Open Access Original research

Comparison between 68Ga-bombesin (68Ga-BZH3) and the cRGD tetramer 68Ga-RGD4 studies in an experimental nude rat model with a neuroendocrine pancreatic tumor cell line

Caixia Cheng1*, Leyun Pan1, Antonia Dimitrakopoulou-Strauss1, Martin Schäfer2, Carmen Wängler3, Björn Wängler3, Uwe Haberkorn1 and Ludwig G Strauss1

Author Affiliations

1 Clinical Cooperation Unit Nuclear Medicine, German Cancer Research Center, Heidelberg, Germany

2 Department of Radiopharmaceutical Chemistry, German Cancer Research Center, Heidelberg, Germany

3 University Hospital Munich, Department of Nuclear Medicine, Ludwig Maximilians-University Munich, Munich, Germany

For all author emails, please log on.

EJNMMI Research 2011, 1:34  doi:10.1186/2191-219X-1-34

The electronic version of this article is the complete one and can be found online at:

Received:28 July 2011
Accepted:13 December 2011
Published:13 December 2011

© 2011 Cheng et al; licensee Springer.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.



Receptor scintigraphy gains more interest for diagnosis and treatment of tumors, in particular for neuroendocrine tumors (NET). We used a pan-Bombesin analog, the peptide DOTA-PEG2-[D-tyr6, β-Ala11, Thi13, Nle14] BN(6-14) amide (BZH3). BZH3 binds to at least three receptor subtypes: the BB1 (Neuromedin B), BB2 (Gastrin-releasing peptide, GRP), and BB3. Imaging of ανβ3 integrin expression playing an important role in angiogenesis and metastasis was accomplished with a 68Ga-RGD tetramer. The purpose of this study was to investigate the kinetics and to compare both tracers in an experimental NET cell line.


This study comprised nine nude rats inoculated with the pancreatic tumor cell line AR42J. Dynamic positron emission tomography (PET) scans using 68Ga-BZH3 and 68Ga-RGD tetramer were performed (68Ga-RGD tetramer: n = 4, 68Ga-BZH3: n = 5). Standardized uptake values (SUVs) were calculated, and a two-tissue compartmental learning-machine model (calculation of K1 - k4 vessel density (VB) and receptor binding potential (RBP)) as well as a non-compartmental model based on the fractal dimension was used for quantitative analysis of both tracers. Multivariate analysis was used to evaluate the kinetic data.


The PET kinetic parameters showed significant differences when individual parameters were compared between groups. Significant differences were found in FD, VB, K1, and RBP (p = 0.0275, 0.05, 0.05, and 0.0275 respectively). The 56- to 60-min SUV for 68Ga-BZH3, with a range of 0.86 to 1.29 (median, 1.19) was higher than the corresponding value for the 68Ga-RGD tetramer, with a range of 0.78 to 1.31 (median, 0.99). Furthermore, FD, VB, K1, and RBP for 68Ga-BZH3 were generally higher than the corresponding values for the 68Ga-RGD tetramer, whereas k3 was slightly higher for 68Ga-RGD tetramer.


As a parameter that reflects receptor binding, the increase of K1 for 68Ga-BZH3 indicated higher expression of bombesin receptors than that of the ανβ3 integrin in neuroendocrine tumors. 68Ga-BZH3 seems better suited for diagnosis of NETs owing to higher global tracer uptake.

68Ga-bombesin; 68Ga-RGD tetramer; PET; kinetic modeling; neuroendocrine tumors


During the past decade, the application of radiolabeled somatostatin analogs in nuclear medicine for diagnostics and therapy of neuroendocrine tumors has achieved success and stimulated the research in receptor targeting of additional tumor types [1]. Positron emission tomography (PET) is the most efficient imaging method in nuclear medicine because of its option of an absolute activity determination, its better contrast resolution, and its higher detection efficiency compared with conventional γ-cameras. PET with 18F-fluorodeoxyglucose (18F-FDG) is frequently used for oncologic applications to assess tissue viability, thereby gain the staging and therapy monitoring by qualitative analysis of SUV and quantitative evaluation based on the compartmental analysis of kinetic parameters [2]. However, not all tumors are 18F-FDG avid, and in particular treated tumorous lesions may demonstrate a low fluorodeoxyglucose (FDG) uptake and can therefore not be delineated using FDG. Therefore, new specific tracers are needed to enhance the sensitivity and specificity of PET. One approach is to study the expression of receptors to gain specificity. Experimental data demonstrated enhanced bombesin (BN) receptors in neuroendocrine tumors (NETs) [3-5].

Bombesin is an amphibian neuropeptide of 14 amino acids that shows a high affinity for the human gastrin-releasing peptide receptor (GRP-r, also known as BB2), which is overexpressed on several types of cancer. In addition, for the neuromedin B (BB1) and the bombesin receptor subtype (BB3), bombesin also shows a high affinity. Thus, radiolabeled BN and BN analogs may prove to be specific tracers for diagnostic and therapeutic targeting of GRP-r-positive tumors in nuclear medicine [6-13]. We have reported 68Ga-labeled bombesin may be helpful for diagnostic reasons in a subgroup of patients with GIST and recurrent gliomas [14,15].

