- Original research
- Open Access
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
© Cheng et al; licensee Springer. 2011
Received: 28 July 2011
Accepted: 13 December 2011
Published: 13 December 2011
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 K 1 - k 4 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, K 1, 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, K 1, and RBP for 68Ga-BZH3 were generally higher than the corresponding values for the 68Ga-RGD tetramer, whereas k 3 was slightly higher for 68Ga-RGD tetramer.
As a parameter that reflects receptor binding, the increase of K 1 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.
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 . 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 . 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 . 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 . 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.  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-t Bu-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 . 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).
Synthesis of BZH3
BZH3 was prepared according to the method described by Schuhmacher et al. . 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.
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.
Quantitative PET parameters for the both tracers' kinetics of 68Ga-BZH3 and 68Ga-RGD4
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, K 1 and k 2, the parameters for phosphorylation and dephosphorylation of intracellular tracer, k 3 and k 4, 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 = (K 1 × k 3)/(k 2 + k 3). Compared to the standard iterative method, the machine learning method has the advantage of a fast convergence and avoidance of over fitting . The model parameters were accepted when K 1 - k 4 was less than 1 and VB exceeded 0. The unit for the rate constants K 1 to k 4 was 1/min. In the case of 68Ga-BZH3 and 68Ga-RGD4, K 1 is associated with receptor binding, k 2 with displacement from the receptor, k 3 with cellular internalisation, and k 4 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 .
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 . 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 . 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.
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.
The value of statistically significant level P using the Wilcoxon rank-sum test
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) . Adams et al. reported the comparison of different tracers in detecting malignant NETs and revealed that increased FDG uptake was associated with malignancy . 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 . We had reported on 68Ga-DOTATOC studies in patients with NETs and an enhanced uptake in metastases of NETs . Furthermore, we have shown that the global DOTATOC uptake in NETs is mainly dependent on k 1 (receptor binding) and VB (fractional blood volume) and less on the k 3 (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 .
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 . 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 . We reported on an enhanced 68Ga-BZH3 uptake in a subgroup of patients with gastrointestinal stromal tumors , and quantitative 68Ga-BZH3 studies were helpful in patients with recurrent gliomas for tumor grading and the differentiation between high- and low-grade tumors . 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 . Concerning the 68Ga-BZH3 kinetics, k 1 is a parameter that reflects the receptor binding and k 3 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 . 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 k 1 for 68Ga-BZH3 (median, 0.3506) as compared with 68Ga-RGD4 (median 0.2728), and comparable k 3 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 . 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 . In particular, there were significant differences between VB, K 1, k 4, 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 . 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 . 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.
- 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.View ArticleGoogle Scholar
- Strauss LG, Conti PS: The application of PET in clinical oncology. J Nucl Med 1991, 32: 623–648.PubMedGoogle Scholar
- 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.PubMed CentralPubMedView ArticleGoogle Scholar
- Ambrosini V, Tomassetti P, Franchi R, Fanti S: Imaging of NETs with PET radiopharmaceuticals. Q J Nucl Med Mol Imaging 2010, 54: 16–23.PubMedGoogle Scholar
- 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.Google Scholar
- 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.PubMedView ArticleGoogle Scholar
- Breeman WAP, de Jong M, Erion JL, Bugaj JE, Srinivasan A, Bernard BF, Kwekkeboom DJ, Visser TJ, Krenning EP: Preclinical comparison of 111 In labeled DTPA- or DOTA-bombesin analogs for receptor targeted scintigraphy and radionuclide therapy. J Nucl Med 2002, 43: 1650–1656.PubMedGoogle Scholar
- 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.PubMedGoogle Scholar
- 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.PubMedGoogle Scholar
