Imaging anti-angiogenic treatment response with DCE-VCT, DCE-MRI and DWI in an animal model of breast cancer bone metastasis

Non-Invasive Characterization of Experimental Bone Metastasis in Obesity Using Multiparametric MRI and PET/CT

The growth of primary tumors and metastases is associated with excess body fat. In bone metastasis formation, the bone marrow microenvironment, and particularly adipocytes, play a pivotal role as growth mediators of disseminated tumor cells in the bone marrow. The aim of the present study is to non-invasively characterize the pathophysiologic processes in experimental bone metastasis resulting from accelerated tumor progression within adipocyte-rich bone marrow using multimodal imaging from magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT). To achieve this, we have employed small animal models after the administration of MDA-MB 231 breast cancer and B16F10 melanoma cells into the bone of nude rats or C57BL/6 mice, respectively. After tumor cell inoculation, ultra-high field MRI and µPET/CT were used to assess functional and metabolic parameters in the bone marrow of control animals (normal diet, ND), following a high-fat diet (HFD), and/or treated with the peroxisome proliferator-activated receptor-gamma (PPARγ) antagonist bisphenol-A-diglycidylether (BADGE), respectively. In the bone marrow of nude rats, dynamic contrast-enhanced MRI (DCE-MRI) and diffusion-weighted imaging (DWI), as well as [18F]fluorodeoxyglucose-PET/CT([18F]FDG-PET/CT), was performed 10, 20, and 30 days after tumor cell inoculation, followed by immunohistochemistry. DCE-MRI parameters associated with blood volume, such as area under the curve (AUC), were significantly increased in bone metastases in the HFD group 30 days after tumor cell inoculation as compared to controls (p < 0.05), while the DWI parameter apparent diffusion coefficient (ADC) was not significantly different between the groups. [18F]FDG-PET/CT showed an enhanced glucose metabolism due to increased standardized uptake value (SUV) at day 30 after tumor cell inoculation in animals that received HFD (p < 0.05). BADGE treatment resulted in the inversion of quantitative DCE-MRI and [18F]FDG-PET/CT data, namely a significant decrease in AUC and SUV in HFD-fed animals as compared to ND-fed controls (p < 0.05). Finally, immunohistochemistry and qPCR confirmed the HFD-induced stimulation in vascularization and glucose activity in murine bone metastases. In conclusion, multimodal and multiparametric MRI and [18F]FDG-PET/CT were able to derive quantitative parameters in bone metastases, revealing an increase in vascularization and glucose metabolism following HFD. Thus, non-invasive imaging may serve as a biomarker for assessing the pathophysiology of bone metastasis in obesity, opening novel options for therapy and treatment monitoring by MRI and [18F]FDG-PET/CT.

Clinical Applications of PET/MR Imaging

PET/MR imaging is in routine clinical use and is at least as effective as PET/CT for oncologic and neurologic studies with advantages with certain PET radiopharmaceuticals and applications. In addition, whole body PET/MR imaging substantially reduces radiation dosages compared with PET/CT which is particularly relevant to pediatric and young adult population. For cancer imaging, assessment of hepatic, pelvic, and soft-tissue malignancies may benefit from PET/MR imaging. For neurologic imaging, volumetric brain MR imaging can detect regional volume loss relevant to cognitive impairment and epilepsy. In addition, the single-bed position acquisition enables dynamic brain PET imaging without extending the total study length which has the potential to enhance the diagnostic information from PET.

Quantitative Dynamic Contrast-Enhanced MRI Identifies Radiation-Induced Vascular Damage in Patients With Advanced Osteoradionecrosis: Results of a Prospective Study

PURPOSE

We aim to characterize the quantitative dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) parameters associated with advanced mandibular osteoradionecrosis (ORN) compared with the contralateral normal mandible.

METHODS AND MATERIALS

Patients with a diagnosis of advanced ORN after curative-intent radiation treatment of head and neck cancer were prospectively enrolled after institutional review board approval and study-specific informed consent were obtained. Quantitative maps generated with the Tofts and extended Tofts pharmacokinetic models were used for analysis. Manual segmentation of advanced ORN 3-dimensional volume was done using anatomic sequences to create ORN volumes of interest (VOIs). Subsequently, normal mandibular VOIs were segmented on the contralateral healthy mandible of similar volume and anatomic location to create control VOIs. Finally, anatomic sequences were coregistered to DCE sequences, and contours were propagated to the respective parameter maps.

RESULTS

Thirty patients were included. The median time to ORN diagnosis after completion of IMRT was 38 months (range, 6-184 months), whereas median time to ORN progression to advanced grade after initial diagnosis was 5.6 months (range, 0-128 months). There were statistically significant higher K^trans and V_e in ORN-VOIs compared with controls (0.23 vs 0.07 min^-1, and 0.34 vs 0.15; P < .0001 for both). The average relative increase of K^trans in ORN-VOIs was 3.2-fold higher than healthy mandibular control VOIs. Moreover, the corresponding rise of V_e in ORN-VOIs was 2.7-fold higher than in the controls. Using combined K^trans and V_e parameters, 27 patients (90%) had at least a 200% increase of either of the studied parameters in the ORN-VOIs compared with their healthy mandible VOIs.

CONCLUSIONS

Our results confirm that there is a quantitatively significant higher degree of leakiness in the mandibular vasculature as measured using DCE-MRI parameters of areas with advanced ORN versus healthy mandible.

Diagnostic value of molybdenum target combined with DCE-MRI in different types of breast cancer

This study compared the diagnostic value of molybdenum target and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in different types of breast cancer. A retrospective analysis was performed on 120 female patients with breast cancer admitted to The First Affiliated Hospital of Zhengzhou University from February 2015 to October 2017. All of them underwent DCE-MRI and molybdenum target examination. Postoperatively, the pathological tissues were examined to determine their molecular typing. The sensitivity and diagnostic coincidence rates of Luminal-B breast cancer with different molecular types diagnosed by molybdenum target combined with DCE-MRI were significantly higher than those of molybdenum target or DCE-MRI alone. There were no statistical differences in sensitivity and diagnostic coincidence rates of breast cancer with different molecular types diagnosed by molybdenum target or DCE-MRI alone between the two groups (P>0.05). Molybdenum target combined with DCE-MRI in the diagnosis of different molecular types of breast cancer is better than the single imaging screening, which is of great clinical significance in the development of individualized comprehensive treatment for breast cancer patients and worthy of wide promotion in clinical practice.

Prediction of therapy response in bone-predominant metastatic breast cancer: comparison of [18F] fluorodeoxyglucose and [18F]-fluoride PET/CT with whole-body MRI with diffusion-weighted imaging

PURPOSE

To compare [18F]-fluorodeoxyglucose (FDG) and [18F]-sodium fluoride (NaF) positron emission tomography/computed tomography (PET/CT) with whole-body magnetic resonance with diffusion-weighted imaging (WB-MRI), for endocrine therapy response prediction at 8 weeks in bone-predominant metastatic breast cancer.

