Tumor Microenvironment-Responsive Smart Nanodrug Delivery Systems for Cancer Theranostics

Abstract

Acidity, hypoxia, redox imbalance, and altered enzyme activity in the tumor microenvironment (TME) can be used to regulate nanocarrier structure and drug release. However, these conditions vary among tumors and across regions within individual tumors and overlap with certain normal physiological and inflammatory processes. This review examines TME-responsive nanomedicines for chemotherapy, phototherapy, immunomodulation, and theranostics in terms of their triggering conditions, response mechanisms, and carrier materials. Particular attention is given to matching activation thresholds to biological compartments, the relationship between delivery and release, and the biological interpretation of imaging signals. By comparing representative original studies, we examine the benefits of multiresponsive designs, potential off-target activation, and manufacturing complexity, while distinguishing the clinical use of conventional nanoformulations from clinical validation of TME-responsive mechanisms. Current studies demonstrate the feasibility of conditional drug release and local microenvironment modulation, but their clinical value remains to be established through consistent product quality, evidence of in vivo activation, and comparative efficacy studies.