Synthesis and biological evaluation of potent alphavbeta3-integrin receptor antagonists

INTRODUCTION: alpha(v)beta(3) Integrin is expressed in sprouting endothelial cells in growing tumors, whereas it is absent in quiescent blood vessels. In addition, various tumor cell types express alpha(v)beta(3) integrin. alpha(v)beta(3) Integrin, a transmembrane heterodimeric protein, binds to the arginine-glycine-aspartic acid (RGD) amino acid sequence of extracellular matrix proteins such as vitronectin and plays a pivotal role in invasion, proliferation and metastasis. Due to the selective expression of alpha(v)beta(3) integrin in tumors, radiolabeled RGD peptides and peptidomimetics are attractive candidates for tumor targeting. METHODS: A cyclic RGD peptide, a peptoid-peptide hybrid, an all-peptoid and a peptidomimetic compound were synthesized, conjugated with 1,4,7,10-tetraazadodecane-N,N',N',N'-tetraacetic acid (DOTA) and radiolabeled with (111)In. Their in vitro and in vivo alpha(v)beta(3)-binding characteristics were determined. RESULTS: IC(50) values were 236 nM for DOTA-E-c(RGDfK), 219 nM for DOTA-peptidomimetic, >10 mM for DOTA-all-peptoid and 9.25 mM for the peptoid-peptide hybrid DOTA-E-c(nRGDfK). (111)In-labeled compounds, except for [(111)In]DOTA-all-peptoid, showed specific uptake in human alpha(v)beta(3)-expressing tumors xenografted in athymic mice. Tumor uptake for [(111)In]DOTA-E-c(RGDfK) was 1.73+/-0.4% ID/g (2 h postinjection) and that of [(111)In]DOTA-peptidomimetic was 2.04+/-0.3% ID/g. Tumor uptake for the peptoid-peptide hybrid [(111)In]DOTA-E-c(nRGDfK) was markedly lower (0.45+/-0.07% ID/g). The all-peptoid [(111)In]DOTA-E-c(nRGnDnFnK) did not show specific uptake in tumors (0.11+/-0.04% ID/g). CONCLUSIONS: The peptidomimetic compound and the cyclic RGD peptide have a high affinity for alpha(v)beta(3) integrin, and these compounds have better tumor-targeting characteristics than the peptoid-peptide hybrid and the all-peptoid.     

99mTc/188Re-labelled lipid nanocapsules as promising radiotracers for imaging and therapy: formulation and biodistribution

Purpose This study focusses on a promising carrier system for imaging and therapeutic purposes using lipid nanocapsules. To assess their potential for clinical use, we labelled nanocapsules with ^99mTc and ¹⁸⁸Re and analysed some kinetic biodistribution parameters after intravenous injection in rats. Methods Lipophilic complexes [^99mTc/¹⁸⁸Re(S₃CPh)₂(S₂CPh)] (^99mTc/¹⁸⁸Re-SSS) were encapsulated within the nanoparticles during their manufacture with quantitative yield and satisfactory radiochemical purity. Rats were injected intravenously with 3.7 MBq ^99mTc/¹⁸⁸Re-labelled nanocapsules and sacrificed at 5, 15 and 30 min and 1, 2, 4, 8, 12, 16, 20 and 24 h. Results Dynamic scintigraphic acquisitions showed predominant hepatic uptake, and ex vivo counting indicated a long circulation time of labelled nanocapsules, with a half-life of 21±1 min for ^99mTc and 22±2 min for ¹⁸⁸Re. Very weak urinary elimination was observed, indicating good stability of ^99mTc and ¹⁸⁸Re labelling. Conclusion ^99mTc/¹⁸⁸Re-SSS nanocapsules can be obtained with high yield and satisfactory radiochemical purity. The biodistributions of ^99mTc/¹⁸⁸Re-labelled nanocapsules are close to those of classical PEG-coated particles and show good stability of ¹⁸⁸Re/^99mTc-SSS labelling.     

