Micro-CT imaging of tumor angiogenesis: quantitative measures describing micromorphology and vascularization.

Angiogenesis is a hallmark of cancer, and its noninvasive visualization and quantification are key factors for facilitating translational anticancer research. Using four tumor models characterized by different degrees of aggressiveness and angiogenesis, we show that the combination of functional in vivo and anatomical ex vivo X-ray micro-computed tomography (µCT) allows highly accurate quantification of relative blood volume (rBV) and highly detailed three-dimensional analysis of the vascular network in tumors. Depending on the tumor model, rBV values determined using in vivo µCT ranged from 2.6% to 6.0%, and corresponds well with the values assessed using IHC. Using ultra-high-resolution ex vivo µCT, blood vessels as small as 3.4 µm and vessel branches up to the seventh order could be visualized, enabling a highly detailed and quantitative analysis of the three-dimensional micromorphology of tumor vessels. Microvascular parameters such as vessel size and vessel branching correlated very well with tumor aggressiveness and angiogenesis. In rapidly growing and highly angiogenic A431 tumors, the majority of vessels were small and branched only once or twice, whereas in slowly growing A549 tumors, the vessels were much larger and branched four to seven times. Thus, we consider that combining highly accurate functional with highly detailed anatomical µCT is a useful tool for facilitating high-throughput, quantitative, and translational (anti-) angiogenesis and antiangiogenesis research.

Quantitative correlation at the molecular level of tumor response to docetaxel by multimodal diffusion-weighted magnetic resonance imaging and [¹8F]FDG/[¹8F]FLT positron emission tomography.

We aimed to quantitatively characterize the treatment effects of docetaxel in the HCT116 xenograft mouse model, applying diffusion-weighted magnetic resonance imaging (MRI) and positron emission tomography (PET) using 2-deoxy-2-[¹8F]fluoro-d-glucose ([¹8F]FDG) and 3'-deoxy-3'-[¹8F]-fluorothymidine ([¹8F]FLT). Mice were imaged at four time points over 8 days. Docetaxel (15 mg/kg) was administered after a baseline scan. Voxel-wise scatterplots of PET and apparent diffusion coefficient (ADC) data of tumor volumes were evaluated with a threshold cluster analysis and compared to histology (GLUT1, GLUT3, Ki67, activated caspase 3a). Compared to the extensive tumor growth observed in the vehicle-treated group (from 0.32 ± 0.21 cm³ to 0.69 ± 0.40 cm³), the administration of docetaxel led to tumor growth stasis (from 0.32 ± 0.20 cm³ to 0.45 ± 0.23 cm³). The [¹8F]FDG/ADC cluster analysis and the evaluation of peak histogram values revealed a significant treatment effect matching histology as opposed to [¹8F]FLT/ADC. [¹8F]FLT uptake and the Ki67 index were not in good agreement. Our voxel-based cluster analysis uncovered treatment effects not seen in the separate inspection of PET and MRI data and may be used as an independent analysis tool. [¹8F]FLT/ADC cluster analysis could still point out the treatment effect; however, [¹8F]FDG/ADC reflected the histology findings in higher agreement.

A longitudinal study assessing lens thickness changes in the eye of the growing beagle using ultrasound scanning: relevance to age of dogs in regulatory toxicology studies.

The lens is formed in utero with new secondary lens fibres added as outer layers throughout life in a growth pattern characteristic of the species. This study examined the time course of beagle lens growth to better understand the optimal starting age of dogs for safety studies to support adult versus paediatric indications, and to assess the feasibility of non-invasively monitoring lens growth with high frequency ultrasound. Ultrasound scanning was performed in six female beagle dogs using the Vevo770. All dogs were imaged in B-mode using local anaesthetic but without sedation. Imaging was carried out every 2 weeks from 8 to 22 weeks of age and then monthly until 62 weeks of age. The dogs tolerated the procedure well. The lens was visible in all dogs and measuring the lens thickness with high frequency ultrasound demonstrated good analytical reproducibility [Root Mean Square (RMS) = 3.13%]. No differences between the left and right eye existed and lens thickness correlated with body weight. The highest weekly growth rate was before 12 weeks of age. A statistically significant difference between monthly thickness was detected until 42 weeks of age at which point growth reached a plateau. During the experiment, lenses grew by 29.7% reaching an average thickness of 6.4 mm ± 0.03. By 10 months of age (the typical age used for routine toxicological evaluation), beagles have reached a plateau in lens growth that is analogous to human adults. Where lens is a target organ of concern it is suggested that beagles under 6 months old may be a better model for determining paediatric safety.

