Molecular Imaging Of Tumor Angiogenesis Research Articles

Molecular Imaging of Tumor Angiogenesis and Therapeutic Effects with Dual Bioluminescence

Angiogenesis is critical for the growth of tumor by supplying nutrients and oxygen that exacerbates the metastasis and progression of cancer. Noninvasive imaging of angiogenesis during the tumor therapeutic processes may provide novel opportunities for image-guided tumor management. Here, we want to develop a mouse animal model for assessing cancer progression and angiogenesis in the same individuals by molecular imaging. Breast cancer model was developed with mouse breast cancer cell line 4T1 carrying a reporter system encoding a triple fusion (TF) reporter gene consisting of renilla luciferase (Rluc), red fluorescent protein (RFP) and herpes simplex virus truncated thymidine kinase (HSV-ttk) in transgenic mice, which expressed firefly luciferase (Fluc) under the promoter of vascular endothelial growth factor receptor 2 (Vegfr2-luc). The mice were subsequently treated with ganciclovir (GCV) and the tumor angiogenesis was tracked by Fluc imaging and the growth status of tumor was monitored by imaging of Rluc simultaneously. Overall, this traceable breast cancer model can simultaneously image the tumor growth and angiogenesis in single individual, which may facilitate a better understanding the mechanisms of angiogenesis in the progression and regression of tumor.

In situ validation of VEGFR-2 and α v ß 3 integrin as targets for breast lesion characterization.

Vascular endothelial growth factor receptor 2 (VEGFR-2) and α v ß 3 integrin are the most frequently addressed targets in molecular imaging of tumor angiogenesis. In preclinical studies, molecular imaging of angiogenesis has shown potential to detect and differentiate benign and malignant lesions of the breast. Thus, in this retrospective clinical study employing patient tissues, the diagnostic value of VEGFR-2, α v ß 3 integrin and vascular area fraction for the diagnosis and differentiation of breast neoplasia was evaluated. To this end, tissue sections of breast cancer (n=40), pre-invasive ductal carcinoma in situ (DCIS; n=8), fibroadenoma (n=40), radial scar (n=6) and normal breast tissue (n=40) were used to quantify (1) endothelial VEGFR-2, (2) endothelial α v ß 3 integrin and (3) total α v ß 3 integrin expression, as well as (4) the vascular area fraction. Sensitivity and specificity to differentiate benign from malignant lesions were calculated for each marker by receiver operating characteristics (ROC) analyses. Whereas vessel density, as commonly used, did not significantly differ between benign and malignant lesions (AUROC: 0.54), VEGFR-2 and α v ß 3 integrin levels were gradually up-regulated in carcinoma versus fibroadenoma versus healthy tissue. The highest diagnostic accuracy for differentiating carcinoma from fibroadenoma was found for total α v ß 3 integrin expression (AUROC: 0.76), followed by VEGFR-2 (AUROC: 0.71) and endothelial α v ß 3 integrin expression (AUROC: 0.68). In conclusion, total α v ß 3 integrin expression is the best discriminator between breast cancer, fibroadenoma and normal breast tissue. With respect to vascular targeting and molecular imaging of angiogenesis, endothelial VEGFR-2 appeared to be slightly superior to endothelial α v ß 3 for differentiating benign from cancerous lesions.

A Lipopeptide-Based αvβ3 Integrin-Targeted Ultrasound Contrast Agent for Molecular Imaging of Tumor Angiogenesis

