(R)-SKBG-1

(R)-SKBG-1 fails to meet criteria (doi.org/10.1021/acs.jmedchem.3c00550) for covalent probes regarding potency (> 1 µM), negative control compound (activity difference between (R)-SKBG-1 and (S)-SKBG-1N is <100) and available profiling data. Moreover, (R)-SKBG-1 binds to >40 targets (10.1038/s41589-023-01270-0). Most but not all of these targets are also bound by the negative control (S)-SKBG-1N. (R)-SKBG-1 may be useful given the limited availability of tools to study NONO but the limitations in selectivity and available data should be considered.

This probe is a recently-developed covalent modulator of NONO function. Chemoproteomics studies demonstrate that the probe shows high selectivity across the proteome, and use of the NONO C145S resistance allele makes clear that key cellular effects of the probe (eg, loss of androgen receptor expression) derive from targeting of NONO at C145. EC50 values for target labeling and various downstream cellular phenotypes are consistently in the 5 µM range, supporting the recommendation for using this probe at concentrations up to 20 µM. No in vivo studies are reported, and the chloroacetamide electrophile is likely to limit stability in vivo and even in DMSO solutions over time. Overall, this is a strong probe for targeting NONO and few alternatives are available. While off-target effects are always possible in other systems, the C145S resistance allele provides an approach to demonstrating that phenotypes observed in other systems derive from probe labeling of NONO.