Specificity and sensitivity of 99mTc-EDDA/HYNIC-Tyr³-octreotide (99mTc-TOC) for imaging neuroendocrine tumors.

OBJECTIVES: Gastroenteropancreatic neuroendocrine tumors (NETs) are cancers originating from neuroendocrine organs such as the pancreas, pituitary, thyroid, and adrenal glands and tumors arising from the diffuse neuroendocrine cells that are widely distributed throughout the body. NETs express somatostatin (SS) and contain a high density of SS receptors; therefore, they can be specifically targeted with SS-based radiopharmaceuticals. The aim of this research was to determine the validity in terms of specificity, sensitivity, and the agreement beyond chance with the biopsy (gold standard) of the 99mTc-EDDA-HYNIC-Tyr³octreotide (99mTc-TOC) to image and localize NETs and their metastases. MATERIALS AND METHODS: Freeze-dried kits containing 0.0125 mg HYNIC-octreotide and co-ligands were easily labeled and quality controlled within the hospital radiopharmacy. Fifty-six consecutive Mexican patients with a previous presumptive diagnosis of NETs underwent several clinical and laboratory studies and were referred to the Nuclear Medicine Department for a routine scan with 99mTc-TOC. The patients were injected with 500-600 MBq 99mTc-TOC, and whole-body images were obtained 2 h later with a SPECT or a SPECT/CT camera. Two nuclear medicine physicians observed the images and classified them as 17 negative and 39 positive. After correlating the image of each patient with our 'gold standard' (biopsy, clinical history, morphological images, and tumor marker assays), the 99mTc-TOC images were classified by the same two physicians as 12 true negatives, five false negatives, 38 true positives and one false positive. RESULTS: The validity of 99mTc-TOC in terms of relative frequencies with corresponding 95% confidence intervals were as follows: 92.3% (64-100%) specificity; 88.4% (78-97%) sensitivity; and the agreement beyond chance was 73% (60-84%). The positive predictive value was 97.4% (87-100%); the negative predicted value was 70.6% (48-93%); the accuracy was 89.3% (89-97%); and the prevalence was 76.8% (64-87%). CONCLUSION: Because of these high values, we strongly recommend scintigraphy with the Mexican-produced 99mTc-TOC for the localization of NETs and their metastases, and we conclude that it is a good tool for detecting neuroendocrine disease in a Mexican population.

(99m)Tc-labelled gold nanoparticles capped with HYNIC-peptide/mannose for sentinel lymph node detection.

UNLABELLED: The aim of this research was to prepare a multifunctional system of technetium-99m-labelled gold nanoparticles conjugated to HYNIC-GGC/mannose and to evaluate its biological behaviour as a potential radiopharmaceutical for sentinel lymph node detection (SLND). METHODS: Hydrazinonicotinamide-Gly-Gly-Cys-NH(2) (HYNIC-GGC) peptide and a thiol-triazole-mannose derivative were synthesized, characterized and conjugated to gold nanoparticles (AuNP, 20 nm) to prepare a multifunctional system of HYNIC-GGC-AuNP-mannose by means of spontaneous reaction of the thiol (Cys) present in HYNIC-GGC sequence and in the thiol-mannose derivative. The nanoconjugate was characterized by transmission electron microscopy (TEM), IR, UV-Vis, Raman, fluorescence and X-ray photoelectron spectroscopy (XPS). Technetium-99m labelling was carried out using EDDA/tricine as coligands and SnCl(2) as reducing agent with further size-exclusion chromatography purification. Radiochemical purity was determined by size-exclusion HPLC and ITLC-SG analyses. In vitro binding studies were carried out in rat liver homogenized tissue (mannose-receptor positive tissue). Biodistribution studies were accomplished in Wistar rats and images obtained using a micro-SPECT/CT system. RESULTS: TEM and spectroscopy techniques demonstrated that AuNPs were functionalized with HYNIC-GGC-NH(2) and thiol-mannose through interactions with thiol groups and the N-terminal amine of cysteine. Radio-chromatograms showed radiochemical purity higher than 95%. (99m)Tc-EDDA/HYNIC-GGC-AuNP-mannose ((99m)Tc-AuNP-mannose) showed specific recognition for mannose receptors in rat liver tissue. After subcutaneous administration of (99m)Tc-AuNP-mannose in rats (footpad), radioactivity levels in the popliteal and inguinal lymph nodes revealed that 99% of the activity was extracted by the first lymph node (popliteal extraction). Biodistribution studies and in vivo micro-SPECT/CT images in Wistar rats showed an evident lymph node uptake (11.58 ± 1.98 %ID at 1 h) which was retained during 24 h with minimal kidney accumulation (0.98 ± 0.10 %ID) and negligible uptake in all other tissues. CONCLUSIONS: This study demonstrated that (99m)Tc-AuNP-mannose remains within the first lymph node during 24 h and therefore might be useful as a target-specific radionanoconjugate for SLND using "1-day" or "2-day" conventional protocols.

