Comparative evaluation of 99Tcm-Hynic-HSA and 99Tcm-MAG3-HSA as possible blood pool agents

Neurotensin(8-13) analogue: radiolabeling and biological evaluation using different chelators

INTRODUCTION

Several strategies on the development of radiopharmaceuticals have been employed. Bifunctional chelators seem to be a promising approach since high radiochemical yields as well as good in vitro and in vivo stability have been achieved. To date, neurotensin analogs have been radiolabeled using the (99m)Tc-carbonyl approach and none was described employing the bifunctional chelating agent technique.

AIM

The purpose of this study was to evaluate the radiochemical and biological behaviour of NT(8-13) analogue radiolabeled with (99m)Tc, using HYNIC and NHS-S-acetyl-MAG(3) as chelator agents.

METHODS

Radiolabeling, in vitro stability toward cysteine and glutathione, partition coefficient and plasma protein binding were assessed for both radioconjugates. Biodistribution in healthy Swiss mice were carried out in order to evaluate the biological behaviour of the radiocomplexes.

RESULTS

Radiochemical yields were higher than 97% and no apparent instability toward transchelant agents was observed for both radioconjugates. A higher lipophilic character was observed for the radioconjugate labeled via MAG(3). The chelators seem to have no effect on the percentage of the radioconjugate bound to plasma proteins. A similar biological pattern was observed for both radioconjugates. Total blood, bone and muscle values revealed a slightly slower clearance for the radiocomplex labeled via MAG(3). Moreover, a remarkable liver and intestinal uptake was observed for the radiocomplex labeled via MAG(3) even at the later time points studied.

CONCLUSION

The high radiochemical yields achieved and the similar in vivo pattern found for both radioconjugates make them potential candidates for imaging tumors using nuclear medicine techniques.

A technetium intermediate specifically promotes deprotection of trifluoroacetyl HYNIC during radiolabelling under mild conditions

The trifluoroacetyl group protects the nucleophilic HYNIC from unwanted side reactions yet allows radiolabelling with technetium-99m under mild conditions, due to efficient and specific promotion of deprotection by a technetium complex intermediate.

SPECT imaging of myocardial infarction using 99mTc-labeled C2A domain of synaptotagmin I in a porcine ischemia-reperfusion model

INTRODUCTION

The C2A domain of synaptotagmin I recognizes necrotic and apoptotic cells by binding to exposed anionic phospholipids. The goal is to explore the potential imaging utility of 99mTc-labeled C2A in the detection of acute cardiac cell death in a porcine model that resembles human cardiovascular physiology.

METHODS

Ischemia (20-25 min) was induced in pigs (M/F, 20-25 kg) using balloon angioplasty. 99mTc-C2A-GST (n=7) or 99mTc-BSA (n=2) was injected intravenously 1-2 h after reperfusion. Noninfarct animals were injected with 99mTc-C2A-GST (n=4). SPECT images were acquired at 3 and 6 h postinjection. Cardiac tissues were analyzed to confirm the presence of cell death.

RESULTS

Focal uptake was detected in five out of seven subjects at 3 h and in all infarct subjects at 6 h postinjection but not in infarct animals injected with 99mTc-BSA or in noninfarct animals with 99mTc-C2A-GST. Gamma counting of infarct versus normal myocardium yielded a 10.2+/-5.7-fold elevation in absolute radioactivity, with histologically confirmed infarction.

CONCLUSIONS

We present data on imaging myocardial cell death in the acute phase of infarction in pigs. C2A holds promise and warrants further development as an infarct-avid molecular probe.

Trifluoroacetyl-HYNIC peptides: synthesis and 99mTc radiolabeling

Fmoc-lys(HYNIC-Boc)-OH, a precursor for solid-phase synthesis of 99mTc-labeled peptides, was synthesized efficiently without HPLC purification. HPLC-ESMS showed that deprotection and decoupling of peptide from the resin with trifluoroacetic acid gave initially HYNIC-peptide, which was trifluoroacetylated upon prolonged incubation. The trifluoroacetyl-HYNIC group was hydrolyzed during 99mTc labeling, rendering deprotection unnecessary. Trifluoroacetyl-HYNIC peptide was 99mTc-labeled as efficiently, producing the same product, as HYNIC-peptide. These modifications enhance the versatility of HYNIC for 99mTc peptide labeling.

