Metabolic stress (for example, low pO 2 , low pH) stimulates cancer progression in a complex and largely unresolved manner. Excessive inorganic phosphate burden is being considered as another stimulator, until now there is no well-designed study to examine the potential benefits of reducing phosphate burden on cancer progression. Sevelamer microspheres, a polymeric phosphate binder, are introduced as embolic material for interventional treatment of rabbit VX2 liver cancer model. This technique is named as "transarterial sevelamer embolization (TASE)." The microspheres prove to be highly biocompatible, and TASE is found to be a safe local-regional technique. Compared with conventional transarterial chemoembolization (TACE), TASE is found to not only occlude the tumor-feeding vessel, but simultaneously deplete intratumoral inorganic phosphate (Pi), thereby inducing severe necrosis as well reducing metastasis and recurrence. Reduced Pi stress inhibits tumor vascularity, invasion, and metastasis by downregulating the angiogenic factors and oncoprotein expression. Energy metabolomics indicate that Pi stress also suppresses tumor anaerobic glycolysis and glutaminolysis. This systemic anti-cancer effect indicates a promising new application for sevelamer and TASE as a potential alternative to conventional TACE for liver cancer treatment.

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Numerous studies have shown the positive correlation between high levels of Pi and tumour progression. A critical goal of macrophage‐based cancer therapeutics is to reduce anti‐inflammatory macrophages (M2) and increase proinflammatory antitumour macrophages (M1). This study aimed to investigate the relationship between macrophage polarization and low‐Pi stress. First, the spatial populations of M2 and M1 macrophages in 22 HCC patient specimens were quantified and correlated with the local Pi concentration. The levels of M2 and M1 macrophage markers expressed in the peritumour area were higher than the intratumour levels, and the expression of M2 markers was positively correlated with Pi concentration. Next, monocytes differentiated from THP‐1 cells were polarized against different Pi concentrations to investigate the activation or silencing of the expression of p65, IκB‐α and STAT3 as well as their phosphorylation. Results showed that low‐Pi stress irreversibly repolarizes tumour‐associated macrophages (TAMs) towards the M1 phenotype by silencing stat6 and activating p65. Moreover, HepG‐2 and SMCC‐7721 cells were cultured in conditioned medium to investigate the innate anticancer immune effects on tumour progression. Both cancer cell lines showed reduced proliferation, migration and invasion, as epithelial–mesenchymal transition (EMT) was inactivated. In vivo therapeutic effect on the innate and adaptive immune processes was validated in a subcutaneous liver cancer model by the intratumoural injection of sevelamer. Tumour growth was significantly inhibited by the partial deprivation of intratumoural Pi as the tumour microenvironment under low‐Pi stress is more immunostimulatory. The anticancer immune response, activated by low‐Pi stress, suggests a new macrophage‐based immunotherapeutic modality.

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