Effect of Inorganic Phosphorus Manipulation on Prostate Cancer Cells In Vitro

Abstract

Prostate Cancer (PC) was ranked as the second most frequently diagnosed cancer and the fifth leading cause of cancer-related deaths among males worldwide. Despite the availability of various treatment regimens, 90% of patients will develop resistance and advance to an aggressive and lethal state known as metastatic castration-resistant PC. Dietary factors were shown to be modifiable risk factors for PC. Specifically, the intake and serum levels of inorganic phosphorus (Pi), a naturally occurring essential mineral, were associated with an increased risk of PC. Observational studies have shed light on the systemic effects of Pi on PC; however, this interplay has not yet been studied in vitro, leaving a gap in the existing literature. Thus, this study aims to determine the tumorigenic effect of increased concentrations of Pi on PLum-AD murine PC cells, at the molecular and cellular levels. Effects of elevated concentrations of sodium phosphate (NaPi) and potassium phosphate (KPi) were assessed on the murine PLum- AD cell line using various in vitro assays. The MTT assay was utilized to determine the proliferative and cytotoxic effects of a wide range of NaPi and KPi concentrations. Additionally, the trypan blue exclusion assay was performed to assess the effect of the treatments on cell viability. Also at the cellular level, the effect of elevated NaPi and KPi on the cell migratory ability was investigated through the wound healing assay. At the molecular level, immunofluorescence staining, and analysis elucidated the effect of elevated concentrations of NaPi and KPi on the protein expression of epithelial- mesenchymal transition (EMT) markers. Our results showed that NaPi and KPi did not affect the proliferation and viability of PLum-AD cells. However, abnormally elevated concentrations of NaPi, but not KPi significantly induced a cytotoxic effect, indicating a possible sodium-dependent transport system involved in the uptake of Pi. While the wound healing assay showed that NaPi and KPi treatments did not alter the migratory ability of PLum-AD cells, immunofluorescence staining and analysis showed an increase in the relative expression of vimentin (Vim), a marker of EMT. Further in vitro studies are needed to elucidate the long-term effect of the treatments, investigate the pathways involved in Pi uptake by PC cells, and identify key signaling pathways implicated in the promotion of EMT. Moreover, in vivo studies are warranted to elucidate the interaction between increased Pi levels and its regulatory systems, and their effect on PC proliferation and progression. In conclusion, by demonstrating the effect of increased Pi concentrations on PC tumorigenesis, novel therapeutic strategies that target Pi in the tumor microenvironment (TME) of PC cells could play a role in the management of the advanced stages.