Browsing by Subject "Inflammatory Breast Neoplasms"

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Smac mimetic Birinapant induces apoptosis and enhances TRAIL potency in inflammatory breast cancer cells in an IAP-dependent and TNF-α-independent mechanism.
    (Breast Cancer Res Treat, 2013-01) Allensworth, Jennifer L; Sauer, Scott J; Lyerly, H Kim; Morse, Michael A; Devi, Gayathri R
    X-linked inhibitor of apoptosis protein (XIAP), the most potent mammalian caspase inhibitor, has been associated with acquired therapeutic resistance in inflammatory breast cancer (IBC), an aggressive subset of breast cancer with an extremely poor survival rate. The second mitochondria-derived activator of caspases (Smac) protein is a potent antagonist of IAP proteins and the basis for the development of Smac mimetic drugs. Here, we report for the first time that bivalent Smac mimetic Birinapant induces cell death as a single agent in TRAIL-insensitive SUM190 (ErbB2-overexpressing) cells and significantly increases potency of TRAIL-induced apoptosis in TRAIL-sensitive SUM149 (triple-negative, EGFR-activated) cells, two patient tumor-derived IBC models. Birinapant has high binding affinity (nM range) for cIAP1/2 and XIAP. Using isogenic SUM149- and SUM190-derived cells with differential XIAP expression (SUM149 wtXIAP, SUM190 shXIAP) and another bivalent Smac mimetic (GT13402) with high cIAP1/2 but low XIAP binding affinity (K (d) > 1 μM), we show that XIAP inhibition is necessary for increasing TRAIL potency. In contrast, single agent efficacy of Birinapant is due to pan-IAP antagonism. Birinapant caused rapid cIAP1 degradation, caspase activation, PARP cleavage, and NF-κB activation. A modest increase in TNF-α production was seen in SUM190 cells following Birinapant treatment, but no increase occurred in SUM149 cells. Exogenous TNF-α addition did not increase Birinapant efficacy. Neutralizing antibodies against TNF-α or TNFR1 knockdown did not reverse cell death. However, pan-caspase inhibitor Q-VD-OPh reversed Birinapant-mediated cell death. In addition, Birinapant in combination or as a single agent decreased colony formation and anchorage-independent growth potential of IBC cells. By demonstrating that Birinapant primes cancer cells for death in an IAP-dependent manner, these findings support the development of Smac mimetics for IBC treatment.
  • Thumbnail Image
    ItemOpen Access
    X-linked inhibitor of apoptosis protein mediates tumor cell resistance to antibody-dependent cellular cytotoxicity.
    (Cell Death Dis, 2016-01-28) Evans, MK; Sauer, SJ; Nath, S; Robinson, TJ; Morse, MA; Devi, GR
    Inflammatory breast cancer (IBC) is the deadliest, distinct subtype of breast cancer. High expression of epidermal growth factor receptors [EGFR or human epidermal growth factor receptor 2 (HER2)] in IBC tumors has prompted trials of anti-EGFR/HER2 monoclonal antibodies to inhibit oncogenic signaling; however, de novo and acquired therapeutic resistance is common. Another critical function of these antibodies is to mediate antibody-dependent cellular cytotoxicity (ADCC), which enables immune effector cells to engage tumors and deliver granzymes, activating executioner caspases. We hypothesized that high expression of anti-apoptotic molecules in tumors would render them resistant to ADCC. Herein, we demonstrate that the most potent caspase inhibitor, X-linked inhibitor of apoptosis protein (XIAP), overexpressed in IBC, drives resistance to ADCC mediated by cetuximab (anti-EGFR) and trastuzumab (anti-HER2). Overexpression of XIAP in parental IBC cell lines enhances resistance to ADCC; conversely, targeted downregulation of XIAP in ADCC-resistant IBC cells renders them sensitive. As hypothesized, this ADCC resistance is in part a result of the ability of XIAP to inhibit caspase activity; however, we also unexpectedly found that resistance was dependent on XIAP-mediated, caspase-independent suppression of reactive oxygen species (ROS) accumulation, which otherwise occurs during ADCC. Transcriptome analysis supported these observations by revealing modulation of genes involved in immunosuppression and oxidative stress response in XIAP-overexpressing, ADCC-resistant cells. We conclude that XIAP is a critical modulator of ADCC responsiveness, operating through both caspase-dependent and -independent mechanisms. These results suggest that strategies targeting the effects of XIAP on caspase activation and ROS suppression have the potential to enhance the activity of monoclonal antibody-based immunotherapy.