Abstract 2594: Characterization of a novel irreversible third generation EGFR TKI that targets T790M-mediated resistant EGFR-mutant NSCLC while sparing wild type EGFR

Activating mutations in EGFR confer constitutive activity providing the oncogenic drive in EGFR-mutant NSCLC. First and 2nd generation EGFR tyrosine kinase inhibitors (TKIs) are effective drugs in this setting, but are constrained by dose-limiting toxicities attributed to inhibition of wild type (WT) EGFR and by drug resistance caused, in the majority of cases, via a T790M secondary mutation in EGFR. We report the pharmacology of a novel irreversible 3rd generation EGFR TKI active against EGFR with activating and T790M mutations, but sparing WT EGFR. Our novel 3rd generation EGFR TKI was studied in a variety of in vitro and in vivo models to determine its inhibitory potencies on different EGFR variants, pharmacokinetics (PK), antitumor efficacy, exposure-response relationships, mechanism of action, and predicted human efficacious dose. In enzyme and cell assays, our compound is a highly potent inhibitor of EGFR double mutants (L858R/T790M and Del/T790M) and EGFR activating mutants (L858R and Del), but a weak inhibitor of WT EGFR (26-fold margin over mutant target potencies). Effects on downstream signaling and function indicate the underlying mechanism of the compound is direct inhibition of EGFR, with subsequent inhibition of downstream signaling that results in apoptosis and viable cell decline. In xenograft mouse models, the compound demonstrates tumor growth inhibition and regression at well-tolerated doses in models driven by EGFR double mutants and EGFR activating mutants. The antitumor efficacy is dose-dependent and strongly correlates with inhibition of EGFR phosphorylation and EGFR-mediated downstream signaling, and induction of apoptosis. Plasma concentrations assumed to be sufficient for efficacy (Ceff) were defined using a mathematical model incorporating the plasma levels of the compound, the associated inhibitory effects on EGFR phosphorylation, and the antitumor efficacy in the double and activating mutant xenograft models. Ceff was in agreement across several models and was used with in vitro human PK properties to calculate required human dose. While our compound possesses a similar profile as other recently disclosed 3rd generation EGFR TKIs, this molecule is distinguished by better potency on the activating mutants and by the widest potency margin on WT EGFR. Given that the target potencies and WT margins of 3rd generation EGFR TKIs have been sufficient for tolerated clinical efficacy in preliminary results, it can be inferred that our compound will have similar promise in the clinic. These results support our compound as a novel EGFR TKI with an inhibitory profile and favorable drug-like properties that suggest utility for treating patients with NSCLC with EGFR activating and resistance mutations. Citation Format: Mike Zientek, Sangita Baxi, Henry Cheng, Valeria Fantin, Jun Li Feng, Allison Given, Zelanna Goldberg, Jie Guo, Michelle Hemkens, John Kath, Jennifer Lafontaine, Gary Li, Pramod Mehta, Brion Murray, Sajiv Nair, Simon Planken, Chad Ray, Yuli Wang, Manli Shi, Anand Sistla, Tod Smeal, Greg Stevens, Wei Tan, Paolo Vicini, Marlena Walls, Liu Yang, Min-Jean Yin, Scott L. Weinrich. Characterization of a novel irreversible third generation EGFR TKI that targets T790M-mediated resistant EGFR-mutant NSCLC while sparing wild type EGFR. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2594. doi:10.1158/1538-7445.AM2015-2594