Probe Selectivity in
Vitro:
In a biochemical screen against 335 wild-type human kinase domains, NVL-520 was highly selective. ROS1 was the most strongly inhibited target, followed by ALK which had 2-fold weaker IC50 than ROS1. Besides ALK, no other kinases were inhibited within 10-fold of the IC50 of NVL-520 for ROS1. NVL-520 had a >50-fold selectivity for ROS1 over 97.9% (328/335) of the tested kinome, with only five additional targets (LTK, FAK, PYK2, FER, and TRKB) inhibited with IC50 between 10- and 50-fold of ROS1. Because TRKB scored in this assay as a weak hit (IC50 = 28-fold above ROS1) and was a key off-target of concern, we further profiled TRKB using additional assays. NVL-520 demonstrated selectivity for both wild-type ROS1 and ROS1 G2032R over TRK (185-fold and 16-fold, respectively;
