Shikonin: From Biosynthesis and Pharmacological Mechanisms to Translational Safety and Drug Delivery

Shikonin (SHK) is a red naphthoquinone produced mainly in the roots of Boraginaceae species and has been investigated for anticancer, anti-inflammatory, antimicrobial, neuroprotective, cardioprotective, hepatoprotective, and wound-healing activities. This review critically integrates botanical sources and biosynthesis with pharmacological mechanisms, preclinical evidence, safety, and delivery strategies. Across cancer models, SHK converges on redox imbalance and regulated cell-death programmes, including apoptosis, cell-cycle arrest, autophagy, necroptosis, ferroptosis, and immunogenic cell death, while modulating NF-κB, MAPK, PI3K/Akt, and related signalling networks. However, the evidence is dominated by heterogeneous in vitro experiments and small-animal studies, with limited pharmacokinetic standardisation, incomplete assessment of selectivity toward diseased versus normal tissues, and almost no robust clinical evaluation. Poor aqueous solubility, chemical and photochemical instability, rapid metabolism, route-dependent exposure, and a context-dependent therapeutic window remain central translational barriers. Liposomes, polymeric micelles, nanoparticles, nanogels, nanoemulsions, and ligand- or stimulus-responsive systems can improve dispersion, tissue accumulation, controlled release, and combination therapy; nevertheless, their long-term safety, manufacturing reproducibility, and comparative advantage over free SHK require rigorous validation. SHK should therefore be regarded as a mechanistically versatile therapeutic lead rather than a clinically established treatment. Translation will depend on exposure-response studies, standardised formulations, clinically relevant models, and well-designed human trials.