-
[show abstract]
[hide abstract]
ABSTRACT: PurposeWe have previously reported that 18F-FB-E[c(RGDyK)]2 (18F-FRGD2) allows quantitative PET imaging of integrin αvβ3 expression. However, the potential clinical translation was hampered by the relatively low radiochemical yield. The goal
of this study was to improve the radiolabeling yield, without compromising the tumor targeting efficiency and in vivo kinetics,
by incorporating a hydrophilic bifunctional mini-PEG spacer.
Methods
18F-FB-mini-PEG-E[c(RGDyK)]2 (18F-FPRGD2) was synthesized by coupling N-succinimidyl-4-18F-fluorobenzoate (18F-SFB) with NH2-mini-PEG-E[c(RGDyK)]2 (denoted as PRGD2). In vitro receptor binding affinity, metabolic stability, and integrin αvβ3 specificity of the new tracer 18F-FPRGD2 were assessed. The diagnostic value of 18F-FPRGD2 was evaluated in subcutaneous U87MG glioblastoma xenografted mice and in c-neu transgenic mice by quantitative microPET imaging studies.
ResultsThe decay-corrected radiochemical yield based on 18F-SFB was more than 60% with radiochemical purity of >99%. 18F-FPRGD2 had high receptor binding affinity, metabolic stability, and integrin αvβ3-specific tumor uptake in the U87MG glioma xenograft model comparable to those of 18F-FRGD2. The kidney uptake was appreciably lower for 18F-FPRGD2 compared with 18F-FRGD2 [2.0 ± 0.2%ID/g for 18F-FPRGD2 vs 3.0 ± 0.2%ID/g for 18F-FRGD2 at 1h post injection (p.i.)]. The uptake in all the other organs except the urinary bladder was at background level.
18F-FPRGD2 also exhibited excellent tumor uptake in c-neu oncomice (3.6 ± 0.1%ID/g at 30min p.i.).
ConclusionIncorporation of a mini-PEG spacer significantly improved the overall radiolabeling yield of 18F-FPRGD2. 18F-FPRGD2 also had reduced renal uptake and similar tumor targeting efficacy as compared with 18F-FRGD2. Further testing and clinical translation of 18F-FPRGD2 are warranted.
European journal of nuclear medicine and molecular imaging 04/2012; 34(11):1823-1831. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Interleukin (IL)-18 plays important roles in cancer progression and metastasis. The goal of this study is to identify cell lines that are most sensitive to stand alone IL-18-binding protein (IL-18bp)-Fc treatment, to study the pharmacokinetics and tumor targeting efficiency of IL-18bp-Fc, and to evaluate the efficacy of IL-18bp-Fc in treating breast cancer experimental lung metastasis by multimodality imaging.
Reverse transcription-PCR, ELISA, and other cell-based assays were done on murine 4T1, CT-26, and B16F10 cells. The most IL-18bp-Fc-sensitive 4T1 cells were stably transfected with firefly luciferase (fLuc) and injected i.v. into female BALB/C mice to establish the experimental lung metastasis model. Tumor targeting efficiency and pharmacokinetics of IL-18bp-Fc was assessed by (64)Cu-DOTA-IL-18bp-Fc positron emission tomography (PET) and biodistribution studies. Two groups of fLuc-4T1 experimental lung metastasis tumor-bearing mice were each given saline or IL-18bp-Fc (1 mg/kg) daily i.p. Bioluminescence imaging, (18)F-FDG PET, and computed tomography scans were done to evaluate the treatment efficacy. Ex vivo experiments were also carried out to validate the imaging results.
IL-18bp-Fc had high and specific accumulation in the fLuc-4T1 lung metastasis tumor as evidenced by both PET and biodistribution studies. Bioluminescence imaging, (18)F-FDG PET, and computed tomography scans all revealed that IL-18bp-Fc treatment was effective in inhibiting the lung metastasis tumor progression, validated by ex vivo examination of the lung.
IL-18bp-Fc therapy can inhibit 4T1 breast cancer experimental lung metastasis. Noninvasive multimodality molecular imaging is a powerful tool for evaluating the tumor targeting efficiency/pharmacokinetics of the drug and effective monitoring of the therapeutic response.
