Inadequate sialylation is known to correlate with a wide variety of serious infectious as well as non-infectious diseases.
Considerable effort has been expended to investigate the role of ST3Gal1 in various types of cancer. Among them are breast-, ovarian-, prostatic- and pancreatic cancer to only mention a few of them. ST3Gal1 was found to enhance cell growth and angiogenesis, and contribute to metastasis by concealing the cells from the immune system. Additionally, elevated expression of this sialyltransferase leads to resistances against established chemotherapeutics.
Subsequently, the selective inhibition of this human glycosyltransferase is a highly desirable objective. Regarding covalent inhibition, tyrosine is a reasonable target for this intention because of its low abundance and amphiphilic structure. Human sialyltransferases share CMP-Neu5Ac as donor and consequently its binding site is conserved among these GT29 enzymes. Accordingly, a possible way of discriminating between different ST enzymes to accomplish the desired selectivity is addressing the substrate binding site. In hST3Gal1 (Figure 1a) there are three tyrosine residues involved in the catalysis of the transfer of sialic acid from CMP-Neu5Ac onto the acceptor glycoside R-Galβ1,3-GalNAc. Two of them (Y230, Y266) contribute to substrate and one (Y191) to donor binding. Both residues are inevitable for catalysis. Sequence alignment reveals that this constitution of the active site is unique among siayltransferases and is thus a promising target. Sharpless et al. recently renewed the concept of Sulfur-(VI)-Fluoride-Exchange (SuFEx) reactions as a click like option, which was initially introduced by Steinkopf et al. in 1927. In preliminary experiments, we found, that besides minor side reactions, the three tyrosine residues located in the active site are modified by a SuFEx reagent. By further refinement and targeting not only one tyrosine residue per SuFEx warhead, but introducing two fluorosulfates in a bifunctional warhead for dual reaction with Y230 and Y266 (Figure1b), we intend to highly enhance selectivity and binding affinity. Further selectivity will be aspired to by enhancing the proximity through coupling the SuFEx reagent with a suitable carbohydrate, for instance sialic acid, Galβ1,3-GalNAc and derivatives thereof. These moieties will be introduced by copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), facilitating quick and adjustable variation of the selectivity-providing structure as well as enabling implementation of different warheads.
- a) I. V. Baskakov, E. Katorcha, Frontiers in neuroscience 2016, 10, 358; b) A. Varki, Nature 2007, 446, 1023; c) N. Sharon, H. Lis, Science 1989, 246, 227-234.
- a) L. Wang, Y. Liu, L. Wu, X. L. Sun, Biochimica et biophysica acta 2016, 1864, 143-153; b) R. Szabo, D. Skropeta, Medicinal Research Reviews 2017, 37, 219-270.
- H. L. Yeo, et al., Int J Cancer 2018.
- Y. Li, S. Luo, W. Dong, X. Song, H. Zhou, L. Zhao, L. Jia, Laboratory Investigation 2016, 96, 731.
- a) W. Steinkopf, Journal für Praktische Chemie 1927, 117, 1-82; b) J. Dong, L. Krasnova, M. G. Finn, K. B. Sharpless, Angewandte Chemie International Edition 2014, 53, 9430-9448.
- a) A. Roy, A. Kucukural, Y. Zhang, Nature Protocols 2010, 5, 725-738; b)J. Yang, Y. Zhang, Nucleic Acids Research, 2015, 43, 174-181, c) C. Zhang, P.L. Freddolino, Y. Zhang, Nucleic Acids Research, 2017, 45, 291-299.