2'-deoxy-2'-[18F] fluoro-D-glucose positron emission tomography, diffusion-weighted magnetic resonance imaging, and choline spectroscopy to predict the activity of cetuximab in tumor xenografts derived from patients with squamous cell carcinoma of the head and neck.

We investigated changes on 2'-deoxy-2'-[18F]fluoro-D-glucose positron emission tomography (18FDG-PET), diffusion-weighted magnetic resonance imaging (DW-MRI), and choline spectroscopy as early markers of cetuximab activity in squamous cell carcinoma of the head and neck (SCCHN). SCCHN patient-derived tumor xenografts models were selected based on their cetuximab sensitivity. Three models were resistant to cetuximab and two were sensitive (one was highly sensitive and the other one was moderately sensitive). Cetuximab was infused on day 0 and 7. Maximal standardized uptake values (SUVmax), apparent diffusion coefficient (ADC), and total choline pool were measured at baseline and at day 8. To investigate the possible clinical relevance of our pre-clinical findings, we also studied the SUVmax and ADC modifications induced by cetuximab in five patients. Cetuximab induced a significant decrease in SUVmax and an increase in ADC at day 8 compared to baseline in the most cetuximab-sensitive model but not in the other models. At day 8, in one resistant model, SUVmax was decreased compared to baseline and was significantly lower than the controls. Choline spectroscopy was not able to predict cetuximab activity. The five patients treated with cetuximab had a 18FDG-PET partial response. One patient had a partial response according to RECISTv1.1. Interestingly, this last had also an increase in ADC value above 25%. Our preclinical data support the use of PDTX to investigate imaging techniques to detect early treatment response. Our pre-clinical and clinical data suggest that DW-MRI and 18FDG-PET should be further investigated to predict cetuximab activity.

An individualized radiation dose escalation trial in non-small cell lung cancer based on FDG-PET imaging.

AIM: The aim of the study was to assess the feasibility of an individualized 18F fluorodeoxyglucose positron emission tomography (FDG-PET)-guided dose escalation boost in non-small cell lung cancer (NSCLC) patients and to assess its impact on local tumor control and toxicity. PATIENTS AND METHODS: A total of 13 patients with stage II-III NSCLC were enrolled to receive a dose of 62.5 Gy in 25 fractions to the CT-based planning target volume (PTV; primary turmor and affected lymph nodes). The fraction dose was increased within the individual PET-based PTV (PTVPET) using intensity modulated radiotherapy (IMRT) with a simultaneous integrated boost (SIB) until the predefined organ-at-risk (OAR) threshold was reached. Tumor response was assessed during follow-up by means of repeat FDG-PET/computed tomography. Acute and late toxicity were recorded and classified according to the CTCAE criteria (Version 4.0). Local progression-free survival was determined using the Kaplan-Meier method. RESULTS: The average dose to PTVPET reached 89.17 Gy for peripheral and 75 Gy for central tumors. After a median follow-up period of 29 months, seven patients were still alive, while six had died (four due to distant progression, two due to grade 5 toxicity). Local progression was seen in two patients in association with further recurrences. One and 2-year local progression free survival rates were 76.9% and 52.8%, respectively. Three cases of acute grade 3 esophagitis were seen. Two patients with central tumors developed late toxicity and died due to severe hemoptysis. CONCLUSION: These results suggest that a non-uniform and individualized dose escalation based on FDG-PET in IMRT delivery is feasible. The doses reached were higher in patients with peripheral compared to central tumors. This strategy enables good local control to be achieved at acceptable toxicity rates. However, dose escalation in centrally located tumors with direct invasion of mediastinal organs must be performed with great caution in order to avoid severe late toxicity.

Single-Artery Human Ear Graft Procurement: A Simplified Approach.

