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PubMedDate not supplied

From symmetrical to asymmetrical nitrido phosphino-thiol complexes: a new class of neutral mixed-ligand (99m)Tc compounds as potential brain imaging agents.

A general procedure is presented for the preparation of a new class of nitrido asymmetrical Tc-99m complexes containing two different bidentate ligands bound to the same [Tc(N)]2+ core that could be used to design either essential or target specific imaging agents. This procedure is based on the chemical properties of a new monosubstituted [Tc(N)(R2PS)Cl(PPh3)] species composed of a TcN multiple bond and an ancillary phosphine thiol ligand (R2PSH). This intermediate readily reacts with bidentate mononegative ligands (S--Y) containing soft pi-donor coordinating atoms to give neutral pentacoordinate asymmetrical complexes of the type [Tc(N)(R2PS)(S--Y)]. The ability of several bidentate ligands containing different combination of heteroatoms (S, N, O) to form complexes with the [Tc(N)(R2PS)]+ building block was investigated. It was found that mononegative dithiocarbamate (DTC) or cysteine carboxyl derivate ligands promptly react with the monosubstituted species to form the final mixed compound in high yield. Preliminary biodistribution data in rats of some representative [Tc(N)(R2PS)(DTC)] compounds revealed an interesting initial brain uptake (in the range 0.20 +/- 0.01% ID/g and 0.91 +/- 0.06% ID/g), indicating their ability to cross in and out of the intact BBB. In these complexes the dithiocarbamate, or more generally the bidentate ligand (S--Y), can be designed to carry a functional group or a bioactive molecule, which could be involved in a trapping mechanism to increase brain retention for longer time intervals. These results could be conveniently utilized to devise a new procedure for the production of a novel class of brain perfusion and/or brain receptor imaging agents.

Animals↗
PubMed2004

Identification of the non-pertechnetate species in Hanford waste tanks, Tc(I)--carbonyl complexes.

Immobilization of the high-level nuclear waste stored at the Hanford Reservation has been complicated by the presence of soluble, lower-valent technetium species. Previous work by Schroeder and Blanchard has shown that these species cannot be removed by ion-exchange and are difficult to oxidize. The Tc K-edge XANES spectra of the species in Tanks SY-101 and SY-103 were reported by Blanchard, but they could not be assigned to any known technetium complex. We report that the XANES spectra are most likely those of Tc(I)-carbonyl species, especially fac-Tc(CO)3(gluconate)(2-). This is further supported by EXAFS and 99Tc-NMR studies in nonradioactive simulants of these tank wastes.

Carbon↗
PubMed2004

Evidence for the interaction of technetium colloids with humic substances by X-ray absorption spectroscopy.

Spectroscopic extended X-ray absorption fine structure (EXAFS) evidence was obtained on the chemical environment of 99Tc(IV) atoms formed upon introduction of TcO4- into four types of laboratory-scale synthetic and natural systems which mimic in situ natural reducing conditions in humic-rich geochemical environments: (a) magnetite/pyrite in synthetic groundwater in the absence of humic substances (HSs), (b) magnetite/pyrite in natural Gorleben groundwater in the presence of HSs, (c) Boom clay sediment mixed with synthetic groundwater, and (d) Gorleben sand mixed with natural Gorleben groundwater. The investigated systems obey to pH 8-9 conditions, and all measured samples show similar EXAFS spectra for Tc, which could be fitted by a hydrated TcO2 x xH2O phase. The results are interpreted as follows: upon introduction of high concentrations (millimolar to micromolar) of TcO4-to chemically reducing environments, small Tc(IV) oxidic polymers are formed, which either may aggregate into larger units (colloids) and finally precipitate or may interact in their polymeric form with (dissolved and immobile) humic substances. This latter type of interaction--Tc(IV) colloid sorption onto HSs--differs significantly from the generally accepted metal--humate complexation and therefore offers new views on the possible reaction pathways of metals and radionuclides in humic-rich environments.

Aluminum Silicates↗
PubMed2002

New N(3)S donor ligand small peptide analogues of the N-mercaptoacetyl-glycylglycylglycine ligand in the clinically used Tc-99m renal imaging agent: evidence for unusual amide oxygen coordination by two new ligands.