Response of HT29 colorectal xenograft model to cediranib assessed with 18 F-fluoromisonidazole positron emission tomography, dynamic contrast-enhanced and diffusion-weighted MRI.

Cediranib is a small-molecule pan-vascular endothelial growth factor receptor inhibitor. The tumor response to short-term cediranib treatment was studied using dynamic contrast-enhanced and diffusion-weighted MRI at 7 T, as well as (18) F-fluoromisonidazole positron emission tomography and histological markers. Rats bearing subcutaneous HT29 human colorectal tumors were imaged at baseline; they then received three doses of cediranib (3 mg/kg per dose daily) or vehicle (dosed daily), with follow-up imaging performed 2 h after the final cediranib or vehicle dose. Tumors were excised and evaluated for the perfusion marker Hoechst 33342, the endothelial cell marker CD31, smooth muscle actin, intercapillary distance and tumor necrosis. Dynamic contrast-enhanced MRI-derived parameters decreased significantly in cediranib-treated tumors relative to pretreatment values [the muscle-normalized initial area under the gadolinium concentration curve decreased by 48% (p=0.002), the enhancing fraction by 43% (p=0.003) and K(trans) by 57% (p=0.003)], but remained unchanged in controls. No change between the pre- and post-treatment tumor apparent diffusion coefficients in either the cediranib- or vehicle-treated group was observed over the course of this study. The (18) F-fluoromisonidazole mean standardized uptake value decreased by 33% (p=0.008) in the cediranib group, but showed no significant change in the control group. Histological analysis showed that the number of CD31-positive vessels (59 per mm(2) ), the fraction of smooth muscle actin-positive vessels (80-87%) and the intercapillary distance (0.17 mm) were similar in cediranib- and vehicle-treated groups. The fraction of perfused blood vessels in cediranib-treated tumors (81 ± 7%) was lower than that in vehicle controls (91 ± 3%, p=0.02). The necrotic fraction was slightly higher in cediranib-treated rats (34 ± 12%) than in controls (26 ± 10%, p=0.23). These findings suggest that short-term treatment with cediranib causes a decrease in tumor perfusion/permeability across the tumor cross-section, but changes in vascular morphology, vessel density or tumor cellularity are not manifested at this early time point.

Use of a novel Arg-Gly-Asp radioligand, 18F-AH111585, to determine changes in tumor vascularity after antitumor therapy.

UNLABELLED: Despite the recent development of various radiolabeled Arg-Gly-Asp (RGD) peptides for imaging the alphavbeta3 integrin receptor, relatively little attention has been focused on the ability of these radiotracers to monitor changes in tumor vascularity after antitumor therapies. This study describes the favorable in vivo kinetics and tumor-targeting properties of 18F-AH111585, a novel 18F-RGD peptide, and its ability to monitor tumor vascularity noninvasively. METHODS: Mice bearing Lewis lung carcinoma (LLC) tumors or Calu-6 non-small cell lung tumor xenografts were used for in vivo biodistribution and small-animal PET imaging studies. In addition, some animals were treated with either low-dose paclitaxel or the vascular endothelial growth factor receptor-2 tyrosine kinase inhibitor ZD4190. Tumor uptake of 18F-AH111585 and microvessel density were then assessed. RESULTS: Biodistribution of 18F-AH111585 demonstrated rapid clearance from the blood and key background organs and good tumor accumulation, with 1.5 percentage injected dose per gram (%ID/g) present at 2 h after injection in LLC tumors. Small-animal PET imaging of Calu-6 tumors allowed visualization of tumors above background tissue, with mean baseline uptake of 2.2 %ID/g. Paclitaxel therapy reduced the microvessel density in LLC tumor-bearing mice and resulted in significantly reduced 18F-AH111585 tumor uptake (P<0.05). ZD4190 therapy resulted in a significant (31.8%) decrease in 18F-AH111585 uptake in Calu-6 tumors, compared with the vehicle control-treated Calu-6 tumors, which had a 26.9% increase in 18F-AH111585 uptake over the same period (P<0.01). CONCLUSION: 18F-AH111585 is a promising 18F-labeled RGD tracer that offers a new approach to noninvasively image tumor vasculature. This tracer may reveal important information in the assessment of the impact of antitumor therapies, in particular those that predominantly target tumor blood vessels.

