This study provides a novel approach for drug development targeting difficult-to-internalize antigens such as FAP and PD-L1. It suggests that exploring non-internalization mechanisms in tumor immunotherapy and solid tumor model construction can overcome the limitations of traditional antibody-drug conjugates.
Literature Overview
The article titled "A binding-to-release strategy for targeted anticancer drug delivery," published in Nature, systematically explores a novel drug delivery strategy targeting antigens with low internalization efficiency. The study points out that traditional antibody-drug conjugates (ADCs) and small molecule-drug conjugates (SMDCs) rely heavily on receptor-mediated endocytosis to release their payloads, which limits the range of targetable antigens. The research team innovatively proposed a "Binding-to-Release" (BTR) strategy, which decouples drug release from the endocytic process through chemical means, utilizing nucleophilic residues within the binding pocket to directly trigger drug release.Background Knowledge
This research aims to address the pain point of low drug delivery efficiency in cancer treatment. Currently, approximately 90% of membrane proteins cannot effectively mediate endocytosis, hindering the development of conjugated drugs targeting critical antigens such as FAP and PD-L1. Traditional "Internalization-to-Release" (ITR) modes often fail on these targets. Furthermore, the multi-step lysosomal transport pathway is inefficient, further limiting therapeutic efficacy. The focus of this study is to develop a release mechanism independent of endocytosis. By utilizing Phosphorus(V)-Phenol Exchange (PhoPEx) chemistry, covalent cleavage is triggered by adjacent nucleophilic residues, such as tyrosine, after the drug binds to the target, achieving efficient and specific drug release and broadening the target selection range for drug conjugates.
Research Methods and Core Experiments
The authors first predicted reactive sites within the FAP binding pocket via molecular docking and developed a PhoPEx chemical linker. In vitro experiments used fluorescent probes to verify the specificity of drug release in the presence of FAP protein. Through point mutation experiments (e.g., Y745F) and Cryo-EM technology, Tyr745 was confirmed as the key amino acid residue triggering release. Subsequently, the team constructed an FAP-BTR-SMDC model and conducted efficacy evaluations in HT1080-FAP cell lines as well as CDX and PDX mouse models. Key evidence showed that the BTR strategy resulted in significantly higher drug exposure (AUC) in tumor tissues compared to the traditional ITR strategy, with a substantial increase in the tumor-to-normal tissue (blood, liver) ratio, proving its in vivo effectiveness.Key Conclusions and Perspectives
Research Significance and Prospects
This discovery has profound implications for drug development, particularly providing viable conjugated drug solutions for membrane proteins traditionally considered "undruggable" or having low endocytic efficiency. In terms of clinical monitoring, BTR-based activated probes can be used for precise detection of FAP expression, assisting in intraoperative assessment of lymph node metastasis. Additionally, this strategy shows great potential in disease modeling, especially in research simulating tumor microenvironment heterogeneity and stromal cell-targeted therapies, allowing for a more realistic reflection of drug distribution and efficacy in complex tissues.
Conclusion
Through the innovative PhoPEx chemistry and BTR strategy, this study successfully overcame the traditional dependency of conjugated drugs on endocytosis, providing a powerful solution for targeted therapy against difficult-to-internalize targets such as FAP and PD-L1. From laboratory chemical design to in vivo validation in PDX models, this work not only significantly improved drug tumor targeting and therapeutic index but also demonstrated the potential to overcome tumor heterogeneity and stromal barriers in solid tumor treatment. This strategy is expected to become a cornerstone of future anticancer drug research, driving more drugs targeting key cancer antigens into clinical translation, ultimately improving patient clinical outcomes and quality of life.
