Molecular imaging of angiogenesis after myocardial infarction by 111In-DTPA-cNGR and 99mTc-sestamibi dual-isotope myocardial SPECT
© Hendrikx et al.; licensee Springer. 2015
Received: 1 October 2014
Accepted: 5 January 2015
Published: 28 January 2015
CD13 is selectively upregulated in angiogenic active endothelium and can serve as a target for molecular imaging tracers to non-invasively visualise angiogenesis in vivo. Non-invasive determination of CD13 expression can potentially be used to monitor treatment response to pro-angiogenic drugs in ischemic heart disease. CD13 binds peptides and proteins through binding to tripeptide asparagine-glycine-arginine (NGR) amino acid residues.
Previous studies using in vivo fluorescence microscopy and magnetic resonance imaging indicated that cNGR tripeptide-based tracers specifically bind to CD13 in angiogenic vasculature at the border zone of the infarcted myocardium.
In this study, the CD13-binding characteristics of an 111In-labelled cyclic NGR peptide (cNGR) were determined. To increase sensitivity, we visualised 111In-DTPA-cNGR in combination with 99mTc-sestamibi using dual-isotope SPECT to localise CD13 expression in perfusion-deficient regions.
Myocardial infarction (MI) was induced in Swiss mice by ligation of the left anterior descending coronary artery (LAD). 111In-DTPA-cNGR and 99mTc-sestamibi dual-isotope SPECT imaging was performed 7 days post-ligation in MI mice and in control mice. In addition, ex vivo SPECT imaging on excised hearts was performed, and biodistribution of 111In-DTPA-cNGR was determined using gamma counting. Binding specificity of 111In-DTPA-cNGR to angiogenic active endothelium was determined using the Matrigel model.
Labelling yield of 111In-DTPA-cNGR was 95% to 98% and did not require further purification. In vivo, 111In-DTPA-cNGR imaging showed a rapid clearance from non-infarcted tissue and a urinary excretion of 82% of the injected dose (I.D.) 2 h after intravenous injection in the MI mice. Specific binding of 111In-DTPA-cNGR was confirmed in the Matrigel model and, moreover, binding was demonstrated in the infarcted myocardium and infarct border zone.
Our newly designed and developed angiogenesis imaging probe 111In-DTPA-cNGR allows simultaneous imaging of CD13 expression and perfusion in the infarcted myocardium and the infarct border zone by dual-isotope micro-SPECT imaging.
KeywordsMyocardial infarction Angiogenesis CD13 Micro-SPECT
The formation of new capillaries from existing micro vessels occurs as a natural healing process following myocardial infarction (MI) . This process, called angiogenesis, is triggered by ischemia and results in partial restoration of blood perfusion in the ischemic zone. Importantly, the extent of angiogenesis is associated with post-infarct remodelling and has positive implications for the prognosis of MI patients . Several therapy approaches, aimed at stimulating angiogenesis in the infarcted area, including gene therapy, intramyocardial administration of pro-angiogenic factors, administration of bone marrow-derived stem cells, and transmyocardial revascularization have been tested [3-12]. To date, results in animal models have been encouraging [3-5]. Nonetheless, the clinical translation of these therapies has proven to be difficult, and the clinical benefit for MI patients has been disappointing and controversial [6-12].
In order to improve treatment options, assessing the efficacy of pro-angiogenic therapies and monitoring the temporal development of angiogenesis, non-invasive methods (e.g. molecular imaging) are warranted. A sensitive and specific molecular imaging marker for angiogenesis, however, is still missing.
Angiogenic vessels demonstrate upregulation of CD13, a membrane-bound aminopeptidase, on activated endothelial cells [13,14]. The cyclic tripeptide Asn-Gly-Arg (cNGR) homes to CD13 expressed on endothelial cells of angiogenic tumour vasculature and angiogenic vessels in the infarcted area and border zones of the myocardium [14-19]. Moreover, evidence was obtained that cNGR does not bind to CD13-positive macrophages in the infarcted myocardium and infarct border zone. This finding was ascribed to cNGR, possibly targeting a subset of post-translationally modified CD13 that might be specific to smaller and perhaps newly formed vessels . Furthermore, using polymerase chain reaction, peak expression of CD13 was shown 7 days after MI in a mouse myocardial infarction model . Non-invasive imaging of CD13 in mice has further been demonstrated with cNGR-labelled paramagnetic quantum dots for molecular magnetic resonance imaging (MRI) . Although angiogenic activity could selectively and non-invasively be depicted in the infarcted heart, molecular imaging with MRI requires high contrast agent dosage, which hampers translation to clinical trials.