In the field of experimental facial vascularized composite tissue allotransplantation, a human auricular subunit model, pedicled on both superficial temporal and posterior auricular arteries, was described. Clinical cases of extensive auricular replantation, however, suggested that a single artery could perfuse the entire flap. In this study, variants of this single-pedicle approach have been studied, aiming to develop a more versatile replantation technique, in which the question of venous drainage has also been addressed. For arterial perfusion study, the authors harvested 11 auricular grafts, either on a single superficial temporal artery pedicle (n = 3) or a double superficial temporal and posterior auricular artery pedicle (n = 8). The authors then proceeded to selective barium injections, in the superficial temporal, posterior auricular, or both superficial temporal and posterior auricular arteries. Arteriograms were acquired with a micro-computed tomographic scan and analyzed on three-dimensionally reconstructed images. Venous drainage was investigated in eight hemifaces, carefully dissected after latex injection. Observations showed a homogenous perfusion of the whole auricle in all arterial graft variants. Venous drainage was highly variable, with either a dominant superficial temporal vein (37.5 percent), dominant posterior auricular vein (12.5 percent), or co-dominant trunks (50 percent). The authors demonstrated that auricular subunit vascularized composite tissue allotransplantation can be performed on a single artery, relying on the dynamic intraauricular anastomoses between superficial temporal artery and posterior auricular branches. Potentially, this vascular versatility is prone to simplify the subunit harvest and allows various strategies for pedicle selection. Venous drainage, however, remains inconstant and thus the major issue when considering auricular transplantation. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, V.

Head-to-Head Comparison of Inflammation and Neovascularization in Human Carotid Plaques: Implications for the Imaging of Vulnerable Plaques.

BACKGROUND: Inflammation and intraplaque neovascularization are acknowledged to be 2 features of plaque vulnerability, although their temporal expression and their respective value in predicting clinical events are poorly understood. To determine their respective temporal associations, we conducted a comprehensive assessment of inflammation and intraplaque neovascularization in the carotid plaque of symptomatic and asymptomatic patients. METHODS AND RESULTS: Thirty patients with severe carotid stenosis underwent 18F-fluorodeoxyglucose-positron emission tomography/computed tomographic imaging. Plaque 18F-fluorodeoxyglucose-uptake, indicative of inflammation, was measured by calculating the target:background ratio. The presence of intraplaque neovascularization during contrast-enhanced ultrasound was judged semiquantitatively; low-grade contrast enhancement (CE) suggested its absence, and high-grade CE, the presence of neovascularization. Carotid surgery was performed 1.6±1.8 days after completing both imaging modalities in all patients, and the presence of macrophages and neovessels was quantified by immunohistochemistry. We identified a significant correlation between the target:background ratio and macrophage quantification (R=0.78; P<0.001). The number of vessels was also significantly higher in carotid plaque with high-CE (P<0.001). Surprisingly, immunohistochemistry showed that high-CE and vessel number were neither associated with an elevated target:background ratio (P=0.28 and P=0.60, respectively) nor macrophage infiltration (P=0.59 and P=0.40, respectively). Finally, macrophage infiltration and target:background ratio were higher in the carotid plaque of symptomatic patients (P=0.021 and P=0.05, respectively), whereas CE grade and the presence of neovessels were not. CONCLUSIONS: Inflammation and intraplaque neovascularization are not systematically associated in carotid plaques, suggesting a temporal separation between the 2 processes. Inflammation seems more pronounced when symptoms are present. These data highlight the challenges that face any imaging strategy designed to assess plaque vulnerability.

Correlation analysis of [18F]fluorodeoxyglucose and [18F]fluoroazomycin arabinoside uptake distributions in lung tumours during radiation therapy.

