Ultra-small particles of iron oxide as peroxidase for immunohistochemical detection.

Dimercaptosuccinic acid (DMSA) modified ultra-small particles of iron oxide (USPIO) were synthesized through a two-step process. The first step: oleic acid (OA) capped Fe(3)O(4) (OA-USPIO) were synthesized by a novel oxidation coprecipitation method in H(2)O/DMSO mixing system, where DMSO acts as an oxidant simultaneously. The second step: OA was replaced by DMSA to obtain water-soluble nanoparticles. The as-synthesized nanoparticles were characterized by TEM, FTIR, TGA, VSM, DLS, EDS and UV-vis. Hydrodynamic sizes and Peroxidase-like catalytic activity of the nanoparticles were investigated. The hydrodynamic sizes of the nanoparticles (around 24.4 nm) were well suited to developing stable nanoprobes for bio-detection. The kinetic studies were performed to quantitatively evaluate the catalytic ability of the peroxidase-like nanoparticles. The calculated kinetic parameters indicated that the DMSA-USPIO possesses high catalytic activity. Based on the high activity, immunohistochemical experiments were established: using low-cost nanoparticles as the enzyme instead of expensive HRP, Nimotuzumab was conjugated onto the surface of the nanoparticles to construct a kind of ultra-small nanoprobe which was employed to detect epidermal growth factor receptor (EGFR) over-expressed on the membrane of esophageal cancer cell. The proper sizes of the probes and the result of membranous immunohistochemical staining suggest that the probes can be served as a useful diagnostic reagent for bio-detection.

Vitamin E succinate-grafted-chitosan/chitosan oligosaccharide mixed micelles loaded with C-DMSA for Hg2+ detection and detoxification in rat liver.

AIM: To determine whether the use of a mixed polymeric micelle delivery system based on vitamin E succinate (VES)-grafted-chitosan oligosaccharide (CSO)/VES-grafted-chitosan (CS) mixed micelles (VES-g-CSO/VES-g-CS MM) enhances the delivery of C-DMSA, a theranostic fluorescent probe, for Hg2+ detection and detoxification in vitro and in vivo. METHODS: Mixed micelles self-assembled from two polymers, VES-g-CSO and VES-g-CS, were used to load C-DMSA and afforded C-DMSA@VES-g-CSO/VES-g-CS MM for cell and in vivo applications. Fluorescence microscopy was used to assess C-DMSA cellular uptake and Hg2+ detection in L929 cells. C-DMSA@VES-g-CSO/VES-g-CS MM was then administered intravenously. Hg2+ detection was assessed by fluorescence microscopy in terms of bio-distribution while detoxification efficacy in Hg2+-poisoned rat models was evaluated in terms of mercury contents in blood and in liver. RESULTS: The C-DMSA loaded mixed micelles, C-DMSA@VES-g-CSO/VES-g-CS MM, significantly enhanced cellular uptake and detoxification efficacy of C-DMSA in Hg2+ pretreated human L929 cells. Evidence from the reduction of liver coefficient, mercury contents in liver and blood, alanine transaminase and aspartate transaminase activities in Hg2+ poisoned SD rats treated with the mixed micelles strongly supported that the micelles were effective for Hg2+ detoxification in vivo. Furthermore, ex vivo fluorescence imaging experiments also supported enhanced Hg2+ detection in rat liver. CONCLUSION: The mixed polymeric micelle delivery system could significantly enhance cell uptake and efficacy of a theranostic probe for Hg2+ detection and detoxification treatment in vitro and in vivo. Moreover, this nanoparticle drug delivery system could achieve targeted detection and detoxification in liver.

An alternative approach to the preparation of (188)Re radiopharmaceuticals from generator-produced [(188)ReO(4)](-): efficient synthesis of (188)Re(V)-meso-2,3-dimercaptosuccinic acid.

