Multimodality molecular imaging of tumor angiogenesis

Future Perspectives for Diagnostic Imaging in Urology: From Anatomic and Functional to Molecular Imaging

The future approach of diagnostic imaging in urology follows the technological progress, which made the visualization of in vivo molecular processes possible.

From anatomo-morphological diagnostic imaging and through functional imaging molecular radiology is reached.

Based on molecular probes, imaging is aimed at assessing the in vivo molecular processes, their physiology and function at cellular level.

The future imaging will investigate the complex tumor functioning as metabolism, aerobic glycolysis in particular, angiogenesis, cell proliferation, metastatic potential, hypoxia, apoptosis and receptors expressed by neoplastic cells.

Methods for performing molecular radiology are CT, MRI, PET-CT, PET-MRI, SPECT and optical imaging. Molecular ultrasound combines technological advancement with targeted contrast media based on microbubbles, this allowing the selective registration of microbubble signal while that of stationary tissues is suppressed.

An experimental study was carried out where the ultrasound molecular probe BR55 strictly bound to prostate tumor results in strong enhancement in the early phase after contrast, this contrast being maintained in the late phase. This late enhancement is markedly significant for the detection of prostatic cancer foci and to guide the biopsy sampling.

The 124I-cG250 molecular antibody which is strictly linked to cellular carbonic anhydrase IX of clear cell renal carcinoma, allows the acquisition of diagnostic PET images of clear cell renal carcinoma without biopsy. This WG-250 (RENCAREX) antibody was used as a therapy in metastatic clear cell renal carcinoma. Future advancements and applications will result in early cancer diagnosis, personalized therapy that will be specific according to the molecular features of cancer and leading to the development of catheter–based multichannel molecular imaging devices for cystoscopy-based molecular imaging diagnosis and intervention.

Design and synthesis of small-molecule fluorescent photoprobes targeted to aminopeptdase N (APN/CD13) for optical imaging of angiogenesis

We report here the synthesis of a nonpeptide, small-molecule fluorescent imaging agent with high affinity to aminopeptidase N (APN/CD13), a key player in a variety of pathophysiological angiogenic processes. On the basis of a recently described lead structure, we synthesized three putative precursor compounds by introducing polyethylene glycol (PEG) spacers comprising amino groups for dye labeling. Different attachment sites resulted in substantial differences in target affinity, cell toxicity, and target imaging performance. In comparison to bestatin, a natural inhibitor of many aminopeptidases, two of our compounds (22, 23) exhibit comparable inhibition potency, while a third (21) does not show any inhibiting effect. Cell binding assays with APN-positive BT-549 and APN-negative BT-20 cells and the final fluorescent probes Cy 5.5-21 and Cy 5.5-23 confirm these findings. The favorable characteristics of Cy 5.5-23 will now be proven in in vivo experiments with murine models of high APN expression and may serve as a tool to better understand APN pathophysiology.

Nanoparticles for Improving Cancer Diagnosis

Despite the progress in developing new therapeutic modalities, cancer remains one of the leading diseases causing human mortality. This is mainly attributed to the inability to diagnose tumors in their early stage. By the time the tumor is confirmed, the cancer may have already metastasized, thereby making therapies challenging or even impossible. It is therefore crucial to develop new or to improve existing diagnostic tools to enable diagnosis of cancer in its early or even pre-syndrome stage. The emergence of nanotechnology has provided such a possibility. Unique physical and physiochemical properties allow nanoparticles to be utilized as tags with excellent sensitivity. When coupled with the appropriate targeting molecules, nanoparticle-based probes can interact with a biological system and sense biological changes on the molecular level with unprecedented accuracy. In the past several years, much progress has been made in applying nanotechnology to clinical imaging and diagnostics, and interdisciplinary efforts have made an impact on clinical cancer management. This article aims to review the progress in this exciting area with emphases on the preparation and engineering techniques that have been developed to assemble "smart" nanoprobes.

An engineering view on megatrends in radiology: digitization to quantitative tools of medicine

Within six months of the discovery of X-ray in 1895, the technology was used to scan the interior of the human body, paving the way for many innovations in the field of medicine, including an ultrasound device in 1950, a CT scanner in 1972, and MRI in 1980. More recent decades have witnessed developments such as digital imaging using a picture archiving and communication system, computer-aided detection/diagnosis, organ-specific workstations, and molecular, functional, and quantitative imaging. One of the latest technical breakthrough in the field of radiology has been imaging genomics and robotic interventions for biopsy and theragnosis. This review provides an engineering perspective on these developments and several other megatrends in radiology.

RGD-based PET tracers for imaging receptor integrin αv β3 expression

Positron emission tomography (PET) imaging of receptor integrin αv β3 expression may play a key role in the early detection of cancer and cardiovascular diseases, monitoring disease progression, evaluating therapeutic response, and aiding anti-angiogenic drugs discovery and development. The last decade has seen the development of new PET tracers for in vivo imaging of integrin αv β3 expression along with advances in PET chemistry. In this review, we will focus on the radiochemistry development of PET tracers based on arginine-glycine-aspartic acid (RGD) peptide, present an overview of general strategies for preparing RGD-based PET tracers, and review the recent advances in preparations of (18) F-labeled, (64) Cu-labeled, and (68) Ga-labeled RGD tracers, RGD-based PET multivalent probes, and RGD-based PET multimodality probes for imaging receptor integrin αv β3 expression.

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.

Radioluminescent gold nanocages with controlled radioactivity for real-time in vivo imaging

Cerenkov luminescence imaging based on light emission from the decay of radionuclides has recently drawn great interest in molecular imaging. In this paper, we report for the first time the Cerenkov luminescence phenomenon of (198)Au isotope, as well as a facile route to the preparation of radioluminescent Au nanocages without additional radiolabeling or dye conjugation. The specific radioactivity of the Au nanocages could be easily and precisely controlled by varying the concentration of H(198)AuCl(4) precursor used for the galvanic replacement reaction. The direct incorporation of (198)Au atoms into the structure of Au nanocages enabled the ability of accurate analysis and real-time imaging in vivo. Furthermore, under biological conditions the radioactive Au nanocages were shown to emit light with wavelengths in the visible and near-infrared regions, enabling luminescence imaging of the whole mice in vivo, as well as the organs ex vivo. When combined with their favorable scattering and absorption properties in the near-infrared region, the radioactive Au nanocages can serve as a new platform for multimodality imaging and will have a significant impact on both small animal and clinical imaging.

