Iodine-123-Vascular Endothelial Growth Factor-165 (^Sup 123^I- VEGF^Sub 165^) Biodistribution, Safety and Radiation Dosimetry in Patients With Pancreatic Carcinoma
Aim. Imaging with radiolabelled vascular endothelial growth factor (VEGF) has been developed for the localisation and diagnosis of a variety of human solid tumors including gastrointestinal tumors.
Methods. In this study we investigated the biodistribution, safety and absorbed dose of iodine-123 radiolabelled VEGF^sub 165^ (^sup 123^I-VEGF^sub 165^) in 9 patients with pancreatic carcinoma. Following intravenous administration of ^sup 123^I-VEGF^sub 165^ (18917 MBq;
Results. The highest absorbed organ doses were found to be thyroid (0.0580.004 mGy/MBq), spleen (0.046 0.017 mGy/MBq), urinary bladder (0.04+0.02 mGy/MBq), lungs (0.034+0.009 mGy/MBq) and kidneys (0.0330.005 mGy/MBq). The effective dose was estimated to be 0.0170.002 mSv/MBq. A majority of primary pancreatic tumors and their metastases were visualized by ^sup 123^I-VEGF^sub 165^ scan.
Conclusion. In vitro binding results confirmed specific binding of ^sup 123^I-VEGF^sub 165^ to pancreatic tumor cells and tissues. ^sup 123^I-VEGF^sub 165^ shows favorable dosimetry and is a safe radiopharmaceutical that may be of potential value for the imaging of VEGF receptor status in vivo.
KEY WORDS: VEGF * Pancreatic neoplasms * Biodistribution * Scintigraphy * Receptors.
Pancreatic cancer has a poor prognosis, and the best chance for survival is to diagnose the tumor at an early stage. However, pancreatic cancers are difficult to diagnose, especially in their early stage.1, 2 Conventional radiological techniques such as computed tomography (CT) and magnetic resonance tomography (MRT) are well established tools for the identification of pancreatic cancer. However, these techniques also have limitations for the differentiation of benign from malignant disease.3 In addition, a major drawback of CT and MRT is that only suspected specific anatomic sites such as the abdomen or chest are usually imaged. Therefore, considerable efforts have been made to develop additional methods for whole-body imaging.
The observation that vascular endothelial growth factor-165 (VEGF^sub 165^) receptors are over-expressed in various human tumor cells 4, 5 and in vascular endothelial cells of different malignant tumors 6-8 has led to the development of new localisation techniques. VEGF^sub 165^ is a 38-kDa dimeric glycoprotein which plays an important role in the process of tumor angiogenesis.9 The actions of VEGF are mediated by specific cell surface membrane receptors.10 VEGF^sub 165^ binds with high affinity to 2 receptors, namely, VEGF receptor (VEGFR) -1 (Flt-1) and VEGFR-2 (KOR).11, 12 Recently, we were able to demonstrate that various tumor cells and tumor tissues express significantly higher amounts of VEGF receptors as compared to adjacent normal tissues or peripheral blood cells.13 The over-expression of specific binding sites for VEGF provided the rationale for the clinical use of radiolabelled VEGF for imaging gastrointestinal tumors.14
Recent studies have shown that over-expression of VEGF receptors is also observed in human pancreatic cancer 15 and VEGF expression is associated with a poor prognosis in human pancreatic cancer and is an independent prognostic marker for cancer recurrence.16 In a previous study of 18 patients,14 a variety of gastrointestinal tumors and metastases were visualized by ^sup 123^I-VEGF^sub 165^ scan. ^sup 123^I-VEGF^sub 165^ receptor scintigraphy may be useful for visualisation of tumor angiogenesis.14 In this work we present our data on the whole-body biodistribution, safety and radiation absorbed dose estimated in humans as well as in vitro binding results.
