Biomedical subjects

C S John

Publications and source records attributed to C S John.

25 records · Page 2Linked to original sources

PubMed1992

Synthesis, characterization and biodistribution of a new hexadentate aminethiol ligand labeled with Tc-99m.

A new hexadentate aminethiol ligand (TACNS) derived from triazacyclononane was synthesized and characterized for the development of technetium radiopharmaceuticals. The ligand formed a neutral, lipophilic and stable complex with [99mTc]pertechnetate in the presence of tin(II)tartarate as a reducing agent. The biodistribution of [99mTc]TACNS indicates slight uptake in brain (0.23% ID/organ at 5 min) with a washout at 30 min to 0.14% ID/organ. A small uptake in heart (0.48% ID at 5 min) was also observed. The characterization of [99mTc]TACNS complex using single crystal x-ray analysis and mass spectroscopy has shown that an Sn-N3S3 complex was formed in which tin is oxidized from Sn(II) to Sn(IV). Pertechnetate was incorporated into the complex as counter anion. The nature of the species formed with Tc-99 and "no-carrier-added" [99mTc]pertechnetate is different as confirmed by ratio TLC. From these results, it is demonstrated that sometimes it may be difficult to predict the structure of new technetium radiopharmaceuticals, especially when stannous ion is used as a reducing agent. Moreover, the nature of the chemical species may not be the same at millimolar and at nanomolar levels.

Animals↗

PubMed1991

Biolocalization and cell labeling properties of neutral-lipophilic 99mTc-amine-phenol chelates.

99mTc-diamine-diphenol chelates are neutral lipophilic chelates exhibiting good stability in aqueous solutions. The cell labeling and biolocalization properties of four different 99mTc-amine-phenol complexes were determined. All four chelates readily labeled leukocytes and RCBs in high yields. Even though 99mTc was retained by the cells, the elution rate of 99mTc from the labeled cells in plasma at 37 degrees C was unacceptably high for potential utility in scintigraphic imaging. The uptake of 99mTc in brain or heart following i.v. injection of the chelates in rats was low and clearance of activity from the blood was slow.

Animals↗

PubMed1991

Preparation, radiolabeling and biodistribution of a new class of bisaminothiol (BAT) ligands as possible imaging agents.

In developing new ligands as potential brain and heart perfusion imaging agents two ligands based upon N2S2 donor atoms with the biphenyl backbone were synthesized. Biphenyl-2,2'-bis(N-1-amino-2-methyl-propane-2-thiol) (BP-BAT-TM) and biphenyl-2,2'-bis(N-1-amino-2-ethyl-butane-2-thiol) (BP-BAT-TE) form stable, neutral and lipid soluble complexes with [99mTc]pertechnetate in the presence of tin(II) tartarate as a reducing agent. The [99mTc]BP-BAT-TM complex penetrates the blood-brain barrier following i.v. injection into rats. Washout from the brain is fast, indicating no retention. The biodistribution of [99mTc]BP-BAT-TE in rats showed an initial heart uptake (0.8%/organ, at 2 min) and a slow washout (0.74% at 15 min). No brain uptake was found (0.05%). Significant uptake and retention in liver was observed. An imaging study of [99mTc]BP-BAT-TE in a monkey showed no brain uptake and a clear indication of liver uptake and gall bladder clearance. These results indicate that this ligand system may be suitable as the basic core structure for the development of new imaging agents. Further studies with structural variations in the biphenyl backbone are warranted to develop new 99mTc imaging agents for clinical applications.

Animals↗

PubMed1990

Labeling of human serum albumin with 105Rh-cysteine complexes.

The conjugation of a complex formed by reacting RhCl3 with cysteine to human serum albumin has been investigated. Approximately 50% of the rhodium (labeled with 105Rh) was converted to the complex. Conjugation of the complex to HSA via the ECDI method resulted in yields of approximately 40% of the total rhodium or approximately 80% of the Rh-cysteine complex. No conjugation was observed in the absence of the ECDI. At approximately equal molar concentrations of rhodium and HSA, an average of approximately 0.4 rhodium atoms per HSA molecule was achieved.

Cysteine↗

PubMed1990

Labeling of proteins using [105Rh]Rh-4-(p-aminobenzyl)-diethylenetriamine.