The design and fabrication of targeted ultrasound contrast agents are key factors in the success of ultrasound molecular imaging applications. Here, we introduce a transformable αvβ3 integrin-targeted microbubble (MB) by incorporation of iRGD-lipopeptides into the MB membrane for non-invasive ultrasound imaging of tumor angiogenesis. First, the iRGD-lipopeptides were synthesized by conjugating iRGD peptides to distearoylphosphatidylethanolamine–polyethylene glycol 2000–maleimide. The resulting iRGD-lipopeptides were used for fabrication of the iRGD-carrying αvβ3 integrin-targeted MBs (iRGD-MBs). The binding specificity of iRGD-MBs for endothelial cells was found to be significantly stronger than that of control MBs (p < 0.01) under in vitro static and dynamic conditions. The binding of iRGD-MBs on the endothelial cells was competed off by pre-incubation with the anti-αv or anti-β3 antibody (p < 0.01). Ultrasound images taken of mice bearing 4T1 breast tumors after intravenous injections of iRGD-MBs or control MBs revealed strong contrast enhancement within the tumors from iRGD-MBs but not from the control MBs; the mean acoustic signal intensity was 10.71 ± 2.75 intensity units for iRGD-MBs versus 1.13 ± 0.18 intensity units for the control MBs (p < 0.01). The presence of αvβ3 integrin was confirmed by immunofluorescence staining. These data indicate that iRGD-MBs can be used as an ultrasound imaging probe for the non-invasive molecular imaging of tumor angiogenesis, and may have further implications for ultrasound image-guided tumor targeting drug delivery.

Ultrasound molecular imaging of tumor angiogenesis with a neuropilin-1-targeted microbubble

Ultrasound molecular imaging has great potential to impact early disease diagnosis, evaluation of disease progression and the development of target-specific therapy. In this paper, two neuropilin-1 (NRP) targeted peptides, CRPPR and ATWLPPR, were conjugated onto the surface of lipid microbubbles (MBs) to evaluate molecular imaging of tumor angiogenesis in a breast cancer model. Development of a molecular imaging agent using CRPPR has particular importance due to the previously demonstrated internalizing capability of this and similar ligands. In vitro, CRPPR MBs bound to an NRP-expressing cell line 2.6 and 15.6 times more than ATWLPPR MBs and non-targeted (NT) MBs, respectively, and the binding was inhibited by pretreating the cells with an NRP antibody. In vivo, the backscattered intensity within the tumor, relative to nearby vasculature, increased over time during the ∼6 min circulation of the CRPPR-targeted contrast agents providing high contrast images of angiogenic tumors. Approximately 67% of the initial signal from CRPPR MBs remained bound after the majority of circulating MBs had cleared (8 min), 8 and 4.5 times greater than ATWLPPR and NT MBs, respectively. Finally, at 7–21 days after the first injection, we found that CRPPR MBs cleared faster from circulation and tumor accumulation was reduced likely due to a complement-mediated recognition of the targeted microbubble and a decrease in angiogenic vasculature, respectively. In summary, we find that CRPPR MBs specifically bind to NRP-expressing cells and provide an effective new agent for molecular imaging of angiogenesis.

Micro-CT Molecular Imaging of Tumor Angiogenesis Using a Magnetite Nano-Cluster Probe

Due to its high resolution, micro-CT is desirable for molecular imaging of tumor angiogenesis. However, the sensitivity of micro-CT to contrast agents is relatively low. Therefore, the purpose of this study is to develop high micro-CT sensitive molecular imaging probes for direct visualization and dynamic monitoring of tumor angiogenesis. To this end, Arg-Gly-Asp (RGD) peptides conjugated magnetite nano clusters (RGD-MNCs) were developed by assembling individual magnetite nano particles into clusters with amphiphilic (maleimide) methoxypoly(ethylene glycol)-b-poly(lactic acid) ((Mal)mPEG-PLA) copolymer and subsequently encoding RGD peptides onto the clusters for specific targeting alpha(v)beta3 integrin. The hydrodynamic size of RGD-MNCs was about 85 nm. To test its specificity, alpha(v)beta3 positive cells (H1299) were incubated with magnetite nano clusters (MNCs), RGD-MNCs or RGD-MNCs competition with free RGD peptides. Prussian Blue staining and inductively coupled plasma optical emission spectrometer (ICP-OES) measurements indicated that the cell uptake of RGD-MNCs was significantly more than that of MNCs, which could be inhibited by free RGD peptides. For detection of tumor angiogenesis, mice bearing H1299 tumors were injected intravenously with RGD-MNCs at the dose of 400 micro mol Fe/kg. Tumor angiogenic hot spots as well as individual angiogenic vessels could be clearly manifested by micro-CT imaging 12 h post injection, which was dynamically monitored with the extension of probe circulation time. Subsequent histological studies of tumor tissues verified that RGD-MNCs registered tumor angiogenic vessels. Our study demonstrated that RGD-MNC probes fabricated in this study could be used to effectively target alpha(v)beta3 integrin. Using high resolution micro-CT in combination with the probes, tumor angiogenesis could be studied dynamically.