- Smith CJ, Sieckman GL, Owen NK, Hayes DL, Mazuru DG, Kannan R, Volkert WA, Hoffman TJ: Radiochemical investigations of gastrin-releasing peptide receptor-specific [ 99m Tc(X)(CO) 3 -Dipr-Ser-Ser-Ser-Gln-Trp-Ala-Val-Gly-His-Leu-Met(NH 2 )] in PC-3, tumor-bearing, rodent models: syntheses, radiolabeling, and in vitro / in vivo studies where Dpr = 2,3-diaminopropionic acid and × = H 2 O or P(CH 2 OH) 3 . Cancer Res 2003, 63: 4082–4088.PubMedGoogle Scholar
- Nock B, Nikolopoulou A, Chiotellis E, Loudos G, Maintas D, Reubi JC, Maina T: 99m Tc-Demobesin 1, a novel potent bombesin analogue for GRP receptor-targeted tumor imaging. Eur J Nucl Med 2003, 30: 247–258.View ArticleGoogle Scholar
- Scopinaro F, DeVincentis G, Varvarigou AD, Laurenti C, Iori F, Remediani S, Chiarini S, Stella S: 99m Tc-Bombesin detects prostate cancer and invasion of pelvic lymph nodes. Eur J Nucl Med 2003, 30: 1378–1382.View ArticleGoogle Scholar
- Smith CJ, Sieckman GL, Owen NK, Hayes DL, Mazuru DG, Volkert WA, Hoffman TJ: Radiochemical investigations of [188 Re( H2 O)(CO )3 -diaminopropionic acid-SSS-bombesin(7–14) N H2 ]: syntheses, radiolabeling and in vitro/in vivo GRP receptor targeting studies. Anticancer Res 2003, 23: 63–70.PubMedGoogle Scholar
- Dimitrakopoulou-Strauss A, Seiz M, Tuettenberg J, Schmieder K, Eisenhut M, Haberkorn U, Strauss LG: Pharmacokinetic studies of 68 Ga-labeled bombesin ( 68 Ga-BZH3) and F-18 FDG PET in patients with recurrent gliomas and comparison to grading. Clin Nucl Med 2011, 36: 101–108.PubMedView ArticleGoogle Scholar
- Dimitrakopoulou-Strauss A, Hohenberger P, Haberkorn U, Mäcke HR, Eisenhut M, Strauss LG: 68 Ga-labeled bombesin studies in patients with gastrointestinal stromal tumors: comparison with 18 F-FDG. J Nucl Med 2007, 48: 1245–1250.PubMedView ArticleGoogle Scholar
- 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.PubMedGoogle Scholar
- 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.PubMedGoogle Scholar
- Beer AJ, Schwaiger M: Imaging of integrin ανβ3 expression. Cancer Metastasis Rev 2008, 27: 631–644.PubMedView ArticleGoogle Scholar
- Cai W, Chen X: Anti-angiogenic cancer therapy based on integrinαVβ3 antagonism. Anti Canc Agents Med Chem 2006, 6: 407–428.View ArticleGoogle Scholar
- Wellings DA, Atherton E: Standard Fmoc protocols. Methods Enzymol 1997, 289: 44–67.PubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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 68 Ga-labeled bombesin (6–14) analog. J Nucl Med 2005, 46: 691–699.PubMedGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.Google Scholar
- 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.View ArticleGoogle Scholar
- Burger C, Buck A: Requirements and implementations of a flexible kinetic modelling tool. J Nucl Med 1997, 38: 181–1823.Google Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.Google Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.Google Scholar
- Guyon I, Weston J, Barnhill S, Vapnik V: Gene selection for cancer classification using support vector machines. Mach Learn 2002, 46: 389–422.View ArticleGoogle Scholar
- 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.PubMedGoogle Scholar
- Kaltsas G, Besser M, Grossman A: The diagnosis and medical management of advanced neuroendocrine tumors. Endocr Rev 2004, 25: 458–511.PubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.View ArticleGoogle Scholar
- Koukouraki S, Strauss LG, Georgoulias V, Schuhmacher J, Haberkorn U, Karkavitsas N, Dimitrakopoulou-Strauss A: Evaluation of the pharmacokinetics of 68 Ga-DOTATOC in patients with metastatic neuroendocrine tumours scheduled for 90 Y-DOTATOC therapy. Eur J Nucl Med Mol Imaging 2006, 33: 460–466.PubMedView ArticleGoogle Scholar
- Koukouraki S, Strauss LG, Georgoulias V, Eisenhut M, Haberkorn U, Dimitrakopoulou-Strauss A: Comparison of the pharmacokinetics of 68 Ga-DOTATOC and [ 18 F]FDG in patients with metastatic neuroendocrine tumours scheduled for 90 Y-DOTATOC therapy. Eur J Nucl Med Mol Imaging 2006, 33: 1115–1122.PubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.PubMed CentralPubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- Hood JD, Cheresh DA: Role of integrins in cell invasion and migration. Nature Reviews Cancer 2002, 2: 91–100.PubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- 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.PubMedGoogle Scholar
- 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.PubMedGoogle Scholar
- Haubner R: αvβ3-Integrin imaging: a new approach to characterise angiogenesis? Eur J Nucl Med Mol Imaging 2006, 33: 54–63.PubMedView ArticleGoogle Scholar
- 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.PubMedView ArticleGoogle Scholar
- Dimitrakopoulou-Strauss A, Strauss LG, Burger C: Quantitative PET studies in pretreated melanoma patients: a comparison of 6-( 18 F)-fluoro- L -dopa with 18 F-FDG and 15 O-water using compartment and noncompartment analysis. J Nucl Med 2001, 42: 248–256.PubMedGoogle Scholar
- Baish JW, Jain RK: Fractals and cancer. Cancer Res 2001, 61: 8347–8350.Google Scholar
- 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 68 Ga-DOTATOC PET and comparison with 18 F-FDG PET. Eur J Nucl Med Mol Imaging 2006, 33: 823–830.PubMedView ArticleGoogle Scholar
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