhancing lesions may persist after standard treatment in GBM patients. • DCE-MRI may help predict the progression of the enhancing lesions. • Mean K ^trans and v _e were lower in progression than in non-progression group. • DCE-MRI may help identify patients requiring close follow-up after standard treatment. • DCE-MRI may help plan treatment strategies for GBM patients.

Glioma FMISO PET/MR Imaging Concurrent with Antiangiogenic Therapy: Molecular Imaging as a Clinical Tool in the Burgeoning Era of Personalized Medicine

The purpose of this article is to provide a focused overview of the current use of positron emission tomography (PET) molecular imaging in the burgeoning era of personalized medicine in the treatment of patients with glioma. Specifically, we demonstrate the utility of PET imaging as a tool for personalized diagnosis and therapy by highlighting a case series of four patients with recurrent high grade glioma who underwent 18F-fluoromisonidazole (FMISO) PET/MR (magnetic resonance) imaging through the course of antiangiogenic therapy. Three distinct features were observed from this small cohort of patients. First, the presence of pseudoprogression was retrospectively associated with the absence of hypoxia. Second, a subgroup of patients with recurrent high grade glioma undergoing bevacizumab therapy demonstrated disease progression characterized by an enlarging nonenhancing mass with newly developed reduced diffusion, lack of hypoxia, and preserved cerebral blood volume. Finally, a reduction in hypoxic volume was observed concurrent with therapy in all patients with recurrent tumor, and markedly so in two patients that developed a nonenhancing reduced diffusion mass. This case series demonstrates how medical imaging has the potential to influence personalized medicine in several key aspects, especially involving molecular PET imaging for personalized diagnosis, patient specific disease prognosis, and therapeutic monitoring.

Non-18F-FDG PET/CT in the management of patients affected by HNC: state-of-the-art

PET/computed tomography with F-fluorodeoxyglucose is considered a powerful molecular imaging technique that can provide useful information in the management of patients affected by head and neck cancer. However, misleading findings have been reported because of nonspecific uptake caused by peritumoural inflammation and physiologic changes in nonmalignant tissues in the head and neck region. More specific β-emitting tracers have been introduced that can track other pathological processes. We aimed to review the existing literature performing the search until June 2015 on non-F-fluorodeoxyglucose PET tracers in head and neck cancer to highlight their role in clinical practice.

Robustness of quantitative hypoxia PET image analysis for predicting local tumor control

BACKGROUND

Previous studies suggested the maximum tumor to background ratio (TBRmax) in FMISO PET images as a potentially predictive parameter for local control after radio-chemotherapy (CRT) in head and neck squamous cell carcinomas (HNSCC). However, different TBRmax thresholds for stratification were reported, implying that a common threshold cannot readily be used among different institutions without the risk of reducing prediction accuracy. Therefore, this study investigated the robustness of using a common pre-defined TBRmax, simulating a multicenter clinical trial.

MATERIAL AND METHODS

FMISO PET/CT was performed four hours post-injection in 22 patients with advanced HNSCC in a phase II FMISO dose escalation study. PET background regions of interest (ROIs) were manually defined in deep neck muscles. TBRmax was calculated as the mean of the highest-valued voxels within the high risk RT planning target volume. Its predictive power with respect to local control was tested, classifying patients using median TBRmax as threshold. The influence of systematically varying quantification between institutions was studied in silico by applying offsets of ± 10% and ± 20% to the TBRmax of all patients, while the threshold remained constant. The effect was analyzed using a receiver operating characteristic (ROC). True positive and false positive rates (TPR/FPR) as well as positive and negative predictive values (PPV/NPV) were evaluated.

RESULTS

For the reference condition without an offset the median TBRmax was 2.0 (1.4-3.5). Patients were classified using this threshold and TPR = 0.7, FPR = 0.4, PPV = 0.5 and NPV = 0.8 were observed. Accuracy declined with increasing offsets. Negative offsets of -10% and -20% resulted in TPR = 0.43 and 0.14, FPR = 0.20 and 0.13, PPV = 0.50 and 0.33 and NPV = 0.75 and 0.68, respectively. Positive offsets of + 10% and + 20% resulted in TPR = 1.00 and 1.00, FPR = 0.53 and 0.67, PPV = 0.47 and 0.41 and NPV = 1.00 and 1.00, respectively.