Materials and methods
Radiolabelling of VEGF
Recombinant human VEGF^sub 165^ (PromoCell GmbH, Heidelberg, Germany) was labelled with iodine-123 by electrophilic radioiodination using Chloramine T as described previously. 13, 14 Briefly, 10 g (0.26 nmol) of ThVEGF^sub 165^ were labelled with about 30 mCi ^sup 123^I-Na (Research Center Karlsruhe, Germany) and 20 g Chloramine T in a 150 l reaction volume. After 3 min the reactions were stopped by addition of 4 l sodium metabisulphite (Na^sub 2^S^sub 2^O^sub 5^, 50 nmol), the reaction mixture was diluted with phosphate-buffered saline (PBS) containing 0.1% human serum albumin (HSA) and applied to a size-exclusion chromatography column (Sephadex G-25 M). The first ^sup 123^I-peak eluting from the column was collected and filtered using a steril membrane (Millex GV 0.2 m). ^sup 123^I-VEGF^sub 165^ was routinely analyzed by paper- electrophoresis on Whatman Nr. 3 MM in 0.1 M barbital buffer (pH=8.6) using a field of 300 V for 10 min and by trichloroacetic acid (TCA) precipitation.
The protocol for administration of ^sup 123^I-VEGF^sub 165^ to patients was approved by the Ethical Committee of the Medical Faculty of the University of Vienna. The study was in accordance with the Declaration of Helsinki. All patients gave written informed consent to participate in the study.
Nine patients (4 female, 5 male; mean age 6211, range 46-81 years) with biopsy-proven pancreatic adenocarcinoma were referred to our department. In all patients, diagnosis and stage of disease were established according to WHO criteria. The location and size of primary tumors and/or spread of metastases were investigated by conventional CT, MRT, endoscopy or by surgery. None of the patients had signs of clinically apparent inflammation or infection at the time of the study.
All 9 patients had primary pancreatic adenocarcinoma. Six patients (60%) had liver metastases, 4 (40%) had lymph node metastases and 3 (30%) had lung metastases.
At the time of scintigraphic evaluation, 8 patients had not previously undergone radiotherapy or chemotherapy; 1 patient had stopped receiving chemotherapy at least 3 weeks before scintigraphic evaluation.
Planar acquisitions of whole-body transmission and emission scans were performed using a double-headed and a large feld of view camera (Millenium VG with Hawkeye, GE Medical Systems, Milwaukee, WI, USA) employing medium-energy high-resolution (MEHR) collimators. A 15% energy window was symmetrically centred at 159 keV.
For each patient a whole-body transmission scan was acquired (scan speed 10 cm/min, matrix 2561 024 pixels) prior to injection of radioligand by placing a flood source containing approximately 370 MBq ^sup 123^I on the posterior γ camera head and recording counts only from the anterior head.
^sup 123^I-VEGF^sub 165^ was administered as a single intravenous bolus injection over 3 min. The administered activity was 18917 MBq corresponding to ≤130 pmole (≤5 g) of VEGF^sub 165^ administered per patient. In order to determine hemodynamic effects of VEGF, blood pressure and heart rate were monitored during tracer application and scintigraphy. The patients received 400 mg sodium perchlorate three times daily over 3 clays for thyroid blockade.
A 30-min dynamic image was recorded starting at the time of injection (matrix 128128 pixels). Serial whole-body images (10 cm/ min; matrix 2561 024 pixels) were obtained 1, 2, 18 as well as 24 h postinjection (PI). Whole-body emission scans were performed simultaneously in anterior and posterior views. To verify that the activity localisation corresponded to the tumor lesions documented by CT scans, SPET studies in combination with CT were obtained 1.5 h PI (60 projections over a 360 rotation, 40 s per step and a 6464 pixel matrix). Planar images were acquired 40 min PI including anterior and posterior views of abdomen and thorax (matrix 256256 pixels; 800 kcts preset). Additional lateral or oblique views of above regions or other regions were obtained when necessary.
To determine the biological clearance of ^sup 123^I-VEGF^sub 165^, blood samples were collected before and 1, 3, 5, 8, 15, 30 min and 1, 2, 18 and 24 h after injection. All urine produced up to 24 h PI was obtained for the following intervals: 0-2, 2-8, 8-16 and 16- 24 h.
