Noninvasive Visualization of the Activated αvβ3 Integrin in Cancer Patients by Positron Emission Tomography and [F]Galacto-RGD

Nuklearmedizinische Klinik und Poliklinik, Technische Universität München, Germany.
PLoS Medicine (Impact Factor: 14.43). 04/2005; 2(3):e70. DOI: 10.1371/journal.pmed.0020070
Source: PubMed


The integrin alphavbeta3 plays an important role in angiogenesis and tumor cell metastasis, and is currently being evaluated as a target for new therapeutic approaches. Several techniques are being studied to enable noninvasive determination of alphavbeta3 expression. We developed [(18)F]Galacto-RGD, a (18)F-labeled glycosylated alphavbeta3 antagonist, allowing monitoring of alphavbeta3 expression with positron emission tomography (PET).
Here we show by quantitative analysis of images resulting from a small-animal PET scanner that uptake of [(18)F]Galacto-RGD in the tumor correlates with alphavbeta3 expression subsequently determined by Western blot analyses. Moreover, using the A431 human squamous cell carcinoma model we demonstrate that this approach is sensitive enough to visualize alphavbeta3 expression resulting exclusively from the tumor vasculature. Most important, this study shows, that [(18)F]Galacto-RGD with PET enables noninvasive quantitative assessment of the alphavbeta3 expression pattern on tumor and endothelial cells in patients with malignant tumors.
Molecular imaging with [(18)F]Galacto-RGD and PET can provide important information for planning and monitoring anti-angiogenic therapies targeting the alphavbeta3 integrins and can reveal the involvement and role of this integrin in metastatic and angiogenic processes in various diseases.

