Abstract 882: Soluble TNF blockade enhances trastuzumab-deruxtecan innate antitumor immune response and type-I IFN signalling in HER2-positive breast cancer

Since DESTINY-Breast03 results where trastuzumab-deruxtecan (T-DXd) showed remarkable overall survival improvement, this drug is used to treat patients with unresectable or metastatic HER2-positive (HER2+) breast cancer who have received prior anti-HER2-based regimen. One antitumor mechanism of T-DXd is attributed to DXd inhibition of topoisomerase I in the tumor cells that internalized the drug, and to the bystander effect of DXd on neighbor tumor cells. Reports describe that topoisomerase I inhibitors produce DNA fragmentation, stimulating cGAS/STING pathway and producing type-I IFN, a key mediator of the innate immune response against tumors. Previously, we reported that soluble TNF (sTNF) overproduction by HER2+ tumors generates resistance to trastuzumab-based therapies. Blocking sTNF with INB03 (DN), a dominant-negative molecule, sensitized tumors to therapy and improved the antitumoral immune response. Here, we explore if blocking sTNF can also improve T-DXd antitumor effect, and its impact on the innate immune response involving cGAS/type-I IFN, in a model with resistance to multiple HER2-targeted therapies. Female nude mice bearing JIMT-1 tumors were treated i.p. twice/week with 5 mg/kg of IgG or 10 mg/kg DN, or with 5, 2.5 or 1.25 mg/kg of T-DXd i.v. on days 0, 7 and 14, or the combination therapies. Tumor volume was measured twice/week for 21 days (n=6-8). Tumor-infiltrating macrophages and NK cells were studied by flow cytometry. ISG15, a downstream mediator of type-I IFN pathway, and cGAS were evaluated by western blot on tumor extracts.The dose-response curves showed a tumor growth inhibition of 83% (T-DXd 5 mg/kg), 61% (T-DXd 2.5 mg/kg) and 37% (T-DXd 1.25 mg/kg) vs. IgG (p<0.0001, 0.0001 and 0.05, respectively). Adding DN enhanced this inhibition to 98% (5 mg/kg), 81% (2.5 mg/kg) and 73% (1.25 mg/kg), p<0.0001 vs. IgG. T-DXd 1.25 mg/kg +DN achieved an antitumor effect that resembles T-DXd 5 mg/kg alone. Furthermore, addition of DN to T-DXd 1.25 and 5 mg/kg increased macrophage infiltration and polarization to the antitumoral M1-like phenotype. T-DXd 1.25 mg/kg +DN treatment mimics the increase of infiltrating NK cells observed in the higher doses of T-DXd alone. Finally, we observed an increase in cGAS and ISG15 expression in tumor extracts form T-DXd 1.25 mg/kg +DN, compared to T-DXd 1.25 mg/kg alone.Our results suggest that sTNF blockade with DN enhances T-DXd antitumor effect, inducing a reinforced innate immune response with increased infiltration of M1-like macrophages and NK cells, and activation of cGAS and type-I IFN pathway, measured by its surrogate ISG15. Adding DN allows to de-escalate T-DXd dose without impairing the antitumor effect. Neutralizing sTNF could improve the outcome of patients treated with T-DXd by enhancing the antitumor immune response. Citation Format: Sofia Bruni, Camila Jencquel, Martin A. Rivas, Roxana Schillaci, Maria F. Mercogliano. Soluble TNF blockade enhances trastuzumab-deruxtecan innate antitumor immune response and type-I IFN signalling in HER2-positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 882.