Complexes of technetium-99m with tetrapeptides containing one alanyl and three glycyl moieties

Recently, we have shown that tetrapeptides can be efficiently labelled with technetium-99m by direct labelling at alkaline pH. Tetrapeptides can be considered derivatives of mercaptoacetyltriglycine (MAG3) in which the mercaptoacetyl moiety is replaced by an amino acid residue. In view of the interesting biological properties of some C-methyl substituted derivatives of^99mTc-MAG3, we have now synthesised and evaluated the complexes of^99mTc with tetrapeptides containing three glycyl (G) moieties and oned- orl-alanyl (A) moiety. In mice,^99mTc-l-GAGG,^99mTc-d-GGAG and^99mTc-l-GGAG showed a rapid and high renal excretion, comparable to that of^99mTc-MAG3. Renal handling was somewhat reduced for isomersd andl of^99mTc-AGGG and^99mTc-d-GAGG and markedly inferior for^99mTc-l-GGGA and^99mTc-d-GGGA. In the baboon,^99mTc-l-AGGG,^99mTc-d-AGGG and^99mTc-l-GAGG showed a comparable or even higher 1-h plasma clearance than^99mTc-MAG3.^99mTc-d-GAGG,^99mTc-l-GGAG and^99mTc-d-GGAG were characterised by a lower plasma clearance and the clearance of^99mTc-l-GGGA and^99mTc-d-GGGA was remarkably low. The three^99mTc-labelled tetrapeptides with the highest plasma clearance in a baboon were compared with^99mTc-MAG3 in a human volunteer.^99mTc-l-AGGG and^99mTc-l-GAGG had a roughly similar plasma clearance as^99mTc-MAG3. The clearance of^99mTc-d-AGGG was significantly lower and liver uptake was clearly visible with this compound. Left kidney renograms of^99mTc-l-AGGG and^99mTc-d-AGGG indicated moderate kidney accumulation. On the other hand, the renogram obtained after injection of^99mTc-l-GAGG had an excellent shape and the maximum kidney concentration was slightly higher than for^99mTc-MAG3. These results show the importance of the position of the methyl substituent on the^99mTc-tetrapeptide with respect to its biological behaviour.     

Technetium-99m tetrofosmin and technetium-99m sestamibi imaging of multiple metastases from differentiated thyroid carcinoma

A 79-year-old male with follicular thyroid carcinoma metastasizing to the lung, bone and lymph nodes was subjected to whole-body scintigraphy using technetium-99m tetrofosmin and^99mTc-sestamibi. Both agents delineated the metastatic lesions and the two image qualities were comparable. We believe that^99mTc-tetrofosmin and^99mTc-sestamibi images may be helpful in localizing metastatic foci and substitute for thallium-201 in the follow-up of patients with differentiated thyroid carcinoma.     

Comparison of technetium 99m-phytate and technetium 99m-sulphur colloid in primary bone tumours

Eleven patients with proven primary bone tumour (five Ewing sarcomas, six osteosarcomas) and two cases of metastatic bone involvement (primary other than bone) were investigated with^99mTc-phytate and^99mTc-sulphur colloid to compare the behaviour of the two radiopharmaceuticals at the tumour site. After intravenous administration of the respective radiopharmaceutical, imaging of the tumour site and its contralateral part was carried out at 15 min and 1 h intervals. The data were stored in our computer. Bone scanning was also carried out in all patients.^99mTc-phytate uptake was observed at the tumour site in ten cases. The^99mTc-sulphur colloid study revealed sparse or no significant uptake in eight cases. In two patients, with osteosarcoma^99mTc-sulphur colloid investigation showed uptake at the primary tumour site. However, the distribution pattern is different from that of^99mTc-phytate. No significant uptake of either 99mTc-phytate or^99mTc-sulphur colloid was observed in the two patients with metastatic skeletal disease. It may be concluded that the unusual accumulation of^99mTc-phytate at the tumour site is not due to any generalized reticuloendothelial phenomenon and that the radiopharmaceutical itself is responsible for this.     