Three new X-ray structurally characterized Re(V)O complexes, ReO(MEG(3)H(2)) (10), ReClO(MAEG(2)H(3)) (11), and [ReO(MECG(2)H(2))](2) (12), were prepared from protected forms of three new ligands, mercaptoethyl-glycylglycylglycine (MEG(3)H(5)), mercaptoacetamide-ethyl-glycylglycine (MAEG(2)H(5)), and mercaptoethyl-carbamoylmethyl-glycylglycine (MECG(2)H(5)). (Subscript on H indicates the number of dissociable protons.) Mercaptoacetyltriglycine (MAG(3)H(5)) is the ligand precursor for the clinically used Tc-99m renal imaging agent. The new potentially N(3)S donor ligands have a glycylglycine carboxyl end as in MAG(3)H(5), but a secondary amine (sp(3) N) replaces one amide (sp(2) N) of MAG(3)H(5). ReO(MEG(3)H(2)) (10) is a typical five-coordinate pseudo-square-pyramidal complex with the oxo ligand at the apex and the trianionic form of MEG(3)H(5) coordinated in the basal plane via N(3)S. In the other complexes, the quadridentate ligand has N(2)OS ligation, with the carbonyl oxygen of the glycyl amide group coordinated trans to the oxo ligand. This unusual ligation mode, which is facilitated by the preferred endo configuration of the ligated glycyl sp(3) N, leaves a vacant basal coordination site. In 11, the chloro ligand completes the equatorial plane, whereas, in 12, a glycine carboxylate oxygen of the ligand on the partner Re completes the equatorial plane. Both complexes thus possess an unexpected pseudo-octahedral geometry. For 10, 11, and 12, the (1)H NMR spectra, monitored from high to low pH, exhibited changes only when the pH was lowered below 6. This finding indicates that at physiological pH these complexes possess the desirable characteristic of existing as one monomeric species having only one ionization state, with the coordinated sp(3) N deprotonated. Below pH 6 and above pH approximately 4, changes in the (1)H NMR shifts indicate that this sp(3) N has become protonated. Thus, the N(3)S ligands in all three complexes exhibit normal coordination above pH approximately 4. However, X-ray data for 11 and 12 and some NMR evidence for 11 indicate that the ligands of the two complexes rearrange at low pH (<3). The striking differences between the solution- and solid-state structures reinforce the caveat that solution structural studies conducted at physiological pH are necessary in order to gain insight into the nature of radiopharmaceuticals.

Crystallography, X-Ray↗
PubMed1989

New brain perfusion imaging agents based on 99mTc-bis(aminoethanethiol) complexes: stereoisomers and biodistribution.

In developing new brain perfusion imaging agents, we prepared 99mTc complexes of racemic mixtures of bis(aminoethanethiol) (BAT) derivatives containing an N'-benzylpiperazinyl (BPA) side chain. Due to the presence of a chiral center, a mixture of diastereomers (syn and anti) following chelation with the 99mTc (no-carrier-added) was obtained. The neutral and lipid-soluble 99mTc-BPA-BAT (99mTc, T1/2 = 6 h) isomers were separated. The syn and anti isomers of carrier-added 99Tc-BPA-BAT (99Tc, T1/2 = 2 x 10(5) years) were also synthesized, separated, and crystallized. The X-ray crystallography of 99Tc-BPA-BAT showed the syn and anti conformations (in relationship with the central TC(=O)N2S2 core). Despite a similarity in the partition coefficients for the two isomers, the syn isomer showed a higher in vivo brain uptake and longer brain retention in rats (2.77 and 1.08% dose/organ at 2 and 15 min) than that of the corresponding anti isomer (0.57 and 0.27% dose/organ at 2 and 15 min). This information is important and should be taken into consideration when new 99mTc-labeled brain perfusion imaging agents are being designed.

Animals↗
PubMed2006

A computational and conceptual density functional theory study of the properties of Re and Tc tricarbonyl complexes.