Clinical Cancer Research 11/2008; 14(19):6137-45. · 7.74 Impact Factor
-
Weibo Cai,
Raphael Guzman,
Andrew R Hsu,
Hui Wang,
Kai Chen,
Guohua Sun,
Atul Gera,
Raymond Choi,
Tonya Bliss, Lina He,
Zi-Bo Li,
Anne-Lise D Maag,
Nobutaka Hori,
Heng Zhao,
Michael Moseley,
Gary K Steinberg,
Xiaoyuan Chen
[show abstract]
[hide abstract]
ABSTRACT: Vascular endothelial growth factor (VEGF) and VEGF receptors (VEGFRs) play important roles during neurovascular repair after stroke. In this study, we imaged VEGFR expression with positron emission tomography (PET) to noninvasively analyze poststroke angiogenesis.
Female Sprague-Dawley rats after distal middle cerebral artery occlusion surgery were subjected to weekly MRI, (18)F-FDG PET, and (64)Cu-DOTA-VEGF(121) PET scans. Several control experiments were performed to confirm the VEGFR specificity of (64)Cu-DOTA-VEGF(121) uptake in the stroke border zone. VEGFR, BrdU, lectin staining, and (125)I-VEGF(165) autoradiography on stroke brain tissue slices were performed to validate the in vivo findings.
T2-weighed MRI correlated with the "cold spot" on (18)F-FDG PET for rats undergoing distal middle cerebral artery occlusion surgery. The (64)Cu-DOTA-VEGF(121) uptake in the stroke border zone peaked at approximately 10 days after surgery, indicating neovascularization as confirmed by histology (VEGFR-2, BrdU, and lectin staining). VEGFR specificity of (64)Cu-DOTA-VEGF(121) uptake was confirmed by significantly lower uptake of (64)Cu-DOTA-VEGF(mutant) in vivo and intense (125)I-VEGF(165) uptake ex vivo in the stroke border zone. No appreciable uptake of (64)Cu-DOTA-VEGF(121) was observed in the brain of sham-operated rats.
For the first time to our knowledge, we successfully evaluated the VEGFR expression kinetics noninvasively in a rat stroke model. In vivo imaging of VEGFR expression could become a significant clinical tool to plan and monitor therapies aimed at improving poststroke angiogenesis.
Stroke 11/2008; 40(1):270-7. · 5.73 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Malignant tumors are capable of degrading the surrounding extracellular matrix, resulting in local invasion or metastasis. Urokinase-type plasminogen activator (uPA) and its cell surface receptor (uPAR) are central molecules in one of the major protease systems involved in extracellular matrix degradation. Noninvasive imaging of this receptor in vivo with radiolabeled peptides that specifically target uPAR may therefore be useful to decipher the potential invasiveness of malignant lesions.
In this study, we developed a (64)Cu-labeled uPAR-binding peptide for positron emission tomography (PET) imaging. A linear, high-affinity uPAR-binding peptide antagonist AE105 was conjugated with 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid (DOTA) and labeled with (64)Cu for microPET imaging of mice bearing U87MG human glioblastoma (uPAR positive) and MDA-MB-435 human breast cancer (uPAR negative).
Surface plasmon resonance measurements show that AE105 with DOTA conjugated at the alpha-amino group (DOTA-AE105) has high affinity toward uPAR. microPET imaging reveals a rapid and high accumulation of (64)Cu-DOTA-AE105 in uPAR-positive U87MG tumors (10.8 +/- 1.5%ID/g at 4.5 hours, n = 3) but not in uPAR-negative MDA-MB-435 tumors (1.2 +/- 0.6%ID/g at 4.5 hours, n = 3). Specificity of this peptide-based imaging of uPAR was validated by further control experiments. First, a nonbinding variant of AE105 carrying a single amino acid replacement (Trp-->Glu) does not target U87MG tumors in vivo. Second, targeting of U87MG tumors by (64)Cu-DOTA-AE105 is specifically inhibited by a nonlabeled antagonist.
