RUSKI-201

Users should note the following limitations: (1) there is still limited SAR reported surrounding the RU-SKI series (e.g., there is no inactive control analog suggested that I am aware of), (2) this series is associated with uncharacterized mechanisms of cytotoxicity, (3) there is limited biophysical data of this chemotype that links direct target engagement in cell-free systems with the reported SAR (e.g., XR, cryo EM, NMR), (4) there is also still limited data showing direct, specific target engagement of this chemotype in cells (e.g., CETSA, pull-downs), and (5) there is limited data describing its cell-free selectivity versus unrelated targets (i.e., selectivity panel). Confidence in this probe could be improved with additional data addressing these aforementioned areas.

Despite this limitations, RU-SKI-201 represents an improvement over the first-generation RU-SKI compounds for Hhat chemical probes and therefore should be used with caution.

Given the historical cytotoxicity of this series and incomplete validation data expected of the highest-quality chemical probes, I would recommend that users of RU-SKI-201 also characterize (1) cellular health (“toxicity”), (2) upstream and downstream pathway targets, and (3) related pathway targets in their particular experimental system to further verify the probe is behaving in a target-based manner rather than through a nonselective or off-target manner.

Users of this compound should be aware that this is a diastereoisomeric mixture besides a conformational mixture of E and Z amide. The invitro and in cell data are produced on this mixture.