Antitumor Activity of a Monoclonal Antibody Targeting Major Histocompatibility Complex Class I–Her2 Peptide Complexes
Menée sur des lignées cellulaires et à l'aide de xénogreffes, cette étude évalue les effets d'un nouvel anticorps monoclonal, appelé RL1B, sur les cellules de cancers surexprimant HER2
Background Applications of trastuzumab are limited to breast cancer patients with high Her2-expressing tumors. We developed a T-cell receptor mimic (TCRm) monoclonal antibody (hereafter called RL1B) that targets the Her2-E75 peptide (residues 369–377)–HLA-A2 complex and examined its effects in Her2-expressing cancer cells.
Methods RL1B binding affinity was determined by surface plasmon resonance and specificity was demonstrated using Her2 antigen-positive and negative tumor cell lines. Immunohistochemistry was used to assess binding to frozen sections of human carcinomas (n = 3). Antitumor activity mediated by RL1B and trastuzumab against Her2+ tumor cell lines was evaluated using the WST-1 cell viability assay and caspase-3 and poly(ADP-ribose) polymerase cleavage assays. A xenograft mouse model (n = 6 per group) was used to assess RL1B antitumor activity. Mechanisms of RL1B-mediated cytotoxicity were evaluated with confocal microscopy, flow cytometry, and histology. All statistical tests were two-sided.
Results RL1B bound with high specificity and affinity to the E75 peptide–HLA-A2 complex in all Her2+ and HLA-A2+ cancer cell lines and human carcinomas. Compared with control antibody, RL1B suppressed growth of low Her2–expressing breast tumors in mice (mean volume, RL1B vs control = 241mm3 vs 1531mm3; P = .0109) and statistically significantly increased mouse survival (P = .0098). It reduced viability compared to control monoclonal antibody–treated cells and statistically significantly increased caspase 3 activation of all Her2+ carcinoma cell lines tested, whereas trastuzumab induced apoptosis only in high Her2–expressing cancer cells. Mechanisms of RL1B cytotoxicity were associated with antibody internalization and intracellular signaling.
Conclusion The TCRm RL1B could be a new approach to immunotherapy of Her2-expressing malignancies.
Journal of the National Cancer Institute , résumé, 2013