Potent synergistic anti-tumor activity of a novel humanized anti-HER2 antibody hersintuzumab in combination with trastuzumab in xenograft models

Immunotherapy of HER2-overexpressing cancers by FDA approved monoclonal antibodies (mAbs) such as trastuzumab and pertuzumab has shown promising results. We have recently produced a novel humanized anti-HER2 mAb, hersintuzumab, which did not sterically inhibit binding of trastuzumab and pertuzumab to HER2, thus recognizing a distinct epitope on subdomain I + II of HER2. In this study, we assessed the in vitro and in vivo anti-tumor activity of this mAb individually and in combination with trastuzumab. Different HER2-overexpressing human cancer cell lines, including SKOV3, NCI-N87 HCC1954 and BT-474 were cultured and binding reactivity of Hersintuzumab to these cell lines was analyzed by flow cytometry. In addition, the inhibitory effect of different concentrations of hersintuzumab, trastuzumab and their combination on tumor cells growth was assessed by XTT assay. For Assessment of tumor growth inhibition in xenograft model, Balb/c athymic nude mice were subcutaneously injected with NCI-N87 and SKOV3 tumor cells and then treated intravenously with these mAbs. Our results showed that hersintuzumab could bind to all HER2-overexpressing cell lines similar to trastuzumab. In vitro experiments showed that both hersintuzumab and trastuzumab individually and in combination inhibited growth of all cell lines with the exception of HCC-1954.Inhibitory effect of the combination of mAbs was significantly higher than that of each mAb alone. Similar results were obtained in the gastric (NCI-N87) and ovarian (SKOV-3) tumor xenograft models. Hersintuzumab in combination with trastuzumab induces synergic anti-tumor effects on HER2-overexpressing cells in vitro and in vivo and is potentially a therapeutic tool for treatment of HER2-overexpressing cancers.