Radioactivity in plasma and urine was monitored in a γ counter. The counting efficiency of the system was determined by counting a calibrated source of ^sup 123^I with similar geometry to that of samples. Radioactivity measurements were corrected for physical decay of ^sup 123^I and expressed as percent of injected activity (% IA). Radioactivity in the urine was used to obtain the cumulative % IA.
In vitro binding studies
Human pancreatic adenocarcinoma cell lines (BxPC-3, PANC-I) were obtained from the American Type Culture Collection (Rockville, MD) and cultured as previously described.17 Cell lines were cultured in RPMI 1640 medium (Seromed, Berlin, Germany) supplemented with 10% fetal calf serum, 4 mmol/L L-glutamine and antibiotics. Cells were fed 2-4 times per week. Cells were gently harvested with a solution of 0.05% trypsin and 0.02% eth\ylenediaminetetraacetic acid (GIBCO Laboratories, Grand Island, NY). Before being used in binding experiments, cells were washed twice in assay buffer containing 50 mM Tris HCl, 5 mM MgCl^sub 2^, 1 mM CaCl^sub 2^ and 0.1 M NaCl, pH 7.5, and about 310^sup 7^ cells were applied in one series of experiments.
Tissue samples of primary pancreatic tumor tissues were derived from patients undergoing surgery after written informed consent was obtained. Tissue samples (3 differentiated adenocarcinomas and 3 undifferentiated adenocarcinomas) were obtained during surgery and immediately placed into liquid nitrogen. Tissue was stored at -70 C until use. Diagnoses were established by histological examination and by immunohistochemistry according to WHO criteria. Tissue cell membrane fractions were prepared according to established methods.1:5 Briefly, tissues were put into 50 mM Tris HCl buffer, pH 7.5 and cut into pieces, and then homogenized by means of ultraturrax and ultrasound. The homogenate was centrifuged at 5 000 g for 10 min at 4 C, washed and resuspended in assay buffer containing 50 mM Tris HCl, 5 mM MgCl^sub 2^, 1 mM CaCl^sub 2^ and 0.1 M NaCl, pH 7.5.
Binding studies were performed with pancreatic tumor cell lines BxCP-3, I3ANC-I and primary tumor cell membranes. Assays were undertaken as reported previously.13 Briefly, in competition experiments, the cells or the membrane fractions were incubated at 4C for 60 min with 0.02 nM labelled ligand in the absence (total binding) and the presence of increasing concentrations (0.001-2 nM) unlabellecl ligancl (unspecific binding). In saturation studies, the cells or membrane fractions were incubated with increasing concentrations of ^sup 123^I-VEGF^sub 165^ (0.001-0.05 nM) in the absence (total binding) or in the presence (unspecific binding) of unlabelled VEGF^sub 165^ (2 nM). After incubation, the reaction mixture was diluted 1:10 with assay buffer (4 C) and rapidly centrifuged (5 000 g, 10 min, 4 C) to separate membrane-bound from free ligand. The resulting pellet was washed twice with assay buffer and its radioactivity was counted in a γ counter for 2 min. Specific binding was determined as the difference between total and non-specific binding. Binding data were analyzed according to Scatchard.18
Biodistribution of ^sup 123^I-VEGF^sub 165^ was quantified by serially conjugate images of the whole-body scans after intravenous injection. The geometric mean (square root of the anterior and posterior counts) of the scanned counts was used in the analysis. The regions of interest (ROIs) over the total body and organs were drawn on the earliest images and placed abutting each other. Shapes and sizes of ROIs were kept constant over all subsequent images. The same set of ROIs was placed on anterior and posterior images after mirroring of posterior images about their long axis. The background correction was performed by using a ROI over the shoulder. In the images some overlap of activity in different organs occurred, for instance, between activity in the right kidney and the liver. Correction for this overlap was done by setting the activity in the right kidney equal to that in the left, unless the apparent activity in the right kidney was less than that in the left kidney. The liver activity, determined in a region that excluded the overlap with the right kidney, was augmented by the difference between right and left kidney, but only if the difference was positive. For attenuation correction, ROIs were placed over various organs and an additional ROI was drawn over an off-body region on the transmission images. A transmission factor reflecting the fraction of counts passing through the organ was calculated for each subject by determining the counts/pixel for each organ ROI divided by the counts/pixel for an unattenuated off-body region. Attenuation correction of the conjugate emission images was performed by dividing the geometric mean of the posterior and anterior counts in each ROI by an attenuation factor equal to the square root of the transmission factor.
