Esterase-Sensitive Prodrugs of a Potent Bisubstrate Inhibitor of Nicotinamide N-Methyltransferase (NNMT) Display Cellular Activity

A recently discovered bisubstrate inhibitor of Nicotinamide N-methyltransferase (NNMT) was found to be highly potent in biochemical assays with a single digit nanomolar IC50 value but lacking in cellular activity. We, here, report a prodrug strategy designed to translate the observed potent biochemical inhibitory activity of this inhibitor into strong cellular activity. This prodrug strategy relies on the temporary protection of the amine and carboxylic acid moieties of the highly polar amino acid side chain present in the bisubstrate inhibitor. The modification of the carboxylic acid into a range of esters in the absence or presence of a trimethyl-lock (TML) amine protecting group yielded a range of candidate prodrugs. Based on the stability in an aqueous buffer, and the confirmed esterase-dependent conversion to the parent compound, the isopropyl ester was selected as the preferred acid prodrug. The isopropyl ester and isopropyl ester-TML prodrugs exhibit improved cell permeability, which also translates to significantly enhanced cellular activity as established using assays designed to measure the enzymatic activity of NNMT in live cells.

Molecular Umbrella as a Nanocarrier for Antifungals

A molecular umbrella composed of two O-sulfated cholic acid residues was applied for the construction of conjugates with cispentacin, containing a “trimethyl lock” (TML) or o-dithiobenzylcarbamoyl moiety as a cleavable linker. Three out of five conjugates demonstrated antifungal in vitro activity against C. albicans and C. glabrata but not against C. krusei, with MIC90 values in the 0.22–0.99 mM range and were not hemolytic. Antifungal activity of the most active conjugate 24c, containing the TML–pimelate linker, was comparable to that of intact cispentacin. A structural analogue of 24c, containing the Nap-NH2 fluorescent probe, was accumulated in Candida cells, and TML-containing conjugates were cleaved in cell-free extract of C. albicans cells. These results suggest that a molecular umbrella can be successfully applied as a nanocarrier for the construction of cleavable antifungal conjugates.

Mass spectrometric analysis of acid-assisted photochemical release of the trimethyl lock system on the monolayers on gold

The acid-assisted photolysis of the trimethyl lock on the surface was characterized by mass spectrometry.