CONCLUSIONS

Using a common pre-defined TBRmax threshold in multicenter trials requires careful standardization and harmonization of all steps from patient preparation to image analysis. Our results indicate that TBRmax should deviate less than 10% from reference conditions (absolute value in this dataset ± 0.2). This conclusion likely applies to all low contrast nitroimidazole hypoxia PET tracers.

The role of PET/CT in the management of patients affected by head and neck tumors: a review of the literature

The management of head and neck tumor (HNSCC) has been changing over the years, especially due to the aid of imaging techniques that help physicians to attain a correct diagnosis. These techniques represent a valuable tool to help tailor treatment and during follow-up of patients affected by malignancies. The aim of this review is to summarize the results of the most recent and relevant studies about the use of PET imaging in HNSCCs. This review is divided into six chapters: (1) The role of PET/CT in the pre-treatment phase; (2) PET/CT and radiotherapy planning; (3) PET/CT in the post-treatment setting; (4) PET/CT and SUVmax for prediction of prognosis; (5) miscellanea on the utility of PET in specific HNSCCs; (6) non-FDG PET tracers used in HNSCC. Promising results have been obtained so far. Despite the encouraging outcomes, more investigations are needed to warrant the value of this technique, especially in the pre-treatment setting.

MiR-210 links hypoxia with cell proliferation regulation in human Laryngocarcinoma cancer

The microRNA hsa-miR-210 (miR-210) is associated with hypoxia; however its function has not fully identified. In the present study, we aim to detect its role concerning proliferation in Laryngocarcinoma. We found that miR-210 was highly expressed in hypoxia, which inhibited proliferation by inducing cell cycle arrest in G1/G0 as well as apoptosis. We further identified that miR-210 targeted fibroblast growth factor receptor-like 1 (FGFRL1). Down regulation of FGFRL1 decreased cell proliferation by promoting proportion of cells in G1/G0 phase and decreasing in S and G2/M phases. Moreover, overexpression of FGFRL1 effectively released the miR-210-induced suppression of SCC10A cell proliferation. Expression of miR-210 repressed tumor xenograft growth in vivo as well. Together, our findings reveal a new mechanism of adaptation to hypoxia that miR-210 inhibits the proliferation via inducing cell cycle arrest and apoptosis by the targeting of FGFRL1. J. Cell. Biochem. 116: 1039-1049, 2015. © 2015 Wiley Periodicals, Inc.

Hypoxia as a Biomarker and for Personalized Radiation Oncology

Tumor hypoxia is a clinically relevant cause of radiation resistance. Direct measurements of tumor oxygenation have been performed predominantly with the Eppendorf histograph and these have defined the reduced prognosis after radiotherapy in poorly oxygenated tumors, especially head-and-neck cancer, cervix cancer and sarcoma. Exogenous markers have been used for immunohistochemical detection of hypoxic tumor areas (pimonidazole) or for positron-emission tomography (PET) imaging (misonidazole). Overexpression of hypoxia-related proteins such as hypoxia-inducible factor-1α (HIF-1α) has also been linked to poor prognosis after radiotherapy and such proteins are considered as potential endogenous hypoxia markers.

F-18 fluoromisonidazole for imaging tumor hypoxia: imaging the microenvironment for personalized cancer therapy