Tumor vasculature targeting and imaging in living mice with reduced graphene oxide

Graphene-based nanomaterials have attracted tremendous attention in the field of biomedicine due to their intriguing properties. Herein, we report tumor vasculature targeting and imaging in living mice using reduced graphene oxide (RGO), which was conjugated to the anti-CD105 antibody TRC105. The RGO conjugate, (64)Cu-NOTA-RGO-TRC105, exhibited excellent stability in vitro and in vivo. Serial positron emission tomography (PET) imaging studies non-invasively assessed the pharmacokinetics and demonstrated specific targeting of (64)Cu-NOTA-RGO-TRC105 to 4T1 murine breast tumors in vivo, compared to non-targeted RGO conjugate ((64)Cu-NOTA-RGO). In vivo (e.g., blocking 4T1 tumor uptake with excess TRC105), in vitro (e.g., flow cytometry), and ex vivo (e.g., histology) experiments confirmed the specificity of (64)Cu-NOTA-RGO-TRC105 for tumor vascular CD105. Since RGO exhibits desirable properties for photothermal therapy, the tumor-specific RGO conjugate developed in this work may serve as a promising theranostic agent that integrates imaging and therapeutic components.

PET imaging of CD105/endoglin expression with a ⁶¹/⁶⁴Cu-labeled Fab antibody fragment

PURPOSE

The goal of this study was to generate and characterize the Fab fragment of TRC105, a monoclonal antibody that binds with high affinity to human and murine CD105 (i.e., endoglin), and investigate its potential for PET imaging of tumor angiogenesis in a small-animal model after (61/64)Cu labeling.

METHODS

TRC105-Fab was generated by enzymatic papain digestion. The integrity and CD105 binding affinity of TRC105-Fab was evaluated before NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) conjugation and (61/64)Cu labeling. Serial PET imaging and biodistribution studies were carried out in the syngeneic 4T1 murine breast cancer model to quantify tumor targeting efficiency and normal organ distribution of (61/64)Cu-NOTA-TRC105-Fab. Blocking studies with unlabeled TRC105 were performed to confirm CD105 specificity of the tracer in vivo. Immunofluorescence staining was also conducted to correlate tracer uptake in the tumor and normal tissues with CD105 expression.

RESULTS

TRC105-Fab was produced with high purity through papain digestion of TRC105, as confirmed by SDS-PAGE, HPLC analysis, and mass spectrometry. (61/64)Cu labeling of NOTA-TRC105-Fab was achieved with about 50 % yield (specific activity about 44 GBq/μmol). PET imaging revealed rapid uptake of (64)Cu-NOTA-TRC105-Fab in the 4T1 tumor (3.6 ± 0.4, 4.2 ± 0.5, 4.9 ± 0.3, 4.4 ± 0.7, and 4.6 ± 0.8 %ID/g at 0.5, 2, 5, 16, and 24 h after injection, respectively; n = 4). Since tumor uptake peaked soon after tracer injection, (61)Cu-labeled TRC105-Fab was also able to provide tumor contrast at 3 and 8 h after injection. CD105 specificity of the tracer was confirmed with blocking studies and histological examination.

CONCLUSION

We report PET imaging of CD105 expression using (61/64)Cu-NOTA-TRC105-Fab, which exhibited prominent and target-specific uptake in the 4T1 tumor. The use of a Fab fragment led to much faster tumor uptake (which peaked at a few hours after tracer injection) compared to radiolabeled intact antibody, which may be translated into same-day immunoPET imaging for clinical investigation.

Positron emission tomography imaging of tumor angiogenesis with a (61/64)Cu-labeled F(ab')(2) antibody fragment

The objective of this study was to characterize the in vitro and in vivo properties of the F(ab')(2) fragment of TRC105, a human/murine chimeric IgG1 monoclonal antibody that binds with high avidity to human and murine CD105 (i.e., endoglin), and investigate its potential for positron emission tomography (PET) imaging of tumor angiogenesis after (61/64)Cu-labeling. TRC105-F(ab')(2) of high purity was produced by pepsin digestion of TRC105, which was confirmed by SDS-PAGE, HPLC analysis, and mass spectrometry. (61/64)Cu-labeling of NOTA-TRC105-F(ab')(2) (NOTA denotes 1,4,7-triazacyclononane-1,4,7-triacetic acid) was achieved with yields of >75% (specific activity: ∼115 GBq/μmol). PET imaging revealed rapid tumor uptake of (64)Cu-NOTA-TRC105-F(ab')(2) in the 4T1 murine breast cancer model (5.8 ± 0.8, 7.6 ± 0.6, 5.6 ± 0.4, 5.0 ± 0.6, and 3.8 ± 0.7% ID/g at 0.5, 3, 16, 24, and 48 h postinjection respectively; n = 4). Since tumor uptake peaked at 3 h postinjection, (61)Cu-NOTA-TRC105-F(ab')(2) also gave good tumor contrast at 3 and 8 h postinjection. CD105 specificity of the tracers was confirmed by blocking studies and histopathology. In conclusion, the use of a F(ab')(2) fragment led to more rapid tumor uptake (which peaked at 3 h postinjection) than radiolabeled intact antibody (which often peaked after 24 h postinjection), which may allow for same day immunoPET imaging in future clinical studies.

Optical imaging

Non-invasive optical imaging techniques, such as fluorescence imaging (FI) or bioluminescence imaging (BLI) have emerged as important tools in biomedical research. As demonstrated in different animal disease models, they enable visualization of physiological and pathophysiological processes at the cellular and molecular level in vivo with high specificity. Optical techniques are easy to use, fast, and affordable. Furthermore, they are characterized by their high sensitivity. In FI, very low amounts of the imaging agent (nano- to femtomol or even less) can be detected. Due to the absorption and scattering of light in tissue, optical techniques exhibit a comparably low spatial resolution in the millimeter range and a depth limit of a few centimeters. However, non-invasive imaging of biological processes in small animals and in outer or inner surfaces as well as during surgery even in humans is feasible. Currently two agents for fluorescence imaging are clinically approved, namely indocyanine green (ICG) and 5-aminolevulinic acid (5-ALA). In the past years, a number of new optical imaging agents for FI and reporter systems for BLI have been developed and successfully tested in animal models. Some of the FI agents might promise the application in clinical oncology. In this chapter, we describe the basic principles of non-invasive optical imaging techniques, give examples for the visualization of biological processes in animal models of cancer, and discuss potential clinical applications in oncology.