A new efficient approach for the preparation of (188)Re radiopharmaceuticals starting from [(188)ReO(4)](-), produced at a carrier-free level through the (188)W/(188)Re generator system, is described. The reaction procedure was based on the combined action of different reagents and has been applied in detail to the preparation of the therapeutic agent (188)Re(V)-DMSA (H(2)DMSA [meso-2,3-dimercaptosuccinic acid]). The most efficient combination required the use of SnCl(2), oxalate ions, and gamma-cyclodextrin. These were reacted with [(188)ReO(4)](-) and H(2)DMSA to afford the final radiopharmaceutical in high radiochemical purity, at room temperature, and in weakly acidic solution. The role played by the various reagents in the reaction was investigated. It was found that SnCl(2) behaved as the actual reducing agent, whereas oxalate and gamma-cyclodextrin greatly enhanced the ease of reduction of [(188)ReO(4)](-) through the action of two hypothetical mechanisms. In the first step of the reaction, oxalate ions gave rise to the formation of Re(VII) complexes with the concomitant expansion of the coordination sphere of the metal. This process strongly favored the electron transfer between Sn(2+) and Re(+7) centers, giving rise to intermediate reduced rhenium complexes. These species were further stabilized by the formation of transient host-guest aggregates with gamma-cyclodextrin and finally converted into (188)Re(V)-DMSA through simple replacement of the coordinated ligands by H(2)DMSA.

Reliable preparation of 99mTc (V) DMSA by a simple modified method using a commercial kit for 99mTc (III) DMSA.

99mTc pentavalent dimercaptosuccinic acid [99mTc (V) DMSA], a useful agent for imaging thyroid medullary carcinoma and other tumors, can be reliably prepared by addition of NaHCO3 and then Na99mTcO4 to a commercial kit for 99mTc trivalent DMSA [99mTc (III) DMSA], followed by bubbling oxygen through the solution for 10 min. 99mTc (V) DMSA made by this method is radiochemically pure and stable for 24 h, and it gives a rat biodistribution similar to that of the agent made by previous methods. Clinical biodistribution and radiation dosimetry studies are planned.

Carrier effect on radiolabeling the polynuclear pentavalent rhenium-186 complex of dimercaptosuccinic acid at alkaline pH: 186Re(V)-DMS.

Radiolabeling with rhenium (Re-186, Re-188), a tumor agent to resemble the pentavalent polynuclear technetium complex of dimercaptosuccinic acid (99mTc[V]-DMS) has been reported for radiotherapeutical use. Nevertheless, despite the periodic analogies between both radiometals, differences in the redox potential and the carrier concentration have made the radiolabeling of the rhenium counterpart difficult. In the present study, the effect of the carrier contained in the reactor-produced Re-186 was estimated as an important factor relevant to the Re-186 radiolabeling of DMS at an alkaline pH. Great effect of the carrier Re with an inverse correlation with the stannous ion was an interesting phenomenon relevant for an assumption on the Sn participation in the complex. Under strict control of various labeling parameters, the 186Re(V)-DMS was made available with high yield (93-97%) at an alkaline pH and at room temperature. The great effect of carrier offers support to the polymeric or polynuclear nature of the rhenium complex of DMS as depicted in the drug design basis of its parent Tc(V)-DMS. The biodistribution studies of Re(V)-DMS showed mimetic characteristics with its parent Tc(V)-DMS drug.

Studies on the preparation and isomeric composition of 186Re- and 188Re-pentavalent rhenium dimercaptosuccinic acid complex.

The preparative conditions for 186Re(V)DMSA and 188Re(V)DMSA (DMSA = meso-dimercaptosuccinic acid), beta-emitting radiopharmaceuticals that have been shown to localize in medullary thyroid carcinoma, require modification depending on the amount of carrier rhenium and the chemical form and medium in which the rhenium is supplied. Preparative conditions are described for use with carrier-free 188ReO4- in saline, and for use with 186ReO4- in saline, sodium hydroxide or nitric acid. Preparation of 186Re(V)DMSA (carrier present up to 2 mg per 2.5 ml reaction volume) requires a DMSA:SnCl2:Re ratio of 10:5:1 at 100 degrees C for 30 min. Addition of excess nitric acid or hydrochloric acid up to a concentration of 155 mM does not reduce the yield from 100%. A commercial DMSA kit vial (e.g. Amerscan DMSA) can be used for preparation of 188Re(V)DMSA (carrier free) provided the required activity is in a volume of less than 1 ml per vial. A convenient method of concentrating the 188Re generator eluate to the required volume is described.

