Pralsetinib

Rearranged during transfection (RET) is a transmembrane receptor tyrosine kinase containing extracellular, transmembrane, and intracellular domains whose activity is required for normal kidney and nervous system development. Constitutive RET activation is achieved through chromosomal rearrangements producing 5' fusions of dimerizable domains to the 3' RET tyrosine kinase domain leading to constitutive dimerization and subsequent autophosphorylation; the most common fusions are KIF5B-RET and CCDC6-RET, although more than 35 genes have been reported to fuse with RET. Constitutive activation leads to increased downstream signalling and is associated with tumour invasion, migration, and proliferation.

Pralsetinib (formerly referred to as BLU-667) was developed through screening more than 10,000 agnostically designed kinase inhibitors followed by extensive chemical modification to improve its properties. Pralsetinib displays in vitro IC50 values for both WT RET as well as several mutant forms, including CCDC6-RET, in the range of 0.3-0.4 nmol/L, and is 100-fold more selective for RET kinase over 96% of 371 kinases tested. It is this specific inhibition of RET kinase that is associated with anti-tumour activity and clinical benefit in patients.

Despite increased selectivity for RET over other kinases, pralsetinib has been reported to inhibit DDR1, TRKC, FLT3, JAK1-2, TRKA, VEGFR2, PDGFRb, and FGFR1-2 at clinically relevant concentrations. The significance of these findings remains uncertain.