Evaluation of 99mTc-MAG3-annexin V: influence of the chelate on in vitro and in vivo properties in mice

We conjugated mercaptoacetyltriglycine (MAG(3)) to rh-annexin V to permit radiolabeling with (99m)Tc in an effort to decrease the high kidney and liver accumulation observed for (99m)Tc-labeled Hynic-annexin V. The 36-kDa protein was conjugated at a 5:1 molar ratio with NHS-MAG(3) in HEPES buffer pH 7.8 at room temperature, then quenched with glycine and purified by dialysis. The biopotency of the resulting MAG(3)-annexin was similar to that of Hynic-annexin as determined by a sensitive red blood cell membrane affinity binding assay and a surface plasmon resonance (SPR) assay. The (99m)Tc radiolabeling of MAG(3)-annexin resulted in radiochemical yields of 90% under mildly basic pH conditions. Biodistribution data in normal mice clearly showed a significant decrease in kidney and liver uptake at 1 h postinjection for the (99m)Tc MAG(3)-annexin compared to the (99m)Tc Hynic-annexin (from 24% ID to 4% ID for the liver, and 45% ID to 15% ID for the kidneys, respectively). Autoradiography of the kidneys showed retention of radioactivity in the collecting tubules following administration of both labeled annexins. The (99m)Tc MAG(3)-annexin biodistribution was also characterized by a lower retention of radioactivity in the whole body, but with small intestine accumulation over fivefold higher than observed with (99m)Tc Hynic-annexin. These findings show a definite improvement in renal and hepatic clearance of the MAG(3) radioligand. However, due to the increased radioactivity uptake in the small intestines, the early in vivo detection of ongoing apoptosis in the lower abdomen might be more difficult with (99m)Tc MAG(3)-annexin. Nevertheless, (99m)Tc MAG(3)-annexin may be an attractive alternative to (99m)Tc Hynic-annexin for the in vivo imaging of phosphatidylserine receptors.

Optimization of the preparation of 99mTc-labeled Hynic-derivatized Annexin V for human use

Hydrazino nicotinate (Hynic) is one of the most attractive bifunctional agents designed for the labeling of proteins with (99m)Tc. Recently, a (99m)Tc-labeled Hynic-Annexin V derivative has been described and successfully evaluated in animal models of apoptosis. Prior to a phase I human study, the preparation of (99m)Tc-Hynic-Annexin V has been optimized. The influence of the Hynic-load of Annexin V, amount of protein, nature and amount of reducing agent, activity and co-ligand on the labeling yield were evaluated using ITLC and size-exclusion FPLC. Optimal labeling yields were obtained when 60-90 microgram Hynic-Annexin V was labeled with up to 1.11 GBq (30 mCi) (99m)TcO(4)-using 10-20 microgram SnCl(2).2H(2)O as reducing agent and 1.5 mg tricine as the co-ligand. Biodistribution in normal mice was comparable to literature data.

Nitriles form mixed-coligand complexes with (99m)Tc-HYNIC-peptide

Using a 12-amino acid peptide conjugated with HYNIC as a model, we investigated nitriles as possible coligands for labeling with (99m)Tc. After the preparation of the (99m)Tc labeled HYNIC-peptide using tricine as coligand, the addition of acetonitile was found by reverse phase HPLC to block further coligand exchange with ethylenediamine diacetic acid (EDDA) at room temperature. The addition of this nitrile changed the pharmacokinetics of the (99m)Tc labeled peptide in normal mice towards faster clearance and significant differences in accumulation in most tissues sampled. By replacing acetonitrile with cyanoacetate, a nitrile not present in the HPLC eluant, it was possible to show the existence of a new, more hydrophilic, species by reverse phase HPLC. We conclude that nitriles can act as coligands for HYNIC-conjugated peptides labeled with (99m)Tc and tricine. Furthermore, the presence of acetonitrile during Sep-Pak or HPLC purification may inadvertently generate a mixed tricine/acetonitile coligand (99m)Tc-HYNIC-peptide complex.