Imaging of vulnerable atherosclerotic plaques with FDG-microPET: no FDG accumulation.

BACKGROUND: Non-invasive methods of evaluating atherosclerosis in humans and experimental animals are needed. Studies indicate that FDG-PET has a potential to detect vulnerable, inflamed atherosclerotic lesions. METHODS: Nine atherosclerotic apoE-deficient mice were PET scanned. Four to determine optimal timing for imaging, and five post mortem after 1h redistribution of FDG and again after sequential removal of the interscapular brown fat and the atherosclerotic aortic arch. Uptake in various tissues in fasting (n=13) and non-fasting (n=7) apoE-deficient mice, including atherosclerotic and non-atherosclerotic aorta, was measured. Finally, accelerated atherosclerosis was induced by carotid ligation (n=12), and FDG-uptake was measured. RESULTS: FDG accumulation initially thought to correspond to the atherosclerotic aortic arch was recorded. Removal of interscapular brown fat, but not atherosclerotic aortic arch, removed the signal. The aortic arch accumulated less FDG than the non-atherosclerotic thoracic aorta both in fasting (ratio 0.5, p=0.008) and non-fasting (ratio 0.33, p=0.02) conditions. Carotid atherosclerosis likewise failed to increase FDG-uptake compared to the non-ligated artery (ratio 1.03). CONCLUSION: Spontaneously developed advanced atherosclerotic lesions in aorta were, paradoxically, associated with reduced FDG uptake, and accelerated carotid atherosclerosis also failed to increase FDG-uptake. The results seriously question the potential of FDG-PET for imagining of advanced, vulnerable atherosclerotic lesions.

A comparison of the imaging characteristics and microregional distribution of 4 hypoxia PET tracers.

UNLABELLED: We compared the imaging characteristics and hypoxia selectivity of 4 hypoxia PET radiotracers ((18)F-fluoromisonidazole [(18)F-FMISO], (18)F-flortanidazole [(18)F-HX4], (18)F-fluoroazomycin arabinoside [(18)F-FAZA], and (64)Cu-diacetyl-bis(N4-methylsemicarbazone) [(64)Cu-ATSM]) in a single murine xenograft tumor model condition using small-animal PET imaging and combined ex vivo autoradiography and fluorescence immunohistochemistry. METHODS: Nude mice bearing SQ20b xenograft tumors were administered 1 of 4 hypoxia PET tracers and images acquired 80-90 min after injection. Frozen sections from excised tumors were then evaluated for tracer distribution using digital autoradiography and compared with histologic markers of tumor hypoxia (pimonidazole, carbonic anydrase 9 [CA9]) and vascular perfusion (Hoechst 33342). RESULTS: The highest tumor uptake was observed with (64)Cu-ATSM (maximum standardized uptake values [SUV(max)], 1.26 ± 0.13) and the lowest with (18)F-FAZA (SUVmax, 0.41 ± 0.24). (18)F-FMISO and (18)F-HX4 had similar intermediate tumor uptake (SUV(max), 0.76 ± 0.38 and 0.65 ± 0.19, respectively). Digital autoradiographs of hypoxia tracer distribution were compared pixel by pixel with images of immunohistochemistry stains. The fluorinated nitroimidazoles all showed radiotracer uptake increasing with pimonidazole and CA9 staining. (64)Cu-ATSM showed the opposite pattern, with highest radiotracer uptake observed in regions with the lowest pimonidazole and CA9 staining. CONCLUSION: The fluorinated nitroimidazoles showed similar tumor distributions when compared with immunohistochemistry markers of hypoxia. Variations in tumor standardized uptake value and normal tissue distribution may determine the most appropriate clinical setting for each tracer. (64)Cu-ATSM showed the highest tumor accumulation and little renal clearance. However, the lack of correlation between (64)Cu-ATSM distribution and immunohistochemistry hypoxia markers casts some doubt on the hypoxia selectivity of (64)Cu-ATSM.

