ERK5-IN-4 (compound 34b) is a potent and specific inhibitor of extracellular signal-related kinase 5 (ERK5) activity, effectively inhibiting both full-length ERK5 and truncated ERK5 (ERK5 ΔTAD) kinase activity in HEK293 cells with IC50 values of 77 nM and 300 nM, respectively [1].

ERK5-IN-4 (compound 34b) is a selective chemical compound that inhibits MAP3K, p38 (IC50 >30 μM), and BRD4 (IC50 >20 μM), with unique activity among ERK5 inhibitors. In HEK293 cells, ERK5-IN-4 (0-100 μM, 72 hours) inhibits ERK5 kinase activity, while lower doses (0-1 μM, 72 hours) activate ERK5 transcriptional activity, facilitating nuclear translocation by separating the C-terminal transcriptional activation domain (TAD) from the nuclear localization sequence (NLS). It inhibits growth in cancer cell lines with GI50 values of 19.6 μM (HEK293), 22.3 μM (A498), 25 μM (SJSA-1), and 26.6 μM (MDA-MB-231) after 72 hours. Its selectivity profile shows dissociation constants (Kd) of 0.046 μM to 2.8 μM against various kinases, indicating broad inhibition. Western Blot analysis of EGF-treated HeLa cells (0.01-3 μM, 1 hour) showed an increase in the upper phospho-ERK5 band, confirming its inhibitory effect.

ERK5-IN-4 (compound 34b), when administered orally at a dosage of 10 mg/kg, exhibits low clearance and has an oral bioavailability of 42% in mice [1]. The pharmacokinetic parameters for ERK5-IN-4 were assessed in an animal model, indicating the following results: after administration via intravenous (i.v.) or oral (p.o.) routes at a 10 mg/kg dose, the clearance (Cl) was recorded at 14 mL/min/kg, the volume of distribution (Vd) at 0.6 L/kg, the half-life (t1/2) at 80 minutes, and the bioavailability (BA) at 42% [1].