The arginine-glycine-aspartic-acid (RGD) motif is known to label angiogenic active endothelium through binding to αvβ3 integrin . In several pre-clinical studies in different neovascularisation models, RGD conjugated agents have been employed [2,22]. However, competition studies in tumour angiogenesis with the NGR and RGD motif demonstrated a threefold higher target homing ratio (tumour/control organ) for NGR than that for RGD .
In this study, we designed and developed a CD13 molecular imaging probe that allowed sensitive visualisation using micro-SPECT imaging. In order to target CD13, we used the cNGR tripeptide, having a tenfold higher targeting efficacy than the linear entity , to design a non-invasive angiogenesis imaging probe. Thereto, the cNGR tripeptide was conjugated with diethylene triamine pentaacetic acid (DTPA), radiolabeled with 111In and evaluated in a mouse model of myocardial infarction in combination with 99mTc-sestamibi in dual-isotope micro-SPECT imaging. In order to determine binding specificity of our newly designed probe, we employed the validated subcutaneous Matrigel plug assay as a model for in vivo angiogenesis.
NAc-Cys(4MeBzl)-Asn(Xanthyl)-Gly-Arg(Tosyl)-Cys(4MeBzl)-Gly-Gly-Lys(2 chloro-Z)-peptide was synthesised by tert-butyloxycarbonyl (tBoc) solid-phase peptide synthesis, on 4-methylbenzhydryl amine resin, as described before [15,24]. After coupling of the last amino acid, the Boc-protecting group was cleaved and the peptide was Nα acetylated (10 mL DMF + 230 μL acetic anhydride + 190 μL pyridine, 2 × 2 min). Resin-bound peptide (0.35 g) was cleaved and simultaneously deprotected in anhydrous HF (1 h, 0°C) with 4 vol.% p-cresol as a scavenger and the product was precipitated with ice-cold diethyl ether, collected on a glass filter, eluted from the filter using H2O/CH3CN/TFA (50:50:0.1 v/v/v) and lyophilized to give crude material containing NAc-Cys-Asn-Gly-Arg-Cys-Gly-Gly-Lys-NH2. Subsequently, 31.1 mg crude NAc-Cys-Asn-Gly-Arg-Cys-Gly-Gly-Lys-NH2 was dissolved in 50 mL 0.1 M TRIS buffer (pH 8), containing 1 M Gn HCl. The resulting solution was stirred for 3 h at room temperature to form the internal disulfide bond. Reaction progress was monitored by analytical HPLC, and after reaction completion, oxidised NAc-Cys-Asn-Gly-Arg-Cys-Gly-Gly-Lys-NH2 was purified by semi-preparative HPLC.
Cys-DTPA was coupled to the C-terminal lysine residue of cNGR peptide through a bifunctional succinimidyl ester-maleimide linker, sulfo-SMCC . Therefore, 6.3 mg (7.6 μmol) cyclic(NAc-Cys-Asn-Gly-Arg-Cys-Gly-Gly-Lys; cNGR) and 3.5 mg (8.0 μmol; 1.1 eq) sulfo-SMCC were dissolved in 2 mL 0.2 M phosphate buffer (pH 7.5) containing 6 M Gn HCl. After 3.5 h, the reaction mixture was purified by semi-preparative HPLC. Finally, 4.1 mg (4.1 μmol) SMCC-cNGR and 3.5 mg (6.2 μmol; 1.5 eq) Cys-DTPA were dissolved in 400 μL 6 M Gn HCl, 0.2 M phosphate buffer (pH 6.5). The resulting solution was stirred at 37°C, and reaction progress was monitored by analytical HPLC. After reaction completion, the reaction mixture was purified by preparative HPLC, resulting in 4.2 mg DTPA-SMCC-cNGR (yield 63.4%; overall yield 34.3%).