Specificity of 99mTc-UBI for detecting infection foci in patients with fever in study.

UNLABELLED: Fever of unknown origin (FUO) represents a challenge to clinical medicine, and bacterial cultures have been considered the 'gold standard' in discriminating between fevers resulting from bacterial infection and sterile inflammations. In nuclear medicine, a synthetic radiolabeled antimicrobial peptide (Tc-UBI) is used to image the molecular localization of infectious microorganisms. OBJECTIVE: The aim of this research was to determine the absolute and relative frequencies of Tc-UBI, by molecular imaging, to detect infection foci in patients with fever in study or FUO. METHODS: Images (207) from 196 patients with FUO acquired with Tc-UBI and a Siemens gammacamera were read by two nuclear medicine physicians and classified as positive or negative for infection foci. The diagnostic value was corroborated with our gold standard, which comprises bacterial cultures of biopsies, blood and urine, plus laboratory studies, morphological images (radiographs, nuclear magnetic resonance, computed tomography) and the clinical history of each patient. The absolute and relative frequencies of Tc-UBI were calculated from the molecular images versus the gold standard. RESULTS: The specificity of Tc-UBI for localizing infection foci and for discarding sterile inflammation was 95.35%, the sensitivity was 97.52%, the positive predictive value was 96.72%, the negative predictive value was 96.47%, the accuracy was 96.62%, and the observed agreement between the bacterial culture and the molecular image was 96.62% (P=0.0001). CONCLUSION: Considering that the absolute and relative frequencies are very high, we propose that, in the future, Tc-UBI molecular imaging could be the gold standard to detect infection sites and to discard sterile inflammation.

Therapeutic 188Re-lanreotide: determination of radiopharmacokinetic parameters in rats.

OBJECTIVES: The radiopharmacokinetic parameters of the therapeutic radiopharmaceutical (188)Re-lanreotide were compared in rats implanted with hepatocarcinoma tumours (n= 18) and healthy rats (n= 18). METHODS: Rats were injected with approximately 1.8 MBq (188)Re-lanreotide (0.1 ml) via the tail vein and blood samples were obtained. The activity per gram of tissue (%IA/g) was calculated and the radiopharmacokinetic parameters determined. Data were fitted using a two-compartment model. KEY FINDINGS: Significant differences were found between healthy and hepatoma rats for beta elimination half-life (22.56 vs 48.14 h); transference constants K(10) (k(e)) (6.44 vs 3.05 h(-1)) and K(12) (2.76 vs 7.09 h(-1)); volume of distribution (2.06 vs 5.45 ml); mean residence time (66.58 vs 95.50 h) and apparent volume of distribution at steady state (131.30 vs 810.37 ml). The tumour/organ ratios after 24 h were 11.20 for tumour/muscle, 8.00 for tumour/liver and 7.72 for tumour/bone. The scintigraphic images obtained therefore had high resolution. CONCLUSIONS: (188)Re-lanreotide had a prolonged beta elimination half-life and increased volume of distribution in rats with hepatocellular carcinoma. This may be beneficial in the diagnosis and therapy of metastatic lesions in patients with cancer.