The expression of GRP receptor in AR42J cell line has been reported by other groups [16,17]. So far, the expression of integrin ανβ3 in AR42J cell line has not been reported yet. However, the integrin ανβ3 plays an important role in angiogenesis and tumor metastasis. It is expressed on activated endothelial cells as well as some tumor cells [18]. Therefore, it is a promising imaging target as a potential surrogate parameter of angiogenic activity.

The 68Ga-RGD tetramer 68Ga-RGD4 is a specific tracer for the integrin ανβ3 [19]. Herein, dynamic PET studies with 68Ga-Bombesin were performed in AR42J tumor-bearing mice to investigate the impact of complementary receptor scintigraphy on diagnosis and the potential of a radionuclide treatment. Furthermore, dynamic 68Ga-RGD4 studies were performed for comparison.

Materials and methods

Synthesis of RGD4

Resins for peptide synthesis, coupling reagents, and Fmoc-protected amino acids were purchased from NovaBiochem. For analytical and semi-preparative high-performance liquid chromatography (HPLC), an Agilent 1200 system was used. The columns used for chromatography were a Chromolith Performance (RP-18e, 100 to 4.6 mm, Merck, Germany) and a Chromolith (RP-18e, 100-10 mm, Merck, Darmstadt, Germany) column, operated with flows of 4 and 8 mL/min, respectively. ESI and MALDI were obtained with a Finnigan MAT95Q and a Bruker Daltonics Microflex (Bruker Daltonics, Bremen, Germany), respectively.

The compound (DOTA-comprising maleimide tetramer (DOTA-Mal4)) was synthesized on solid support by standard Fmoc solid-phase peptide synthesis as described by Wellings et al. [20] on a standard rink amide resin. After coupling of Fmoc-Lys(Mtt)-OH to this resin (100 μmol), the Mtt-protecting group was removed by successive incubation with 1.75% TFA in DCM followed by coupling of tris-tBu-DOTA and Fmoc-Lys(Fmoc)-OH under standard conditions. After removal of both lysine Fmoc protecting groups using deprotection times of twice 2 min and twice 5 min, Fmoc-Lys(Fmoc)-OH was coupled twice. After removal of all four lysine Fmoc protecting groups using deprotection times of twice 2 min and twice 10 min, maleimidobutyric acid was coupled applying the standard protocol. The product was cleaved from the solid support and deprotected using a mixture of TFA (trifluoroacetic acid)/TIS (triisopropylsilane)/H2O (95:2.5:2.5) for 45 min. The product was purified by semi-preparative HPLC using a gradient of 0% to 30% MeCN in 6 min and was obtained as a white solid upon lyophilization (49.8 mg, 31.6 μmol, 32%). ESI-MS (m/z) for [M + H]+ (calculated): 1,576.76 (1,576.76) and [M + 2H]2+ (calculated): 788.89 (788.88).

c(RGDfK)-PEG1-SH was synthesized on a preloaded Fmoc-Asp(NovaSyn TGA)-Oall resin (100 μmol) to which were subsequently coupled Fmoc-Gly-OH, Fmoc-Arg(Pbf)-OH, Fmoc-Lys(Mtt)-OH, and Fmoc-D-Phe-OH using standard coupling protocols. After allyl-deprotection, the peptide was cyclized and after removal of the Mtt-protecting group by successive incubation with 1.75% TFA in DCM, Fmoc-PEG1-OH, and SATA (N-succinimidyl-S-acetylthioacetate) were coupled. The product was cleaved from the solid support and deprotected using a mixture of TFA (trifluoroacetic acid)/TIS (triisopropylsilane)/H2O (95:2.5:2.5) for 45 min followed by an incubation with a hydroxylamine-containing solution (H2O + 0.1%TFA/MeCN + 0.1%TFA/50% hydroxylamine × HCl solution in water (750:750:25 μL)) for 5 min. The product was purified by semi-preparative HPLC using a gradient of 0% to 40% MeCN in 6 min and was obtained as a white solid upon lyophilization (33.2 mg, 40.4 μmol, 40%). ESI-MS (m/z) for [M + H]+ (calculated): 823.38 (823.37).

The conjugation of c(RGDfK)-PEG1-SH to DOTA-Mal4 was carried out to yield DOTA-comprising RGD tetramer (DOTA-RGD4) as described before [21]. In brief, a solution of c(RGDfK)-PEG1-SH (15.6 mg, 19.0 μmol) in phosphate buffer (500 μL, 0.1 M, pH 6.0) was added to a solution of DOTA-Mal4 (5 mg, 3.2 μmol) in MeCN/phosphate buffer (0.1 M, pH 5.0) 1:1 (250 μL) and the pH of the mixture was adjusted to 7.4 by the addition of phosphate buffer (0.5 M, pH 7.4, approximately 100 μL). After 10 min, the product was purified by semi-preparative HPLC using a gradient of 0% to 40% MeCN in 6 min and was obtained as a white solid upon lyophilization (13.8 mg, 2.8 μmol, 89%). ESI-MS (m/z) for [M + Kcomplexed + 4H]4+ (calculated): 1,227.05 (1,227.05) and (m/z) for [M + Kcomplexed + Nasalt + 4H]4+ (calculated): 1,232.55 (1,232.55).

DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N″,N'″-tetraacetic acid. PEG is ethylene glycol (2-aminoethyl-carboxy-methyl ether). RGD is a cyclic pentapeptide containing the amino acid sequence D-Phe-Lys-Arg-Gly-Asp. Figure 1 shows the chemical structure of 68Ga-RGD4.

thumbnailFigure 1. The chemical structure of 68Ga-RGD4.