Polyaspartic acid coated iron oxide nanoprobes for PET/MRI imaging

Iron oxide nanoparticles, due to their exceptional magnetic property, biocompatibility, and biodegradability, have long been studied as contrast agents for magnetic resonance imaging (Xie et al., Curr Med Chem 16(10):1278-1294, 2009; Xie et al., Adv Drug deliv Rev 62(11):1064-1079, 2010). While previous applications mostly target reticuloendothelial system (RES) organs such as liver and lymph nodes, recent efforts have been made to impart targeting peptides or antibodies onto particle surface to enable site-specific targeting after systemic administration (Xie et al., Adv Drug Deliv Rev 62(11):1064-1079, 2010; Cai and Chen, Small 3(11):1840-1854, 2007; Corot et al., Adv Drug Deliv Rev 58 (14):1471-1504, 2006; Xie et al., Acc Chem Res 44(10):883-892). Moreover, other imaging functionalities can be loaded onto nanoparticles to achieve multimodality imaging probes (Cai and Chen, Small 3(11):1840-1854, 2007; Lee et al., J Nucl Med Soc Nucl Med 49(8):1371-1379, 2008). In this protocol, we describe the procedure of constructing an iron oxide nanoparticle (IONP)-based probe with high affinity towards integrin αvβ3 for positron emission tomography (PET) and magnetic resonance imaging (MRI) dual modality imaging. The related characterizations and validation experiments, including particle concentration determination, Prussian blue staining, animal model preparation, and in vivo PET/MRI imaging will also be discussed.

Preclinical molecular imaging using PET and MRI

Molecular imaging fundamentally changes the way we look at cancer. Imaging paradigms are now shifting away from classical morphological measures towards the assessment of functional, metabolic, cellular, and molecular information in vivo. Interdisciplinary driven developments of imaging methodology and probe molecules utilizing animal models of human cancers have enhanced our ability to non-invasively characterize neoplastic tissue and follow anti-cancer treatments. Preclinical molecular imaging offers a whole palette of excellent methodology to choose from. We will focus on positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques, since they provide excellent and complementary molecular imaging capabilities and bear high potential for clinical translation. Prerequisites and consequences of using animal models as surrogates of human cancers in preclinical molecular imaging are outlined. We present physical principles, values and limitations of PET and MRI as molecular imaging modalities and comment on their high potential to non-invasively assess information on hypoxia, angiogenesis, apoptosis, gene expression, metabolism, and cell trafficking in preclinical cancer research.

Pattern analysis accounts for heterogeneity observed in MRI studies of tumor angiogenesis

MRI is a method of choice for assessing anatomical structures or angiogenesis-related parameters noninvasively during tumor progression. Typically, tumor tissue displays a high degree of heterogeneity that can be evaluated using pattern analysis (PA), which comprises shape and texture analysis. This work aims at implementing PA methods to study angiogenesis in a murine tumor model and testing its sensitivity with regard to detecting changes elicited by administration of a drug. Twelve balb/c-nude mice were injected subcutaneously with 10(6) C51 cells (colon carcinoma). A first group (N = 6) of animals was treated with dimethyloxalylglycine, a drug known to stabilize hypoxia-inducible-factor-α, which among other functions, is involved in angiogenesis. The second group (N = 6) was treated with saline. MRI experiments assessing tumor blood volume and permeability-maps (K(trans) ) were performed immediately before and 6 days after drug treatment. Data have been analyzed using standard histogram analysis and PA. Standard histogram analysis did not reveal any difference between the two groups, neither before nor after the treatment. In contrast, PA revealed significant differences between drug and placebo treated mice in the texture of the TBV and K(trans) maps after drug treatment, but not with regard to tumors shapes. The results indicated that in view of the heterogeneity of tumor tissue, standard histogram analysis appears insensitive in picking-up differences in response to treatment, while PA appears to be particularly sensitive to changes in texture.

Target-specific copper hybrid T7 phage particles

Target-specific nanoparticles have attracted significant attention recently, and have greatly impacted life and physical sciences as new agents for imaging, diagnosis, and therapy, as well as building blocks for the assembly of novel complex materials. While most of these particles are synthesized by chemical conjugation of an affinity reagent to polymer or inorganic nanoparticles, we are promoting the use of phage particles as a carrier to host organic or inorganic functional components, as well as to display the affinity reagent on the phage surface, taking advantage of the fact that some phages host well-established vectors for protein expression. An affinity reagent can be structured in a desired geometry on the surface of phage particles, and more importantly, the number of the affinity reagent molecules per phage particle can be precisely controlled. We previously have reported the use of the T7 phage capsid as a template for synthesizing target-specific metal nanoparticles. In this study herein, we reported the synthesis of nanoparticles using an intact T7 phage as a scaffold from which to extend 415 copies of a peptide that contains a hexahistidine (6His) motif for capture of copper ions and staging the conversion of copper ions to copper metal, and a cyclic Arginine-Glycine-Aspartic Acid (RGD4C) motif for targeting integrin and cancer cells. We demonstrated that the recombinant phage could load copper ions under low bulk copper concentrations without interfering with its target specificity. Further reduction of copper ions to copper metal rendered a very stable copper hybrid T7 phage, which prevents the detachment of copper from phage particles and maintains the phage structural integrity even under harsh conditions. Cancer cells (MCF-7) can selectively uptake copper hybrid T7 phage particles through ligand-mediated transmembrane transportation, whereas normal control cells (MCF-12F) uptake 1000-fold less. We further demonstrated that copper hybrid T7 phage could be endocytosed by cancer cells in culture.