BACKGROUND: PET-guided dose painting (DP) aims to target radioresistant tumour regions in order to improve radiotherapy (RT) outcome. Besides the well-known [18F]fluorodeoxyglucose (FDG), the hypoxia positron emission tomography (PET) tracer [18F]fluoroazomycin arabinoside (FAZA) could provide further useful information to guide the radiation dose prescription. In this study, we compare the spatial distributions of FDG and FAZA PET uptakes in lung tumours. MATERIAL AND METHODS: Fourteen patients with unresectable lung cancer underwent FDG and FAZA 4D-PET/CT on consecutive days at three time-points: prior to RT (pre), and during the second (w2), and the third (w3) weeks of RT. All PET/CT were reconstructed in their time-averaged midposition (MidP). The metabolic tumour volume (MTV: FDG standardised uptake value (SUV) > 50% SUVmax), and the hypoxic volume (HV: FAZA SUV > 1.4) were delineated within the gross tumour volume (GTVCT). FDG and FAZA intratumoral PET uptake distributions were subsequently pairwise compared, using both volume-, and voxel-based analyses. RESULTS: Volume-based analysis showed large overlap between MTV and HV: median overlapping fraction was 0.90, 0.94 and 0.94, at the pre, w2 and w3 time-points, respectively. Voxel-wise analysis between FDG and FAZA intratumoral PET uptake distributions showed high correlation: median Spearman's rank correlation coefficient was 0.76, 0.77 and 0.76, at the pre, w2 and w3 time-points, respectively. Interestingly, tumours with high FAZA uptake tended to show more similarity between FDG and FAZA intratumoral uptake distributions than those with low FAZA uptake. CONCLUSIONS: In unresectable lung carcinomas, FDG and FAZA PET uptake distributions displayed unexpectedly strong similarity, despite the distinct pathways targeted by these tracers. Hypoxia PET with FAZA brought very little added value over FDG from the perspective of DP in this population.

Long-Term In Vivo Monitoring of Adult-Derived Human Liver Stem/Progenitor Cells by Bioluminescence Imaging, Positron Emission Tomography, and Contrast-Enhanced Computed Tomography.

Adult-derived human liver stem/progenitor cells (ADHLSCs) have the potential to alleviate liver injury. However, the optimal delivery route and long-term biodistribution of ADHLSCs remain unclear. In this article, we used a triple fusion reporter system to determine the kinetic differences in the biodistribution of ADHLSCs following intrasplenic (IS) and intrahepatic (IH) administration in severe combined immunodeficiency/beige mice. ADHLSCs were transduced with a lentiviral vector expressing a triple fusion reporter comprising renilla luciferase, monomeric red fluorescent protein, and truncated HSV-1 thymidine kinase. The stability and duration of the transgenes, and the effects of transduction on the cell properties were evaluated in vitro. The acute retention and long-term engraftment in vivo were revealed by positron emission tomography and bioluminescence imaging (BLI), respectively, followed by histochemical analysis. We showed that ADHLSCs can be safely transduced with the triple fusion reporter. Radiolabeled ADHLSCs showed acute cell retention at the sites of injection. The IH group showed a confined BLI signal at the injection site, while the IS group displayed a dispersed distribution at the upper abdominal liver area, and a more intense signal. In conclusion, ADHLSCs could be monitored by BLI for up to 4 weeks with a spread out biodistribution following IS injection.

Evolution of [18F]fluorodeoxyglucose and [18F]fluoroazomycin arabinoside PET uptake distributions in lung tumours during radiation therapy.

BACKGROUND: Dose painting (DP) aims to improve radiation therapy (RT) outcome by targeting radioresistant tumour regions identified through functional imaging, e.g., positron emission tomography (PET). Importantly, the expected benefit of DP relies on the ability of PET imaging to identify tumour areas which could be consistently targeted throughout the treatment. In this study, we analysed the spatial stability of two potential DP targets in lung cancer patients undergoing RT: the tumour burden surrogate [18F]fluorodeoxyglucose (FDG) and the hypoxia surrogate [18F]fluoroazomycin arabinoside (FAZA). MATERIALS AND METHODS: Thirteen patients with unresectable lung tumours underwent FDG and FAZA 4D-PET/CT before (pre), and during the second (w2) and third (w3) weeks of RT. All PET/CT were reconstructed in their time-averaged midposition (MidP) for further analysis. The metabolic tumour volume (MTV: FDG standardised uptake value (SUV) > 50% SUVmax) and the hypoxic volume (HV: FAZA SUV >1.4) were delineated within the gross tumour volume (GTVCT). The stability of FDG and FAZA PET uptake distributions during RT was subsequently assessed through volume-overlap analysis and voxel-based correlation analysis. RESULTS: The volume-overlap analysis yielded median overlapping fraction (OF) of 0.86 between MTVpre and MTVw2 and 0.82 between MTVpre and MTVw3. In patients with a detectable HV, median OF was 0.82 between HVpre and HVw2 and 0.90 between HVpre and HVw3. The voxel-based correlation analysis yielded median Spearman's correlation coefficient (rS) of 0.87 between FDGpre and FDGw2 and 0.83 between FDGpre and FDGw3. Median rS was 0.78 between FAZApre and FAZAw2 and 0.79 between FAZApre and FAZAw3. CONCLUSIONS: FDG and FAZA PET uptake distributions were spatially stable during the 3 first weeks of RT in patients with unresectable lung cancer, both based on volume- and voxel-based indicators. This might allow for a consistent targeting of high FDG or FAZA PET uptake regions as part of a DP strategy.