Synthesis of BZH3

BZH3 was prepared according to the method described by Schuhmacher et al. [14]. BZH3 is DOTA-PEG2-[D-Tyr6 -β-Ala11 -Thi13 -Nle14 ]BN(6-14) amide.

Radiolabeling of BZH3 and RGD4

68Ga was used for labeling of both tracers and was obtained from a 68Ge/68Ga generator, which consists of a column containing a self-made phenolic ion-exchanger loaded with 68Ge and coupled in series with a small-sized anion-exchanger column (AG 1-X8 Cl-, mesh 200 to 400, Bio-Rad, Hercules, CA, USA) to concentrate 68Ga during elution. This generator provides 68Ga with an average yield of 60% for > 1.5 years. 68Ga-BZH3 and 68Ga-RGD4 were prepared according to the method described by Schuhmacher et al. and Jae Min Jeong et al., respectively [22,23]. The specific activity (the amount of radioactivity per peptide amount) of 68Ga-BZH3 and 68Ga-RGD4 were measured to be 28 and 22 MBq/nmol, respectively, which is sufficient for an efficient receptor imaging in vivo. Furthermore, a binding affinity of 4.973 μM (IC50) was obtained for 68Ga-RGD4 binding to ανβ3, which indicated that 68Ga-RGD4 could be used as PET tracer with ανβ3-positive neuroendocrine pancreatic tumor cell line.

Cell lines

The AR42J cell line, derived from a rat exocrine pancreas neuroendocrine tumor, was used. Cells were obtained from the European Collection of Cell Cultures and were grown in RPMI 1640 medium supplemented with 2 mmol/L glutamine and 10% fetal calf serum. Adherent cells were dislodged with trypsin/ethylenediaminetetraacetic acid (0.02%: 0.05%, w/v). For PET-studies, 5 × 106 cells in 200 μl RPMI without supplements were inoculated subcutaneously in the right hind leg of Wistar rats.


The study included nine AR 42 J tumor-bearing nude rats. We grouped all rats according to PET tracers (B, 68Ga-BZH3 and R, 68Ga-RGD4), used in dynamic PET scanning, as noted in Table 1. Dynamic PET studies were performed for 60 min after the intravenous application of 10 to 30 MBq 68Ga-RGD4 or 20 to 40 MBq 68Ga-BZH3, using a 28-frame protocol (ten frames of 30 s, five frames of 60 s, five frames of 120 s, and eight frames of 300 s). Two animals can be examined in parallel per scanning by a homemade injector (Figure 2). A dedicated PET-CT system (Biograph™ mCT, 128 S/X, Siemens Co, Erlangen, Germany) with an axial field of view of 21.6 cm with TrueV, operated in a three-dimensional mode, was used for all animal studies. The system provides the simultaneous acquisition of 369 transverse slices with a slice thickness of 0.6 mm. The animals were positioned in the axial plane of the system to maintain the best resolution in the center of the system. All PET images were attenuation-corrected and an image matrix of 400 × 400 pixels was used for iterative image reconstruction (voxel size 1.565 × 1.565 × 0.6 mm) based on the syngo MI PET/CT 2009C software version. After the end of the dynamic series an ultrahigh resolution CT with 85 mA, 80 kV and a pitch of 0.85 cm was performed for attenuation correction of the acquired dynamic emission data. The reconstructed images were converted to SUV images based on the formula [24]: SUV = Tissue concentration (becquerel per gram)/[injected dose (becquerel per gram))/body weight (gram)]. The SUV 55 to 60 min post-injection was used for the assessment of both tracers. The SUV images were used for all further quantitative evaluations.

Table 1. Quantitative PET parameters for the both tracers' kinetics of 68Ga-BZH3 and 68Ga-RGD4

thumbnailFigure 2. Experimental setting. Our experimental setting demonstrating two rats prior to positioning in the PET-CT scanner and homemade injector (two animals can be examined in parallel per scanning).

Dynamic PET data were evaluated using the software package PMOD (provided courtesy of PMOD Technologies Ltd., Zuerich, Switzerland) [25,26]. Areas with enhanced tracer uptake on transaxial, coronal, and sagittal images were evaluated visually. A volume of interest consists of several regions of interest over the target area. Irregular regions of interest were drawn manually. A detailed quantitative evaluation of tracer kinetics requires the use of compartmental modeling. A two-tissue-compartment model was used to evaluate the dynamic studies. This methodology is standard, particularly for the quantification of dynamic 18F-FDG studies [27,28].

In animals, a partial volume correction must be applied to the data due to the small size of the input and tumor volumes of interest (VOIs). Herein, the recovery coefficient was 0.85 for a diameter of 8 mm and 0.32 for a diameter of 3 mm based on phantom measurements as well as the recent parameter settings used with the reconstruction software. For the input function the mean values of the VOI data obtained from the heart were used. We used a preprocessing tool, which allowed a fit of the input curve by a sum of up to three decaying exponentials. The learning-machine two-tissue-compartment model was used for the fitting and provided five parameters: the transport parameters for tracer into and out of the cell, K1 and k2, the parameters for phosphorylation and dephosphorylation of intracellular tracer, k3 and k4, and the fractional blood volume, also called vessel density (VB), which reflects the amount of blood in the VOI. Following compartment analysis, we calculated the global influx of tracer from the compartment data using the formula: influx = (K1 × k3)/(k2 + k3). Compared to the standard iterative method, the machine learning method has the advantage of a fast convergence and avoidance of over fitting [29]. The model parameters were accepted when K1 - k4 was less than 1 and VB exceeded 0. The unit for the rate constants K1 to k4 was 1/min. In the case of 68Ga-BZH3 and 68Ga-RGD4, K1 is associated with receptor binding, k2 with displacement from the receptor, k3 with cellular internalisation, and k4 with externalisation.

