Novel Dual Strategy Based on EPR/AT for Optimizing Therapeutic Effect by Improving Drug Delivery System Physicochemical Properties and Regulating TME.

The clinical advancement of cancer nanomedicine is significantly hindered by its limited accumulation in tumors, a key factor behind the frequent failure of nanodrugs in clinical trials. The effectiveness of these nanodrugs is closely tied to their route of administration, whether oral, transdermal, intravenous, or intracerebral, as each path presents unique physiological barriers that impede bioavailability and precise tumor targeting. Among the major causes of poor accumulation are rapid clearance by the mononuclear phagocyte system, opsonization accompanied by protein corona formation, renal filtration, and the abnormal, heterogeneous nature of tumor vasculature that restricts passive targeting via the enhanced permeability and retention (EPR) effect. In response, active targeting (AT) strategies have been widely explored, including surface modification with ligands, antibodies, or aptamers designed to bind specifically to overexpressed receptors on cancer cells or blood vessels. Despite these efforts, challenges such as the dense extracellular matrix, elevated interstitial fluid pressure, and the notable inconsistency of the EPR effect between animal models and human patients continue to limit therapeutic penetration. This review offers a systematic examination of nanodrug delivery pathways and the reasons behind their inadequate accumulation, highlighting the potential of both active targeting and combined passive-active strategies to enhance tumor-specific delivery. Overcoming these biological barriers through refined nano-design is crucial for developing the next generation of nanomedicines with improved tumor accumulation and treatment outcomes.