Synthesis of oxytocin HYNIC derivatives as potential diagnostic agents for breast cancer.

Two synthetic procedures for HYNIC oxytocin labeling were developed: one based on an orthogonal protection approach and the other with prelabeled (Boc)HYNIC-(Fmoc) amino acids. Both procedures were compared and applied to the preparation of several HYNIC-oxytocin derivatives where ligand position and amino acid (lysine and phenylalanine) were varied. Additionally, an oxytocin derivative labeled with HYNIC in the alpha-amino group of the Cys1 residue was also prepared. 99mTc-ethylendiaminediacetic acid (EDDA) labeling efficiencies were examined for all the derivatives, resulting in two candidates which showed affinity for the oxytocin receptor. Further biochemical experiments demonstrated that 99mTc-EDDA/HYNIC-Cys1-OT-CONH2 could be used as a potential radiopharmaceutical for breast cancer diagnosis.

[Current developments in SPECT/CT systems using 99mTc-radiopharmaceuticals]. / Estado actual y futuro de la gammagrafía SPECT/CT con Radiofármacos de 99mTc.

The 3 foundations of nuclear medicine are radiation conscious personnel, specific radiopharmaceuticals and equipment. The trend in molecular radiopharmacy is to develop new radiopharmaceuticals targeting peptides and receptors. 99mTc-radiopharmaceuticals give important clinical and molecular information especially in endocrinology, oncology and cardiology. The basic equipment has relied on crystal scintillation detector gamma cameras and the obtained images represent organ function provided by the specific radiopharmaceutical. Gamma cameras for single emission computed tomography (SPECT) can be added to an X-ray computed tomography (CT) equipment to form a hybrid (SPECT/ CT). The system is coupled to computer algorithms and special software to acquire and process the separate studies and fuse the two images to give a 3-D image of organ function plus anatomy. The new semiconductor or solid state detectors are a big improvement in commercial hybrid scintillation cameras and micro-SPECT/CT. Fused images obtained with SPECT/CT have been very useful in almost all medical areas and play an important role in preclinical research. The aim of this work is to present the current status and future trends of SPECT/CT systems in the clinical practice of nuclear medicine using technetium-99m radiopharmaceuticals. The development of molecular, functional and genetic imaging tools aided by new technology and SPECT/CT image fusion will enhance accurate diagnoses, and understanding of molecular mechanisms of disease and their respective response to radiopharmaceutical therapy.

Radiopharmacokinetic and dosimetric parameters of 188Re-lanreotide in athymic mice with induced human cancer tumors.

Radiolabeled peptides, like the somatostatin analogs, have been used for peptide receptor-mediated radionuclide therapy (PRMRT) in metastatic neuroendocrine tumors. The eight amino acid peptide 3-(2-naphthalenyl)-D-alanyl-L-cysteinyl-L-tyrosyl-D-tryptophyl-L-lysyl-L-valyl-L-cysteinyl-L-threoninamide,cyclic(2-->7)-disulfide (9Cl) (lanreotide) was found to bind to the five somatostatin tumor receptors. Lanreotide has been labeled via the bifunctional chelating agent, DOTA, to (111)In, and (90)Y. A direct labeling method was used to label lanreotide with (188)Re. Athymic mice with implanted human cancer tumors (uterine-cervix, renal, and neuroblastoma) were injected with radiochemically pure (188)Re-lanreotide (1.11 MBq). The percent injected activity (%IA/g) from serial blood samples was the input data for the WinNonlin computer program to obtain radiopharmacokinetic parameters. The organs' percent injected activity per gram of tissue (%IA/g) was extrapolated to the weights of a 70 kg male model organs and the number of nuclear transitions (N) were the input for the OLINDA/EXM program to obtain dosimetry estimates. Induced uterine-cervix tumors (HeLa cells) show a mean 2.4 %IA/g uptake up to 24 h and the tumor/blood ratio was over 1.85 (1.5-24 h post-injection) confirming (188)Re-lanreotide remains bound to the tumor. The estimated tumor absorbed dose was 460 mGy/MBq. Human effective dose was 0.0182 mSv/MBq. Therefore, (188)Re-lanreotide is a good candidate for PRMRT and a clinical trial is being planned in order to acquire individual dosimetric data.

