Abstract
Proton beam irradiation is a form of advanced radiotherapy providing superior distributions of a low LET radiation dose relative to that of photon therapy for the treatment of cancer. Even though this clinical treatment has been developing for several decades, the proton radiobiology critical to the optimization of proton radiotherapy is far from being understood. Proteomic changes were analyzed in human melanoma cells treated with a sublethal dose (3 Gy) of proton beam irradiation. The results were compared with untreated cells. Two-dimensional electrophoresis was performed with mass spectrometry to identify the proteins. At the dose of 3 Gy a minimal slowdown in proliferation rate was seen, as well as some DNA damage. After allowing time for damage repair, the proteomic analysis was performed. In total 17 protein levels were found to significantly (more than 1.5 times) change: 4 downregulated and 13 upregulated. Functionally, they represent four categories: (i) DNA repair and RNA regulation (VCP, MVP, STRAP, FAB-2, Lamine A/C, GAPDH), (ii) cell survival and stress response (STRAP, MCM7, Annexin 7, MVP, Caprin-1, PDCD6, VCP, HSP70), (iii) cell metabolism (TIM, GAPDH, VCP), and (iv) cytoskeleton and motility (Moesin, Actinin 4, FAB-2, Vimentin, Annexin 7, Lamine A/C, Lamine B). A substantial decrease (2.3 x) was seen in the level of vimentin, a marker of epithelial to mesenchymal transition and the metastatic properties of melanoma.
Highlights
Proton therapy is used worldwide to treat several types of cancer due to superior targeting and energy deposition [1,2]
Proton Beam Irradiation Cells in suspension in phosphate buffer saline (PBS) at 16106 cells/ml were transported on ice to the proton beam facility. 1.5 ml of the cell suspension was irradiated at RT in an Eppendorf vial placed in a positioning holder
Cell Growth Inhibition and DNA Damage 3 Gy of proton beam irradiation slowed down cell growth in culture by app. 15% (Fig. 1 A)
Summary
Proton therapy is used worldwide to treat several types of cancer due to superior targeting and energy deposition [1,2]. In spite of the fact that proton therapy is used clinically with great success, not much is known about the biological effects of proton radiation. A substantial body of data has been accumulated on the biological effectiveness of proton radiation [3,4,5,6,7,8,9,10,11,12,13], and on some mechanisms of proton-induced cell death [14,15,16,17], but many other biological effects of the proton beam are unclear [1]. As proton irradiation is considered to be low-LET radiation (,20 keV/mm), its biological effects are assumed to be similar to those induced by photon radiation. There is some experimental data demonstrating that this is not always the case [1,18]
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