Discovery of a PCAF Bromodomain Chemical Probe.
Moustakim M., Clark PGK., Trulli L., Fuentes de Arriba AL., Ehebauer MT., Chaikuad A., Murphy EJ., Mendez-Johnson J., Daniels D., Hou C-FD., Lin Y-H., Walker JR., Hui R., Yang H., Dorrell L., Rogers CM., Monteiro OP., Fedorov O., Huber KVM., Knapp S., Heer J., Dixon DJ., Brennan PE.
The p300/CBP-associated factor (PCAF) and related GCN5 bromodomain-containing lysine acetyl transferases are members of subfamily I of the bromodomain phylogenetic tree. Iterative cycles of rational inhibitor design and biophysical characterization led to the discovery of the triazolopthalazine-based L-45 (dubbed L-Moses) as the first potent, selective, and cell-active PCAF bromodomain (Brd) inhibitor. Synthesis from readily available (1R,2S)-(-)-norephedrine furnished L-45 in enantiopure form. L-45 was shown to disrupt PCAF-Brd histone H3.3 interaction in cells using a nanoBRET assay, and a co-crystal structure of L-45 with the homologous Brd PfGCN5 from Plasmodium falciparum rationalizes the high selectivity for PCAF and GCN5 bromodomains. Compound L-45 shows no observable cytotoxicity in peripheral blood mononuclear cells (PBMC), good cell-permeability, and metabolic stability in human and mouse liver microsomes, supporting its potential for in vivo use.