Gallic Acid Enhances the Anticancer Activity of Docetaxel in Triple-Negative Breast Cancer Cells

Experimental evidence has shown that gallic acid (GA), a naturally occurring polyphenolic compound, and docetaxel (DTX), a taxane chemotherapeutic agent, each possess antitumor activity against multiple cancer types. Although both compounds have been investigated individually, their combined effects in triple-negative breast cancer (TNBC) have received limited attention, and the molecular basis of their interaction remains unclear. The present study examined the in vitro effects of GA and DTX in MDA-MB-231 TNBC cells while simultaneously assessing their comparative cytotoxicity in HaCaT human keratinocytes. Evaluation of treatment efficacy included measurement of cell viability by the MTT assay and assessment of drug interactions using the Chou-Talalay combination index (CI) method. Apoptosis together with cell-cycle distribution was subsequently examined using both Annexin V/PI flow cytometry and TALI^® image-based cytometry. Additional analyses included β-tubulin immunofluorescence (IF), caspase-9 immunocytochemistry, ELISA, wound-healing assays, quantitative real-time PCR, and bioinformatic analyses to investigate treatment-associated biological alterations. Combined exposure to GA and DTX produced a significant reduction in cell viability and exhibited synergistic activity in MDA-MB-231 cells. The coordinated biological response to the combined treatment was characterized by increased apoptotic cell death, arrest of the cell cycle at the G2/M phase, extensive disorganization of the β-tubulin network, and enhanced caspase-9 immunoreactivity. Beyond its effects on cell survival, the combined regimen substantially decreased the release of IL-6, IL-8, and TNF-α, limited wound-healing capacity, and reshaped the expression profile of the apoptosis- and cell cycle-related genes BCL2, BAX, CASP9, and CDKN1A. Bioinformatic analyses further revealed enrichment of apoptosis- and cell-cycle-associated pathways that were generally consistent with the experimental observations. The overall pattern of experimental responses indicates that combining GA with DTX enhances the in vitro antitumor efficacy of DTX in TNBC cells by simultaneously influencing apoptotic pathways, cell-cycle regulation, inflammatory cytokine secretion, and cellular migratory capacity. Although the bioinformatic findings provide supportive hypothesis-generating evidence, additional studies using three-dimensional models, in vivo experiments, and functional validation approaches are necessary to confirm the underlying molecular mechanisms and to further define the translational potential of this therapeutic combination.