Multimodality Imaging Identifies Distinct Metabolic Profiles In Vitro and In Vivo.

The study of alterations of tumor metabolism should allow the identification of new targets for innovative anticancer strategies. Metabolic alterations are generally established in vitro, and conclusions are often extrapolated to the in vivo situation without further tumor metabolic phenotyping. To highlight the key role of microenvironment on tumor metabolism, we studied the response of glycolytic and oxidative tumor models to metabolic modulations in vitro and in vivo. MDA-MB-231 and SiHa tumor models, characterized in vitro as glycolytic and oxidative, respectively, were studied. Theoretically, when passing from a hypoxic state to an oxygenated state, a Warburg phenotype should conserve a glycolytic metabolism, whereas an oxidative phenotype should switch from glycolytic to oxidative metabolism (Pasteur effect). This challenge was applied in vitro and in vivo to evaluate the impact of different oxic conditions on glucose metabolism. 18F-fluorodeoxyglucose uptake, lactate production, tumor oxygenation, and metabolic fluxes were monitored in vivo using positron emission tomography, microdialysis, electron paramagnetic resonance imaging, and 13C-hyperpolarizated magnetic resonance spectroscopy, respectively. In vitro, MDA-MB-231 cells were glycolytic under both hypoxic and oxygenated conditions, whereas SiHa cells underwent a metabolic shift after reoxygenation. On the contrary, in vivo, the increase in tumor oxygenation (induced by carbogen challenge) led to a similar metabolic shift in glucose metabolism in both tumor models. The major discordance in metabolic patterns observed in vitro and in vivo highlights that any extrapolation of in vitro metabolic profiling to the in vivo situation should be taken cautiously and that metabolic phenotyping using molecular imaging is mandatory in vivo.

Biodistribution of (125)I-labeled anti-endoglin antibody using SPECT/CT imaging: Impact of in vivo deiodination on tumor accumulation in mice.

INTRODUCTION: Radiolabeled antibodies directed against endoglin (CD105) are promising tools for imaging and antiangiogenic cancer therapy. To validate iodinated antibodies as reliable tracers, we investigated the influence of the radiolabeling method (direct or indirect) on their in vivo stability. METHODS: Anti-CD105 mAbs were radioiodinated directly using chloramine-T ((125)I-anti-CD105-mAbs) or indirectly using D-KRYRR peptide as a linker ((125)I-KRYRR-anti-CD105-mAbs). The biodistribution was studied in B16 tumor-bearing mice via SPECT/CT imaging. RESULTS: Radioiodinated mAbs were stable in vitro. In vivo, thyroid showed the most important increase of uptake after 24h for (125)I-anti-CD105-mAbs (91.9±4.0%ID/ml) versus(125)I-KRYRR-anti-CD105-mAbs (4.4±0.6%ID/ml). Tumor uptake of (125)I-anti-CD105-mAbs (0.9±0.3%ID/ml) was significantly lower than that of (125)I-KRYRR-anti-CD105-mAbs (4.7±0.2%ID/ml). CONCLUSIONS: An accurate characterization of the in vivo stability of radioiodinated mAbs and the choice of an appropriate method for the radioiodination are required, especially for novel targets. The indirect radioiodination of internalizing anti-CD105 mAbs leads to more stable tracer by decreasing in vivo deiodination and improves the tumor retention of radioiodinated mAbs. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: To date, the only antiangiogenic antibody approved for clinical indications is bevacizumab. There is a need to develop more antibodies that have targets highly expressed on tumor endothelium. CD105 represents a promising marker of angiogenesis, but its therapeutic relevance in cancer needs to be further investigated. In this context, this study suggests the potential use of indirectly iodinated anti-CD105 mAbs for tumor imaging and for therapeutic purposes.

