Inorganic Phosphate Prevents Erk1/2 and Stat3 Activation and Improves Sensitivity to Doxorubicin of MDA-MB-231 Breast Cancer Cells.
Due to its expression profile, triple-negative breast cancer (TNBC) is refractory to the most effective targeted therapies available for breast cancer treatment. Thus, cytotoxic chemotherapy represents the mainstay of treatment for early and metastatic TNBC. Therefore, it would be greatly beneficial to develop therapeutic approaches that cause TNBC cells to increase their sensitivity to cytotoxic drugs. Inorganic phosphate (Pi) is emerging as an important signaling molecule in many cell types. Interestingly, it has been shown that Pi greatly enhances the sensitivity of human osteosarcoma cell line (U2OS) to doxorubicin. We investigated the effects of Pi on the sensitivity of TNBC cells to doxorubicin and the underlying molecular mechanisms, carrying out flow cytometry-based assays of cell-cycle progression and cell death, MTT assays, direct cell number counting and immunoblotting experiments. We report that Pi inhibits the proliferation of triple-negative MDA-MB-231 breast cancer cells mainly by slowing down cell cycle progression. Interestingly, we found that Pi strongly increases doxorubicin-induced cytotoxicity in MDA-MB-231 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 dynamically accompanied by profound changes in Erk1/2 and Stat3 protein and phosphorylation levels. Altogether, our data enforce the evidence of Pi acting as a signaling molecule in MDA-MB-231 cells, capable of inhibiting Erk and Stat3 pathways and inducing sensitization to doxorubicin of TNBC cells, and suggest that targeting Pi levels at local sites might represent the rationale for developing effective and inexpensive strategies for improving triple-negative breast cancer therapy.
Department of Biochemistry, Biophysics and General Pathology, Medical School, Second University of Naples, via L. De Crecchio 7, 80138 Naples, Italy. sapioluigi@hotmail.it.
Luigi
L
Sapio
Department of Biochemistry, Biophysics and General Pathology, Medical School, Second University of Naples, via L. De Crecchio 7, 80138 Naples, Italy. sapioluigi@hotmail.it.
Luca
L
Sorvillo
Department of Biochemistry, Biophysics and General Pathology, Medical School, Second University of Naples, via L. De Crecchio 7, 80138 Naples, Italy. michela_illiano@libero.it.
Michela
M
Illiano
Department of Biochemistry, Biophysics and General Pathology, Medical School, Second University of Naples, via L. De Crecchio 7, 80138 Naples, Italy. emilio.chiosi@unina2.it.
Emilio
E
Chiosi
Department of Biochemistry, Biophysics and General Pathology, Medical School, Second University of Naples, via L. De Crecchio 7, 80138 Naples, Italy. annamaria.spina@unina2.it.
Annamaria
A
Spina
Department of Biochemistry, Biophysics and General Pathology, Medical School, Second University of Naples, via L. De Crecchio 7, 80138 Naples, Italy. silvio.naviglio@unina2.it.
Silvio
S
Naviglio
D001943:Breast Neoplasms / Q000201:enzymology; D045744:Cell Line, Tumor; D004317:Doxorubicin / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects
D010710:Phosphates; D050796:STAT3 Transcription Factor; D004317:Doxorubicin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3
Erk1/2; Stat3; combination antitumor therapy; doxorubicin; inorganic phosphate