BLU-554 is a potent fibroblast growth factor receptor 4 (FGFR4) inhibitor.

Fibroblast growth factor receptor 4 (FGFR-4) is a protein that in humans is encoded by the FGFR-4 gene. This protein is a member of the fibroblast growth factor receptor family, where amino acid sequence was highly conserved between members throughout evolution. FGFR family members 1-4 differ from one another in their ligand affinities and tissue distribution. A full-length representative protein consists of an extracellular region composed of three immunoglobulin-like domains, a single hydrophobic membrane-spanning segment and a cytoplasmic tyrosine kinase domain. The extracellular portion of the protein interacts with fibroblast growth factors, setting in motion a cascade of downstream signals, ultimately influencing mitogenesis and differentiation. The genomic organization of the FGFR-4 gene encompasses 18 exons. Although alternative splicing has been observed, there is no evidence that the C-terminal half of the Iglll domain of this protein varies between three alternate forms, as indicated for FGFR 1-3[1].

References:
[1]. Neil Bifulco, et al. Inhibitors of the fibroblast growth factor receptor. PCT Int. Appl. (2015), WO 2015061572 A1 20150430.