Overview of the number of animals that were subjected to different SPECT scans
Injected activity (MBq)
Number of Swiss mice used
In vivo; MI mice
8 consecutive time frames (15 min each)
30 to 100 MBq 111In-DTPA-cNGR co-injected with 100 to 150 MBq 99mTc-sestamibi
In vivo; control mice
8 consecutive time frames (15 min each)
30 to 100 MBq 111In-DTPA-cNGR co-injected with 100 to 150 MBq 99mTc-sestamibi
Ex vivo; heart slices of MI mice
1 time frame (240 min)
Out of 7 MI mice, 4 were used for ex vivo scanning purposes
Ex vivo; explanted Matrigels
1 time frame (180 min)
90 to 110 MBq 111In-DTPA-cNGR
Ten micrograms of DTPA-cNGR was dissolved in 0.5 ml of NaAc buffer (0.5 M, pH6) and radiolabeled with 111InCl3 (400 to 600 MBq, in ± 0.2 ml 0.1 M HCl, Mallinckrodt, Petten, The Netherlands) at room temperature for 30 min. Product purity was checked by HPLC (Shimadzu Corporation, Columbia, MD, USA) using an Aeris WIDEPORE 3.6u XB-C18 column 250 × 4.6 mm (Phenomenex, Utrecht, The Netherlands) eluted with a gradient from 0.1% trifluoroacetic acid (TFA) in water (0 to 3 min) to acetonitrile (ACN) over the course of 20 min at a flow rate of 1 ml/min.
99mTc-sestamibi was prepared with freshly eluted pertechnetate from a 99Mo/99mTc generator (UltraTechneKow, Mallinckrodt Medical, Petten, The Netherlands). A fraction of the eluate was added to the lyophilized sestamibi-kit (Mallinckrodt Medical, Petten, The Netherlands), and the product was prepared according to manufacturer guidelines. Quality controls were satisfactory for every synthesis (radiochemical purity >98%).
Mice were anesthetised with isoflurane (induction 2.5%; maintenance; 1.5%), a catheter was placed in the tail vein and the animals were positioned in the micro-SPECT camera (MiLabs, Utrecht, The Netherlands).
Using this formula, we were able to determine the following CFs: CFTc = 635 MBq and CFIn = 648 MBq.
For body weight, we assumed that 1 g of body weight equalled 1 ml.
In order to quantify the absolute uptake of 111In-DTPA-cNGR in the different heart pieces, gamma counting was performed using an automated NaI(Tl) gamma counter (Wallac Wizard, Turku, Finland). Additionally, we dissected the vital organs of the mice to study overall biodistribution. The uptake of 111In-DTPA-cNGR was determined 2 h post-injection (p.i.) for both MI (n ≥ 5) and control animals (n ≥ 4). Data were expressed as percentage of injected dose per gram tissue (%ID/g). Urinal excretion was expressed as %ID.
Following ex vivo SPECT scans, the explanted Matrigels were kept for gamma counting. Muscular tissue from the hind limb was harvested as a reference. The activity per Matrigel was corrected for ID and weight of the matrigel.
Data were expressed as averages for each group ± standard error of the mean (SEM). To test the significance, we performed unpaired one-tailed student's t-test and p < 0.05 was considered statistically significant. Data were analysed using Microsoft Excel (version 2010).
After cleavage from the solid support with HF, the linear NGR peptide was cyclised by the formation of an internal disulfide bond. This resulted in a mass reduction of 2 by the loss of two protons. MALDI-ToF analysis of the linear peptide showed a mass of 835.47 (calculated: 834.97; C30H54N14O10S2 [M + H]+). For the oxidised peptide, a mass of 833.30 was observed on ESI-MS (calculated: 832.95; C30H52N14O10S2 [M + H]+) Subsequently, a linker that contains both an NHS ester and a maleimide reactive group was coupled to the Nε-group of lysine. Finally, the maleimide group was used to couple Cys-DTPA. cNGR-SMCC-DTPA was obtained in an overall yield of 34.3%. ESI-MS of cNGR-SMCC-DTPA: m/z C63H102N20O24S3 [M + H]+ calculated monoisotopic mass: 1618.65; found: 1619.72.
Synthesis of 111In-DTPA-cNGR
The labelling yield of 111In-DTPA-cNGR was 95% to 99% for every synthesis and did not require further purification.
