Fundamental Studies of the Effects of Auger Electrons Emitted in Different Subcellular Compartments of Human Cells

俄歇电子(AEs)是由放射性核素(如99mTc、111In、67Ga)发射的通过电子俘获(EC)衰变的极低能电子(&lt；25keV)。这些放射性核素被用于SPECT的核医学，因为它们也会发射光子。此外，AEs正在研究用于癌细胞的精确照射，因为它们具有亚细胞范围(nm到µm)和高线性能量转移(let=1-23kev/µm)，对敏感的细胞隔室造成致命损害。人们认为，靠近细胞核的AE发射是通过造成DNA双链断裂(DSB)来杀死细胞的，但最近的报道表明，AE也通过对细胞膜造成氧化损伤来杀死细胞。这提出了一个耐人寻味的问题，即是否有其他目标对声发射造成伤害。这是一个未开发的地区。我们提出了一项研究计划，以研究在癌细胞和正常细胞的细胞膜、细胞质、线粒体、核膜或细胞核中发射的AEs的影响。这些基础研究对用于核医学的发射AE的放射性核素具有重要的健康物理意义，也将为未来发射AE的放射治疗剂的设计提供参考。我们将设计新型的“纳米穿梭”运输工具，将111In、67Ga或99mTc运送到选定的亚细胞隔间。纳米航天飞机将由金纳米颗粒(AuNPs)和定位于细胞表面av？3整合素的多肽以及将内化的AuNPs发送到亚细胞隔间的归巢多肽组成。这些AuNPs将被荧光标记，以可视化它们的亚细胞分布，并将被与111In、67Ga或99mTc络合的聚合物标记。沉积在亚细胞隔室中的放射性数量将通过细胞分级来测量，并用于估计吸收的剂量。剂量将通过蒙特卡罗N粒子(MCNP6)建模计算，然后与亚细胞舱中声发射的放射生物学效应相关联。将通过测定细胞的克隆存活率来研究声发射的放射生物学效应。细胞死亡的机制将通过探测细胞的细胞膜损伤、线粒体膜电位的破坏、由于核膜损伤而形成的微核以及通过免疫荧光检测DNA双链断裂来研究。我们的长期目标是开发研究细胞内短程辐射影响的工具，并了解人体细胞内辐射的放射生物学和剂量学特性。拟议的研究计划将为三名具有不同专业知识的新研究生(两名博士和一名硕士)提供一个出色的跨学科HQP培训环境，他们将作为一个团队合作开发和表征纳米航天飞机，研究不同亚细胞舱中发射的AEs的放射生物学效应，并对细胞剂量学进行建模。

Auger electrons (AEs) are very low energy electrons (<25 keV) emitted by radionuclides (e.g. 99mTc, 111In, 67Ga) that decay by electron capture (EC). These radionuclides are used in nuclear medicine for SPECT since they also emit ?-photons. In addition, AEs are being studied for precise irradiation of cancerous cells because they have a subcellular range (nm to µm) and high linear energy transfer (LET=1-23 keV/µm) that inflicts lethal damage on sensitive cell compartments. It was assumed that AE emission in close proximity to the nucleus was required to kill cells, by inflicting DNA double-strand breaks (DSBs), but it was recently reported that AEs also kill cells by causing oxidative damage to the cell membrane. This raises the intriguing question about whether or not there are other targets for AE damage. This is an unexplored area. We propose a program of research to study the effects of AEs emitted at the cell membrane, in the cytoplasm, mitochondria, nuclear envelope or nucleus of cancerous and normal cells. These fundamental studies have important health physics implications for AE-emitting radionuclides used in nuclear medicine, and will also inform on the design of AE-emitting radiotherapeutic agents in the future. We will engineer novel "nano-shuttle" delivery vehicles to route 111In, 67Ga or 99mTc to the selected subcellular compartments. The nano-shuttles will consist of gold nanoparticles (AuNPs) modified with peptides that target cell surface avß3 integrins, and with homing peptides that route the internalized AuNPs to subcellular compartments. The AuNPs will be fluorescently-labeled to visualize their subcellular distribution and will be labeled with polymers that complex 111In, 67Ga or 99mTc. The amount of radioactivity deposited in subcellular compartments will be measured by cell fractionation and used to estimate the absorbed doses. Doses will be calculated by Monte Carlo N-Particle (MCNP6) modeling, and then correlated with the radiobiological effects of AE emission in the subcellular compartments. The radiobiological effects of AE emission will be studied by determining the clonogenic survival of the cells. The mechanism of cell death will be examined by probing the cells for cell membrane damage, disruption of mitochondrial membrane potential, micronucleus formation due to nuclear envelope damage and DNA DSBs by immunofluorescence for ?-H2AX. Our long-term aim is to develop the tools for studying the effects of short-range radiations in cells, and to understand the radiobiological and dosimetric properties of radiations in human cells. The proposed research program will provide an outstanding trans-disciplinary HQP training environment for 3 new graduate students (two PhD and one MSc) with different expertise who will work collaboratively as a team to develop and characterize the nano-shuttles, study the radiobiological effects of AEs emitted in the different subcellular compartments, and model the cellular dosimetry.