PATIENTS AND METHODS

Thirty-one patients scheduled for endocrine therapy had up to five bone metastases measured [FDG, NaF PET/CT: maximum standardized uptake value (SUVmax); WB-MRI: median apparent diffusion coefficient (ADCmed)] at baseline and 8 weeks. To detect the flare phenomenon, a 12-week NaF PET/CT was also performed if 8-week SUVmax increased. A 25% parameter change differentiated imaging progressive disease (PD) from non-PD and was compared to a 24-week clinical reference standard and progression-free survival (PFS).

RESULTS

Twenty-two patients (median age, 58.6 years, range, 40-79 years) completing baseline and 8-week imaging were included in the final analysis. Per-patient % change in NaF SUVmax predicted 24-week clinical PD with sensitivity, specificity and accuracy of 60, 73.3, and 70%, respectively. For FDG SUVmax the results were 0, 100, and 76.2% and for ADCmed, 0, 100 and 72.2%, respectively. PFS < 24 weeks was associated with % change in SUVmax (NaF: 41.7 vs. 0.7%, p = 0.039; FDG: - 4.8 vs. - 28.6%, p = 0.005) but not ADCmed (- 0.5 vs. 10.1%, p = 0.098). Interlesional response heterogeneity occurred in all modalities and NaF flare occurred in seven patients.

CONCLUSIONS

FDG PET/CT and WB-MRI best predicted clinical non-PD and both FDG and NaF PET/CT predicted PFS < 24 weeks. Lesional response heterogeneity occurs with all modalities and flare is common with NaF PET/CT.

New challenges in integrated diagnosis by imaging and osteo-immunology in bone lesions

INTRODUCTION

High-resolution imaging is the gold standard to measure the functional and biological features of bone lesions. Imaging markers have allowed the characterization both of tumour heterogeneity and metabolic data. Besides, ongoing studies are evaluating a combined use of 'imaging markers', such as SUVs, MATV, TLG, ADC from PET and MRI techniques respectively, and several 'biomarkers' spanning from chemokine immune-modulators, such as PD-1, RANK/RANKL, CXCR4/CXCL12 to transcription factors, such as TP53, RB1, MDM2, RUNX family, EZH2, YY1, MAD2. Osteoimmunology may improve diagnosis and prognosis leading to precision medicine in bone lesion treatment. Areas covered: We investigated modalities (molecular and imaging approach) useful to identify bone lesions deriving both from primary bone tumours and from osteotropic tumours, which have a higher incidence, prevalence and prognosis. Here, we summarized the recent advances in imaging techniques and osteoimmunology biomarkers which could play a pivotal role in personalized treatment. Expert commentary: Although imaging and molecular integration could allow both early diagnosis and stratification of cancer prognosis, large scale clinical trials will be necessary to translate pilot studies in the current clinical setting.

ABBREVIATIONS

ADC: apparent diffusion coefficient; ALCAM: Activated Leukocyte Cell Adhesion Molecule; ALP: Alkaline phosphatases; BC: Breast cancer; BSAP: B-Cell Lineage Specific Activator; BSAP: bone-specific alkaline phosphatase; BSP: bone sialoprotein; CRIP1: cysteine-rich intestinal protein 1; CD44: cluster of differentiation 44; CT: computed tomography; CXCL12: C-X-C motif ligand 12; CXCR4: C-X-C C-X-C chemokine receptor type 4; CTLA-4: Cytotoxic T-lymphocyte antigen 4; CTX-1: C-terminal end of the telopeptide of type I collagen; DC: dendritic cell; DWI: Diffusion-weighted MR image; EMT: mesenchymal transition; ET-1: endothelin-1; FDA: Food and Drug Administration; FDG: ¹⁸F-2-fluoro-2-deoxy-D-glucose; FGF: fibroblast growth factor; FOXC2: forkhead box protein C2: HK-2: hexokinase-2; ICTP: carboxyterminal cross-linked telopeptide of type I collagen; IGF-1R: Insulin Like Growth Factor 1 Receptor; ILC: innate lymphocytes cells; LC: lung cancer; IL-1: interleukin-1; LYVE1: lymphatic vessel endothelial hyaluronic acid receptor 1; MAD2: mitotic arrest deficient 2; MATV: metabolically active tumour volume; M-CSF: macrophage colony stimulating factor; MM: multiple myeloma; MIP1a: macrophage inflammatory protein 1a; MSC: mesenchymal stem cell; MRI: magnetic resonance imaging; PC: prostate cancer; NRP2: neuropilin 2; OPG: osteoprotogerin; PDGF: platelet-derived growth factor; PD-1: Programmed Cell Death 1; PET: positron emission tomography; PINP: procollagen type I N propeptide; PROX1: prospero homeobox protein 1; PSA: Prostate-specific antigen; PTH: parathyroid hormone; RANK: Receptor activator of NF-kB ligand; RECK: Reversion-inducing-cysteine-rich protein; SEMAs: semaphorins; SPECT: single photon computed tomography; SUV: standard uptake value; TLG: total lesion glycolysis; TP53: tumour protein 53; VCAM-1: vascular endothelial molecule-1; VOI: volume of interest; YY1: Yin Yang 1.

Perspectives: MRI of angiogenesis

Angiogenesis, the expansion of the vascular bed, is an important component in remodeling of tissues and organs. Such remodeling is essential for coping with substantial and sustained increase in the demands for supply of oxygen and nutrients and the timely removal of waste products. The vasculature, and its effectiveness in systemic delivery to all parts of the body, regulates the distribution of immune cells and the delivery of therapeutics as well as the dissemination of disease. Therefore, the vascular bed is possibly one of the key organs involved in homeostasis, in health and disease. The critical role of the vasculature in health, and the accessibility to non invasive probing by MRI, renders MRI as a modality of choice for monitoring the vasculature and its adaption to challenges.

Functional and Hybrid Imaging of Bone Metastases

Bone metastases are common, cause significant morbidity, and impact on healthcare resources. Although radiography, computed tomography (CT), magnetic resonance imaging (MRI), and bone scintigraphy have frequently been used for staging the skeleton, these methods are insensitive and nonspecific for monitoring treatment response in a clinically relevant time frame. We summarize several recent reports on new functional and hybrid imaging methods including single photon emission CT/CT, positron emission tomography/CT, and whole-body MRI with diffusion-weighted imaging. These modalities generally show improvements in diagnostic accuracy for staging and response assessment over standard imaging methods, with the ability to quantify biological processes related to the bone microenvironment as well as tumor cells. As some of these methods are now being adopted into routine clinical practice and clinical trials, further evaluation with comparative studies is required to guide optimal and cost-effective clinical management of patients with skeletal metastases. © 2018 American Society for Bone and Mineral Research.