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    • "Evaluation of RLPs in vivo was carried out using αvβ3 integrin receptor expressing M21 cells, whereas M21-L cells, which do not express the receptor, acted as negative control.34 M21 cells were maintained in DMEM and M21-L cells in RPMI 1640, both cell culture media supplemented with 10% volume/volume (v/v) heat-inactivated fetal bovine serum and 1% v/v penicillin/streptomycin/glutamine solution. "
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    ABSTRACT: Purpose Liposomes have been proposed to be a means of selectively targeting cancer sites for diagnostic and therapeutic applications. The focus of this work was the evaluation of radiolabeled PEGylated liposomes derivatized with varying amounts of a cyclic arginyl–glycyl–aspartic acid (RGD) peptide. RGD peptides are known to bind to αvβ3 integrin receptors overexpressed during tumor-induced angiogenesis. Methods Several liposomal nanoparticles carrying the RGD peptide targeting sequence (RLPs) were synthesized using a combination of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, cholesterol, diethylenetriaminepentaacetic acid-derivatized lipids for radiolabeling, a polyethylene glycol (PEG) building block, and a lipid-based RGD building block. Relative amounts of RGD and PEG building blocks were varied. In vitro binding affinities were determined using isolated αvβ3 integrin receptors incubated with different concentrations of RLPs in competition with iodine-125-labeled cyclo-(-RGDyV-). Binding of the indium-111-labeled RLPs was also evaluated. Biodistribution and micro single photon emission computed tomography/computed tomography imaging studies were performed in nude mice using different tumor xenograft models. Results RLPs were labeled with indium-111 with high radiochemical yields. In vitro binding studies of RLPs with different RGD/PEG loading revealed good binding to isolated receptors, which was dependent on the extent of RGD and PEG loading. Binding increased with higher RGD loading, whereas reduced binding was found with higher PEG loading. Biodistribution showed increased circulating time for PEGylated RLPs, but no dependence on RGD loading. Both biodistribution and micro single photon emission computed tomography/computed tomography imaging studies revealed low, nonspecific tumor uptake values. Conclusion In this study, RLPs for targeting angiogenesis were described. Even though good binding to αvβ3 integrin receptors was found in vitro, the balance between PEGylation and RGD loading clearly requires optimization to achieve targeting in vivo. These data form the basis for future development and provide a platform for the investigation of multimodal approaches.
    Full-text · Article · Nov 2012 · International Journal of Nanomedicine
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    • "18F-labeled RGD peptides including galacto-RGD [31], fluciclatide [38], and FPPRGD2 [39] have been used to treat cancer patients, and the FDA has approved the use of 18F-FPPRGD2 PET/CT imaging for evaluation of antiangiogenic therapy in solid tumors. However, the procedures for preparing such tracers are rather complex and time consuming, which limits their widespread clinical use [40]. "
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    ABSTRACT: 64Cu-cyclam-RAFT-c(-RGDfK-)4 is a novel multimeric positron emission tomography (PET) probe for aVb3 integrin imaging. Its uptake and αvβ3 expression in tumors showed a linear correlation. Since αvβ3 integrin is strongly expressed on activated endothelial cells during angiogenesis, we aimed to determine whether 64Cu-cyclam- RAFT-c(-RGDfK-)4 PET can be used to image tumor angiogenesis and monitor the antiangiogenic effect of a novel multi-targeted tyrosine kinase inhibitor, TSU-68. Athymic nude mice bearing human hepatocellular carcinoma HuH-7 xenografts, which expressed negligible aVb 3 levels on the tumor cells, received intraperitoneal injections of TSU-68 or the vehicle for 14 days. Antiangiogenic effects were determined at the end of therapy in terms of 64Cu-cyclam-RAFTc(- RGDfK-)4 uptake evaluated using PET, biodistribution assay, and autoradiography, and they were compared with microvessel density (MVD) determined by CD31 immunostaining. 64Cu-cyclam-RAFT-c(-RGDfK-)4 PET enabled clear tumor visualization by targeting the vasculature, and the biodistribution assay indicated high tumor-to-blood and tumor-to-muscle ratios of 31.6 ± 6.3 and 6.7 ± 1.1, respectively, 3 h after probe injection. TSU-68 significantly slowed tumor growth and reduced MVD; these findings were consistent with a significant reduction in the tumor 64Cucyclam- RAFT-c(-RGDfK-)4 uptake. Moreover, a linear correlation was observed between tumor MVD and the corresponding standardized uptake value (SUV) (r = 0.829, P = 0.011 for SUVmean; r = 0.776, P = 0.024 for SUVmax) determined by quantitative PET. Autoradiography and immunostaining showed that the distribution of intratumoral radioactivity and tumor vasculature corresponded. We concluded that 64Cu-cyclam-RAFT-c(-RGDfK-)4 PET can be used for in vivo angiogenesis imaging and monitoring of tumor response to antiangiogenic therapy.
    Full-text · Article · May 2012 · Angiogenesis
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    • "To date, several clinical trials with RGD-based tracers are either completed or in progress. 18F-galacto-RGD PET tracer was tested in cancer patients 51-58. The tracer is safe with an overall patient exposure similar to that from 18F-FDG imaging. "
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    ABSTRACT: Angiogenesis is a fundamental requirement for tumor growth and therefore it is a primary target for anti-cancer therapy. Molecular imaging of angiogenesis may provide novel opportunities for early diagnostic and for image-guided optimization and management of therapeutic regimens. Here we reviewed the advances in targeted imaging of key biomarkers of tumor angiogenesis, integrins and receptors for vascular endothelial growth factor (VEGF). Tracers for targeted imaging of these biomarkers in different imaging modalities are now reasonably well-developed and PET tracers for integrin imaging are currently in clinical trials. Molecular imaging of longitudinal responses to anti-angiogenic therapy in model tumor systems revealed a complex pattern of changes in targeted tracer accumulation in tumor, which reflects drug-induced tumor regression followed by vascular rebound. Further work will define the competitiveness of targeted imaging of key angiogenesis markers for early diagnostic and image-guided therapy.
    Full-text · Article · May 2012 · Theranostics
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