The successful demonstration of the ability of a (64)Cu labeled uPAR-specific probe to visualize uPAR expression in vivo may allow clinical translation of this class of radiopharmaceuticals for uPAR-positive cancer detection and patient stratification for uPA/uPAR system-based cancer therapy.
Clinical Cancer Research 08/2008; 14(15):4758-66. · 7.74 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This study used integrin alpha v beta3 as a target for tumor-specific delivery of tumor necrosis factor-alpha (TNF). The fusion protein RGD4C-TNF bound specifically to alpha v beta3 as evidenced by cell receptor binding assay and noninvasive micro-positron emission tomography imaging. 64Cu-DOTA-RGD4C-TNF had significantly higher activity accumulation in integrin-positive tumors (U87MG and MDA-MB-435) but not in integrin-negative tumors (C6) compared with 64Cu-DOTA-TNF. The magnitude of tumor uptake of 64Cu-DOTA-RGD4C-TNF correlated well with the alpha v beta3 level (U87MG > MDA-MB-435 > C6). Tumor accumulation of 64Cu-DOTA-RGD4C-TNF could be effectively blocked by c(RGDyK) peptide in alpha v beta3-positive tumor models, suggesting alpha v beta3 specificity of RGD4C-TNF fusion protein in vivo. Furthermore, although the fusion of RGD4C moiety to TNF had little effect on the bioactivity and cytotoxicity of RGD4C-TNF compared with TNF in cell culture, RGD4C-TNF was significantly more potent than TNF in inhibiting orthotopic MDA-MB-435 tumor growth. Ex vivo tissue staining confirmed specific cytotoxicity of RGD4C-TNF against integrin-positive tumor cells and tumor vasculature.
Molecular Cancer Therapeutics 05/2008; 7(5):1044-53. · 5.23 Impact Factor
-
Martin Rodriguez-Porcel,
Weibo Cai,
Olivier Gheysens,
Jürgen K Willmann,
Kai Chen,
Hui Wang,
Ian Y Chen, Lina He,
Joseph C Wu,
Zi-bo Li,
Khalid A Mohamedali,
Sehoon Kim,
Michael G Rosenblum,
Xiaoyuan Chen,
Sanjiv Sam Gambhir
[show abstract]
[hide abstract]
ABSTRACT: Myocardial infarction (MI) leads to left ventricular (LV) remodeling, which leads to the activation of growth factors such as vascular endothelial growth factor (VEGF). However, the kinetics of a growth factor's receptor expression, such as VEGF, in the living subject has not yet been described. We have developed a PET tracer (64Cu-DOTA-VEGF121 [DOTA is 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid]) to image VEGF receptor (VEGFR) expression after MI in the living subject.
In Sprague-Dawley rats, MI was induced by ligation of the left coronary artery and confirmed by ultrasound (n = 8). To image and study the kinetics of VEGFRs, 64Cu-DOTA-VEGF121 PET scans were performed before MI induction (baseline) and on days 3, 10, 17, and 24 after MI. Sham-operated animals served as controls (n = 3).
Myocardial origin of the 64Cu-DOTA-VEGF121 signal was confirmed by CT coregistration and autoradiography. VEGFR specificity of the 64Cu-DOTA-VEGF121 probe was confirmed by in vivo use of a 64Cu-DOTA-VEGFmutant. Baseline myocardial uptake of 64Cu-DOTA-VEGF121 was minimal (0.30 +/- 0.07 %ID/g [percentage injected dose per gram of tissue]); it increased significantly after MI (day 3, 0.97 +/- 0.05 %ID/g; P < 0.05 vs. baseline) and remained elevated for 2 wk (up to day 17 after MI), after which time it returned to baseline levels.
We demonstrate the feasibility of imaging VEGFRs in the myocardium. In summary, we imaged and described the kinetics of 64Cu-DOTA-VEGF121 uptake in a rat model of MI. Studies such as the one presented here will likely play a major role when studying pathophysiology and assessing therapies in different animal models of disease and, potentially, in patients.
