TAS-121, a selective mutant EGFR inhibitor, shows activity against tumors expressing various EGFR mutations including T790M and uncommon mutations G719X.

TAS-121 is a novel orally active selective covalent inhibitor of the mutant epidermal growth factor receptor (EGFR). We performed preclinical characterization of TAS-121 and compared its efficacy and selectivity for common EGFR mutations (Ex19del and L858R), first- and second- generation EGFR-tyrosine kinase inhibitor (EGFR-TKI) resistance mutation (T790M), and uncommon mutations (G719X and L861Q) with those of other EGFR-TKIs. We also commenced investigation of the clinical benefits of TAS-121. The 50% inhibitory concentration (IC50) for intracellular EGFR phosphorylation was determined by using Jump-In GripTite HEK293 cells transiently transfected with EGFR expression vectors. Mouse xenograft models were used to evaluate the antitumor activity of TAS-121. TAS-121 potently inhibited common activating and resistance EGFR mutations to the same extent as another third-generation EGFR-TKI (osimertinib). In addition, TAS-121 showed equivalent inhibitory activity against some uncommon mutations such as G719X and L861Q. Furthermore, TAS-121 demonstrated greater selectivity for mutant EGFRs versus the wild-type EGFR compared with other EGFR-TKIs. Moreover, TAS-121 displayed antitumor activity in SW48 (EGFR G719S) and NCI-H1975 (EGFR L858R/T790M) xenograft models, and achieved an objective response in NSCLC patients with EGFR mutations including G719A mutation. In conclusion, TAS-121 is a novel third-generation EGFR-TKI and demonstrates anti-tumor activities in patients with NSCLC expressing either common or uncommon EGFR mutations.