LAUSR

Clinical trials showed that trastuzumab deruxtecan (T-DXd) provides durable responses for patients with HER2+ and HER2 low metastatic breast cancer (BC), determined by immunohistochemistry. Approximately 50% of patients with HER2+ metastatic BC were still alive and progression-free at 24 months (DESTINY-Breast03). We proved that mucin 4 (MUC4) expression is an independent predictor of poor response to trastuzumab in HER2+ BC patients. In JIMT-1 tumors we proved that soluble TNFα (sTNFα) upregulates MUC4, conferring trastuzumab resistance by hiding its epitope on the HER2 molecule and reducing its binding. Here, we study whether sTNFα blockade with INB03 (DN) plays a role in regulation of innate immunity to enhance T-DXd antitumor effects in a multiple HER2-targeted therapy-resistant model. Nude mice bearing HER2+MUC4+ JIMT-1 tumor, primary resistant to trastuzumab, pertuzumab and lapatinib, were treated with IgG 5 mg/kg, T-DXd 5 mg/kg (T-DXd 5), 2.5 mg/kg (T-DXd 2.5) or 1.25 mg/kg (T-DXd 1.25), DN 10 mg/kg or the combined therapies. T-DXd and IgG were administered i.v. on days 0, 7 and 14. DN was administered i.p. twice a week for 3 weeks. Tumor growth was monitored. Mitotic index was analyzed in H&E tumor sections. The tumor-infiltrating innate cells, macrophages, NK cells and myeloid-derived suppressor cells (MDSCs), were studied by flow cytometry. T-DXd dose-response curves exhibited tumor growth inhibitions of 83% (T-DXd 5), 61% (T-DXd 2.5) and 37% (T-DXd 1.25) vs IgG-treated tumors. DN alone had no antitumor effect. T-DXd+DN reinforced the antitumor effect, as tumor growth inhibition escalated to 98% (T-DXd 5+DN), 81% (T-DXd 2.5+DN) and 73% (T-DXd 1.25+DN). A reduced number of mitotic figures were observed in T-DXd 5, T-DXd 1.25+DN and T-DXd 5+DN. Combining DN with T-DXd 1.25 and 5 enhanced the infiltration of resident macrophages and promoted polarization to the M1-like phenotype The tumor associated macrophages (TAMs) were similar among treatments. However, the combination T-DXd 1.25+DN showed an increase in M1-like tumor associated macrophages (TAMs) and a decrease in M2-like TAMs vs T-DXd 1.25 alone. T-DXd 1.25+DN treatment mimics the increase of infiltrating NK cells observed in the T-DXd 2.5 and 5 doses Finally, adding DN to T-DXd 2.5 and 5 diminishes MDSCs infiltration. Combination therapies were well tolerated without evidence of toxicity. Our results suggest that sTNFα blockade enhances T-DXd effect in a multiple HER2-targeted therapy resistant model. Adding DN allows to lower T-DXd doses to induce a reinforced antitumor innate immune response, reduced tumor cell mitosis and achieve similar tumor inhibition. Since sTNFα and MUC4 expression proved to be important variables in the response to T-DXd, neutralizing this cytokine may open new therapeutic strategies to treat patients with MUC4 expressing tumors or have progression on T-DXd therapy. Citation Format: Sofia Bruni, Florencia L. Mauro, Sofia Naveiro, Maria F. Mercogliano, Roxana Schillaci. Soluble TNFα blockade improves effectiveness of trastuzumab deruxtecan and boosts antitumor potential of macrophages in a HER2+ tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2273.