Abstract 510: Neurotransmitter receptor antagonists and metronomic chemotherapy: A promising novel approach for brain metastases in breast cancer

Brain metastases (BM) from breast cancer are a significant clinical issue with a poor prognosis. New therapies targeting the tumor microenvironment are promising. Various types of neurotransmitter (NT) receptors (e.g., glutamatergic, dopaminergic, serotoninergic receptors) are expressed on breast cancer (BC) cells, modulating cell proliferation, survival, and migration. We propose a novel approach for BM treatment using NT receptor antagonists in combination with metronomic chemotherapy (mCHEMO) - the frequent and regular administration of drug doses, for extended time, without breaks - to block the pro-tumoral interaction between cancer cells and the brain microenvironment, increasing therapeutic efficacy and reducing toxicity. The Kaplan-Meier plotter website was used to assess the impact of the NT receptor gene expression of our interest on overall survival (OS) in metastatic BC patients. Real-Time PCR assessed NT receptor gene expression in monolayer and spheroid cultures of MCF-7 (ER+), MDA-MB-231 (triple-negative), and MDA-MB-361 (HER2+) BC cell lines. Proliferation assays were performed on BC cell lines exposed to metronomic temozolomide (TMZ) and NT receptor antagonists (memantine, ML00253764, SB-269970, clozapine) for 144h daily treatments. The synergism of the concomitant combinations between low-dose TMZ and NT receptor antagonists was evaluated by the combination index method.The Kaplan-Meier analysis showed that a higher level of NT receptors expression is associated with worse OS rates in metastatic BC, particularly with elevated GRIN1 and MC4R. Indeed, genes of NT receptors were highly expressed in BC cell lines. The MC4R antagonist ML00253764 was active on tumor cell lines with a strong antiproliferative effect on MDA-MB-231, showing IC50 value of 4.72 nM. The NMDA antagonist memantine was very effective on MDA-MB-361 with a concentration- and time-dependent effect (IC50 at 144h 168.1 nM), while the 5-HT7 receptor antagonist SB-269970 showed encouraging antiproliferative results on MCF-7 (IC50 9.61 nM). Metronomic TMZ decreased cell proliferation in tumor cell lines. The concomitant combinations of TMZ+ML00253764, TMZ+memantine, and TMZ+SB-269970 showed marked synergisms, notably on MDA-MB-361 cells. These findings build rational bases for the promising therapeutic approach, including NT receptor antagonists and metronomic TMZ, for breast cancer BM. Moreover, in vitro experiments demonstrated a key role of NT receptor on cell proliferation due to the activity of pharmacological antagonists alone or with mCHEMO. These results support further in vitro 3D investigation on multicellular spheroids and in vivo experiments on BM models to validate our pioneering therapeutic hypothesis, which could be easily translated into future clinical trials. Citation Format: Arianna Bandini, Paola Orlandi, Marta Banchi, Giulio Francia, Guido Bocci. Neurotransmitter receptor antagonists and metronomic chemotherapy: A promising novel approach for brain metastases in 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 510.