Signal Transduction and Targeted Therapy | Employing Epigenetic Protein Degradation Techniques to Block CCL5-Mediated Photodynamic Therapy

This study develops a novel tumor microenvironment-responsive delivery platform that significantly enhances the antitumor efficacy of photodynamic therapy by co-delivering an epigenetic protein degrader and a photosensitizer. It also reveals for the first time that upregulation of CCL5 is a new mechanism underlying photodynamic therapy resistance, offering a groundbreaking strategy to overcome treatment resistance.

 

Literature Overview

The article titled 'Employing epigenetic protein degradation techniques to block CCL5-mediated photodynamic therapy via a programmed delivery platform,' published in the journal *Signal Transduction and Targeted Therapy*, reviews and summarizes research on enhancing antitumor effects by combining epigenetic protein degradation technology with photodynamic therapy through a programmed delivery platform. The study constructs a nanodelivery system with targeting capability, pH-responsive charge reversal, and glutathione (GSH)-responsive drug release properties, enabling the synergistic delivery of bromodomain-containing protein 4 (BRD4) degrader ARV-825 and photosensitizer Ce6. This system significantly improves drug accumulation at tumor sites, enhances the efficacy of photodynamic therapy, and activates antitumor immune responses by suppressing PD-L1 and CD47 expression and inhibiting M2 macrophage polarization. More importantly, the study identifies for the first time that photodynamic therapy induces treatment resistance by upregulating CCL5 expression, and that targeted degradation of BRD4 effectively blocks this pathway, thereby overcoming resistance. The entire passage is coherent and logical, ending with a Chinese period.

Background Knowledge

Photodynamic therapy (PDT), as a minimally invasive antitumor treatment, relies on photosensitizers to generate reactive oxygen species (ROS) under laser irradiation at specific wavelengths, killing tumor cells, disrupting vasculature, and activating the immune system, showing broad application prospects in light-sensitive tumors such as breast cancer and melanoma. However, the efficacy of PDT is limited by insufficient photosensitizer accumulation in tumor tissues and the development of treatment resistance in tumor cells. Recent studies indicate that epigenetic regulation, such as histone acetylation and methylation, is widely involved in tumor immune escape and therapy resistance. Targeted protein degradation technologies (e.g., PROTAC) can specifically degrade target proteins via the ubiquitin-proteasome system, with BRD4 degrader ARV-825 shown to enhance chemosensitivity and inhibit M2 macrophage polarization. However, both photosensitizers and protein degraders suffer from poor water solubility and insufficient targeting. Nanodelivery systems, particularly micellar systems based on biocompatible polymers such as poly(lactic-co-glycolic acid) (PLGA) and polyethylene glycol (PEG), can enhance intratumoral drug accumulation via the enhanced permeability and retention (EPR) effect. Nevertheless, conventional nanocarriers still face challenges such as slow response kinetics and off-target effects. Therefore, constructing an intelligent delivery platform with multiple responsiveness, high targeting, and synergistic therapeutic functions has become a key breakthrough for improving PDT efficacy. This study addresses this challenge by designing a programmed delivery system aimed at simultaneously overcoming drug delivery and resistance mechanisms, offering new insights into combination cancer therapy.

 

 

Research Methods and Experiments

The study designed and constructed a tumor microenvironment-responsive nanomicellar system, RDP, based on the CAPIR cascade (circulation, accumulation, penetration, internalization, release), for co-loading the photosensitizer chlorin e6 (Ce6) and the BRD4 degrader ARV-825, forming ARV/Ce6@RDP micelles. The system consists of three functional polymers: MPEG-SS-PCL with redox responsiveness for GSH-triggered drug release; cRGD-PEG-PCL with targeting capability to recognize integrin αvβ3 overexpressed on tumor cells; and PCL-PEG-PEI-DM with pH-responsive charge reversal, switching from negative to positive charge in the acidic tumor microenvironment to promote cellular uptake. The micelle's size, zeta potential, drug loading, and responsiveness were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV-Vis spectroscopy. In 4T1 breast cancer and B16F10 melanoma cell lines, cellular uptake efficiency was evaluated using flow cytometry and high-content imaging (HCI), while in vitro antitumor effects were assessed via MTT, Annexin V/PI staining, and cell cycle analysis. In mouse tumor models, in vivo drug distribution and accumulation were monitored using live imaging, tumor growth curves and survival rates were recorded, and immunohistochemistry, TUNEL, and flow cytometry were performed to investigate the therapeutic mechanisms. Additionally, RNA-seq was used to screen for PDT resistance-related genes, and the role of CCL5 in resistance and its regulation by ARV-825 were validated using qPCR and Western blot.