Evolution of Tc-99m in diagnostic radiopharmaceuticals

The progress in diagnostic nuclear medicine over the years since the discovery of 99mTc is indeed phenomenal. Over 80% of the radiopharmaceuticals currently being used make use of this short-lived, metastable radionuclide, which has reigned as the workhorse of diagnostic nuclear medicine. The preeminence of 99mTc is attributable to its optimal nuclear properties of a short half-life and a gamma photon emission of 140 keV, which is suitable for high-efficiency detection and which results in low radiation exposure to the patient. 99mTcO4-, which is readily available as a column eluate from a 99Mo/99mTc generator, is reduced in the presence of chelating agents. The versatile chemistry of technetium emerging from the 8 possible oxidation states, along with a proper understanding of the structure-biologic activity relationship, has been exploited to yield a plethora of products meant for morphologic and functional imaging of different organs. This article reviews the evolution of 99mTc dating back to its discovery, the development of 99Mo/99mTc generators, and the efforts to exploit the diverse chemistry of the element to explore a spectrum of compounds for diagnostic imaging, planar, and single photon emission computed tomography. A brief outline of the 99mTc radiopharmaceuticals currently being used has been categorically presented according to the organs being imaged. Newer methods of labeling involving bifunctional chelating agents (which encompass the "3 + 1" ligand system, Tc(CO)3(+1)-containing chelates, hydrazinonicotinamide, water-soluble phosphines, and other Tc-carrying moieties) have added a new dimension for the preparation of novel technetium compounds. These developments in technetium chemistry have opened new avenues in the field of diagnostic imaging. These include fundamental aspects in the design and development of target-specific agents, including antibodies, peptides, steroids, and other small molecules that have specific receptor affinity.

[(99m)Tc]MAG(3)-mannosyl-dextran: a receptor-binding radiopharmaceutical for sentinel node detection

Technetium-99m-labeled benzoyl-mercaptoacetylglycylglycyl-glycine-mannosyl-dextran ([(99m)Tc]MAG(3)-mannosyl-dextran) is a receptor-binding radiotracer that binds to mannose-binding protein, a receptor expressed by recticuloendothelial tissue. This agent is composed of a 10.5-kilodalton molecule of dextran and multiple units of mannose, and benzoyl-mercaptoacetylglycylglycyl-glycine (BzMAG(3)). The tetraflorophenol-activated ester of BzMAG(3) and the imidate of thiomannose were used to covalently attach BzMAG(3) and mannose to an amino-terminated conjugate of dextran. This yielded a 19-kilodalton macromolecule consisting of 3 BzMAG(3) and 21 mannose units per dextran. Dynamic light scattering was used to measure a mean diameter of 5.5 nanometers for BzMAG(3)-mannosyl-dextran and 0.28 microns for filtered Tc-99m sulfur colloid. A preliminary sentinel node detection study employing right fore and hind footpad injections of [(99m)Tc]MAG(3)-mannosyl-dextran and left fore and hind footpad injections of filtered Tc-99m sulfur colloid demonstrated greater sentinel lymph node uptake by the receptor-binding agent.

The effect of molecular weight on nonspecific accumulation of (99m)T-labeled proteins in inflammatory foci

Although several proteins have been proposed and tested for scintigraphic detection of infection, the most optimal characteristics of a protein for this application have not yet been determined. Molecular weight (MW) of the protein, its charge, shape, carbohydrate content, characteristics of the radionuclide and receptor interactions are factors that could affect the in vivo behavior of the infection imaging agent. The effect of molecular weight on nonspecific accumulation of (99m)Tc-labeled proteins in inflammatory foci was studied in a rat model.

METHODS

Eleven proteins whose MWs ranged from 2.5 kDa up to 800 kDa were labeled with (99m)Tc using the hydrazinonicotinamide (HYNIC) chelator. Rats with S. aureus infection were injected i.v. with 15 MBq (99m)Tc-labeled protein. Gamma camera images were acquired and biodistribution of the radiolabel was determined ex vivo.

