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Issue 41, 2015
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Design, characterization and cellular uptake studies of fluorescence-labeled prototypic cathepsin inhibitors

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Abstract

Besides their extracellular activity crucial for several pathophysiological conditions, human cysteine cathepsins, in particular cathepsins K and S, represent important intracellular targets for drug development. In the present study, a prototypic dipeptide nitrile inhibitor structure was equipped with a coumarin moiety to function as a fluorescent reporter group. In a second inhibitor, a PEG linker was introduced between the dipeptide nitrile and the fluorophore. These tool compounds 6 and 7 were characterized by kinetic investigations as covalent reversible inhibitors of human cathepsins L, S, K and B. Probe 6 showed a pronounced inhibitory activity against cathepsins K and S, which was corroborated by modeling of inhibition modes. Probe 7 was highly potent (Ki = 93 nM) and selective for cathepsin S. To examine the ability of both probes to enter living cells, human embryonic kidney 293 cells were targeted. At a concentration of 10 μM, cellular uptake of probe 6 was demonstrated by fluorescence measurement after an incubation time of 30 min and 3 h, respectively. The probe's concentration in cell lysates was ascertained on the basis of the emission at 492 nm upon excitation at 450 nm, and the results were expressed as concentrations of probe 6 relative to the protein concentration originating from the lysate. After incubation of 10 μM of probe 6 for 3 h, the cellular uptake was confirmed by fluorescence microscopy. HPLC was used to assess the probes’ lipophilicity, and the obtained log D7.4 value of 2.65 for probe 6 was in agreement with the demonstrated cellular uptake.

Graphical abstract: Design, characterization and cellular uptake studies of fluorescence-labeled prototypic cathepsin inhibitors

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Supplementary files

Article information


Submitted
02 Aug 2015
Accepted
19 Aug 2015
First published
19 Aug 2015

Org. Biomol. Chem., 2015,13, 10310-10323
Article type
Paper
Author version available

Design, characterization and cellular uptake studies of fluorescence-labeled prototypic cathepsin inhibitors

F. Kohl, J. Schmitz, N. Furtmann, A. Schulz-Fincke, M. D. Mertens, J. Küppers, M. Benkhoff, E. Tobiasch, U. Bartz, J. Bajorath, M. Stirnberg and M. Gütschow, Org. Biomol. Chem., 2015, 13, 10310
DOI: 10.1039/C5OB01613D

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