Besides the compartmental analysis, a non-compartmental model based on the fractal dimension was used. The fractal dimension is a parameter of heterogeneity and was calculated for the time-activity data of each individual volume of interest. The values fro fractal dimension vary from 0 to 2, showing the deterministic or chaotic distribution of tracer activity. We used a subdivision of 7 × 7 and a maximal SUV of 20 for the calculation of fractal dimension [30].

Statistical analysis

Statistical evaluation was performed with Stata/SE 10.1 (StataCorp, College Station, TX, USA). Statistical evaluation was performed using the descriptive statistics and scatter plots. The classification analysis was performed using the GenePET software [31]. The software applies the support vector machines (SVM) algorithm and provides a classification analysis by optimizing a hyperplane between the target variables. The algorithm for selection or elimination of variables, the feature ranking, can be based on different criteria, e.g., F test, Mann-Whitney test, or the SVM ranking feature elimination (SVM RFE) approach [32]. The SVM RFE algorithm computes a multidimensional weight vector for the PET variables and the square of the vector is used to calculate the ranking criteria. For comparison between two tracers, the two-sided Wilcoxon rank-sum test was applied for all PET parameters, SUV, and the fractal dimension (FD), using a single parameter analysis. P values < 0.05 were considered significant.


Figure 3 is a representative set of time-activity data obtained with a image-derived measured blood input function, which illustrates the good statistical quality of the data and model fit using nonlinear regression and two-tissue-compartment model.

thumbnailFigure 3. Representative blood input function (filled yellow squares) and tumor tissue tracer concentrations. Obtained in a 60-min acquisition sequence (left, 68Ga-BZH3; right, 68Ga-RGD4). Filled green squares are tracer concentrations for each image, while the smooth line through the data is the two-tissue-compartment model fit to the data. A smooth line (interpolation) was drawn through the input function data to illustrate the shape of the curve.

Table 1 presents the mean, median, minimum, and maximum values as well as the standard deviation for the SUV, FD, and kinetic values of all parameters for both tracers (Table 1). In the whole paper, B and R represent 68Ga-BZH3 and 68Ga-RGD4 respectively. The Wilcoxon rank-sum test was used to reveal statistically significant differences between all variables.

Figure 4 shows an example of 3D fused PET-CT images for 68Ga-RGD4 and 68Ga-Bombesin. The 68Ga-BZH3 image clearly showed enhanced 68Ga-BZH3 uptake in the tumor area in the lower leg. 68Ga-BZH3 uptake in the evaluated tumor lesions was generally higher than 68Ga-RGD4 uptake.

thumbnailFigure 4. 3D fused PET-CT images for 68Ga-RGD4 (left) and 68Ga-Bombesin (right). Besides the tumor region in the lower leg. The tracer uptake in other sites covered heart (exhibit for 68Ga-RGD4), liver, kidney, urinary bladder, and testicles (left for male rat).

Box plots of 68Ga-BZH3 and 68Ga-RGD4 uptake (56- to 60-min SUV) in tumor tissue and FD are presented in Figure 5. The corresponding quantitative data and the corresponding P values are presented in Table 1 and 2. The 56- to 60-min SUV for 68Ga-BZH3, with a range of 0.86 to 1.29 (median 1.19) was higher than the corresponding value for 68Ga-RGD4, with a range of 0.78 to 1.31 (median 0.99). However, there was no significant difference in the median SUV between the two tracers. Interestingly, the median FD for 68Ga-BZH3 (1.1425) was significantly higher as compared with 68Ga-RGD4 (1.039) (P = 0.0275) at a level of P < 0.05. The transport rate constants K1 and k3 (1/min), the receptor binding potential (RBP) and the vascular fraction VB of both tracers are presented in Figure 6. Kinetic data demonstrate higher the values of VB for 68Ga-BZH3 as compared with 68Ga-RGD4 (0.0903 vs. 0.0574); furthermore, VB was relatively low for both tracers, not exceeding 0.2. Furthermore, the values of K1 and RBP were higher for 68Ga-BZH3 than the corresponding values for 68Ga-RGD4 (0.3506 vs. 0.2728 and 0.0607 vs. 0.0442, respectively). In addition, comparable k3 values without significant difference for both tracers were displayed in Figure 6.

thumbnailFigure 5. Box-Whiskers plots of the median SUV 55 to 60 min and FD for both tracers. *P values < 0.05. B, 68Ga-BZH3; R, 68Ga-RGD4.

Table 2. The value of statistically significant level P using the Wilcoxon rank-sum test

thumbnailFigure 6. Box-Whiskers plots of median values for both tracers for vB, K1, k3 and RBP. *P values < 0.05). B, 68Ga-BZH3; R, 68Ga-RGD4.