Examining changes in [18 F]FDG and [18 F]FLT uptake in U87-MG glioma xenografts as early response biomarkers to treatment with the dual mTOR1/2 inhibitor AZD8055.

PURPOSE: The mTOR kinase inhibitor AZD8055 inhibits both mTORC1 and mTORC2 leading to disruption of glucose metabolism and proliferation pathways. This study assessed the impact of single and multiple doses of AZD8055 on the uptake of the glucose metabolism marker 2-deoxy-2-[(18) F]fluoro-D-glucose ([(18) F]FDG) and the proliferation marker 3'-deoxy-3'-[(18) F]fluorothymidine ([(18) F]FLT) in U87-MG glioma xenografts. PROCEDURES: Mice bearing U87-MG tumours received either vehicle or AZD8055 (20 mg/kg) once daily p.o. Mice were imaged with either [(18) F]FDG or [(18) F]FLT PET to assess treatment response. Comparisons were made between in vivo imaging and ex vivo histopathology data. RESULTS: Tumour uptake of [(18) F]FDG was reduced by 33 % 1 h after a single dose of AZD8055 and by 49 % following 4 days of dosing. These changes coincided with suppression of the mTOR pathway biomarkers pS6 and pAKT. In contrast, the effect of AZD8055 on [(18) F]FLT uptake was inconsistent. CONCLUSIONS: The very rapid change in [(18) F]FDG uptake following acute AZD8055 treatment suggests that this could be used as an early mechanistic biomarker of metabolic changes resulting from mTOR inhibition. The utility of [(18) F]FLT for measuring the anti-proliferative effect of AZD8055 remains unclear.

2-Deoxy-2-[18F]fluoro-D-glucose positron emission tomography demonstrates target inhibition with the potential to predict anti-tumour activity following treatment with the AKT inhibitor AZD5363.

PURPOSE: The phosphatidyl inositol 3 kinase, AKT and mammalian target of rapamycin are frequently deregulated in human cancer and are among one of the most promising targets for cancer therapy. AZD5363 (AstraZeneca) is an AKT inhibitor in phase 1 clinical trials. Given its utility in assessing glucose metabolism, we investigated the role of 2-Deoxy-2-[18F]fluoro-D-glucose (18F-FDG) positron emission tomography (PET) as a biomarker to demonstrate target inhibition and its potential to predict and demonstrate the anti-tumour activity of AZD5363. METHODS: 18F-FDG PETscans were performed in nude mice in a number of xenograft models (U87-MG glioblastoma, BT474C breast carcinoma and Calu-6 lung). Mice were fasted prior to imaging, and either static or dynamic 18F-FDG PET imaging was performed. RESULTS: We have shown that 18F-FDG uptake in tumour xenografts was reduced by 39% reduction compared to vehicle after a single dose of AZD5363, demonstrating activation of the AKT pathway after only 4 h of dosing. Multiple doses of AZD5363 showed an anti-tumour volume effect and a reduction in 18F-FDG uptake (28% reduction compared to vehicle), highlighting the potential of 18F-FDG PET as an efficacy biomarker. Furthermore, the degree of inhibition of 18F-FDG uptake corresponded with the sensitivity of the tumour model to AZD5363. The use of dynamic 18F-FDG PET and a two-compartmental analysis identified the mechanism of this change to be due to a change in cellular uptake of 18F-FDG following administration of AZD5363. CONCLUSIONS: We conclude that 18F-FDG PET is a promising pharmacodynamic biomarker of AKT pathway inhibition, with potential to predict and demonstrate anti-tumour activity. It is a biomarker that may stop ineffective drug schedules, helping to make early stop decisions and identify responding subsets of patients, resulting in improved clinical decision making both during drug development and patient management.

An evaluation of 2-deoxy-2-[18F]fluoro-D-glucose and 3'-deoxy-3'-[18F]-fluorothymidine uptake in human tumor xenograft models.