Journal of Nuclear Medicine 05/2008; 49(4):667-73. · 6.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Targeting drugs to receptors involved in tumor angiogenesis has been demonstrated as a novel and promising approach to improve cancer treatment. In this study, we evaluated the anti-tumor efficacy of a dimeric RGD peptide-paclitaxel conjugate (RGD2-PTX) in an orthotopic MDA-MB-435 breast cancer model.
To assess the effect of conjugation and the presence of drug moiety on the MDA-MB-435 tumor and normal tissue uptake, the biodistribution of (3)H-RGD2-PTX was compared with that of (3)H-PTX. The treatment effect of RGD2-PTX and RGD2+PTX was measured by tumor size, (18)F-FDG/PET, (18)F-FLT/PET, and postmortem histopathology.
By comparing the biodistribution of (3)H-RGD2-PTX and (3)H-PTX, we found that (3)H-RGD2-PTX had higher initial tumor exposure dose and prolonged tumor retention than (3)H-PTX. Metronomic low-dose treatment of breast cancer indicated that RGD2-PTX is significantly more effective than PTX+RGD2 combination and solvent control. Although in vivo (18)F-FLT/PET imaging and ex vivo Ki67 staining indicated little effect of the PTX-based drug on cell proliferation, (18)F-FDG/PET imaging showed significantly reduced tumor metabolism in the RGD2-PTX-treated mice versus those treated with RGD2+PTX and solvent control. Terminal uridine deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining also showed that RGD2-PTX treatment also had significantly higher cell apoptosis ratio than the other two groups. Moreover, the microvessel density was significantly reduced after RGD2-PTX treatment as determined by CD31 staining.
Our results demonstrate that integrin-targeted delivery of paclitaxel allows preferential cytotoxicity to integrin-expressing tumor cells and tumor vasculature. The targeted delivery strategies developed in this study may also be applied to other chemotherapeutics for selective tumor killing.
European journal of nuclear medicine and molecular imaging 04/2008; 35(8):1489-98. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Carbon nanotubes are promising new materials for molecular delivery in biological systems. The long-term fate of nanotubes intravenously injected into animals in vivo is currently unknown, an issue critical to potential clinical applications of these materials. Here, using the intrinsic Raman spectroscopic signatures of single-walled carbon nanotubes (SWNTs), we measured the blood circulation of intravenously injected SWNTs and detect SWNTs in various organs and tissues of mice ex vivo over a period of three months. Functionalization of SWNTs by branched polyethylene-glycol (PEG) chains was developed, enabling thus far the longest SWNT blood circulation up to 1 day, relatively low uptake in the reticuloendothelial system (RES), and near-complete clearance from the main organs in approximately 2 months. Raman spectroscopy detected SWNT in the intestine, feces, kidney, and bladder of mice, suggesting excretion and clearance of SWNTs from mice via the biliary and renal pathways. No toxic side effect of SWNTs to mice was observed in necropsy, histology, and blood chemistry measurements. These findings pave the way to future biomedical applications of carbon nanotubes.
Proceedings of the National Academy of Sciences 03/2008; 105(5):1410-5. · 9.68 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Noninvasive positron emission tomography (PET) imaging of vascular endothelial growth factor receptor 2 (VEGFR-2) expression could be a valuable tool for evaluation of patients with a variety of malignancies, and particularly for monitoring those undergoing antiangiogenic therapies that block VEGF/VEGFR-2 function. The aim of this study was to develop a VEGFR-2-specific PET tracer.
The D63AE64AE67A mutant of VEGF(121) (VEGF(DEE)) was generated by recombinant DNA technology. VEGF(121) and VEGF(DEE) were purified and conjugated with DOTA for (64)Cu labeling. The DOTA conjugates were tested in vitro for VEGFR-2 specificity and functional activity. In vivo tumor targeting efficacy and pharmacokinetics of (64)Cu-labeled VEGF(121) and VEGF(DEE) were compared using an orthotopic 4T1 murine breast tumor model. Blocking experiments, biodistribution studies, and immunofluorescence staining were carried out to confirm the noninvasive imaging results.