PET with FDG is frequently used for oncological application to assess tissue viability. However, owing to the low FDG uptake in some tumor types, like in the neuroendocrine carcinomas, there is a need for new radiotracers. One idea is to study the expression of different receptors in order to guide diagnostics and even more therapy in that direction, e.g. using a radionuclide-based therapy. NETs originate mostly from the gastroenteropancreatic tract and express specific receptors like amine and peptide receptors (somatostatin, vasointestinal peptide receptors, bombesin, cholecystokinin, gastrin and/or substance P) [33]. Adams et al. reported the comparison of different tracers in detecting malignant NETs and revealed that increased FDG uptake was associated with malignancy [34]. In nude mice bearing the AR4-2J tumor, tumor uptake of both 90Y and 111In-DOTATOC 4 h after injection was five times higher than with 111In-DTPA-octreotide [35]. We had reported on 68Ga-DOTATOC studies in patients with NETs and an enhanced uptake in metastases of NETs [36]. Furthermore, we have shown that the global DOTATOC uptake in NETs is mainly dependent on k1 (receptor binding) and VB (fractional blood volume) and less on the k3 (internalization). 68Ga-DOTATOC was better suited than 18F-FDG for the diagnosis of metastatic NETs. The 68Ga-DOTATOC uptake was also used as a parameter for a radionuclide therapy with 90Y-DOTATOC. Patients with lesions demonstrating an enhanced 68Ga-DOTATOC uptake (> 5.0 SUV) were selected for radionuclide therapy [37].

Bombesin and the two mammalian bombesin-like peptides, BB1 and BB2 regulate many biologic response processes through activation of distinct receptor subtypes, including modulation of smooth muscle contraction, secretion of neuropeptides and hormones, as well as stimulation of cell growth [38,39]. Activation of neuromedin B (BB1) receptors has been reported in various human cancers [39]. Experimental studies demonstrated an enhanced bombesin receptor expression in several human adult glioblastoma cell lines as well as in two pediatric human glioblastoma cell lines [38]. We reported on an enhanced 68Ga-BZH3 uptake in a subgroup of patients with gastrointestinal stromal tumors [15], and quantitative 68Ga-BZH3 studies were helpful in patients with recurrent gliomas for tumor grading and the differentiation between high- and low-grade tumors [14]. In addition, other bombesin analogues 64Cu-, 99mTc-, 188Re-, 177Lu-, 90Y-, and 111In have been reported to be promising radiotracers for PET imaging of many human cancers overexpressing the GRP receptor such as breast cancer and prostate carcinoma [6-13,40,41].

Integrins play a key role in angiogenesis and tumor metastasis by mediating tumor cell invasion and movement across blood vessel, whereas integrins expressed on endothelial cells modulate cell migration and survival during the angiogenic cascade. A common feature of many integrins like ανβ3 is that they bind to extracellular matrix proteins via the three amino acid sequence arginine-glycine-aspartic acid (RGD) [42,43]. Radiolabeled RGD-peptides, the integrin ανβ3-specific tracers, have been developed for PET and SPECT imaging. A mass of data suggested that ανβ3 expression can be quantified by radiolabeled RGD-peptides [44-46]. In this study, 68Ga-BZH3 and 68Ga-RGD4 were used as tracers for PET to assess the receptor expression in AR42J tumor-bearing nude rats by comparison.

Quantitative dynamic PET provides the possibility for absolute tracer quantification and is superior to static images, which are widely used, but do not provide information on tracer kinetics. Furthermore, the use of a two-compartment model is the superior approach for the assessment of tracer kinetics, and is accepted for research purposes [27]. Concerning the 68Ga-BZH3 kinetics, k1 is a parameter that reflects the receptor binding and k3 is a parameter that reflects the internalization of the tracer. A lower receptor binding of 68Ga-BZH3 was reported in gliomas as compared with 68Ga-DOTATOC in meningiomas, but higher internalization, were proved [47]. In the present study, the comparison of the 68Ga-BZH3 kinetics with the 68Ga-RGD4 kinetics in the ARJ 42 tumor-bearing nude rats revealed higher mean values of k1 for 68Ga-BZH3 (median, 0.3506) as compared with 68Ga-RGD4 (median 0.2728), and comparable k3 values (median, 0.1177 vs. 0.1180). According to these data, the tracers' accumulation in this neuroendocrine tumor cell line is primarily depends on the receptor binding and less on the internalization.

Generally, 68Ga-BZH3 uptake was lower than 18F-FDG [15]. Herein, we found 68Ga-BZH3 uptake was higher than that of 68Ga-RGD4, and the values were relatively comparable in comparison to that reported in gliomas [14]. In particular, there were significant differences between VB, K1, k4, RBP, and FD. The fractional blood values VB of 68Ga-BZH3 were higher than that of 68Ga-RGD4 (median, 0.0903 vs. 0.0574), however for both tracers they are low in comparison to those reported for other tracers, like 68Ga-DOTATOC and 18F-FDG. This is in accordance to previous published data, e.g. in melanoma patients and confirm the hypothesis that the absolute value of VB depend on the applied tracer [48]. The VB and RBP values for 68Ga-BZH3 were more spread out than those determined for 68Ga-RGD4. A possible explanation is that the tracer uptake of 68Ga-RGD4 was generally lower than that of 68Ga-BZH3.

