Data_Sheet_1_Radiosensitization Effect of Gold Nanoparticles in Proton Therapy.docx

The number of proton therapy facilities and the clinical usage of high energy proton beams for cancer treatment has substantially increased over the last decade. This is mainly due to the superior dose distribution of proton beams resulting in a reduction of side effects and a lower integral dose compared to conventional X-ray radiotherapy. More recently, the usage of metallic nanoparticles as radiosensitizers to enhance radiotherapy is receiving growing attention. While this strategy was originally intended for X-ray radiotherapy, there is currently a small number of experimental studies indicating promising results for proton therapy. However, most of these studies used low proton energies, which are less applicable to clinical practice; and very small gold nanoparticles (AuNPs). Therefore, this proof of principle study evaluates the radiosensitization effect of larger AuNPs in combination with a 200 MeV proton beam. CHO-K1 cells were exposed to a concentration of 10 μg/ml of 50 nm AuNPs for 4 hours before irradiation with a clinical proton beam at NRF iThemba LABS. AuNP internalization was confirmed by inductively coupled mass spectrometry and transmission electron microscopy, showing a random distribution of AuNPs throughout the cytoplasm of the cells and even some close localization to the nuclear membrane. The combined exposure to AuNPs and protons resulted in an increase in cell killing, which was 27.1% at 2 Gy and 43.8% at 6 Gy, compared to proton irradiation alone, illustrating the radiosensitizing potential of AuNPs. Additionally, cells were irradiated at different positions along the proton depth-dose curve to investigate the LET-dependence of AuNP radiosensitization. An increase in cytogenetic damage was observed at all depths for the combined treatment compared to protons alone, but no incremental increase with LET could be determined. In conclusion, this study confirms the potential of 50 nm AuNPs to increase the therapeutic efficacy of proton therapy.

近十年来，质子治疗（proton therapy）设施的数量以及用于癌症治疗的高能质子束的临床应用规模均实现了显著增长。这一趋势主要源于质子束相较于传统X射线放疗（X-ray radiotherapy）更优异的剂量分布特性，可有效降低治疗副作用与整体照射剂量。近年来，以金属纳米颗粒作为放射增敏剂以强化放疗效果的研究思路受到了越来越多的关注。尽管该策略最初是为X射线放疗设计的，但目前已有少量实验研究表明其应用于质子治疗时也可获得良好效果。然而，此类研究大多采用了不适用于多数临床场景的低能质子束，且使用尺寸极小的金纳米颗粒（AuNPs）。为此，本原理验证性研究针对尺寸更大的金纳米颗粒（AuNPs）与200 MeV质子束联合使用的放射增敏效果进行了评估。本研究将CHO-K1细胞置于浓度为10 μg/ml的50 nm金纳米颗粒（AuNPs）中孵育4小时，随后在NRF iThemba LABS设施中接受临床质子束照射。通过电感耦合等离子体质谱法（inductively coupled mass spectrometry）与透射电子显微镜（transmission electron microscopy）验证了金纳米颗粒的细胞内化现象，结果显示金纳米颗粒在细胞胞质中呈随机分布，甚至有部分紧贴核膜。与单纯质子照射相比，金纳米颗粒与质子束联合照射可提升细胞杀伤率：在2戈瑞（Gy）剂量下杀伤率提升27.1%，6戈瑞（Gy）剂量下提升43.8%，这证实了金纳米颗粒的放射增敏潜力。此外，本研究沿质子深度剂量曲线的不同位置对细胞进行照射，以探究金纳米颗粒放射增敏效果的线性能量转移（Linear Energy Transfer, LET）依赖性。相较于单纯质子照射，联合治疗组在所有深度位置均观测到细胞遗传损伤的增加，但未发现损伤程度随线性能量转移（LET）出现显著递增。综上，本研究证实了50 nm金纳米颗粒（AuNPs）可有效提升质子治疗的临床疗效。