Tumor affinity of 99mTc-labeled radiopharmaceuticals, 99mTc-Sn-urokinase and 99mTc-Sn-mannitol

Biolgic distribution of 99mTc-labeled fibrinolytic agent, urokinase, and 99mTc-labeled mannitol, which was obtained as a side-product in the preparation of 99mTc(Sn)-urokinase, have been studied in Ehrlich's tumor-bearing mice to get a promising indicator for the positive delineation of malignant tumor. The preparation of 99mTc-labeled radiopharmaceuticals, 99mTc-UK and 99mTc-Man, was made by the reduction with stannous chloride and labeling efficiency was examined by Sephadex G-25M gel chromatography and by silica gel plate thin layer chromatography. Labeling yield of 99mTc-UK by Sephadex G25M in 0.9% NaCl eluant was 13% and that of 99mTc-Man by TLC in 85% methanol solvent was over 95%. A higher uptake to the implanted solid tumor tissue in mice was found in 99mTc-Man than in 99mTc-UK, of which the excellent tumor accumulation was expected from the positive delineation of malignant tumor with 131I-fibrinogen, 131I-fibrinogen antibody and 125I-plasmin. The poor result in 99mTc-UK, however, may be attributed to the poor fibrinolytic activity of Ehrlich's tumor. In biologic distribution of 99mTc-UK was found high concentration for liver kidney and stomach. In the other hand, a higher tumor tissue uptake, a fast blood disappearance and a low concentration for different organs were found in biologic distribution of 99mTc-Man. Therefore, 99mTc-Man may be assumed as a more preferable 99mTc-labeled tumor localizing radiopharmaceuticals, to which it would be needed as absolute biologic characteristics that 99mTc-labeled compounds possess a high tumor uptake as well as a fast blood disappearance with a low uptake for different organs. However, the possible delineation with 99mTc-labeled fibrinolytic agents, including urokinase and streptokinase, may be promised for malignant tumors in human-subject, which generally have a higher activity in fibrinogenesis than in fibrinolysis.     

Study on tumor affinity of technetium-99m-labeled radiopharmaceuticals. (1) 99mTc-pertechnetate, 99mTc-human serum albumin, and 99mTc-trasylol]

This paper describes biologic distributions, sequential images and macroautoradiograms of 99mTcO4 (pertechnetate), 99mTc-Sn-HSA (human serum albumin) and 99mTc-Sn-TSL (trasylol) in tumor-bearing mice as the first report on tumor affinity of 99mTc-labeled radiopharmaceutical. (1) Maximum tumor concentration (% administered dose/g of tissue weight) of 99mTcO4, 99mTc-HSA and 99mTc-TSL in Ehrlich's tumor-bearing mice resulted in 2.03+/-0.57 at 1 hr, 4.02+/-0.19 at 3 hr and 1.97+/-0.31 at 1 hr respectively. (2) However, tumor to blood concentration ratio of 99mTc-HSA was lowest among them. (3) The corrected tumor accumulation (% 100g dose/g of tissue wt.=% dose/% body weight) of 99mTc-TSL to Ehrlich's tumor in mouse was not different from that of Yoshida's sarcoma in rat, on the contrary to our expectation that the tumor concentration of 99mTc-TSL in them might be different due to differency of the tissue fibrinolytic activity between the respective tumors. (4) Sequential images of the implanted tumor in mouse was best positively delineated with 99mTc-HSA. (5) Macroautoradiograms of Ehrlich's tumor with 99mTcO4, 99mTc-HSA and 99mTc-TSL demonstrated the following findings: all of them were not only accumulated markedly into the tumor cells which were shown as basophilic tissue with H?matoxylin-Eosin staining but also accumulated around the tumor tissue and on the interstitial tissue which were stained as eosinophilic tissue with the above same staining.     