Cancer is often characterized by chaotic, poorly regulated growth. Recent studies have shown that fractal geometry can be useful to describe the pathological architecture of tumors and angiogenesis. Fractals can be useful measures of pathologies of the vascular architecture, the tumor border, and the cellular morphology [49]. The FD is used to characterize the chaotic nature of the tracer's distribution in primary tumors and metastases, based on the box counting procedure of chaos theory, for the analysis of dynamic PET data. In the present study, FD values for 68Ga-BZH3 were ranged from 1.066 to 1.150 (median, 1.142), higher than that for 68Ga-RGD4 (median, 0.989), but both are lower compared with those measured in malignancies with different tracers, such as 68Ga-DOTATOC, 18F-FDG, 15O-water, and 18F-DOPA (a median FD exceed 1.25) [48,50].


In general, a high SUV indicates high receptor binding. The preliminary results give evidence for a higher BZH3 uptake, which is related to higher bombesin and neuromedin B gene expression than that of ανβ3 in neuroendocrine tumors. 68Ga-BZH3 seems better for diagnosis of NETs owing to higher values of global tracer uptake. Further studies with a larger number of animals and in patients are needed to confirm these preliminary results.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

CC participated in the whole study and wrote the manuscript. LP performed the statistical analysis. MS, CW, and BW carried out the synthesis of tracers. ADS and LGS did the design of the study and revised the whole manuscript. UH gave financial support. All authors read and approved the final manuscript.


  1. Hoffman TJ, Quinn TP, Volkert WA: Radiometallated receptor-avid peptide conjugates for specific in vivo targeting of cancer cells.

    Nul Med Biol 2001, 28:527-539. OpenURL

  2. Strauss LG, Conti PS: The application of PET in clinical oncology.

    J Nucl Med 1991, 32:623-648. OpenURL

  3. Sancho V, Di Florio A, Moody TW, Jensen RT: Bombesin receptor-mediated imaging and cytotoxicity: review and current status.

    Curr Drug Deliv 2011, 8:79-134. OpenURL

  4. Ambrosini V, Tomassetti P, Franchi R, Fanti S: Imaging of NETs with PET radiopharmaceuticals.

    Q J Nucl Med Mol Imaging 2010, 54:16-23. OpenURL

  5. Bodei L, Ferone D, Grana CM, Cremonesi M, Signore A, Dierckx RA, Paganelli G: Peptide receptor therapies in neuroendocrine tumors.

    J Endocrinol Invest 32(4):360-369. OpenURL

  6. Van de Wiele C, Dumont F, Van den Broecke R, Oosterlinck W, Cocquyt V, Serreyn R, Peers S, Thornback J, Slegers G, Dierckx RA: Technetium-99 m RP527, a GRP analogue for visualisation of GRP receptor-expressing malignancies: a feasibility study.

    Eur J Nucl Med 2000, 27:1694-1699. OpenURL

  7. Breeman WAP, de Jong M, Erion JL, Bugaj JE, Srinivasan A, Bernard BF, Kwekkeboom DJ, Visser TJ, Krenning EP: Preclinical comparison of 111In labeled DTPA- or DOTA-bombesin analogs for receptor targeted scintigraphy and radionuclide therapy.

    J Nucl Med 2002, 43:1650-1656. OpenURL

  8. Hoffman TJ, Gali H, Smith CJ, Sieckman GL, Hayes DL, Owen NK, Volkert WA: Novel series of In-111 labeled bombesin analogs as potential radiopharmaceuticals for specific targeting of gastrin-releasing peptide receptors expressed on human prostate cancer cells.

    J Nucl Med 2003, 44:823-831. OpenURL

  9. Van de Wiele C, Dumont F, Dierckx RA, Peers SH, Thornback JR, Slegers G, Thierens H: Biodistribution and dosimetry of 99mTc-RP 527, a gastrin-releasing peptide (GRP) agonist for the visualization of GRP receptor-expressing malignancies.

    J Nucl Med 2001, 42:1722-1727. OpenURL

  10. Smith CJ, Sieckman GL, Owen NK, Hayes DL, Mazuru DG, Kannan R, Volkert WA, Hoffman TJ: Radiochemical investigations of gastrin-releasing peptide receptor-specific [99mTc(X)(CO)3-Dipr-Ser-Ser-Ser-Gln-Trp-Ala-Val-Gly-His-Leu-Met(NH2)] in PC-3, tumor-bearing, rodent models: syntheses, radiolabeling, and in vitro/in vivo studies where Dpr = 2,3-diaminopropionic acid and × = H2O or P(CH2OH)3.

    Cancer Res 2003, 63:4082-4088. OpenURL

  11. Nock B, Nikolopoulou A, Chiotellis E, Loudos G, Maintas D, Reubi JC, Maina T: 99mTc-Demobesin 1, a novel potent bombesin analogue for GRP receptor-targeted tumor imaging.

    Eur J Nucl Med 2003, 30:247-258. OpenURL

  12. Scopinaro F, DeVincentis G, Varvarigou AD, Laurenti C, Iori F, Remediani S, Chiarini S, Stella S: 99mTc-Bombesin detects prostate cancer and invasion of pelvic lymph nodes.

    Eur J Nucl Med 2003, 30:1378-1382. OpenURL

  13. Smith CJ, Sieckman GL, Owen NK, Hayes DL, Mazuru DG, Volkert WA, Hoffman TJ: Radiochemical investigations of [188Re(H2O)(CO)3-diaminopropionic acid-SSS-bombesin(7-14) NH2]: syntheses, radiolabeling and in vitro/in vivo GRP receptor targeting studies.

