CYTOSTATIC EFFECTS AND MECHANISMS OF ACTION OF BACTERIAL LECTIN OF BACILLUS SUBTILIS IMV B-7724 ON BREAST CANCER CELL LINES OF DIFFERENT MOLECULAR SUBTYPES

Abstract

Background. Lectins are carbohydrate-binding proteins with diverse biological activities, and they are increasingly recognized for their potential in cancer diagnostics and therapy. Aim of the study was to investigate the cytostatic and cytotoxic effects of the bacterial lectin of Bacillus subtilis IMV B-7724 on breast cancer (BC) cell lines of different molecular subtypes. Materials and Methods. Experiments were performed on the T47D (luminal A), MCF‑ 7 (luminal B), and MDA-MB-468 (basal, triple-negative) cell lines. Cytotoxicity was assessed by crystal violet staining and LC₅₀/LC₃₀ determination. Cytomorphological alterations were analyzed using the Romanowsky — Giemsa staining and ImageJ morphometry. A flow cytometry was applied to evaluate the cell cycle distribution and apoptosis (Annexin V/PI assay). The expression of proliferation and apoptosis regulators (Ki-67, p53, BCL-2, BAX) was examined by immunocytochemistry. Results. The lectin exerted dose-dependent cytotoxicity across all tested cell lines, with LC₅₀ values ranging between 351—419 μg/mL. The morphological analysis revealed subtype-specific alterations, including cell rounding, nuclear condensation, and decreased cytoplasmic volume, indicative of the apoptotic process. The flow cytometry showed distinct cell cycle arrest patterns: S-phase accumulation in T47D, G2/M blockade in MCF‑ 7, and combined S- and G2/M-phase arrest in MDA-MB-468. The viability assays confirmed a significant reduction of live cells, predominantly through late apoptosis and necrosis, with the strongest effect observed in T47D cells. The immunocytochemistry demonstrated a marked downregulation of Ki-67 and BCL-2, increased p53 expression, and BAX upregulation in MCF‑ 7 cells, whereas T47D cells displayed a paradoxical BAX suppression despite the apoptotic features. Conclusions. Lectin of B. subtilis IMV B-7724 exerts multifaceted effects on BC cells of different molecular subtypes, including the suppression of cell proliferation, activation of apoptosis, and cell cycle modulation. The observed differences between the BC cell lines suggest that the lectin efficacy depends on both the molecular profile of the cells and the mode of apoptosis regulation (p53-dependent or p53-independent), warranting further studies to identify key targets.