Tumor Blood Vessel Visualization

Noninvasive multimodal imaging of tumor blood vessels allows the qualitative and quantitative assessment of morphological, functional, and molecular features of tumor angiogenesis longitudinally in a living organism. In this chapter we focus on the application of magnetic resonance imaging (MRI), computed tomography (CT), ultrasound (US), and positron emission tomography (PET) in tumor blood vessel visualization on the example of breast cancer bone metastasis in a nude rat model. Thereby, materials and methods are described that are needed to obtain complementary data on tumor vascularization from these imaging techniques.

Accelerated Brain DCE-MRI Using Iterative Reconstruction With Total Generalized Variation Penalty for Quantitative Pharmacokinetic Analysis: A Feasibility Study

PURPOSE

To investigate the feasibility of using undersampled k-space data and an iterative image reconstruction method with total generalized variation penalty in the quantitative pharmacokinetic analysis for clinical brain dynamic contrast-enhanced magnetic resonance imaging.

METHODS

Eight brain dynamic contrast-enhanced magnetic resonance imaging scans were retrospectively studied. Two k-space sparse sampling strategies were designed to achieve a simulated image acquisition acceleration factor of 4. They are (1) a golden ratio-optimized 32-ray radial sampling profile and (2) a Cartesian-based random sampling profile with spatiotemporal-regularized sampling density constraints. The undersampled data were reconstructed to yield images using the investigated reconstruction technique. In quantitative pharmacokinetic analysis on a voxel-by-voxel basis, the rate constant K^trans in the extended Tofts model and blood flow F_B and blood volume V_B from the 2-compartment exchange model were analyzed. Finally, the quantitative pharmacokinetic parameters calculated from the undersampled data were compared with the corresponding calculated values from the fully sampled data. To quantify each parameter's accuracy calculated using the undersampled data, error in volume mean, total relative error, and cross-correlation were calculated.

RESULTS

The pharmacokinetic parameter maps generated from the undersampled data appeared comparable to the ones generated from the original full sampling data. Within the region of interest, most derived error in volume mean values in the region of interest was about 5% or lower, and the average error in volume mean of all parameter maps generated through either sampling strategy was about 3.54%. The average total relative error value of all parameter maps in region of interest was about 0.115, and the average cross-correlation of all parameter maps in region of interest was about 0.962. All investigated pharmacokinetic parameters had no significant differences between the result from original data and the reduced sampling data.

CONCLUSION

With sparsely sampled k-space data in simulation of accelerated acquisition by a factor of 4, the investigated dynamic contrast-enhanced magnetic resonance imaging pharmacokinetic parameters can accurately estimate the total generalized variation-based iterative image reconstruction method for reliable clinical application.

Multimodal imaging of bone metastases: From preclinical to clinical applications

Metastases to the skeletal system are commonly observed in cancer patients, highly affecting the patients' quality of life. Imaging plays a major role in detection, follow-up, and molecular characterisation of metastatic disease. Thus, imaging techniques have been optimised and combined in a multimodal and multiparametric manner for assessment of complementary aspects in osseous metastases. This review summarises both application of the most relevant imaging techniques for bone metastasis in preclinical models and the clinical setting.

Contrast-Enhanced Computed Tomography Evaluation of Hepatic Metastases in Breast Cancer Patients Before and After Cytotoxic Chemotherapy or Targeted Therapy

PURPOSE

To evaluate change in size vs computed tomography (CT) density of hepatic metastases in breast cancer patients before and after cytotoxic chemotherapy or targeted therapy.

METHODS

A database search in a single institution identified 48 breast cancer patients who had hepatic metastases treated with either cytotoxic chemotherapy alone or targeted therapy alone, and who had contrast-enhanced CT (CECT) scans of the abdomen at baseline and within 4 months of initiation of therapy in the past 10 years. Two radiologists retrospectively evaluated CT scans and identified up to 2 index lesions in each patient. The size (centimeters) of each lesion was measured according to Response Evaluation Criteria in Solid Tumors (RECIST) criteria, and CT density (Hounsfield units) was measured by drawing a region of interest around the margin of the entire lesion. The percent change in sum of lesion size and mean CT density on pre- and post-treatment scans was computed for each patient; results were compared within each treatment group.

RESULTS

Thirty-nine patients with 68 lesions received cytotoxic chemotherapy only; 9 patients with 15 lesions received targeted therapy only. The mean percent changes in sum of lesion size and mean CT density were statistically significant within the cytotoxic chemotherapy group before and after treatment, but not significant in the targeted therapy group. The patients in the targeted therapy group tend to have better 2-year survival. The patients who survived at 2 years tend to have more decrease in tumour size in the cytotoxic chemotherapy group.

CONCLUSION

Cytotoxic chemotherapy produced significant mean percent decrease in tumour size and mean CT density of hepatic metastases from breast cancer before and after treatment, whereas targeted therapy did not. Nonetheless, there is a trend that the patients in the targeted therapy group had better 2-year survival rate. This suggests that RECIST is potentially inadequate in evaluating tumour response in breast cancer liver metastases treated with targeted therapy alone, calling for an alternative marker for response evaluation in this subset of patients.

Monitoring the response of bone metastases to treatment with Magnetic Resonance Imaging and nuclear medicine techniques: a review and position statement by the European Organisation for Research and Treatment of Cancer imaging group

Assessment of the response to treatment of metastases is crucial in daily oncological practice and clinical trials. For soft tissue metastases, this is done using computed tomography (CT), Magnetic Resonance Imaging (MRI) or Positron Emission Tomography (PET) using validated response evaluation criteria. Bone metastases, which frequently represent the only site of metastases, are an exception in response assessment systems, because of the nature of the fixed bony defects, their complexity, which ranges from sclerotic to osteolytic and because of the lack of sensitivity, specificity and spatial resolution of the previously available bone imaging methods, mainly bone scintigraphy. Techniques such as MRI and PET are able to detect the early infiltration of the bone marrow by cancer, and to quantify this infiltration using morphologic images, quantitative parameters and functional approaches. This paper highlights the most recent developments of MRI and PET, showing how they enable early detection of bone lesions and monitoring of their response. It reviews current knowledge, puts the different techniques into perspective, in terms of indications, strengths, weaknesses and complementarity, and finally proposes recommendations for the choice of the most adequate imaging technique.

Assessing treatment response of osteolytic lesions by manual volumetry, automatic segmentation, and RECIST in experimental bone metastases

RATIONALE AND OBJECTIVES

Aim of the study was to compare between volumetric and unidimensional approaches for treatment response monitoring in a nude rat model of experimental bone metastases. For the volumetric approach, an automated segmentation algorithm of osteolytic lesions was introduced and compared to manual volumetry.

