P2.14-10 Identification of Frequent, Activating HER2 Mutations and HER2 Inhibitor Response and Resistance in Canine Lung Cancer

Abstract

Naturally occurring primary canine lung cancers share clinical and pathologic features with human never-smoker lung cancer, but their genetic and biologic underpinnings have been unknown. We mapped the genomic landscape of canine lung cancer, discovering somatic HER2 (ERBB2) mutations in ∼38% of canine pulmonary adenocarcinomas (cPACs). We describe our genomic findings, effects of HER2 mutations on cell signaling and HER2 inhibitor response/resistance, and results of pharmacokinetic (PK) studies of the HER2 inhibitor neratinib in healthy dogs. We performed multi-platform genomic analysis of 92 primary canine lung tumors or cell lines. We evaluated HER2 signaling by Western blot. Neratinib and lapatinib responses were assessed in HER2-mutant and wild-type cPAC cell lines in vitro. HER2-mutant cell lines were continuously treated with IC50 neratinib doses to select for drug resistance, then evaluated for resistance mutations. Neratinib tolerability and PK were evaluated in healthy, mixed-breed, middle-aged dogs given a single 6 mg/kg oral neratinib dose with or without maropitant citrate or loperamide. Plasma samples for PK were collected pre-dose and timepoints from 0.5-24h after dosing. Canine lung cancers exhibited low tumor mutation burden. HER2 was the most commonly mutated gene in cPACs, occurring in ∼38%, but was absent from canine adenosquamous or squamous cell carcinomas. HER2 hotspot V659E transmembrane domain (TMD) mutations were most common and comparable to activating TMD mutations in human cancer. HER2 V659E correlated with constitutive phosphorylation of Akt in cPAC cell lines. HER2 V659E lines displayed hypersensitivity to neratinib and lapatinib relative to wild-type lines. Continuous treatment of HER2-mutant cell lines led to rapid development of resistance. Characterization of resistance-driving alterations is ongoing, as are efficacy studies in mouse xenografts. A dose of 6 mg/kg neratinib in healthy dogs showed that neratinib was tolerable and achieved therapeutic levels from IC50 studies. Evaluation of neratinib tolerability and efficacy in dogs bearing HER2-mutant lung cancer is ongoing. HER2 TMD mutations are common in otherwise low-mutation-burden primary canine lung cancers. They confer constitutive HER2 signaling and HER2 inhibitor response in cell lines. Dosing and tolerability studies in healthy dogs have shown that therapeutically relevant doses are achievable. Study of HER2 inhibitor response/resistance in cell lines and mouse xenografts is ongoing as is clinical evaluation of neratinib activity in dogs with spontaneous lung cancer. These data offer immediate diagnostic and therapeutic opportunities for pet dogs and bear implications for comparative understanding of human never-smoker lung cancers and other HER2-mutant cancers.