Micro-SPECT imaging and analysis
Overview of the SUVs of 99m Tc-sestamibi and 111 In-DTPA-cNGR in healthy control mice ( n = 5) and MI mice ( n = 7)
Standardised uptake values (SUV)
1. Basal anterior
1.87 ± 0.34
1.94 ± 0.36
0.16 ± 0.05
0.24 ± 0.04
2. Basal anteroseptal
1.63 ± 0.28
1.72 ± 0.33
0.16 ± 0.05
0.21 ± 0.03
3. Basal inferoseptal
1.54 ± 0.29
1.38 ± 0.28
0.13 ± 0.06
0.20 ± 0.02
4. Basal inferior
1.77 ± 0.28
1.64 ± 0.24
0.15 ± 0.05
0.23 ± 0.03
5. Basal inferolateral
1.68 ± 0.30
1.78 ± 0.31
0.14 ± 0.04
0.23 ± 0.03*
6. Basal anterolateral
1.95 ± 0.33
2.11 ± 0.39
0.18 ± 0.06
0.26 ± 0.04
7. Mid anterior
1.80 ± 0.30
1.18 ± 0.26
0.15 ± 0.05
0.21 ± 0.02
8. Mid anteroseptal
1.67 ± 0.28
1.73 ± 0.27
0.14 ± 0.06
0.20 ± 0.02
9. Mid inferoseptal
1.80 ± 0.34
1.82 ± 0.30
0.12 ± 0.06
0.18 ± 0.03
10. Mid inferior
1.72 ± 0.28
1.85 ± 0.31
0.12 ± 0.05
0.17 ± 0.03
11. Mid inferolateral
1.71 ± 0.25
1.60 ± 0.32
0.11 ± 0.04
0.20 ± 0.03
12. Mid anterolateral
2.03 ± 0.32
1.15 ± 0.37
0.15 ± 0.05
0.24 ± 0.01*
13. Apical anterior
1.64 ± 0.30
0.49 ± 0.10*
0.11 ± 0.03
0.21 ± 0.02*
14. Apical septal
1.82 ± 0.34
1.55 ± 0.25
0.12 ± 0.04
0.20 ± 0.03
15. Apical inferior
1.67 ± 0.28
1.36 ± 0.35
0.10 ± 0.03
0.18 ± 0.03*
16. Apical lateral
1.60 ± 0.30
0.64 ± 0.24*
0.14 ± 0.04
0.22 ± 0.02*
1.47 ± 0.34
0.39 ± 0.17*
0.10 ± 0.03
0.20 ± 0.03*
Biodistribution of 111In-DTPA-cNGR
Binding of 111In-DTPA-cNGR to angiogenic active endothelium
Angiogenesis is associated with post-infarct remodelling and has important implications for prognosis following MI . While previous research has mainly focused on developing pro-angiogenic therapies to stimulate angiogenesis in the infarcted myocardium [28,29], a clinically applicable method for the evaluation of these therapies is still lacking. Most clinical studies thus far have relied on indirect evidence of myocardial angiogenesis. For example, changes in stress-induced ischemia and myocardial perfusion were assessed by treadmill exercise testing and dual-isotope gated SPECT thallium-201/99mTc-sestamibi perfusion SPECT imaging at baseline, day 29, day 57 and day 180 after administration of the pro-angiogenic recombinant-fibroblast growth factor 2 (rFGF2) in a clinical study . In another study, using a single intracoronary infusion of rFGF2, patients experienced increased quality of life (assessed by Seattle Angina Questionnaire) and exercise tolerance (assessed by treadmill exercise testing). Moreover, in this study, MRI demonstrated increased regional wall thickening and a reduction in the extent of the ischemic area compared to baseline .
A clinical trial was performed in which patients with exertional angina were treated with the pro-angiogenic recombinant human vascular endothelial growth factor (rhVEGF) . In this trial, no improvement in exercise treadmill test time or myocardial perfusion, as assessed by rest-stress thallium-201/99mTc-sestamibi (gated) SPECT scanning protocol, was detected. However, patients experienced a significant improvement in angina class at day 120 after the first administration of rhVEGF . Furthermore, in a small phase 1 clinical study using VEGF gene transfer, all patients had significant reduction in angina and objective evidence of reduced ischemia was documented using dobutamine 99mTc-sestamibi SPECT imaging. Post-operative left ventricular ejection fraction (LVEF) was either unchanged or improved. Moreover, the Rentrop scoring system, indicating the coronary collateral filling as assessed by coronary angiography, improved in all patients .