A computational and conceptual density functional study has been performed on metal tricarbonyl complexes (MTC) of both Re(I) and Tc(I). The fully optimized complexes of fac-[Tc(OH(2))(CO(3))](+) and mer-[Tc(OH(2))(CO(3))](+) show geometries that compare favorably with the X-ray data. These structures were used as a starting point to investigate the relative stability of MTC complexes with various ligands containing combinations of N, O, and S as chelating atoms and to evaluate the stabilizing/destabilizing influence of these ligands. Both for Tc and for Re complexes the nitrogen content turns out to be decisive in the stability of the metaltricarbonyl complexes, the finer details being determined by the hardness sequence N > O > S. As the core of the complexes, [(M(CO)(3)(+)], is hard, the main ordering parameter is changed as compared to our previous studies on Tc(V) [3+1] complexes where the number of sulfur atoms was decisive in accordance with the much softer character of the MOCl core. All results are successfully interpreted in terms of the hard and soft acids and bases principle (HSAB) at the local level.

Carbonates↗
PubMed1997

Improvement in specificity of [14C]d-xylose breath test for bacterial overgrowth.

The aim of the study was to determine whether the specificity of the [14C]d-xylose breath test could be improved, by excluding false-positive tests due to premature colonic metabolism of the [14C]d-xylose caused by rapid colonic transit. Forty-seven patients with suspected small bowel bacterial overgrowth were investigated by (1) aspiration and culture of duodenal fluid and (2) a [14C]d-xylose breath test. Those with either a positive duodenal culture or breath test had a repeat [14C]d-xylose breath test given with one of three transit markers (barium, Gastrografin or 99mTc-labeled tin colloid) to determine if the site of metabolism was in the small bowel or colon. Fourteen patients had positive duodenal cultures, four of whom had a negative [14C]d-xylose breath test, 15 patients had a positive [14C]d-xylose breath test, three of which were due to colonic metabolism of the xylose. Where transit markers were used, 14C was detectable in the breath and serum before barium had entered the small bowel, thus the barium did not comigrate with the xylose. Gastrografin accelerated small bowel transit, leading to malabsorption of the xylose in the small intestine and subsequent colonic metabolism of the xylose. 99mTc-labeled tin colloid had no obvious disadvantages and appeared to be the marker of choice. The use of a transit marker increased the specificity of the [14C]d-xylose breath test from 85% to 94%. The specificity of the [14C]d-xylose breath test for the detection of small bowel bacterial overgrowth is improved to greater than 90% by the use of an appropriate transit marker.

Bacteria↗
PubMed1999

Lung clearance of intratracheally instilled 99mTc-tobramycin using pulmonary surfactant as vehicle.

1. The use of pulmonary exogenous surfactant as a vehicle for intratracheally administered antibiotics to improve local antimicrobial therapy has been proposed. The present study investigated lung clearance rates in the rat of intratracheally instilled technetium labelled tobramycin with and without the addition of surfactant to the antibiotic solution. 2. The influence of surfactant on 99mTc-tobramycin lung clearance rates was studied dynamically with a gamma-camera in anaesthetized spontaneously breathing animals and in mechanically ventilated animals. 3. The results show that instillation of 99mTc-tobramycin with use of surfactant as vehicle significantly increases 99mTc-tobramycin lung clearance compared to instillation of 99mTc-tobramycin solution alone (P=0.006 between the two spontaneously breathing groups of animals and P=0.02 between the two ventilated groups of animals, ANOVA for repeated time measurements). The half life (t1/2) of composite clearance curves in spontaneous breathing animals was 147 min for animals receiving 99mTc-tobramycin versus 61 min for animals receiving 99mTc-tobramycin with surfactant. In mechanically ventilated animals this was 163 min versus 51 min, respectively. 4. It is concluded that exogenous surfactant, used as vehicle for intratracheally instilled 99mTc-tobramycin, increases lung clearance rate of 99mTc-tobramycin in rats.

Administration, Inhalation↗
PubMed1990

Determination of low-energy beta-emitter radionuclides deposited on surfaces by attapulgite treatment.

A method for the determination of surface contamination of various materials by 3H and 99Tc is reported. Both 3H and 99Tcm are widely used in chemical and clinical applications. The isotopes 99Tc, the decay product of 99Tcm, and 3H are soft beta-emitter radionuclides and the use of unsealed sources can frequently produce contamination and excessive internal dosing for workers. The removal of radionuclides from surfaces was effected with attapulgite, a clay with a high absorption capacity for many organic and inorganic substances. The determination was carried out by extracting the absorbed radionuclide from the clay and then measuring it in a beta-scintillation counter. The determination limits of the method, 20 Bq cm-2 for 3H and 100 Bq cm-2 for 99Tc, are below the "derived working limits" for these radionuclides.