RESULTS

From biodistribution data no significant correlation was found between abscess uptake and molecular size of the (99m)Tc-labeled proteins that were studied. Fast blood clearance with predominant uptake in liver and spleen was found for the largest proteins (MW 669 kDa-800 kDA). For proteins of intermediate size (MW 66 kDa -206 kDa) we found relatively slow blood clearance with relatively moderate uptake in liver and spleen. For smaller proteins (MW 2.5 kDa -29 kDa) rapid blood clearance with predominant kidney uptake was observed. The abscess uptake of the (99m)Tc-labeled proteins (%ID/g, 24 h p.i.) was highest for serum proteins IgG and BSA. Abscess uptake correlated well with blood levels: r = 0.95 and 0.84 at 4 and 24 h respectively (P < 0.005). The abscess-to-muscle ratios varied from 2.1 to 17.8 at 24 h p.i. with highest values for alpha-2 macroglobulin (MW 725 kDa) and the intermediate sized proteins (MW 66-206 kDa). Gamma camera imaging showed localization of all radiotracers at the site of infection with abscess-to-background ratios (A/B) ranging from 1.4 to 7.0 (IgG) at 20 h p.i. The serum proteins IgG and BSA showed highest blood levels and best infection imaging characteristics.

CONCLUSION

Not molecular weight but blood residence time is the principal factor that determines localization of a nonspecific tracer protein in infectious foci. The ideal nonspecific infection imaging agent is a protein with a long circulatory half-life. From the proteins tested here IgG and albumin showed the best characteristics for an infection imaging agent.

(99m)Tc-HYNIC-derivatized ternary ligand complexes for (99m)Tc-labeled polypeptides with low in vivo protein binding

6-Hydrazinopyridine-3-carboxylic acid (HYNIC) is a representative agent used to prepare technetium-99m ((99m)Tc)-labeled polypeptides with tricine as a coligand. However, (99m)Tc-HYNIC-labeled polypeptides show delayed elimination rates of the radioactivity not only from the blood but also from nontarget tissues such as the liver and kidney. In this study, a preformed chelate of tetrafluorophenol (TFP) active ester of [(99m)Tc](HYNIC)(tricine)(benzoylpyridine: BP) ternary complex was synthesized to prepare (99m)Tc-labeled polypeptides with higher stability against exchange reactions with proteins in plasma and lysosomes using the Fab fragment of a monoclonal antibody and galactosyl-neoglycoalbumin (NGA) as model polypeptides. When incubated in plasma, [(99m)Tc](HYNIC-Fab)(tricine)(BP) showed significant reduction of the radioactivity in high molecular weight fractions compared with [(99m)Tc](HYNIC-Fab)(tricine)(2.) When injected into mice, [(99m)Tc](HYNIC-NGA)(tricine)(BP) was metabolized to [(99m)Tc](HYNIC-lysine)(tricine)(BP) in the liver with no radioactivity detected in protein-bound fractions in contrast to the observations with [(99m)Tc](HYNIC-NGA)(tricine)(2.) In addition, [(99m)Tc](HYNIC-NGA)(tricine)(BP) showed significantly faster elimination rates of the radioactivity from the liver as compared with [(99m)Tc](HYNIC-NGA)(tricine)(2.) Similar results were observed with (99m)Tc-labeled Fab fragments where [(99m)Tc](HYNIC-Fab)(tricine)(BP) exhibited significantly faster elimination rates of the radioactivity not only from the blood but also from the kidney. These findings indicated that conjugation of [(99m)Tc](HYNIC)(tricine)(BP) ternary ligand complex to polypeptides accelerated elimination rates of the radioactivity from the blood and nontarget tissues due to low binding of the [(99m)Tc](HYNIC)(tricine)(BP) complex with proteins in the blood and in the lysosomes. Such characteristics would render the TFP active ester of [(99m)Tc](HYNIC)(tricine)(BP) complex attractive as a radiolabeling reagent for targeted imaging.

