Intratumoral inorganic phosphate deprivation: A new anticancer strategy?

Tumor epidemiology, as well as tumor microenvironments and cancer cell signaling study, has been presented with statistical relevance of inorganic phosphate (Pi) to tumorigenesis. Although serum Pi is still not acknowledged as a clinical tumor biomarker, abnormally high Pi concentration in serum or tumor lesions is gradually recognized as a characteristic of malignancy. On the other hand, phosphate binder (e.g. La₂ (CO₃)₃, Fosrenols) has been clinically approved to treat hyperphosphatemia, a metabolic disease characterized by a high serum phosphate level. We hypothesize that, if reducing phosphate burden comes to benefit tumor therapy, could systemic or intratumoral administration of phosphate binder effectively deprive tumor Pi concentration, and then inhibit tumor growth and metastases? From the past clinical and preclinical outcomes, we'd conclude that Pi is not only a metabolite during tumor growth but also a force to trigger tumor progression and metastases. Two types of cancer models were developed to initiate this study. Firstly, a patient-derived xenograft mouse model of colorectal cancer was designed, where mice were administered systemically or intratumorally with lanthanum acetate (a molecular phosphate binder), and the serum or intratumoral Pi concentration levels were found to a dropdown. Secondly, a rabbit VX2 liver tumor was set up for the local-regional therapy model, where lanthanum acetate was intratumorally administered by the standard transcatheter arterial chemoembolization procedure, and it significantly reduced intratumoral Pi concentration. Therefore, Pi deprivation by phosphate binder might be a new anticancer strategy if reducing phosphate burden could effectively arrest tumor growth and delay metastatic progression.