2,3-Dimercaptosuccinic-acid chelates--1. Structure and pharmacokinetic studies

Alkaline degradation of lyophilized DMSA prior to labeling with 99mTc: Identification and development of the degradation pathway by HPLC and MS

INTRODUCTION

Complexes of technetium-99m (99mTc) with meso-dimercaptosuccinic acid (DMSA) have been widely used as diagnostic agents in nuclear medicine. The degradation products (DP) of DMSA formed under different forced conditions have been identified through HPLC-DAD and LC-MSⁿ studies. In this study, the DMSA kit was subjected to forced degradation under hydrolysis conditions as prescribed by the International Conference on Harmonization (ICH) guideline Q1A.

METHODS

Chromatographic separation was accomplished on a reverse phase Shim-Pack VP-ODS (150 mm × 4.6 mm; 5 μm) analytical column using the gradient elution method. LC-MSⁿ analysis was performed using an Esquire 3000 Plus ion trap mass spectrometer, operating under electrospray ionization (ESI).

RESULTS

No products were found under acidic or neutral stress conditions. All the products found were identified through LC-MSⁿ analyses and their fragmentation pathways were proposed. The DMSA standard degraded into an adduct DMSA dimer (2DMSA[-2H+Na]⁺) and adduct DMSA bound to fumaric acid and dithioglucolic acid (DTGA). In the DMSA kit, the degradation products were dimers and trimers of DMSA with tin. A possible degradation pathway is presented.

CONCLUSIONS

This method proved to be convenient and effective since it provided fast and efficient separation of DMSA from its degradation products. The degradation studies carried out were able to delineate the stability of the DMSA standard and the DMSA kit.

Insight into the structure and stability of Tc and Re DMSA complexes: A computational study

Meso-2,3-dimercaptosuccinic acid (DMSA) is used in nuclear medicine as ligand for preparation of diagnostic and therapy radiopharmaceuticals. DMSA has been the subject of numerous investigations during the past three decades and new and significant information of the chemistry and pharmacology of DMSA complexes have emerged. In comparison to other ligands, the structure of some DMSA complexes is unclear up today. The structures and applications of DMSA complexes are strictly dependent on the chemical conditions of their preparation, especially pH and components ratio. A computational study of M-DMSA (M=Tc, Re) complexes has been performed using density functional theory. Different isomers for M(V) and M(III) complexes were studied. The pH influence over ligand structures was taken into account and the solvent effect was evaluated using an implicit solvation model. The fully optimized complex syn-endo Re^(V)-DMSA shows a geometry similar to the X-ray data and was used to validate the methodology. Moreover, new alternative structures for the renal agent ^99mTc^(III)-DMSA were proposed and computationally studied. For two complex structures, a larger stability respect to that proposed in the literature was obtained. Furthermore, Tc^(V)-DMSA complexes are more stable than Tc^(III)-DMSA proposed structures. In general, Re complexes are more stable than the corresponding Tc ones.

Quantum chemistry calculations of technetium and rhenium compounds with application in radiopharmacy: review

Quantum chemistry calculations are a powerful tool in the development of new ^99mTc and ^186/188Re radiopharmaceuticals.

Tc-99m DMSA Uptake by Metastatic Colorectal Carcinoma

Extrarenal uptake of Tc-99m DMSA is not seen very often. It has previously been described in metastatic disease and was mainly attributed to the presence of V-DMSA in the injected solution. We report a clinical case of incidental visualization of metastatic bone disease of the colon in a patient with renal failure. This could be the result of not only the presence of V-DMSA, but also the renal failure and the atypia of the lesions.

Alguns aspectos sobre geradores e radiofármacos de tecnécio-99m e seus controles de qualidade

Radiofármacos marcados com tecnécio-99m são os principais agentes para diagnósticos utilizados nas clínicas de medicina nuclear, em função de uma série de características físicas do radionuclídeo e pela praticidade dos radiofármacos serem preparados no local de uso, por meio de uma reação de complexação entre um agente complexante (fármaco) e o tecnécio-99m. Entretanto, durante esta reação podem ser geradas algumas impurezas que proporcionam a formação de produtos com baixa qualidade ou com características diferentes das desejadas. No presente trabalho serão apresentados alguns dos fatores que podem interferir na qualidade dos radiofármacos e os controles que podem ser utilizados para garantir sua qualidade.

A kinetic model for 99mTc-DMSA in the rat

A pharmacokinetic model was developed for the renal imaging agent 99mTc-DMSA in anesthetized rats, which incorporated data from serial measurements of blood and urine simultaneously with dynamic images obtained over an 8-h period. Animals which received a 10 mg/kg dose of unlabeled DMSA immediately before 99mTc-DMSA injection had a significantly reduced kidney accumulation and greater urinary elimination of 99mTc than animals which received the radiopharmaceutical alone. The kidney clearance was also significantly lower in rats receiving unlabeled DMSA, but no significant difference was determined between the urine clearance estimates of the two animal groups. Because the increase in the amount eliminated in the urine was not coupled with a significant change in urine clearance, it would appear that unlabeled DMSA saturated the kidney uptake mechanism(s) of 99mTc-DMSA without modifying the urinary clearance process. This interpretation is consistent with the hypothesis that renal handling of 99mTc-DMSA is governed by both glomerular filtration and peritubular capillary uptake. The simultaneous acquisition of blood, urine and non invasive image data allows for a comprehensive and informative model of the physiological disposition of 99mTc-DMSA.

Comparison of two 99mTc(V)-dimercaptosuccinic acid preparations

99mTc(V)-DMSA labelled either by increasing the pH together with a low concentration of Sn, or by increasing the pH only are compared in vitro and in vivo. The gel chromatographic separation shows that after incubation with blood, all the 99mTc(V)-DMSA preparations are stable and do not bind to the plasma proteins. The behavior in rats as well as in clinical studies does not demonstrate any distinctive characteristics between the different radiomolecules. It seems that the pH of the solution is an important factor which controls the formation of 99mTc(V)-DMSA.