Abstract P1-04-04: Activating HER2 mutations promote oncogenesis and resistance to HER2-targeted therapies in breast cancer

Abstract

Abstract Purpose: Somatic mutations in the tyrosine kinase domain of human epidermal growth factor receptor2 (HER2) have been reported to lead to resistance to HER2-targeted therapies in HER2-positive breast cancer, while activating mutations of HER2 have been described in HER2-negative breast cancer. The prevalence, clinicopathological characteristics, and phenotypes of HER2 mutations are not well established, thus we sought to describe the HER2 mutation profile of Chinese breast cancer patients. Methods: DNA samples were gathered from breast cancer patients undergoing neoadjuvant (N=102) or adjuvant therapy (N=498) at Fudan University Shanghai Cancer Center between January 1, 2006 and December 31, 2012. Sanger sequencing was performed to analyze all exons of HER2 to identify somatic mutations. To determine the phenotypes of novel HER2 mutations, in vitro kinase assays, protein structure analysis, cell culture, and xenograft experiments were conducted. Results: 10 HER2 somatic mutations were observed in 17 patients (17/600, 2.83%). 7 novel HER2 mutations were uncovered, 4 in the transmembrane domain and 3 in the kinase domain. Kinase domain mutations L768S and V773L were detected in HER2-negative tumors, while K753E was found in HER2-positive disease. In vitro kinase assays found that L768S and V773L exhibited a significant increase of tyrosine kinase-specific activity, while Western blots showed that L768S and V773L strongly increased phosphorylation of all signaling proteins in both MCF10A and MCF7cell lines, indicating that they were activating mutations. In Matrigel cultures, L768S and V773L formed acini when seeded in vehicle, but maintained spherical morphology when seeded in culture containing trastuzumab. The addition of lapatinib in Matrigel culture inhibited the growth of all except K753E, which was successfully inhibited by neratinib. Similarly, L768S, V773L and K753E increased the number of cell colonies formed in soft agar, trastuzumab and lapatinib treatment decreased the number of colonies formed by L768S and V773L, but only neratinib could inhibit the colony growth of K753E. Xenograft showed L768S and V773L displayed a more rapid growth, while K753E showed resistance to lapatinib in vivo. MCF10A cells bearing K753E mutation were found to be resistant to lapatinib (IC50>10,000 nmol/L), but could be inhibited by neratinib, though requiring a relatively higher dosage (IC50 of 32 nmol/L) than HER2 WT (IC50 of 480 nmol/L for lapatinib, <2 nmol/L for neratinib) and other HER2 mutations. Meanwhile, clinical follow-up showed that the 2 patients with K753E mutation who received adjuvant trastuzumab treatment presented with either brain or bone metastasis, in their 3rd and 5th year after initial cancer diagnosis, suggesting K753E mutation may have a role in trastuzumab resistance as well. Conclusions: HER2 somatic mutations were found in 2.83% of patients in this study. HER2-positive tumors harboring certain HER2 kinase domain resistance mutations may not benefit from trastuzumab or lapatinib treatment, and neratinib may offer an alternative treatment option for these patients. HER2-negative disease with activating mutations may benefit from HER2-targeted therapies, and may be of interest in prospective clinical trials. Citation Format: Wen-Jia Zuo, Yi-Zhou Jiang, Ke-Da Yu, Zhi-Ming Shao. Activating HER2 mutations promote oncogenesis and resistance to HER2-targeted therapies in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-04-04.