Preparation of99Mo,132Te isotopes and99mTc,132I generators

Adsorption and desorption of⁹⁵Zr−⁹⁵Nb,⁹⁹Mo,¹⁰³Ru,¹³²Te and²³⁹Np in a HCl-alumina system were studied in order to purify⁹⁹Mo and¹³²Te obtained by the cation-exchange separation of fission products and to prepare highly pure^99mTc and¹³²I generators.⁹⁹Mo and¹³²Te, of which radionuclidic purity was over 99.99% and 99.999%, respectively, could be obtained by passing the cation-exchange separated Mo and Te fractions through alumina columns, by washing with HCl and finally by eluting⁹⁹Mo with 1M NH₄OH and¹³²Te with 3M NaOH. In order to raise the recovery of⁹⁹Mo and¹³²Te from the alumina columns, they should be eluted as quickly as possible after the adsorption. The direct use of the alumina column containing⁹⁹Mo or¹³²Te as the generator allowed milking of^99mTc or¹³²I, of which radionuclidic purity was over 99.999%. Milking yields of^99mTc with 0.1M HCl and¹³²I with 0.01M NH₄OH were 77% and 90%, respectively. The latter value was much higher than that in usual performance of the generator.     

Comparison of some physicochemical and pharmacokinetical parameters of 99mTc-PAH, 99mTc-MAG3 and 131I-OIH

The purpose of this study was to compare some physicochemical characteristics as well as pharmacokinetic behavior of ^99mTc-PAH, as a novel renal agent, with ^99mTc-MAG₃ and ¹³¹I-OIH. ^99mTc-PAH was prepared from lyophilized kit by adding ^99mTcO₄ ^–. Labeled complex was stabile and high radiochemical purity radiopharmaceutical, with a low percentage of protein bound to human albumin and hydrophilic character. In spite of its smaller renal uptake, ^99mTc-PAH gave satisfactory renal images. ^99mTc-PAH showed faster urinary elimination than ^99mTc-MAG₃ and similar to those one for ¹³¹I-OIH. The comparison of pharmacokinetic parameters of ^99mTc-PAH, ^99mTc-MAG₃ and ¹³¹I-OIH indicated the favorable characteristics of ^99mTc-PAH.     

In vivo and in vitro 99mTc-protein bound of renal agents: 99mTc-prylidinomethyltetracycline (99mTc-Sn-Pmt) and 99mTc-Sn-Gluco-ene-diolate (99mTc-Gluco)

Protein binding affects tissue distribution, plasma clearance and uptake of renal radiopharmaceuticals. The ^99mTc bound to plasma protein after incubation ^99mTc-Gluco-ene-diolate (^99mTc-Sn-Gluco) agent or ^99mTc-prylidinomethyl-tetracycline (^99mTc-Sn-PMT) agent with plasma protein. It was observed that the protein bound to ^99mTc is lesser extent with (^99mTc-Sn-Gluco) agent than with the ^99mTc-PMT agent. ^99mTc-Sn-PMT is excreted more rapidly than ^99mTc-Sn-Gluco. On the other hand the percentage binding to protein seems to depend on the origin of the protein and or the type of protein (human or animal). However lower human protein binding or higher protein binding were observed with ^99mTc-Sn-Gluco or with ^99mTc-Sn-PMT, respectively compared with the binding to rat protein. The unbroken down of the chemical form of the origin of these two agents and the highest of ^99mTc-Sn-Gluco remained as origin in urine indicate that ^99mTc-Sn-Gluco are more stable than ^99mTc-Sn-PMT.Concerning the type of protein binding to ^99mTc-Sn-PMT or to ^99mTc-Sn-Gluco, it was observed that Human Plasma Protein is greater binding than Human serum protein or than IgG.     

Synthesis, quality control and biodistribution of 99mTc-Kanamycin

Summary Kanamycin is an antibiotic used for treatment of infections when penicillin or other less toxic drugs cannot be used. Kanamycin was labeled with technetium-99m pertechnetate using SnCl₂^. 2H₂O as reducing agent. The labeling efficiency depends on the ligand/reductant ratio, pH, and volume of reaction mixture. Radiochemical purity and stability of ^99mTc-Kanamycin was determined by thin layer chromatography. Biodistribution studies of ^99mTc-Kanamycin were performed in rats and rabbits. A significantly higher accumulation of ^99mTc-Kanamycin was seen at sites of S. aureusinfected animals (rat/rabbit).     

