Boswellic Acid Enhances Gemcitabine's Inhibition of Hypoxia-Driven Angiogenesis in Human Endometrial Cancer

Background and Objectives: Endometrial carcinoma is among the most common gynecological malignancies, with recurrence and chemoresistance remaining major clinical challenges. This study aimed to evaluate the combined effects of Boswellic acid (BA), a natural pentacyclic triterpene, and Gemcitabine (GEM), a nucleoside analog chemotherapeutic, on hypoxia, angiogenesis, and apoptosis in human endometrial cancer cells. Materials and Methods: ECC-1 cells were treated with BA, GEM, or their combination under normoxic and hypoxic conditions. Cell viability (MTT assay); nuclear morphology (NucBlue staining); cell cycle distribution (PI flow cytometry); angiogenesis (VEGF ELISA expression); apoptosis (Caspase-3/7 activity; Bax; Bcl-2 expression); inflammatory cytokines (IL-1β; IL-6; TNF-α); and gene ontology enrichment were analyzed. Results: Both BA and GEM reduced cell viability in a dose- and time-dependent manner, with the combination producing synergistic cytotoxicity and lower IC₅₀ values. Hypoxia enhanced drug sensitivity, particularly in combination therapy. BA and GEM significantly suppressed HIF-1α and VEGF expression, with maximal inhibition observed in the combination group. Apoptotic induction was confirmed by increased Bax and Caspase-3 and decreased Bcl-2 expression, together with elevated Caspase-3/7, -8, and -9 activity. Pro-inflammatory cytokine levels were markedly reduced, and gene ontology analysis revealed enrichment of apoptotic, anti-proliferative, and anti-angiogenic pathways. Conclusions: BA + GEM combination synergistically suppresses hypoxia-driven angiogenesis and promotes apoptosis in endometrial cancer cells. These findings support its potential as an adjuvant therapeutic approach, warranting further preclinical and clinical validation.