PURPOSE: The aim of this study is to assess the variability of 2-deoxy-2-[(18)F]fluoro-D: -glucose ([(18)F]-FDG) and 3'-deoxy-3'-[(18)F]-fluorothymidine ([(18)F]-FLT) uptake in pre-clinical tumor models and examine the relationship between imaging data and related histological biomarkers. PROCEDURES: [(18)F]-FDG and [(18)F]-FLT studies were carried out in nine human tumor xenograft models in mice. A selection of the models underwent histological analysis for endpoints relevant to radiotracer uptake. Comparisons were made between in vitro uptake, in vivo imaging, and ex vivo histopathology data using quantitative and semi-quantitative analysis. RESULTS: In vitro data revealed that [1-(14)C]-2-deoxy-D: -glucose ([(14)C]-2DG) uptake in the tumor cell lines was variable. In vivo, [(18)F]-FDG and [(18)F]-FLT uptake was highly variable across tumor types and uptake of one tracer was not predictive for the other. [(14)C]-2DG uptake in vitro did not predict for [(18)F]-FDG uptake in vivo. [(18)F]-FDG SUV was inversely proportional to Ki67 and necrosis levels and positively correlated with HKI. [(18)F]-FLT uptake positively correlated with Ki67 and TK1. CONCLUSION: When evaluating imaging biomarkers in response to therapy, the choice of tumor model should take into account in vivo baseline radiotracer uptake, which can vary significantly between models.

MEDI3617, a human anti-angiopoietin 2 monoclonal antibody, inhibits angiogenesis and tumor growth in human tumor xenograft models.

Angiopoietin 2 (Ang2) is an important regulator of angiogenesis, blood vessel maturation and integrity of the vascular endothelium. The correlation between the dynamic expression of Ang2 in tumors with regions of high angiogenic activity and a poor prognosis in many tumor types makes Ang2 an ideal drug target. We have generated MEDI3617, a human anti-Ang2 monoclonal antibody that neutralizes Ang2 by preventing its binding to the Tie2 receptor in vitro, and inhibits angiogenesis and tumor growth in vivo. Treatment of mice with MEDI3617 resulted in inhibition of angiogenesis in several mouse models including: FGF2-induced angiogenesis in a basement extract plug model, tumor and retinal angiogenesis. In xenograft tumor models, treatment with MEDI3617 resulted in a reduction in tumor angiogenesis and an increase in tumor hypoxia. The administration of MEDI3617 as a single agent to mice bearing human tumor xenografts resulted in tumor growth inhibition against a broad spectrum of tumor types. Combining MEDI3617 with chemotherapy or bevacizumab resulted in a delay in tumor growth and no body weight loss was observed in the combination groups. These results, combined with pharmacodynamic studies, demonstrate that treatment of tumor-bearing mice with MEDI3617 significantly inhibited tumor growth as a single agent by blocking tumor angiogenesis. Together, these data show that MEDI3617 is a robust antiangiogenic agent and support the clinical evaluation and biomarker development of MEDI3617 in cancer patients.

Preclinical pharmacology of AZD5363, an inhibitor of AKT: pharmacodynamics, antitumor activity, and correlation of monotherapy activity with genetic background.

AKT is a key node in the most frequently deregulated signaling network in human cancer. AZD5363, a novel pyrrolopyrimidine-derived compound, inhibited all AKT isoforms with a potency of 10 nmol/L or less and inhibited phosphorylation of AKT substrates in cells with a potency of approximately 0.3 to 0.8 µmol/L. AZD5363 monotherapy inhibited the proliferation of 41 of 182 solid and hematologic tumor cell lines with a potency of 3 µmol/L or less. Cell lines derived from breast cancers showed the highest frequency of sensitivity. There was a significant relationship between the presence of PIK3CA and/or PTEN mutations and sensitivity to AZD5363 and between RAS mutations and resistance. Oral dosing of AZD5363 to nude mice caused dose- and time-dependent reduction of PRAS40, GSK3ß, and S6 phosphorylation in BT474c xenografts (PRAS40 phosphorylation EC(50) ~ 0.1 µmol/L total plasma exposure), reversible increases in blood glucose concentrations, and dose-dependent decreases in 2[18F]fluoro-2-deoxy-D-glucose ((18)F-FDG) uptake in U87-MG xenografts. Chronic oral dosing of AZD5363 caused dose-dependent growth inhibition of xenografts derived from various tumor types, including HER2(+) breast cancer models that are resistant to trastuzumab. AZD5363 also significantly enhanced the antitumor activity of docetaxel, lapatinib, and trastuzumab in breast cancer xenografts. It is concluded that AZD5363 is a potent inhibitor of AKT with pharmacodynamic activity in vivo, has potential to treat a range of solid and hematologic tumors as monotherapy or a combinatorial agent, and has potential for personalized medicine based on the genetic status of PIK3CA, PTEN, and RAS. AZD5363 is currently in phase I clinical trials.

