Li Yujie, Zhang Hongyan, Wei Jiale, Jin Wanyu, Tong Qi, Ye Yuhao, Xie Qiong, Li Qiushuang, Cheng Guilin, Xiong Yang
School of Pharmaceutical Sciences, Zhejiang Chinese Medical University, Hangzhou, Zhejiang, 310053, China.
School of Biological and Pharmaceutical Engineering, West Anhui University, Lu'an 237012, PR China.
Phytomedicine. 2025 Sep 19;148:157275. doi: 10.1016/j.phymed.2025.157275.
Triple-negative breast cancer (TNBC) exhibits a low response rate to immune checkpoint inhibitors such as anti-PD-L1 antibodies, partly due to immune evasion mediated by membrane-bound PD-L1 (mPD-L1) on tumor cells and PD-L1⁺ derived extracellular vesicles (EVs). Cancer-associated adipocytes (CAAs) further exacerbate this immunosuppressive microenvironment by secreting free fatty acids and adipokines that promote mPD-L1 expression and PD-L1⁺ EVs release. Current strategies, such as high-dose antibodies or EVs secretion inhibitors, are limited by high toxicity, non-specificity, and neglect of CAAs' role, highlighting the need for safer and more effective combination therapies.
This study aims to develop a celastrol-loaded liposomal system (Cel/Lip) to improve the bioavailability and reduce the toxicity of celastrol (Cel), while evaluating its role in modulating PD-L1 expression and the tumor microenvironment.
Cel/Lip was prepared using the ethanol injection method. A comprehensive evaluation of the combined therapeutic effects and mechanisms of Cel/Lip with anti-PD-L1 therapy was conducted through multiparametric assessments including flow cytometry, Western blot, and immunofluorescence microscopy. In vitro experiments analyzed the effects of Cel-Lip on mPD-L1 expression and PD-L1⁺ EVs secretion in 4T1 cells. In vivo studies using an orthotopic 4T1 tumor model assessed the impact of Cel-Lip on PD-L1 levels in tumor tissues and circulating EVs, CAAs infiltration, immunosuppressive cell populations, and response to anti-PD-L1 treatment.
We revealed that CAAs significantly elevated mPD-L1 expression in tumor cells and promoted PD-L1⁺ EVs production, consequently impairing CD8T cell function and creating a major obstacle to immunotherapy efficacy. The prepared Cel/Lip exhibited a uniform particle size distribution (106.93 ± 0.33 nm). In vitro, this nanosystem simultaneously downregulated mPD-L1 expression and reduced PD-L1⁺ EVs release. In vivo, it significantly suppressed PD-L1 expression, inhibited CAAs-mediated lipid infiltration, and decreased immunosuppressive cell populations. Importantly, Cel/Lip demonstrated synergistic antitumor effects when combined with aPD-L1 therapy, offering a safe and highly effective treatment strategy with significant clinical potential for TNBC.
Cel/Lip provides a safe and highly effective strategy for the treatment of TNBC. Cel/Lip reduces CAA-induced mPD-L1 upregulation on tumor cells, thereby remodeling the immunosuppressive tumor microenvironment (TME) by promoting cytotoxic T cell infiltration and activation. Furthermore, it suppresses the secretion of PD-L1⁺ EVs, thereby preventing systemic T cell exhaustion in circulation and enhancing the availability of aPD-L1 at target tumor sites. Together, these mechanisms overcome key limitations of aPD-L1 monotherapy and significantly amplify antitumor efficacy.