For each ROI, i.e., each organ, the geometric mean of total anterior and posterior counts was calculated. The total body geometric mean activity calculated on the 1st image (l h PI) was taken as total injected activity, considering that no urine was excreted prior to the 1st whole-body scan. The activity in total body and different organs was expressed as the percentage of the injected activity (% IA) calculated by the following equation:
[(geometric mean counts in organ or total body)/(geometric mean counts in first total body)]100%.
For each patient, time-activity curves were generated for the defined organs. For the calculation of the residence time, mono- or bi-exponential decay was fitted to the time-activity curve and the area under the curve was used for the calculation in the MIRDOSE. Target organ absorbed radiation doses and effective dose (ED) calculations were calculated by applying the MIRD schema using the MIRDOSE 3.0 program (Oak Ridge National Laboratories, Oak Ridge, TN, USA).19 Obtained individual residence times were used in the dosimetiy calculations.
Values are expressed as meanSD. For statistical analyses, the χ^sup 2^ test was used to compare sites detection by 2 techniques.
Radiochemicalpurity and bioactivity of ^sup 123^I-VEGF^sub 165^ ^sup 123^I-VEGF^sub 165^ was obtained in a radiochemical yield of about 25%, in a specific activity of about 1.1 mCi/g and in a radiochemical purity of more than 97%. The biological activity of unlabelled and labelled VEGF^sub 165^ were identical as assessed by ^sup 3^H-thymicline uptake assay on human umbilical vein enclothelial cells (HUVECs).
Paper-electrophoresis and TCA precipitation analysis of the plasma samples 30 min after ^sup 123^I-VEGF^sub 165^ administration showed that over 86% (n=4) of the activity was present as unchanged ^sup 123^I-VEGF^sub 165^.
Safety of ^sup 123^I-VEGF^sub 165^
After intravenous injection of ^sup 123^I-VEGF^sub 165^, patients showed no clinical adverse reaction, and no side effects were noted with the exception of a transient and non-significant decrease of both systolic and diastolic blood pressure during the initial minutes after ^sup 123^I-VEGF^sub 165^ application. Mean blood pressure l min after ^sup 123^I-VEGF^sub 165^ injection decreased by 5-10% (systolic blood pressure: before 133 versus 119 mmHg after injection; diastolic blood pressure before 75 versus 69 mmHg after injection) and reached baseline values within 5 min after injection. No change in heart rate was observed after intravenous injection of ^sup 123^I-VEGF^sub 165^.
Whole body biodistribution of ^sup 123^I-VEGF^sub 165^
Representative time-activity curves for blood and various organs are shown in Figures IA and IB, respectively. After intravenous injection, ^sup 123^I-VEGF^sub 165^ was rapidly cleared from the circulation, radioactivity in the blood rapidly decreased to less than 42% of the injected activity within the first 30 min after injection of ^sup 123^I-VEGF^sub 165^ (Figure 1A). After a rapid distribution phase, blood ^sup 123^I-VEGF^sub 165^ levels declined more slowly. The time-activity curves obtained from the lungs, liver, heart, kidneys and spleen showed a relatively slow decrease (Figure 1B). As shown in Figure 1C, the mean cumulative activity excreted in the urine was 5111% IA 2 h PI and 7810% IA 16 h PI for ^sup 123^I-VEGF^sub 165^. Approximately 866% of the injected activity was recovered in the urine by 24 h PI.
