Tanshinone IIA normalized hepatocellular carcinoma vessels and enhanced PD-1 inhibitor efficacy by inhibiting ELTD1

Background: Hepatocellular carcinoma responds poorly to immune checkpoint inhibitors, such as PD-1 inhibitors, primarily due to the low infiltration capacity of TILs in the TME. Abnormal vasculature is an important factor which limiting the infiltration of TILs. According to recent research, targeting ELTD1 expression may improve TILs delivery to reverse immunosuppression and boost tumor responses to immunotherapy. Research has demonstrated that Tanshinone IIA (TSA) improves blood vessel normalization, but the precise mechanism is yet unknown. Purpose: The purpose of this study is to investigate the molecular processes for TSA's pro-vascular normalization of HCC in vitro and in vivo. Methods: We established a mouse H22-luc in situ liver tumor model to evaluate the role of TSA vascular normalization and the immunosuppressive microenvironment. The role of ELTD1 in vascular and immune crosstalk was evaluated by bioinformatic analysis of the TCGA database. By creating a transwell co-culture cell model, the effects of TSA on enhancing tumor endothelial cell activities and ELTD1 intervention were evaluated. Results: We investigated the effect of Tanshinone IIA (TSA), a major component of Salvia miltiorrhiza Bge., on the normalization of vasculature in situ HCC models. Our results demonstrated that TSA elicited vascular normalization in a hepatocellular carcinoma model in situ. In addition, the combination of TSA with anti-PD-1 significantly inhibited tumor development due to increased infiltration of immune cells in the tumor. Mechanistically, we demonstrated that TSA improved the immunosuppressive microenvironment by inhibiting tumor growth by suppressing ELTD1 expression, inhibiting downstream JAK1 and JAK2, promoting the expression of ZO-1, occlaudin, Claudin 5, and Col IV, and promoting vascular integrity and perfusion in situ. Conclusions: This study reveals a new mechanism between TSA and ELTD1 for vascular normalization, suggesting that therapeutic or pharmacological intervention with ELTD1 may enhance the efficacy of PD-1 inhibitors in HCC.