Antiangiogenic-targeting drug-loaded microbubbles combined with focused ultrasound for glioma treatment

Current chemotherapeutic agents do not only kill tumor cells but also induce systemic toxicity that significantly limits their dosage. Focused ultrasound (FUS) in the presence of microbubbles (MBs) is capable of transient and local opening of the blood-brain barrier (BBB) that enhances chemotherapeutic drug delivery into the brain parenchyma for glioma treatment. Our previous results demonstrated the success of combining the use of drug (1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU)-loaded MBs with FUS-induced BBB opening to improve local drug delivery and reduce systemic toxicity. Here we introduce novel VEGF-targeting, drug-loaded MBs that significantly further enhance targeted drug release and reduce tumor progression in a rat model, using the FUS-BBB opening strategy. This study suggests a promising direction for future MB design aimed at targeted brain tumor therapy, and the possible future extension of MB application towards theragnostic use.

Strain-Promoted Catalyst-Free Click Chemistry for Rapid Construction of (64)Cu-Labeled PET Imaging Probes

A rapid, efficient, and catalyst-free click chemistry method for the construction of (64)Cu-labeled PET imaging probes was reported based on the strain-promoted aza-dibenzocyclooctyne ligation. This new method was exemplified in the synthesis of (64)Cu-labeled RGD peptide for PET imaging of tumor integrin αvβ3 expression in vivo. The catalyst-free click chemistry reaction proceeded with a fast rate and eliminated the contamination problem of the catalyst Cu(I) ions interfering with the (64)Cu radiolabeling procedure under the conventional Cu-catalyzed 1,3-dipolar cycloaddition condition. The new strategy is simple and robust, and the resultant (64)Cu-labeled RGD probe was obtained in an excellent yield and high specific activity. PET imaging and biodistribution studies revealed significant, specific uptake of the "click" (64)Cu-labeled RGD probe in integrin αvβ3-positive U87MG xenografts with little uptake in nontarget tissues. This new approach is versatile, which warrants a wide range of applications for highly diverse radiometalated bioconjugates for radioimaging and radiotherapy.

Tumor functional and molecular imaging utilizing ultrasound and ultrasound-mediated optical techniques

Tumor functional and molecular imaging has significantly contributed to cancer preclinical research and clinical applications. Among typical imaging modalities, ultrasonic and optical techniques are two commonly used methods; both share several common features such as cost efficiency, absence of ionizing radiation, relatively inexpensive contrast agents, and comparable maximum-imaging depth. Ultrasonic and optical techniques are also complementary in imaging resolution, molecular sensitivity, and imaging space (vascular and extravascular). The marriage between ultrasonic and optical techniques takes advantages of both techniques. This review introduces tumor functional and molecular imaging using microbubble-based ultrasound and ultrasound-mediated optical imaging techniques.

A synergistically enhanced T(1) -T(2) dual-modal contrast agent

Monodisperse Gd(2) O(3) -embedded iron oxide (GdIO) nanoparticles can simultaneously enhance the local magnetic field intensities of each other under an external magnetic field and result in synergistic enhancement of T(1) and T(2) effects. GdIO nanoparticles have the unique property to be both T(1) and T(2) contrast agents and can potentially lead to higher accuracy in cancer diagnosis, particularly liver tumors.

Folic acid-conjugated LaF3:Yb,Tm@SiO2 nanoprobes for targeting dual-modality imaging of upconversion luminescence and X-ray computed tomography

Development of multimodal contrast agents for in vivo simultaneous multimodality imaging is an emerging interdiscipline that is paving the avenue toward the goal of personalized medicine. Herein, folic acid-conjugated silica-modified LaF(3):Yb,Tm upconversion nanoparticles (UCNPs@SiO(2)-FA) with high La content in a single particle were strategically designed and prepared for simultaneously targeting dual-modality imaging of upconversion luminescence (UCL) and X-ray computed tomography (CT). LaF(3) UCNPs were synthesized by a novel oleic acid (OA)/ionic liquid (IL) two-phase system. Afterward, a folic acid molecule was covalently anchored on the surface of UCNPs with a silane coupling agent. The UCNPs@SiO(2)-FA exhibits good stability, water dispersibility and solubility, low cytotoxicity, good biocompatibility, highly selective targeting, excellent X-ray attenuation, and UCL emission under excitation at 980 nm. In vivo UCL and CT images of mice show the UCNPs@SiO(2)-FA can be used in targeting dual-modality imaging. These results suggest that the as-prepared nanoprobe is a good candidate with excellent imaging and targeting ability for targeting dual-modality imaging of UCL and CT.

Positron emission tomography imaging of vascular endothelial growth factor receptor expression with (61)Cu-labeled lysine-tagged VEGF121

Overexpression of vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFRs) indicates poor prognosis for cancer patients in a variety of clinical studies. Our goal is to develop a tracer for positron emission tomography (PET) imaging of VEGFR expression using recombinant human VEGF121 with three lysine residues fused to the N-terminus (denoted as K3-VEGF121), which can facilitate radiolabeling without affecting its VEGFR binding affinity. K3-VEGF121 was conjugated with 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) and labeled with (61)Cu (t1/2: 3.3 h; 62% β(+)). The IC50 value of NOTA-K3-VEGF121 for VEGFR-2 was comparable to that of K3-VEGF121 (1.50 and 0.65 nM, respectively) based on a cell binding assay. (61)Cu labeling was achieved with good yield (55 ± 10%) and specific activity (4.2 GBq/mg). Serial PET imaging showed that the 4T1 tumor uptake of (61)Cu-NOTA-K3-VEGF121 was 3.4 ± 0.5, 4.9 ± 1.0, 5.2 ± 1.0, and 4.8 ± 0.8%ID/g (n = 4) at 0.5, 2, 4, and 8 h postinjection, respectively, which was consistent with biodistribution data measured by γ counting. Blocking experiments and ex vivo histology confirmed the VEGFR specificity of (61)Cu-NOTA-K3-VEGF121. Extrapolated human dosimetry calculation showed that liver was the organ with the highest radiation dose. The use of (61)Cu as the radiolabel is desirable for small proteins such as K3-VEGF121, which has a much higher β(+) branching ratio than the commonly used (64)Cu (62% vs 17%), thereby offering stronger signal intensity and lower tracer dose for PET imaging.

