PFI-3

This is a first-in-class inhibitor of the BAF bromodomains BRG and BRM. Data is only available for cell-based interogations. In this setting, PFI-3 should enable a range of studies around the cell-based consequences of modulating these important epigenetic targets.

PFI-3 represents a well-studied and selective probe for the targets listed, suitable for cellular work.  Care is needed in choosing appropriate cellular concentrations – target engagement is reported at 1uM but other studies report effects at different concentration ranges (Ding et al <0.1uM; Vangamundi et al report 5uM cellular IC50).  The use of the negative control PFI-3oMet is strongly recommended.  The probe developers do not recommend in vivo use; Ding et al report efficacy in a mouse model at 50 mg/kg p.o. so this may be feasible. Obtaining good quality PK data (not presented) is strongly recommended prior to any in vivo work, particularly given the potential for hydrolytic instability in acid - the compound contains a potentially unstable enamide group.  Stability is shown in PBS and cell media for 1 week at neutral pH so there should be no issue for cellular work, however care should be taken with long term storage in solution, or if use at acidic or basic pHs is required which could accelerate decomposition.

The compound showed potent inhibitory activity against SMARCA2/4 ATPase. The Kd is 54 - 97 nM determined by the ITC experiment, and 110 nM determined by the BLI technique. A total of 48 and 32 bromodomain subfamily members were tested for the binding specificity of the compound in two independent studies and only SMARCA2/4 and PB1 were hit. The selectivity against other more general targets was also tested by Fedorov et al., and the compound only showed slight binding to four GPCRs with micromolar affinity. The cell potency of the compound varies from 1 uM to 5.6 uM depending on the experimental protocols. In a cytotoxicity assay focusing on an NCI-60 panel of tumor cell lines, the compound didn't show any cytotoxicity at 10 uM. However, the inactive control compound should be used since the compound is weakly potent in the cell assay.