    Anticancer Res 2003, 23:63-70. OpenURL

  14. Dimitrakopoulou-Strauss A, Seiz M, Tuettenberg J, Schmieder K, Eisenhut M, Haberkorn U, Strauss LG: Pharmacokinetic studies of 68Ga-labeled bombesin (68Ga-BZH3) and F-18 FDG PET in patients with recurrent gliomas and comparison to grading.

    Clin Nucl Med 2011, 36:101-108. OpenURL

  15. Dimitrakopoulou-Strauss A, Hohenberger P, Haberkorn U, Mäcke HR, Eisenhut M, Strauss LG: 68Ga-labeled bombesin studies in patients with gastrointestinal stromal tumors: comparison with 18F-FDG.

    J Nucl Med 2007, 48:1245-1250. OpenURL

  16. Singh P, Draviam E, Guo YS, Kurosky A: Molecular characterization of bombesin receptors on rat pancreatic acinar AR42J cells.

    Am J Physiol 1990, 258:G803-9. OpenURL

  17. vanderSpek JC, Sutherland JA, Zeng H, Battey JF, Jensen RT, Murphy JR: Inhibition of protein synthesis in small cell lung cancer cells induced by the diphtheria toxin-related fusion protein DAB389 GRP.

    Cancer Res 1997, 57:290-294. OpenURL

  18. Beer AJ, Schwaiger M: Imaging of integrin ανβ3 expression.

    Cancer Metastasis Rev 2008, 27:631-644. OpenURL

  19. Cai W, Chen X: Anti-angiogenic cancer therapy based on integrinαVβ3 antagonism.

    Anti Canc Agents Med Chem 2006, 6:407-428. OpenURL

  20. Wellings DA, Atherton E: Standard Fmoc protocols.

    Methods Enzymol 1997, 289:44-67. OpenURL

  21. Wängler C, Maschauer S, Prante O, Schafer M, Schirrmacher R, Bartenstein P, Eisenhut M, Wängler B: Multimerization of cRGD peptides by click chemistry: synthetic strategies, chemical limitations, and influence on biological properties.

    Chembiochem 2010, 11:2168-2181. OpenURL

  22. Schuhmacher J, Zhang H, Doll J, Mäcke HR, Matys R, Hauser H, Henze M, Haberkorn U, Eisenhut M: GRP receptor-targeted PET of a rat pancreas carcinoma xenograft in nude mice with a 68Ga-labeled bombesin (6-14) analog.

    J Nucl Med 2005, 46:691-699. OpenURL

  23. Jeong JM, Hong MK, Chang YS, Lee YS, Kim YJ, Cheon GJ, Lee DS, Chung JK, Lee MC: Preparation of a promising angiogenesis PET imaging agent: 68Ga-labeled c(RGDyK)-isothiocyanatobenzyl-1,4,7- triazacyclononane-1,4,7-triacetic acid and feasibility studies in mice.

    J Nucl Med 2008, 49:830-836. OpenURL

  24. Pan L, Mikolajczyk K, Strauss LG, Haberkorn U, Dimitrakopoulou-Strauss A: Machine learning based parameter imaging and kinetic modelling of PET data.

    J Nucl Med 2007, 48(2):158. OpenURL

  25. Mikolajczyk K, Szabatin M, Rudnicki P, Grodzki M, Burger C: A JAVA environment for medical image data analysis: initial application for brain PET quantitation.

    Med Inform 1998, 23:207-214. OpenURL

  26. Burger C, Buck A: Requirements and implementations of a flexible kinetic modelling tool.

    J Nucl Med 1997, 38:181-1823. OpenURL

  27. Miyazawa H, Osmont A, Petit-Taboue MC, Tillet I, Travère JM, Young AR, Barré L, MacKenzie ET, Baron JC: Determination of 18F-fluoro-2-deoxy-d-glucose rate constants in the anesthetized baboon brain with dynamic positron tomography.

    J Neurosci Methods 1993, 50:263-272. OpenURL

  28. Sokoloff L, Smith CB: Basic principles underlying radioisotopic methods for assay of biochemical processes in vivo. In The Metabolism of the Human Brain Studies with Positron Emission Tomography. Edited by Greitz T, Ingvar DH, Widén L. New York, NY: Raven Press; 1983:123-148. OpenURL

  29. Strauss LG, Pan L, Koczan D, Klippel S, Mikolajczyk K, Burger C, Haberkorn U, Schönleben K, Thiesen HJ, Dimitrakopoulou-Strauss A: Fusion of positron emission tomography (PET) and gene array data: a new approach for the correlative analysis of molecular biological and clinical data.

    IEEE Trans Med Imaging 2007, 26:804-812. OpenURL

  30. Dimitrakopoulou-Strauss A, Strauss LG, Mikolajczyk Burger C, Lehnert T, Bernd L, Ewerbeck V: On the fractal nature of dynamic positron emission tomography (PET) studies.

    World J Nucl Med 2003, 2:306-313. OpenURL

  31. Guyon I, Weston J, Barnhill S, Vapnik V: Gene selection for cancer classification using support vector machines.

    Mach Learn 2002, 46:389-422. OpenURL

  32. Hawkins RA, Choi Y, Hung S, Messa C, Hoh CK, Phelps ME: Quantitating Tumor Glucose Metabolism with FDG and PET.

    J Nucl Med 1992, 33:339-344. OpenURL

  33. Kaltsas G, Besser M, Grossman A: The diagnosis and medical management of advanced neuroendocrine tumors.

    Endocr Rev 2004, 25:458-511. OpenURL

  34. Adams S, Baum R, Rink T, Schumm-Dräger PM, Usadel KH, Hör G: Limited value of fluorine-18 fluorodeoxyglucose positron emission tomography for the imaging of neuroendocrine tumours.