Magnesium↗
PubMed1998

Radionuclide scanning in parathyroid diseases.

BACKGROUND: New radionuclide agents and scanning procedures have markedly improved preoperative parathyroid gland localization. The aim of this review was to evaluate the results of parathyroid scanning and to clarify its current place in the clinical management of parathyroid diseases. METHODS: The literature describing the different radioisotopes and available scanning techniques was analysed and their clinical outcome in various parathyroid diseases was evaluated. RESULTS: Using 99mTc-radiolabelled sestamibi or other 9mTc-labelled cationic complexes, parathyroid scintigraphy detects 87 per cent of solitary adenomas (n=894), 55 per cent of abnormal glands in patients with multiglandular disease (n=303) and 75 per cent of persistent or recurrent lesions in patients with previous neck surgery (n=240). If necessary, three-dimensional imaging techniques can clarify the spatial localization of an ectopic uptake focus. The positive predictive value of the available scanning procedures is over 95 per cent, but false-positive uptake may be encountered. CONCLUSION: Radionuclide parathyroid gland scanning with 99mTc-labelled cationic complexes is the initial non-invasive method of choice for preoperative parathyroid gland localization in patients at special risk and/or with previous neck exploration. While scanning has also been proposed to facilitate parathyroidectomy, there is no objective evidence to support its routine use before a first-time surgical procedure.

False Positive Reactions↗
PubMed2002

Radio-guided sentinel node detection for gastric cancer.

BACKGROUND: Radio-guided detection of sentinel nodes (SNs) has been used to predict regional metastases in patients with malignant melanoma and breast cancer. However, the validity of the SN hypothesis is still controversial for gastrointestinal cancers including gastric cancer. The aim of this study was to test the feasibility and accuracy of radio-guided mapping of SNs for gastric cancer. METHODS: Some 145 consecutive patients with gastric cancer diagnosed as T1 or T2 and evaluated clinically as N0 were enrolled. Endoscopic injection of technetium-99m-radiolabelled tin colloid was performed before operation and radioactive SNs were identified with a gamma probe. Standard radical gastrectomy with lymphadenectomy was performed in all patients and all resected nodes were evaluated by routine histopathological examination. RESULTS: Using radio-guided methods, SNs were detected in 138 (95.2 per cent) of 145 patients. The SN was positive in 22 of 24 patients with lymph node metastasis. The incidence of metastasis in the SNs (7.8 per cent) was significantly higher than that in the non-SNs (0.3 per cent) (P < 0.01). The diagnostic accuracy according to SN status was 98.6 per cent (136 of 138). CONCLUSION: Radio-guided SN mapping is an accurate diagnostic procedure for detecting lymph node metastasis in patients with early-stage gastric cancer.

Chi-Square Distribution↗
PubMed2003

Sentinel node biopsy in breast cancer: validation study and comparison of blue dye alone with triple modality localization.

BACKGROUND: Sentinel node biopsy (SNB) for breast cancer patients is a new technique with the potential to provide an accurate staging of the axillary nodal status while avoiding the morbidity of an axillary dissection. The objective of the present study is to validate the use of sentinel node biopsy in a New Zealand hospital and to compare the ability of patent blue dye (PB) alone with triple modality (TM) (preoperative lymphoscintigraphy, intraoperative gamma probe and intraoperative blue dye) to identify the sentinel node. METHODS: A total of 104 patients who had a palpable breast lump that was confirmed to be malignant by radiology and cytology and a clinical diagnosis of stage I or stage II breast cancer, were enrolled for SNB and randomly assigned to triple modality or blue dye alone for the localization of the sentinel node. Axillary dissection was performed after the sentinel node(s) had been removed. RESULTS: There were 63 patients in the PB group and 41 patients in the TM group. Both groups are comparable, with a similar mean age and primary tumour size. A sentinel node was identified in 57 (90%) of the PB group patients and 40 (98%) of the TM group patients. Of these 23 (37%) of the PB group and 23 (56%) in the TM group had axillary nodes positive for malignancy. There was one false negative SNB in the PB group and two false negative results in the TM group. Therefore, the PB group had an accuracy of 98% and a sensitivity of 96% compared to an accuracy of 95% and a sensitivity of 91% for the TM group. CONCLUSION: The results of the present study validate the use of SNB in suitable breast cancer patients. Identification and the accuracy of the sentinel node localization were similar between the two groups. Therefore, in hospital centres without adequate access to a nuclear medical facility, it would be feasible to conduct SNB using blue dye alone.