Hypoxia in solid tumors is one of the seminal mechanisms for developing aggressive trait and treatment resistance in solid tumors. This evolutionarily conserved biological mechanism along with derepression of cellular functions in cancer, although resulting in many challenges, provide us with opportunities to use these adversities to our advantage. Our ability to use molecular imaging to characterize therapeutic targets such as hypoxia and apply this information for therapeutic interventions is growing rapidly. Evaluation of hypoxia and its biological ramifications to effectively plan appropriate therapy that can overcome the cure-limiting effects of hypoxia provides an objective means for treatment selection and planning. Fluoromisonidazole (FMISO) continues to be the lead radiopharmaceutical in PET imaging for the evaluation, prognostication, and quantification of tumor hypoxia, one of the key elements of the tumor microenvironment. FMISO is less confounded by blood flow, and although the images have less contrast than FDG-PET, its uptake after 2 hours is an accurate reflection of inadequate regional oxygen partial pressure at the time of radiopharmaceutical administration. By virtue of extensive clinical utilization, FMISO remains the lead candidate for imaging and quantifying hypoxia. The past decade has seen significant technological advances in investigating hypoxia imaging in radiation treatment planning and in providing us with the ability to individualize radiation delivery and target volume coverage. The presence of widespread hypoxia in the tumor can be effectively targeted with a systemic hypoxic cell cytotoxin or other agents that are more effective with diminished oxygen partial pressure, either alone or in combination. Molecular imaging in general and hypoxia imaging in particular will likely become an important in vivo imaging biomarker of the future, complementing the traditional direct tissue sampling methods by providing a snap shot of a primary tumor and metastatic disease and in following treatment response and will serve as adjuncts to personalized therapy.

Integration of imaging into clinical practice to assess the delivery and performance of macromolecular and nanotechnology-based oncology therapies

Functional and molecular imaging has become increasingly used to evaluate interpatient and intrapatient tumor heterogeneity. Imaging allows for assessment of microenvironment parameters including tumor hypoxia, perfusion and proliferation, as well as tumor metabolism and the intratumoral distribution of specific molecular markers. Imaging information may be used to stratify patients for targeted therapies, and to define patient populations that may benefit from alternative therapeutic approaches. It also provides a method for non-invasive monitoring of treatment response at earlier time-points than traditional cues, such as tumor shrinkage. Further, companion diagnostic imaging techniques are becoming progressively more important for development and clinical implementation of targeted therapies. Imaging-based companion diagnostics are likely to be essential for the validation and FDA approval of targeted nanotherapies and macromolecular medicines. This review describes recent clinical advances in the use of functional and molecular imaging to evaluate the tumor microenvironment. Additionally, this article focuses on image-based assessment of distribution and anti-tumor effect of nano- and macromolecular systems.

Imaging tumour hypoxia with positron emission tomography

Hypoxia, a hallmark of most solid tumours, is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. Given its prominent role in oncology, accurate detection of hypoxia is important, as it impacts on prognosis and could influence treatment planning. A variety of approaches have been explored over the years for detecting and monitoring changes in hypoxia in tumours, including biological markers and noninvasive imaging techniques. Positron emission tomography (PET) is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels. This review provides an overview of imaging hypoxia with PET, with an emphasis on the advantages and limitations of the currently available hypoxia radiotracers.

Positron emission tomography to assess hypoxia and perfusion in lung cancer

In lung cancer, tumor hypoxia is a characteristic feature, which is associated with a poor prognosis and resistance to both radiation therapy and chemotherapy. As the development of tumor hypoxia is associated with decreased perfusion, perfusion measurements provide more insight into the relation between hypoxia and perfusion in malignant tumors. Positron emission tomography (PET) is a highly sensitive nuclear imaging technique that is suited for non-invasive in vivo monitoring of dynamic processes including hypoxia and its associated parameter perfusion. The PET technique enables quantitative assessment of hypoxia and perfusion in tumors. To this end, consecutive PET scans can be performed in one scan session. Using different hypoxia tracers, PET imaging may provide insight into the prognostic significance of hypoxia and perfusion in lung cancer. In addition, PET studies may play an important role in various stages of personalized medicine, as these may help to select patients for specific treatments including radiation therapy, hypoxia modifying therapies, and antiangiogenic strategies. In addition, specific PET tracers can be applied for monitoring therapy. The present review provides an overview of the clinical applications of PET to measure hypoxia and perfusion in lung cancer. Available PET tracers and their characteristics as well as the applications of combined hypoxia and perfusion PET imaging are discussed.