A bifunctional ligand 4-(p-aminobenzyl)-diethylenetriamine has been synthesized. 105Rh complexes with this ligand were prepared with an overall yield of 79% at pH 9.0 in bicarbonate buffer. The preformed complex was converted to the isothiocyanate derivative using thiophosgene. Conjugation yields of 75% with IgG and 85% with HSA could be obtained for a 4 h conjugation reaction. Affinity chromatography of human-IgG coupled to the rhodium complex in an anti-human IgG agarose gel indicated no denaturation of the labeled protein. The procedure reported here can be adapted for the preparation of 105Rh-labeled antibodies for therapeutic applications.

Immunoglobulin G↗

PubMedDate not supplied

Labeling of human IgG with rhodium-105 using a new pentadentate bifunctional ligand.

We report the labeling of human gamma globulin with the 105Rh complex of a new pentadentate bifunctional ligand, 1,7-bis(2-hydroxybenzyl)-4-(p-aminobenzyl)diethylenetriamine. Complexes of this ligand with 105Rh were prepared by refluxing rhodium carrier spiked with 105Rh at pH9 in bicarbonate buffer. The complex was treated with an excess concentration of thiophosgene to prepare the isothiocyanate derivative which was extracted into CHCl3. The CHCl3 extract was dried and dissolved in DMF and reacted with a borate solution of human gamma globulin. Labeling yields were generally high and varied from 73% to 93%, depending upon the concentration of human gamma globulin and the isothiocyanate derivative of the complex used. The overall recovery of rhodium activity varied from 59% to 75% without taking into account activity lost due to decay. The conjugation reaction was complete by 4 h. From 0.4 to 8.5 atoms of Rh could be incorporated per molecule of protein by this method. The activated isothiocyanate complex did not show any degradation when stored at room temperature for up to 4 days and then used for conjugation.

Chelating Agents↗

PubMedDate not supplied

99mTc-labeled sigma-receptor-binding complex: synthesis, characterization, and specific binding to human ductal breast carcinoma (T47D) cells.

sigma-Receptors have recently been shown to be expressed in a variety of human tumor cells. In an attempt to prepare 99mTc chelates that would bind to sigma-receptors and be useful for imaging sigma-receptor-positive tumors, we have synthesized and characterized a bisaminothiol (BAT) chelate appended with a sigma-receptor pharmacophore. The synthesis of target ligand VII was accomplished in three steps starting from bicyclic imidazolidino[1,2-d]dithiazapine. The labeling of the BAT ligand with 99mTc was carried out in high yields (> 80%) using stannous tartarate as a reducing agent, resulting in the target sigma-receptor-binding chelate [99mTc]BAT-EN6, III. Similarly, 99gTc chelate with ligand VII was prepared from ammonium pertechnetate by reduction with stannous tartarate. 99nTc-radiolabeled chelate was purified by reversed phase HPLC, and cell binding with human breast ductal carcinoma (T47D) was performed. A high degree of specific binding (90-97%) was obtained when sigma-receptor ligands such as halogenated phenylethylenediamines were used to determine nonspecific binding. A modest affinity dose-dependent inhibition of binding was found with BD1008, I, and 4-IPEMP, II (IC50 = 47 +/- 2 and 59 +/- 5 nM, respectively), known sigma-ligands. No specific binding was found with [99mTc]BAT, VIII [without appended sigma-pharmacophore (N-alkyl-substituted ethylenediamine)], showing that biological activity resulted from the pendent pharmacophore. 99gTc complex was found to be a potent inhibitor (Ki = 42.7 +/- 8.5 nM) of [3H]DTG binding in guinea pig brain membranes. Scatchard analysis of [99mTc]BAT-EN6 (spiked with [99gTc]BAT-EN6) binding in T47D breast cancer cells showed a saturable binding, with a Kd of 43.5 +/- 14.7 nM and a Bmax of 3121 +/- 130 fmol/(mg of protein). A biodistribution study of [99mTc]BAT-EN6 chelates in Sprague Dawley rats showed hepatic clearance, as expected. A blocking study at 4 h postinjection using 2 mumol of BD1008 with [99mTc]BAT-EN6 showed a significant decrease of radiopharmaceutical in liver (15.32 vs 22.31% ID/organ) and kidney (1.01 vs 2.21% ID/ organ), organs known to possess high concentrations of sigma-receptors. These results imply that [99mTc]BAT-EN6 binds with high affinity to sigma-receptors expressed in human breast tumor cells, and it may be useful for imaging breast cancer.

Animals↗