PET/SPECT imaging of hindlimb ischemia: focusing on angiogenesis and blood flow

Peripheral artery disease (PAD) is a result of the atherosclerotic narrowing of blood vessels to the extremities, and the subsequent tissue ischemia can lead to the up-regulation of angiogenic growth factors and formation of new vessels as a recovery mechanism. Such formation of new vessels can be evaluated with various non-invasive molecular imaging techniques, where serial images from the same subjects can be obtained to allow the documentation of disease progression and therapeutic response. The most commonly used animal model for preclinical studies of PAD is the murine hindlimb ischemia model, and a number of radiotracers have been investigated for positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging of PAD. In this review article, we summarize the PET/SPECT tracers that have been tested in the murine hindlimb ischemia model as well as those used clinically to assess the extremity blood flow.

Continuous sensing of tumor-targeted molecular probes with a vertical cavity surface emitting laser-based biosensor

Molecular optical imaging is a widespread technique for interrogating molecular events in living subjects. However, current approaches preclude long-term, continuous measurements in awake, mobile subjects, a strategy crucial in several medical conditions. Consequently, we designed a novel, lightweight miniature biosensor for in vivo continuous optical sensing. The biosensor contains an enclosed vertical-cavity surface-emitting semiconductor laser and an adjacent pair of near-infrared optically filtered detectors. We employed two sensors (dual sensing) to simultaneously interrogate normal and diseased tumor sites. Having established the sensors are precise with phantom and in vivo studies, we performed dual, continuous sensing in tumor (human glioblastoma cells) bearing mice using the targeted molecular probe cRGD-Cy5.5, which targets αVβ3 cell surface integrins in both tumor neovasculature and tumor. The sensors capture the dynamic time-activity curve of the targeted molecular probe. The average tumor to background ratio after signal calibration for cRGD-Cy5.5 injection is approximately 2.43±0.95 at 1 h and 3.64±1.38 at 2 h (N=5 mice), consistent with data obtained with a cooled charge coupled device camera. We conclude that our novel, portable, precise biosensor can be used to evaluate both kinetics and steady state levels of molecular probes in various disease applications.

Nanosized multifunctional liposomes for tumor diagnosis and molecular imaging by SPECT/CT

Among currently used cancer imaging methods, nuclear medicine modalities provide metabolic information, whereas modalities in radiology provide anatomical information. However, different modalities, having different acquisition times in separate machines, decrease the specificity and accuracy of images. To solve this problem, hybrid imaging modalities were developed as a new era, especially in the cancer imaging field. With widespread usage of hybrid imaging modalities, specific contrast agents are essentially needed to use in both modalities, such as single-photon emission computed tomography/computed tomography (SPECT/CT). Liposomes are one of the most desirable drug delivery systems, depending on their suitable properties. The aim of this study was to develop a liposomal contrast agent for the diagnosis and molecular imaging of tumor by SPECT/CT. Liposomes were prepared nanosized, coated with polyethylene glycol to obtain long blood circulation, and modified with monoclonal antibody 2C5 for specific tumor targeting. Although DTPA-PE and DTPA-PLL-NGPE (polychelating amphilic polymers; PAPs) were loaded onto liposomes for stable radiolabeling for SPECT imaging, iopromide was encapsulated into liposomes for CT imaging. Liposomes [(DPPC:PEG(2000)-PE:Chol:DTPA-PE), (PL 90G:PEG(2000)-PE:Chol:DTPA-PE), (DPPC:PEG(2000)-PE:Chol:PAPs), (PL 90G:PEG(2000)-PE:Chol:PAPs), (60:0.9:39:0.1% mol ratio)] were characterized in terms of entrapment efficiency, particle size, physical stability, and release kinetics. Additionally, in vitro cell-binding studies were carried out on two tumor cell lines (MCF-7 and EL 4) by counting radioactivity. Tumor-specific antibody-modified liposomes were found to be effective multimodal contrast agents by designating almost 3-8 fold more uptake than nonmodified ones in different tumor cell lines. These results could be considered as an important step in the development of tumor-targeted SPECT/CT contrast agents for cancer imaging.

Specific biomarkers of receptors, pathways of inhibition and targeted therapies: pre-clinical developments

A deeper understanding of the role of specific genes, proteins, pathways and networks in health and disease, coupled with the development of technologies to assay these molecules and pathways in patients, promises to revolutionise the practice of clinical medicine. Especially the discovery and development of novel drugs targeted to disease-specific alterations could benefit significantly from non-invasive imaging techniques assessing the dynamics of specific disease-related parameters. Here we review the application of imaging biomarkers in the management of patients with brain tumours, especially malignant glioma. In our other review we focused on imaging biomarkers of general biochemical and physiological processes related with tumour growth such as energy, protein, DNA and membrane metabolism, vascular function, hypoxia and cell death. In this part of the review, we will discuss the use of imaging biomarkers of specific disease-related molecular genetic alterations such as apoptosis, angiogenesis, cell membrane receptors and signalling pathways and their application in targeted therapies.

Specific biomarkers of receptors, pathways of inhibition and targeted therapies: clinical applications

A deeper understanding of the role of specific genes, proteins, pathways and networks in health and disease, coupled with the development of technologies to assay these molecules and pathways in patients, promises to revolutionise the practice of clinical medicine. In particular, the discovery and development of novel drugs targeted to disease-specific alterations could benefit significantly from non-invasive imaging techniques assessing the dynamics of specific disease-related parameters. Here we review the application of imaging biomarkers in the management of patients with brain tumours, especially malignant glioma. This first part of the review focuses on imaging biomarkers of general biochemical and physiological processes related to tumour growth such as energy, protein, DNA and membrane metabolism, vascular function, hypoxia and cell death. These imaging biomarkers are an integral part of current clinical practice in the management of primary brain tumours. The second article of the review discusses the use of imaging biomarkers of specific disease-related molecular genetic alterations such as apoptosis, angiogenesis, cell membrane receptors and signalling pathways. Current applications of these biomarkers are mostly confined to experimental small animal research to develop and validate these novel imaging strategies with future extrapolation in the clinical setting as the primary objective.