Analogy between tumor uptake of technetium(V)-99m dimercaptosuccinic acid (DMSA) and technetium-99m-MDP.

Sixty patients with a variety of malignant tumors were examined with Tc-99m(V) dimercaptosuccinic acid (DMSA) prepared by modification of a commercially available DMSA kit. Significant uptake of Tc-99m(V)-DMSA was observed in a number of tumors, offering additional clinically useful information. In the majority of cases in this study, however, the benefit of the Tc-99m(V)-DMSA image was limited because of low sensitivity. The most striking observation was the similarity between the tumor concentration of Tc-99m(V)-DMSA and the Tc-99m-MDP uptake in the tumor on the regular bone image. Therefore, patients with Tc-99m-MDP uptake in nonosseous tumor sites on the bone scan may be suitable candidates for tumor imaging with Tc-99m(V)-DMSA.

Preparation of [186Re]Re-DMSA and its bio-distribution studies.

99mTc(V)-DMSA is widely used for imaging medullary carcinoma and hence 186/188Re(V)-DMSA is suggested as a potential agent for treating medullary carcinoma. In the present paper, we report the work carried out for the preparation of [186Re]Re(V)-DMSA and it's bio-distribution studies in Wistar rats. The complex was prepared by reducing 186Re (100 micrograms, 0.54 microM, approximately 150 MBq) in the presence of DMSA (2 mg, 11 microM) with stannous chloride (0.4 mg, 2.2 microM) in acidic medium at pH 2. The reaction was taken to completion by heating the complex in a boiling water bath for 30 min. Bio-distribution studies carried out revealed that pharmacological behaviour of 186Re(V)-DMSA is similar to that of 99mTc(V)-DMSA except that the kidney uptake is marginally higher. The kidney uptake reduced significantly when the pH of the complex was adjusted to 8 prior to injection. The in vitro stability studies of this complex suggest that the product formed is stable and could be used for clinical trials.

Preparation and in vivo evaluation of 90Y-meso-dimercaptosuccinic acid (90Y-DMSA) for possible therapeutic use: comparison with 99mTc-DMSA.

INTRODUCTION: The aim of this study was to find out if (90)Y could form a stabile complex with meso-2,3-dimercaptosuccinic acid (DMSA) and if (90)Y-DMSA may have potential for tumor therapy in the palliative treatment of bone metastases. METHODS: The preparing of (90)Y-DMSA was carried out by varying experimental parameters, such as ligand concentration, pH, time, and temperature of the reaction, in order to maximize the labeling yield. Analysis of the complexes enclosed the radiochemical quality control (instant thin-layer chromatography, paper chromatography, and high-performance liquid chromatography), determination of pharmacokinetical parameters as well as biodistribution study in healthy male Wistar rats. In vitro stability of the complexes was tested too. RESULTS: (90)Y-DMSA could be prepared in high yields (>95%) under optimized conditions of reaction. Stability studies in saline and human serum in vitro showed no significant release of activity from the ligand over 24 hours and 10 days, respectively. The preliminary biodistribution results in rat at 2 hours indicated that (90)Y-DMSA, at both pH levels, was significantly retained into bone. The uptake in the kidneys was lower for (90)Y-DMSA at pH 8.0 then at pH 3.0. The retention in other organs was negligible. CONCLUSIONS: (90)Y complexes could be made with ease with DMSA. (90)Y-DMSA was obtained in good yield and was found to be very stable. A promising biodistribution result of this complex pointed at potential in the palliative treatment of bone metastases.

Preparation and biological characterization of isomeric 188Re(V) oxocomplexes with tetradentate S4 ligands derived from meso-dimercaptosuccinic acid for labeling of biomolecules.