Figure 1.-Time-activity curves for ^sup 123^I-VEGF^sub 165^ for the blood (A), various organs (B: [black triangle up], liver; [black square], lungs; ∀, kidneys;), heart; [black triangle down], spleen) and excretion of ^sup 123^I-VEGF^sub 165^ in the urine (C) in 1 patient, calculated from direct measurements of counts in organ- specific ROIs or in blood or in urine. Data are expressed as percentage of administrated activity (% IA) or profile of the cumulative activity excreted in the urine.
Figure 2 shows sequential anterior images obtained with ^sup 123^I-VEGF^sub 165^ with the collimator placed over the abdomen and part of the thorax. The images obtained during the initial 15 to 30 min are shown. There is a rapid uptake of ^sup 123^I-VEGF^sub 165^ by the primary pancreatic adenocarcinoma. The accumulation of ^sup 123^I-VEGF^sub 165^ in the primary pancreatic tumor was visualized within 30 min after the injection of ^sup 123^I-VEGF^sub 165^ and was still demonstrable after at least 3 h.
Table I shows the mean residence time (T) based on the time- activity curves of ^sup 123^I-VEGF^sub 165^ and the mean radiation absorbed doses (D) in organs and tissues calculated for ^sup 123^I- VEGF^sub 165^.
The highest radiation absorbed doses were calculated for thyroid (0.0580.004 mGy/MBq), spleen (0.0460.017 mGy/MBq), urinary bladder (0.0400.020 mGy/MBq), lungs (0.0340.009 mGy/MBq), kidneys (0.0330.005 mGy/MBq) and liver (0.0190.002 mGy/MBq). The ED was estimated to be 0.0170.002 mSv/MBq.
^sup 123^I-VEGF^sub 165^ receptor imaging in pancreatic cancer
Primary pancreatic adenocarcinomas (Figure 3) and liver metastases were visualized by SPET scanning shortly (30 min) after injection of ^sup 123^I-VEGF^sub 165^ and were still visible at 3 h after application. For liver and lung metastases an enhanced tracer uptake was observed in some of the lesions whereas others showed a heterogenous accumulation of the tracer compared to normal liver or lung tissue. The overall sensitivity of ^sup 123^I-VEGF^sub 165^ receptor scintigraphy for detecting primary pancreatic tumors and their metastases was 64% (14 of 22 lesions). ^sup 123^I-VEGF^sub 165^ receptor scintigraphy visualized primary pancreatic adenocarcinomas in 7 of 9 patients (sensitivity, 78%). Lymph node metastases were seen in 3 of 4 patients (75%), and liver metastases in 3 of 6 patients (50%). \Lung metastases were detected only in 1 of 3 patients (33%). For metastases, tumor size measured between 2.1 and 3.6 cm at ^sup 123^I-VEGF^sub 165^ positive sites and between 0.7 and 2.5 cm at ^sup 123^I-VEGF^sub 165^ negative sites. In 1 patient with primary pancreatic cancer, CT showed a large primary lesion in the pancreas, while ^sup 123^I-VEGF^sub 165^ receptor scintigraphy indicated the presence of a ringshaped tracer accumulation around the lesion (Figure 4), histological examination revealed the presence of central necrosis of the primary tumor after surgery. Furthermore, ^sup 123^I-VEGF^sub 165^ scan visualized an abdominal lymph node metastasis formation which was missed by CT.
Figure 2.-Sequential anterior images obtained with ^sup 123^I- VEGF^sub 165^ with the collimator placed over the abdomen and part of the thorax. The images obtained during the initial 15 to 30 min are shown. There is a rapid uptake of ^sup 123^I-VEGF^sub 165^ by the primary pancreatic adenocarcinoma ([arrow up]).
TABLE I.-Residence times and absorbed doses (D) of organs and total body for ^sup 123^I-VEGF^sub 165^ (n=5).
The uptake ratios between pancreatic primary tumor and background ranged from 1.3 to 2.7. The sensitivity of ^sup 123^I-VEGF^sub 165^ receptor scintigraphy varied from 75% for lymph node lesions to 33% for lung metastases. False negative ^sup 123^I-VEGF^sub 165^ receptor scan results of primary lesions were obtained in 2 patients with undifferentiated adenocarcinoma, 1 of them received the last cycle of chemotherapy (docetaxel and gemcitabine) 3 weeks ago.