Antimony↗
PubMed2003

Single institution's initial experience with sentinel lymph node biopsy in breast cancer patients.

BACKGROUND: The sentinel lymph node is the first draining node from a cancer-bearing area and is therefore the first to manifest metastasis. In breast cancer it has been shown to predict the axillary status. Axillary dissection provides information determining prognosis and need for adjuvant therapy but carries a certain morbidity. Our aim was to determine the feasibility of detecting the sentinel node in a teaching hospital and whether the sentinel node accurately predicts the axillary status. METHODS: All patients with stage I and II breast cancer and non-palpable axillary nodes were eligible, including those with previous excision biopsy. We excluded pregnant women, those with previous axillary surgery and women with advanced breast cancer with enlarged axillary nodes. The sentinel node was detected with technetium-99m-labelled tin colloid and vital blue dye and removed, and axillary clearance was performed. RESULTS: A total of 312 patients were examined from August 1996 to December 1998. The mean age was 53 years (range 28-83) and mean tumour size 2.6 cm (range 0.2-9.0). The detection rate of the sentinel node was 86%. The sentinel lymph node predicted the axillary status with a sensitivity of 83% and specificity of 100%. The false-negative rate was 16.7%. CONCLUSIONS: Detection of the sentinel lymph node is feasible and it can accurately predict the nodal status of the axilla. However, the high false-negative rate precludes as yet the use of sentinel lymph node biopsy in replacing axillary clearance as the standard of care for breast cancer.

Adult↗
PubMed2000

Applicability of the sentinel node technique to Merkel cell carcinoma.

BACKGROUND: Merkel cell carcinoma (MCC) resembles malignant melanoma in several ways. Both are cutaneous lesions of the same embryonic origin. Both have an unpredictable biologic behavior, early regional lymph node involvement, early distant metastases, and high recurrence rate. OBJECTIVE: To apply the sentinel node technique described for melanoma to MCC in light of the common biologic features of these two tumors. METHODS: Preoperative lymphoscintigraphy, intraoperative lymphatic mapping, and sentinel node biopsy and frozen section histology were performed to guide the surgical treatment of three patients with MCC. RESULTS: Application of this approach in patients with MCC is feasible, reproducible, and seems reliable. CONCLUSION: The use of the sentinel node technique for MCC will reduce the number of unnecessary lymphadenectomies, will enable identification of microscopic metastases to lymph nodes, and will improve the stratification and accrual of patients into adjuvant treatment protocols. It may even lead to a survival benefit.

Aged↗
PubMedDate not supplied

Sentinel lymph node identification for patients with breast cancer using large-size radiotracer particles: technetium-99m-labeled tin colloids produced excellent results.

Sentinel lymph node (SLN) biopsies using radioactive tracers have been reported to detect the metastatic status of the axillary lymph nodes in breast cancer patients. However, the optimal radioactive tracer particle sizes remain to be determined. In this study, identification of SLNs with large radiolabeled tin colloid particles was evaluated. Seventy-five patients with T1-2, N0 breast cancer were enrolled. Two hours prior to surgery, 1 to 2.5 mL technetium-99m-labeled tin colloid particles were injected around the tumor under ultrasonographic guidance. Immediately before the operation, dye fluids were also injected around the tumor to increase the interstitial pressure. After axillary dissection, lymph nodes with x100 or more uptake of radioactivity than the mean of the other lymph nodes are considered to be SLN. All lymph nodes from the axillary dissections were pathologically investigated, and the characteristics of SLNs were evaluated. SLNs were clearly identified in 74 of 75 patients (98.7%). Of 37 patients without SLN metastasis, pathological investigation revealed no further involvement of the remaining non-SLNs. The SLNs tended to be larger in size, and more than 50% were located in the lower medial site of the axilla. This is the first study to show that SLNs could successfully be identified with radiolabeled tin colloid particles. When SLNs were negative for metastases, non-SLNs were always negative.

Breast Neoplasms↗