Cell binding assay demonstrated that VEGF(DEE) had about 20-fold lower VEGFR-1 binding affinity and only slightly lower VEGFR-2 binding affinity as compared with VEGF(121). MicroPET imaging studies revealed that both (64)Cu-DOTA-VEGF(121) and (64)Cu-DOTA-VEGF(DEE) had rapid and prominent activity accumulation in VEGFR-2-expressing 4T1 tumors. The renal uptake of (64)Cu-DOTA-VEGF(DEE) was significantly lower than that of (64)Cu-DOTA-VEGF(121) as rodent kidneys expressed high levels of VEGFR-1 based on immunofluorescence staining. Blocking experiments and biodistribution studies confirmed the VEGFR specificity of (64)Cu-DOTA-VEGF(DEE).
We have developed a VEGFR-2-specific PET tracer, (64)Cu-DOTA-VEGF(DEE). It has comparable tumor targeting efficacy to (64)Cu-DOTA-VEGF(121) but much reduced renal toxicity. This tracer may be translated into the clinic for imaging tumor angiogenesis and monitoring antiangiogenic treatment efficacy.
European journal of nuclear medicine and molecular imaging 01/2008; 34(12):2001-10. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In this study, we evaluated the 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced acute and chronic inflammation in living mice by PET imaging of TNF-alpha and integrin alpha(v)beta(3) expression.
TPA was topically applied to the right ear of BALB/c mice every other day to create the inflammation model. (64)Cu-DOTA-etanercept and (64)Cu-DOTA-E{E[c(RGDyK)](2)}(2) were used for PET imaging of TNF-alpha and integrin alpha(v)beta(3) expression in both acute and chronic inflammation. Hematoxylin and eosin staining, ex vivo autoradiography, direct tissue sampling, and immunofluorescence staining were also performed to confirm the non-invasive PET imaging results.
The ear thickness increased significantly and the TNF-alpha level more than tripled after a single TPA challenge. MicroPET imaging using (64)Cu-DOTA-etanercept revealed high activity accumulation in the inflamed ear, reaching 11.1 +/- 1.3, 13.0 +/- 2.0, 10.9 +/- 1.4, 10.2 +/- 2.2%ID/g at 1, 4, 16, and 24 h post injection, respectively (n = 3). Repeated TPA challenges caused TPA-specific chronic inflammation and reduced (64)Cu-DOTA-etanercept uptake due to lowered TNF-alpha expression. (64)Cu-DOTA-E{E[c(RGDyK)](2)}(2) uptake in the chronically inflamed ears (after four and eight TPA challenges) was significantly higher than in the control ears and those after one TPA challenge. Immunofluorescence staining revealed increased integrin beta(3) expression, consistent with the non-invasive PET imaging results using (64)Cu-DOTA-E{E[c(RGDyK)](2)}(2) as an integrin alpha(v)beta(3)-specific radiotracer. Biodistribution and autoradiography studies further confirmed the quantification capability of microPET imaging.
Successful PET imaging of TNF-alpha expression in acute inflammation and integrin alpha(v)beta(3) expression in chronic inflammation provides the rationale for multiple target evaluation over time to fully understand the inflammation processes.
European journal of nuclear medicine and molecular imaging 12/2007; 34(11):1832-42. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have previously reported that (18)F-FB-E[c(RGDyK)](2) ((18)F-FRGD2) allows quantitative PET imaging of integrin alpha(v)beta(3) expression. However, the potential clinical translation was hampered by the relatively low radiochemical yield. The goal of this study was to improve the radiolabeling yield, without compromising the tumor targeting efficiency and in vivo kinetics, by incorporating a hydrophilic bifunctional mini-PEG spacer.
(18)F-FB-mini-PEG-E[c(RGDyK)](2) ((18)F-FPRGD2) was synthesized by coupling N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) with NH(2)-mini-PEG-E[c(RGDyK)](2) (denoted as PRGD2). In vitro receptor binding affinity, metabolic stability, and integrin alpha(v)beta(3) specificity of the new tracer (18)F-FPRGD2 were assessed. The diagnostic value of (18)F-FPRGD2 was evaluated in subcutaneous U87MG glioblastoma xenografted mice and in c-neu transgenic mice by quantitative microPET imaging studies.