Hypoxia in head and neck cancer in theory and practice: a PET-based imaging approach

Hypoxia plays an important role in tumour recurrence among head and neck cancer patients. The identification and quantification of hypoxic regions are therefore an essential aspect of disease management. Several predictive assays for tumour oxygenation status have been developed in the past with varying degrees of success. To date, functional imaging techniques employing positron emission tomography (PET) have been shown to be an important tool for both pretreatment assessment and tumour response evaluation during therapy. Hypoxia-specific PET markers have been implemented in several clinics to quantify hypoxic tumour subvolumes for dose painting and personalized treatment planning and delivery. Several new radiotracers are under investigation. PET-derived functional parameters and tracer pharmacokinetics serve as valuable input data for computational models aiming at simulating or interpreting PET acquired data, for the purposes of input into treatment planning or radio/chemotherapy response prediction programs. The present paper aims to cover the current status of hypoxia imaging in head and neck cancer together with the justification for the need and the role of computer models based on PET parameters in understanding patient-specific tumour behaviour.

The meaning, measurement and modification of hypoxia in the laboratory and the clinic

Hypoxia was identified as a microenvironmental component of solid tumours over 60 years ago and was immediately recognised as a potential barrier to therapy through the reliance of radiotherapy on oxygen to elicit maximal cytotoxicity. Over the last two decades both clinical and experimental studies have markedly enhanced our understanding of how hypoxia influences cellular behaviour and therapy response. Furthermore, they have confirmed early assumptions that low oxygenation status in tumours is an exploitable target in cancer therapy. Generally such approaches will be more beneficial to patients with hypoxic tumours, necessitating the use of biomarkers that reflect oxygenation status. Tissue biomarkers have shown utility in many studies. Further significant advances have been made in the non-invasive measurement of tumour hypoxia with positron emission tomography, magnetic resonance imaging and other imaging modalities. Here, we describe the complexities of defining and measuring tumour hypoxia and highlight the therapeutic approaches to combat it.

Molecular imaging of tumor hypoxia with positron emission tomography

The problem of tumor hypoxia has been recognized and studied by the oncology community for over 60 years. From radiation and chemotherapy resistance to the increased risk of metastasis, low oxygen concentrations in tumors have caused patients with many types of tumors to respond poorly to conventional cancer therapies. It is clear that patients with high levels of tumor hypoxia have a poorer overall treatment response and that the magnitude of hypoxia is an important prognostic factor. As a result, the development of methods to measure tumor hypoxia using invasive and noninvasive techniques has become desirable to the clinical oncology community. A variety of imaging modalities have been established to visualize hypoxia in vivo. Positron emission tomography (PET) imaging, in particular, has played a key role for imaging tumor hypoxia because of the development of hypoxia-specific radiolabelled agents. Consequently, this technique is increasingly used in the clinic for a wide variety of cancer types. Following a broad overview of the complexity of tumor hypoxia and measurement techniques to date, this article will focus specifically on the accuracy and reproducibility of PET imaging to quantify tumor hypoxia. Despite numerous advances in the field of PET imaging for hypoxia, we continue to search for the ideal hypoxia tracer to both qualitatively and quantitatively define the tumor hypoxic volume in a clinical setting to optimize treatments and predict response in cancer patients.

Molecular PET imaging for biology-guided adaptive radiotherapy of head and neck cancer

Integration of molecular imaging PET techniques into therapy selection strategies and radiation treatment planning for head and neck squamous cell carcinoma (HNSCC) can serve several purposes. First, pre-treatment assessments can steer decisions about radiotherapy modifications or combinations with other modalities. Second, biology-based objective functions can be introduced to the radiation treatment planning process by co-registration of molecular imaging with planning computed tomography (CT) scans. Thus, customized heterogeneous dose distributions can be generated with escalated doses to tumor areas where radiotherapy resistance mechanisms are most prevalent. Third, monitoring of temporal and spatial variations in these radiotherapy resistance mechanisms early during the course of treatment can discriminate responders from non-responders. With such information available shortly after the start of treatment, modifications can be implemented or the radiation treatment plan can be adapted tailing the biological response pattern. Currently, these strategies are in various phases of clinical testing, mostly in single-center studies. Further validation in multicenter set-up is needed. Ultimately, this should result in availability for routine clinical practice requiring stable production and accessibility of tracers, reproducibility and standardization of imaging and analysis methods, as well as general availability of knowledge and expertise. Small studies employing adaptive radiotherapy based on functional dynamics and early response mechanisms demonstrate promising results. In this context, we focus this review on the widely used PET tracer (18)F-FDG and PET tracers depicting hypoxia and proliferation; two well-known radiation resistance mechanisms.