MATERIAL AND METHODS

Nude rats bearing osteolytic metastases were treated with zoledronate and sunitinib and compared to controls. Treatment response was assessed longitudinally in vivo using flat-panel volumetric computed tomography at days 30, 35, 45, and 55 after tumor cell inoculation. The mean sizes and volumes of osteolytic lesions were determined according to response evaluation criteria in solid tumors (RECIST) and by automated and manual volumetry (software: MITK [The Medical Imaging Interaction Toolkit, Heidelberg, Germany] and VIRTUOS, Heidelberg, Germany).

RESULTS

In contrary to RECIST, the manual volumetric approach indicated a significant decrease in osteolytic lesion volume in response to treatment. The presented automatic segmentation algorithm for treatment monitoring identified bone metastases adequately and assessed changes in the osteolytic lesion volume over time according to manual volumetry.

CONCLUSIONS

In an animal model, volumetric treatment response assessment of osteolytic bone metastases is superior to unidimensional measurements, and automated volumetric segmentation may be a valuable alternative to manual volume determination.

Osteoporosis influences osteogenic but not angiogenic response during bone defect healing in a rat model

Angiogenesis is pivotal for bone metabolism and bone defect healing. Yet the role of vascularization in osteoporosis and osteoporotic bone repair mechanisms is unclear. Here we investigated effects of osteoporotic phenotype on vascularization during bone defect healing in a rodent osteotomy model using volumetric computed tomography (VCT), dynamic contrast-enhanced VCT (DCE-VCT), dynamic contrast-enhanced MRI (DCE-MRI) and histology. In 16 rats, 8 with physiological bone status (SHAM) and 8 with osteoporotic bone status induced by ovariectomy (OVX) in combination with a vitamin D- and low calcium diet, wedge-shaped defects were created at the left distal femur and stabilized internally by T-shaped miniplate. MRI and VCT were performed in all animals 6 weeks after this procedure. By VCT, relative bone density in the defect was evaluated. Using DCE-VCT and DCE-MRI, parameters associated with regional blood volume were calculated in the bone defect, vicinity of the defect, surrounding muscles and bone marrow: Amplitude A and exchange rate constant Kep (DCE-MRI, respectively) as well as peak enhancement PE and area under the curve AUC (DCE-VCT, respectively). In animals of osteoporotic phenotype, bone density within the osseous defect was significantly reduced as compared to SHAM rats. Vascularization parameters determined by DCE-MRI and DCE-VCT in the defect were significantly elevated compared to the adjacent tissues for both SHAM and OVX groups. However, comparing SHAM and OVX rats, no statistically different values were found by DCE-MRI and DCE-VCT concerning any determined vascularization parameter within the bone defect. Furthermore, parameters of vascularization were increased for OVX as compared to SHAM rats within the bone marrow although significant difference was only found for A. In a rat osteotomy model we showed that at the reparative healing stage, osteoporotic phenotype did influence osteogenic but not angiogenic response within bone defect as imaged by DCE-MRI and DCE-VCT. This study provides insight into the relationship between angiogenesis and osteogenesis during osteoporosis-related compromised bone healing.

Dynamic gadobutrol-enhanced MRI predicts early response to antivascular but not to antiproliferation therapy in a mouse xenograft model

PURPOSE

Dynamic contrast-enhanced magnetic resonance imaging has been described as a method to assess tumor vascularity and, therefore, is discussed as a noninvasive biomarker for drug response prediction in tumor therapies. Because antiangiogenic and antiproliferative drugs are frequently combined for therapy, the aim was to investigate (1) the early response predictability and (2) the extent to which these therapy types influence dynamic contrast-enhanced magnetic resonance imaging with gadobutrol soon after therapy initiation.

METHODS

Mice bearing a KPL-4 tumor were treated with either bevacizumab as an antiangiogenic drug or trastuzumab as a cytotoxic anti-tumor drug. The gadobutrol-contrast agent exposure of the tumor was recorded before and at several time points after therapy initiation to examine the response prediction by dynamic contrast-enhanced magnetic resonance imaging.

RESULTS

Both therapies resulted in significant tumor growth attenuation over 30 days of therapy, but the individual response to each therapy was different. Specifically, bevacizumab affected the dynamic gadobutrol-enhanced MRI-derived area under the curve at early time points (≤8 days), while trastuzumab did not.

CONCLUSION

The area under the curve obtained from dynamic gadobutrol-enhanced MRI predicted early tumor response to the antiangiogenic drug bevacizumab, but not to the anti-tumor cell drug trastuzumab. This indicates that the area under the curve may be useful for assessing early antiangiogenic but not antiproliferative drug effects.

Quantitative assessment of microcirculation and diffusion in the bone marrow of osteoporotic rats using VCT, DCE-MRI, DW-MRI, and histology

BACKGROUND

Etiologic and pathophysiologic role of functional bone marrow processes is not fully understood especially in the case of osteoporosis.

PURPOSE

To investigate the role of vascularization and diffusion in rat models of osteoporosis through a cross-correlation between non-invasive in-vivo imaging and invasive ex-vivo imaging of bone, bone marrow, and in particular of microcirculation.

MATERIAL AND METHODS

Osteoporosis was induced in rats by combining ovariectomy (OVX) with calcium and Vitamin D3 deficiency, or with glucocorticoid (dexamethasone). For comparison, controls underwent a sham surgery. In in-vivo investigations, animals (n = 36) were examined by volumetric CT (VCT) and MRI at 1, 3, or 12 months post surgery. Using VCT, bone morphology was monitored and relative bone density r within pelvis was extracted. With DCE-MRI and DW-MRI, parameters A (amplitude), Kep (exchange rate constant), and ADC (apparent diffusion coefficient) were acquired for regions of lumbar vertebrae, pelvis, and femur. In ex-vivo investigations, selective histological sections of pelvis were either stained with hematoxylin and eosin (HE stain) for quantifying vessel size and density or immunostained for collagen IV and α-smooth muscle actin to assess vessel maturity (SMA/collagen IV ratio).

RESULTS

After 12 months, decrease in DCE-MRI parameter Kep was found in all locations of osteoporotic rats (strongest in femur and lumbar vertebrae) while no significant differences were seen for parameter A and DW-MRI parameter ADC. Furthermore, vessel rarefication and maturation were observed on the histological level in animals with osteoporotic phenotype. In particular in the pelvis, the osteoporotic individuals (irrespective of the osteoporosis inducers applied) exhibited decreased Kep, significantly reduced vessel density, significantly increased vessel maturity, as well as statistically unaltered A, ADC, and vessel diameter.

CONCLUSION

Changes in microcirculation but not diffusion in the bone marrow of osteoporotic rats are detected by DCE-MRI and DW-MRI due to vessel rarefication and maturation.