In vitro binding Of ^sup 123^I-VEGF^sub 165^ to pancreatic tumor cell lines and primary pancreatic adenocarcinomas
Primary pancreatic adenocarcinomas and pancreatic tumor cell lines were analyzed for the expression of specific VEGF binding sites. As shown in Table II, ^sup 123^I-VEGF^sub 165^ bound specifically to PANC-I (B^sub max^, 11.22.8 fmol/10^sup 7^ cells K^sub d^, 11020 pM), BxPC-3 (B^sub max^, 35.06.0 fmol/10^sup 7^ cells; K^sub d^,, 15024 pM), and 3 differentiated adenocarcinoma tissues (B^sub max^, 15.65.2 fmol/10^sup 7^ cells; K^sub d^, 14318 pM) with one class of high affinity receptors. The binding of ^sup 123^I-VEGF^sub 165^ to PANC-I (IC^sub 50^,14030 pM) and BxPC-3 (IC^sub 50^,12025 pM) as well as differentiated adenocarcinomas (IC^sub 50^, 6410 pM) was displaced by unlabelled VEGF^sub 165^. No remarkable specific binding sites were detected in undifferentiated adenocarcinoma samples.
Recent studies have observed that various tumor cells including pancreatic cancer cells and endothelial cells of proliferating tumors over-express receptors for VEGF^sub 165^.4-8′ 15,2() In our previous studies we have shown that significantly higher amounts of VEGF receptors were fount! in various human tumor cells and tumor tissues as compared to adjacent normal tissues or peripheral blood cells. 1^ These observations led us to develop a receptor scintigraphic technique by using ^sup 123^I-VEGF^sub 165^ as radioligancl.1”
Figure 3.-Imaging of a primary pancreatic adenocarcinoma by means of ^sup 123^I-VHGF^sub 165^ receptor scintigraphy. IV) The pancreatic adcnocarcinoma in the corresponding transverse slice of conventional (T scanning. B) A transverse slice of the Sl1IiT study performed 1.5 h PI.
Figure 4.-Visualization ol’a primary pancreatic adcnocarcinoma with central necrosis by scanning with ^sup 123^I-VEGF^sub 165^ transverse slice of CT scanning. B) The corresponding transverse slice of the SPIiT study. C) The image fusion perlormed 1.5 h Pl showing a ring-shaped tracer accumulation around the lesion.
TABU; U.-Minding (^sup 123^I-VEGF^sub 165^ Io pancrcalic lumorcell lines and [Mncrealic cancer tissues (n=3).
In the present study, no severe side effects were observed by using ‘^sup 123^I-VEGF^sub 165^ although a transient and non- significant decrease of blood pressure during the initial minutes after ^sup 123^I-VEGF^sub 165^ application. The biological activities of unlabelecl and ^sup 123^I-labellecl VEGF^sub 165^, as assessed by thymidine-uptake were identical.
So far, no data are available for the biodistribution and in vivo binding behavior of VEGF^sub 165^. We have demonstrated for the first time the biodistribution and radiation dosimetry of intraveneously injected ^sup 123^IVEGF^sub 165^ in human organs and tissues. The observation that the high absorbed radiation doses in humans were delivered to the spleen, lungs and liver, indicates that these are the main ^sup 123^I-VEGF^sub 165^ retention human tissues. Radiolabelled VEGF^sub 165^ was relatively rapidly cleared from the circulation through the kidneys and urinary system.
