Synthesis and characterisation of irreversible transglutaminase 2-inhibitors with albumin binding moiety


Synthesis and characterisation of irreversible transglutaminase 2-inhibitors with albumin binding moiety

Wodtke, R.; Schlitterlau, P.; Brandt, F.; Laube, M.; Kopka, K.; Pietzsch, H.-J.; Pietzsch, J.; Löser, R.

The development of radiotracers for transglutaminase 2 (TGase 2) based on irreversible inhibitors appears highly attractive to further uncover the role of that enzyme for the emergence and progression of various tumours. [1] In this context, the ¹⁸F-labelled analogue of Nε-acryloyl-L-lysine 1, developed in our lab, showed great potential as radiometric tool for in vitro investigations. However, application for in vivo imaging is strongly limited by its unfavourable pharmacokinetic properties such as fast blood clearance and metabolism. A common approach to improve biodistribution and blood circulation time of drugs is the reversible conjugation to human serum albumin (HSA). Recently, compound 2 was identified as HSA binder with good affinity (Kd = 3.2 µM). [2] Successful application of 2 was demonstrated for pharmacokinetic tuning of various radiolabelled compounds, but rather for hydrophilic than for hydrophobic molecules. [3] Moreover, compound 2 offers the possibility for radiolabelling with iodine-123. [4]
For the purpose to develop radiotracers for TGase 2 with HSA binding capability, we designed compound 3 as lead structure containing the HSA binding moiety of 2 linked via a triazole ring as an amide bioisostere to the part of the TGase 2-inhibitor. Conjugation of alkyne-functionalised Nε-acryloyl-L-lysines and Boc-protected (R)-6-amino-2-azidohexanoic acid by copper-catalysed azide/alkyne cycloaddition followed by Boc deprotection and introduction of 4-(4-iodophenyl)butanoic acid via the respective N-hydroxysuccinimide ester gave access to 3 and two further derivatives with 3,5 and 2,5 substitution pattern at the pyridine ring. Evaluation of these compounds (and their alkyne precursors) by in-house assay methods revealed excellent inhibitory potencies towards TGase 2 (kinact/KI = 10,800 and 3,880 M-1s-1 for 3 and 1, respectively) and good binding affinities to HSA (Kd = 2.3 µM for 3). Overall, this indicates a promising basis for the application of this dual-targeting approach. Current studies focus on the radiolabelling of compound 3 with iodine-123 using the respective arylboronic acid as precursor which can be obtained via the same synthetic route.

Literature:

[1] Pietsch et al. Bioorg. Med. Chem. Lett. 2013, 23, 6528. [2] Dumelin et al. Angew. Chem. Int. Ed. 2008, 47, 3196. [3] Brandt et al. Nucl. Med. Biol. 2019, 70, 46. [4] Wen et al. Mol. Pharmaceutics 2019, 16, 816.

  • Lecture (Conference) (Online presentation)
    Frontiers in Medicinal Chemistry, 08.-10.03.2021, Darmstadt, Deutschland

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Publ.-Id: 33483