Radiolabeling, quality control and kit formulation of a new 99mTc-labeled antibiotic: 99mTc-doxycycline hyclate

Since radiolabeled antibiotics specifically bind to the bacterial components they are promising radiopharmaceuticals for the precise diagnosis and detection of infectious lesions. Doxycycline hyclate (DOX) was chosen to investigate as a new radiolabeled antibacterial agent since its bacteriostatic activity against a wide variety of microorganisms. The aim of the present study is to develop simple and easy formulation of DOX with ^99mTc ready to use kit. ^99mTc-DOX was developed and standardized under varying conditions of reducing and antioxidant agent concentration, pH, radioactivity dose and reducing agent type. Labeling studies were performed by changing the selected parameters one by one and optimum labeling conditions were determined. After observing the conditions for maximum labeling efficiency and stability, lyophilized freeze dry kits were prepared accordingly. Radiochemical purity was determined with RTLC and RHPLC which was found more than >95 %. Two different freeze dry kits were formulated with optimum labeling conditions. The improved kits were found stable up to 6 months.     

Study on tumor affinity of technetium-99m-labeled radiopharmaceuticals. (2) 99mTc-Sn-diphosphonate (99mTc-EHDP), 99mTc-Sn-dimercaptosuccinic acid (99mTc-DMSA), and 99mTc-Sn-diethyl stilbestrol diphosphate (99mTc-DSDP)]

The authors have examined the tumor affinity of various 99mTc-labelled radiopharmaceuticals to Ehrlich's tumor for the purpose of delineating positively human malignant neoplasm. This paper includes biologic distributions of 99mTc-Sn-diphosphonate (99mTc-EHDP), 99mTc-Sn-dimercaptosuccinic acid (99mTc-DMSA) and 99mTc-Sn-diethyl stilbestrol diphosphate (99mTc-DSDP, 99mTc-Honvan) as the second report on the tumor affinity to the Ehrlich-bearing mice. (a) Tumor concentration of 99mTc-EHDP was lowest and the positive delineation of implanted tumor with 99mTc-EHDP was poorest in sequential images, though the active accumulation to some soft tissue maglinant neoplasms, the breast cancer and the thyroid cancer, has been reported. (b) Tumor concentration and tumor to blood ratio of 99mTc-DMSA were not so high on the contrary of our expectation that 197Hg-DMSA may show the high tumor concentration and the high tumor to blood ratio like 197Hg chlormerodrin as same renal scanning radiopharmaceuticals. (c) Tumor concentration of 99mTc-DSDP was highest. Tumor to blood concentration ratio, however, was lower than that of the above mentioned radiopharmaceuticals but tumor to liver ratio and/or tumor to lung ratio was over 1.0 at the earlier time. Biologic distribution of 99mTc-DSDP was similar to that of 32P labeled DSDP and then it is presumed that 99mTc is labeled at phosphate ester of DSDP which is dephospholytated immediately by phospholylase in vivo following the intravenous injection. Therefore, it may be assumed that the accumulation mechanism of 99mTc-DSDP to Ehrlich's tumor is related to the phospholylase activity in neoplasms but is not known precisely.     

Synthesis,characterization and biodistribution of 99mTc-Bioquin-HMPAO (99mTc-BH) as a novel brain imaging agent

Recently, the development of novel brain imaging agents has aroused much interest thanks to limited number of brain cancer or diseases diagnosis agents. It is aimed to synthesize a novel brain imaging agent including a promise for further studies on AD diagnosis potential and investigate its bioaffinity with biodistribution studies on healthy Balb/c mice. A novel radiolabeled agent was synthesized and characterized. Quality control of ^99mTc-BH was performed utilizing solvent extraction and chromatographic (Radio TLC and Radio HPLC) methods. Bioaffinity of the ^99mTc-BH was investigated on male Balb/c mice at various time points (5, 30, 60, 120 min post-injection). Paper electrophoresis showed that ^99mTc-BH has a neutral structure. Radiochemical purity of ^99mTc-BH was over 95 % with appropriate stability for imaging period. Selected brain regions have uptakes over 4 % ID/g following intravenous injection. Hippocampus has uptake approximately 10 % ID/g. ^99mTc-BH has shown brain uptake, so it may prove to be valuable for brain imaging as a novel technetium-labeled agent. Further investigations with AD animal model are our on going effort to show that this agent has AD diagnosis potential.     