Comparison of99mTc(V)-DMSA,201Tl and99mTc-MIBI imaging in the follow-up of patients with medullary carcinoma of the thyroid

Radionuclide scanning with tumour-seeking agents such as pentavalent technetium-99m dimercaptosuccinic acid [^99mTc(V)-DMSA], thallium-201 and technetium-99m sestamibi (MIBI) has been reported to be useful in the detection of medullary thyroid carcinoma (MTC). We undertook a study in 14 MTC patients to determine the comparative imaging potential of²⁰¹Tl, MIBI and^99mTc(V)-DMSA in the detection of recurrent or metastatic MTC. All patients underwent total thyroidectomy and had persistently elevated serum calcitonin levels after the surgery. Scintigraphic studies were carried out 20 min after the injection of 111 MBq of²⁰¹Tl or 555 MBq of MIBI and 2 h following the injection of 370 MBq of^99mTc(V)-DMSA. All scintigraphic findings were correlated with contemporaneous CT or MRI studies. CT, MRI and bone scans showed 42 (26 bone, 16 soft tissue) metastatic sites in 11 of the 14 patients. In the remaining three patients no lesions were detected during diagnostic evaluation.^99mTc(V)-DMSA showed all of the soft tissue metastases but could not show two bone lesions. On the other hand, MIBI imaging was false-negative in 22 (52%) sites and²⁰¹Tl was false-negative in 34 (80%) sites. Overall, lesion detection sensitivities for^99mTc(V)-DMSA, MIBI and²⁰¹Tl were 95%, 47% and 19% respectively. We conclude that^99mTc(V)-DMSA is clearly superior to MIBI and²⁰¹Tl in the follow-up of MTC patients.     

Intraindividual comparison of 99mTc-labelled anti-SSEA-1 antigranulocyte antibody and 99mTc-HMPAO labelled white blood cells for the imaging of infection

Technetium-99m labelled antigranulocyte antibodies are ready to use and are sensitive and specific in the diagnosis of infectious diseases. ^99mTc-SSEA antigranulocyte antibodies have a very high affinity constant (K _d 10^–12 M) for human neutrophils (PMNs), and excellent imaging qualities with high target/background ratios. The aim of this study was to compare the diagnostic accuracy of the ^99mTc-anti-SSEA-1 monoclonal antibody (Mab) with that of ^99mTc-hexamethylpropylene amine oxime (HMPAO)-labelled white blood cells (WBCs). To this end, 17 patients with 23 proven infectious foci were examined with 555 MBq ^99mTc-anti-SSEA-1 MAb and with 370 MBq ^99mTc-HMPAO labelled autologous leucocytes within a period of 7 days. All the infections were confirmed by culture, biopsy, surgery and follow-up. Whole-body images and planar spot views with the antibody were performed at 1-h, 4-h and 24-h post injection; the biodistribution of the antibody was quantified, absorbed radiation doses were calculated and the diagnostic results were compared with the ^99mTc-HMPAO WBC images. Human anti-mouse antibody (HAMA) evaluation was performed in all patients before and 3 months after antibody injection. Blood was drawn at different times after ^99mTc-anti-SSEA-1 MAb injection to determine the amount of granulocyte-associated radioactivity and to calculate recovery. ^99mTc-anti-SSEA-1 MAb scintigraphy detected all 23 lesions, while 21 were detected with ^99mTc-HMPAO WBC scan. In this small group of patients, the sensitivity and specificity of ^99mTc-anti-SSEA-1 MAb scintigraphy were 95% and 96% respectively, as compared with 91% and 82% respectively for ^99mTc-HMPAO WBC scan. An increasing uptake of the injected activity in the lesion at different time points was indicative of high affinity and of specific PMN binding.There was no HAMA formation. In four of five patients investigated, a transient mild leukopenia was found at 15 min p.i.. There was increased uptake of the antibody in liver and spleen and normal uptake in kidneys and bone marrow.The estimated radiation doses for the whole body and the red bone marrow were 1.1×10^–2 cGy/37 MBq and 5.3×10^–2 cGy/37 MBq, respectively. The activity associated to the PMNs in vivo was 33.5%, 30.6%, 21.3% and 9% at 5, 15, 30 and 45 min. post-injection, respectively. It is councluded that use of ^99mTc-anti-SSEA-1 antigranulocyte antibodies demonstrates promising results comparable to those obtained with ^99mTc-labelled autologous WBCs. The ^99mTc-labelled MAb is ready to use, has excellent image qualities and a high target/background ratio. Received 16 October and in revised form 17 December 1997     