Plasma protein binding of (99m)Tc-labeled hydrazino nicotinamide derivatized polypeptides and peptides

6-Hydrazinopyridine-3-carboxylic acid (HYNIC) constitutes one of the most attractive reagents to prepare (99m)Tc-labeled polypeptides and peptides of various molecular weights in combination with two tricine molecules as coligands. Indeed, (99m)Tc-HYNIC-conjugated IgG showed biodistribution of radioactivity similar to that of (111)In-DTPA-conjugated IgG. However, recent studies indicated significant plasma protein binding when the (99m)Tc labeling procedure was expanded to low molecular weight peptides. In this study, pharmacokinetics of (99m)Tc-HYNIC-conjugated IgG, Fab and RC160 using tricine were compared with their radioiodinated counterparts to evaluate this (99m)Tc-labeling method. In mice, [(99m)Tc](HYNIC-IgG)(tricine)(2) and [(99m)Tc](HYNIC-Fab)(tricine)(2) showed persistent localization of radioactivity in tissues when compared with their (125)I-labeled counterparts. [(99m)Tc](HYNIC-IgG)(tricine)(2) eliminated from the blood at a rate similar to that of (125)I-labeled IgG, while [(99m)Tc](HYNIC-Fab)(tricine)(2) showed significantly slower clearance of the radioactivity than (125)I-labeled Fab. On size-exclusion HPLC analyses, little changes were observed in radiochromatograms after incubation of [(99m)Tc](HYNIC-IgG)(tricine)(2) in murine plasma. However, [(99m)Tc](HYNIC-Fab)(tricine)(2) and [(99m)Tc](HYNIC-RC160)(tricine)(2) demonstrated significant increases in the radioactivity in higher molecular weight fractions in plasma. Formation of higher molecular weight species was reduced when [(99m)Tc](HYNIC-RC160)(tricine)(2) was stabilized with nicotinic acid (NIC) to generate [(99m)Tc](HYNIC-RC160)(tricine)(NIC). [(99m)Tc](HYNIC-RC160)(tricine)(NIC) also demonstrated significantly faster clearance of the radioactivity from the blood than [(99m)Tc](HYNIC-RC160)(tricine)(2). These findings suggested that one of the tricine coligands in (99m)Tc-HYNIC-labeled (poly)peptides would be replaced with plasma proteins to generate higher molecular weight species that exhibit slow blood clearance. In addition, the molecular sizes of parental peptides played an important role in the progression of the exchange reaction of one of the tricine coligands with plasma proteins.

Different chelators and different peptides together influence the in vitro and mouse in vivo properties of 99Tcm

Relatively few studies comparing different methods of labelling peptides with 99Tcm have been reported. In this investigation, we evaluated the influence of three chelators on the in vitro and in vivo properties of two small, similar peptides (HNE2 and HNE4) labelled with 99Tcm. Both peptides were labelled with hydrazinonicotinamide (HYNIC) (tricine) at pH 5-6 and with diethylenetriaminepentaacetic acid (DTPA) and mercaptoacetyltriglycine (MAG3) at both pH 5-6 and 7-8. All ten preparations were brought to pH 7.2 immediately after labelling. Each preparation labelled well and control labelling showed each label to be attached specifically at chelation sites. Analysis of 37 degrees C human serum incubates showed little evidence of label instability but high protein binding in several cases. The stability of 99Tcm to cysteine challenge for labelled DTPA- and MAG3-peptides was similar but lower than that for the HYNIC-peptides. Reverse phase HPLC of the DTPA-peptides, but not the MAG3-peptides, showed different 99Tcm species depending on labelling pH. The 3 h biodistributions in normal mice were generally independent of labelling pH for both MAG3-peptides but were heavily influenced by labelling pH for both DTPA-peptides. While significant differences in biodistribution for the same labelling method were evident between peptides, as expected, far larger differences in the case of both peptides resulted from changing chelators and, in the case of DTPA, changing the labelling method. In summary, the chelators and labelling methods influenced the biodistribution of 99Tcm in a characteristic fashion common to both peptides. Differences in biodistribution due to the different peptides were relatively small and generally lost in the much larger differences due to chelator and labelling method. In conclusion, it may be important to compare chelators and labelling methods before selecting a 99Tcm labelling method for any particular peptide.