天冬胶作为血管栓塞剂毒性实验的初步报告

目的:从其毒性和相关特性方面研究天冬胶作为血管栓塞剂的可行性。方法:昆明小鼠腹腔注射天冬胶后观察外貌行为、食物消耗、体重情况。最后检测WBC、血小板、RBC和Hb浓度;测定血清ALT、肌酐和尿素氮浓度。病理检查心、肝、肾、脾、脑、腹膜、生精组织及腹壁肌肉。大腿肌肉注射天冬胶的小鼠1、3、7 d后各处死,取局部肌肉标本送病理检查。结果:1.仅实验组给药后第1天反应稍差及食量显著低于对照组(P<0.001)外,第2天起各组外貌行为无异常、食量无显著差异(均P>0.05)。2.各组小鼠的体重随时间而增加,除实验组2于实验1周后增长速度显著低于实验组1(P<0.02)和对照组(P<0.001)外,其他无显著差异。3.各组血WBC、血小板、RBC、Hb及血清ALT、肌酐和尿素氮浓度无显著差别。4.仅1个实验组小鼠肝脏内可见多灶性淋巴细胞和其他炎症细胞浸润区,其他组肝脏表现正常。实验组腹膜出现少许慢性炎症细胞的浸润和间皮细胞的增生。其他均无病理改变。大腿肌肉内仅见少许残留异物,无病理改变。结论:天冬胶使用安全、生物相容性较好,作为血管栓塞剂有较好的前景。     

Ferumoxides and Tc-99m sulfur colloid: Comparison of the tumor-to-liver uptake in focal nodular hyperplasia

The tumor-to-liver uptake of two reticuloendothelial agents, namely ferumoxides and technetium-99m (Tc-99m) sulfur colloid, was compared in focal nodular hyperplasia (FNH). Twelve patients with FNH who had undergone ferumoxides-enhanced MR imaging and planar Tc-99m sulfur colloid scintigraphy within 1 year were included from the study. Fourteen patients with FNH with a diameter larger than 3 cm were selected for the comparison. The tumor-to-liver ferumoxides uptake was calculated and the Tc-99m sulfur colloid uptake was assessed visually. Ferumoxides uptake was observed in all but one patient with FNH (mean tumor-to-liver ratio = .36). The six tumors showing normal (n = 5) or increased (n = 1) radiocolloid uptake when compared to the liver accumulated more ferumoxides than the eight tumors showing decreased radiocolloid uptake (P < .01). However, in some tumors, no direct relation was observed between ferumoxides and Tc-99m sulfur colloid uptake. Our observations suggest that ferumoxides uptake might not exactly mimic Tc-99m sulfur colloid uptake in FNH.     

Flow characteristics of soft-tissue vascular anomalies evaluated by direct puncture scintigraphy

Soft-tissue vascular anomalies such as haemangioma and vascular malformation are treated by surgical resection, arterial embolization or sclerotherapy. Because the effect of sclerotherapy, i.e. the percutaneous injection of sclerosing agents, depends on intralesional haemodynamics, estimation of flow characteristics of soft-tissue vascular anomalies is essential when determining appropriate patient management. However, lesions are at present divided into only two groups: high flow and low flow. We have developed a new method, direct puncture scintigraphy, to evaluate in detail the haemodynamics of vascular anomalies under conditions simulating sclerotherapy. Twenty-six soft-tissue vascular anomalies in 21 patients were studied. After 30 MBq of technetium-99m Sn colloid was injected percutaneously into the intravascular space of the lesion, dynamic imaging was performed for 5 min. A time-activity curve for the lesion was generated, with the infiltrated activity on injection subtracted. A monoexponential curve was fitted to the declining phase of the time-activity curve, and mean vascular transit time (MTT) was obtained. The lesions were classified into high-flow and low-flow lesions based on radionuclide angiography with intravenous injection of^99mTc-labelled red blood cells, and estimates of MTT in the two groups were compared. The imaging procedures were carried out with no major complications, and broad intralesional diffusion of^99mTc-Sn colloid was achieved in most lesions. The high-flow lesions (six lesions) had a short MTT, ranging from 1.6 to 3.4 s, while the low-flow lesions (20 lesions) had a longer MTT, with no overlap between the groups. MTT showed a wide range in low-flow lesions: it was less than 30 s in six lesions and more than 10 min in five other lesions. Direct puncture scintigraphy provides a quantitative indicator of the flow characteristics of soft-tissue vascular anomalies, and may aid in determining treatment strategies for patients with vascular anomalies.     