The pro-angiogenic effect of transmyocardial laser revascularisation (TMLR) was assessed in a small clinical study (seven patients) by Rimoldi et al. While angina scores (Canadian Cardiovascular Society) decreased significantly, exercise tolerance (treadmill testing), 12-min walk distance and the LVEF (assessed by radionuclide ventriculography) remained unchanged. Moreover, despite subjective improvement in some patients, myocardial blood flow (as assessed by 15O-labelled water) during dobutamine in lasered segments failed to show any significant increase .
Clearly, improved myocardial perfusion or function can be used as indirect evidence for angiogenesis in the infarcted myocardium. Reduced angina scores, increased treadmill exercise times and improved myocardial perfusion as measured by angiography, SPECT, PET and MRI all seem to indicate recovery . However, despite the ability of these methods to indicate recovery, it often takes several months before any improvement can be detected. Therefore, these methods, used in current MI patient care, lack the sensitivity to monitor, or predict, pro-angiogenic treatment. To make direct angiogenesis imaging available for MI patient care, sensitive and specific non-invasive direct angiogenesis imaging probes are required.
To our knowledge, this is the first time CD13 expression was visualised with a nuclear cNGR probe in a mouse model of MI using dual-isotope micro-SPECT imaging. Simultaneous perfusion-imaging enabled us to visualise the angiogenesis process in the border zone of the infarct and the infarcted tissue itself. According to previous studies from our lab, angiogenesis is expected to occur in the infarct area and border zone of the infarct [15,20]. Additionally, in co-localisation experiments using the fluorescently labelled endothelial cell marker anti-CD31-PE, the fluorescently labelled angiogenic active endothelial cell marker anti-CD105-FITC and fluorescently labelled cNGR conjugates, evidence for preferential binding of cNGR conjugates to angiogenic active endothelial cells of capillaries and larger vessels with an inner diameter up to 15 μm was provided [15,20]. Moreover, despite the abundant presence of CD13-positive macrophages, fluorescently labelled cNGR did not bind to anti-CD13-FITC labelled macrophages . In the current study, we used the exact same animal model and the same cNGR moiety, assuring identical experimental conditions. Extrapolating from these data, we therefore consider binding of our 111In-DTPA-cNGR imaging probe to be specific for angiogenic endothelium.
Specific binding of our probe is further emphasised by enhanced binding of 111In-DTPA-cNGR to angiogenic active endothelium in a specific model for angiogenesis. Unfortunately (hFGF2-supplemented) Matrigels, implanted in the flanks for optimal stimulation of angiogenesis, were unrecognisable on in vivo SPECT scans as high renal uptake hampered image analysis. Therefore, we explanted the Matrigels and performed ex vivo SPECT scans that indicated higher uptake of 111In-DTPA-cNGR in hFGF2-supplemented Matrigels compared with control Matrigels. Moreover, the uptake of 111In-DTPA-cNGR in hFGF2-supplemented Matrigels was higher compared with that in the control Matrigels as indicated by gamma counting. hFGF2-supplemented Matrigels displayed significantly higher uptake than control muscle tissue, indicating active angiogenesis.
To use this imaging probe in a clinical setting, the probe should display a high specific target uptake and fast clearance from non-specific organs. The biodistribution characteristics of our probe were studied 2 h post-injection and demonstrated a rapid clearance in the urine which is a favourable clearance pathway. This is in contrast with results for the hydrophilic RGD probe, mainly studied for tumour angiogenesis imaging, that demonstrates unfavourable binding to kidneys, spleen, lungs, liver, and gastrointestinal system thereby hampering the image quality .
We simultaneously imaged and quantified cardiac uptake of 99mTc and 111In in the AHA 17 segment model. The isotope uptake per segment was quantified using isotope specific CFs, assessed in phantom studies. Furthermore, isotope uptake was expressed in the clinically used SUV parameter, which normalises for injected dose and body weight. Although normalisation for body weight might be considered irrelevant for a rapidly excreted tracer that does not reach a uniform distribution throughout the body, we believe that the body weight bias in our quantification is limited due to the fact that all the animals used in this study were of similar age and body weight.
We found target-specific binding of our new angiogenesis imaging probe as evidenced by the significantly enhanced SUVs in six segments in the infarcted myocardium and the infarct border zone. To even further improve dual-isotope micro-SPECT imaging of perfusion defects and mirroring 111In-DTPA-cNGR uptake in the hearts of the MI mice, we are currently pursuing strategies to further enhance probe-target interaction through multivalent binding which may result in higher image quality. The proof of principle of this approach has already been demonstrated in studies from Li et al. and Dijkgraaf et al., in which tumour uptake increased with increasing RGD valency [35,36].