DW-MRI and (18) F-FLT PET for early assessment of response to radiation therapy associated with hypoxia-driven interventions. Preclinical studies using manipulation of oxygenation and/or dose escalation.

Early markers of treatment response may help in the management of patients by predicting the outcome of a specific therapeutic intervention. Here, we studied the potential value of diffusion-weighted MRI (DW-MRI) and (18)F-fluorothymidine ((18)F-FLT), markers of cell death and cell proliferation respectively, to predict the response to irradiation. In addition, dose escalation and/or carbogen breathing were used to modulate the response to irradiation. The studies were performed on two hypoxic rat tumor models: rhabdomyosarcoma and 9L-glioma. The rats were imaged using MRI and PET before and two days after the treatment. In both tumor models, changes in ADC (apparent diffusion coefficient) and (18)F-FLT SUV (standardized uptake value) were significantly correlated with the tumor growth delay. For both tumor models, the ADC values increased in all irradiated groups two days after the treatment while they decreased in the untreated groups. At the same time, the uptake of (18)F-FLT increased in the untreated groups and decreased in all treated groups. Yet, ADC values were not sensitive enough to predict the added value of dose escalation or carbogen breathing in either model. Change in (18)F-FLT uptake was able to predict the higher tumor response when using increased dose of irradiation, but not when using a carbogen breathing challenge. Our results also emphasize that the magnitude of change in (18)F-FLT uptake was strongly dependent on the tumor model.

Impact of Oxygenation Status on 18F-FDG Uptake in Solid Tumors.

The influence of changes in tumor oxygenation (monitored by EPR oximetry) on the uptake of 18F-FDG tracer was evaluated using micro-PET in two different human tumor models. The 18F-FDG uptake was higher in hypoxic tumors compared to tumors that present a pO2 value larger than 10 mmHg.

Multi-modality imaging to assess metabolic response to dichloroacetate treatment in tumor models.

Reverting glycolytic metabolism is an attractive strategy for cancer therapy as upregulated glycolysis is a hallmark in various cancers. Dichloroacetate (DCA), long used to treat lactic acidosis in various pathologies, has emerged as a promising anti-cancer drug. By inhibiting the pyruvate dehydrogenase kinase, DCA reactivates the mitochondrial function and decreases the glycolytic flux in tumor cells resulting in cell cycle arrest and apoptosis. We recently documented that DCA was able to induce a metabolic switch preferentially in glycolytic cancer cells, leading to a more oxidative phenotype and decreasing proliferation, while oxidative cells remained less sensitive to DCA treatment. To evaluate the relevance of this observation in vivo, the aim of the present study was to characterize the effect of DCA in glycolytic MDA-MB-231 tumors and in oxidative SiHa tumors using advanced pharmacodynamic metabolic biomarkers. Oxygen consumption, studied by 17O magnetic resonance spectroscopy, glucose uptake, evaluated by 18F-FDG PET and pyruvate transformation into lactate, measured using hyperpolarized 13C-magnetic resonance spectroscopy, were monitored before and 24 hours after DCA treatment in tumor bearing mice. In both tumor models, no clear metabolic shift was observed. Surprisingly, all these imaging parameters concur to the conclusion that both glycolytic tumors and oxidative tumors presented a similar response to DCA. These results highlight a major discordance in metabolic cancer cell bioenergetics between in vitro and in vivo setups, indicating critical role of the local microenvironment in tumor metabolic behaviors.

The increase in tumor oxygenation under carbogen breathing induces a decrease in the uptake of [(18)F]-fluoro-deoxy-glucose.