Molecular imaging of tumor angiogenesis with VEGFR2 targeting microbubbles in colon cancer bearing nude mice

Objective To evaluate the effect of tumor neovascularization imaging in a nude mouse model of colon cancer by contrast ultrasound molecular imaging (UMI) of VEGF receptor 2 (kinase insert domain receptor,KDR).Methods Targeted microbubbles (MBt) were built by conjugating K237,a small peptide with high affinity for KDR,to liposome microbubbles through a biotin-avidin bridge.Control microbubbles (MBc) with control peptide were prepared by the same method.Nude mice models of LS174T human colon cancer were established.MBt and MBc were injected intravenously in twelve mice in random order with an interval of 30 min.MBt were injected in another six mice after K237-peptide blocking.UMI was performed in all mice at 5 min postinjection to observe the imaging difference and measure the video intensity (Ⅵ) of tumor tissues in different groups.One-way analysis of variance and the least significant difference t test were performed to analyze the difference of tumor VI in the groups with MBt,MBc and K237 blocking.Immunohistochemistry was applied to detect the expression and distribution of KDR in tumor tissue and adjacent tumor tissues.Results K237 peptide was successfully conjugated to the surface of microbubbles through biotin-avidin mediation.Ultrasound imaging signal of the tumor was high in the MBt group,while there were no significant enhancement in the groups of K237 blocking and MBc.The VI in MBt,MBc and K237 blocking groups was significantly different (F =39.130,P ＜ 0.01).There was a significant difference of VI in the MBt group compared to the MBc group (30.18 ± 9.56 vs 8.28 ± 4.74,t =6.91,P ＜0.01).In the K237 blocking group Ⅵ was significantly lower than that in the MBt group (9.23 ± 3.44 vs 30.18 ± 9.56,t =4.91,P ＜ 0.01).Immunohistochemistry results showed that KDR was highy expressed in tumor tissue.Conclusions KDR-targeting liposome contrast microbubbles may specifically and efficiently link to tumor vascular endothelial cells in vivo.Thus it may be used for UMI of tumor angiogenesis. Key words: Colonic neoplasms; Neovascularization; Receptors, vascular endothelial growth factor; Ultrasonography; Microbubbles; Mice, nude

A concise review of magnetic resonance molecular imaging of tumor angiogenesis by targeting integrin &amp;alpha;v&amp;beta;3 with magnetic probes

Angiogenesis is an essential step for the growth and spread of malignant tumors. Accurate detection and quantification of tumor angiogenesis is important for early diagnosis of cancers as well as post therapy assessment of antiangiogenic drugs. The cell adhesion molecule integrin αvβ3 is a specific marker of angiogenesis, which is highly expressed on activated and proliferating endothelial cells, but generally not on quiescent endothelial cells. Therefore, in recent years, many different approaches have been developed for imaging αvβ3 expression, for the detection and characterization of tumor angiogenesis. The present review provides an overview of the current status of magnetic resonance molecular imaging of integrin αvβ3, including the new development of high sensitive contrast agents and strategies for improving the specificity of targeting probes and the biological effects of imaging probes on αvβ3 positive cells.

Multimeric System of 99mTc-Labeled Gold Nanoparticles Conjugated to c[RGDfK(C)] for Molecular Imaging of Tumor α(v)β(3) Expression