Despite displaying enhanced, specific uptake in the infarcted myocardium and infarct border zone, we observed several remarkable and so far inexplicable features of our probe. We found the overall uptake to be higher in every section of the infarcted hearts compared with that in the healthy control hearts. This may be due to enhanced post-infarct overall stress in the heart, but we cannot confirm such a finding at this moment. Moreover, kidney uptake was significantly higher in the healthy control mice compared to that in the MI mice. Although we currently have no direct link between the infarct and these findings, these discoveries we made using SPECT scans were overlooked in earlier studies employing two-photon microscopy and MRI and may be of considerable importance for future studies employing the cNGR molecule as a molecular angiogenesis imaging probe.
In this study, we opted for 111In due to the fact that pre-clinical SPECT scanners outclass pre-clinical PET scanner in terms of spatial resolution. Of course, the use of 111In in a clinical situation may be less favourable due to its long physical half-life of 2.8 days and resolution limitations. While pre-clinical SPECT scanners outclass pre-clinical PET scanners in terms of spatial resolution, in the clinical setting, this is reversed. Therefore, angiogenesis imaging via the cNGR tripeptide in MI patients would benefit from the use of a clinical PET system. Future research should therefore focus on the development of a high-resolution cNGR-based PET imaging probe, for example by replacing 111In by the PET isotope 68Ga.
In conclusion, in this study, we designed and developed a molecular angiogenesis imaging probe that allowed us to sensitively visualise CD13 in the border zone of infarcted myocardium and infarcted myocardium itself using dual-isotope SPECT imaging. Analysis of acquired SPECT images in the AHA 17 segment model revealed target-specific uptake of our new angiogenesis imaging probe in areas of decreased perfusion. Furthermore, we noticed rapid clearance via the urinary tract and low uptake in non-specific organs. However, for the cNGR tripeptide to be considered as a clinical angiogenesis imaging tool, specific target uptake has to increase. Therefore, we are currently pursuing a multi-valent cNGR motif with supposed longer half-life and higher target affinity.
diethylene triamine pentaacetic acid
left anterior descending coronary artery
human fibroblast growth factor 2
standardised uptake value
This study was performed within the framework of the Center for Translational Molecular Medicine (CTMM), project EMINENCE (grant 01C-204) and the Weijerhorst foundation. We would like to thank Christian Urbach for his technical support and Sandra Zimny and Martine Hulsbosch for their logistic support.
- Battegay EJ. Angiogenesis: mechanistic insights, neovascular diseases, and therapeutic prospects. J Mol Med. 1995;73:333–46.PubMedView ArticleGoogle Scholar
- Meoli DF, Sadeghi MM, Krassilnikova S, Bourke BN, Giordano FJ, Dione DP, et al. Noninvasive imaging of myocardial angiogenesis following experimental myocardial infarction. J Clin Invest. 2004;113:1684–91.PubMed CentralPubMedView ArticleGoogle Scholar
- Allen KB, Dowling RD, Fudge TL, Schoettle GP, Selinger SL, Gangahar DM, et al. Comparison of transmyocardial revascularization with medical therapy in patients with refractory angina. N Engl J Med. 1999;341:1029–36.PubMedView ArticleGoogle Scholar
- Giordano FJ, Ping P, McKirnan MD, Nozaki S, DeMaria AN, Dillmann WH, et al. Intracoronary gene transfer of fibroblast growth factor-5 increases blood flow and contractile function in an ischemic region of the heart. Nat Med. 1996;2:534–9.PubMedView ArticleGoogle Scholar