Key Conclusions and Perspectives

• The ARV/Ce6@RDP micelles, successfully constructed with targeting capability, pH-responsive charge reversal, and GSH-responsive drug release, have a size of approximately 100 nm, with surface charge switching from negative to positive at pH 6.8, and drug release triggered in high-GSH environments
• ARV/Ce6@RDP micelles significantly enhance Ce6 accumulation in 4T1 and B16F10 tumor models compared to non-targeted control groups, confirming the synergistic effect of cRGD-mediated targeting and enhanced uptake in acidic microenvironments
• In vitro experiments show that ARV/Ce6@RDP significantly increases intracellular ROS levels under laser irradiation, enhancing cytotoxicity and apoptosis rates, and inducing cell cycle arrest, with superior effects compared to ARV-825 or Ce6 alone
• The combination therapy effectively inhibits pro-survival signaling pathways such as AKT, ERK, and STAT3 by degrading BRD4, and downregulates c-Myc expression, thereby synergistically enhancing the antitumor effects of PDT
• ARV/Ce6@RDP significantly activates antitumor immune responses, evidenced by enhanced immunogenic cell death (ICD), promoted dendritic cell (DC) maturation, increased CD8+ T cell infiltration, and reduced infiltration of Treg cells and M2 macrophages
• The system effectively downregulates the expression of immune checkpoint PD-L1 and the 'don't eat me' signal CD47 on tumor cells, reversing the immunosuppressive microenvironment
• The study is the first to discover that photodynamic therapy upregulates the expression of chemokine CCL5, thereby mediating treatment resistance; ARV-825 inhibits CCL5 transcription by degrading BRD4, significantly overcoming this resistance mechanism
• In mouse models of breast cancer and melanoma, ARV/Ce6@RDP significantly suppresses primary tumor growth, prolongs survival, and effectively inhibits postoperative tumor recurrence and lung metastasis, without exhibiting significant systemic toxicity

Research Significance and Prospects

This study innovatively combines epigenetic protein degradation technology with photodynamic therapy, achieving precise synergistic treatment through an intelligent delivery platform, significantly enhancing the direct cytotoxic effects of PDT while effectively activating systemic antitumor immune responses. Its greatest scientific contribution lies in being the first to identify CCL5 as a key mediator of PDT resistance and proposing a novel strategy of blocking this pathway through targeted BRD4 degradation, offering a new perspective on understanding photodynamic resistance mechanisms.

The design concept of this delivery system—multi-level responsiveness, targeted accumulation, and synergistic mechanisms—provides an important model for developing next-generation combination therapy nanomedicines. Future research could further explore the applicability of this strategy in other light-sensitive tumors or extend it to other epigenetic targets. Moreover, the clinical potential of CCL5 as a resistance biomarker warrants deeper investigation, potentially providing new tools for PDT efficacy prediction and personalized therapy. This work provides a solid theoretical and experimental foundation for enhancing the clinical translatability of photodynamic therapy.

 

 

Conclusion

This study developed a novel tumor microenvironment-responsive delivery platform, ARV/Ce6@RDP, which enables efficient synergy between photodynamic therapy and epigenetic regulation by co-delivering the BRD4 degrader ARV-825 and the photosensitizer Ce6. The system features targeting capability, pH-responsive charge reversal, and GSH-responsive drug release, significantly improving drug accumulation and cellular uptake at tumor sites. The study found that the combination therapy not only enhances tumor cell apoptosis and cell cycle arrest but also reshapes the antitumor immune microenvironment by suppressing PD-L1 and CD47 expression and reversing M2 macrophage polarization. More importantly, the study reveals for the first time that photodynamic therapy induces resistance by upregulating CCL5 expression, and that ARV-825 effectively blocks this pathway by degrading BRD4, significantly improving therapeutic outcomes. In breast cancer and melanoma models, this strategy markedly suppresses tumor growth, recurrence, and metastasis, with favorable safety. This work provides a novel mechanistic explanation and intervention strategy for overcoming photodynamic therapy resistance, advancing its clinical translational applications.

 

Tingting Yang, Yuzhu Hu, Anjie Guo, Yongzhong Cheng, and Xiang Gao. Employing epigenetic protein degradation techniques to block CCL5-mediated photodynamic therapy via a programmed delivery platform. Signal Transduction and Targeted Therapy.