Effective Delivery of Rutin Through Astragalus Polysaccharides Micelles for Downregulating PD-L1 by Inhibiting Matrix Metalloproteinases

Melanoma, a malignancy characterized by high aggressiveness and fatality, is often treated by reactivating the immune system using immune checkpoint inhibitors. Research indicates that inhibition of matrix metalloproteinases (MMPs) can effectively block immune checkpoints. However, the current MMP inhibitor, rutin (RUT), lacks efficient delivery mechanisms to target the tumor microenvironment (TME). Therefore, this study aimed to develop pH-responsive micelles for targeted and accurate delivery into the TME, overcoming the limitations of RUT itself. RUT-carboxyphenylboronic acid (CPBA) was synthesized by coupling the boronic acid group of CPBA with the catechol group of RUT using 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and N-Hydroxysuccinimide (NHS) as coupling agents, which was then esterified with Astragalus polysaccharide (ASP) to obtain ASP-CPBA-RUT (ACR) micelles. The ACR micelles demonstrate the ability to selectively release ASP and RUT within the acidic extracellular TME (pH = 6.8). Compared to RUT, the ACR micelles had a significantly enhanced antimelanoma effect, with a melanoma suppressive effect of 67.25% (1.49 times that of RUT), a larger area of melanoma cell necrosis, and a longer life cycle in tumor-bearing mice. Through the modulation of the CD8⁺T/Treg and CD4⁺T/Treg ratios within the TME, as well as the reduction of MDSC and MDSCs cell infiltration and the enhancement of interferon-γ (IFN-γ) secretion, the ACR micelles achieved a synergistic regulation of the TME by ASP and RUT while enhancing the effectiveness of PD-L1 immunotherapy. In conclusion, ACR micelles demonstrate TME-stimulated responsive drug release capabilities and can reverse the immunosuppressive TME while enhancing the effectiveness of PD-L1 immune checkpoint therapy. This innovative drug delivery system not only presents a promising strategy for immunotherapy in melanoma treatment, but also introduces a novel method for delivering active components of traditional Chinese medicine to the TME.