Low-energy shock waves promote the cisplatin chemosensitivity of human osteosarcoma MNNG/HOS cells via the P2X7/Akt/mTOR pathway

Abstract

Background: The current dilemma of osteosarcoma treatment is the resistance of chemotherapeutic drugs after long-term usage, which also introduces life-threatening side effects.

Methods and results: To minimize chemoresistance in osteosarcoma patients, the authors applied shock waves (SWs) to human osteosarcoma MNNG/HOS cells, then evaluated the cell viability and extracellular ATP levels, and further investigated the effect of SWs on cisplatin (DDP) cytotoxicity in MNNG/HOS cells. The authors' results showed that 400 SW pulses at 0.21 mJ/mm² exhibited little influence on the MNNG/HOS cell viability. In addition, this SW condition significantly promoted the extracellular ATP release in MNNG/HOS cells. Importantly, low-energy SWs obviously increased Akt and mammalian target of rapamycin (mTOR) phosphorylation and activation in MNNG/HOS cells, which could be partially reversed in the presence of P2X7 siRNA. The authors also found that low-energy SWs strongly increased the DDP sensitivity of MNNG/HOS cells in the absence of P2X7.

Conclusions: For the first time, the authors found that SW therapy reduced the DDP resistance of MNNG/HOS osteosarcoma cells when the ATP receptor P2X7 was downregulated. SW therapy may provide a novel treatment strategy for chemoresistant human osteosarcoma.

Keywords: DDP; P2X7; human osteosarcoma; shock wave.

Figure 1

Optimization of SW conditions for human osteosarcoma MNNG/HOS cells. MNNG/HOS cells were exposed to 400 SW pulses at different levels for 0 h (A) and 24 h (B). The cell viability was evaluated using a cell counting kit-8 kit. Data are shown as the mean±SD, n=5, *P<0.05, one-way analysis of variance. OD, optical density. SW, shock wave.

Figure 2

Low-energy SWs induced extracellular ATP release in MNNG/HOS cells. Cells were treated with SWs, as indicated, and the ATP level was determined by an enzyme-linked immunosorbent assay kit for ATP. Data are shown as the mean±SD, n=3, *P<0.05, one-way analysis of variance. SWs, shock waves.

Figure 3

Low-energy SWs activated the Akt/mammalian target of rapamycin (mTOR) pathway through P2X7. (A) A western blot assay confirmed that P2X7 was knocked down after cells were transfected with P2X7 siRNA. (B) The p-Akt and p-mTOR levels after treatment with low-energy SWs and P2X7 siRNA were assessed by a western blot assay. (C) The mRNA expression levels of Akt and mTOR after treatment with low-energy SWs and P2X7 siRNA were assessed by a quantitative polymerase chain reaction assay. Data are shown as the mean±SD, n= 3, *P<0.05, one-way analysis of variance. SWs, shock waves.

Figure 4

Low-energy shock waves (SWs) enhanced cisplatin (DDP)-mediated MNNG/HOS cell apoptosis. MNNG/HOS cells were treated with SWs, DDP, and P2X7 siRNA, as indicated, and then apoptosis was detected using an annexin V–propidium iodide assay. SWs, shock waves.