Clinical usefulness of In-111 chloride and Tc-99m Sn colloid scintigraphy in the diagnosis of intrathoracic extramedullary hematopoiesis

We report a case of intrathoracic extramedullary hematopoiesis associated with hemolytic anemia. While the paravertebral localization of the lesions demonstrated on CT and MRI was suspicious of intrathoracic extramedullary hematopoiesis, In-111 chloride and Tc-99m Sn colloid bone marrow scintigraphies showing a bone marrow element of the lesion were useful to confirm the diagnosis.     

Evaluation of the renal excretion characteristics of technetium-99m mercaptoacetylglycyl-D-alanylglycine in healthy volunteers

During a study of C-methyl derivatives of technetium-99m mercaptoacetyltriglycine (^99mTc-MAG3) it was found that the isomer of ^99mTc-mercaptoacetylgly-cyl-D-alanylglycine (^99m-TC-MAGAG-DA) is superior to ^99mTc-MAG₃ with regard to its renal excretion characteristics in both mice and the baboon. We have now compared the renal handling of ^99mTc-MAGAG-DA and ^99mTc-MAG₃ in 6 healthy volunteers in a paired study. Renograms of ^99mTc-MAGAG-DA show a shorter time to renal maximum and a lower residual renal activity at 30 min post-injection (p.i.). The urinary excretion of ^99mTc-MAGAG-DA is higher at both 30 and 60 min p.i. The plasma concentration of ^99mTc-MAGAG-DA is lower than that of ^99mTc-MAG₃ at each moment up to 60 min p.i., and the plasma clearance is accordingly higher. It is concluded that ^99mTc-MAGAG-DA is excreted more efficiently than ^99mTc-MAG₃, but the preparation of ^99mTc-MAGAG-DA requires a HPLC purification step, and this limits its practical clinical usefulness. Offprint requests to: G.M. Bormans     

CT-guided lymphoscintigraphy in patients with squamous cell carcinoma of the head and neck: a feasibility study

Accurate knowledge of lymphatic drainage facilitates planning of surgery for patients with squamous cell carcinoma of the head and neck. The aim of this study was to evaluate the feasibility of a new injection technique for lymph node detection in patients with squamous cell carcinoma of the hypopharynx and larynx, in whom simple peritumoural injection is hampered by the tumour localisation. Computed tomography (CT)-guided lymphoscintigraphy was performed in a total of 13 patients with squamous cell carcinoma of the hypopharynx and larynx who could not be injected by simple visual inspection. In a first step, contrast medium-enhanced axial 5-mm-thick CT slices of the neck were obtained. After tumour localisation on these CT images, 1–2 ml contrast medium and, in the event of appropriate distribution, subsequently 50 MBq technetium-99m colloid were injected at one to three peritumoural sites under CT guidance. Peritumoural tracer distribution was controlled by thin-slice CT. Subsequently, planar scintigrams from anterior, right and left lateral views were obtained. In all patients, peritumoural colloid application was feasible, as shown on control CT scans. Post injection, neither severe nor minor complications were noted. The patients complained of only low pain sensations with an average score of 1.8 on a pain scale from 0 to 10. Lymphatic drainage was identified in nine of the 13 patients, with a total of 14 detected lymph nodes. In six patients, ipsilateral sentinel lymph nodes were visualised; bilateral sentinel lymph nodes were identified in one patient and contralateral lymphatic drainage was observed in two patients. CT-guided lymphoscintigraphy is a feasible and minimally invasive diagnostic tool for sentinel lymph node detection in patients with squamous cell carcinoma of the hypopharynx and the larynx. In contrast to endoscopic colloid injection under general anaesthesia, this technique seems to be a well-tolerated method for lymphatic mapping prior to surgical procedures.     