Integrin α(V)β(3) plays a critical role in tumor angiogenesis and metastasis. Suitably radiolabeled cyclic RGD peptides can be used for noninvasive imaging of α(V)β(3) expression. The aim of this research was to prepare a multimeric system of technetium-99m-labeled gold nanoparticles conjugated to c[RGDfK(C)] and to evaluate its biological behavior as a potential radiopharmaceutical for molecular imaging of tumor angiogenesis. Hydrazinonicotinamide-GGC (HYNIC-GGC) and c[RGDfK(C)] peptides were synthesized and conjugated to gold nanoparticles (AuNP, 20 nm) by means of spontaneous reaction of the thiol groups of cysteine. The nanoconjugate was characterized by TEM, FT-IR, UV-vis, XPS, and Raman spectroscopy. To obtain (99m)Tc-HYNIC-GGC-AuNP-c[RGDfK(C)] ((99m)Tc-AuNP-RGD), the (99m)Tc-HYNIC-GGC radiopeptide was first prepared and added to 1.5 mL of AuNP solution (1 nM) followed by c[RGDfK(C)] (10 μL, 50 μM) at 18 °C with stirring for 15 min. Radiochemical purity (RP) was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in α(V)β(3) receptor-positive C6 glioma cancer cells. Biodistribution studies were accomplished in athymic mice with C6-induced tumors with blocked and nonblocked receptors, and images were obtained using a micro-SPECT/CT. TEM and spectroscopy techniques demonstrated that AuNPs were functionalized with peptides. RP was 96 ± 2% without postlabeling purification. (99m)Tc-AuNP-RGD showed specific recognition for α(V)β(3) integrins expressed in C6 cells, and 3 h after i.p. administration in mice, the tumor uptake was 8.18 ± 0.57% ID/g. Micro-SPECT/CT images showed evident tumor uptake. (99m)Tc-AuNP-RGD demonstrates properties suitable for use as a target-specific agent for molecular imaging of tumor α(V)β(3) expression.

Abstract SY20-01: PET-guided and ultrasound-enhanced nanotherapy

Abstract Nanoencapsulation has the potential to reduce systemic toxicity while increasing the accumulation of drugs within tumors. In order to optimize therapeutic efficacy, we employ imaging to assess target availability and particle pharmacokinetics. We report on advances in the application of imaging to optimize nanotherapeutics. First, micron-sized bubbles have long been employed in cardiology to assess perfusion, and are widely available in Europe for the assessment of tumor perfusion. Such microbubbles can quantitatively assess the response of the vasculature to therapeutics, even differentiating the effects of unique anti-angiogenic therapeutics. Recently, microbubbles targeted to vascular integrins and VEGF have demonstrated the potential to detect and characterize tumors and are poised to enter human trials. With targeted ultrasound agents, multiple vascular receptors can be queried at a single study date. We will demonstrate the use of an RGD-targeted microbubble to assess syngeneic mouse tumors in a repeatable and specific fashion. The accumulation of targeted microbubbles on tumor endothelium occurs within 1-2 minutes (1), facilitating the personalized choice of therapies. Further, we have labeled nanoparticles for imaging with positron emission tomography (PET) and have demonstrated the use of such particles to detect the transition from premalignant to malignant lesions in preclinical studies. Nanoparticles, including 4×4×14 nm albumin (2), 100-nm liposomes and micron-diameter microbubbles (3), have been labeled for nuclear imaging of the shell (4-6) and in parallel the core of the particle has been imaged to assess stability. In particular, the accumulation of radiolabelled albumin, as assessed by PET, increased in a sensitive and gradual fashion over a malignant transition. PET imaging of radiolabelled particles also shows the potential to identify small regions of multifocal or metastatic disease that might otherwise be missed and facilitates mapping the heterogeneity of accumulation of particles with a diameter on the order of 100 nm or more. Based on such data, we have created an image-guided pharmacokinetic model encompassing particle circulation and stability (7) and applied this model and associated labeling methods to provide head-to-head comparisons of the pharmacokinetics of various nanotechnologies. In preclinical studies, stable particles accumulate to ∼5-10% ID/g within 24 hours. In a syngeneic mouse model, such accumulation can be locally increased to ∼20% ID/g with the application of therapeutic ultrasound (8, 9). Finally, in order to capitalize on the potential of nanomedicine, our laboratory has been focused on the development of particles that minimize systemic toxicity. With this approach, drug scheduling can be optimized for therapeutic impact. For example, we have formed a precipitate complex between copper and doxorubicin within nanoparticles (9). The advantage of this approach is that the particles are loaded at neutral pH and the copper-doxorubicin complex remains intact until a low pH environment is encountered in a lysosome or tumor. We found that the cardiac toxicity of doxorubicin was not detectable with this approach, while the tumor efficacy was undiminished. After a 28-day course of therapy with copper-doxorubicin liposomes, augmented with ultrasound, syngeneic tumors regressed to a premalignant phenotype of ∼ (1 mm)3 or could not be detected.