Non-invasive imaging for studying anti-angiogenic therapy effects

Noninvasive imaging plays an emerging role in preclinical and clinical cancer research and has high potential to improve clinical translation of new drugs. This article summarises and discusses tools and methods to image tumour angiogenesis and monitor anti-angiogenic therapy effects. In this context, micro-computed tomography (µCT) is recommended to visualise and quantify the micro-architecture of functional tumour vessels. Contrast-enhanced ultrasound (US) and magnetic resonance imaging (MRI) are favourable tools to assess functional vascular parameters, such as perfusion and relative blood volume. These functional parameters have been shown to indicate anti-angiogenic therapy response at an early stage, before changes in tumour size appear. For tumour characterisation, the imaging of the molecular characteristics of tumour blood vessels, such as receptor expression, might have an even higher diagnostic potential and has been shown to be highly suitable for therapy monitoring as well. In this context, US using targeted microbubbles is currently evaluated in clinical trials as an important tool for the molecular characterisation of the angiogenic endothelium. Other modalities, being preferably used for molecular imaging of vessels and their surrounding stroma, are photoacoustic imaging (PAI), near-infrared fluorescence optical imaging (OI), MRI, positron emission tomography (PET) and single photon emission computed tomography (SPECT). The latter two are particularly useful if very high sensitivity is needed, and/or if the molecular target is difficult to access. Carefully considering the pros and cons of different imaging modalities in a multimodal imaging setup enables a comprehensive longitudinal assessment of the (micro)morphology, function and molecular regulation of tumour vessels.

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.

Calibration of cone beam CT using relative attenuation ratio for quantitative assessment of bone density: a small animal study

PURPOSE

Cone beam computed tomography (CBCT) has the disadvantage of providing non-quantitative results for bone density determination. The aim of this study is to calibrate CBCT results by using an internal reference (such as muscle) for quantitatively assessing bone density.

METHODS

We developed a new method using the relative attenuation ratio between two nearby materials (such as bone and muscle) for systemic error correction in CBCT that depends on the relative object position in the image volume. Phantom calibration was performed to calculate the acquired attenuation ratio in Hounsfield units (HU), comparable to the results from clinical multislice spiral computed tomography (MSCT). In addition, a small animal study with an osteoporotic rat model was evaluated to show the feasibility of this presented method to quantitatively assess bone density using a CBCT system.

RESULTS

The phantom study results showed that the calibration process successfully corrected the systemic inaccuracy from CBCT, and the calibrated HU values agreed with the values measured from MSCT. In the small animal study, the quantitative bone densities assessed from the calibrated CBCT results were consistent with the results from MSCT data.

CONCLUSION

A practical method to quantitatively estimate attenuation (HU) values for bone tissues from CBCT scans that are comparable to MSCT scans is proposed. The method may improve the quantification ability of CBCT scanning without any additional hardware requirements.

Multimodality imaging of tumor and bone response in a mouse model of bony metastasis

Cancer drug development generally performs in vivo evaluation of treatment effects that have traditionally relied on detection of morphologic changes. The emergence of new targeted therapies, which may not result in gross morphologic changes, has spurred investigation into more specific imaging methods to quantify response, such as targeted fluorescent probes and bioluminescent cells. The present study investigated tissue response to docetaxel or zoledronic acid (ZA) in a mouse model of bony metastasis. Intratibial implantations of breast cancer cells (MDA-MB-231) were monitored throughout this study using several modalities: molecular resonance imaging (MRI) tumor volume and apparent diffusion coefficient (ADC), micro-computed tomography (µCT) bone volume, bioluminescence imaging (BLI) reporting cancer cell apoptosis, and fluorescence using Osteosense 800 and CatK 680-FAST. Docetaxel treatment resulted in tumor cell kill reflected by ADC and BLI increases and tumor volume reduction, with delayed bone recovery seen in µCT prefaced by increased osteoblastic activity (Osteosense 800). In contrast, the ZA treatment group produced similar values in MRI, BLI, and Osteosense 800 fluorescence imaging readouts when compared to controls. However, µCT bone volume increased significantly by the first week post-treatment and the CatK 680-FAST signal was slightly diminished by 4 weeks following ZA treatment. Multimodality imaging provides a more comprehensive tool for new drug evaluation and efficacy screening through identification of morphology as well as function and apoptotic signaling.

Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) in Preclinical Studies of Antivascular Treatments

Antivascular treatments can either be antiangiogenic or targeting established tumour vasculature. These treatments affect the tumour microvasculature and microenvironment but may not change clinical measures like tumour volume and growth. In research on antivascular treatments, information on the tumour vasculature is therefore essential. Preclinical research is often used for optimization of antivascular drugs alone or in combined treatments. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is an in vivo imaging method providing vascular information, which has become an important tool in both preclinical and clinical research. This review discusses common DCE-MRI imaging protocols and analysis methods and provides an overview of preclinical research on antivascular treatments utilizing DCE-MRI.

Multi-modal imaging of angiogenesis in a nude rat model of breast cancer bone metastasis using magnetic resonance imaging, volumetric computed tomography and ultrasound

Angiogenesis is an essential feature of cancer growth and metastasis formation. In bone metastasis, angiogenic factors are pivotal for tumor cell proliferation in the bone marrow cavity as well as for interaction of tumor and bone cells resulting in local bone destruction. Our aim was to develop a model of experimental bone metastasis that allows in vivo assessment of angiogenesis in skeletal lesions using non-invasive imaging techniques. For this purpose, we injected 10(5) MDA-MB-231 human breast cancer cells into the superficial epigastric artery, which precludes the growth of metastases in body areas other than the respective hind leg. Following 25-30 days after tumor cell inoculation, site-specific bone metastases develop, restricted to the distal femur, proximal tibia and proximal fibula. Morphological and functional aspects of angiogenesis can be investigated longitudinally in bone metastases using magnetic resonance imaging (MRI), volumetric computed tomography (VCT) and ultrasound (US). MRI displays morphologic information on the soft tissue part of bone metastases that is initially confined to the bone marrow cavity and subsequently exceeds cortical bone while progressing. Using dynamic contrast-enhanced MRI (DCE-MRI) functional data including regional blood volume, perfusion and vessel permeability can be obtained and quantified. Bone destruction is captured in high resolution using morphological VCT imaging. Complementary to MRI findings, osteolytic lesions can be located adjacent to sites of intramedullary tumor growth. After contrast agent application, VCT angiography reveals the macrovessel architecture in bone metastases in high resolution, and DCE-VCT enables insight in the microcirculation of these lesions. US is applicable to assess morphological and functional features from skeletal lesions due to local osteolysis of cortical bone. Using B-mode and Doppler techniques, structure and perfusion of the soft tissue metastases can be evaluated, respectively. DCE-US allows for real-time imaging of vascularization in bone metastases after injection of microbubbles. In conclusion, in a model of site-specific breast cancer bone metastases multi-modal imaging techniques including MRI, VCT and US offer complementary information on morphology and functional parameters of angiogenesis in these skeletal lesions.

