The stability of99mTc phosphorus compounds in plasma both in vivo and in vitro

The in vivo and in vitro stability of^99mTc hydroxyethlylidene diphosphonate, 99^mTc methylenediphosphonate and^99mTc pyrophosphate in plasma has been studied using paper chromatographic technique as the analytical tool. The results indicate that the amounts of^99mTc activity found both at the origin and R_f range of^99mTcO₄ ^? for in vivo experiments are slightly greater than those for either in vitro or control experiments. However, this amount of^99mTc activity represents about 0.16–0.4% of the injected dose. Therefore, it is suggested that^99mTc phosphorus radiopharmaceuticals are stable in vivo and neither oxidation nor hydrolysis of these bone imaging agents occurs in the blood.     

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.     

Development of electrochemical labelling procedures using MEK extracted99mTc

Electrolytic labelling procedures have been reported for various^99mTc radiopharmaceuticals which differ widely in the choice of the electrodes, working pH, applied voltage and the quantity of current passed. The authors have studied the electrolytic labelling of^99mTc EHDP, gluconate and glucoheptonate with MEK extracted^99mTc using tin electrodes under different experimental conditions. The results have, shown that these compounds can be efficiently labelled with^99mTc in a single step procedure avoiding multiple pH adjustments. Labelling of human serum albumin microspheres suitable for lung imaging with^99mTc by the electrolytic method is also reported.     

A novel electrochemical <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generator

A novel electrochemical process to avail clinical grade ^99mTc from (n,γ)⁹⁹Mo has been demonstrated. The electrochemical parameters were optimized to maximize the ^99mTc yield with minimal ⁹⁹Mo contamination. ⁹⁹Mo/^99mTc generators containing up to 29.6 GBq (800 mCi) ⁹⁹Mo were developed and their performance were extensively evaluated for 10 days without changing the operating conditions. Very high radioactive concentration of ^99mTcO₄ ⁻ of acceptable quality, commensurate with hospital radiopharmacy requirements could be availed from the system with >90% yield. The compatibility of the product for the formulation of ^99mTc labeled radiopharmaceuticals such as ^99mTc-DMSA and ^99mTc-EC was found to be satisfactory in terms of high labeling yields. The proposed route represents an important step for enhancing the scope of accessing clinical grade ^99mTc from low specific activity (n, γ)⁹⁹Mo.     

Radiopharmaceuticals for renal studies: Evaluation of protein binding

Determination of total in vitro protein binding was evaluated for the following radiopharmaceuticals:^99mTc-diethylenetriaminepentaacetic acid (DTPA),^99mTc-dimercaptosuccinic acid (DMSA),^99mTc-glucoheptonate (GH) and^99mTc-fosfomycin (PHO). For that they were incubated wtih human serum at 37°C. After three and sixty minutes of incubation, the bound fraction was evaluated by two different methods: gel filtration and precipitation with trichloroacetic acid (TCA). The percentage of the^99mTc-kidney agents bound by human serum proteins is different for each one. Determination by TCA precipitation always leads to higher results. For renal imaging agents (DMSA, GH and PHO) the percentage of binding by each serum proteic constituent was also evaluated by electrophoretic analysis. All proteic constituents of human serum bind with those radiopharmaceuticals but the percentage of binding is different in accordance with both the radiopharmaceutical and the proteic constituent.     

99mTc-labeling and in vitro characterization of N4- and N3S-RGDS-derivative peptides

The aim of this work was to characterize the in vitro behavior of N4- and N3S-RGDS-derivative peptides labeled with ^99mTc. Peptides AGGG-Abu-GRGDSPK-NH₂ (F22) and C(acm)-GGG-Abu-GRGDSPK-NH₂ (SMA1) were synthesized by solid phase. The stability of ^99mTc-labeled peptides was assessed in a 30-fold molar excess of cysteine and in plasma. The affinity for plasma proteins was also evaluated. Labeling yield was >95% for both peptides. ^99mTc-F22 was not stable in presence of cysteine, but 63% of ^99mTc remained chelated to SMA1 up to 24 hours. Both peptides showed low affinity to plasma proteins. N3S-RGDS-derivative peptide (SMA1) showed more stable coordination binding with ^99mTc and a higher stability in plasma with regard to N4-RGDS-derivative peptide (F22).     