Technetium-99m antimyosin antibody (3–48) myocardial imaging: human biodistribution,safety and clinical results in detection of acute myocardial infarction

Technetium-99m antimyosin (^99mTc-AM) antibody imaging may have significant advantages over indium-111 antimyosin in clinical practice. The purpose of this study was to determine the human biodistribution, the safety profile and the sensitivity of^99mTc-AM (3–48) imaging in the detection of both Q-wave and non-Q-wave myocardial infarction (MI). Biodistribution and safety parameters were mainly determined in 12 normal healthy volunteers while 40 patients with proven MI (22 Q-wave, 18 non-Q-wave) were injected with^99mTc-AM (20–25 mCi) between 5 h and 7 days after the onset of acute chest pain. Three standard planar views were performed at 6 h and at 24 h post injection. Both sets of images were completed in 33 patients while two patients were imaged only at 6 h, three patients only at 18 h and one at 18 and 24 h. One patient was not imaged. Vital signs and ECG were recorded and blood samples for haematology, biochemistry and human antimurine antibodies (HAMA) and urinalysis were obtained in all volunteers and patients. No serious adverse reactions or side-effects attributable to^99mTc-AM have been reported. No volunteers or patients developed allergic reactions or significant increases in HAMA titres. Reading of^99mTc-AM imaging was performed by two blinded experienced observers. The sensitivity of^99mTc-AM in the detection of MI was 100% (21/21) for Q-wave and 83.3% (15/18) for non-Q-wave infarctions. The overall sensitivity was 92.3% (36/39). The three false-negative cases were inferoposterior MI. A certain degree of uptake focalization was seen in 26 out of 35 (74.2%) at 6 h. At 24 h, two patients (5.8%) did not show^99mTc-AM uptake while 22 (64.7%) showed intense focal uptake, seven (20.6%) moderate uptake and 3 (8.9%) slight uptake. It is concluded that^99mTc-AM (3–48) imaging is safe and shows high sensitivity in the detection of both Q-wave and non-Q-wave MI even with early imaging (6 h post injection). These promising results warrant further clinical investigation.     

Radioimmunoscintigraphy with technetium-99m labelled monoclonal antibody, 1A3, in colorectal cancer

This study of radioimmunoscintigraphy (RIS) was primarily undertaken to determine how the imaging results related to surgical findings. Technetium-99m radiolabelled 1A3, a monoclonal antibody against a columnar cell surface antigen, was used. No adverse effects or thyroid uptake was observed in 127 studies. The 85 primary colorectal cancers were all image positive. In the assessment of recurrent tumour in the abdomen or pelvis, the accuracy was 33/35 (94%), including true-positive findings in some whose serum carcinoembryonic antigen was normal. There was a positive predictive value for abdominal or pelvic recurrence of 92% and a negative predictive value of 100%, at a prevalence of 66%. In those patients whose liver was able to be evaluated, the accuracy was 72/79 (91%). There was a positive predictive value for liver metastases of 88% and a negative predictive value of 93%, at a prevalence of 32%. The simple procedure for labelling antibody with ^99mTc and its ready availability allow a completed report to be given within 24 h of the request.     

Noninvasive imaging of tumor integrin expression using <Superscript>18</Superscript>F-labeled RGD dimer peptide with PEG<Subscript>4</Subscript> linkers

