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Updated: May 21, 2026
Cytotoxic Efficacy of Photodynamic Therapy in Osteosarcoma Cells In Vitro
Published on: March 18, 2014
Inorganic phosphate enhances sensitivity of human osteosarcoma U2OS cells to doxorubicin via a p53-dependent pathway
Annamaria Spina1, Luca Sorvillo, Francesca Di Maiolo
1Department of Biochemistry and Biophysics, Medical School, Second University of Naples, Naples, Italy.
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.
Insights
Inorganic phosphate (Pi) enhances chemotherapy effectiveness in osteosarcoma by inducing p53-dependent apoptosis and inhibiting the ERK pathway. This suggests targeting Pi levels could improve osteosarcoma treatment outcomes.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Osteosarcoma is a primary bone cancer with poor prognosis despite current treatments.
- Inorganic phosphate (Pi) has previously shown potential in inhibiting osteosarcoma cell proliferation and aggressiveness.
- Novel therapeutic strategies are crucial for improving osteosarcoma patient outcomes.
Purpose of the Study:
- To investigate the effect of inorganic phosphate (Pi) on the chemosensitivity of osteosarcoma cells.
- To elucidate the molecular mechanisms underlying Pi's influence on osteosarcoma chemosensitivity.
- To determine if Pi can enhance the efficacy of chemotherapy drugs in osteosarcoma treatment.
Main Methods:
- Utilized p53-wild type (U2OS), p53-null (Saos), and p53-mutant (MG63) osteosarcoma cell lines.
- Assessed cell proliferation, cell cycle progression, and apoptosis induction.
- Analyzed protein expression (Bcl-2, p53, mdm2, p21, Bax) and caspase activation (caspase-3, PARP cleavage).
- Investigated the role of the p53 pathway using a p53 inhibitor (pifithrine-alpha) and examined the ERK1/2 pathway.
Main Results:
- Pi inhibited proliferation in p53-wild type U2OS cells by slowing cell cycle progression without inducing apoptosis.
- Pi significantly enhanced doxorubicin-induced cytotoxicity in U2OS cells via apoptosis, evidenced by increased sub-G1 population, Bcl-2 downregulation, caspase-3 activation, and PARP cleavage.
- This enhanced cytotoxicity was p53-dependent, as indicated by increased p53 protein levels and its target genes (mdm2, p21, Bax), and was reduced by pifithrine-alpha.
- Pi also led to ERK1/2 pathway inhibition in response to doxorubicin treatment.
- These effects were not observed in p53-null Saos and p53-mutant MG63 cells.
Conclusions:
- Inorganic phosphate (Pi) acts as a signaling molecule that can inhibit the ERK pathway.
- Pi sensitizes osteosarcoma cells to doxorubicin by inducing p53-dependent apoptosis.
- Targeting inorganic phosphate (Pi) levels presents a potential therapeutic strategy for improving osteosarcoma treatment by enhancing chemotherapy efficacy.
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