Technetium-99m Radiopharmaceuticals for Ideal Myocardial Perfusion Imaging: Lost and Found Opportunities

The favorable nuclear properties in combination with the rich coordination chemistry make technetium-99m the radioisotope of choice for the development of myocardial perfusion tracers. In the early 1980s, [^99mTc]Tc-Sestamibi, [^99mTc]Tc-Tetrofosmin, and [^99mTc]Tc-Teboroxime were approved as commercial radiopharmaceuticals for myocardial perfusion imaging in nuclear cardiology. Despite its peculiar properties, the clinical use of [^99mTc]Tc-Teboroxime was quickly abandoned due to its rapid myocardial washout. Despite their widespread clinical applications, both [^99mTc]Tc-Sestamibi and [^99mTc]Tc-Tetrofosmin do not meet the requirements of an ideal perfusion imaging agent due to their relatively low first-pass extraction fraction and high liver absorption. An ideal radiotracer for myocardial perfusion imaging should have a high myocardial uptake; a high and stable target-to-background ratio with low uptake in the lungs, liver, stomach during the image acquisition period; a high first-pass myocardial extraction fraction and very rapid blood clearance; and a linear relationship between radiotracer myocardial uptake and coronary blood flow. Although it is difficult to reconcile all these properties in a single tracer, scientific research in the field has always channeled its efforts in the development of molecules that are able to meet the characteristics of ideality as much as possible. This short review summarizes the developments in ^99mTc myocardial perfusion tracers, which are able to fulfill hitherto unmet medical needs and serve a large population of patients with heart disease, and underlines their strengths and weaknesses, the lost and found opportunities thanks to the developments of the new ultrafast SPECT technologies.     

Organometallic Tc-technetium(I)- and Re-rhenium(I)-folate derivatives for potential use in nuclear medicine

The folate receptor (FR) is a high affinity membrane protein which is overexpressed on a wide variety of tumor cells, but highly restricted in normal tissues. Therefore folate derivatives labeled with short living isotopes such as ^99mTc (γ, t_1/2 = 6 h) or ¹⁸⁸Re (β⁻, t_1/2 = 17 h) could be used for tumor diagnosis and therapy. In this respect there is a great interest to develop organometallic technetium(I) and rhenium(I) modified folate radiopharmaceuticals. For this purpose folic acid was functionalized with a tridentate picolylamine monoacetic acid chelating system. The chelating system was selectively coupled via an aminohexane spacer to the γ- or α-carboxyl group of the glutamate moiety of folic acid to obtain the corresponding γ- or α-folate derivative or - if directly attached to pteroic acid - the pteroate derivative. The derivatives were reacted with the precursor [M(OH₂)₃(CO)₃]⁺ (M = ^99mTc, Re) to form uniform organometallic folate complexes under mild reaction conditions. All compounds were chemically characterized by means of NMR, MS, IR and HPLC. The determination of the IC₅₀-values for the PAMA-γ-folate derivative (100 nM) and the corresponding organometallic rhenium complex (110 nM) proved retained receptor binding properties. The radiolabeling with [^99mTc(OH₂)₃(CO)₃]⁺ was achieved in excellent yield (>95%) at low ligand concentration (10⁻⁴ M). The cell binding (>45% of total activity) and internalization (>15% of total activity) of all ^99mTc-complexes was very high and specificity for the FR was proved by their complete displacement with excess folic acid. The ^99mTc-complexes were positively tested for their plasma stability and for the absence of binding to plasma proteins.     

Radiocharacterization of the 99mTc�Crufloxacin complex and biological evaluation in Staphylococcus aureus infected rat model

^99mTc?Crufloxacin (^99mTc?CRUN) complex was prepared by reaction of different amounts of reduced sodium pertechnetate with different amount of Rufloxacin (RUN) antibiotic for the in vivo scintigraphic localization of the Staphylococcus aureus (S. aureus) infectious foci in Male Wister Rats (MWR) model. The ^99mTc?CRUN complex was radiochemically and biologically characterized in terms of radiochemical stability in saline, serum, in vitro binding with S. aureus and biodistribution in artificially infected with S. aureus MWR. The ^99mTc?CRUN complex showed stability more than 90% up to 240 min in normal saline with a maximum stability value of 98.10 ± 0.18% at 30 min after reconstitution. At 37 °C the complex showed in vitro permanence in serum up to 16 h with 13.90% side products during incubation. The ^99mTc?CRUN complex showed saturated in vitro binding with S. aureus at different intervals with a maximum uptake value of 71.50%. Infected to normal muscle, infected to inflamed and inflamed to normal muscles ratios were approximately 6.04, 4.31 and 1.40. Based on the stability of the complex in saline, serum, in vitro binding with S. aureus and biodistribution results, the ^99mTc?CRUN complex is recommended for in vivo scintigraphic localization of the S. aureus in vivo infectious foci in human.     

