Abstract B171: U3-1287 (AMG 888), a fully human anti-HER3 mAb, demonstrates in vitro and in vivo efficacy in NSCLC models

Background: EGFR TKIs have demonstrated activity in NSCLC, however most patients are resistant or acquire resistance to therapy. HER3 is a member of the EGFR family of receptors and is considered a target for NSCLC treatment. Though HER3 lacks kinase activity, it is a scaffold for PI3K signaling for the HER family via heterodimeric interactions. In preclinical models, activation of HER3 is a resistance mechanism (de novo and acquired) to current HER inhibitors. Herein, we report the activity of U3-1287 (AMG 888) in preclinical models of human NSCLC. We also evaluate human NSCLC tumor specimens for detectable pHER3, pAKT and HRG, the ligand for HER3. Methods: To determine the inhibition of HER3 oncogenic signaling, A549 and Calu-3 NSCLC cells were treated with 100 nM of U3-1287 (AMG 888), panitumumab, lapatinib or control for 1 hour. To determine in vitro efficacy on anchorage independent growth, A549 cells were treated with 10 g/mL U3-1287 (AMG 888), other HER family Abs or control mAb in serum containing medium. Tumor cell colonies formed in the absence of exogenous ligand for 10 days and were stained with MTT and quantified using a Scanalyzer HTS camera imaging system. To determine in vivo efficacy, mice bearing ∼200 mm3 A549 or Calu-3 NSCLC xenografts were treated 2x/week with anti-HER family inhibitors or control. A549 xenograft tumors were analyzed for the inhibition of pHER3 byWestern blotting. The anti-tumor effect of U3-1287 (AMG 888) with EGFR inhibitors was tested in the Calu-3 NSCLC xenograft model. Levels of pHER3, pAKT and HRG in 20 NSCLC patient specimens were determined by Western blotting. Results: Treatment with U3-1287 (AMG 888) resulted in inhibition of pHER3 in both NSCLC cell lines. pAKT was inhibited in the A549 cell line with U3-1287 (AMG 888) as a single agent and in A549 and Calu-3 cells to a greater extent when combined with another HER family inhibitor. U3-1287 (AMG 888) inhibited colony growth by 50% (p Conclusions: U3-1287 (AMG 888) inhibits proximal and distal HER3 oncogenic signaling and cell growth in NSCLC cell lines in vitro and in vivo. NSCLC xenografts are sensitive to U3-1287 (AMG 888) treatment as single agent or in combination with the anti-EGFR agents. The preclinical data together with the detectable levels of activated HER3 in patient samples provide evidence for the potential clinical application of U3-1287 (AMG 888) in NSCLC. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B171.