Abstract 36: Functional characterization of ERBB2 mutations and response to targeted therapies

Amplification of HER2 (ERBB2) has been well characterized as an oncogenic driver, but only recently have mutations in ERBB2 also been shown to have activating and tumorigenic potential. We sought to characterize a large number of ERBB2 mutations seen in sequencing data from patients at MSKCC as well as the cBioPortal for Cancer Genomics, and determine the therapeutic response of these mutations to HER2 targeted therapies. HER2 is a transmembrane tyrosine kinase that is responsible for regulating cell growth and proliferation, among other cell processes. The ERBB2 gene is amplified in approximately 25% of breast cancers and in this disease, HER2 directed therapies are now a component of standard care. More recently, ERBB2 mutations were identified in a variety of cancers, most commonly cancers of the urinary tract but also at lower frequency in cancers of the breast, stomach, colon and lung, among others. Recent data has shown that select ERBB2 mutations activate HER kinase signaling and promote anchorage independent growth in vitro and tumor formation in mice. However, only a small number of ERBB2 mutations have been reported and biologically characterized as oncogenic in preclinical models. Moreover, the therapeutic impact of ERBB2 mutations has not been validated. To screen for activating potential of a large number of ERBB2 mutations, cells were transiently transfected to express ERBB2 mutants generated using site-directed mutagenesis. Expression of several mutations led to increased receptor activation and downstream signaling, as determined by levels of phosphorylated HER2, AKT, ERK, and S6 protein, whereas other mutations had little impact on activity compared to a wild type HER2 control. Stable cell lines were then generated to express the activating mutations and tested for transforming ability in soft agar. Mutations promoted colony formation, with certain mutations producing more colonies. Cells were also grown in the presence of the dual EGFR/HER2 inhibitor, neratinib. While certain mutations were more sensitive to lower doses of neratinib, addition of neratinib at higher doses abrogated colony formation in soft agar for all mutations. While a number of ERRB2 mutations have been shown to have tumorigenic potential, not all mutations respond similarly to HER2 targeted therapies. We hope to create an annotated database of alterations so that in the future, patients can be screened for specific mutations to minimize ineffective and unnecessary treatment options.

Citation Format: Hannah Johnsen, Aphrothiti Hanrahan, Alexis Jones, David Solit. Functional characterization of ERBB2 mutations and response to targeted therapies. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr 36.