The effect of tumor size on F-18-labeled fluorodeoxyglucose and fluoroerythronitroimidazole uptake in a murine sarcoma model

Eribulin improves tumor oxygenation demonstrated by 18F-DiFA hypoxia imaging, leading to radio-sensitization in human cancer xenograft models

PURPOSE

Eribulin, an inhibitor of microtubule dynamics, is known to show antitumor effects through its remodeling activity in the tumor vasculature. However, the extent to which the improvement of tumor hypoxia by eribulin affects radio-sensitivity remains unclear. We utilized 1-(2,2-dihydroxymethyl-3-¹⁸F-fluoropropyl)-2-nitroimidazole (¹⁸F-DiFA), a new PET probe for hypoxia, to investigate the effects of eribulin on tumor hypoxia and evaluate the radio-sensitivity during eribulin treatment.

METHODS

Mice bearing human breast cancer MDA-MB-231 cells or human lung cancer NCI-H1975 cells were administered a single dose of eribulin. After administration, mice were injected with ¹⁸F-DiFA and pimonidazole, and tumor hypoxia regions were analyzed. For the group that received combined treatment with radiation, ¹⁸F-DiFA PET/CT imaging was performed before tumors were locally X-irradiated. Tumor size was measured every other day after irradiation.

RESULTS

Eribulin significantly reduced ¹⁸F-DiFA accumulation levels in a dose-dependent manner. Furthermore, the reduction in ¹⁸F-DiFA accumulation levels by eribulin was most significant 7 days after treatment. These results were also supported by reduction of the pimonidazole-positive hypoxic region. The combined treatment showed significant retardation of tumor growth in comparison with the control, radiation-alone, and drug-alone groups. Importantly, tumor growth after irradiation was inversely correlated with ¹⁸F-DiFA accumulation.

CONCLUSION

These results demonstrated that ¹⁸F-DiFA PET/CT clearly detected eribulin-induced tumor oxygenation and that eribulin efficiently enhanced the antitumor activity of radiation by improving tumor oxygenation.

Hypoxia Mediates Tumor Malignancy and Therapy Resistance

Hypoxia is a hallmark of the tumor microenvironment and contributes to tumor malignant phenotypes. Hypoxia-inducible factor (HIF) is a master regulator of intratumoral hypoxia and controls hypoxia-mediated pathological processes in tumors, including angiogenesis, metabolic reprogramming, epigenetic reprogramming, immune evasion, pH homeostasis, cell migration/invasion, stem cell pluripotency, and therapy resistance. In this book chapter, we reviewed the causes and types of intratumoral hypoxia, hypoxia detection methods, and the oncogenic role of HIF in tumorigenesis and chemo- and radio-therapy resistance.

How to Modulate Tumor Hypoxia for Preclinical In Vivo Imaging Research

Tumor hypoxia is related with tumor aggressiveness, chemo- and radiotherapy resistance, and thus a poor clinical outcome. Therefore, over the past decades, every effort has been made to develop strategies to battle the negative prognostic influence of tumor hypoxia. For appropriate patient selection and follow-up, noninvasive imaging biomarkers such as positron emission tomography (PET) radiolabeled ligands are unprecedentedly needed. Importantly, before being able to implement these new therapies and potential biomarkers into the clinical setting, preclinical in vivo validation in adequate animal models is indispensable. In this review, we provide an overview of the different attempts that have been made to create differential hypoxic in vivo cancer models with a particular focus on their applicability in PET imaging studies.

A Comparative Study of Noninvasive Hypoxia Imaging with 18F-Fluoroerythronitroimidazole and 18F-Fluoromisonidazole PET/CT in Patients with Lung Cancer

PURPOSE

This is a clinical study to compare noninvasive hypoxia imaging using 18F-fluoroerythronitroimidazole (18F-FETNIM) and 18F-fluoromisonidazole (18F-FMISO) positron emission tomography/computed tomography (PET/CT) in patients with inoperable stages III-IV lung cancer.

METHODS

A total of forty-two patients with inoperable stages III-IV lung cancer underwent 18F-FETNIM PET/CT (n = 18) and 18F-FMISO PET/CT (n = 24) before chemo/radiation therapy. The standard uptake values (SUVs) of malignant and normal tissues depict 18F-FETNIM PET/CT and 18F-FMISO PET/CT uptake. Tumor-to-blood ratios (T/B) were used to quantify hypoxia.

