This study provides a novel chemical delivery paradigm for drug development targeting low-endocytosis-efficiency sites, inspiring researchers to redesign the release mechanisms of Antibody-Drug Conjugates (ADCs).
Literature Overview
The article "A binding-to-release strategy for targeted anticancer drug delivery," published in Nature, systematically explores a new strategy termed "Binding-to-Release" (BTR) to overcome the reliance of traditional drug conjugates on receptor-mediated endocytosis. The paper details the mechanism of utilizing Phosphorus(V)-Phenol Exchange (PhoPEx) chemistry to directly trigger drug release via neighboring nucleophilic residues upon binding to the target pocket, thereby achieving efficient tumor-targeted delivery without the need for endocytosis.Background Knowledge
In current cancer therapy, the success of Antibody-Drug Conjugates (ADCs) and Small-Molecule Drug Conjugates (SMDCs) largely depends on efficient target endocytosis and lysosomal transport. However, only about 10% of human membrane proteins possess high endocytic efficiency, rendering many therapeutically promising targets, such as Fibroblast Activation Protein (FAP) and Programmed Death-Ligand 1 (PD-L1), difficult to utilize effectively due to low endocytosis rates. The traditional "Endocytosis-to-Release" (ITR) model faces bottlenecks on these targets, including rapid drug dissociation, swift clearance, and limited efficacy. Furthermore, the multi-step inefficiency of the lysosomal transport pathway further restricts the amount of intracellular drug release. Therefore, developing a strategy that does not rely on endocytosis and can trigger release directly at the extracellular binding site has become a key entry point for expanding the scope of tumor therapy targets.
Research Methods and Core Experiments
The authors first developed the Phosphorus(V)-Phenol Exchange (PhoPEx) chemical reaction, a chemical tool inspired by Sulfur(VI)-Fluoride Exchange (SuFEx), capable of triggering drug release within the target binding pocket via proximity effects. The research team used molecular docking to predict key nucleophilic residues in the FAP binding pocket and synthesized FAP-targeted conjugates equipped with fluorescent reporters and cytotoxic drugs (such as MMAE). Through in vitro fluorescence release assays, cell toxicity experiments, and in vivo imaging techniques, the specific release and killing effects of PhoPEx conjugates on FAP-positive cells were verified, while excluding the influence of endocytosis. The study also employed site-directed mutagenesis, tandem mass spectrometry (MS/MS), and Cryo-Electron Microscopy (Cryo-EM) to precisely locate Tyr745 as the key residue triggering the reaction. Additionally, the team compared the pharmacokinetic profiles and anti-tumor efficacy of the BTR strategy versus the traditional ITR strategy in CDX (Cell-Derived Xenograft) and PDX (Patient-Derived Xenograft) models.Key Conclusions and Perspectives
Research Significance and Prospects
This discovery provides a breakthrough complementary strategy for the field of drug development, making it possible to target low-endocytosis membrane proteins traditionally considered "undruggable." By achieving extracellular in situ release, the BTR strategy not only improves drug distribution within the tumor microenvironment but also utilizes the bystander effect to kill neighboring antigen-negative cells, which is particularly important for treating highly heterogeneous solid tumors. Additionally, the strategy holds immense potential for clinical monitoring, such as using activated fluorescent probes to detect lymph node metastasis in real-time during surgery, thereby improving diagnostic accuracy. In the future, the PhoPEx-based BTR platform is expected to become an important tool for disease modeling and the development of new conjugated drugs, driving progress in the treatment of more refractory cancers.
Conclusion
This study, by innovatively proposing the "Binding-to-Release" (BTR) strategy, successfully breaks the traditional reliance of drug conjugates on receptor-mediated endocytosis, opening a new pathway for cancer treatment. Utilizing PhoPEx chemistry, the research team achieved efficient drug release on low-endocytosis-efficiency targets such as FAP and PD-L1, significantly enhancing tumor targeting and reducing systemic toxicity. This achievement not only resolves the long-standing endocytosis bottleneck in drug development but also provides a powerful tool for treating the solid tumor microenvironment. From chemical design in the laboratory to excellent performance in preclinical models, the BTR strategy demonstrates immense potential for translation from basic research to clinical application. It is poised to become an indispensable component of future tumor care systems, bringing new hope to patients with more refractory diseases.
