Supplemental Fig.S3. In pancreatic cancer cells, ch9F7-F11-Emb is a negative allosteric modulator of NRG1-mediated signaling. The low-fucose non-NRG1 competing allosteric anti-HER3 antibody ch9F7-F11-Emb inhibits in a dose-dependent manner NRG1-mediated cell signaling more efficiently than the ligand-competing H4B-121-Emb antibody. BxPC3 cells were pre-stimulated with 1nM NRG1 for 5min, before adding antibodies at various concentrations for another 25min. After cell lysis, the expression levels of total and phosphorylated HER3 (Tyr1289, Tyr1197 and Tyr1222), and total and phosphorylated AKT (Ser473) were measured by western blotting (A) using the appropriate antibodies. Phosphorylation was then pixel-quantified with Image J (B) and shown relative to the maximal phosphorylation (100%) evaluated in NRG1-stimulated cells without antibody treatment (M). Results are the mean {plus minus} SD of three independent experiments
ARTICLE ABSTRACT
Exploratory clinical trials using therapeutic anti-HER3 antibodies strongly suggest that neuregulin (NRG1; HER3 ligand) expression at tumor sites is a predictive biomarker of anti-HER3 antibody efficacy in cancer. We hypothesized that in NRG1-expressing tumors, where the ligand is present before antibody treatment, anti-HER3 antibodies that do not compete with NRG1 for receptor binding have a higher receptor-neutralizing action than antibodies competing with the ligand for binding to HER3. Using time-resolved–fluorescence energy transfer (TR-FRET), we demonstrated that in the presence of recombinant NRG1, binding of 9F7-F11 (a nonligand-competing anti-HER3 antibody) to HER3 is increased, whereas that of ligand-competing anti-HER3 antibodies (H4B-121, U3-1287, Ab#6, Mab205.10.2, and MOR09825) is decreased. Moreover, 9F7-F11 showed higher efficacy than antibodies that compete with the ligand for binding to HER3. Specifically, 9F7-F11 inhibition of cell proliferation and of HER3/AKT/ERK1/2 phosphorylation as well as 9F7-F11–dependent cell-mediated cytotoxicity were higher in cancer cells preincubated with recombinant NRG1 compared with cells directly exposed to the anti-HER3 antibody. This translated in vivo into enhanced growth inhibition of NRG1-expressing BxPC3 pancreatic, A549 lung, and HCC-1806 breast cell tumor xenografts in mice treated with 9F7-F11 compared with H4B-121. Conversely, both antibodies had similar antitumor effect in NRG1-negative HPAC pancreatic carcinoma cells. In conclusion, the allosteric modulator 9F7-F11 shows increased anticancer effectiveness in the presence of NRG1 and thus represents a novel treatment strategy for NRG1-addicted tumors. Mol Cancer Ther; 16(7); 1312–23. ©2017 AACR.