Ultrasound Molecular Imaging of Tumor Angiogenesis With an Integrin Targeted Microbubble Contrast Agent

Ultrasound molecular imaging is an emerging technique for sensitive detection of intravascular targets. Molecular imaging of angiogenesis has strong potential for both clinical use and as a research tool in tumor biology and the development of antiangiogenic therapies. Our objectives are to develop a robust ultrasound contrast agent platform using microbubbles (MB) to which targeting ligands can be conjugated by biocompatible, covalent conjugation chemistry, and to develop a pure low mechanical index (MI) imaging processing method and corresponding quantification method. The MB and the imaging methods were evaluated in a mouse model of breast cancer in vivo. We used a cyclic arginine-glycine-aspartic acid (cRGD) pentapeptide containing a terminal cysteine group conjugated to the surface of MB bearing pyridyldithio-propionate (PDP) for targeting αvβ3 integrins. As negative controls, MB without a ligand or MB bearing a scrambled sequence (cRAD) were prepared. To enable characterization of peptides bound to MB surfaces, the cRGD peptide was labeled with FITC and detected by plate fluorometry, flow cytometry, and fluorescence microscopy. Targeted adhesion of cRGD-MB was demonstrated in an in vitro flow adhesion assay against recombinant murine αvβ3 integrin protein and αvβ3 integrin-expressing endothelial cells (bEnd.3). The specificity of cRGD-MB for αvβ3 integrin was demonstrated by treating bEnd.3 EC with a blocking antibody. A murine model of mammary carcinoma was used to assess targeted adhesion and ultrasound molecular imaging in vivo. The targeted MB were visualized using a low MI contrast imaging pulse sequence, and quantified by intensity normalization and 2-dimensional Fourier transform analysis. The cRGD ligand concentration on the MB surface was ∼8.2 × 10(6) molecules per MB. At a wall shear stress of 1.0 dynes/cm, cRGD-MB exhibited 5-fold higher adhesion to immobilized recombinant αvβ3 integrin relative to nontargeted MB and cRAD-MB controls. Similarly, cRGD-MB showed significantly greater adhesion to bEnd.3 EC compared with nontargeted MB and cRAD-MB. In addition, cRGD-MB, but not nontargeted MB or cRAD-MB, showed significantly enhanced contrast signals with a high tumor-to-background ratio. The adhesion of cRGD-MB to bEnd.3 was reduced by 80% after using anti-αv monoclonal antibody to treat bEnd.3. The normalized image intensity amplitude was ∼0.8, 7 minutes after the administration of cRGD-MB relative to the intensity amplitude at the time of injection, while the spatial variance in image intensity improved the detection of bound agents. The accumulation of cRGD-MB was blocked by preadministration with an anti-αv blocking antibody. The results demonstrate the functionality of a novel MB contrast agent covalently coupled to an RGD peptide for ultrasound molecular imaging of αvβ3 integrin and the feasibility of quantitative molecular ultrasound imaging with a low MI.

Quantum dots for multimodal molecular imaging of angiogenesis

Quantum dots exhibit unique optical properties for bioimaging purposes. We have previously developed quantum dots with a paramagnetic and functionalized coating and have shown their potential for molecular imaging purposes. In the current mini-review we summarize the synthesis procedure, the in vitro testing and, importantly, the in vivo application for multimodal molecular imaging of tumor angiogenesis.

VEGFR‐2 Targeted Microbubble Contrast Agents for Ultrasound Molecular Imaging of Tumor Angiogenesis

