Mistletoe Lectin Overcomes Macrophage-Mediated Chemo-Resistance in 3D Co-Culture Models of Triple-Negative Breast Cancer

Tumor-associated macrophages (TAMs) contribute to chemoresistance in triple-negative breast cancer (TNBC), yet strategies to reprogram TAMs while enhancing chemotherapy efficacy remain limited. This study investigated whether Viscum album L. var. coloratum agglutinin (VCA) could sensitize TNBC cells to doxorubicin (DOX) and modulate TAM-mediated chemoresistance in three-dimensional (3D) co-culture models.

MDA-MB-231 TNBC cells were co-cultured with RAW264.7 macrophages in collagen-embedded 3D spheroids. Spheroid viability was assessed using an ATP-based luminescent assay. Cytokine secretion and epithelial-mesenchymal transition (EMT) markers were measured using ELISA and Western blotting. Drug synergy was evaluated using combination index (CI) calculations.

VCA-DOX combination demonstrated synergistic cytotoxicity exclusively in co-culture spheroids (CI = 0.72), reducing viability to 25.9% (p < 0.001), while showing no synergy in monoculture (CI = 1.52). Combination treatment decreased VEGF secretion by 49% and IL-6 by 74%, while elevating TNF-α 2.7-fold, suggesting macrophage reprogramming. VCA enhanced E-cadherin expression while suppressing mesenchymal markers in co-culture spheroids and reduced Matrigel invasion by 60% (p < 0.001).

VCA-DOX combination demonstrates synergistic anticancer effects through TAM reprogramming and enhanced chemosensitization specifically in 3D co-culture models, warranting further investigation for overcoming macrophage-mediated chemoresistance in TNBC.