Release of endogenous danger signals from HIFU-treated tumor cells and their stimulatory effects on APCs

https://doi.org/10.1016/j.bbrc.2005.07.071Get rights and content

Abstract

The effects of high-intensity focused ultrasound (HIFU) on the release of endogenous danger signals from tumor cells and subsequent activation of antigen-presenting cells (APCs) were evaluated in vitro. MC-38 mouse tumor cells were treated using a 1.1 MHz HIFU transducer under two different protocols (P = 6.7 MPa, 30% duty cycle, 5 s vs. P = 10.7 MPa, 3% duty cycle, 30 s) to produce either thermal necrosis or mechanical lysis of the tumor cells. Here, we report that HIFU treatment can cause the release of endogenous danger signals (ATP and hsp60) and exposure of dendritic cells (DCs) and macrophages to the supernatants of HIFU-treated tumor cells leads to an increased expression of co-stimulatory molecules (CD80 and CD86) with enhanced secretion of IL-12 by the DCs and elevated secretion of TNF-α by the macrophages. The potency in APC activation produced by mechanical lysis is much stronger than thermal necrosis of the tumor cells. These findings suggest that optimization of treatment strategy may help to enhance HIFU-elicited anti-tumor immunity.

Section snippets

Materials and methods

Cell cultures. RAW264.7 mouse macrophage cell line was obtained from American Type Culture Collection (Manassas, VA). The MC-38 mouse colon adenocarcinoma tumor cell line was kindly provided by Dr. Jeffrey Schlom of NCI (Bethesda, MD). Cell lines were maintained in complete Dulbecco’s modified Eagle’s medium (DMEM), supplemented with 10% heat-inactivated fetal bovine serum (FBS) (Gibco, USA) at 37 °C and 5% CO2. Tumor cells used in the experiments were in log-phase with 24 h doubling time. Before

Thermal and mechanical lysis of the tumor cells produced by a HIFU transducer

Current HIFU therapy is focused almost exclusively on producing thermal ablation of the tumor tissues. However, both thermal and mechanical damage may be caused by HIFU through heat impulse and acoustic cavitation. Here, we compared the HIFU-induced damage of MC-38 tumor cells using two different exposure strategies, with one emphasizing the thermal effect but the other emphasizing the mechanical effect produced by the same 1.1 MHz HIFU transducer under different output conditions. The acoustic

Discussion

Using tumor cell line MC-38, we have demonstrated in vitro that HIFU treatment can cause both thermal and mechanical necrosis, leading to the release of endogenous danger signals (ATP and hsp60) from the damaged tumor cells. We have further demonstrated that the released danger signals can stimulate the maturation of APCs, such as DCs and macrophages. Most importantly, the immuno-stimulatory effect of mechanically lysed tumor cells was found to be much stronger than that of thermally ablated

Acknowledgment

This work was supported in part by NIH Grant No. RO1-EB02682.

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