A new type of tetradentate S4 ligand has been synthesized by bridging two molecules of meso-2,3-dimercaptosuccinic acid for stable binding and easy conjugation of rhenium-188 to tumor targeting structures. The stereoisomeric tetrathiolato S4 ligands form very robust anionic five-coordinated oxorhenium(V) and oxotechnetium(V) complexes. Two routes for the preparation of the (188)Re(V) oxocomplexes with (iBu)2N(O)C-C(SH)C(SH)C(O)NH(CH2)3NH(CH2)3NHC(O)C(SH)C(SH)C(O)N(iBu)2 (ligand 1) and its hydrophilic crown ether derivative (ligand 2) were tested and optimized. Several isomers were separated by HPLC from the preparation solutions and characterized in vitro and in vivo. The identity of the species obtained was determined by comparison with the HPLC profiles of reference (185/187)Re analogues and (99/99m)Tc complexes which were characterized by ESI-MS. All of them were absolutely stable in rat and human plasma solutions. Challenge experiments with cysteine corroborated the high inertness of the isomers toward ligand exchange reactions. Various in vivo samples, taken off at different times from blood, intestine, and urine of rats, confirmed the high in vivo stability of the (188)Re-S4 complexes. Biodistribution studies using male Wistar rats were performed and exhibited a high uptake and fast clearance from the liver of the more lipophilic cis and trans isomers of complex I (log P(o/w) between 1.5 and 1.7), whereas the isomers of the hydrophilic complex II (log P(o/w) about -1.75) were rapidly excreted via the renal and the hepatobiliary pathway. The low level of activity in the stomach confirms good in vivo stability. Thus, these new (188)Re-S4 complexes fulfill the requirements for a stable and high specific activity labeling of biomolecules with rhenium-188.

Synthesis, structure, and properties of rac-2,3-dimercaptosuccinic acid, a potentially useful chelating agent for toxic metals.

rac-2,3-Dimercaptosuccinic acid (rac-DMSA) may be a more effective antidote for the treatment of heavy metal poisoning than meso-2,3-dimercaptosuccinic acid (meso-DMSA), which is used at present. A comparative study of these two chelating agents has been undertaken in order to investigate this possibility. The structures of rac-DMSA and the precursor in its synthesis, rac-2,3-bis(acetylthio)succinic acid, have been determined by single-crystal X-ray analysis and compared with the structures of the corresponding meso compounds. The concentration distributions of the various ionic and molecular species of rac-DMSA that are present in aqueous solutions in the pH range 1.8-12.8 have been calculated from the four acid dissociation constants that have been determined potentiometrically at an ionic strength of 0.10. The conformations of these species in aqueous solutions have been determined by 1H NMR spectroscopy as a function of pH. The rac-DMSA exists in the crystal lattice as a double-stranded structure in which each molecule is in a gauche configuration. The meso-DMSA, however, exists in a single strand in which each molecule has adopted an anti configuration and the individual molecules are joined together at each end by hydrogen bonds. These differences in the conformations of rac- and meso-DMSA may account for the significant difference in the solubilities of the two compounds in aqueous solutions. In acidic solutions at elevated temperatures of about 95 degrees C, rac-DMSA is slowly but irreversibly converted to meso-DMSA. This conversion does not occur at ambient temperatures.

Conformations of zinc chelates of meso- and rac-2,3-dimercaptosuccinic acid in aqueous solution.

