Evaluation of AZD8931, an Equipotent Inhibitor of erbB1, erbB2, and erbB3 Receptor Signaling, on Ligand Stimulated Breast Cancer Cell Lines with Differing Levels of erbB2 Expression. (2009)

Abstract Background: Further treatment options for patients whose breast cancers do not overexpress erbB2 are required. AZD8931, an equipotent, reversible inhibitor of erbB1 (HER1, EGFR), erbB2 (HER2), and erbB3 (HER3) receptor signaling may be useful in this setting and may lead to inhibition of tumor cell proliferation, invasion, metastasis, angiogenesis and tumor cell survival.Objectives: To compare the activity of AZD8931 with other erbB inhibitors (gefitinib [G] and lapatinib [L]) in breast cancer cell lines stimulated with erbB ligands.Methods: A panel of 9 breast cancer cell lines with differing erbB2 expression levels were used: erbB2+/ER+ (BT474c; MDA-MB-361); erbB2+/ER- (MDA-MB-453; SKBR-3); erbB2-/ER+ (MCF7; T47D; ZR75-1); or erbB2-/ER- (MDA-MB-231; MDA-MB-468). Following overnight serum starvation, cells were incubated with AZD8931, G or L (0-10 µM) for 90 min and then stimulated with erbB ligands (50 ng/ml; EGF, TGFα, amphiregulin, epiregulin, betacellulin, neuregulin1, or HBEGF) for 5 min before lysis. Levels of phosphorylated erbB1, erbB2, and erbB3 were analyzed by ELISA. For IC50 determination, mean basal phosphorylation was subtracted. Geometric mean IC50s were calculated from triplicate assays and 2-sided unequal variance t-tests compared logIC50s.Results: AZD8931 demonstrated potent inhibitory activity (IC50s ≤10610 nM) when phosphorylation of erbB1, erbB2 or erbB3 receptors was driven by any erbB ligand. G demonstrated potent inhibitory activity (IC50s ≤20 nM) when the phosphorylation of erbB1 and erbB2 was driven by any erbB ligand. L more strongly inhibited the phosphorylation of erbB2 (IC50s ≤10 nM) than erbB1 (IC50s &lt;400 nM) and showed a ligand and cell-dependant range of activities against erbB3 phosphorylation. AZD8931 was particularly differentiated from G and L in the inhibition of neuregulin1-driven erbB3 phosphorylation: IC50s were lower for AZD8931 (1-5 nM) than for G (1-120 nM) or L (20-80 nM) in the majority of the cell lines tested. Inhibition of erbB1 phosphorylation driven by EGF (IC50s ≤ vs &gt;20 nM), TGFα (≤5 vs &gt;20 nM), HB-EGF (≤ vs &gt;25 nM), or betacellulin (≤6 vs 10-118 nM) also indicated more potent inhibitory activity for AZD8931 over L in cell lines that respond to ligand stimulation. No phosphorylation response to amphiregulin was seen in any of the cell lines.Conclusion: This study demonstrates that in a range of breast cell lines with varying levels of erbB2 expression, AZD8931 is a potent and balanced inhibitor of erbB1, erbB2, and erbB3 signaling. The pharmacological profile of AZD8931 is thus distinct from G and L and suggests that AZD8931 offers an agent to test the hypothesis that combined, balanced inhibition of erbB signaling could provide clinical benefit. AZD8931 may be particularly useful in the treatment of solid tumors that do not overexpress erbB2 including trastuzumab-ineligible breast cancer, an area of unmet medical need. AZD8931 is being evaluated in a Phase I clinical trial. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5059.