Profiling Inhibitor Scaffolds for the Cancer Target Jumonji-C Domain-Containing Protein 6

The human 2-oxoglutarate-dependent oxygenase Jumonji-C domain-containing protein 6 (JMJD6) catalyzes post-translational C-5 lysyl residue hydroxylation in multiple proteins. Aberrant JMJD6 catalysis is associated with the upregulation of androgen receptor splice variant 7 (AR-V7), which confers resistance towards antiandrogens used for prostate cancer treatment; JMJD6 is thus a promising cancer target. To date, few small-molecule JMJD6 inhibitors are reported, likely in part reflecting a lack of robust assays to monitor effects of small molecules on catalysis by isolated JMJD6. The use of solid-phase extraction coupled to mass spectrometry assays is described to screen scaffolds for the development of selective JMJD6 inhibitors. The results reveal that the reported JMJD6 inhibitors WL12, SKLB325, and Compound 7p manifest relatively inefficient JMJD6 inhibition in vitro. By contrast, some, but not all, clinically used inhibitors of the human hypoxia-inducible factor-α prolyl hydroxylase domain-containing proteins (PHDs) efficiently inhibit isolated JMJD6, in particular Enarodustat and Desidustat. The results identify attractive scaffolds for the development of selective, cell permeable JMJD6 inhibitors and suggest that JMJD6 inhibition is a potential off-target effect of PHD inhibitors in clinical use.