Technetium-99m labeling of a molecule bearing easily reducible groups

Chemical stability of the naphthol-azo dye Evans Blue (EB) was examined in the presence of acidic stannous chloride (SnCl₂), with a view to preparing an instant cold kit. EB was found to be reactive toward this reducing agent, yielding the metal-chelating molecule 1,7-diamino-8-naphthol-2,4-disulfonic acid at high acidity and high stannous concentrations. This reduction reaction was undesirable in the cold kit preparation. The conditions were determined where reduction was inhibited, at pH = 5.0 and with a mole ratio of EB to SnCl₂ = [10:1], effecting the facile preparation of stable cold kits. Successful ^99mTc-labeling of an EB cold kit using these conditions resulted in the desired product with 98% radiochemical purity. Based on the radiolabeling efficiencies of chosen model compounds, it was rationalized that ^99mTc metal predominantly coordinated with the 1-amino-8-hydroxy groups in the EB molecule to form ^99mTc-EB.     

Uterine technetium-99m mercaptoacetyltriglycine and diethylene triamine penta-acetic acid uptake in the scintigraphic evaluation of transplanted kidneys

An anuric 35-year-old woman with a renal transplant underwent serial renal scintigraphy studies to screen the kidney function. A hypervascular pelvic mass in the region of the bladder was identified during technetium-99m mercaptoacetyltriglycine (MAG₃) and also during^99m Tc diethylene triamine penta-acetic acid (DT-PA) scintigraphy. She was in the secretory phase of the uterine cycle during the study and had no gynaecological problem to explain the radioactivity accumulation. The accumulation of ^99mTc-MAG₃ mimicking the bladder was considered as uterine activity. To our knowledge, this is the first case of uterine visualization with ^99mTc-MAG₃.     

Imaging of HER2-expressing tumours using a synthetic Affibody molecule containing the <Superscript>99m</Superscript>Tc-chelating mercaptoacetyl-glycyl-glycyl-glycyl (MAG3) sequence

Purpose Expression of human epidermal growth factor receptor type 2 (HER2) in malignant tumours possesses well-documented prognostic and predictive value. Non-invasive imaging of expression can provide valuable diagnostic information, thereby influencing patient management. Previously, we reported a phage display selection of a small (about 7 kDa) protein, the Affibody molecule Z_HER2:342, which binds HER2 with subnanomolar affinity, and demonstrated the feasibility of targeting of HER2-expressing xenografts using radioiodinated Z_HER2:342. The goal of this study was to develop a method for ^99mTc labelling of Z_HER2:342 using the MAG3 chelator, which was incorporated into Z_HER2:342 using peptide synthesis, and evaluate the targeting properties of the labelled conjugate. Methods MAG3-Z_HER2:342 was assembled using Fmoc/tBu solid phase peptide synthesis. Biochemical characterisation of the agent was performed using RP-HPLC, ESI-MS, biosensor studies and circular dichroism. A procedure for ^99mTc labelling in the presence of sodium/potassium tartrate was established. Tumour targeting was evaluated by biodistribution study and gamma camera imaging in xenograft-bearing mice. Biodistribution of ^99mTc-MAG3-Z_HER2:342 and ¹²⁵I-para-iodobenzoate -Z_HER2:342 was compared 6 h p.i. Results Synthetic MAG3-Z_HER2:342 possessed an affinity of 0.2 nM for HER2 receptors. The peptide was labelled with ^99mTc with an efficiency of about 75–80%. Labelled ^99mTc-MAG3-Z_HER2:342 retained capacity to bind specifically HER2-expressing SKOV-3 cells in vitro. ^99mTc-MAG3-Z_HER2:342 showed specific tumour targeting with a contrast similar to a radioiodinated analogue in mice bearing LS174T xenografts. Gamma camera imaging demonstrated clear and specific visualisation of HER2 expression. Conclusion Incorporation of a mercaptoacetyl-containing chelating sequence during chemical synthesis enabled site-specific ^99mTc labelling of the Z_HER2:342 Affibody molecule with preserved targeting capacity.     

