The Smac Mimetic BV6 Improves NK Cell-Mediated Killing of Rhabdomyosarcoma Cells by Simultaneously Targeting Tumor and Effector Cells

Abstract

Rhabdomyosarcoma (RMS), the most common cancer of connective tissues in pediatrics, is often resistant to conventional therapies. One underlying mechanism of this resistance is the overexpression of Inhibitor of Apoptosis (IAP) proteins, leading to a dysfunctional cell death program within tumor cells. Smac mimetics (SM) are small molecules that can reactivate the cell death program by antagonizing IAP proteins and thereby compensating their overexpression. Here, we report that SM sensitize two RMS cell lines (RD and RH30) toward natural killer (NK) cell-mediated killing on the one hand, and increase the cytotoxic potential of NK cells on the other. The SM-induced sensitization of RH30 cells toward NK cell-mediated killing is significantly reduced through blocking tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) on NK cells prior to coculture. In addition, the presence of zVAD.fmk, a pancaspase inhibitor, rescues tumor cells from the increase in killing, indicating an apoptosis-dependent cell death. On the NK cell side, the presence of SM in addition to IL-2 during the ex vivo expansion leads to an increase in their cytotoxic activity against RH30 cells. This effect is mainly TNFα-dependent and partially mediated by NK cell activation, which is associated with transcriptional upregulation of NF-κB target genes such as IκBα and RelB. Taken together, our findings implicate that SM represent a novel double-hit strategy, sensitizing tumor and activating NK cells with one single drug.

ASTX660, an antagonist of cIAP1/2 and XIAP, increases antigen processing machinery and can enhance radiation-induced immunogenic cell death in preclinical models of head and neck cancer

“…Previous studies suggest that IAP antagonists, in addition to their ability to enhance sensitivity to TNF-mediated apoptosis of cancer cells, are able to modulate diverse innate and adaptive anti-tumor immune responses. 8,18,20,21,25,26,42 Promising pre-clinical data across multiple cancer models and numerous ongoing clinical trials involving IAP antagonists (NCT02503423, NCT02649673, NCT03111992) highlight the great potential for combining these novel agents with chemotherapy, radiation and/or immunotherapies such as checkpoint inhibitors. 20,21,26 Despite significant advances in understanding how IAP antagonists enhance anti-tumor functions of immune cells, 20,21,25 the tumor-cell-intrinsic mechanisms involved in inducing these immune responses remain largely unexplored, particularly in HNSCC.…”

The Immuno-Modulatory Effects of Inhibitor of Apoptosis Protein Antagonists in Cancer Immunotherapy

“…There have been several reports that IAP antagonists potentiate Hodgkin lymphoma susceptibility towards NK cell-mediated killing [97,98], and a TNF-dependent increase in the effector function of NK cells in vitro following the administration of birinapant has been reported [85]. Similarly, BV6 improves NK cell-mediated killing of rhabdomyosarcoma cells by sensitising them to NK cell-mediated killing through TNF, whilst simultaneously enhancing the cytotoxic potential of the NK cells through increasing NK cell activation [99]. Furthermore, the administration of AG-1387 resulted in a five-fold increase in NK cell tumour infiltration, as well as inducing tumour cell apoptosis directly in a hepatocellular carcinoma xenograph model [80].…”

Mechanisms of Resistance to NK Cell Immunotherapy

“…Similarly, resistance to NK cell killing may be overcome by using SMAC mimetics, a new class of targeted drugs that act as IAP antagonists. SMAC mimetics increase NK cell proliferation in vitro and in vivo [120], increase cytotoxicity [121][122][123][124] and overcome rituximab resistance in preclinical models of B cell lymphoma [125]. Furthermore, SMAC mimetics sensitize sarcomas and hematological cancers to CIK cell adoptive therapy [126,127] and they have also demonstrated clinical efficacy in mouse models of glioblastoma and osteosarcoma, alone or in combination with checkpoint blockade [128,129].…”