Accumulation, elimination and retention of 99Tc by duckweed

This study deals with the accumulation dynamics of the long-lived fission product technetium (⁹⁹Tc) in duckweed. Duckweed serves as model for aquatic plants, because of its representative foliar uptake for ⁹⁹Tc. This study shows that ⁹⁹Tc is irreversibly accumulated and distributed over cytoplasm, chloroplasts and mitochondria. Autoradiography showed that ⁹⁹Tc was not transported to new biomass. Irreversible storage of ⁹⁹Tc in plant biomass means that steady-state situations cannot be interpreted as a balance between uptake and elimination of ⁹⁹Tc, but that ⁹⁹Tc continuously builds up in each single duckweed plant and overall Tc concentrations are averaged over new biomass.     

Preparation,molecular modeling and biodistribution of 99mTc-phytochlorin complex

Phytochlorin [21H, 23H-Porphine-7-propanoicacid, 3-carboxy-5-(carboxymethyl)13-ethenyl-18-ethyl-7,8-dihydro-2,8,12,17-tetramethyl-,(7S,8S)] was labeled with ^99mTc and the factors affecting the labeling yield of ^99mTc-phytochlorin complex were studied in details. At pH 10, ^99mTc-phytochlorin complex was obtained with a high radiochemical yield of 98.4 ± 0.6 % by adding ^99mTc to 100 mg phytochlorin in the presence of 75 μg SnCl₂·2H₂O after 30 min reaction time. The molecular modeling study showed that the structure of ^99mTc-phytochlorin complex presents nearly linear HO–Tc–OH unit with an angle of 179.27° and a coplanar Tc(N1N2N3N4) unit. Biodistribution of ^99mTc-phytochlorin complex in tumor bearing mice showed high T/NT ratio (T/NT = 3.65 at 90 min post injection). This preclinical study showed that ^99mTc-phytochlorin complex is a potential selective radiotracer for solid tumor imaging and afford it as a new radiopharmaceutical suitable to proceed through the clinical trials for tumor imaging.     

Desorption of99Mo from spent99Mo/99mTc generator

A simple method for desorption and purification of⁹⁹Mo from spent⁹⁹Mo/^99mTc generators is described. The alumina column was washed successively with 0.9% saline water, 35% H₂O₂, and then the⁹⁹Mo was eluted with 2M NH₄OH. Ammonia and residual H₂O₂ were removed by heating the eluate. Finally,⁹⁹Mo solution was passed through a 0.2 m membrane filter to remove precipitated aluminium hydroxide.     

Synthesis, structure elucidation, and redox properties of 99Tc complexes of lacunary Wells-Dawson polyoxometalates: insights into molecular 99Tc-metal oxide interactions

The isotope (99)Tc (β(max), 293.7; half-life, 2.1 × 10(5) years) is an abundant product of uranium-235 fission in nuclear reactors and is present throughout the radioactive waste stored in underground tanks at the Hanford and Savannah River sites. Understanding and controlling the extensive redox chemistry of (99)Tc is important in identifying tunable strategies to separate (99)Tc from spent fuel and from waste tanks and, once separated, to identify and develop an appropriately stable waste form for (99)Tc. Polyoxometalates (POMs), nanometer-sized models for metal oxide solid-state materials, are used in this study to provide a molecular level understanding of the speciation and redox chemistry of incorporated (99)Tc. In this study, (99)Tc complexes of the (α(2)-P(2)W(17)O(61))(10-) and (α(1)-P(2)W(17)O(61))(10-) isomers were prepared. Ethylene glycol was used as a "transfer ligand" to minimize the formation of TcO(2)·xH(2)O. The solution structures, formulations, and purity of Tc(V)O(α(1)/α(2)-P(2)W(17)O(61))(7-) were determined by multinuclear NMR. X-ray absorption spectroscopy of the complexes is in agreement with the formulation and structures determined from (31)P and (183)W NMR. Preliminary electrochemistry results are consistent with the EXAFS results, showing a facile reduction of the Tc(V)O(α(1)-P(2)W(17)O(61))(7-) species compared to the Tc(V)O(α(2)-P(2)W(17)O(61))(7-) analog. The α(1) defect is unique in that a basic oxygen atom is positioned toward the α(1) site, and the Tc(V)O center appears to form a dative metal-metal bond with a framework W site. These attributes may lead to the assistance of protonation events that facilitate reduction. Electrochemistry comparison shows that the Re(V) analogs are about 200 mV more difficult to reduce in accordance with periodic trends.     