Ultrasound molecular imaging is an emerging technique for detecting intravascular targets. We have developed a novel microbubble (MB) ultrasound contrast agent covalently coupled to a recombinant single‐chain VEGF construct (scVEGF), which binds VEGFR‐2 (KDR) on the angiogenic endothelium. Ligand conjugation was first validated with a fluorophore (BODIPY‐cystine), and covalently bound dye was detected by fluorometry and flow cytometry. MB were subsequently conjugated to scVEGF, which bound at ~100,000 molecules/MB (ELISA). Targeted adhesion of scVEGF‐MB was demonstrated with in vitro flow assays. At 0.5 dynes/cm2, scVEGF‐MB exhibited 5‐fold higher adhesion to both recombinant murine VEGFR‐2 and porcine aortic endothelial cells transfected with VEGFR‐2 (PAE/KDR) compared to non‐targeted control MB. Additionally, scVEGF‐MB targeted to immobilized VEGFR‐2 in an ultrasound flow phantom showed an 8‐fold increase in mean acoustic signal relative to casein‐coated control channels. A murine model of colon adenocarcinoma was used to assess targeted adhesion in vivo, and scVEGF MB, but not control MB, showed significantly higher ultrasound contrast signal enhancement in tumors. These results demonstrate the functionality of a novel scVEGF‐bearing microbubble contrast agent, which could be a valuable research tool for molecular imaging of VEGFR‐2. Supported by NIH 1R43EB007857.

Improved Magnetic Resonance Molecular Imaging of Tumor Angiogenesis by Avidin-Induced Clearance of Nonbound Bimodal Liposomes

Angiogenic, that is, newly formed, blood vessels play an important role in tumor growth and metastasis and are a potential target for tumor treatment. In previous studies, the alpha(v)beta(3) integrin, which is strongly expressed in angiogenic vessels, has been used as a target for Arg-Gly-Asp (RGD)-functionalized nanoparticulate contrast agents for magnetic resonance imaging-based visualization of angiogenesis. In the present study, the target-to-background ratio was increased by diminishing the nonspecific contrast enhancement originating from contrast material present in the blood pool. This was accomplished by the use of a so-called avidin chase, which allowed rapid clearance of non-bound paramagnetic RGD-biotin-liposomes from the blood circulation. C57BL/6 mice, bearing a B16F10 mouse melanoma, received RGD-functionalized or untargeted biotin-liposomes, which was followed by avidin infusion or no infusion. Precontrast, postcontrast, and postavidin T(1)-weighted magnetic resonance images were acquired at 6.3 T. Postcontrast images showed similar percentages of contrast-enhanced pixels in the tumors of mice that received RGD-biotin-liposomes and biotin-liposomes. Post avidin infusion this percentage rapidly decreased to precontrast levels for biotin-liposomes, whereas a significant amount of contrast-enhanced pixels remained present for RGD-biotin-liposomes. These results showed that besides target-associated contrast agent, the circulating contrast agent contributed significantly to the contrast enhancement as well. Ex vivo fluorescence microscopy confirmed association of the RGD-biotin-liposomes to tumor endothelial cells both with and without avidin infusion, whereas biotin-liposomes were predominantly found within the vessel lumen. The clearance methodology presented in this study successfully enhanced the specificity of molecular magnetic resonance imaging and opens exciting possibilities for studying detection limits and targeting kinetics of site-directed contrast agents in vivo.

Multimodality Molecular Imaging of Tumor Angiogenesis

Molecular imaging is a key component of 21st-century cancer management. The vascular endothelial growth factor (VEGF)/VEGF receptor signaling pathway and integrin alpha v beta 3, a cell adhesion molecule, play pivotal roles in regulating tumor angiogenesis, the growth of new blood vessels. This review summarizes the current status of tumor angiogenesis imaging with SPECT, PET, molecular MRI, targeted ultrasound, and optical techniques. For integrin alpha v beta 3 imaging, only nanoparticle-based probes, which truly target the tumor vasculature rather than tumor cells because of poor extravasation, are discussed. Once improvements in the in vivo stability, tumor-targeting efficacy, and pharmacokinetics of tumor angiogenesis imaging probes are made, translation to clinical applications will be critical for the maximum benefit of these novel agents. The future of tumor angiogenesis imaging lies in multimodality and nanoparticle-based approaches, imaging of protein-protein interactions, and quantitative molecular imaging. Combinations of multiple modalities can yield complementary information and offer synergistic advantages over any modality alone. Nanoparticles, possessing multifunctionality and enormous flexibility, can allow for the integration of therapeutic components, targeting ligands, and multimodality imaging labels into one entity, termed "nanomedicine," for which the ideal target is tumor neovasculature. Quantitative imaging of tumor angiogenesis and protein-protein interactions that modulate angiogenesis will lead to more robust and effective monitoring of personalized molecular cancer therapy. Multidisciplinary approaches and cooperative efforts from many individuals, institutions, industries, and organizations are needed to quickly translate multimodality tumor angiogenesis imaging into multiple facets of cancer management. Not limited to cancer, these novel agents can also have broad applications for many other angiogenesis-related diseases.