Labeling proteins with Tc-99m via hydrazinonicotinamide (HYNIC): optimization of the conjugation reaction

At present there is considerable interest in labeling peptides with Tc-99m for the development of target specific radiopharmaceuticals for imaging purposes. In the present study the conjugation of the bifunctional coupling agent succinimidyl-hydrazinonicotinamide (S-HYNIC) was studied and optimized in a series of peptides [molecular weight (MW) 6.5-14.3 kDa]. Aprotinin (MW 6.5 kDa), cytochrome C (MW 12.4 kDa), alpha-lactalbumin (MW 14.2 kDa), and lysozyme (MW 14.3 kDa) were conjugated with S-HYNIC via the epsilon amino groups of their lysine residues. The effects of molar conjugation ratio, reaction temperature, pH, and protein concentration were studied. Reaction products were analyzed both with respect to the HYNIC-substitution ratio (spectrophotometrically) as well as to the labeling efficiency silica gel-instant thin layer chromatography (SG-ITLC) and molecular size fast performance liquid chromatography (FPLC). The effects of conjugation on biological activity were studied in three proteins binding to receptors on leukocytes: interleukin-8 (MW 8.5 kDa), interleukin-1alpha (MW 17 kDa), and interleukin-1 receptor antagonist (MW 17 kDa). The labeling efficiency of aprotinin, cytochrome c, alpha-lactalbumin, and lysozyme conjugated under optimal conjugation conditions exceeded 90%. Specific activities obtained were up to 7.5 MBq/microg. Conjugation was most efficient at 0 degrees C (as compared to 20 and 40 degrees C), at pH 8.2 (as compared to 6.0, 7.2, and 9.5), and at protein concentrations > or = 2. 5 mg/mL. In general, efficiency increased with increasing molar conjugation ratio (protein-HYNIC-ratio 1:3 < 1:6 < 1:15<1:30). For the receptor binding proteins, biological activity was preserved only under the mildest conjugation conditions. For each of these proteins an inverse relation between labeling efficiency and receptor binding capacity was found. Labeling proteins with (99m)Tc using S-HYNIC is easy, rapid, and efficient, and preparations with high specific activity can be obtained. However, biological activity of proteins may be lost at high HYNIC-substitution ratios. With the proteins tested here a careful balancing of reaction conditions resulted in acceptable, although suboptimal, labeling efficiencies and preservation of biological activity.

3'-99mTc-labeling and biodistribution of a CAPL antisense oligodeoxynucleotide

CAPL is a cancer-related gene shown to be overexpressed during tumor metastasis formation. A CAPL antisense oligodeoxynucleotide (ODN), GX-1, and a random control ODN (CTRL1) were 3'-conjugated to MAG3, labeled with technetium-99m, purified, and the biodistribution of the radiolabeled conjugates in normal mice was studied. A 99mTc-MAG3-GX-1 complex of >97% radiochemical purity was obtained and the product was stable for >6 h as determined by reversed phase high performance liquid chromatography (HPLC). Biodistribution studies of the 99mTc-MAG3-ODNs in groups of four normal mice, sacrificed 5 min and 60 min after injection, demonstrated that the radiolabeled ODNs were distributed in an unspecific manner. The excretion route was mainly urinary. At 60 min, 55.2% of the injected dose of 99mTc-MAG3-GX-1 and 72.4% of 99mTc-MAG3-CTRL1 was found in the urine. This finding is clearly different from previously reported data on tritiated 20-mer phosphodiester ODNs, as well as the unconjugated 99mTc-MAG3 chelate, suggesting that 99mTc-MAG3 coupled to the 3'-end of ODNs has an influence on the biodistribution of the oligo, and possibly has a protective function to enzymatic degradation in vivo.