RESULTS

All patients with lung cancer underwent 18F-FETNIM PET/CT and 18F-FMISO PET/CT successfully. Compared to 18F-FMISO, 18F-FETNIM showed similar uptake in muscle, thyroid, spleen, pancreas, heart, lung and different uptake in blood, liver, and kidney. Significantly higher SUV and T/B ratio with 18F-FMISO (2.56±0.77, 1.98±0.54), as compared to 18F-FETNIM (2.12±0.56, 1.42±0.33) were seen in tumor, P = 0.022, <0.001. For the patients with different histopathological subtypes, no significant difference of SUV (or T/B ratio) was observed both in 18F-FMISO and 18F-FETNIM in tumor. A significantly different SUV (or T/B ratio) was detected between < = 2cm, 2~5cm, and >5cm groups in 18F-FMISO PET/CT, P = 0.015 (or P = 0.029), whereas no difference was detected in 18F-FMISO PET/CT, P = 0.446 (or P = 0.707). Both 18F-FETNIM and 18F-FMISO showed significantly higher SUVs (or T/B ratios) in stage IV than stage III, P = 0.021, 0.013 (or P = 0.032, 0.02).

CONCLUSION

18F-FMISO showed significantly higher uptake than 18F-FETNIM in tumor/non-tumor ratio and might be a better hypoxia tracer in lung cancer.

Comparison of 18F-Fluoroerythronitroimidazole and 18F-fluorodeoxyglucose positron emission tomography and prognostic value in locally advanced non-small-cell lung cancer

INTRODUCTION

The aim of this study was to compare glucose metabolism and hypoxia using 18F- fluorodeoxyglucose (18F-FDG) and 18F-fluoroerythronitroimidazole (18F-FETNIM) positron emission tomography (PET) and investigate their prognostic role on survival in patients with locally advanced non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

Twenty-six patients with NSCLC were imaged with 18F-FETNIM PET/computed tomography (CT), and 11 cases also with 18F-FDG PET/CT imaging among those with significant 18F-FETNIM uptake, a few days before any chemo/adiation therapy. The maximum standardized uptake value (SUVmax) was used to depict 18F-FDG uptake, and hypoxic volume (HV) and tumor:blood ratio (T/Bmax) were used to quantify hypoxia. Overall survival (OS) after treatment was selected as the endpoint of the study.

RESULTS

Twenty-two patients (84.6%) had significant 18F-FETNIM uptake in the primary tumor. The correlations between the overall tumor SUVmax of 18F-FDG and HV, T/Bmax ratio of 18F-FENTIM in 11 patients were small and without significant difference. In univariate analyses, log-rank tests were used to compare Kaplan-Meier survival curves. 18F-FETNIM T/Bmax ratio and HV were strong predictors for OS, and 18F-FDG uptake of the primary lesions did not have a significant relationship with survival. In multivariate survival analysis, only 18F-FETNIM T/Bmax ratio was found to be an independent prognostic factor.

CONCLUSION

Imaging using both 18F-FETNIM and 18F-FDG appears to be beneficial in the evaluation of solid tumors. 18F-FETNIM imaging provides us with a valuable method to detect tumor hypoxia and predict OS. These preliminary results warrant validation in larger trials.

In Vivo Follow-up of Rat Tumor Models with 2-Deoxy-2-[F-18]fluoro-d-glucose/Dual-Head Coincidence Gamma Camera Imaging

Before studying the impact of 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) imaging with a dual-head coincidence gamma camera (DHC) for the follow-up of animal tumor models, we wanted to optimize this technique.

METHODS

Three different animal tumor models (osteosarcoma, melanoma, and breast cancer) were studied after FDG injection. Dynamic and dual time point FDG/DHC imaging were studied from one hour to five hours postinjection. In vitro tumor cell FDG uptake was assessed in eight different tumor cell lines. In one model (osteosarcoma), tumor growth, lung metastasis emergence, and survival were assessed by classical clinical follow-up and compared to FDG imaging in a control group (n = 6) and in a group treated by endostatin liposome complexes (n = 6).