The use and importance of liposomes in positron emission tomography

Among different imaging modalities, Positron Emission Tomography (PET) gained importance in routine hospital practice depending on ability to diagnose diseases in early stages and tracing of therapy by obtaining metabolic information. The combination of PET with Computed Tomography (CT) forms hybrid imaging modality that gives chance to obtain better images having higher resolution by fusing both functional and anatomical images in the same imaging modality at the same time. Therefore, better contrast agents are essentially needed. The advance in research about developing drug delivery systems as specific nanosized targeted systems gained an additional importance for obtaining better diagnosis and therapy of different diseases. Liposomes appear to be more attractive drug delivery systems in delivering either drugs or imaging ligands to target tissue or organ of diseases with higher accumulation by producing in nano-scale, long circulating by stealth effect and specific targeting by modifying with specific ligands or markers. The combination of positron emitting radionuclides with liposomes are commonly in research level nowadays and there is no commercially available liposome formulation for PET imaging. However by conjugating positron emitter radionuclide with liposomes can form promising diagnostic agents for improved diagnosis and following up treatments by increasing image signal/contrast in the target tissue in lower concentrations by specific targeting as the most important advantage of liposomes. More accurate and earlier diagnosis of several diseases can be obtained even in molecular level with the use of stable and effectively radiolabeled molecular target specific nano sized liposomes with longer half-lived positron emitting radionuclides.

Nanotechnology-based approaches in anticancer research

Cancer is a highly complex disease to understand, because it entails multiple cellular physiological systems. The most common cancer treatments are restricted to chemotherapy, radiation and surgery. Moreover, the early recognition and treatment of cancer remains a technological bottleneck. There is an urgent need to develop new and innovative technologies that could help to delineate tumor margins, identify residual tumor cells and micrometastases, and determine whether a tumor has been completely removed or not. Nanotechnology has witnessed significant progress in the past few decades, and its effect is widespread nowadays in every field. Nanoparticles can be modified in numerous ways to prolong circulation, enhance drug localization, increase drug efficacy, and potentially decrease chances of multidrug resistance by the use of nanotechnology. Recently, research in the field of cancer nanotechnology has made remarkable advances. The present review summarizes the application of various nanotechnology-based approaches towards the diagnostics and therapeutics of cancer.

Dynamic PET and Optical Imaging and Compartment Modeling using a Dual-labeled Cyclic RGD Peptide Probe

Purpose: The aim of this study is to determine if dynamic optical imaging could provide comparable kinetic parameters to that of dynamic PET imaging by a near-infrared dye/⁶⁴Cu dual-labeled cyclic RGD peptide.

Methods: The integrin α_vβ₃ binding RGD peptide was conjugated with a macrocyclic chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) for copper labeling and PET imaging and a near-infrared dye ZW-1 for optical imaging. The in vitro biological activity of RGD-C(DOTA)-ZW-1 was characterized by cell staining and receptor binding assay. Sixty-min dynamic PET and optical imaging were acquired on a MDA-MB-435 tumor model. Singular value decomposition (SVD) method was applied to compute the dynamic optical signal from the two-dimensional optical projection images. Compartment models were used to quantitatively analyze and compare the dynamic optical and PET data.

Results: The dual-labeled probe ⁶⁴Cu-RGD-C(DOTA)-ZW-1 showed integrin specific binding in vitro and in vivo. The binding potential (Bp) derived from dynamic optical imaging (1.762 ± 0.020) is comparable to that from dynamic PET (1.752 ± 0.026).

Conclusion: The signal un-mixing process using SVD improved the accuracy of kinetic modeling of 2D dynamic optical data. Our results demonstrate that 2D dynamic optical imaging with SVD analysis could achieve comparable quantitative results as dynamic PET imaging in preclinical xenograft models.

Synthesis and in vitro evaluation of [18F](R)-FEPAQ: a potential PET ligand for VEGFR2

Synthesis and in vitro evaluation of [(18)F](R)-N-(4-bromo-2-fluorophenyl)-7-((1-(2-fluoroethyl)piperidin-3-yl)methoxy)-6-methoxyquinazolin-4-amine ((R)-[(18)F]FEPAQ or [(18)F]1), a potential imaging agent for the VEGFR2, using phosphor image autoradiography are described. Synthesis of 2, the desfluoroethyl precursor for (R)-FEPAQ was achieved from t-butyl 3-(hydroxymethyl)piperidine-1-carboxylate (3) in five steps and in 50% yield. [(18)F]1 was synthesized by reaction of sodium salt of compound 2 with [(18)F]fluoroethyl tosylate in DMSO. The yield of [(18)F]1 was 20% (EOS based on [(18)F]F(-)) with >99% radiochemical purity and specific activity of 1-2 Ci/μmol (n=10). The total synthesis time was 75 min. The radiotracer selectively labeled VEGFR2 in slide-mounted sections of human brain and higher binding was found in surgically removed human glioblastoma sections as demonstrated by in vitro phosphor imager studies. These findings suggest [(18)F]1 may be a promising radiotracer for imaging VEGFR2 in brain using PET.

Radiolabelled RGD peptides for imaging and therapy

Imaging of angiogenesis has become increasingly important with the rising use of targeted antiangiogenic therapies like bevacizumab (Avastin). Non-invasive assessment of angiogenic activity is in this respect interesting, e.g. for response assessment of such targeted antiangiogenic therapies. One promising approach of angiogenesis imaging is imaging of specific molecular markers of the angiogenic cascade like the integrin α(v)β(3). For molecular imaging of integrin expression, the use of radiolabelled peptides is still the only approach that has been successfully translated into the clinic. In this review we will summarize the current data on imaging of α(v)β(3) expression using radiolabelled RGD peptides with a focus on tracers already in clinical use. A perspective will be presented on the future clinical use of radiolabelled RGD peptides including an outlook on potential applications for radionuclide therapy.

A molecular imaging primer: modalities, imaging agents, and applications

Molecular imaging is revolutionizing the way we study the inner workings of the human body, diagnose diseases, approach drug design, and assess therapies. The field as a whole is making possible the visualization of complex biochemical processes involved in normal physiology and disease states, in real time, in living cells, tissues, and intact subjects. In this review, we focus specifically on molecular imaging of intact living subjects. We provide a basic primer for those who are new to molecular imaging, and a resource for those involved in the field. We begin by describing classical molecular imaging techniques together with their key strengths and limitations, after which we introduce some of the latest emerging imaging modalities. We provide an overview of the main classes of molecular imaging agents (i.e., small molecules, peptides, aptamers, engineered proteins, and nanoparticles) and cite examples of how molecular imaging is being applied in oncology, neuroscience, cardiology, gene therapy, cell tracking, and theranostics (therapy combined with diagnostics). A step-by-step guide to answering biological and/or clinical questions using the tools of molecular imaging is also provided. We conclude by discussing the grand challenges of the field, its future directions, and enormous potential for further impacting how we approach research and medicine.

