Abstract P5-18-10: Chemotherapy can enhance trastuzumab-mediated ADCC

Abstract

Abstract Trastuzumab, a recombinant humanized monoclonal antibody directed to the HER2 protein, has shown survival benefits in women with HER2-positive breast cancer, and treatment is now FDA-approved in combination with chemotherapy. However, some patients do not respond clinically to trastuzumab, pointing to the need for further definition of trastuzumab killing activity on tumor cells to optimize this therapy. Recent clinical data indicate a synergistic therapeutic effect between trastuzumab and taxanes in HER2-positive breast cancer patients, but the mechanism(s) underlying this synergy remains unclear. Because drug-stressed cells can dynamically regulate factors that favor activity of immune effector cells, and because trastuzumab-mediated ADCC is crucially dependent on NK cell activity, we hypothesize that this synergy reflects enhanced trastuzumab-mediated ADCC on tumor cells due to improved rather than impaired participation of immune effectors resulting from drug-induced stress. To test this hypothesis, we investigated the effect of chemotherapy in HER2-positive breast carcinoma models on NK receptor ligands and correlated the changes in these molecules with the ability of trastuzumab to mediate ADCC. Flow cytometry revealed a 4-fold upmodulated surface expression of NKG2D (MICA, MICB, ULBP1, ULBP2) and DNAM-1 (CD112 and CD155) ligands in HER2-positive breast carcinoma cell lines BT474 and MDA-MB-361 treated for 6 hr with taxotere at a 72-hr IC50 dose, consistent with results of Western blot analysis using soluble lysates obtained from chemotherapy-treated HER2-positive breast carcinoma xenografts. The enhanced expression of NKG2D and DNAM-1 ligands in breast carcinoma cells was accompanied by about a 50% increase in trastuzumab-mediated in vitro ADCC in chemotherapy-treated versus untreated cells. Antibodies blocking NKG2D and DNAM-1, but not control monoclonal antibody, abolished the chemotherapy-induced increase of in vitro trastuzumab-dependent ADCC. Increased expression of NK ligands in taxotere-treated BT474 cells was associated with cytoskeletal damage assessed by confocal microscopy; at 72 hr after chemotherapy, NK ligands returned to basal levels, pointing to the importance of duration of NK ligand enhancement for the chemotherapy-induced trastuzumab-mediated ADCC. Together, our results indicate that chemotherapy can modulate expression levels of NK-activating ligands on human breast carcinoma cells in correlation with trastuzumab-mediated ADCC, raising the possibility of identifying optimal chemotherapy administration schedules to maximize activity of trastuzumab-mediated ADCC effectors. (Partially supported by AIRC) Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-18-10.