AX-15836 shows more than 1,000-fold selectivity for ERK5 over a panel of over 200 kinases. It also exhibits selectivity over BRD4 with a K _d of 3,600 nM. AX15836 shows similar intracellular potency (4–9 nM) across all cells tested, including peripheral blood mononuclear cells (PBMCs), endothelial cells, and oncogenic cell lines. AX15836 was completely ineffective (EC ₅₀ >10 μM) to suppress inflammatory cytokine response, suggesting that it was the BRD inhibition component of the compounds that mediated cytokine reduction. In HUVEC and HeLa cell types, samples treated with AX15836 shows very few genes to be differentially expressed. AX15836 could clearly inhibit the EGF-stimulated, phosphorylated form of ERK5 in HeLa cells.