Evaluation of fresh and old eluate of <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generators used for labeling of different pharmaceutical kits

Summary Sixty ⁹⁹Mo/^99mTc wet column generators, loaded with two different ⁹⁹Mo activities, were analyzed in order to assess the quality of their eluates. Each elution was used for labeling of different radiopharmaceuticals, in order to evaluate whether “risky” elutions, namely those performed just after generator delivery and at 72 hours or more from the last elution, could be conveniently employed when fresh available radioactivity is not enough for the planned labeling or when shipping problems arise, or delay in delivery of a new generator occurs. Radiochemical quality control of all radiopharmaceuticals labeled with these elutions was performed. The elutions differed mainly in ⁹⁹Tc ground state (^99gTc) and amounts of oxidizing impurities. Radiolabeling procedures, however, were not affected, suggesting that these “risky” elutions might be appropriately used, in “emergency” conditions, for labeling radiopharmaceuticals although their radiochemical purity control is recommended prior to patient administration.     

Effect of cuprous ion on labeling of three skeletal imaging agents with99mTc

The effect of increased content of copper on the radiochemical composition of three skeletal imaging agents:^99mTc(Sn)-methylene diphosphonate (MDP),^99mTc(Sn)-pyrophosphate (PYP) and^99mTc(Sn)-2,3-dicarboxypropane-1, 1-diphosphonate (DPD) was observed only in the case of^99mTc(Sn)-MDP. It was found that the radiochemical purity of this radiopharmaceutical falls to about 50% when the copper content reaches about 10^–5 mol dm^–3. According to the results of radiochemical and biological analyses, it could be concluded that with the increase of copper content, the content of free pertechnetate rises, too. The two other radiopharmaceuticals,^99mTc(Sn)-PYP and^99mTc(Sn)-DPD, were found to be stable under the given experimental conditions.     

Synthesis of 99mTc-cationic steroid antimicrobial-107 and in vitro evaluation

Ceragenins/cationic steroid antimicrobials (CSAs) are a group of cholic acid derivatives with many properties that make them favourable for application as anti-infective agents. CSA-107 is also a member of this group that was labelled with ^99mTc by using SnCl₂·2H₂O as reducing agent and Na–K tartrate as transchelating agent. Labelling efficiency was optimized by varying the amount of reducing agent, pH, and time of incubation. Labelling efficiency and the stability of ^99mTc-CSA-107 in human serum was determined by paper and thin layer chromatography, which were >95 and >90 % respectively. In vitro binding of ^99mTc-CSA-107 was >95 % determined by using Staphylococcus aureus bacteria.     

Two novel procedures of preparation for [Tc(CO)<Subscript>2</Subscript>(NO)]<Superscript>2+</Superscript>labeled by EHIDA and its biodistribution

To develop potential new Tc radiopharmaceuticals, a novel compound [^99mTc(CO)₂(NO)(EHIDA)]⁰ (EHIDA: 2,6-diethylphenylcarbamoylmethyliminodiacetic acid) has been prepared by reacting [^99mTc(CO)₃)(EHIDA)]⁻ with NOBF₄ both in water and acetonitrile. The conversion of [^99mTc(CO)₃)(EHIDA)]⁻ to [^99mTc(CO)₂(NO)(EHIDA)]⁰ was supported by TLC, HPLC and eletrophoresis. The radiochemical purity (more than 99%) was proved by TLC and HPLC. The biodistribution in mice demonstrated that [Tc(CO)₂(NO)(EHIDA)]⁰ showed higher uptake in blood, kidney and lung (15 min, blood: 19.24±2.95; kidney: 13.61±3.49; lung: 10.81±1.09.) but a lower uptake in liver (15 min, 5.73±0.74). The slower clearances (120 min, blood: 12.75±1.34; kidney: 13.61±3.49) from blood and kidney were also found. This research describes two methods for the conversion of [^99mTc(CO)₃]⁺ into [^99mTc(CO)₂)(NO)]²⁺ by using NOBF₄ as the source of NO⁺ both in organic solvent and water. The latter method offers the possibility to introduce the NO-group in high yield in water.     

Purity control of the radiopharmaceutical thiamine pyrophosphate-Sn-99mTc

A new purity control method was developed in order to assure the radiochemical purity of thiamine pyrophosphate-Sn-^99mTc. The method described consists in ascending cromatography using Whatman N^o 1 for support and 5% sodium citrate as solvent. It is capable of detecting free^99mTcO ₄ ^– and colloid formation, the most frequent impurities found in^99mTc radiopharmaceuticals.     

Synthesis and preclinical pharmacological evaluation of a novel 99mTc–shikonin as a potential tumor imaging agent

Shikonin was isolated from Ratanjot pigment then the obtained shikonin was well characterized. This study is aimed to optimize radiolabeling yield of shikonin with ^99mTc with respect to factors that affect the reaction conditions such as shikonin amount, SnCl₂·2H₂O amount, reaction time and pH of the reaction mixture. In vitro stability of the radiolabeled complex was checked and it was found to be stable for up to 6?h. Biodistribution studies showed that, ^99mTc?Cshikonin accumulate in tumor sites with higher T/NT than other currently available ^99mTc(CO)₃-VIP, ^99mTc?Cnitroimidazole analogues and ^99mTc?Cpolyamine analogues indicating that shikonin deliver ^99mTc to the tumor sites with a percentage sufficient for imaging and can overcome many drawbacks of other radiopharmaceuticals used for tumor imaging.     

