JNK3-IN-8

JNK3-IN-8 is a potent JNK3 inhibitor with good selectivity within the JNK MAPK family. It is a carbamate pro-drug and the compound will convert into the hydroxyl analogue in vivo and in cells. Introduction of the carbamate was necessary to make this compound suitable for in vivo studies. For cell-based studies, the hydroxyl derivative would be sufficient. The compound has only been screened against 50 kinases. Thus, there can be potential off-targets that are currently unknown. The high concentration used (20 µM in cellular assays) is surprisingly high considering that the in vitro potency in enzyme kinetic assays is 1000-fold higher. Selectivity screening has been carried out at 1 µM and it is likely that at 20 µM, JNK3-IN-8 will also inhibit other JNK family members and potentially other kinases. There is no negative control compound for JNK3-IN-8 and as far as I know, there is no orthogonal compound that would inhibit exclusively JNK3.

The concentration of 20 uM is clearly too high as in vitro JNK2 IC50 = 2203 nM and JNK1 > 10 uM. The free drug concentrations in cells, and/or JNK3 occupancy are unknown. In the selectivity panel, there are only 50 kinases, and the probe was screened at 1 uM - several kinases here would be considerably inhibited at 20 uM, let alone considering the broader family. Cell effects are tested at 10, 20 uM concentrations of the probe which are way in excess of its in vitro potency. No PKPD data (using free drug levels and target engagement) were provided in the publication, making it impossible to assess suitability for in vivo use.