rac-2,3-Dimercaptosuccinic acid (DMSA) was found to be superior to meso-2,3-dimercaptosuccinc acid in mobilizing in vivo heavy metals such as Cd, Hg, and Pb. The disadvantage of using rac-DMSA alone as a clinical antidote for heavy metal poisoning is that it causes a greater loss of endogenous zinc than its meso isomer. The difference between the two diastereoisomers of DMSA in the excretion of endogenous zinc has been rationalized on the basis of the differences in the conformations of their zinc complexes. The zinc complexes of rac-DMSA in aqueous solution are more stable than the corresponding complexes of its meso isomer because the rac-DMSA ligands always adopt staggered anti conformations, in which the electrostatic repulsion between two bulky carboxylate groups is minimized; in contrast, unlike in the crystal lattice, meso-DMSA ligands always adopt staggered gauche conformations in their zinc complexes. The conformations of various monomeric and dimeric zinc complexes with rac- and meso-2,3-dimercaptosuccinic acid in aqueous solution were determined by IR spectroscopy and proton NMR spectroscopy as a function of zinc:ligand ratio, by proton NMR spectroscopy as a function of pD, and by variable-temperature 13C NMR spectroscopy. rac-DMSA in ZnL2(6-) coordinates with zinc ion via two thiolate groups and one carboxylate group, whereas in Zn2L2(4-) each ligand complexes two zinc ions by using one carboxylate group and one thiolate group in the beta-position to bind to the same zinc ion.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis, structure, and stability of the zinc complex of the dimethyl ester of meso-2,3-dimercaptosuccinic acid.

The dimethyl ester of meso-2,3-dimercaptosuccinic acid (meso-DiMeDMSA) reacts with Zn2+ ions to form protonated and polynuclear complexes. The species [Zn2L3H]- and [Zn2L3]2- are formed at pH values between 3 and 6.5 and have overall formation constants of 10(37.53) and 10(32.52), respectively, whereas the mononuclear complex [ZnL2]2- is formed at physiological pH and has a formation constant of 10(18.06). The mononuclear complex was synthesized and isolated as an ion association complex with the tetramethylammonium ion, [(Me)4N]2[Zn(DiMeDMSA)2], and its structure in solution was determined by low-temperature 1H and 13C NMR spectroscopy. In this structure the Zn2+ ion is tetrahedrally coordinated to four thiolate groups from two meso-DiMeDMSA molecules.

Synthesis and characterization of [186Re]rhenium(V)dimercaptosuccinic acid: a possible tumour radiotherapy agent.

[186Re]Re(V)DMSA, a beta-emitting analogue of the tumour imaging radiopharmaceutical pentavalent [99mTc]Tc(V)DMSA of possible value in tumour therapy, is readily prepared by stannous reduction of [186Re]ReO4 in the presence of dimercaptosuccinic acid at 100 degrees C using a commercial DMSA kit as used for renal imaging with 99mTc, and purified using a disposable sample preparation column. The complex has been identified as [ReO(DMSA)2] by NMR, optical and i.r., spectroscopy and elemental analysis.

Cadmium mobilization in vivo by intraperitoneal or oral administration of monoalkyl esters of meso-2,3-dimercaptosuccinic acid in the mouse.

The relative activities of a series of nine monoalkyl esters of meso-2,3-dimercaptosuccinic acid have been examined as agents for the mobilization of cadmium from mice one week after intraperitoneal administration of cadmium chloride. Eight of these are newly synthetized; all are of the type ROOCCH(SH)CH(SH)COOH, were R = Me, MMDMS; R = C2H5, MEDMS; R = (CH2)2CH3, Mn-PDMS; R = CHMe2, Mi-PDMS; R = (CH2)3CH3, Mn-BDMS; R = CH2CHMe2, Mi-BDMS; R = (CH2)4CH3, Mn-ADMS; R = (CH2)2CHMe2, Mi-ADMS; and R = (CH2)5CH3, Mn-HDMS. All are soluble in dilute sodium bicarbonate solutions and can be administered as aqueous solutions. Cadmium mobilization data were collected on each compound using mice previously loaded with cadmium; the monoesters were administered at a level of 0.40 mmol/kg intraperitoneally daily for five days. Data on whole body cadmium mobilization indicated that the monoester with the isoamyl group was the most effective under the conditions used. The relative whole body cadmium mobilization increased with the number of carbon atoms in the alkyl group of the monoester up to C5 and then decreased for the C6 compound. Cadmium removal from the kidneys and liver was also measured. It was found that the monoisoamyl ester was the most effective in removing cadmium from both the liver and the kidneys. The monoisoamyl ester also proved to be very effective in mobilizing cadmium from both the liver and the kidneys when given orally. This is the first compound which is reported capable of mobilizing cadmium in vivo from aged deposits after oral administration.

