SKI-73

There are insufficient data to assess the selectivity of the probe. Data are only given for the PRMT family. Wider screening of both the probe and the prodrug is required. Moreover, the use of a prodrug makes things less than ideal, especially when potent ligands for CARM1 already exist. This probe might be suitable to explore some subtleties of co-factor competitive inhibitors but there is no general evidence that this is different to substrate competitive inhibition. It appears that concentrations in excess of 1uM are required for cell activity, which is a large drop-off from in vitro activity. I would worry about other effects resulting from treating cells with redox-active quinones at this concentration without further data.

SKI-73 is a prodrug of SKI-72. SKI-73 and SKI-72 should be used for cell-based and in vitro experiments, respectively

SKI-73 is the prodrug of the PRMT4(CARM1) inhibitor SKI-72 (IC50 = 13 nM). SKI-72 is > 30-fold selective versus other PRMT family members (PRMT7 IC50 = 400 nM). The compound is provided with its closely matched inactive control SKI-73N, a prodrug of the less active compound SKI-72N (PRMT4 IC50 = 1.04 uM and inactive against all other PRMT family members). SKI-72 is SAM-competitive and substrate non-competitive. Confirmation of binding to PRMT4 has been demonstrated by SPR and protein-ligand crystallography in PRMT4. The cell-penetrant prodrug SKI-73N is active in cell-based assays assessing inhibition of methylation of known PRMT4 substrates (BAF165, IC50 = 538 nM; PABP-1, IC50 = 1.43 uM; and MED12, IC50 = 500 nM to 2600 nM dependent upon the cell line). The negative control SKI-73N is inactive in these cell-based assays. Notable (approx. 40%) inhibition of cell growth in MCF7 cells using SKI-73 at a 10 uM concentration and some inhibition of cell growth at 1 uM (approx. 15%) suggests that this compound should not be used in cell-based experiments at concentrations above 5 uM. Wider profiling of SKI-73 of SKI-72 is not presented and no data have been reported to support in vivo use of these chemical tools.