Purpose  Various radiolabeled Arg-Gly-Asp (RGD) peptides have been previously investigated for tumor integrin α_vβ₃ imaging. To further develop RGD radiotracers with enhanced tumor-targeting efficacy and improved in vivo pharmacokinetics, we designed a new RGD homodimeric peptide with two PEG₄ spacers (PEG₄ = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) between the two monomeric RGD motifs and one PEG₄ linker on the glutamate α-amino group (¹⁸F-labeled PEG₄-E[PEG₄-c(RGDfK)]₂, P-PRGD2), as a promising agent for noninvasive imaging of integrin expression in mouse models. Methods  P-PRGD2 was labeled with ¹⁸F via 4-nitrophenyl 2-¹⁸F-fluoropropionate (¹⁸F-FP) prosthetic group. In vitro and in vivo characteristics of the new dimeric RGD peptide tracer ¹⁸F-FP-P-PRGD2 were investigated and compared with those of ¹⁸F-FP-P-RGD2 (¹⁸F-labeled RGD dimer without two PEG₄ spacers between the two RGD motifs). The ability of ¹⁸F-FP-P-PRGD2 to image tumor vascular integrin expression was evaluated in a 4T1 murine breast tumor model. Results  With the insertion of two PEG₄ spacers between the two RGD motifs, ¹⁸F-FP-P-PRGD2 showed enhanced integrin α_vβ₃-binding affinity, increased tumor uptake and tumor-to-nontumor background ratios compared with ¹⁸F-FP-P-RGD2 in U87MG tumors. MicroPET imaging with ¹⁸F-FP-P-PRGD2 revealed high tumor contrast and low background in tumor-bearing nude mice. Biodistribution studies confirmed the in vivo integrin α_vβ₃-binding specificity of ¹⁸F-FP-P-RGD2. ¹⁸F-FP-P-PRGD2 can specifically image integrin α_vβ₃ on the activated endothelial cells of tumor neovasculature. Conclusion   ¹⁸F-FP-P-PRGD2 can provide important information on integrin expression on the tumor vasculature. The high integrin binding affinity and specificity, excellent pharmacokinetic properties and metabolic stability make the new RGD dimeric tracer ¹⁸F-FP-P-PRGD2 a promising agent for PET imaging of tumor angiogenesis and for monitoring the efficacy of antiangiogenic treatment. Electronic supplementary material  The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Diffuse Myocardial Uptake of 99mTc-HDP in Multiple Myeloma

Soft tissue uptake is a rare finding in bone scintigraphy, with an incidence of 2%. Although the mechanism has not yet been fully clarified, several causes have been reported for this unusual uptake pattern. This paper presents a case of diffuse myocardial accumulation of technetium-99m hydroxymethylene diphosphonate (^99mTc-HDP) without either solid/visceral organ or soft tissue with multiple myeloma (MM) in skeletal scintigraphy. A 93-year-old man with hypertension and chronic heart failure for 14 years underwent bone scanning due to a 2-month history of back pain within a 1-year period of MM. Three hours later, ^99mTc-HDP late static images showed diffuse myocardial radiotracer accumulation and there were no other sites of abnormal soft tissue or visceral uptake. Myocardial accumulation had disappeared on 24-h delayed static images. This accumulation was thought to be related with AL-type amyloidosis associated with MM.     

Technetium-99m labeling of tityustoxin and venom from the scorpion Tityus serrulatus

The tityustoxin, the most toxic fraction from scorpion Tityus serrulatus venom, has been used as a tool in several neurochemical and neuropharmacological studies. Biological activities of labeled and unlabeled tityustoxin and venom were compared. The samples were labeled in the presence of stannous chloride and sodium borohydride with a yield of 60–70% for the venom and 75–85% for tityustoxin and then chromatographed in Sephadex G-10. Biological activities of tityustoxin and venom were preserved after labeling.     

Multivalent cyclic RGD ligands: influence of linker lengths on receptor binding

Peptides involving the RGD motive (arginine–glycine–aspartic acid) recognize members of the integrin receptor family. Since the receptors are located mainly on the surface of endothelial cells, structural modifications including multimers of c(RGDfE) were recently found to improve the binding avidity for α_vβ₃ integrin significantly. The multivalent RGD peptides exhibited rather loose linkages partly including oligo(ethylene glycol) spacers (EG_n) with different chain lengths. Therefore, the dependence of multivalent RGD systems with and without EG_n linkers were investigated on their binding properties to cultured α_vβ₃ integrin-expressing U87MG cells.