Molecular recognition and stability of 99mTc-UBI 29-41 based on experimental and semiempirical results.

99mTc-UBI 29-41 is an antimicrobial peptide fragment that directly radiolabeled with 99mTc shows high in vitro and in vivo stability, rapid background clearance, minimal accumulation in non-target tissues and rapid detection of infection sites. Molecular mechanics (MM) calculation has been an essential tool in explaining experimental results associated with molecular recognition and stability. This work is an attempt to explain the 99mTc-UBI 29-41 specificity for bacteria and to understand from a structural point of view, the experimental results indicative of a molecular recognition and stability not well favored for two other cationic peptides (99mTc-Tat-1-Scr and 99mTc-Tat-2-Scr ) used as control. Structures of 99mTc-UBI, 99mTc-Tat-1-Scr, 99mTc-Tat-2-Scr and of the corresponding free cationic peptides were built and the optimized structures, in the best stable configurations, were calculated by a MM procedure. In order to correlate the calculated and experimental results, in vitro stability tests with cysteine challenge and stability to dilution in human serum and in saline solution, were performed for the three labeled cationic peptides. The three complexes can be represented by the general formula [Tc(V)(O)(H2O)2(Lysn=1,2-Argn=0,1-peptide)]10+,11+. The potential energies were 104.5, 95.6 and 90.8 kcal/mol for 99mTc-Tat-1-Scr, 99mTc-Tat-2-Scr and 99mTc-UBI 29-41, respectively. Experimental and calculated results were in good agreement. It is thus possible to predict and explain that in similar solution media 99mTc-Tat-2-Scr would be more stable than 99mTc-Tat-1-Scr and why 99mTc-UBI shows the highest stability. In conclusion, the in vitro specific binding to bacteria and the accumulation at infection sites in humans of 99mTc-labeled UBI could be the result of its high thermodynamic stability, selectivity and stereospecificity.

Preparation of (166)Dy/(166)Ho-EDTMP: a potential in vivo generator system for bone marrow ablation.

BACKGROUND AND AIM: Bone-seeking radiopharmaceuticals have been proposed for delivering ablative radiation doses to marrow in multiple myeloma and other haematological malignancies. The aim of this research was to examine the feasibility of labelling ethylenediaminetetramethylenephosphonate (EDTMP) with Dy/Ho as an in vivo generator system and to evaluate whether the in vitro and in vivo stability of Dy-EDTMP and Ho-EDTMP complexes is maintained when the daughter Ho is formed. METHODS: Dy was obtained by neutron irradiation of enriched Dy2O3 in a TRIGA Mark III reactor. Labelling was carried out in an aqueous phosphate medium at pH 8.0 by addition of DyCl3 to EDTMP at a molar ratio 1:1.75. Dy/Ho labelled EDTMP was obtained with a 99.3+/-0.6% radiochemical purity determined by thin-layer chromatography and high-performance liquid chromatography. RESULTS: In vitro studies demonstrated that Dy/Ho-EDTMP is unstable after dilution in saline and stable in human serum and no translocation of the daughter nucleus occurring subsequent to beta decay of Dy which could produce release of Ho. Biodistribution in mice shows a fast blood clearance after administration of Dy/Ho-EDTMP with a skeletal uptake of 22.32+/-1.86% ID/g at 2 h and 20.12+/-1.94% ID/g after 10 d, a rapid renal elimination and no accumulation in other organs. Theoretical bone marrow absorbed dose calculations indicate that the Dy/Ho-EDTMP in vivo generator system would produce 7.80 times more radiation dose to marrow than that produced by Sm-EDTMP and 3.47 times more than Ho-DOTMP per unit of initial activity retained in the skeleton. CONCLUSION: The prepared radiolabelled EDTMP has adequate properties as a stable in vivo generator system for bone marrow ablation.