We investigated the impact of oxygenation status (measured by EPR oximetry) on the uptake of (18)F-FDG (measured by PET) in two different tumor models during a carbogen breathing challenge. We observed a significant drop in (18)F-FDG uptake under carbogen breathing that suggests a rapid metabolic adaptation to the oxygen environment.

Hypoxia-guided adaptive radiation dose escalation in head and neck carcinoma: a planning study.

OBJECTIVE: To evaluate from a planning point of view the dose distribution of adaptive radiation dose escalation in head and neck squamous cell carcinoma (HNSCC) using (18)F-Fluoroazomycin arabinoside (FAZA) positron emission tomography/computed tomography (PET-CT). MATERIAL/METHODS: Twelve patients with locally advanced HNSCC underwent three FAZA PET-CT before treatment, after 7 fractions and after 17 fractions of a carboplatin-5FU chemo-radiotherapy regimen (70 Gy in 2 Gy per fraction over 7 weeks). The dose constraints were that every hypoxic voxel delineated before and during treatment (newborn hypoxic voxels) should receive a total dose of 86 Gy. A median dose of 2.47 Gy per fraction was prescribed on the hypoxic PTV defined on the pre-treatment FAZA PET-CT; a median dose of 2.57 Gy per fraction was prescribed on the newborn voxels identified on the first per-treatment FAZA PET-CT; a median dose of 2.89 Gy per fraction was prescribed on the newborn voxels identified on the second per-treatment FAZA PET-CT. RESULTS: Ten of 12 patients had hypoxic volumes. Six of 10 patients completed all the FAZA PET-CT during radiotherapy. For the hypoxic PTVs, the average D50% matched the prescribed dose within 2% and the homogeneity indices reached 0.10 and 0.12 for the nodal PTV 86 Gy and the primary PTV 86 Gy, respectively. Compared to a homogeneous 70 Gy mean dose to the PTVs, the dose escalation up to 86 Gy to the hypoxic volumes did not typically modify the dose metrics on the surrounding normal tissues. CONCLUSION: From a planning point of view, FAZA-PET-guided dose adaptive escalation is feasible without substantial dose increase to normal tissues above tolerance limits. Clinical prospective studies, however, need to be performed to validate hypoxia-guided adaptive radiation dose escalation in head and neck carcinoma.

Predictive value of (18)F-FAZA PET imaging for guiding the association of radiotherapy with nimorazole: a preclinical study.

PURPOSE: To assess the predictive value of hypoxia imaging by (18)F-FAZA PET in identifying tumors that may benefit from radiotherapy combined with nimorazole, a hypoxic radiosensitizer. MATERIAL AND METHODS: Rats of two tumor models (Rhabdomyosarcoma and 9L-glioma) were divided into two treated groups: radiotherapy (RT) alone or RT plus nimorazole. (18)F-FAZA PET images were obtained to evaluate tumor hypoxia before the treatment. Treatment outcome was assessed through the tumor growth time assay, defined as the time required for tumor to grow to 1.5 times its size before irradiation. RESULTS: For rhabdomyosarcomas, the benefit of adding nimorazole to RT was not significant when considering all tumors. When stratifying into more and less hypoxic tumors according to the median (18)F-FAZA T/B ratio, we found that the combined treatment significantly improved the response of the "more hypoxic" subgroup, while there was no significant difference in the tumor growth time between the two treatment modalities for the "less hypoxic" subgroup. For 9L-gliomas, a clear benefit was demonstrated for the group receiving RT+nimorazole. However, the individual responses within the RT+nimorazole group were highly variable and independent of the (18)F-FAZA uptake. CONCLUSIONS: (18)F-FAZA PET may be useful to guide hypoxia-directed RT using nimorazole as radiosensitizer. It identified a subgroup of more hypoxic tumors (displaying T/B ratio>2.72) that would benefit from this combined treatment. Nevertheless, the predictive power was limited to rhabdomyosarcomas and ineffective for 9L-gliomas.

Reprogramming of tumor metabolism by targeting mitochondria improves tumor response to irradiation.