New Trends in Molecular Imaging of Tumor Angiogenesis

Tumor development leading to cancer is a complex process involving several steps. Among them, angiogenesis, ie growth of new tumor induced blood vessels is one of the most important therapeutic targets in the search for anticancer agents. One point which remain to be addressed is the detection of tumor angiogenic areas, ie tumor angiogenesis imaging. After presenting the key points of tumor development which lead to neoangiogenesis, and providing an overview of the main therapeutic approaches in this field, this review focuses on the recent progress in angiogenesis imaging, namely the one dealing with matrix metalloproteases. These enzymes are indeed present to major phenomena of the tumor progression. The different imaging approaches are described, namely the ones using optical, radiochemical or magnetic resonance ones.

Monitoring Response to Anticancer Therapy by Targeting Microbubbles to Tumor Vasculature

New strategies to detect tumor angiogenesis and monitor response of tumor vasculature to therapy are needed. Contrast ultrasound imaging using microbubbles targeted to tumor endothelium offers a noninvasive method for monitoring and quantifying vascular effects of antitumor therapy. We investigated the use of targeted microbubbles to follow vascular response of therapy in a mouse model of pancreatic adenocarcinoma. Microbubbles conjugated to monoclonal antibodies were used to image and quantify vascular effects of two different antitumor therapies in s.c. and orthotopic pancreatic tumors in mice. Tumor-bearing mice were treated with anti-vascular endothelial growth factor (VEGF) monoclonal antibodies and/or gemcitabine, and the localization of microbubbles to endoglin (CD105), VEGF receptor 2 (VEGFR2), or VEGF-activated blood vessels (the VEGF-VEGFR complex) was monitored by contrast ultrasound. Targeted microbubbles showed significant enhancement of tumor vasculature when compared with untargeted or control IgG-targeted microbubbles. Video intensity from targeted microbubbles correlated with the level of expression of the target (CD105, VEGFR2, or the VEGF-VEGFR complex) and with microvessel density in tumors under antiangiogenic or cytotoxic therapy. We conclude that targeted microbubbles represent a novel and attractive tool for noninvasive, vascular-targeted molecular imaging of tumor angiogenesis and for monitoring vascular effects specific to antitumor therapy in vivo.

Multimodality Imaging

Noninvasive “multimodal” in vivo imaging is not just becoming standard practice in the clinic, but is rapidly changing the evolving field of experimental imaging of genetic expression (“molecular imaging”). The development of multimodality methodology based on nuclear medicine (NM), positron emission tomography (PET) imaging, magnetic resonance imaging (MRI), and optical imaging is the single biggest focus in many imaging and cancer centers worldwide and is bringing together researchers and engineers from the far-ranging fields of molecular pharmacology to nanotechnology engineering. The rapid growth of in vivo multimodality imaging arises from the convergence of established fields of in vivo imaging technologies with molecular and cell biology. The cross-pollination of these disciplines has been accelerated in part by the establishment of the National Institutes of Health NCI P20 and P50 awards, for example, and by the sheer potential of the technology. Multimodality imaging is widely considered to involve the incorporation of two or more imaging modalities, usually within the setting of a single examination using, for example, dual- or triple-labeled optical or nuclear medicine “reporter” agents or by performing ultrasound or optical studies within the MR, single-photon emission computed tomography (SPECT), or x-ray computed tomography (CT) environment. Clinically, the best example of multimodality imaging is seen in the rapid evolution of PET-SPECT and PET-CT scanner hybrids. The PET modality has developed into perhaps the most used “multimodal” imaging method. The incorporation of PET into single, hybrid, and multimodality units to provide functional (typically from injected F-18DG studies) and anatomic information is becoming extremely popular,1–2 so much so that, for example, PET/CT hybrids can be found in outpatient screening centers located in shopping malls. The role of any multimodal imaging …