Methods

We synthesized a series of di-, tri- and tetravalent rigid scaffolds (terephthalic acid, trimesic acid and adamantane-1,3,5,7-tetracarboxylic acid) conjugated to c(RGDyK) ligands, which were linked contiguously or separated by the oligo(ethylene glycol) spacers. The inhibition constants of these c(RGDyK) derivatives were determined by competition assays with ¹²⁵I-labeled echistatin.

Results

While c(RGDyK) function is a relative weak competitor against [¹²⁵I]echistatin (K_i, 329±18 nM) for α_vβ₃ integrin-expressing U87MG cells, RGD dimers improved the competition potency considerably (K_i, 64±23 nM). This effect was even more pronounced with the RGD trimers (K_i, 40±7 nM) and tetramers (K_i, 26±9 nM). The introduction of EG_n spacers and the increase of linker lengths proved to be detrimental since more competitors were needed to compete with [¹²⁵I]echistatin. The EG₆ group, for example, reduced the inhibition constants by 29% (dimer), 57% (trimer) and 97% (tetramer).

Conclusion

The binding experiments performed with the three forms of multivalent RGD ligands indicate the weakening of competitive potency against [¹²⁵I]echistatin with the introduction of EG_n spacers. This effect may be related to the decrease of the effective RGD molarity, which becomes most prominent within the tetravalent series.     

Preclinical evaluation of technetium 99m-labeled P1827DS for infection imaging and comparison with technetium 99m IL-8

BACKGROUND: The technetium 99 m (99mTc)-radiolabeled, leukocyte-avid peptide-glycoseaminoglycan complex, [99mTc]P1827DS, has been synthesized as an improved infection/inflammation imaging agent to [99mTc]P483H (LeukoTect, Diatide). In a phase I/II clinical trail, [99mTc]P483H images were equivalent to those obtained with 111In ex vivo labeled leukocytes. However, there was physiologic accumulation of radioactivity in the body that could hamper interpretation of the images. In this study, the potential of [99mTc]P1827DS for infection imaging was assessed in comparison with [99mTc]P483H and the well-described imaging agent [99mTc] hydrazinonicotinamide (HYNIC)-interleukin 8 (IL-8). METHODS: The binding of [99mTc]P1827DS to human blood cell was studied in vitro. A rabbit Escherichia coli infection model was used to perform the biodistribution and imaging studies with [99mTc]P1827DS, [99mTc]P483H and [99mTc]HYNIC-IL-8. RESULTS: [99mTc]P1827DS binds to leukocytes but not to erythrocytes. The leukocyte binding was not saturable up to an investigated concentration of 10 microM. The accumulation of [99mTc]P1827/DS at the infection site strongly depends on the P1827/DS ratio and was optimal at a molar ratio of 10:1. [99mTc]P1827DS shows improved biodistribution over [99mTc]P483H with similar uptake at the infection site. Abscess uptake of [99mTc]HYNIC-IL-8 was approximately three times higher than that of [99mTc]P1827DS. [99mTc]HYNIC-IL-8 showed high accumulation in the kidneys, whereas [99mTc]P1827DS showed high lung uptake and slightly higher accumulation in the liver and spleen. CONCLUSION: [99mTc]P1827DS is a potential new inflammation imaging agent, which clearly visualized the abscess in the rabbit E. coli infection model and showed improved biodistribution compared to [99mTc]P483H. However, the infection uptake and biodistribution of [99mTc]P1827DS is not superior to that of [99mTc]HYNIC-IL-8 in this animal model.     

Review of imaging techniques for the diagnosis of breast cancer: a new role of prone scintimammography using technetium-99m sestamibi

Imaging techniques currently used for the diagnosis of breast cancer are reviewed and compared. Besides mammography, magnetic resonance imaging, positron emission tomography, and thallium-201 scintimammography, a new role of technetium-99m sestamibi scintimammography is discussed. It is concluded that while mammography remains the procedure of choice in screening asymptomatic women for breast cancer, other imaging methods play an important role in detecting malignancies in symptomatic patients.^99mTc-sestamibi scintimammography has high sensitivity and improves the specificity of conventional mammography for the detection of breast cancer; with this technique, prone imaging is preferable to supine imaging.^99mTc-sestamibi scintimammography thus deserves further study as a screening technique.     

