Abstract 4799: Inhibition of HER2 mutant non-small cell lung cancer using 3rd generation EGFR/HER2 inhibitors

HER2 is modified in approximately 20% of lung cancers and is mutated in approximately 2-3% of non-small cell lung cancer (NSCLC). Several HER2 mutations within the tyrosine kinase domain are activating mutations, and irreversible EGFR TKIs such as afatinib are known to be effective at inhibiting HER2 phosphorylation in tumor cells expressing HER2 activating mutations. However, the clinical use of these second generation irreversible EGFR inhibitors, such as afatinib, has been limited by adverse toxicities such as skin rash and diarrhea. Our recent study in lung cancer showed that ibrutinib, a well-tolerated TKI currently FDA approved for B-cell lymphoma, is capable of inhibiting EGFR. Study by others also demonstrated that ibrutinib can inhibit HER2 phosphorylation in HER2 overexpressing breast cancer cell lines. In addition, recent studies in other cancers show that the effects of ibrutinib can be amplified in combination of with other small molecule inhibitors targeting AKT and mTOR. Therefore, we hypothesized that HER2 overexpression or activating mutations render NSCLC tumor cells sensitive to ibrutinib. To investigate this, we generated a panel of Ba/F3 cell lines expressing twelve individual clinically observed HER2 mutations and evaluated the transforming capability of the mutations as indicated by sustained cell viability following IL-3 deprivation. Common HER2 mutations such as A775insYVMA, G776del/insVV, and G776C V777insC as well as others were observed to be activating mutations. Mutant HER2 expressing Ba/F3 cells and the human HER2 mutant NSCLC cell line, H1781, were then screened against first, second, and third generation EGFR/HER2 inhibitors including ibrutinib, and cell viability was determined by the Cell Titer Glo assay. Drugs effective in growth inhibition were verified by Western blot analysis. The results showed that EGFR TKI erlotinib and the EGFR/HER2 TKI lapatinib failed to inhibit cell proliferation. However, ibrutinib and third generation EGFR/HER2 TKIs, EGF816 and AZD9291, inhibited cell proliferation and induced apoptosis at sub-micromolar concentrations. Western blotting analysis showed dose dependent decreases in phosphorylation of HER2 as well as HER2 downstream signaling molecules such as p-AKT, and p-MAPK. In order to determine if targeting downstream effectors of HER2 in combination with inhibition of the receptor would increase inhibition of cell proliferation and induction of apoptosis, we screened ibrutinib, EGF816 and AZD9291 in combination with both mTOR and AKT inhibitors. There was a modest additive effect when ibrutinib was used in combination with everolimus, an mTOR inhibitor, but there was no additive effect of EGF816 or AZD9291 was used in combination with everolimus. These results indicate that EGF816, AZD9291, or ibrutinib alone or in combination with mTOR inhibition may be effective therapeutic strategies for the treatment of HER2-driven NSCLC. Citation Format: Jacqulyne P. Robichaux, Monique Nilsson, Bingliang Fang, John V. Heymach. Inhibition of HER2 mutant non-small cell lung cancer using 3rd generation EGFR/HER2 inhibitors. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4799.