RESULTS

Images obtained five hours after injection were more reliable for tumor growth follow-up than standard images (one hour). In vitro tumor cell FDG uptake confirmed in vivo imaging studies. In eight different tumor cell lines the FDG uptake was higher after five hours incubation than after one hour (p < 0.002). With FDG follow-up, we found that FDG uptake was strongly correlated with survival and that lung metastasis larger than 5 mm could be detected.

CONCLUSION

Using the optimization proposed above, DHC/FDG functional imaging seems to be a powerful tool to study rat tumor models and to help develop novel cancer therapies.

Diagnostic value and limitations of fluorine-18 fluorodeoxyglucose positron emission tomography for cartilaginous tumors of bone

BACKGROUND

A variety of imaging modalities are currently used for the preoperative evaluation of cartilage tumors. Although the anatomic details of the lesions are demonstrated well on computerized tomography and magnetic resonance images, those studies yield little information about the biologic activity of the tumors. In this study, we investigated the glucose metabolism of cartilage tumors measured by positron emission tomography and its correlation with histopathologic grades.

METHODS

Thirty-five biopsy-proven cartilaginous tumors in twenty-seven patients were studied with plain radiographs, bone-scanning, magnetic resonance imaging, and positron emission tomography. The glucose metabolism in these cartilaginous tumors was measured quantitatively by calculating the maximal standardized uptake value of the region of interest. This value was then correlated with histopathologic grade, tumor size, recurrence, and metastasis.

RESULTS

There were thirteen benign bone tumors, twelve grade-I chondrosarcomas, and ten high-grade (grade-II or III) chondrosarcomas. The mean maximal standard uptake values were 1.147 +/- 0.751 in the benign tumors, 0.898 +/- 0.908 in the grade-I chondrosarcomas, and 6.903 +/- 5.581 in the high-grade chondrosarcomas. There was no significant difference in these values between the benign cartilage tumors and the grade-I chondrosarcomas (p > 0.05). However, there was a significant difference between the low-grade (benign and grade-I) and high-grade chondrosarcomas (p = 0.009). Metastasis, but not tumor size or recurrence, was associated with a higher standard uptake value (p = 0.031). Two large pelvic grade-I chondrosarcomas demonstrated no radioisotope uptake on bone-scanning or on positron emission tomography. Positron emission tomography demonstrated grade-II and III metastatic lesions in the lung and other anatomic locations. When the cutoff for the standardized uptake value was set at 2.3 for grade-II or III chondrosarcomas, the positive predictive value was 0.82 (95% confidence interval, 0.48 to 0.97) and the negative predictive value was 0.96 (95% confidence interval, 0.77 to 1.00).

CONCLUSIONS

Grade-II and III chondrosarcomas have a higher glucose metabolism than do low-grade cartilage tumors. However, the measurement of glucose metabolism by positron emission tomography alone cannot distinguish between benign and grade-I malignant cartilaginous tumors. It is important to understand the advantages and disadvantages of imaging modalities for accurate interpretation of results. Although positron emission tomography has limitations, it may be useful for predicting high-grade chondrosarcomas.

LEVEL OF EVIDENCE

Diagnostic study, Level II-1 (development of diagnostic criteria on basis of consecutive patients [with universally applied reference "gold" standard]). See Instructions to Authors for a complete description of levels of evidence.

Imaging perfusion and hypoxia with PET to predict radiotherapy response in head-and-neck cancer

PURPOSE

The outcome of locally advanced head-and-neck cancer often is poor. An important determinant of treatment failure is tumor hypoxia arising from an inappropriate blood supply. Quantitation of the hypoxic fraction and blood flow in vivo may provide prognostic information and a means to target specifically tumor cells resistant to conventional treatment.

METHODS AND MATERIALS

Twenty-one patients with head-and-neck cancer underwent multitracer positron emission tomography (PET) before the start of preoperative or definitive radiotherapy (RT). Tumor blood flow was measured using the [(15)O]H(2)O autoradiographic technique followed by evaluation of oxygenation status using [(18)F]fluoroerythronitroimidazole ([(18)F]FETNIM). [(18)F]fluorodeoxyglucose PET was performed on a separate day to calculate the metabolically active tumor volume. The definition of the fractional hypoxic volume (FHV) in the tumor was determined by multiple voxel-wise measurements of the uptake of [(18)F]FETNIM in well-oxygenated tissues and tumor. PET findings were then correlated with the RT outcome and survival.

