Drozitumab, a Human Agonist Monoclonal Antibody to TRAIL-R2 Induces Apoptosis in Triple-Negative Breast Cancer Cell Lines with Mesenchymal Features

Breast cancers can be divided into distinct subtypes that express estrogen receptors (ER), progesterone receptors (PR), those that have amplification of HER2/Neu, and those that lack expression of ER or PR and lack amplification of Her2/Neu (so called triple negative breast cancer or TNBC).  Previously, we have shown that a recombinant GST fusion protein with TNF-related Apoptosis Inducing Ligand (GST-TRAIL) selectively kills TNBC cells with mesenchymal features by activation of TRAIL receptor 2 (TRAIL-R2).  In this study we have characterized the growth inhibitory effects of a clinically relevant agonistic antibody to TRAIL-R2, referred to as Drozitumab.  To determine the selectivity of Drozitumab, we chose a panel of 15 breast cancer cell lines including 3 ER/PR positive cell lines, 4 HER2/Neu amplified cell lines, and 8 triple-negative cell lines.  Treatment of these cells with Drozitumab selectively killed TNBC cell lines with mesenchymal features.  ER positive, HER2/Neu amplified and TNBC cell lines with epithelial features were resistant to Drozitumab induced cell death.  Drozitumab induced caspase activation (measured by activation of the initiator caspase 8, activation of the downstream caspases 3/7, and PARP cleavage).  The toxicity of Drozitumab was blocked by the pan-caspase inhibitor z-VAD-FMK.  This was identical to the pattern seen with GST-TRAIL.  Cross-linking with an anti-FC antibody enhanced the efficacy of Drozitumab as shown by the more rapid appearance of cleaved caspase 8, greater caspase 3/7 activity, and more rapid PARP cleavage. This data suggests that TRAIL-R2 targeted therapies may have therapeutic potential in the treatment of TNBC with mesenchymal features.