Ethanol protects from injury due to ischemia and reperfusion by increasing vascularity via vascular endothelial growth factor

The cardioprotective effects of moderate ethanol consumption have been known for years and have generally been ascribed to long-term effects of alcohol on blood lipids. However, other mechanisms, particularly ethanol-induced increase in blood vessel density, may also be involved. Our goal was to understand the relationship between ethanol consumption, new blood vessel formation in vivo and protection from injury due to ischemia and ischemia/reperfusion. Using paired ethanol fed and control rats, we assessed capillary density in the heart, brain and skeletal muscle by immunostaining and quantified expression of vascular endothelial growth factor (VEGF) by Western blot analysis and immunocytochemistry. Numbers of vessels were significantly increased in the brain, heart and skeletal muscle of animals fed ethanol-rich diets. VEGF (and its receptors) were upregulated in these organs. These effects were very rapid: highly significantly increased vascularization was seen within 2 weeks of commencing alcohol feeding. A neutralizing VEGF antibody, bevacizumab, inhibited new blood vessel formation induced by moderate doses of ethanol. Ethanol consumption increased vascularization and promoted skeletal muscle regeneration following hindlimb ischemia; these effects were prevented by bevacizumab. Finally, ethanol consumption protected myocardium following experimental ischemia/reperfusion.

CONCLUSION

Experimental ethanol ingestion rapidly increases VEGF production, significantly increasing the capillary bed in the heart, brain, and skeletal muscle. Moreover, the ethanol-induced increase of blood vessel density is protective against ischemic events (i.e., hindlimb ischemia and myocardium ischemia/reperfusion) and promotes skeletal muscle regeneration.

DCE and DW-MRI monitoring of vascular disruption following VEGF-Trap treatment of a rat glioma model

Vascular-targeted therapies have shown promise as adjuvant cancer treatment. As these agents undergo clinical evaluation, sensitive imaging biomarkers are needed to assess drug target interaction and treatment response. In this study, dynamic contrast enhanced MRI (DCE-MRI) and diffusion-weighted MRI (DW-MRI) were evaluated for detecting response of intracerebral 9 L gliosarcomas to the antivascular agent VEGF-Trap, a fusion protein designed to bind all forms of Vascular Endothelial Growth Factor-A (VEGF-A) and Placental Growth Factor (PGF). Rats with 9 L tumors were treated twice weekly for two weeks with vehicle or VEGF-Trap. DCE- and DW-MRI were performed one day prior to treatment initiation and one day following each administered dose. Kinetic parameters (K(trans), volume transfer constant; k(ep), efflux rate constant from extravascular/extracellular space to plasma; and v(p), blood plasma volume fraction) and the apparent diffusion coefficient (ADC) over the tumor volumes were compared between groups. A significant decrease in kinetic parameters was observed 24 hours following the first dose of VEGF-Trap in treated versus control animals (p < 0.05) and was accompanied by a decline in ADC values. In addition to the significant hemodynamic effect, VEGF-Trap treated animals exhibited significantly longer tumor doubling times (p < 0.05) compared to the controls. Histological findings were found to support imaging response metrics. In conclusion, kinetic MRI parameters and change in ADC have been found to serve as sensitive and early biomarkers of VEGF-Trap anti-vascular targeted therapy.

Evaluation of DCE-MRI postprocessing techniques to assess metastatic bone marrow in patients with prostate cancer

Dynamic contrast-enhanced magnetic resonance imaging was performed in control patients with normal bone marrow and patients with untreated bone metastases of prostate cancer (PCa). Perfusion data were assessed using region of interest-based and pixel-wise current standard postprocessing techniques (signal intensity pattern, increase in signal intensity, upslope, time to peak, extended Kety model, k-means clustering). Bone marrow perfusion is significantly increased in bone metastases of PCa compared to normal bone marrow. Pixel-wise kinetic modeling should be recommended to assess tumoral processes affecting bone marrow microcirculation.

Is apparent diffusion coefficient reliable and accurate for monitoring effects of antiangiogenic treatment in a longitudinal study?

PURPOSE

To evaluate the reliability and accuracy of the apparent diffusion coefficient (ADC) for monitoring antiangiogenic treatment in a longitudinal study.

MATERIALS AND METHODS

Tumor volume and ADC were monitored by T2-weighted magnetic resonance imaging (MRI) and diffusion-weighted MRI, respectively, in 18 mice with angiogenesis-dependent tumors (U118MG) before (day 0) and after 2, 7, 14, and 21 days of administration of the antiangiogenic agent sunitinib maleate (n = 12) or vehicle (n = 6). Percent changes in tumor volume and ADC were calculated and correlations between tumor volume and ADC were evaluated.

RESULTS

Tumor volume and ADC showed a negative correlation at 69 of the 72 (96%) follow-up measurements. In the 13 mice with tumor regrowth, ADC started to decrease before (27%) or at the same time (73%) as tumor regrowth. Pretreatment ADC and percent change in ADC change on days 0-2 were similar in mice with positive and negative responses to treatment (0.851 vs. 0.999, 24% vs. 16%). Percent change of ADC showed significant negative correlation with percent change in tumor volume in both the control (r = -0.69) and treated (r = -0.65) groups.

CONCLUSION

Percent change in ADC is a reliable and accurate marker for monitoring the effects of antiangiogenic treatment, whereas pretreatment ADC and early changes in ADC (ie, days 0-2) are limited in predicting treatment outcome.

Value of DCE-MRI and FDG-PET/CT in the prediction of response to preoperative chemotherapy with bevacizumab for colorectal liver metastases

Background:

The purpose of this study was to assess the role of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and ¹⁸F-fluorodeoxyglucose positron emission tomography computed tomography (FDG-PET/CT) for evaluation of response to chemotherapy and bevacizumab and for prediction of progression-free survival (PFS) in patients with metastatic colorectal cancer (mCRC) with potentially resectable liver lesions.

Methods:

A total of 19 mCRC patients were treated with FOLFOX/FOLFIRI and bevacizumab followed by surgery. Dynamic contrast-enhanced magnetic resonance imaging and FDG-PET/CT were performed before treatment and after cycle 5. PET results were quantified by calculating maximum standardised uptake value (SUV_max) whereas area under the enhancement curve (AUC), initial AUC (iAUC) and the endothelial transfer constant (K^trans) were used to quantify DCE-MRI. Pathological analysis of the resection specimen was performed, including measurement of microvessel density (MVD) and proliferation index.

Results:

Both AUC and iAUC were significantly decreased following bevacizumab therapy (median change of 22% (P=0.002) and 40% (P=0.001) for AUC and iAUC, respectively). Progression-free survival benefit was shown for patients with >40% reduction in K^trans (P=0.019). In the group of radiological responders, the median baseline SUV_max was 3.77 (IQR: 2.88–5.60) compared with 7.20 (IQR: 4.67–8.73) in nonresponders (P=0.021). A higher follow-up SUV_max was correlated with worse PFS (P=0.012). Median MVD was 10.9. Progression-free survival was significantly shorter in patients with an MVD greater than 10, compared with patients with lower MVD (10 months compared with 16 months, P=0.016).