Clinical significance of technetium-99m methylene diphosphonate myocardial uptake: association with carcinoma of the prostate

Benign myocardial uptake of technetium-99m labelled phosphates, not related to cardiac or metabolic disorders, has been documented except in the case of^99mTc-methylene diphosphonate (MDP). The aim of this study was to assess the frequency of myocardial uptake and its possible association with malignant tumours in general and prostatic carcinoma in particular. We reviewed bone scintigrams performed with either^99mTc-hydroxydiphosphonate (HDP) or^99mTc-MDP over a period of more than 2 years for all patients with prostatic carcinoma and a matching group of patients suffering from other malignant and non-malignant disorders. A total of 965 scintigrams of 812 patients (males=559, females=253; age range 50–91 years, average age 69.2 years) were reviewed. Increased myocardial uptake was detected in 19 scintigrams (MDP=13, HDP=6) of 18 patients (17 males, one female). Most of the male patients with increased myocardial uptake had prostatic carcinoma (13/17) and were over 80 years of age (12/17). All patients were free of any cardiac or noncardiac disorder that might account for such uptake. When scintigraphy was repeated in the same patient, the uptake of^99mTc-HDP was more diffuse and of higher grade than that of^99mTc-MDP Benign myocardial uptake of^99mTc-MDP is more common than previously thought. Although uptake of radiophosphates is attributed to asymptomatic atherosclerotic changes associated with old age, a strong association with prostatic carcinoma exists which may indicate variations in the bone: soft tissue affinity of different MDP complexes.     

Cyclotron production of (99m)Tc: experimental measurement of the (100)Mo(p,x)(99)Mo, (99m)Tc and (99g)Tc excitation functions from 8 to 18 MeV

Introduction

The cyclotron-based ¹⁰⁰Mo(p,2n)^99mTc transformation has been proposed as a viable alternative to the reactor based ²³⁵U(n,f)⁹⁹Mo→^99mTc strategy for production of ^99mTc. Despite efforts to theoretically model the amount of ground-state ^99gTc present at end of bombardment for the (p,2n) reaction, experimental validation has yet to be performed. The co-production of ^99gTc may have important implications in both the subsequent radiopharmaceutical chemistry and patient dosimetry upon injection.

Methods

To determine the extent of ^99gTc co-production, we have experimentally measured the ¹⁰⁰Mo(p,x)⁹⁹Mo, ^99mTc, and ^99gTc excitation functions in the 8–18 MeV range using a combination of natural abundance and 97.42% enriched ¹⁰⁰Mo foils along with γ-ray spectrometry and ICP-MS. Although the excitation functions for production of ⁹⁹Mo and ^99mTc have been presented previously in the literature, to the best of our knowledge, this work presents the first experimental evaluation of the ¹⁰⁰Mo(p,2n)^99gTc excitation function.

Results

From the experimental cross-section measurements, the ^99mTc production yields and ^99mTc/^99m+gTc nuclei ratio were calculated for various thick target irradiation conditions. Results suggest that TBq quantities of ^99mTc can be achieved with a ^99mTc/^99m+gTc nuclei ratio that is on par with the current ⁹⁹Mo/^99mTc generator standard eluted at a 24-h frequency.

Conclusion

These findings suggest that the cyclotron production of ^99mTc may be a feasible alternative to the current reactor-based production strategy.     

