Pharmaceutical Analytical Chemistry: Open Access
Open Access

Abstract

Liquid Chromatography-Mass Spectrometry to Monitor the Labeling Process Stability and Identify Derivatives during the Preparation of 188Re-MN-16ET: A Radiopharmaceutical for Hepatoma

Wei-Hsi Chen, Pei-Cheng Wang, Yu-Chieh Hsiao, Tsai-Yueh Luo and I-Chung Tang

The labeling process stability of a radiopharmaceutical, radio isotope rhenium-labeled N-[2-mercaptoethyl]- 3-aza-19-ethyloxycarbonyl-3-[2-mercaptoethyl] octadecanoate (188Re-MN-16ET) for treatment of hepatocellular carcinoma (HCC) from its precursor, triphenylmethyl (Ph3C-) group protected-MN-16ET with 188ReO4- was surveyed and identified the derivatives from both reactant and product. After incubation for various specified periods of up to 6 h under various labeling reaction conditions, including acetic acid or mixed with normal saline, room temperature or a reaction temperature of 100°C, and the radiolytic effect of Re-188, the levels of protected-MN-16ET and Re-MN- 16ET in solutions were analyzed by high performance liquid chromatography-tandem mass spectrometry (HPLCMS/ MS) to study the impacts of the labeling process on their structural stabilities and the derivatives that arise from decomposition when preparing 188Re-MN-16ET from stock solution. This information is the key to determine whether 188Re-MN-16ET is structurally accurate and suitable for its intended use. The results showed that the major factor that impacts the structural stability of the product, Re-MN-16ET, is 188ReO4-; however, a thermal (100°C) effect on the precursor, protected-MN-16ET, was also observed. After 1 h incubation with 188ReO4- (100°C), the abundances of Re-MN-16ET and protected-MN-16ET were reduced by approximately 15% and 25%, respectively. The major decomposition products were Re-MN-16COOH and intra-molecular disulfide derivative. Moreover, the auto-radiolysis effect of Re-188 (60 mCi) on 188Re-MN-16ET was not clearly observable until 140 h. On the other hand, a stability study of Re-MN-16ET in plasma showed that 8% remained after incubation for 1 h; the metabolite was Re-MN-16COOH, which is identical to the hepatic bio-transformed product.