This study developed a PTAC platform using PSMA as a lysosome-targeting receptor, enabling efficient and specific lysosomal degradation of membrane proteins such as EGFR and PD-L1. The DC50 values of Ctx-L3 and Atz-L5 reached as low as 4.3 pM and 2 pM, respectively, making them among the most potent degraders reported to date.
Literature Overview
The article titled 'Development of Prostate-Specific Lysosome-Targeting Degraders,' published in the Journal of the American Chemical Society, reviews and summarizes a novel strategy for selectively degrading membrane and extracellular proteins in prostate cancer cells by utilizing prostate-specific membrane antigen (PSMA) as a lysosome-targeting receptor (LTR). The study constructed PSMA-targeting chimeras (PTACs), achieving efficient, rapid, sustained, and specific lysosomal degradation of therapeutically relevant membrane proteins such as EGFR and PD-L1. The platform's applicability in both antibody- and small-molecule-based modalities was experimentally validated, demonstrating its significant potential for precision therapy in prostate cancer. The research further revealed a nonlinear relationship between degradation efficiency and ligand affinity, highlighting the advantage of high-affinity degraders in resisting endogenous competition. This work expands the scope of targeted protein degradation (TPD) technologies and provides a new therapeutic tool for PSMA-positive diseases.Background Knowledge
Targeted protein degradation (TPD) has recently emerged as a pivotal strategy for treating diseases such as cancer, showing great promise in overcoming drug resistance associated with traditional inhibitors and targeting 'undruggable' proteins. The classical PROTAC technology relies on the ubiquitin-proteasome system and primarily targets intracellular proteins, with limited efficacy against membrane and extracellular proteins. To address this limitation, novel strategies such as lysosome-targeting chimeras (LYTACs) have been developed, leveraging lysosome-targeting receptors (LTRs) to mediate endocytosis and lysosomal degradation. However, most LTRs are broadly expressed across various tissues, lacking tissue specificity, which may lead to off-target toxicity. Therefore, developing degradation platforms with high tissue specificity remains a key challenge for enabling precision therapy. Prostate-specific membrane antigen (PSMA) is highly expressed in the majority of prostate cancer cells but is nearly absent in normal tissues, making it an ideal tissue-specific target. PSMA has already been successfully used in PET imaging and targeted radioligand therapy for prostate cancer, validating its targeting capability. This study innovatively exploits the high specificity of PSMA by using it as a lysosome-targeting receptor to construct the PTAC platform, aiming to achieve prostate cancer-specific protein degradation. This approach addresses the lack of tissue specificity in existing LYTAC technologies and offers a novel paradigm for precision treatment of prostate cancer and other PSMA-positive diseases.
Research Methods and Experiments
The study first designed and synthesized various biotinylated PSMA ligands with different linkers (L1-biotin to L5-biotin), assessing their internalization capacity by measuring the uptake efficiency of fluorescently labeled streptavidin (antibiotin-647) in different prostate cancer cell lines. The results showed that L5-biotin, containing a short peptide and aromatic structure, exhibited the strongest uptake efficiency in a dose-dependent manner. Subsequently, the researchers constructed PTACs targeting EGFR by conjugating cetuximab (Ctx) with PSMA ligands L3 or L5 via copper-free click chemistry, generating Ctx-L3 and Ctx-L5. The degradation efficacy of these PTACs against EGFR was evaluated in PSMA-positive cells, and the degradation mechanism was investigated through competition assays and treatment with endocytosis inhibitors as well as lysosome/proteasome inhibitors. Furthermore, the platform was extended to target PD-L1 by constructing both antibody-based (Atz-L5) and small-molecule-based (BMS-L5 series) PTACs, with their degradation potency and efficiency systematically evaluated.Key Conclusions and Perspectives
Research Significance and Prospects
This study successfully established the first PSMA-based lysosome-targeting degradation platform (PTAC), providing a novel tool for the targeted protein degradation field. The platform not only overcomes the lack of tissue specificity in conventional LYTACs but also achieves ultra-efficient degradation of therapeutically relevant targets such as EGFR and PD-L1, with DC50 values in the pM range—leading among comparable technologies. This opens new avenues for developing precision therapeutics for prostate cancer. In particular, PD-L1 degradation offers promise for overcoming tumor immune evasion and enhancing antitumor immune responses.
Future research directions include evaluating the pharmacological and pharmacokinetic properties of PTACs in animal models, as well as exploring their stability, distribution, and toxicity in vivo. Additionally, extending the PTAC strategy to other PSMA-positive diseases, such as certain neuroendocrine tumors, is a promising direction. Optimizing the potency of small-molecule PTACs and developing orally available degraders will be critical steps toward clinical translation. Overall, the PTAC platform represents a significant advancement in precision medicine and targeted degradation technologies, with broad clinical potential.
Conclusion
This study innovatively utilizes prostate-specific membrane antigen (PSMA) as a lysosome-targeting receptor to develop a PSMA-targeting chimera (PTAC) platform, enabling efficient, specific, rapid, and sustained lysosomal degradation of membrane and extracellular proteins in PSMA-positive prostate cancer cells. The research not only demonstrates the feasibility of using PSMA as an LTR but also constructs degraders targeting EGFR and PD-L1, with Ctx-L3 and Atz-L5 achieving pM-level degradation potency—ranking among the most potent degraders reported to date. The study reveals a complex relationship between degradation efficiency and ligand affinity, emphasizing the advantage of high-affinity degraders in resisting endogenous competition. The successful development of the PTAC platform provides a new tissue-specific strategy for targeted protein degradation, addressing the lack of targeting precision in existing technologies. This technology holds great promise for prostate cancer therapy, particularly through PD-L1 degradation to enhance antitumor immune responses. Moreover, the platform’s dual-mode design (antibody and small molecule) highlights its flexibility and scalability. This work significantly expands the application boundaries of targeted protein degradation, offering a powerful new tool for the precision treatment of PSMA-positive diseases and marking a significant advancement in the field of precision medicine.
