Simultaneous induction of immunogenic cell death and PD-L1 downregulation by bufalin-based nanovaccines for potentiate HCC immunotherapy

Immunotherapy is a promising treatment in hepatocellular carcinoma (HCC), but with low response rate clinically. Immunogenic cell death (ICD) is considered as a strategy to enhance immunotherapy response. However, chemotherapeutic drugs with ICD make tumor cells upregulating PD-L1 expression to deactivate T-cells via PD-1/PD-L1 pathway. Here, Bufalin (Buf) was validated for the first time as an ICD inducer. Buf triggered reactive oxygen species (ROS) related endoplasmic reticulum (ER) stress to elicit apoptosis and ICD via PERK/eIF2α/ATF-4/CHOP in HCC cells. Additionally, Buf downregulated the expression of PD-L1 to avoid immune escape. Buf can simultaneously activate dendritic cell (DC) maturation and interrupt the PD-1/PD-L1 pathway. To amplify immunotherapy and decrease adverse cardiac reactions of Buf, SP94-modified liposome-coated zeolite imidazolate framework-8 loaded with Buf (Buf-ZIF-lipo-SP94) was designed to effectively increase drug accumulation in tumor by HCC-specific targeting SP94 receptor-mediated endocytosis. Importantly, ZIF-8 with the ability of triggering ROS generation itself synergized Buf to induce stronger ICD effects. Buf-ZIF-lipo-SP94 achieved synergistic effects with anti-PD-L1 for HCC immunotherapy, showing better tumor inhibition rate (>90 %), survival of animals and safety. This study uncovered the potential of Buf in inducing ICD and downregulating PD-L1 expression, developing a Buf-loaded nanovaccine for combination strategy of immunotherapy in HCC.