BACKGROUND: The Warburg phenotype identified decades ago describes tumor cells with increased glycolysis and decreased mitochondrial respiration even in the presence of oxygen. This particular metabolism also termed 'aerobic glycolysis' reflects an adaptation of tumor cells to proliferation in a heterogeneous tumor microenvironment. Although metabolic alterations in cancer cells are common features, their impact on the response to radiotherapy is not yet fully elucidated. This study investigated the impact of cellular oxygen consumption inhibition on the tumor response to radiotherapy. MATERIAL AND METHODS: Warburg-phenotype tumor cells with impaired mitochondrial respiration (MD) were produced and compared in respect to their metabolism to the genetically matched parental cells (WT). After characterization of their metabolism we compared the response of MD cells to irradiation in vivo and in vitro to the genetically matched parental cells (WT). RESULTS: We first confirmed that MD cells were exclusively glycolytic while WT cells exhibited mitochondrial respiration. We then used these cells for assessing the response of WT and MD tumors to a single dose of radiation and showed that the in vivo tumor growth delay of the MD group was increased, indicating an increased radiosensitivity compared to WT while the in vitro ability of both cell lines to repair radiation-induced DNA damage was similar. CONCLUSION: Taken together, these results indicate that in addition to intrinsic radiosensitivity parameters the tumor response to radiation will also depend on their metabolic rate of oxygen consumption.

Potential role of hypoxia imaging using (18)F-FAZA PET to guide hypoxia-driven interventions (carbogen breathing or dose escalation) in radiation therapy.

BACKGROUND AND PURPOSE: Hypoxia-driven intervention (oxygen manipulation or dose escalation) could overcome radiation resistance linked to tumor hypoxia. Here, we evaluated the value of hypoxia imaging using (18)F-FAZA PET to predict the outcome and guide hypoxia-driven interventions. MATERIAL AND METHODS: Two hypoxic rat tumor models were used: rhabdomyosarcoma and 9L-glioma. For the irradiated groups, the animals were divided into two subgroups: breathing either room air or carbogen. (18)F-FAZA PET images were obtained just before the irradiation to monitor the hypoxic level of each tumor. Absolute pO2 were also measured using EPR oximetry. Dose escalation was used in Rhabdomyosarcomas. RESULTS: For 9L-gliomas, a significant correlation between (18)F-FAZA T/B ratio and tumor growth delay was found; additionally, carbogen breathing dramatically improved the tumor response to irradiation. On the contrary, Rhabdomyosarcomas were less responsive to hyperoxic challenge. For that model, an increase in growth delay was observed using dose escalation, but not when combining irradiation with carbogen. CONCLUSIONS: (18)F-FAZA uptake may be prognostic of outcome following radiotherapy and could assess the response of tumor to carbogen breathing. (18)F-FAZA PET may help to guide the hypoxia-driven intervention with irradiation: carbogen breathing in responsive tumors or dose escalation in tumors non-responsive to carbogen.

A prospective clinical study of ¹8F-FAZA PET-CT hypoxia imaging in head and neck squamous cell carcinoma before and during radiation therapy.

PURPOSE: Hypoxia in head and neck squamous cell carcinoma (HNSCC) is associated with poor prognosis and outcome. (18) F-Fluoroazomycin arabinoside (FAZA) is a positron emission tomography (PET) tracer developed to enable identification of hypoxic regions within tumor. The aim of this study was to evaluate the use of (18) F-FAZA-PET for assessment of hypoxia before and during radiation therapy. METHODS: Twelve patients with locally advanced HNSCC underwent (18) F-FAZA-PET scans before and at fraction 7 and 17 of concomitant chemo-radiotherapy. A hypoxic voxel was defined as a voxel expressing a standardized uptake value (SUV) equal or above the SUVmean of the posterior contralateral neck muscles plus three standard deviations. The fractional hypoxic volume fraction (FHV) and the spatial move of hypoxic volumes during treatment were analyzed. RESULTS: A hypoxic volume could be identified in ten patients before treatment. FAZA-PET FHV varied from 0 to 54.3% and from 0 to 41.4% in the primary tumor and in the involved node, respectively. Six out of these ten patients completed all the FAZA-PET-computed tomography (CT) during the radiotherapy. In all patients, FHV and SUVmax values decreased. All patient presented a spatial move of hypoxic volume, but only three patients had newborn hypoxic voxels after 17 fractions. CONCLUSION: This study indicated that (18) F-FAZA-PET could be used to identify and quantify tumor hypoxia before and during concomitant radio-chemotherapy in patients with locally advanced HNSCC. In addition to the information on prognostic value, the use of (18) F-FAZA-PET allowed the delineation of hypoxic volumes for dose escalation protocols. However, due to fluctuation of hypoxia during treatment, repeated scan will have to be performed (i.e. adaptive radiotherapy).

