Inorganic phosphate enhances sensitivity of human osteosarcoma U2OS cells to doxorubicin via a p53‐dependent pathway

Abstract

Osteosarcoma is the most common malignant primary bone tumor in children and adolescents. The clinical outcome for osteosarcoma remains discouraging despite aggressive surgery and intensive radiotherapy and chemotherapy regimens. Thus, novel therapeutic approaches are needed. Previously, we have shown that inorganic phosphate (Pi) inhibits proliferation and aggressiveness of human osteosarcoma U2OS cells identifying adenylate cyclase, beta3 integrin, Rap1, ERK1/2 as proteins whose expression and function are relevantly affected in response to Pi. In this study, we investigated whether Pi could affect chemosensitivity of osteosarcoma cells and the underlying molecular mechanisms. Here, we report that Pi inhibits proliferation of p53-wild type U2OS cells (and not of p53-null Saos and p53-mutant MG63 cells) by slowing-down cell cycle progression, without apoptosis occurrence. Interestingly, we found that Pi strongly enhances doxorubicin-induced cytotoxicity in U2OS, and not in Saos and MG63 cells, by apoptosis induction, as revealed by a marked increase of sub-G1 population, Bcl-2 downregulation, caspase-3 activation, and PARP cleavage. Remarkably, Pi/doxorubicin combination-induced cytotoxicity was accompanied by an increase of p53 protein levels and of p53 target genes mdm2, p21 and Bax, and was significantly reduced by the p53 inhibitor pifithrine-alpha. Moreover, the doxorubicin-induced cytotoxicity was associated with ERK1/2 pathway inhibition in response to Pi. Altogether, our data enforce the evidence of Pi as a novel signaling molecule capable of inhibiting ERK pathway and inducing sensitization to doxorubicin of osteosarcoma cells by p53-dependent apoptosis, implying that targeting Pi levels might represent a rational strategy for improving osteosarcoma therapy.

Downregulation of phosphoglycerate dehydrogenase inhibits proliferation and enhances cisplatin sensitivity in cervical adenocarcinoma cells by regulating Bcl-2 and caspase-3

“…So the overexprssion of Bcl-2 and downexpression of cleaved caspase-3 inhibit apoptosis and induce resistance to chemotherapy. 25,26 We observed decreasing Bcl-2 and increasing cleaved caspase-3 expression in PHGDH knockdown HeLa cells. Unfortunately, a direct link between PHGDH and Bcl-2 or caspase-3 remains unelucidated.…”

The Possible use of Inorganic Phosphate in Osteosarcoma Therapy

“…More recently, my group has described that in wild-type p53-containing osteosarcoma U2OS cells, but not in p53-null Saos and p53-mutant MG63 osteosarcoma cells, Pi is capable of inducing sensitization to doxorubicin [14]. My group found evidence that the enhancement of doxorubicininduced cytotoxicity by Pi occurs via p53-dependent apoptosis and through a mechanism involving ERK1/2 downregulation [14].…”

“…Similar to doxorubicin [14], a possible role of p53 and/or ERK1/2 in the enhancement of Taxol-induced cytotoxicity by Pi in U2OS is currently under investigation.…”

“…My group found evidence that the enhancement of doxorubicininduced cytotoxicity by Pi occurs via p53-dependent apoptosis and through a mechanism involving ERK1/2 downregulation [14].…”

“…In recent years, my group has published a series of articles directed at determining the For reprint orders, please contact: reprints@futuremedicine.com future science group Editorial Naviglio consequences of elevated Pi on the behavior of human osteosarcoma cells, and on the underlying molecular mechanisms [12][13][14][15]. Throughout my group's studies, my group has used a spectrum of final concentrations of Pi (1-10 mM) to cover the physiologic range in humans and to be in agreement with most of the published studies on Pi-triggered effects.…”