Graphene: a versatile nanoplatform for biomedical applications

Graphene, with its excellent physical, chemical, and mechanical properties, holds tremendous potential for a wide variety of biomedical applications. As research on graphene-based nanomaterials is still at a nascent stage due to the short time span since its initial report in 2004, a focused review on this topic is timely and necessary. In this feature review, we first summarize the results from toxicity studies of graphene and its derivatives. Although literature reports have mixed findings, we emphasize that the key question is not how toxic graphene itself is, but how to modify and functionalize it and its derivatives so that they do not exhibit acute/chronic toxicity, can be cleared from the body over time, and thereby can be best used for biomedical applications. We then discuss in detail the exploration of graphene-based nanomaterials for tissue engineering, molecular imaging, and drug/gene delivery applications. The future of graphene-based nanomaterials in biomedicine looks brighter than ever, and it is expected that they will find a wide range of biomedical applications with future research effort and interdisciplinary collaboration.

Radiolabeled γ-AApeptides: a new class of tracers for positron emission tomography

A γ-AApeptide-based tracer for positron emission tomography imaging of integrin α(v)β(3) is reported. Despite its shorter sequence and linear nature, this tracer had comparable integrin α(v)β(3) binding affinity to the cyclic arginine-glycine-aspartic acid peptide but significantly higher resistance to enzymatic degradation and better stability.

Review of functional/anatomical imaging in oncology

Patient management in oncology increasingly relies on imaging for diagnosis, response assessment, and follow-up. The clinical availability of combined functional/anatomical imaging modalities, which integrate the benefits of visualizing tumor biology with those of high-resolution structural imaging, revolutionized clinical management of oncologic patients. Conventional high-resolution anatomical imaging modalities such as computed tomography (CT) and MRI excel at providing details on lesion location, size, morphology, and structural changes to adjacent tissues; however, these modalities provide little insight into tumor physiology. With the increasing focus on molecularly targeted therapies, imaging radiolabeled compounds with PET and single-photon emission tomography (SPECT) is often carried out to provide insight into a tumor's biological functions and its surrounding microenvironment. Despite their high sensitivity and specificity, PET and SPECT alone are substantially limited by low spatial resolution and inability to provide anatomical detail. Integrating SPECT or PET with a modality capable of providing these (i.e. CT or MR) maximizes their separate strengths and provides anatomical localization of physiological processes with detailed visualization of a tumor's structure. The availability of multimodality (hybrid) imaging with PET/CT, SPECT/CT, and PET/MR improves our ability to characterize lesions and affect treatment decisions and patient management. We have just begun to exploit the truly synergistic capabilities of multimodality imaging. Continued advances in the development of instrumentation and imaging agents will improve our ability to noninvasively characterize disease processes. This review will discuss the evolution of hybrid imaging technology and provide examples of its current and potential future clinical uses.

Monitoring Breast Tumor Lung Metastasis by U-SPECT-II/CT with an Integrin α(v)β(3)-Targeted Radiotracer( 99m)Tc-3P-RGD(2)

Purpose: The purpose of this study was to evaluate the capability of u-SPECT-II/CT to monitor the progression of breast cancer lung metastasis using ^99mTc-3P-RGD₂ as a radiotracer.

Methods: The breast cancer lung metastasis model was established by tail-vein injection of 2 x 10⁵ - 1.5 x 10⁶ MDA-MB-231 cells into each athymic nude mouse. SPECT/CT studies were performed at a specified time after inoculation of MDA-MB-231 cells. Histological staining was used to further confirm the presence of lung metastases.

Results: We found that both inoculation time and tumor cell load had significant influence on the extent of lung metastasis. For example, if animals were injected with 2 x 10⁵ MDA-MB-231 cells, there were no detectable metastatic breast tumors in the lungs after 8 weeks. If animals were injected with 1 x 10⁶ MDA-MB-231 cells, there were many tumors in both lungs at week 8. When 1.5 x 10⁶ MDA-MB-231 cells were injected, the animal became very weak by week 7. We also found a rare example of breast cancer metastasis in the muscle and mediastinal lymph nodes. The tumor necrotic regions were clearly delineated by u-SPECT-II/CT.

Conclusion: This study clearly demonstrated that ^99mTc-3P-RGD₂ is an excellent radiotracer for noninvasive imaging of metastatic breast tumors in the lungs, mediastinal lymph nodes and muscles. ^99mTc-3P-RGD₂ SPECT/CT is an outstanding platform for monitoring the progression of breast cancer lung metastases, semi-quantification of breast tumor load in the lungs and delineation of tumor necrosis in small animals.

Introduction: feature issue on phantoms for the performance evaluation and validation of optical medical imaging devices

The editors introduce the Biomedical Optics Express feature issue on "Phantoms for the Performance Evaluation and Validation of Optical Medical Imaging Devices." This topic was the focus of a technical workshop that was held on November 7-8, 2011, in Washington, D.C. The feature issue includes 13 contributions from workshop attendees.

Gd3+ complex-modified NaLuF4-based upconversion nanophosphors for trimodality imaging of NIR-to-NIR upconversion luminescence, X-Ray computed tomography and magnetic resonance

Multimodality molecular imaging has recently attracted much attention, because it can take advantage of individual imaging modalities by fusing together information from several molecular imaging techniques. Herein, we report a multifunctional lanthanide-based nanoparticle for near-infrared to near-infrared (NIR-to-NIR) upconversion luminescence (UCL), X-ray computed tomography (CT) and T(1)-enhanced magnetic resonance (MR) trimodality in-vivo imaging. By careful selection of the lanthanide elements, core-shell structured lanthanide-based nanoparticles, NaLuF(4):Yb(3+),Tm(3+)@SiO(2)-GdDTPA nanoparticles (UCNP@SiO(2)-GdDTPA) have been designed and synthesized. We also prove that the application of UCNP@SiO(2)-GdDTPA for NIR-to-NIR UCL, CT and MRI multi-modality in-vivo imaging can be established successfully. In addition, the biological toxicity of UCNP@SiO(2)-GdDTPA is evaluated by the methyl thiazolyl tetrazolium (MTT) assay and histological analysis of viscera sections.