The design of a pentavalent 99mTc-dimercaptosuccinate complex as a tumor imaging agent.

In our search for a technetium-tumor seeking agent, the chemical characteristic of polynuclear Ga-citrate attracted our attention. On this basis, we selected the ligand dimercaptosuccinic acid (DMS) and appropriate labeling conditions in the design of 99mTc(V)-DMS. Chemical characterization was performed by thin layer chromatography, electrophoresis, Sephadex column chromatography and spectrophotometric studies at the chemical concentration (99Tc). Biodistribution in mice bearing Ehrlich ascites tumor and scintigraphic images in VX-2 tumor-bearing rabbit, indicated the great applicability of 99mTc(V)-DMS as a new tumor imaging agent. Its distinctive characteristic, different from the kidney imaging agent (99mTc-DMSA) is demonstrated and the biological implication of hydrolytic polynucleation of pentavalent technetium, through an anionic specie Tc(V)O3-(4), in the tumor cell is discussed.

Synthesis and properties of the monomethyl ester of meso-dimercaptosuccinic acid and its chelates of lead (II), cadmium(II), and mercury(II).

The monomethyl ester of meso-dimercaptosuccinic acid (MoMeDMSA) and its chelates with lead(II), cadmium(II), and mercury(II) have been synthesized. The mercury(II) chelate of MoMeDMSA is formed by the coordination of the two sulfur atoms in MoMeDMSA, whereas the lead(II) and cadmium(II) chelates are formed by the coordination of one sulfur and one oxygen atom. The solubilities of the chelates are pH dependent; the mercury(II) chelate dissolves when the uncoordinated carboxylic acid dissociates, but the lead(II) and cadmium(II) chelates are solubilized only after the uncoordinated mercapto group is dissociated. The cadmium(II) chelate is dimeric and the lead(II) and mercury(II) chelates are monomeric at the concentrations and conditions used in this study. The acid dissociation constants of the chelating agent and the uncoordinated groups in its metal chelates have been determined in 50% v/v methanol-water. These acid-base properties in addition to the polarity of the chelating agent contribute to the effectiveness in the in vivo mobilization of intracellular in vivo deposits of cadmium. The biliary excretion of cadmium in rats increased by a factor of 173 upon administration of the relatively toxic, nonpolar dimethyl ester of DMSA whereas the administration of the less toxic, more polar monomethyl ester increased the biliary excretion of cadmium by a factor of 63. On the other hand, meso-DMSA which is highly polar and less toxic is known to be without effect on biliary excretion of cadmium. The monomethyl DMSA, therefore, appears to have properties that are intermediate between those of DMSA and its dimethyl ester, as far as both chelating properties and biliary excretion of cadmium are concerned.

Cadmium mobilization by monoaralkyl- and monoalkyl esters of meso-2,3-dimercaptosuccinic acid and by a dithiocarbamate.

Syntheses and relative cadmium mobilizing properties are described for three new monoaralkyl esters (HOOCCH(SH)CH(SH)COOR, where R = phenylethyl ((CH2)2C6H5), MPhEDMS; R = 3-phenylpropyl ((CH2)3C6H5), MPhPDMS; and R = 2-phenoxyethyl ((CH2)2OC6H5). MPhOEDMS) of meso-2,3-dimercaptusuccinic acid. These were prepared by the reaction of the corresponding alcohol with meso-2,3-dimercaptosuccinic acid (DMSA) in aqueous HCl. When administered intraperitoneally to cadmium-loaded mice at 0.50 mmol/kg/day for four consecutive days, all induced significant reductions in the whole body cadmium levels. MPhEDMS, 60%; MPhPDMS, 66%; and MPhOEDMS, 58% in comparison with control levels. At the same dosage monoisoamyl meso-2,3-dimercaptosuccinate (Mi-ADMS) and a dithiocarbamate, sodium N-benzyl-4-O-(beta-D-galactopyranosyl)-D-glucamine-N-carbodithioate++ + (BLDTC) induced reductions of 65% and 57%, respectively. Hepatic and renal cadmium were also depleted significantly, while brain cadmium levels were unchanged. These compounds induced a significant reduction in the cadmium levels of the spleen, and one, MPhOEDMS, produced a 10% decrease in pancreatic cadmium. The manner in which the later injections removed smaller fractions of the total body cadmium is consistent with a bodily distribution of these compounds by which they are concentrated primarily in the kidneys and the liver, with much smaller amounts reaching other organs. It is proposed that these compounds enter renal and hepatic cells through an anion transport system.