- Hendel RC, Henry TD, Rocha-Singh K, Isner JM, Kereiakes DJ, Giordano FJ, et al. Effect of intracoronary recombinant human vascular endothelial growth factor on myocardial perfusion: evidence for a dose-dependent effect. Circulation. 2000;101:118–21.PubMedView ArticleGoogle Scholar
- Lazarous DF, Scheinowitz M, Shou M, Hodge E, Rajanayagam S, Hunsberger S, et al. Effects of chronic systemic administration of basic fibroblast growth factor on collateral development in the canine heart. Circulation. 1995;91:145–53.PubMedView ArticleGoogle Scholar
- Rosengart TK, Lee LY, Patel SR, Sanborn TA, Parikh M, Bergman GW, et al. Angiogenesis gene therapy: phase I assessment of direct intramyocardial administration of an adenovirus vector expressing VEGF121 cDNA to individuals with clinically significant severe coronary artery disease. Circulation. 1999;100:468–74.PubMedView ArticleGoogle Scholar
- Schofield PM, Sharples LD, Caine N, Burns S, Tait S, Wistow T, et al. Transmyocardial laser revascularisation in patients with refractory angina: a randomised controlled trial. Lancet. 1999;353:519–24.PubMedView ArticleGoogle Scholar
- Udelson JE, Dilsizian V, Laham RJ, Chronos N, Vansant J, Blais M, et al. Therapeutic angiogenesis with recombinant fibroblast growth factor-2 improves stress and rest myocardial perfusion abnormalities in patients with severe symptomatic chronic coronary artery disease. Circulation. 2000;102:1605–10.PubMedView ArticleGoogle Scholar
- Unger EF, Banai S, Shou M, Lazarous DF, Jaklitsch MT, Scheinowitz M, et al. Basic fibroblast growth factor enhances myocardial collateral flow in a canine model. Am J Physiol. 1994;266:H1588–95.PubMedGoogle Scholar
- Vale PR, Losordo DW, Milliken CE, Maysky M, Esakof DD, Symes JF, et al. Left ventricular electromechanical mapping to assess efficacy of phVEGF(165) gene transfer for therapeutic angiogenesis in chronic myocardial ischemia. Circulation. 2000;102:965–74.PubMedView ArticleGoogle Scholar
- Tse HF, Lau CP. Therapeutic angiogenesis with bone marrow-derived stem cells. J Cardiovasc Pharmacol Ther. 2007;12:89–97.PubMedView ArticleGoogle Scholar
- Corti A, Curnis F, Arap W, Pasqualini R. The neovasculature homing motif NGR: more than meets the eye. Blood. 2008;112:2628–35.PubMed CentralPubMedView ArticleGoogle Scholar
- Pasqualini R, Koivunen E, Kain R, Lahdenranta J, Sakamoto M, Stryhn A, et al. Aminopeptidase N is a receptor for tumor-homing peptides and a target for inhibiting angiogenesis. Cancer Res. 2000;60:722–7.PubMedGoogle Scholar
- Buehler A, van Zandvoort MA, Stelt BJ, Hackeng TM, Schrans-Stassen BH, Bennaghmouch A, et al. cNGR: a novel homing sequence for CD13/APN targeted molecular imaging of murine cardiac angiogenesis in vivo. Arterioscler Thromb Vasc Biol. 2006;26:2681–7.PubMedView ArticleGoogle Scholar
- Arap W, Pasqualini R, Ruoslahti E. Cancer treatment by targeted drug delivery to tumor vasculature in a mouse model. Science. 1998;279:377–80.PubMedView ArticleGoogle Scholar
- Curnis F, Arrigoni G, Sacchi A, Fischetti L, Arap W, Pasqualini R, et al. Differential binding of drugs containing the NGR motif to CD13 isoforms in tumor vessels, epithelia, and myeloid cells. Cancer Res. 2002;62:867–74.PubMedGoogle Scholar
- Oostendorp M, Douma K, Hackeng TM, Dirksen A, Post MJ, van Zandvoort MA, et al. Quantitative molecular magnetic resonance imaging of tumor angiogenesis using cNGR-labeled paramagnetic quantum dots. Cancer Res. 2008;68:7676–83.PubMedView ArticleGoogle Scholar
- Dijkgraaf I, Van de Vijver P, Dirksen A, Hackeng TM. Synthesis and application of cNGR-containing imaging agents for detection of angiogenesis. Bioorg Med Chem. 2013;21:3555–64.PubMedView ArticleGoogle Scholar
- Oostendorp M, Douma K, Wagenaar A, Slenter JM, Hackeng TM, van Zandvoort MA, et al. Molecular magnetic resonance imaging of myocardial angiogenesis after acute myocardial infarction. Circulation. 2010;121:775–83.PubMedView ArticleGoogle Scholar
