BAY-8400

BAY-8400 is only a weakly active and selective inhibitor of DNA-PK, compared to AZD7648. The small difference in antiproliferative activity of BAY-8400 in the absence and presence of DSB-inducing challenges is only 7-fold (360 nM vs. 2540 nM). This observation is an indication for additional unknown pharmacological activities that should be avoided. Therefore, my suggestion would be to limit the cellular test concentration to 500 nM. The in vivo profile of BAY-8400 is also not completely evaluated and in the absence of dose dependency studies, the modulation of proximal or distal PD markers and timely resolved PK/PD studies, I would recommend using AZD7648 instead of BAY-8400 as a DNA-PK probe.

The compound BAY-8400, represents an additional alternative compound for a selective DNA-PK inhibitor, besides the inhibitor AZD7648. However, it should be taken into account that the compound BAY-8400 does not show sufficient selectivity in vitro to the closely related kinases (IC50s: DNAPK 81 nM; PI3Kb 117 nM; ATR 394 nM; mTOR: 1910 nM). The other members of the PIKK family (SMG1 & TRRAP) are also missing in the screening panel. From the closely related family of PI3Ks, there were only two representatives in the screening panel (PI3KC2g & PI3KC2a), of which PI3KC2g was most significantly affected, so that further off-targets must also be taken into account here. In the cellular results, it is noticeable that the IC50 in cellulo is smaller than the biochemical in-vitro IC50, which could possibly indicate additional off-targets. In addition, the cellular on- & off-targets effects were all carried out in different cell lines. Therefore, additional cellular target engagement would be desirable to better assess cellular selectivity. Since a negative control substance is unfortunately also not available, my recommendation would therefore be to test the BAY-8400 compound only in combination with AZD7648 in order to have an additional cross-validation of the results.