RESULTS

High blood flow was associated with poor local control after RT (p = 0.021) and with poor survival (p = 0.018). Patients with a FHV greater or equal to the median had significantly worse survival than those with a FHV less than the median (p = 0.036). The relationship between tumor hypoxia and FHV was supported in 3 patients who underwent invasive measurement of the tissue O(2) partial pressure.

CONCLUSION

High tumor blood flow predicted for a poor response to RT in head-and-neck cancer. The use of [(18)F]FETNIM for assessment of radiobiologic hypoxia requires a study with greater statistical power. PET with [(15)O]H(2)O or [(18)F]FETNIM may become useful in clinical trials in which novel therapeutic agents targeting tumor vasculature or hypoxia are evaluated.

Comparison of the biodistribution of two hypoxia markers [18F]FETNIM and [18F]FMISO in an experimental mammary carcinoma

The first aim of this study was to compare the hypoxia imaging ability of fluorine-18 fluoroerythronitroimidazole ([18F]FETNIM) with that of fluorine-18 fluoromisonimidazole ([18F]FMISO) in murine tumours of different sizes under two different oxygenation conditions. Secondly, we wanted to assess the biodistribution of the markers in normal tissues under similar conditions. Female CDF1 mice with a C3H mammary carcinoma grown on their backs were used. Tumours were size matched and animals breathed either normal air (21% O(2)) or carbogen gas (95% O(2) + 5% CO(2)). The gassing procedure was begun 5 min before the intravenous injection of either [18F]FETNIM or [18F]FMISO and continued until the mice were sacrificed at 120 min. Blood, tumour, muscle, heart, lung, liver, kidney and fat were removed, counted for radioactivity and weighed. The tumour and muscle were frozen and cut with a cryomicrotome into sections. The spatial distribution of radioactivity from the tissue sections was determined with digital autoradiography. Estimation of the necrotic fraction was made on sections from formalin-fixed tumours. Digital autoradiography showed that the whole tumour-to-muscle radioactivity uptake ratios were significantly higher in normal air-breathing mice than in carbogen-treated mice for both [18F]FETNIM (4.9+/-2.6 vs 1.8+/-0.5; P<0.01) and [18F]FMISO (4.4+/-1.0 vs 1.5+/-0.4; P<0.01). The carbogen treatment had only slight effects on the biodistribution of either marker in normal tissues. The necrotic fraction determined in tumours did not correlate with the tumour volume or with the tumour-to-muscle radioactivity uptake ratio. This study shows that the uptake of both [18F]FETNIM and [18F]FMISO correlates with the oxygenation status in tumours. In addition, our data show no significant difference in the intratumoral uptake between the two markers. However, significantly higher radioactivity uptake values were measured for [18F]FMISO than for [18F]FETNIM in normal tissues.

Noninvasive imaging of lentiviral-mediated reporter gene expression in living mice

Lentiviral-mediated gene delivery holds significant promise for sustained gene expression within living systems. Vesicular stomatitis virus glycoprotein-pseudotyped human immunodeficiency virus type 1-based lentiviral vectors can be used to introduce transgenes in a broad spectrum of dividing as well as nondividing cells. In the current study, we construct a lentiviral vector carrying two reporter genes separated by an internal ribosomal entry site and utilize that virus in delivering both genes into neuroblastoma cells in cell culture and into cells implanted in living mice. We utilize two reporter genes, a mutant herpes simplex virus type 1 (HSV1) sr39tk as a reporter gene compatible with positron emission tomography (PET) and a bioluminescent optical reporter gene, firefly luciferase (Fluc), to image expression in living mice by an optical charge-coupled device (CCD) camera. By using this lentivirus, neuroblastoma (N2a) cells are stably transfected and a high correlation (R(2) = 0.91) between expressions of the two reporter genes in cell culture is established. Imaging of both reporter genes using microPET and optical CCD camera in living mice is feasible, with the optical approach being more sensitive, and a high correlation (R(2) = 0.86) between gene expressions is again observed in lentiviral-infected N2a tumor xenografts. Indirect imaging of HSV1-sr39tk suicide gene therapy utilizing Fluc is also feasible and can be detected with increased sensitivity by using the optical CCD. These preliminary results validate the use of lentiviral vectors carrying reporter genes for multimodality imaging of gene expression and should have many applications, including imaging of xenografts, metastasis, and cell trafficking as well as noninvasive monitoring of lentiviral-mediated gene delivery and expression.