Conclusion:

High relative decrease in K^trans, low follow-up SUV_max and low MVD are favourable prognostic factors for mCRC patients treated with bevacizumab before surgery.

Prediction of glioblastoma multiform response to bevacizumab treatment using multi-parametric MRI

Glioblastoma multiform (GBM) is a highly malignant brain tumor. Bevacizumab is a recent therapy for stopping tumor growth and even shrinking tumor through inhibition of vascular development (angiogenesis). This paper presents a non-invasive approach based on image analysis of multi-parametric magnetic resonance images (MRI) to predict response of GBM to this treatment. The resulting prediction system has potential to be used by physicians to optimize treatment plans of the GBM patients. The proposed method applies signal decomposition and histogram analysis methods to extract statistical features from Gd-enhanced regions of tumor that quantify its microstructural characteristics. MRI studies of 12 patients at multiple time points before and up to four months after treatment are used in this work. Changes in the Gd-enhancement as well as necrosis and edema after treatment are used to evaluate the response. Leave-one-out cross validation method is applied to evaluate prediction quality of the models. Predictive models developed in this work have large regression coefficients (maximum R² = 0.95) indicating their capability to predict response to therapy.

Differential microstructure and physiology of brain and bone metastases in a rat breast cancer model by diffusion and dynamic contrast enhanced MRI

Pharmacological approaches to treat breast cancer metastases in the brain have been met with limited success. In part, the impermeability of the blood brain barrier (BBB) has hindered delivery of chemotherapeutic agents to metastatic tumors in the brain. BBB-permeable chemotherapeutic drugs are being developed, and noninvasively assessing the efficacy of these agents will be important in both preclinical and clinical settings. In this regard, dynamic contrast enhanced (DCE) and diffusion weighted imaging (DWI) are magnetic resonance imaging (MRI) techniques to monitor tumor vascular permeability and cellularity, respectively. In a rat model of metastatic breast cancer, we demonstrate that brain and bone metastases develop with distinct physiological characteristics as measured with MRI. Specifically, brain metastases have limited permeability of the BBB as assessed with DCE and an increased apparent diffusion coefficient (ADC) measured with DWI compared to the surrounding brain. Microscopically, brain metastases were highly infiltrative, grew through vessel co-option, and caused extensive edema and injury to the surrounding neurons and their dendrites. By comparison, metastases situated in the leptomenengies or in the bone had high vascular permeability and significantly lower ADC values suggestive of hypercellularity. On histological examination, tumors in the bone and leptomenengies were solid masses with distinct tumor margins. The different characteristics of these tissue sites highlight the influence of the microenvironment on metastatic tumor growth. In light of these results, the suitability of DWI and DCE to evaluate the response of chemotherapeutic and anti-angiogenic agents used to treat co-opted brain metastases, respectively, remains a formidable challenge.

Dynamic contrast-enhanced MR imaging findings of bone metastasis in patients with prostate cancer

AIM: To evaluate the dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) findings of bone metastasis in prostate cancer patients.

METHODS: Sixteen men with a diagnosis of metastatic prostate cancer to bones were examined with DCE-MRI at 1.5 Tesla. The mean contrast agent concentration vs time curves for bone metastasis and normal bone were calculated and K^trans and ve values were estimated and compared.

RESULTS: An early significant enhancement (wash-out: n = 6, plateau: n = 8 and persistent: n = 2) was detected in all bone metastases (n = 16). Bone metastasis from prostate cancer showed significant enhancement and high K^trans and ve values compared to normal bone which does not enhance in the elderly population. The mean K^trans was 0.101/min and 0.0051/min (P < 0.001), the mean ve was 0.141 and 0.0038 (P < 0.001), for bone metastases and normal bone, respectively.

CONCLUSION: DCE-MRI and its quantitative perfusion parameters may have a role in improving the detection of skeletal metastasis in prostate cancer patients.

Applications of molecular imaging

Today molecular imaging technologies play a central role in clinical oncology. The use of imaging techniques in early cancer detection, treatment response, and new therapy development is steadily growing and has already significantly impacted on clinical management of cancer. In this chapter, we overview three different molecular imaging technologies used for the understanding of disease biomarkers, drug development, or monitoring therapeutic outcome. They are (1) optical imaging (bioluminescence and fluorescence imaging), (2) magnetic resonance imaging (MRI), and (3) nuclear imaging (e.g., single-photon emission computed tomography (SPECT) and positron emission tomography (PET)). We review the use of molecular reporters of biological processes (e.g., apoptosis and protein kinase activity) for high-throughput drug screening and new cancer therapies, diffusion MRI as a biomarker for early treatment response and PET and SPECT radioligands in oncology.

Cilengitide inhibits progression of experimental breast cancer bone metastases as imaged noninvasively using VCT, MRI and DCE-MRI in a longitudinal in vivo study

The aim of this study was to investigate the effect of inhibiting αvβ(3)/α(v) β(5) integrins by cilengitide in experimentally induced breast cancer bone metastases using noninvasive imaging techniques. For this purpose, nude rats bearing established breast cancer bone metastases were treated with cilengitide, a small molecule inhibitor of αvβ(3) and αvβ(5) integrins (75 mg/kg, five days per week; n = 12 rats) and compared to vehicle-treated control rats (n = 12). In a longitudinal study, conventional magnetic resonance imaging (MRI) and flat panel volumetric computed tomography were used to assess the volume of the soft tissue tumor and osteolysis, respectively, and dynamic contrast-enhanced (DCE-) MRI was performed to determine functional parameters of the tumor vasculature reflecting blood volume and blood vessel permeability. In rats treated with cilengitide, VCT and MRI showed that osteolytic lesions and the respective bone metastatic soft tissue tumors progressed more slowly than in vehicle-treated controls. DCE-MRI indicated a decrease in blood volume and an increase in vessel permeability and immunohistology revealed increased numbers of immature vessels in cilengitide-treated rats compared to vehicle controls. In conclusion, treatment of experimental breast cancer bone metastases with cilengitide resulted in pronounced antiresorptive and antitumor effects, suggesting that αvβ(3)/αvβ(5) inhibition may be a promising therapeutic approach for bone metastases.

Assessment of Response to Therapy for Bone Metastases: Is it Still a Challenge in Oncology?

Bone is one of the most common sites of metastases from cancer. Most anticancer treatments are highly toxic but only a fraction of all patients respond to them. Guidelines are needed to evaluate the response in the routine practice of oncology as well as in clinical trials in which new treatment options are evaluated. All current imaging procedures have major limitations. This article reviews old and new criteria for response evaluation. The major problem of accurate response evaluation in bone disease is discussed in detail. Some examples from our daily practice illustrate the difficulties. The indications for bone biopsy are also reviewed.

