Abstract 5876: Soluble TNF blockade as a strategy to enhance tyrosine-kinase inhibitor response and control metastatic burden in HER2-positive breast cancer

Abstract Tyrosine kinase inhibitors (TKIs), such as lapatinib and tucatinib, are used to treat metastatic HER2-positive breast cancer, especially those located in the brain, as they can cross the blood-brain barrier. Although both TKIs improve survival, there is still an urge to boost their efficacy and overcome resistance. We have demonstrated that soluble TNF (sTNF) blockade overcomes resistance to trastuzumab-based therapies targeting HER2 by downregulating mucin 4 (MUC4), which shields its epitope on the HER2 molecule. Now, we asked whether sTNF neutralization might overcome TKI-based therapy resistance or enhance its antitumor activity.We used the HER2+/MUC4+ JIMT-1 and its brain-tropic subline JIMT-1BR3-luc cell lines, resistant to lapatinib. For proliferation and cell migration assays, cells were treated with 1 µM lapatinib or 10 µM tucatinib, either alone or combined with 10 µg/ml of a dominant negative (DN) protein that neutralizes sTNF. For preclinical studies, female nude mice bearing JIMT-1 tumors received vehicle, 100 mg/kg lapatinib via oral gavage daily, 10 mg/kg DN i.p. twice a week, or the combination (n=5/group). For JIMT-1BR3-luc tumors, mice were treated with vehicle, 100 mg/kg tucatinib via oral gavage daily, DN twice weekly, or both (n=9/group). Tumor volume was measured biweekly for 21 days; metastases were detected ex vivo by IVIS luminescence.Neither lapatinib nor DN alone impacted JIMT-1 cell proliferation, but their combination reduced cell proliferation by 60%. For JIMT-1Br-luc cells, DN and tucatinib decreased cell proliferation by 35 % and 55%, respectively, and the combination enhanced the effect to 80%. Cell migration was significantly inhibited in both cell lines by their respective combo treatment, compared to the monotherapies.In preclinical studies, treatment with DN, lapatinib, or tucatinib did not affect the primary tumor growth, compared to the vehicle. However, the combination of DN and lapatinib reduced JIMT-1 tumor growth by 77% and, in the case of JIMT-Br-luc tumors, treatment with DN and tucatinib inhibited tumor growth by 68%, compared to the monotherapies. The percentage of JIMT-Br-luc tumor-bearing mice with lung metastases was 100% in the vehicle group, 75% in the DN group, 37.5% in the tucatinib group, and 12.5% in the combined group. Animals with brain and liver metastases accounted for 50% and 75% respectively, in the vehicle group, and were 90-100% reversed upon treatment with either tucatinib or DN, or the combination.These findings highlight that sTNF blockade can overcome lapatinib resistance and improve tucatinib inhibitory effect on cell proliferation, both in vitro and in vivo. In addition, DN was able to curb brain and liver metastasis and lung metastases in combination with tucatinib, underscoring the potential benefit of its use in combination with TKIs in advanced HER2-positive breast cancer patients. Citation Format: Sofia Bruni, Marla Ladera, Camila Jencquel, Federico Waisberg, Martin A. Rivas, Roxana Schillaci, Maria Florencia Mercogliano. Soluble TNF blockade as a strategy to enhance tyrosine-kinase inhibitor response and control metastatic burden in HER2-positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 5876.