Transarterial Embolization Using an Inorganic Phosphate Binder Modulates Immunity and Angiogenesis-related Factors in a Rat Model of Liver Cancer.

Abstract

Purpose: To determine how low inorganic phosphate stress (LIPS) induced by sevelamer transartieral embolization (S-TAE) affects immune regulation and angiogenesis in hepatocellular carcinoma (HCC).

Material and methods: Transcatheter arterial embolization (TAE) using conventional lipiodol plus Poly (vinyl alcohol) (PVA) microsphere and S-TAE were conducted on a McA-RH7777 orthotopic liver tumor model in rats, followed by the assessment of alterations in immunity- and angiogenesis-related factors. The cells were cultured under hypoxic conditions and stimulated with LIPS to analyze the modulation of programmed cell death 1 ligand 1 (PD-L1), vascular endothelial growth factor (VEGFα), and transforming growth factor-β1 (TGF-β1) expression through Western blotting, qRT‒PCR, and immunofluorescence assays. Cell migratory capacity and angiogenesis were also evaluated.

Results: TAE increased the expression of neoplastic PD-L1 and VEGFα, and S-TAE, which depletes intratumoral Pi, downregulated the expression of PD-L1, VEGFα and TGF-β1, and augmented the infiltration of CD8+ T-cells, thereby inhibited angiogenesis and activated anticancer immunity. In vitro, the study demonstrated that LIPS inhibits hypoxia-induced upregulation of PD-L1 expression and the HIF-1α/VEGFα axis. Moreover, LIPS inhibited the tube formation ability of Human Umbilical Vein Endothelial Cells (HUVECs) and the migration ability and epithelial-mesenchymal transition (EMT) process of cancer cells under hypoxic conditions.

Conclusions: S-TAE inhibited the expression of PD-L1 and VEGFα, thereby activated anti-tumor immunity and suppressing tumor angiogenesis. All the findings reveal the biology of tumors under low Pi stress and suggest the potential therapeutic value of S-TAE.