Direct correlation between positron emission tomographic images of two reporter genes delivered by two distinct adenoviral vectors

Biodistribution, magnitude and duration of a therapeutic transgene's expression may be assessed by linking it to the expression of a positron emission tomography (PET) reporter gene (PRG) and then imaging the PRG's expression by a PET reporter probe (PRP) in living animals. We validate the simple approach of co-administering two distinct but otherwise identical adenoviruses, one expressing a therapeutic transgene and the other expressing the PRG, to track the therapeutic gene's expression. Two PET reporter genes, a mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) and dopamine-2 receptor (D(2)R), each regulated by the same cytomegalovirus (CMV) promoter, have been inserted into separate adenoviral vectors (Ad). We demonstrate that cells co-infected with equivalent titers of Ad-CMV-HSV1-sr39tk and Ad-CMV-D(2)R express both reporter genes with good correlation (r(2) = 0.93). Similarly, a high correlation (r(2) = 0.97) was observed between the expression of both PRGs in the livers of mice co-infected via tail-vein injection with equivalent titers of these two adenoviruses. Finally, microPET imaging of HSV1-sr39tk and D(2)R expression with 9-(4-[(18)F]fluoro-3-hydroxymethylbutyl) guanine ([(18)F]FHBG) and 3-(2-[(18)F]fluoroethyl)spiperone ([(18)F]FESP), utilizing several adenovirus-mediated delivery routes, illustrates the feasibility of evaluating relative levels of transgene expression in living animals, using this approach.

A mouse model for calculating the absorbed beta-particle dose from (131)I- and (90)Y-labeled immunoconjugates, including a method for dealing with heterogeneity in kidney and tumor

Flynn, A. A., Green, A. J., Pedley, R. B., Boxer, G. M., Boden, R. and Begent, R. H. J. A Mouse Model for Calculating the Absorbed Beta-Particle Dose from (131)I- and (90)Y-Labeled Immunoconjugates, Including a Method for Dealing with Heterogeneity in Kidney and Tumor. Radiat. Res. 156, 28-35 (2001). Conventional internal radiation dosimetry methods assume that the beta-particle energy is absorbed uniformly and completely in the source organ and that the radioactivity is distributed uniformly in the source. However, in mice, a considerable proportion of the beta-particle energy can escape the source organ, resulting in large cross-organ doses. Furthermore, the distribution of radioactivity is generally heterogeneous in kidney and tumor. Therefore, a model was developed to account for cross-organ doses and for the effects of heterogeneity in kidney and tumor in mice for two of the most important radionuclides used in therapy, (131)I and (90)Y. Most mouse organs were modeled as single-compartment ellipsoids or cylinders, while heterogeneity in kidney and in tumor was addressed by using two compartments to represent the cortex and the medulla and viable and necrotic cells, respectively. The dimensions of these models were taken from previous studies, with the exception of kidney and tumor, which were defined using radioluminography and mosaics of high-power microscopy images. The absorbed fractions in each compartment were calculated using beta-particle point dose kernels. The self-organ dose was significantly higher for (131)I compared to (90)Y in all compartments, but a considerable amount of beta-particle energy was shown to escape the source organ for both radionuclides, with as much as 85% and 36% escaping the marrow for (90)Y and (131)I, respectively. The cortex was found to occupy a greater proportion of the total kidney volume than the medulla, and consequently the self-dose was higher in the cortex. In addition, the thickness of the viable shell in the tumor increased with tumor size, as did the self-dose fractions in both necrotic and viable areas. This dosimetry model improves dose estimates in mice and gives a conceptual basis for considering dosimetry in humans.