    Eur J Nucl Med 1998, 25:79-83. OpenURL

  35. Heppeler A, Froidevaux S, Mäcke HR, Jermann E, Béhé M, Powell P, Hennig M: Radiometal-labelled macrocyclic chelator-derivatised somatostatin analogue with superb tumor-targeting properties and potential for receptor-medicated internal radiotherapy.

    Chem Eur J 1999, 5:1974-1981. OpenURL

  36. Koukouraki S, Strauss LG, Georgoulias V, Schuhmacher J, Haberkorn U, Karkavitsas N, Dimitrakopoulou-Strauss A: Evaluation of the pharmacokinetics of 68Ga-DOTATOC in patients with metastatic neuroendocrine tumours scheduled for 90Y-DOTATOC therapy.

    Eur J Nucl Med Mol Imaging 2006, 33:460-466. OpenURL

  37. Koukouraki S, Strauss LG, Georgoulias V, Eisenhut M, Haberkorn U, Dimitrakopoulou-Strauss A: Comparison of the pharmacokinetics of 68Ga-DOTATOC and [18F]FDG in patients with metastatic neuroendocrine tumours scheduled for 90Y-DOTATOC therapy.

    Eur J Nucl Med Mol Imaging 2006, 33:1115-1122. OpenURL

  38. Sharif TR, Luo W, Sharif M: Functional expression of bombesin receptor in most adult and pediatric human glioblastoma cell lines; role in mitogenesis and in stimulating the mitogen-activated protein kinase pathway.

    Mol Cell Endocrinol 1997, 130:119-130. OpenURL

  39. Jensen RT, Battey JF, Spindle ER, Benya RV: International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signalling, and functions in normal and disease states.

    Pharmacol Rev 2008, 60:1-42. OpenURL

  40. Ait-Mohand S, Fournier P, Dumulon-Perreault V, Kiefer GE, Jurek P, Ferreira CL, Benard F, Guerin B: Evalution of 64Cu-labeled bifunctional chelate-bombesin conjugates.

    Bioconjug Chem 2011, 22:1729-1735. OpenURL

  41. Santos-Cuevas CL, Ferro-Flores G, Rojas-Calderon EL, Garcia-Becerra R, Ordaz-Rosado D, Arteaga de Murphy C, Pedraza-Lopez M: 99mTc-N2S2-Tat (49-57)-bombesin internalized in nuclei of prostate and breast caner cells: kinetics, dosimetry and effect on cellular proliferation.

    Nucl Med Commun 2011, 32:303-313. OpenURL

  42. Hood JD, Cheresh DA: Role of integrins in cell invasion and migration.

    Nature Reviews Cancer 2002, 2:91-100. OpenURL

  43. Xiong JP, Stehle T, Zhang R, Joachimiak A, Frech M, Goodman SL, Arnaout MA: Crystal structure of the extracellular segment of integrin ανβ3 in complex with an Arg-Gly-Asp ligand.

    Science 2002, 296:151-155. OpenURL

  44. Haubner R, Wester HJ, Reuning U, Senekowitsch-Schmidtke R, Diefenbach B, Kessler H, Stöcklin G, Schwaiger M: Radiolabeled αvβ3 integrin antagonists: a new class of tracers for tumor targeting.

    J Nucl Med 1999, 40:1061-1071. OpenURL

  45. Haubner R, Wester HJ, Weber WA, Mang C, Ziegler SI, Goodman SL, Senekowitsch-Schmidtke R, Kessler H, Schwaiger M: Noninvasive imaging of αvβ3 integrin expression using 18F-labeled RGD-containing glycopeptide and positron emission tomography.

    Cancer Res 2001, 61:1781-1785. OpenURL

  46. Haubner R: αvβ3-Integrin imaging: a new approach to characterise angiogenesis?

    Eur J Nucl Med Mol Imaging 2006, 33:54-63. OpenURL

  47. Bodei L, Ferone D, Grana CM, Cremonesi M, Signore A, Dierckx RA, Paganelli G: Peptide receptor therapies in neuroendocrine tumors.

    J Endocrinol Invest 2009, 32:360-369. OpenURL

  48. Dimitrakopoulou-Strauss A, Strauss LG, Burger C: Quantitative PET studies in pretreated melanoma patients: a comparison of 6-(18F)-fluoro-L-dopa with 18F-FDG and 15O-water using compartment and noncompartment analysis.

    J Nucl Med 2001, 42:248-256. OpenURL

  49. Baish JW, Jain RK: Fractals and cancer.

    Cancer Res 2001, 61:8347-8350. OpenURL

  50. Dimitrakopoulou-Strauss A, Georgoulias V, Eisenhut M, Herth F, Koukouraki S, Mäcke HR, Haberkorn U, Strauss LG: Quantitative assessment of SSTR2 expression in patients with non-small cell lung cancer using 68Ga-DOTATOC PET and comparison with 18F-FDG PET.

    Eur J Nucl Med Mol Imaging 2006, 33:823-830. OpenURL