(89)Zr-labeled anti-endoglin antibody-targeted gold nanoparticles for imaging cancer: implications for future cancer therapy.

AIMS: Antibody-labeled gold nanoparticles represent an attractive tool for cancer imaging and therapy. In this study, the anti-CD105 antibody was conjugated with gold nanoparticles (AuNPs) for the first time. The antibody biodistribution in mice before and after conjugation to AuNPs was studied, with a focus on tumor targeting. MATERIALS & METHODS: Antibodies were radiolabeled with 89Zr before conjugation to AuNPs (5 nm). Immunonanoconjugates were characterized in vitro in terms of size, stability in plasma and binding to the target. Quantitative PET imaging and ICP-MS analysis assessed in vivo distribution and specific tumor targeting of tracers. RESULTS: The tumor uptake of immunoconjugates was preserved up to 24 h after injection, with high tumor contrast and selective tumor targeting. No major tracer accumulation was observed over time in nonspecific organs. ICP-MS analysis confirmed the antibody specificity after nanoparticle conjugation. CONCLUSION: The anti-CD105 antibody conjugation to AuNPs did not greatly affect CD105-dependent tumor uptake and the efficacy of tumor targeting for cancer detection.

Antibody-functionalized nanoparticles for imaging cancer: influence of conjugation to gold nanoparticles on the biodistribution of 89Zr-labeled cetuximab in mice.

Antibody-labeled gold nanoparticles represent a promising novel tool regarding cancer imaging and therapy. Nevertheless, the characterization of biodistribution of such immunonanocarriers has been poorly documented. In this study, the biodistribution of (89)Zr-labeled cetuximab before and after the coupling reaction to gold nanoparticles (AuNPs) was compared and the quantitative imaging performance of (89)Zr immuno-PET was evaluated. Cetuximab was functionalized with the desferal moiety and labeled with (89)Zr ((89)Zr-Df-Bz-NCS-cetuximab). AuNPs with a mean diameter of 5 nm were synthesized according a new method developed in the laboratory, and conjugated to (89)Zr-Df-Bz-NCS-cetuximab using carbodiimide chemistry (AuNPs-PPAA-cetuximab-(89)Zr). The two tracers were injected in A431 xenograft-bearing mice. Tumor and liver uptakes were assessed at different times after injection using quantitative PET imaging. The in vivo specificity of the binding was investigated using a saturating dose of unlabeled cetuximab. Radiolabeled cetuximab was conjugated to AuNPs with a coupling reaction yield >75%. All conjugates were stable in vitro and to a lesser extent in plasma. In vivo distribution studies revealed no significant difference in tumor uptake for cetuximab conjugated to nanoparticles up to 72 h after injection, compared with unconjugated cetuximab. Immuno-PET studies showed that AuNPs-PPAA-cetuximab-(89)Zr provided high tumor-to-background ratio. The liver uptake of AuNPs-PPAA-cetuximab-(89)Zr was higher, compared with (89)Zr-Df-Bz-NCS-cetuximab. In vivo blocking experiments demonstrated selective tumor targeting after coupling reaction. This study showed that the conjugation of AuNPs to cetuximab did not affect its tumor accumulation and that the efficacy of EGFR-targeted nanoparticles was unaltered. The (89)Zr-labeled cetuximab-targeted gold nanoparticles could be a valuable tool for theranostic purposes.