SMAC Mimetic Debio 1143 and Ablative Radiation Therapy Synergize to Enhance Antitumor Immunity against Lung Cancer

Abstract

Purpose: Adaptive antitumor immunity following ablative radiotherapy (ART) is attenuated by host myeloid-derived suppressor cell (MDSC), tumor-associated macrophage (TAM), and regulatory T-cell (Treg) infiltrates. We hypothesized treatment with ART and a secondary mitochondrialderived activators of caspase (SMAC) mimetic could reverse the immunosuppressive lung cancer microenvironment to favor adaptive immunity.Experimental Design: To evaluate for synergy between ART and the SMAC mimetic Debio 1143 and the dependence upon CD8 þ T cells and TNFa, we used LLC-OVA syngeneic mouse model of lung cancer and treated them with Debio 1143 and/or ART (30 Gy) with or without anti-CD8, anti-TNFa, or anti-IFNg antibodies. Tumorinfiltrating OVA-specific CD8 þ T cells, Tc1 effector cells, MDSCs, TAMs, and Tregs, were quantified by flow cytometry. Tc1-promoting cytokines TNFa, IFNg, and IL1b and the immunosuppressive IL10 and Arg-1 within LLC-OVA tumor tissue or mouse serum were measured by RT-PCR and ELISA.Results: ART delayed tumor growth, and the addition of Debio 1143 greatly enhanced its efficacy, which included several complete responses. These complete responders rejected an LLC-OVA tumor rechallenge. ART and Debio 1143 synergistically induced a tumor-specific, Tc1 cellular and cytokine response while eliminating immunosuppressive cells and cytokines from the tumor microenvironment. Depletion of CD8 þ cells, TNFa, and IFNg with blocking antibody abrogated synergy between ART and Debio 1143 and partially restored tumor-infiltrating MDSCs.Conclusions: Debio 1143 augments the tumor-specific adaptive immunity induced by ART, while reversing host immunosuppressive cell infiltrates in the tumor microenvironment in a TNFa, IFNg, and CD8 þ T-cell-dependent manner. This provides a novel strategy to enhance the immunogenicity of ART. The combination of ART and Debio 1143 reduces immunosuppressive cell populations and produces an OVA-specific cytotoxic T-cell response in the tumor microenvironment. A, CD8 þ T lymphocytes primed with OVA-tetramer were quantified in LLC-OVA tumors using flow cytometry, and are expressed as a percentage of CD8 þ cells. IFNg (B) and TNFa (C) expression among OVA þ CD8 þ lymphocytes was determined by flow cytometry. These cells are expressed as a percentage of CD8 þ cells. D, Tumors were analyzed for the MDSC markers CD45/Gr1/CD11b using flow cytometry. CD11b þ Gr-1 þ cells are expressed as a percentage of CD45 þ cells. E, LLC-OVA tumors were assessed for the TAM markers CD45/F4/80/CD11b by flow cytometry. The percentage of TAMs is expressed as a percentage of CD45 þ cells. F, LLC-OVA tumors were assessed for the Treg markers CD4/FOXP3/CD25 by flow cytometry. Tregs are expressed as a percentage of CD4 þ cells. All plots show a representative sample (left) and are expressed as a mean with 5 plotted replicates (right). Statistical differences were assessed using the unpaired Student t test. P values are indicated as follows: Ã , P < 0.05; ÃÃ , P < 0.01; ÃÃÃ , P < 0.001.

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

“…Our study builds upon these prior findings by showing that ASTX660 can induce expression of classic ICD markers in sensitive cell lines in vitro, suggesting that this mechanism of anti-tumor immunity is intact for a subset of HNSCC tumors. Another study showed synergistic anti-tumor immunity when combining IAP antagonist Debio 1143 with XRT in lung cancer models, 48 a relationship that Figure 4. ASTX660 enhances TIL-mediated killing of HNSCC cell lines.…”

ANTP‐SmacN7 fusion peptide‐induced radiosensitization in A549 cells and its potential mechanisms

“…IAP inhibition has attracted extensive attention over the last decade. With the in‐depth study of IAP functional sites, the antitumor and radiosensitizing effects of Smac and its mimetics have become an important research focus …”

Potential of E3 Ubiquitin Ligases in Cancer Immunity: Opportunities and Challenges

“…In addition, APG-1387 could induce tumor cell death and enhance innate antitumor immunity in HBV-positive hepatocellular carcinoma with a high expression of cIAP2 and stimulate adaptive immunity in vitro by reducing Treg differentiation and PD-1 expression [ 158 ]. The SMAC mimic Debio 1143 enhanced tumor-specific adaptive immunity induced by ablation radiotherapy [ 208 ]. In addition, IAP antagonists could significantly improve the antitumor effects of cells or other immune agents in combination therapy, including chimeric antigen receptor (CAR) T-cells, cytokine-induced killer cells, NKT cell inducers α-GalCer, TNF-α, and PD-1 blockade [ 13 ].…”