The decay-corrected radiochemical yield based on (18)F-SFB was more than 60% with radiochemical purity of >99%. (18)F-FPRGD2 had high receptor binding affinity, metabolic stability, and integrin alpha(v)beta(3)-specific tumor uptake in the U87MG glioma xenograft model comparable to those of (18)F-FRGD2. The kidney uptake was appreciably lower for (18)F-FPRGD2 compared with (18)F-FRGD2 [2.0 +/- 0.2%ID/g for (18)F-FPRGD2 vs 3.0 +/- 0.2%ID/g for (18)F-FRGD2 at 1 h post injection (p.i.)]. The uptake in all the other organs except the urinary bladder was at background level. (18)F-FPRGD2 also exhibited excellent tumor uptake in c-neu oncomice (3.6 +/- 0.1%ID/g at 30 min p.i.).
Incorporation of a mini-PEG spacer significantly improved the overall radiolabeling yield of (18)F-FPRGD2. (18)F-FPRGD2 also had reduced renal uptake and similar tumor targeting efficacy as compared with (18)F-FRGD2. Further testing and clinical translation of (18)F-FPRGD2 are warranted.
European journal of nuclear medicine and molecular imaging 11/2007; 34(11):1823-31. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In vivo imaging of alpha(v)beta(3) expression has important diagnostic and therapeutic applications. Multimeric cyclic RGD peptides are capable of improving the integrin alpha(v)beta(3)-binding affinity due to the polyvalency effect. Here we report an example of (18)F-labeled tetrameric RGD peptide for PET of alpha(v)beta(3) expression in both xenograft and spontaneous tumor models.
The tetrameric RGD peptide E{E[c(RGDyK)](2)}(2) was derived with amino-3,6,9-trioxaundecanoic acid (mini-PEG; PEG is poly(ethylene glycol)) linker through the glutamate alpha-amino group. NH(2)-mini-PEG-E{E[c(RGDyK)](2)}(2) (PRGD4) was labeled with (18)F via the N-succinimidyl-4-(18)F-fluorobenzoate ((18)F-SFB) prosthetic group. The receptor-binding characteristics of the tetrameric RGD peptide tracer (18)F-FPRGD4 were evaluated in vitro by a cell-binding assay and in vivo by quantitative microPET imaging studies.
The decay-corrected radiochemical yield for (18)F-FPRGD4 was about 15%, with a total reaction time of 180 min starting from (18)F-F(-). The PEGylation had minimal effect on integrin-binding affinity of the RGD peptide. (18)F-FPRGD4 has significantly higher tumor uptake compared with monomeric and dimeric RGD peptide tracer analogs. The receptor specificity of (18)F-FPRGD4 in vivo was confirmed by effective blocking of the uptake in both tumors and normal organs or tissues with excess c(RGDyK).
The tetrameric RGD peptide tracer (18)F-FPRGD4 possessing high integrin-binding affinity and favorable biokinetics is a promising tracer for PET of integrin alpha(v)beta(3) expression in cancer and other angiogenesis related diseases.
Journal of Nuclear Medicine 10/2007; 48(9):1536-44. · 6.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Integrin alpha(v)beta(3) plays a critical role in tumor angiogenesis and metastasis. Suitably radiolabeled cyclic arginine-glycine-aspartic (RGD) peptides can be used for noninvasive imaging of alpha(v)beta(3) expression and targeted radionuclide therapy. In this study, we developed (64)Cu-labeled multimeric RGD peptides, E{E[c(RGDyK)](2)}(2) (RGD tetramer) and E(E{E[c(RGDyK)](2)}(2))(2) (RGD octamer), for PET imaging of tumor integrin alpha(v)beta(3) expression.
Both RGD tetramer and RGD octamer were synthesized with glutamate as the linker. After conjugation with 1,4,7,10-tetra-azacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA), the peptides were labeled with (64)Cu for biodistribution and small-animal PET imaging studies (U87MG human glioblastoma xenograft model and c-neu oncomouse model). A cell adhesion assay, a cell-binding assay, receptor blocking experiments, and immunohistochemistry were also performed to evaluate the alpha(v)beta(3)-binding affinity/specificity of the RGD peptide-based conjugates in vitro and in vivo.