Synthesis and Characterization of Organohydrazino Complexes of Technetium, Rhenium, and Molybdenum with the {M(eta(1)-H(x)()NNR)(eta(2)-H(y)()NNR)} Core and Their Relationship to Radiolabeled Organohydrazine-Derivatized Chemotactic Peptides with Diagnostic Applications

The reduction of perrhenate, molybdate and pertechnetate with 2-hydrazinopyridine dihydrochloride in methanol has led to the preparation of a class of complexes containing the {M(eta(1)-NNC(5)H(4)NH(x)())(eta(2)-HNNH(y)()C(5)H(4)N)} core, represented by [TcCl(3)(NNC(5)H(4)NH)(HNNC(5)H(4)N)] (2), [ReCl(3)(NNC(5)H(4)NH)(HNNC(5)H(4)N)] (3), and [MoCl(3)(NNC(5)H(4)NH)(HNNHC(5)H(4)N)] (6). The reaction of 3 with NEt(3) results in the formation of [HNEt(3)][[ReCl(3)(NNC(5)H(4)N)(HNNC(5)H(4)N)].H(2)O (4) by deprotonation of the pyridine nitrogen site. Similarly, the reduction of perrhenate with 2-hydrazino-2-imidazoline hydrobromide has led to the preparation of the analogous [ReCl(3)(NNC(3)H(4)N(2)H)(HNNHC(3)H(4)N(2)H)] (5). Reaction of 3 with pyridine-2-thiol and pyrimidine-2-thiol yields two structurally characterized derivatives with a modified {Re(eta(1)-NNC(5)H(4)N)(eta(2)-HNNC(5)H(4)N)} core, [Re(C(5)H(4)NS)(2)(NNC(5)H(4)N)(HNNC(5)H(4)N)] (8) and [Re(C(4)H(3)N(2)S)(2)(NNC(5)H(4)N)(HNNC(5)H(4)N)] (9), respectively. Reaction of 6 with pyrimidine-2-thiol led to the isolation of the analogous [Mo(C(4)H(3)N(2)S)(2)(NNC(5)H(4)N)(HNNHC(5)H(4)N)] (11) and the seven-coordinate monohydrazine core complex [Mo(C(4)H(3)N(2)S)(3)(NNC(5)H(4)N)].CH(2)Cl(2) (12). In similar fashion, the reaction of 2 with pyridine-2-thiol yielded a complex structurally analogous to 8, [Tc(C(5)H(4)NS)(2)(NNC(5)H(4)N)(HNNC(5)H(4)N)] (7). Crystal data for 3, C(10)H(10)Cl(3)N(6)Re: triclinic, P&onemacr;, a = 7.527(2) Å, b = 7.599(2) Å, c = 13.118(3) Å, alpha = 106.55(3) degrees, beta = 90.28(3) degrees, gamma = 93.83(3) degrees, V = 717.4(4) Å(3), Z = 2. For 4, C(16)H(27)Cl(3)N(7)ORe: orthorhombic, P2(1)2(1)2(1), a = 7.503(2) Å, b = 10.3643(2) Å, c = 30.1590(5) Å, V = 2345.20(6) Å(3), Z = 2. For 5, C(6)H(12)Cl(3)N(8)Re: monoclinic, P2(1)/n, a = 9.093(2) Å, b = 11.105(2) Å, c = 14.295(3) Å, beta = 94.71(3) degrees, V = 1438.6(7) Å(3), Z = 4. For 6, C(10)H(11)Cl(3)N(6)Mo: monoclinic, P2(1)/c, a = 15.366(3) Å, b = 7.804(2) Å, c = 12.378(3) Å, beta = 95.92(3) degrees, V = 1476.4(5) Å(3), Z = 4. For 7, C(20)H(17)N(8)S(2)Tc: monoclinic, P2(1), a = 8.827(2) Å, b = 9.278(2) Å, c = 13.304(3) Å, beta = 98.92(3) degrees, V = 1076.5(5) Å(3), Z = 2, 2564 reflections. For 8, C(20)H(17)N(8)S(2)Re: monoclinic, P2(1), a = 8.848(2) Å, b = 9.190(2) Å, c = 13.293(3) Å, beta = 98.89(3) degrees, V = 1067.9(5) Å(3), Z = 2. For 9, C(18)H(15)N(10)S(2)Re: monoclinic, P2(1), a = 8.796(2) Å, b = 9.008(2) Å, c = 13.208(3) Å, beta = 97.90(3) degrees, V = 1036.6(5) Å(3), Z = 2. For 12, C(18)H(15)N(9)S(3)Cl(2)Mo: monoclinic, P2(1)/n, a = 10.52900(10) Å, b = 15.1116(3) Å, c = 15.8193(3) Å, beta = 108.4790(10) degrees, V = 2387.23(7) Å(3), Z = 4. Complexes 2 and 3 serve as models for the binding of Tc(V)-oxo and Re(V)-oxo species to hydrazinonicotinamide (HYNIC)-conjugated chemotactic peptides. Furthermore, since the use of the pyrimidinethiol coligand in the {(99m)Tc-HYNIC-peptide} radiochemical species results in favorable pharmacokinetics, the thiolate derivatives 8 and 9 provide models for possible modes of interaction of metal-hydrazine cores with coligands in the radiopharmaceutical reagents.

