Radiolabeling characterization and bioevaluation of n acetylneuraminic acid for its potential role in imaging of cancer sialylation a preclinical study

Abstract

Sialic acids are the terminal moieties of the carbohydrate chain of glycoconjugates that are reported to be elevated during malignancy and are described as a result of spontaneous release of aberrant sialic acid rich glycoproteins and glycolipids. several lines of evidence imply that the increased sialylated antigens expression on cancer cells significantly correlates with the poor prognosis of patients. Thus, sialic acid is an important constituent exhibiting characteristic changes of transformed cells and can be exploited for targeting cancer cells with regard to cancer diagnosis and therapeutics. Therefore, the present study was conceived to optimize the radiolabeling of N-acetylneuraminic acid (the most predominant sialic acid form in mammalian cells) with 99mTc and its preclinical bioevaluation as radionuclide imaging probe in animal model of carcinogenesis. The study radiolabeled Neu5Ac with 99mTc effectively with gt90% labeling efficiency. Optimization of reaction constituents was carried out to obtain maximum percent radiolabeling yield, which was analysed by ITLC. Theradiolabeling of Neu5Ac with 99mTc was confirmed by mass spectra (ESI-MS) and HPLC. In the present study, HPLC analysis of the labeling mixture revealed the formation of a main product 99mTc-Neu5Ac, with a retention time of 7.34 min while cold Neu5Ac peak appeared at retention time 7.83 min. Further, the mass spectrum of the reaction mixture revealed a (m/z)+of 412.2, corresponding to 99mTc-Neu5Ac which corroborates with the possible predicted structure. Another peak was observed at 724, which indicate a fraction of radiocomplex with possible dimerization of neu5Ac with 99mTc. The net charge on 99mTc and 99mTc labeled Neu5Ac were negative as indicated by their paper electrophoretic mobilities. The protein binding of 99mTc-Neu5Ac assessed in serum was found to belt50%. In-vitro binding studies revealed that 99mTc-Neu5Ac is specifically taken up by HT-29 cell. In conclusion 99mTc-Neu5Ac exhibits selectively for neoplastic colon tissue.