Determination of the technetium-99m mercaptoacetyltriglycine plasma clearance in children by means of a single blood sample: a multicentre study

A multicentre European study was undertaken in order to determine a reasonable algorithm allowing the determination of overall technetium-99m mercaptoacetyltriglycine clearance using a single blood sample. Employing multiple blood sample clearance as a reference method, it was shown that an acceptable estimation of the MAG3 renal clearance could be obtained using a blood sample taken at any time between 30 and 40 min after tracer injection. After correction for body surface area, comparison of clearance determined using (a) the single blood sample and (b) the multiple blood samples provided a coefficient of correlation of 0.949 and an SEE of 27 ml/min. This algorithm is valid for clearance values higher than 100 ml/min/1.73 m² and for children older than 1 year of age.     

Influence of the bifunctional chelate on the biological behavior of (99m)Tc-labeled chemotactic peptide conjugates

Conjugates of For-MLFK and For-NleLFNleYK with S-benzyl mercaptoacetyl dipeptides containing, respectively, zero, one, and two carboxyl functions in their structures were prepared and labeled with ^99mTc. In vitro binding studies using isolated human granulocytes indicated specific receptor binding of the radiolabeled conjugates. The fraction of granulocyte-associated activity was determined after incubation with total blood. Biodistribution studies of the ^99mTc-peptides in normal mice revealed a very fast blood clearance proceeding mainly via the hepatobiliary system. Urinary excretion was higher for conjugates containing carboxyl functions in their ligand structures.     

Estimation of glomerular filtration rate using 99mTc-DTPA and the gamma camera

Two methods of glomerular filtration rate estimation have been evaluated, based on the intravenous administration of ^99mTc-DTPA and the measurement of renal time activity curves by means of a computer linked gamma camera. A single 20 min plasma sample was also required. These methods were designed to minimize the component of error arising from decay statistics. One method was based on using a constant fraction of the cardiac activity in lieu of a perirenal region of interest for the background correction, the other was based on deconvolution by a constrained least squares technique. The first method, based on modifying the background correction, led to poor results (residual standard deviation 18.9 ml/min when compared with the plasma clearance method). The second method, based on constrained least squares deconvolution, worked as well as previously reported methods (residual standard deviation 14.5 ml/min) and appears suitable for clinical use.     

Synthesis and evaluation of the tc-complexes of -cysteine acetyldiglycine (a hybrid of MAG3 and -EC) and of -β-homocysteine acetyldiglycine

ABSTRACT. -Cysteine acetyldiglycine ( CAG2), a hybrid compound of EC and MAG3, and its -β-homocysteine analogue HAG2 were synthesized. After labeling with ^99mTc, ^99mTc- CAG2 and ^99mTc- HAG2 gave two peaks on high performance liquid chromatography. Urinary excretion of both isomers of ^99mTc- -CAG2 and ^99mTc- -HAG2 was slower than for the “parent” complexes ^99mTc-MAG3 or ^99mTc- EC. Isomer B of ^99mTc- -CAG2 showed pronounced kidney retention in mice (57% of ID in kidneys at 30 min postinjection), but further evaluation in baboon did not reproduce this phenomenon.     

Development and preclinical characterisation of <Superscript>99m</Superscript>Tc-labelled Affibody molecules with reduced renal uptake