- Dijkgraaf I, Beer AJ, Wester HJ. Application of RGD-containing peptides as imaging probes for alphavbeta3 expression. Front Biosci. 2009;14:887–99.View ArticleGoogle Scholar
- Mulder WJ, Strijkers GJ, Habets JW, Bleeker EJ, van der Schaft DW, Storm G, et al. MR molecular imaging and fluorescence microscopy for identification of activated tumor endothelium using a bimodal lipidic nanoparticle. FASEB J. 2005;19:2008–10.PubMedGoogle Scholar
- Colombo G, Curnis F, De Mori GM, Gasparri A, Longoni C, Sacchi A, et al. Structure-activity relationships of linear and cyclic peptides containing the NGR tumor-homing motif. J Biol Chem. 2002;277:47891–7.PubMedView ArticleGoogle Scholar
- Schnolzer M, Alewood P, Jones A, Alewood D, Kent SB. In situ neutralization in Boc-chemistry solid phase peptide synthesis. Rapid, high yield assembly of difficult sequences. Int J Pept Protein Res. 1992;40:180–93.PubMedView ArticleGoogle Scholar
- Van de Vijver P, Suylen D, Dirksen A, Dawson PE, Hackeng TM. Nepsilon-(thiaprolyl)-lysine as a handle for site-specific protein conjugation. Biopolymers. 2010;94:465–74.PubMedView ArticleGoogle Scholar
- Lutgens E, Daemen MJ, de Muinck ED, Debets J, Leenders P, Smits JF. Chronic myocardial infarction in the mouse: cardiac structural and functional changes. Cardiovasc Res. 1999;41:586–93.PubMedView ArticleGoogle Scholar
- van der Have F, Vastenhouw B, Ramakers RM, Branderhorst W, Krah JO, Ji C, et al. U-SPECT-II: an ultra-high-resolution device for molecular small-animal imaging. J Nucl Med. 2009;50:599–605.PubMedView ArticleGoogle Scholar
- Molin D, Post MJ. Therapeutic angiogenesis in the heart: protect and serve. Curr Opin Pharmacol. 2007;7:158–63.PubMedView ArticleGoogle Scholar
- Simons M. Angiogenesis: where do we stand now? Circulation. 2005;111:1556–66.PubMedView ArticleGoogle Scholar
- Laham RJ, Chronos NA, Pike M, Leimbach ME, Udelson JE, Pearlman JD, et al. Intracoronary basic fibroblast growth factor (FGF-2) in patients with severe ischemic heart disease: results of a phase I open-label dose escalation study. J Am Coll Cardiol. 2000;36:2132–9.PubMedView ArticleGoogle Scholar
- Henry TD, Annex BH, McKendall GR, Azrin MA, Lopez JJ, Giordano FJ, et al. The VIVA trial: vascular endothelial growth factor in ischemia for vascular angiogenesis. Circulation. 2003;107:1359–65.PubMedView ArticleGoogle Scholar
- Losordo DW, Vale PR, Symes JF, Dunnington CH, Esakof DD, Maysky M, et al. Gene therapy for myocardial angiogenesis: initial clinical results with direct myocardial injection of phVEGF165 as sole therapy for myocardial ischemia. Circulation. 1998;98:2800–4.PubMedView ArticleGoogle Scholar
- Rimoldi O, Burns SM, Rosen SD, Wistow TE, Schofield PM, Taylor G, et al. Measurement of myocardial blood flow with positron emission tomography before and after transmyocardial laser revascularization. Circulation. 1999;100:II134–8.PubMedView ArticleGoogle Scholar
- Mitsos S, Katsanos K, Koletsis E, Kagadis GC, Anastasiou N, Diamantopoulos A, et al. Therapeutic angiogenesis for myocardial ischemia revisited: basic biological concepts and focus on latest clinical trials. Angiogenesis. 2012;15:1–22.PubMedView ArticleGoogle Scholar
- Dijkgraaf I, Rijnders AY, Soede A, Dechesne AC, van Esse GW, Brouwer AJ, et al. Synthesis of DOTA-conjugated multivalent cyclic-RGD peptide dendrimers via 1,3-dipolar cycloaddition and their biological evaluation: implications for tumor targeting and tumor imaging purposes. Org Biomol Chem. 2007;5:935–44.PubMedView ArticleGoogle Scholar
- Li ZB, Chen K, Chen X. (68)Ga-labeled multimeric RGD peptides for microPET imaging of integrin alpha(v)beta (3) expression. Eur J Nucl Med Mol Imaging. 2008;35:1100–8.PubMedView ArticleGoogle Scholar
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.