Co-delivery of axitinib and PD-L1 siRNA for the synergism of vascular normalization and immune checkpoint inhibition to boost anticancer immunity.

Immune checkpoint inhibition (ICI) has become the mainstay of immunotherapy for the treatment of renal cell carcinoma (RCC). However, only a small portion of patients exhibit a positive response to PD-1/PD-L1 blockade therapy and the key reason is that RCC belongs to a vascular-rich tumor for promoting immunosuppression. Specifically, the dysfunctional tumor vasculature hinders effector T cell infiltration and induces immunosuppressive tumor microenvironment via the release of cytokine, which attenuates the therapeutic efficacy of ICI. Therefore, regulating abnormal tumor vasculature may be a promising strategy to overcome the immunosuppressive microenvironment and enhance ICI therapy. Here, we propose an NGR peptide-modified actively targeted liposome (Axi/siRNA^PD-L1@NGR-Lipo) to encapsulate the anti-angiogenic agents Axitinib and PD-L1 siRNA to promote tumor vasculature normalization and relieve immune evasion for enhanced anti-tumor immunotherapy. With NGR-mediated tumor homing and active targeting, Axi/siRNA^PD-L1@NGR-Lipo could act on tumor vascular endothelial cells to inhibit neo-angiogenesis, increase pericyte coverage and vascular perfusion, and normalize the structure and function of tumor blood vessels. Meanwhile, it also enhanced immune effector T cells and NK cells infiltration and reduced the proportion of immunosuppressive T cells including MDSC cells and Tregs, thus improving the tumor immunosuppressive microenvironment. Moreover, Axi/siRNA^PD-L1@NGR-Lipo reduced the expression of PD-L1 protein in tumor cells, restored the recognition and killing ability of cytotoxic T cells, and relieved immune evasion. As expected, Axi/siRNA^PD-L1@NGR-Lipo displayed superior anti-tumor and anti-metastatic efficacy in mice bearing RCC. Overall, this study demonstrated the important potential of regulating abnormal tumor vasculature to reshape the immunosuppressive microenvironment and boost ICI therapy, which represents a promising avenue for the synergistic anti-tumor with cancer immunotherapy.