RGD octamer had significantly higher integrin alpha(v)beta(3)-binding affinity and specificity than RGD tetramer analog (inhibitory concentration of 50% was 10 nM for octamer vs. 35 nM for tetramer). (64)Cu-DOTA-RGD octamer had higher tumor uptake and longer tumor retention than (64)Cu-DOTA-RGD tetramer in both tumor models tested. The integrin alpha(v)beta(3) specificity of both tracers was confirmed by successful receptor-blocking experiments. The high uptake and slow clearance of (64)Cu-DOTA-RGD octamer in the kidneys was attributed mainly to the integrin positivity of the kidneys, significantly higher integrin alpha(v)beta(3)-binding affinity, and the larger molecular size of the octamer, as compared with the other RGD analogs.
Polyvalency has a profound effect on the receptor-binding affinity and in vivo kinetics of radiolabeled RGD multimers. The information obtained here may guide the future development of RGD peptide-based imaging and internal radiotherapeutic agents targeting integrin alpha(v)beta(3).
Journal of Nuclear Medicine 08/2007; 48(7):1162-71. · 6.38 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Cetuximab, a chimeric monoclonal antibody targeting epidermal growth factor receptor (EGFR) on the surface of cancer cells, was approved by the FDA to treat patients with metastatic colorectal cancer. It is currently also in advanced-stage development for the treatment of several other solid tumors. Here we report for the first time the quantitative positron emission tomography (PET) imaging of EGFR expression in xenograft-bearing mice using 64Cu-labeled cetuximab.
We conjugated cetuximab with macrocyclic chelating agent 1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid (DOTA), labeled with 64Cu, and tested the resulting 64Cu-DOTA-cetuximab in seven xenograft tumor models. The tracer uptake measured by PET was correlated with the EGFR expression quantified by western blotting. The estimated human dosimetry based on the PET data in Sprague-Dawley rats was also calculated.
MicroPET imaging showed that 64Cu-DOTA-cetuximab had increasing tumor activity accumulation over time in EGFR-positive tumors but relatively low uptake in EGFR-negative tumors at all times examined (<5%ID/g). There was a good correlation (R2=0.80) between the tracer uptake (measured by PET) and the EGFR expression level (measured by western blotting). Human dosimetry estimation indicated that the tracer may be safely administered to human patients for tumor diagnosis, with the dose-limiting organ being the liver.
The success of EGFR-positive tumor imaging using 64Cu-DOTA-cetuximab can be translated into the clinic to characterize the pharmacokinetics, to select the right population of patients for EGFR-targeted therapy, to monitor the therapeutic efficacy of anti-EGFR treatment, and to optimize the dosage of either cetuximab alone or cetuximab in combination with other therapeutic agents.
European journal of nuclear medicine and molecular imaging 06/2007; 34(6):850-8. · 4.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Single-walled carbon nanotubes (SWNTs) exhibit unique size, shape and physical properties1, 2, 3 that make them promising candidates for biological applications. Here, we investigate the biodistribution of radio-labelled SWNTs in mice by in vivo positron emission tomography (PET), ex vivo biodistribution and Raman spectroscopy. It is found that SWNTs that are functionalized with phospholipids bearing polyethylene-glycol (PEG) are surprisingly stable in vivo. The effect of PEG chain length on the biodistribution and circulation of the SWNTs is studied. Effectively PEGylated SWNTs exhibit relatively long blood circulation times and low uptake by the reticuloendothelial system (RES). Efficient targeting of integrin positive tumour in mice is achieved with SWNTs coated with PEG chains linked to an arginine–glycine–aspartic acid (RGD) peptide. A high tumour accumulation is attributed to the multivalent effect of the SWNTs. The Raman signatures of SWNTs are used to directly probe the presence of nanotubes in mice tissues and confirm the radio-label-based results.
Nature Nanotechnology 12/2006; 2(1):47-52. · 27.27 Impact Factor
