Importance of DMSA stability, its consequence for Sn(DMSA)2 complex formation and relevance to 99mTc-DMSA radipharmacs preparation

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.