99mTc-MIBI scintigraphy in metastatic renal cell carcinoma: clinical validation of the relationship between99mTc-MIBI uptake and P-alvcoprotein expression in tumour tissue

Technetium-99m hexakis-2-methoxyisobutyl-isonitrile (MIBI) and thallium-201 imaging was performed in a patient with metastatic renal cell carcinoma (RCC), which is a well-known tumour type demonstrating P1-glycoprotein (PGP) overexpression. Two scintigraphic patterns - TI(+)/MIBI(–) in primary tumour and TI(+)/MIBI(+) in metastatic tumour — were observed, suggesting high- and low-level PGP expression, respectively. Immunochemical study for PGP revealed strong staining of the primary tumour cells. This case clinically validates the previously suggested relationship between^99mTc-MIBI uptake and PGP expression.     

<Superscript>68</Superscript>Ga-labeled NOTA-RGD-BBN peptide for dual integrin and GRPR-targeted tumor imaging

Purpose  Radiolabeled Arg-Gly-Asp (RGD) and bombesin (BBN) peptide analogs have been extensively investigated for the imaging of tumor integrin α_vβ₃ and gastrin-releasing peptide receptor (GRPR) expression, respectively. Recently, we designed and synthesized a RGD-BBN heterodimeric peptide from c(RGDyK) and BBN(7–14) through a glutamate linker. The goal of this study was to investigate the dual receptor-targeting property and tumor diagnostic value of RGD-BBN heterodimeric peptide labeled with generator-eluted ⁶⁸Ga (t_1/2 68 min, β⁺ 89% and EC 11%), ⁶⁸Ga-NOTA-RGD-BBN. Methods  RGD-BBN heterodimer was conjugated with 1,4,7-triazacyclononanetriacetic acid (NOTA) and labeled with ⁶⁸Ga. The dual receptor binding affinity was investigated by a radioligand competition binding assay. The in vitro and in vivo dual receptor targeting of ⁶⁸Ga-NOTA-RGD-BBN was evaluated and compared with that of ⁶⁸Ga-NOTA-RGD and ⁶⁸Ga-NOTA-BBN. Results  NOTA-RGD-BBN had integrin α_vβ₃ and GRPR binding affinities comparable to those of the monomeric RGD and BBN, respectively. The dual receptor targeting property of ⁶⁸Ga-NOTA-RGD-BBN was validated by blocking studies in a PC-3 tumor model. ⁶⁸Ga-NOTA-RGD-BBN showed higher tumor uptake than ⁶⁸Ga-NOTA-RGD and ⁶⁸Ga-NOTA-BBN. ⁶⁸Ga-NOTA-RGD-BBN can also image tumors with either integrin or GRPR expression. Conclusion   ⁶⁸Ga-NOTA-RGD-BBN exhibited dual receptor targeting properties both in vitro and in vivo. The favorable characterizations of ⁶⁸Ga-NOTA-RGD-BBN such as convenient synthesis, high specific activity, and high tumor uptake, warrant its further investigation for clinical cancer imaging. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Abnormal uptake of technetium-99m hexakis-2-methoxyisobutylisonitrile in a primary cardiac lymphoma

Abnormally high uptake of technetium-99m hexakis-2-methoxyisobutylisonitrile (^99mTc-SESTAMIBI) in the right ventricle and in the septum was observed in a 47-year-old woman initially presenting with dysarthria and left hemiparesis. Endomyocardial biopsy demonstrated a high-grade malignant non-Hodgkin's lymphoma. Complete remission was achieved by combined cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy and radiotherapy of the heart and mediastinum. The post-remission single photon emission tomography (SPET) ^99mTc-SESTAMIBI study showed a homogeneous distribution pattern, in agreement with echocardiography computed tomography and magnetic resonance imaging. Increased uptake of ^99mTc-SESTAMIBI, a myocardial perfusion agent, has been observed in some benign and malignant tumours. It may prove to be useful in the diagnosis and follow-up of malignancies. Offprint requests to: G. Medolago     

Radiosynthesis of 99mTc(CO)3-Clinafloxacin Dithiocarbamate and Its Biological Evaluation as a Potential Staphylococcus aureus Infection Radiotracer

Background

Clinafloxacin dithiocarbamate (CNND) was radiolabeled with technetium-99m (^99mTc) using [^99mTc(CO)₃(H₂O)₃]⁺ and assessed for its radiochemical stability in saline and serum, its in vitro binding with methicillin-resistant Staphylococcus aureus (MRSA) and biodistribution in female nude mice (FNM) artificially infected with live and heat-killed MRSA.

