Elevenostat Is an HDAC6/Class I-Biased Multi-HDAC Inhibitor Rather than an HDAC11-Selective Chemical Probe

Histone deacetylase 11 (HDAC11) is a lysine defatty-acylase with emerging roles in immunity, metabolism, and disease, creating a need for rigorously validated isoform-selective inhibitors. Elevenostat/JB3-22 has been used as an HDAC11 inhibitor, but its HDAC isoform selectivity has remained insufficiently defined. Here, we re-evaluated Elevenostat using recombinant human HDAC isoforms, orthogonal HDAC11 activity assays, and cellular pharmacodynamic readouts. Elevenostat inhibited HDAC11 only weakly, with IC50 values of 10.2 µM in a fluorogenic assay and 32.1 µM in an HPLC-based fatty-acyl substrate assay. Full HDAC1–11 profiling revealed preferential inhibition of the class IIb enzymes HDAC6 and HDAC10 (IC50 = 3.2 and 8.9 nM, respectively), as well as class I HDACs, whereas HDAC11 was the least sensitive isoform. In cells, Elevenostat increased acetylated α-tubulin and histone acetylation and reduced cell viability, consistent with HDAC6 and class I HDAC engagement. These data demonstrate that Elevenostat/JB3-22 is not an HDAC11-selective chemical probe, but a class I/class IIb-biased multi-HDAC hydroxamate. Biological conclusions based solely on Elevenostat treatment should therefore be interpreted with caution.