99mTc-glucoheptonate-guanine: Synthesis, biodistribution and imaging in animals

The aim of the current study was to design a nucleotide-based radiopharmaceutical which could be labeled with ^99mTc and to investigate its radiopharmaceutical efficiency and stability. GHA (glucoheptonate) was used as bifunctional chelate. GHA was labeled with ^99mTc by SnCl₂ reduction method first, and then G (guanine) was conjugated with ^99mTc-GHA at 90 °C. In order to determine its radiopharmaceutical stability, thin layer radio chromatography (TLRC) and electrophoresis were employed. In addition, the results were confirmed using high performance liquid radio chromatography (HPLRC). Scintigraphic imaging was performed on rats with mammary tumors, while tissue distribution was determined on Albino Wistar rats. Labeling yield was found to be over 95% and the labeled complex maintained its stability during the study period. The lipophilicity of the ^99mTc-GHG was measured and the partition coefficient (logP) of the labeled compound calculated. The results demonstrated that the uptake of ^99mTc-GHG (^99mTc-glucoheptonate-guanine) reached its maximum at 3 hours p.i. in stomach and intestines. Main way of excretion was renal. Hepatobiliary excretion was also observed. In conclusion, ^99mTc-GHG may be useful as a nucleotide-based radiopharmaceutical for in vivo applications.     

MO tripeptide diastereomers (M=99/99mTc, Re): models to identify the structure of 99mTc peptide targeted radiopharmaceuticals

Biologically active molecules, such as many peptides, serve as targeting vectors for radiopharmaceuticals based on 99mTc. Tripeptides can be suitable chelates and are easily and conveniently synthesized and linked to peptide targeting vectors through solid-phase peptide synthesis and form stable TcVO complexes. Upon complexation with [TcO]3+, two products form; these are syn and anti diastereomers, and they often have different biological behavior. This is the case with the approved radiopharmaceutical [99mTcO]depreotide ([99mTcO]P829, NeoTect) that is used to image lung cancer. [99mTcO]depreotide indeed exhibits two product peaks in its HPLC profile, but assignment of the product peaks to the diastereomers has proven to be difficult because the metal peptide complex is difficult to crystallize for structural analysis. In this study, we isolated diastereomers of [99TcO] and [ReO] complexes of several tripeptide ligands that model the metal chelator region of [99mTcO]depreotide. Using X-ray crystallography, we observed that the early eluting peak (A) corresponds to the anti diastereomer, where the Tc=O group is on the opposite side of the plane formed by the ligand backbone relative to the pendant groups of the tripeptide ligand, and the later eluting peak (B) corresponds to the syn diastereomer, where the Tc=O group is on the same side of the plane as the residues of the tripeptide. 1H NMR and circular dichroism (CD) spectroscopy report on the metal environment and prove to be diagnostic for syn or anti diastereomers, and we identified characteristic features from these techniques that can be used to assign the diastereomer profile in 99mTc peptide radiopharmaceuticals like [99mTcO]depreotide and in 188Re peptide radiotherapeutic agents. Crystallography, potentiometric titration, and NMR results presented insights into the chemistry occurring under physiological conditions. The tripeptide complexes where lysine is the second amino acid crystallized in a deprotonated metallo-amide form, possessing a short N1-M bond. The pKa measurements of the N1 amine (pKa approximately 5.6) suggested that this amine is rendered more acidic by both metal complexation and the presence of the lysine residue. Furthermore, peptide chelators incorporating a lysine (like the chelator of [TcO]depreotide) likely exist in the deprotonated form in vivo, comprising a neutral metal center. Deprotonation possibly mediates the interconversion process between the syn and anti diastereomers. The N1 amine group on non-lysine-containing metallopeptides is not as acidic (pKa approximately 6.8) and does not deprotonate and crystallize as do the metallo-amide species. Three of the tripeptide ligands (FGC, FSC, and FKC) were radiolabeled with 99mTc, and the individual syn and anti isomers were isolated for biodistribution studies in normal female nude mice. The main organs of uptake were the liver, intestines, and kidneys, with the FGC compounds exhibiting the highest liver uptake. In comparing the diastereomers, the syn compounds had substantially higher organ uptake and slower blood clearance than the anti compounds.