Inhibition of PHPT1 by phenylarsonic acids

The human protein histidine phosphatase PHPT1 is involved in several important cellular pathways and has been implicated in various cancers. However, the biological roles of this enzyme are not well understood due to a lack of chemical tools that enable its study. Herein we have identified phenylarsonic acids as general scaffolds which inhibit PHPT1 activity. Notably, phenylarsonic acids can be embedded into peptide sequences, providing the first known peptide-based inhibitors of PHPT1. In a counterscreen against a small panel of phosphatases, we demonstrate that these compounds exhibit some selectivity for PHPT1. Moreover, we show that these compounds exhibit mixed inhibition. We provide evidence that reduction of the phenylarsonic acids in situ by reducing agents like dithiothreitol (DTT) to provide phenylarsine species gives rise to the observed PHPT1 inhibition. These As(III) species are known to be thiophilic and can interact with solvent-exposed cysteine residues of proteins. Finally, we demonstrate that mutating the three cysteine residues of PHPT1 to alanine results in a significant decrease in enzyme inhibition by the phenylarsonic acids, suggesting that these compounds likely interact at least in part with Cys residues in PHPT1.