Meso-2,3-dimercaptosuccinic acid mono-N-alkylamides: syntheses and biological activity as novel in vivo cadmium mobilizing agents.

Three meso-2,3-dimercaptosuccinic acid mono-N-alkylamides (meso-RNHCOCH(SH)CH(SH)-COOH, where R = CHMe2, Mi-PDMA; CH2CHMe2, Mi-BDMA; and CH2CH2CHMe2, Mi-ADMA), were prepared via a synthetic route using the sulfhydryl-protected anhydride. 2,2-Dimethyl-1,3-dithiolane-4,5-cis-dicarboxylic acid anhydride was opened up with 1 mol of corresponding amine to give the SH-protected monoamide. Subsequent deblocking of the vicinal dithiol functionality was accomplished by conversion of the dithiolane into the mercury complex followed by reaction with H2S to give the target molecule. The potential utility of these compounds in chronic cadmium intoxication was examined by evaluation of their cadmium mobilizing efficacy in vivo in cadmium-loaded female albino rats using sodium N-benzyl-D-glucamine-N-carbodithioate (BGDTC) as the standard drug. Compared to BGDTC, the new compounds were, except at the highest dosage studied, equally or more effective in decreasing retention of hepatic cadmium, while mostly less effective in decreasing renal cadmium. The greatest reductions were obtained with Mi-BDMS at 4 x 1.5 mmol/kg, where liver and kidney cadmium levels were reduced to 12% and 59% of control levels, while at the same dosage BGDTC induced a reduction to 50% and 13% of control levels. The order of the efficacy of the monoamides as hepatic cadmium mobilizing agents was found to be Mi-PDMA > Mi-BDMA > Mi-ADMA. However, the isopropyl analog, though very effective at reducing hepatic cadmium at a low dosage, was found to be more toxic than the isobutyl and isoamyl monoamides. While the new compounds were shown to be effective cadmium mobilizing agents, the specific compounds examined did not possess optimized structures in terms of the balance between effectiveness and toxicity.

Design of in vivo cadmium-mobilizing agents: synthesis and properties of monobenzyl meso-2,3-dimercaptosuccinate.

A novel method for the synthesis of monoesters of meso-2,3-dimercaptosuccinic acid (DMSA) is presented which utilizes the reaction of the vicinal sulfhydryl-protected anhydride with the corresponding alcohol in the presence of a base. The product is then treated successively with mercuric chloride to remove the protecting group and form the mercuric complex, and hydrogen sulfide to regenerate thiol groups by removal of mercury as HgS. This strategy was exploited to synthesize monobenzyl meso-2,3-dimercaptosuccinate (MBzDMS), C6H5CH2O(O)CCH(SH)CH(SH)C(O)OH, and demonstrates a feasible synthesis of monoesters difficult to obtain by direct esterification, via the use of the reactive anhydride. The resultant compound was found to be an effective cadminum-mobilizing agent when used with cadmium-exposed rats or mice and when administered by any one of several routes (ip, iv, po). This monobenzyl ester (MBzDMS) of DMSA was found to be somewhat less effective than the corresponding monoisoamyl ester (Mi-ADMS) in mobilizing cadmium from such cadmium deposits. The ability of MBzDMS to mobilize cadmium into the urine is significantly decreased by the coadministration of p-aminobenzoic acid, in support of the hypothesis that MBzDMS enters renal cells via an anion transport system. An analysis of the structural features of vicinal dithiols examined as antagonists for chronic cadmium intoxication allows a hypothesis to be formulated indicating essential features required for the design of effective new cadmium antagonists of this type.