The overexpression of Human epidermal growth factor receptor 3 (HER3) and increased Neuregulin (NRG) production are well known resistance mechanisms to Human epidermal growth factor receptor 2 (HER2) kinase inhibitors. FDA-approved HER2 kinase inhibitors show significantly decreased activities in the presence of NRG, which induces HER2-HER3 heterodimer and activates HER3. VRN10s, HER2 kinase inhibitors, maintained potency to inhibit proliferation of HER2-positive breast cancer cell lines even in the presence NRG1. Western blot confirmed that VRN10s inhibited phosphorylation of HER2 and HER3 as well as downstream signaling, such as AKT and ERK pathways. Emergence of acquired resistance mutations against tyrosine kinase inhibitors (TKI) are also nearly inevitable, but less is known about the acquired drug resistance mutations of the HER2 kinase domain. To predict the drug resistance mutations against two representative HER2 TKIs, Tucatinib (non-covalent) and Neratinib (covalent), we performed an ENU mutagenesis assay and identified HER2 mutant sequences from clonal cells survived from Tucatinib and Neratinib treatment in Ba/F3 HER2 WT cells. There were 9 types of Tucatinib-resistant mutations. The most common Tucatinib-resistant mutation type was T862A/S, which was found in 5 out of total 15 clones. All types of mutations showed 6~70 folds resistance for Tucatinib compared to WT. These mutant types were also resistant against another non-covalent HER2 TKI, Lapatinib. In case of Neratinib, HER2 S963P was derived from two different clones, showing 4~8 folds resistance against Neratinib compared to WT. However, a series of VRN10 was relatively sensitive toward all Tucatinib or Neratinib resistant mutants. Based on our in vitro assay and ENU mutagenesis studies, VRN10s can be a new option to overcome HER2 TKI drug resistance derived by HER3 activation or HER2 mutagenesis.

Citation Format: Chan Mi Park, Jihye Yoo, Mingyeong Son, Hong-ryul Jung, Jin-Hee Park, Jeongbum Son, Eunhwa Ko, Sunghwan Kim. VRN10s, a series of HER2 inhibitors to overcome NRG-mediated drug resistance and acquired-drug resistant HER2 mutations [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P067.