Permeability to macromolecular contrast media quantified by dynamic MRI correlates with tumor tissue assays of vascular endothelial growth factor (VEGF)

PURPOSE

To correlate dynamic MRI assays of macromolecular endothelial permeability with microscopic area-density measurements of vascular endothelial growth factor (VEGF) in tumors.

METHODS AND MATERIAL

This study compared tumor xenografts from two different human cancer cell lines, MDA-MB-231 tumors (n=5), and MDA-MB-435 (n=8), reported to express respectively higher and lower levels of VEGF. Dynamic MRI was enhanced by a prototype macromolecular contrast medium (MMCM), albumin-(Gd-DTPA)35. Quantitative estimates of tumor microvascular permeability (K(PS); μl/min × 100 cm(3)), obtained using a two-compartment kinetic model, were correlated with immunohistochemical measurements of VEGF in each tumor.

RESULTS

Mean K(PS) was 2.4 times greater in MDA-MB-231 tumors (K(PS)=58 ± 30.9 μl/min × 100 cm(3)) than in MDA-MB-435 tumors (K(PS)=24 ± 8.4 μl/min × 100 cm(3)) (p<0.05). Correspondingly, the area-density of VEGF in MDA-MB-231 tumors was 2.6 times greater (27.3 ± 2.2%, p<0.05) than in MDA-MB-435 cancers (10.5 ± 0.5%, p<0.05). Considering all tumors without regard to cell type, a significant positive correlation (r=0.67, p<0.05) was observed between MRI-estimated endothelial permeability and VEGF immunoreactivity.

CONCLUSION

Correlation of MRI assays of endothelial permeability to a MMCM and VEGF immunoreactivity of tumors support the hypothesis that VEGF is a major contributor to increased macromolecular permeability in cancers. When applied clinically, the MMCM-enhanced MRI approach could help to optimize the appropriate application of VEGF-inhibiting therapy on an individual patient basis.

Biomedical informatics--a confluence of disciplines?

BACKGROUND

Biomedical informatics is a broad discipline that borrows many methods and techniques from other disciplines.

OBJECTIVE

To reflect a) on the character of biomedical informatics and to determine whether it is multi-disciplinary or inter-disciplinary; b) on the question whether biomedical informatics is more than the sum of its supporting disciplines and c) on the position of biomedical informatics with respect to related disciplines.

METHOD

Inviting an international group of experts in biomedical informatics and related disciplines on the occasion of the 50th anniversary of Methods of Information in Medicine to present their viewpoints.

RESULTS AND CONCLUSIONS

This paper contains the reflections of a number of the invited experts on the character of biomedical informatics. Most of the authors agree that biomedical informatics is an interdisciplinary field of study where researchers with different scientific backgrounds alone or in combination carry out research. Biomedical informatics is a very broad scientific field and still expanding, yet comprised of a constructive aspect (designing and building systems). One author expressed that the essence of biomedical informatics, as opposed to related disciplines, lies in the modelling of the biomedical content. Interdisciplinarity also has consequences for education. Maintaining rigid disciplinary structures does not allow for sufficient adaptability to capitalize on important trends nor to leverage the influences these trends may have on biomedical informatics. It is therefore important for students to become aware of research findings in related disciplines. In this respect, it was also noted that the fact that many scientific fields use different languages and that the research findings are stored in separate bibliographic databases makes it possible that potentially connected findings will never be linked, despite the fact that these findings were published. Bridges between the sciences are needed for the success of biomedical informatics.

Perfusion MRI for monitoring the effect of sorafenib on experimental prostate carcinoma: a validation study

OBJECTIVE

The purpose of this study was to investigate with immunohistochemical validation whether dynamic contrast-enhanced MRI with small-molecule contrast medium is useful for monitoring the effects of the multikinase inhibitor sorafenib on prostate carcinomas in rats.

MATERIALS AND METHODS

Copenhagen rats (n = 20) into which prostate carcinoma (MAT-Ly-Lu-B2) had been implanted subcutaneously were imaged on the day of implantation and 7 days later with 3-T dynamic gadobutrol-enhanced MRI. The therapy group (n = 10) received daily administration of 10 mg/kg body weight sorafenib. Quantitative measurements of tumor perfusion, tumor vascularity, and permeability-surface area product were calculated with a two-compartment model. Dynamic contrast-enhanced MRI values were correlated with immunohistochemical results for validation.

RESULTS

Tumor perfusion in sorafenib-treated prostate carcinoma declined significantly from day 0 to day 7 (47.9 ± 36.8 mL/100 mL/min to 24.4 ± 18.6 mL/100 mL/min; p < 0.05). No significant effect on permeability-surface area product was observed in either the therapy or the control group (p > 0.05). Tumor vascularity decreased significantly (p < 0.05) from day 0 to day 7 under sorafenib treatment (15.6% ± 11.4% to 5.4% ± 2.1%). Immunohistochemical analysis revealed significantly lower tumor vascularity in the therapy than in the control group (rat endothelial cell antigen 1, 74.4 ± 16.9 cells vs 197 ± 75.4 cells; p < 0.05). In sorafenib-treated tumors, significantly more apoptotic cells (terminal deoxynucleotidyl transferase-mediated nick end labeling, 6923 ± 3761 vs 3167 ± 1500; p < 0.05) and significantly fewer proliferating cells (Ki-67, 10,198 ± 3064 vs 15,003 ± 3674; p < 0.05) were observed than in the control group. Modest but significant correlations were observed between tumor perfusion and immunohistochemical tumor cell apoptosis (r = -0.56; p < 0.05) and between tumor perfusion and immunohistochemical tumor vascularity (r = 0.56; p < 0.05).

CONCLUSION

Tumor perfusion quantified with gadobutrol-enhanced dynamic contrast-enhanced MRI can be used as a noninvasive surrogate parameter for monitoring the antiangiogenic, antiproliferative, and proapoptotic effects of sorafenib on prostate carcinoma allografts as validated with immunohistochemical analysis.