Sensitivity to pertuzumab (2C4) in ovarian cancer models: cross-talk with estrogen receptor signaling.

Pertuzumab (Omnitarg, rhuMab 2C4) is a humanized monoclonal antibody, which inhibits HER2 dimerization. Because it has shown some clinical activity in ovarian cancer, this study sought to identify predictors of response to this agent in a model of ovarian cancer. A panel of 13 ovarian cancer cell lines was treated with heregulin beta1 (HRGbeta1) or transforming growth factor-alpha, and cell proliferation was assessed. Both agents increased cell number in the majority of cell lines studied, the response to both being similar (r = 0.83; P = 0.0004, Pearson test). HRGbeta1 stimulation could be partially reversed by pertuzumab in 6 of 13 cell lines, with complete reversal in PE04 and PE06 cells. Addition of pertuzumab to transforming growth factor-alpha-stimulated cells produced growth inhibition in 3 of 13 cell lines (PE01, PE04, and PE06). The magnitude of HRGbeta1-driven growth stimulation correlated significantly with an increase in extracellular signal-regulated kinase 2 (P = 0.037) but not Akt (P = 0.99) phosphorylation. Such HRGbeta1-driven phosphorylation of extracellular signal-regulated kinase 1/2 and Akt could be reduced with pertuzumab, accompanied by changes in cell cycle distribution. In cell lines responsive to pertuzumab, HRGbeta1-enhanced phosphorylation of HER2 (Tyr(877)) was reduced. Estrogen-stimulated changes in growth, cell cycle distribution, and signaling were reversed by pertuzumab, indicating cross-talk between HER2 and estrogen signaling. These data indicate that there is a subset of ovarian cancer cell lines sensitive to pertuzumab and suggest possible predictors of response to identify patients who could benefit from this therapy. Furthermore, we have identified an interaction between HER2 and estrogen signaling in this disease.