Synthesis and biodistribution of two novel 99mTc “3+1”mixed ligand complexes as potential brain perfusion agents

The research in the last decade has been mainly aimed at the development of technetium-99m radiopharmaceuticals, among which are the “3+1”mixed ligand complexes. Two novel [^99mTc]“3+1”mixed ligand complexes each carrying the tridentate ligand, the N-(o-Methylthiophenyl)ethylenediamine or the N-(o-Methylthiophenyl)-b-mercaptoacetamide in combination with monothiolate coligand were produced using stannous chloride as reductant and glucoheptonate as transfer ligand. The identification of [^99mTc]-6 and [^99mTc]-7 was established by thin layer chromatography. The radiochemical purity of two complexes was over 90%. Biodistribution data in mice showed that both [^99mTc]-6 and [^99mTc]-7 can penetrate the intact blood-brain barrier and exhibited retention in mice brain. The brain uptakes (%ID/g) were 1.76, 1.17, 0.90 and 0.68, 0.38 ,0.37 at 2, 30, and 60 minutes i.v. postinjection for [^99mTc]-6 and [^99mTc]-7, respectively. Examples in this report comfirm us that it is promising to develop ^99mTc complexes as potential brain perfusion agents based on modifying either the tridentate or the monodentate ligands. This revised version was published online in August 2006 with corrections to the Cover Date.     

99mTc-ceftriaxone, as a targeting radiopharmaceutical for scintigraphic imaging of infectious foci due to Staphylococcus aureus in mouse model

^99mTc-labeled antibiotics have opened an exciting field of research in infectious diseases diagnosis. Direct labeling of ceftriaxone with ^99mTc was carried out using the various amounts of ceftriaxone and SnCl₂·2H₂O at different pH and incubation time intervals to find the highest radiochemistry efficiency with high stability at room temperature and human blood serum. ITLC-SG and HPLC were performed to measure the radiochemical purity of the conjugate. The binding study showed 45 % specific binding to Staphylococcus aureus. The biodistribution study and scintigraphic imaging showed the localization of ^99mTc-ceftriaxone at the site of infection in comparison with normal and inflamed muscles with high sensitivity and specificity in mouse model. The results showed that ^99mTc-ceftriaxone is a promising candidate as a targeting radiopharmaceutical for Staphylococcal infection imaging in humans which needs further investigations.     

Impact of Different [Tc(N)PNP]-Scaffolds on the Biological Properties of the Small cRGDfK Peptide: Synthesis,In Vitro and In Vivo Evaluations

Background: The [^99mTc][Tc(N)(PNP)] system, where PNP is a bisphosphinoamine, is an interesting platform for the development of tumor ‘receptor-specific’ agents. Here, we compared the reactivity and impact of three [Tc(N)(PNP)] frameworks on the stability, receptor targeting properties, biodistribution, and metabolism of the corresponding [^99mTc][Tc(N)(PNP)]-tagged cRGDfK peptide to determine the best performing agent and to select the framework useful for the preparation of [^99mTc][Tc(N)(PNP)]-housing molecular targeting agents. Methods: cRGDfK pentapeptide was conjugated to Cys and labeled with each [Tc(N)(PNP)] framework. Radioconjugates were assessed for their lipophilicity, stability, in vitro and in vivo targeting properties, and performance. Results: All compounds were equally synthetically accessible and easy to purify (RCY ≥ 95%). The main influences of the synthon on the targeting peptide were observed in in vitro cell binding and in vivo. Conclusions: The variation in the substituents on the phosphorus atoms of the PNP enables a fine tuning of the biological features of the radioconjugates. ws[^99mTc][Tc(N)(PNP3OH)]– and [^99mTc][Tc(N)(PNP3)]– are better performing synthons in terms of labeling efficiency and in vivo performance than the [^99mTc][Tc(N)(PNP43)] framework and are therefore more suitable for further radiopharmaceutical purposes. Furthermore, the good labeling properties of the ws[^99mTc][Tc(N)(PNP3OH)]– framework can be exploited to extend this technology to the labeling of temperature-sensitive biomolecules suitable for SPECT imaging.     

Influence of bilirubin on the distribution of99mTc-HIDA and99mTc-IODIDA in rats and their interaction with HSA

The interaction of bilirubin and^99mTc-HIDA and^99mTc-IODIDA has been studied in rats. The mechanism of this interaction has been examined at the level of binding with human serum albumin (HSA) by the in vitro method. Percentage of binding with HSA, and affinity constants for^99mTc-IODIDA were determined with and without bilirubin. Bilirubin was labeled with^99mTc and its interaction with HSA was also examined.