Technetium-99m antibodies labeled with MAG3 and SHNH: an in vitro and animal in vivo comparison

The in vitro stability and animal pharmacokinetics of 99mTc bound to Sandoz and C110 IgG antibodies via a modified MAG3 has been compared with the hydrazino nicotinamide (SHNH) moiety as standard. For both antibodies, the stabilities of the label to challenge at up to 50:1 cysteine: IgG molar ratio were comparable, but at higher molar ratios, MAG3 showed greater instabilities. For the Sandoz antibody, size-exclusion HPLC analysis of 37 degrees C serum incubates and plasma samples from injected mice showed no clearly distinguishable differences. In the C110 case, some increased high molecular weight radioactivity was apparent with MAG3. Biodistributions in normal mice showed significant differences only in liver (Sandoz) and liver, spleen, intestines, stomach, and blood (C110), with SHNH usually providing higher levels. Thus, for two different antibodies and under the conditions of this study, the MAG3 chelator provided a 99mTc label with properties similar to that of SHNH moiety.

Technetium-99m labelled hydrazinonicotinamido human non-specific polyclonal immunoglobulin G for detection of infectious foci: a comparison with two other technetium-labelled immunoglobulin preparations

Recently a new linker - hydrazinonicotinate (HYNIC) - was introduced for labelling of proteins and peptides with technetium-99m. HYNIC and other linkers have been used for labelling of human non-specific polyclonal immunoglobulin G (hIgG) with 99mTc for the detection of infections. In this study we compared the tissue distribution of three different 99mTc-hIgG preparations in groups of five Wistar rats with a focal intramuscular infection with Staphylococcus aureus. We compared 99mTc-HYNIC-hIgG with 99mTc-hIgG labelled via the so-called Schwarz method (reduction of disulphide bonds) and with the 99mTc-labelled commercially available Technescan-HIG. Unlike the HYNIC linker, in the two other labelling methods free sulph-hydryl groups are involved in the binding of 99mTc. High-performance liquid chromatography analysis of the labelled preparations and of plasma samples revealed aggregate or polymer formation in all three agents; this was least pronounced in the product labelled by means of the Schwarz method. The tested preparations did not show signs of degradation in vitro. The difference in linker chemistry was reflected in the tissue distribution. Thus the biodistribution of 99mTc-HYNIC-hIgG was significantly different from the distribution of the two other preparations: abscess (1.4%+/-0.2%ID/g), muscle, liver, spleen, plasma, lung, bone marrow, and small intestine concentrations were higher at 24 h p.i.; kidney uptake (1.19%+/-0.08%ID/g) was significantly lower. The abscess-to-plasma and the abscess-to-muscle ratios (0.5 and 11, respectively), however, were in the same range for the three preparations tested. Quantitative analysis of the scintigraphs revealed that the total body clearance of 99mTc-HYNIC-hIgG was significantly slower than for the other agents. The abscess uptake of 99mTc-HYNIC-hIgG as a percentage of the remaining body activity was significantly higher. Based on its high abscess uptake, its low uptake in the kidneys and the high percentage of its abscess uptake in relation to the remaining body activity, we conclude that 99mTc-HYNIC-hIgG seems superior to the two other preparations tested for the detection of infections.