Dual IGF-I/II-neutralizing antibody MEDI-573 potently inhibits IGF signaling and tumor growth.

Insulin-like growth factors (IGF), IGF-I and IGF-II, are small polypeptides involved in regulating cell proliferation, survival, differentiation, and transformation. IGF activities are mediated through binding and activation of IGF-1R or insulin receptor isoform A (IR-A). The role of the IGF-1R pathway in promoting tumor growth and survival is well documented. Overexpression of IGF-II and IR-A is reported in multiple types of cancer and is proposed as a potential mechanism for cancer cells to develop resistance to IGF-1R-targeting therapy. MEDI-573 is a fully human antibody that neutralizes both IGF-I and IGF-II and inhibits IGF signaling through both the IGF-1R and IR-A pathways. Here, we show that MEDI-573 blocks the binding of IGF-I and IGF-II to IGF-1R or IR-A, leading to the inhibition of IGF-induced signaling pathways and cell proliferation. MEDI-573 significantly inhibited the in vivo growth of IGF-I- or IGF-II-driven tumors. Pharmacodynamic analysis demonstrated inhibition of IGF-1R phosphorylation in tumors in mice dosed with MEDI-573, indicating that the antitumor activity is mediated via inhibition of IGF-1R signaling pathways. Finally, MEDI-573 significantly decreased (18)F-fluorodeoxyglucose ((18)F-FDG) uptake in IGF-driven tumor models, highlighting the potential utility of (18)F-FDG-PET as a noninvasive pharmacodynamic readout for evaluating the use of MEDI-573 in the clinic. Taken together, these results demonstrate that the inhibition of IGF-I and IGF-II ligands by MEDI-573 results in potent antitumor activity and offers an effective approach to selectively target both the IGF-1R and IR-A signaling pathways.

Pharmacological validation of a telemetric model for the measurement of bronchoconstriction in conscious rats.

INTRODUCTION: Telemetric measurement of intra-pleural pressure in conscious animals that are restrained in head-out plethysmography chambers enables determination of airway resistance. Originally proposed over 10 years ago, pharmacological validation of this technique is limited. Here airway resistance in conscious, instrumented rats was compared to measurement in anaesthetised rats via a fluid filled oesophageal catheter following administration of two different pharmacological agents. METHODS: Male rats were implanted with telemetry devices and were trained to accept the restraint of head-out plethysmography chambers. A separate group of male rats were anaesthetised, placed in a body-enclosed plethysmography chamber and were prepared with a tracheal, oesphageal and jugular vein cannulae. Methacholine or NECA were given intravenously and changes in ventilation and airway resistance were measured. RESULTS: The pressure signal obtained in the telemetered rats was found to be extremely variable. Variability was confounded by excessive struggling, particularly during the infusion periods. Misplacement of the pressure sensitive catheter tip and prior habituation to the chamber were not factors in signal variability. Consequently, no dose-response relationship to either pharmacological agent was established in this model. Dose-dependent increases in resistance to both methacholine and NECA were measured in anaesthetised rats using body-enclosed plethysmography. DISCUSSION: Given the variability of the pressure signal within and between rats, the feasibility of a model in conscious rats for the measurement of airway resistance is questioned. Improved restraint methods or alternative models in conscious animals should therefore be explored. In the meantime, assessment of airway resistance is best confined to the anaesthetised rat.