The biodistribution of ^sup 123^I-rh-annexin V 21 and salmon calcitonin 22 have previously been described in human 21,22 and rats.21 For example, in rats,21 the iodine-123 radiolabelled recombinant human annexin V exhibited preferential accumulation in liver, kidney, stomach and lung tissue. The clearance was predominantly urinary. In humans, ^sup 123^I-rh-annexin V accumulated primarily in the thyroid, the kidneys, the blader, the heart wall, the liver and bone surfaces.21 The visualization of the thyroid and stomach on delayed images could be explained by progressive ^sup 123^I-rh-annexin V deiodination with the production of free iodine. Similarly, Blower etal.22 found that the radioactivity close was highest in the thyroid presumably because of uptake of free iodide released from the peptide. Of the remaining organs the liver, bladder wall and kidneys received a significant dose. In our study we have shown that the radiation absorbed dose was highest in thyroid, followed by spleen, bladder, lungs, kidneys, liver and heart wall after administration of ^sup 123^I-VEGF^sub 165^. It is of interest that the gallbladder was not visualized with ^sup 123^I-VEGF^sub 165^ in any of the patients, which may suggest negligible biliary elimination. No substantial uptake by normal gastrointestinal tissue was noted. This unique VEGF^sub 165^ biodistribution is an apparent advantage for the imaging of gastrointestinal tumors. The absence of uptake in normal bone marrow facilitates the evaluation of spine and limbs as compared with other radiolabelled agents showing bone marrow uptake as part of their physiological distribution, e.g. gallium-67.
The molecular basis of interaction of VEGF with tumors is not completely understood. A number of recent studies suggest that VEGF binds to its target cells by cell surface membrane receptors. An over-expression of receptors for VEGF^sub 165^ on the tumor cells and tumor vascular endothelial cells have been demonstrated.4-8, 15,20 Using a direct receptor binding assay, a class of saturable VEGF^sub 165^ receptors has been identified on pancreatic tumor cell lines BxCP-3, PANC-I, and differentiated human pancreatic adenocarcinomas, but not on undifferentiated adenocarcinomas. The results of this study may suggest that highly differentiated tumor expresses more VEGF^sub 165^ receptors than undifferentiated ones, while undifferentiated tumors tend to lose the ability to express receptors for VEGF^sub 165^. Human cancers are known to be highly heterogeneous, even within a single tumor, because of their nature of increased genetic instability and resulting heterogeneous genetic changes within one individual.^ Recently, Itakura etal^ have also found that various human pancreatic cancer cells express VEGFR1 and VEGFR-2. Based on the specific biodistribution of ^sup 123^I- VEGF^sub 165^ and its high affinity for tumor cells. It is to speculate that positive in vivo images obtained after injection ^sup 123^I-VEGF^sub 165^ is most likely due to the interaction between VEGF^sub 165^ and its receptors.
Our in vitro results show that human pancreatic adenocarcinoma expresses VEGF receptors for ^sup 123^IVEGF^sub 165^. Correspondingly, our in vivo study demonstrates that human pancreatic cancers and their metastases can be revealed by ^sup 123^I-VEGF^sub 165^ receptor scintigraphy. Overall, ^sup 123^I- VEGF^sub 165^ has a favorable dosimetry and is a safe radiopharmaceutical that may be of potential value for the imaging of VEGF receptor status in -vivo.
Acknowledgements.-This study was supported in part by Pfeiffer Scholarship of Austrian Society of Nuclear Medicine 2003 and the “Jubilaeumsfonds” of the Austrian National Bank (Project No. 8320).
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S. LI1, M. PECK-RADOSAVLJEVIC 2, O. KIENAST 1 J. PREITFELLNER 1, E. HAVLIK 3, W. SCHIMA 4, T. TRAUB-WEIDINGER 1, S. GRAF 5, M. BEHESHTI 1, M. SCHMID 2, P. ANGELBERGER 6, R. DUDCZAK 1
1 Department of Nuclear Medicine Medical University of Vienna, Vienna, Austria
2 Department of Internal Medicine IV Division of Gastroenterology and Hepatology Medical University of Vienna, Vienna, Austria
3 Institute for Biomedical Technology and Physik Medical University of Vienna, Vienna, Austria
4 Department of Radiology, Medical University of Vienna, Vienna, Austria
5 Department of Internal Medicine II, Division of Cardiology Medical University of Vienna, Vienna, Austria,
6 Austrian Research Center, Seibersdorf, Austria
Address reprint requests to: S. Li, MD, Department of Nuclear Medicine, University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. E-mail: firstname.lastname@example.org
Copyright Edizioni Minerva Medica Sep 2004