Methods

In normal saline (NS) the ^99mTc(CO)₃-clinafloxacin dithiocarbamate (^99mTc(CO)₃-CNND) showed radiochemical stability with a maximum value of 99.10 ± 0.20% and remained stable up to 4 h (92.65 ± 0.18%).

Results

In human serum at 37°C within 16 h of incubation, 14.85% side products as a result of de-tagging developed. Incubation with MRSA gave saturated binding with a maximum value of 72.75 ± 1.20%. Almost six-fold higher uptake was seen in the infected muscle of the FNM as compared to the inflamed and normal muscle. The ^99mTc(CO)₃-CNND complex showed a normal route of excretion from the body of the FNM model.

Conclusion

The higher stability in NS, HS, saturated in vitro binding with a live strain of MRSA and six-fold higher uptake in the target organ showed the ^99mTc(CO)₃-CNND complex to be a potential MRSA infection radiotracer.     

Role of technetium-99m sestamibi scintimammography and contrast-enhanced magnetic resonance imaging for the evaluation of indeterminate mammograms

This study evaluated and compared technetium-99m sestamibi scintimammography (SMM) and breast magnetic resonance imaging (MRI) results in patients with indeterminate mammograms to determine whether either technique can improve the sensitivity and specificity for the diagnosis of breast carcinoma. From 123 consecutive patients who underwent physical examination, mammography, SMM, and histopathologic confirmation, a subgroup of 82 patients presenting with indeterminate mammograms was studied. Sixty-eight patients underwent contrast-enhanced MRI. SMM results were scored on the basis of the intensity and pattern of sestamibi uptake. MRI images were scored on the basis of signal intensity increase after administration of contrast material as well as the enhancement pattern and speed of gadolinium uptake. The results obtained with the two techniques were compared and related to the final histopathologic diagnoses. Considering indeterminate findings as positive, the sensitivity of SMM was 79% and the specificity, 70%. MRI displayed a sensitivity of 84% and a specificity of 49%. When indeterminate results were considered negative, the sensitivity and specificity of SMM were 62% and 83%, respectively. MRI revealed a sensitivity and specificity of 56% and 79%, respectively. The calculated sensitivities and specificities demonstrate the diagnostic limitations of both SMM and MRI in the evaluation of patients with indeterminate mammographic findings. Due to the higher specificity, SMM may be the preferred modality in the evaluation of selected patients with breast abnormalities. Received 16 April and in revised form 12 June 1997     

Angiogenesis-Targeted 68Ga-DOTA-RGD2 PET/CT Imaging: a Potential Theranostic Application in the Case of Chondrosarcoma

Chondrosarcoma is a cartilaginous tumor of mesenchymal origin. The histology and grade of the tumor determine the chances of relapse and survival. These tumors usually respond poorly to chemo-radiotherapy in cases of non-resectable and recurrent disease. ¹⁸F-FDG PET/CT has been used in evaluation of recurrence. However, these tumors show only mild to moderate FDG avidity due to their lower mitotic activity and large acellular matrix. These tumors are known to have a high degree of angiogenesis, especially in those of higher grade. We present a case of a 53-year-old man with grade II chondrosarcoma of the left femur showing only mild avidity on ¹⁸F-FDG PET/CT but showing moderate to intense tracer avidity on ⁶⁸Ga-DOTA-RGD₂ PET/CT. This may enable the use of angiogenesis-targeted positron and beta-emitting radiopharmaceuticals as a potentially new theranostic alternative treatment in cases of refractory metastatic chondrosarcoma.     

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.