Synergistic anti-tumor effects of novel two-domain soluble Fms-like tyrosine kinase-1 and paclitaxel on three-dimensional breast cancer models: implications for targeted therapy.

backgroundThree-dimensional (3D) multicellular spheroids mimic tumor architecture, diffusion limits, and drug resistance more effectively than two-dimensional (2D) monolayers. Triple-negative breast cancer (TNBC) remains highly aggressive, with limited benefits from anti-vascular endothelial growth factor (VEGF) therapy. We investigated the synergistic effects of a novel two-domain soluble Fms-like tyrosine kinase-1 (2d-sFlt-1) in enhancing paclitaxel efficacy compared with bevacizumab using 3D breast cancer models.

methods3D spheroids derived from triple-negative (MDA-MB-231 and MDA-MB-468) and luminal (MCF-7) breast cancer cell lines, as well as tumor-endothelial co-culture spheroids, were treated with paclitaxel alone or in combination with 2d-sFlt-1 or bevacizumab. Treatment efficacy was evaluated through drug-sensitivity, proliferation, viability, migration, and morphometric analyses, along with assessments of angiogenesis, epithelial-to-mesenchymal transition (EMT), and focal adhesion kinase (FAK) signaling. Statistical significance was determined using non-parametric tests or one- and two-way ANOVA with appropriate multiple comparisons.

resultsTransition from 2D monolayer to 3D spheroid culture markedly increased paclitaxel resistance, with IC₅₀ values elevated by roughly 25-fold. Co-treatment with 2d-sFlt-1 markedly enhanced paclitaxel efficacy, reducing the IC₅₀ values by approximately 10-fold in MDA-MB-231 spheroids and 6-fold in MDA-MB-468 spheroids, whereas bevacizumab produced only modest effects. Paclitaxel and 2d-sFlt-1 combination further suppressed spheroid growth and proliferation in both TNBC and luminal breast cancer models. In MDA-MB-231 spheroids, combination therapy reversed EMT by increasing E-cadherin while downregulating N-cadherin, SNAIL, and TWIST, and further reduced VEGF secretion and angiogenic tube formation. In tumor-endothelial co-cultures, FAK signaling was markedly reduced after combination treatment. Across all models and assays, paclitaxel and 2d-sFlt-1 combination consistently outperformed monotherapy and paclitaxel plus bevacizumab, underscoring its potential as a mechanistically synergistic strategy for overcoming chemoresistance in triple-negative breast cancer.

conclusions2d-sFlt-1 enhanced paclitaxel efficacy in physiologically relevant 3D breast cancer models. In MDA-MB-231 spheroids, the combination reduced chemoresistance and invasive growth through coordinated modulation of angiogenesis, EMT, and FAK signaling. In MDA-MB-468 and MCF-7 spheroids, it primarily increased cytotoxicity and growth inhibition, indicating a conserved functional benefit across subtypes. These findings provide a rationale for further mechanistic validation and preclinical evaluation of 2d-sFlt-1 plus paclitaxel to define dosing, safety, and translational feasibility in aggressive breast cancers.