Purpose  Affibody molecules are low molecular weight proteins (7 kDa), which can be selected to bind to tumour-associated target proteins with subnanomolar affinity. Because of rapid tumour localisation and clearance from nonspecific compartments, Affibody molecules are promising tracers for molecular imaging. Earlier, ^99mTc-labelled Affibody molecules demonstrated specific targeting of tumour xenografts. However, the biodistribution was suboptimal either because of hepatobiliary excretion or high renal uptake of the radioactivity. The goal of this study was to optimise the biodistribution of Affibody molecules by chelator engineering. Materials and methods  Anti-HER2 Z_HER2:342 Affibody molecules, carrying the mercaptoacetyl-glutamyl-seryl-glutamyl (maESE), mercaptoacetyl-glutamyl-glutamyl-seryl (maEES) and mercaptoacetyl-seryl-glutamyl-glutamyl (maSEE) chelators, were prepared by peptide synthesis and labelled with ^99mTc. The tumour-targeting capacity of these conjugates was compared with each other and with the best previously available conjugate, ^99mTc-maEEE-Z_HER2:342, in nude mice bearing SKOV-3 xenografts. The tumour-targeting capacity of the most promising conjugate, ^99mTc-maESE-Z_HER2:342, was compared with radioiodinated Z_HER2:342. Results  All novel conjugates demonstrated successful tumour targeting and a low degree of hepatobiliary excretion. The renal uptakes of serine-containing conjugates, 33 ± 5, 68 ± 21 and 71 ± 10%IA/g, for^99mTc-maESE-Z_HER2:342, ^99mTc-maEES-Z_HER2:342 and ^99mTc-maSEE-Z_HER2:342, respectively, were significantly reduced in comparison with ^99mTc-maEEE-Z_HER2:342 (102 ± 13%IA/g). For ^99mTc-maESE-Z_HER2:342, a tumour uptake of 9.6 ± 1.8%IA/g and a tumour-to-blood ratio of 58 ± 6 were reached at 4 h p.i. Conclusions  A combination of serine and glutamic acid residues in the chelator sequence confers increased renal excretion and relatively low renal uptake of ^99mTc-labelled Affibody molecules. In combination with preserved targeting capacity, this improved imaging of targets in abdominal area.     

<Superscript>99m</Superscript>Tc-labelled HYNIC-minigastrin with reduced kidney uptake for targeting of CCK-2 receptor-positive tumours

Purpose Different attempts have been made to develop a suitable radioligand for targeting CCK-2 receptors in vivo, for staging of medullary thyroid carcinoma (MTC) and other receptor-expressing tumours. After initial successful clinical studies with [DTPA⁰,DGlu¹]minigastrin (DTPA-MG0) radiolabelled with ¹¹¹In and ⁹⁰Y, our group developed a ^99mTc-labelled radioligand, based on HYNIC-MG0. A major drawback observed with these derivatives is their high uptake by the kidneys. In this study we describe the preclinical evaluation of the optimised shortened peptide analogue, [HYNIC⁰,DGlu¹,desGlu^2–6]minigastrin (HYNIC-MG11). Methods ^99mTc labelling of HYNIC-MG11 was performed using tricine and EDDA as coligands. Stability experiments were carried out by reversed phase HPLC analysis in PBS, PBS/cysteine and plasma as well as rat liver and kidney homogenates. Receptor binding and cell uptake experiments were performed using AR4-2J rat pancreatic tumour cells. Animal biodistribution was studied in AR4-2J tumour-bearing nude mice. Results Radiolabelling was performed at high specific activities and radiochemical purity was >90%. ^99mTc-EDDA-HYNIC-MG11 showed high affinity for the CCK-2 receptor and cell internalisation comparable to that of ^99mTc-EDDA-HYNIC-MG0. Despite high stability in solution, a low metabolic stability in rat tissue homogenates was found. In a nude mouse tumour model, very low unspecific retention in most organs, rapid renal excretion with reduced renal retention and high tumour uptake were observed. Conclusion ^99mTc-EDDA-HYNIC-MG11 shows advantages over ^99mTc-EDDA-HYNIC-MG0 in terms of lower kidney retention with unchanged uptake in tumours and CCK-2 receptor-positive tissue. However, the lower metabolic stability and impurities formed in the labelling process still leave room for further improvement. Parts of this study were presented at the Annual Congress of the European Association of Nuclear Medicine, Istanbul, Turkey, October 2005 and at the 7th International Symposium on Technetium in Chemistry and Nuclear Medicine, Bressanone, Italy, September 2006.