Honokiol and Its Emerging Role in Breast Cancer Therapy

Honokiol (HNK), a bioactive compound found in Magnolia species, is a promising, multifunctional agent with therapeutic effects on breast cancer (BrCa). Preclinical evidence, including in vitro and in vivo studies, suggests that HNK inhibits essential oncogenic pathways and reduces oxidative stress, inflammation, metabolic reprogramming, and cancer stemness. HNK demonstrates synergistic activity with chemotherapy, endocrine therapy, targeted therapy, and immune checkpoint inhibitors, increasing sensitivity to treatment across models of ER+, PR+, and HER2+ BrCas, as well as triple-negative breast cancers (TNBC). Nanotechnological delivery systems enhance the solubility, bioavailability, and intratumoral accumulation of HNK, increasing its translational capacity. Although clinical data remain very limited, current evidence in humans is insufficient to draw definitive conclusions regarding the safety and efficacy of HNK. This review summarizes mechanistic, preclinical, and emerging clinical data, highlights challenges in formulation and pharmacokinetics, and anticipates future trends in incorporating HNK into multimodal therapy for BrCa.