Bone vascularization and trabecular bone formation are mediated by PKB alpha/Akt1 in a gene-dosage-dependent manner: in vivo and ex vivo MRI

PKBalpha/Akt1, a protein kinase, is a major mediator of angiogenic signaling. The purpose of this study was to determine the role of PKB alpha/Akt1 in bone vascularization and development. For that aim, macromolecular dynamic contrast enhanced MRI was applied to examine in vivo vascular changes in long bones of 40-day-old growing PKB alpha/Akt1-deficient, heterozygous, and wild-type mice. Ex vivo microMRI and microCT were applied to monitor the impact of PKB alpha/Akt1 gene dosage on trabecular bone formation during endochondral bone growth. PKB alpha/Akt1-deficient mice and, remarkably, also heterozygous mice showed significantly reduced blood volume fraction in the humerus compared to wild-type mice. Moreover, PKB alpha/Akt1-deficient mice showed a more severe vascular deficiency with reduced permeability. microCT and microMRI of trabeculae revealed impaired bone formation in both PKB alpha/Akt1-deficient and heterozygous mice, whereas cortical bone parameters were only reduced in PKB alpha/Akt1-deficient mice. Reduction of metaphyseal blood vessel invasion, concomitant with aberrant trabeculae and shorter long bones, demonstrates a gene-dose-dependent role for PKB alpha/Akt1 in regulation of overall size and endochondral bone growth. MRI proved to provide high sensitivity for in vivo detection of subtle gene dose effects leading to impaired bone vascularity and for uncovering changes in trabecular bone.

Drug-induced vessel remodeling in bone metastases as assessed by dynamic contrast enhanced magnetic resonance imaging and vessel size imaging: a longitudinal in vivo study

PURPOSE

The aim of this study was to assess the antiangiogenic treatment effects of zoledronic acid (ZA) and sunitinib malate (SM) noninvasively in experimental breast cancer bone metastases by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and vessel size imaging.

EXPERIMENTAL DESIGN

Nude rats bearing bone metastases after inoculation of MDA-MB-231 breast cancer cells were treated with ZA (40 microg/kg weekly; n = 8 rats), SM (20 mg/kg daily; n = 8 rats), or their combination (ZA and SM; n = 8 rats) and compared with sham-treated controls (n = 10 rats). Vascular changes in bone metastases were longitudinally imaged in vivo using DCE-MRI [amplitude (A) and exchange rate coefficient (k(ep))] and vessel size imaging [blood volume (BV) and vessel size index (VI)]. In addition, antiresorptive and antitumor changes were assessed in these lesions by flat-panel volumetric computed tomography as well as morphologic MRI and diffusion-weighted imaging.

RESULTS

In bone metastases, significant changes in A, k(ep), BV, and VI in accordance with decreased blood volume and vessel permeability as well as with increased mean vessel diameters were observed after application of ZA and SM as compared with controls. In this longitudinal study, antiangiogenic changes preceded the inhibition of osteolysis and antitumor effects after treatment.

CONCLUSIONS

These results indicate vessel remodeling in breast cancer bone metastases on ZA and SM treatment and implicate substantial effects on imaging and treatment of malignant bone lesions.

Applications of molecular MRI and optical imaging in cancer

Some of the most exciting advances in molecular-functional imaging of cancer are occurring at the interface between chemistry and imaging. Several of these advances have occurred through the development of novel imaging probes that report on molecular pathways, the tumor micro-environment and the response of tumors to treatment; as well as through novel image-guided platforms such as nanoparticles and nanovesicles that deliver therapeutic agents against specific targets and pathways. Cancer cells have a remarkable ability to evade destruction despite the armamentarium of drugs currently available. While these drugs can destroy cancer cells, normal tissue toxicity is a major limiting factor, a problem further compounded by poor drug delivery. One major challenge for chemistry continues to be to eliminate cancer cells without damaging normal tissues. Here we have selected examples of MRI and optical imaging, to demonstrate how integrating imaging with novel probes can facilitate the successful treatment of this multifaceted disease.

Hypoxia and TGF-beta drive breast cancer bone metastases through parallel signaling pathways in tumor cells and the bone microenvironment

Background

Most patients with advanced breast cancer develop bone metastases, which cause pain, hypercalcemia, fractures, nerve compression and paralysis. Chemotherapy causes further bone loss, and bone-specific treatments are only palliative. Multiple tumor-secreted factors act on the bone microenvironment to drive a feed-forward cycle of tumor growth. Effective treatment requires inhibiting upstream regulators of groups of prometastatic factors. Two central regulators are hypoxia and transforming growth factor (TGF)- β. We asked whether hypoxia (via HIF-1α) and TGF-β signaling promote bone metastases independently or synergistically, and we tested molecular versus pharmacological inhibition strategies in an animal model.

Methodology/Principal Findings

We analyzed interactions between HIF-1α and TGF-β pathways in MDA-MB-231 breast cancer cells. Only vascular endothelial growth factor (VEGF) and the CXC chemokine receptor 4 (CXCR4), of 16 genes tested, were additively increased by both TGF-β and hypoxia, with effects on the proximal promoters. We inhibited HIF-1α and TGF-β pathways in tumor cells by shRNA and dominant negative receptor approaches. Inhibition of either pathway decreased bone metastasis, with no further effect of double blockade. We tested pharmacologic inhibitors of the pathways, which target both the tumor and the bone microenvironment. Unlike molecular blockade, combined drug treatment decreased bone metastases more than either alone, with effects on bone to decrease osteoclastic bone resorption and increase osteoblast activity, in addition to actions on tumor cells.

Conclusions/Significance

Hypoxia and TGF-β signaling in parallel drive tumor bone metastases and regulate a common set of tumor genes. In contrast, small molecule inhibitors, by acting on both tumor cells and the bone microenvironment, additively decrease tumor burden, while improving skeletal quality. Our studies suggest that inhibitors of HIF-1α and TGF-β may improve treatment of bone metastases and increase survival.

Imaging response to systemic therapy for bone metastases

In patients with osteotropic primary tumours such as breast and prostate cancer, imaging treatment response of bone metastases is essential for the clinical management. After treatment of skeletal metastases, morphological changes, in particular of bone structure, occur relatively late and are difficult to quantify using conventional X-rays, CT or MRI. Early treatment response in these lesions can be assessed from functional imaging techniques such as dynamic contrast-enhanced techniques by MRI or CT and by diffusion-weighted MRI, which are quantifiable. Among the techniques within nuclear medicine, PET offers the acquisition of quantifiable parameters for response evaluation. PET, therefore, especially in combination with CT and MRI using hybrid techniques, holds great promise for early and quantifiable assessment of treatment response in bone metastases. This review summarises the classification systems and the use of imaging techniques for evaluation of treatment response and suggests parameters for the early detection and quantification of response to systemic therapy.