Monte Carlo Simulations Reveal New Design Principles for Efficient Nanoradiosensitizers Based on Nanoscale Metal–Organic Frameworks

Abstract

photon-matter interactions, the photoelectric process is more likely to occur on high-Z elements where photoelectrons are ejected following photon absorption. Auger electrons are further generated after the holes are filled by higher-orbital electrons. In addition, inorganic nanoparticles (NPs) usually possess higher densities compared to organic molecules, leading to further enhancement of energy deposition on a per unit space basis. As a result, various studies have explored the potential of high-Z element-based nanoradiosensitizers such as gold nanoparticles (Au NPs) and hafnium oxide nanoparticles (HfO 2 NPs) to amplify the generation of photoelectrons and Auger electrons. Hainfeld et al. reported improved survival of EMT-6 mammary carcinoma-bearing mice by 1 year after treatment with Au NPs and X-rays. [32] Notably, NBTXR3, a 50 nm HfO 2 NP developed by Nanobiotix, received European market approval (CE Mark) as a medical device for the treatment of locally advanced soft tissue sarcoma in 2019. [33,34] The sizes of NPs can impact their radiosensitizing effects. [35] In the study of Au NPs with various sizes, Misawa et al. found that smaller Au NPs showed greater yields of ROS including hydroxyl radical and superoxide, [36] suggesting the positive effects of high surface areas on NP radiosensitization. However, the interplay between a nanoradiosensitizer and a biological system is much more complicated. First, NPs of sizes ranging from 10 to 200 nm can preferentially accumulate in tumor tissues via the enhanced permeability and retention effect. [37] NPs smaller than 10 nm can be easily cleared through renal filtration without significant accumulation in tumors. [38] Second, the sizes of NPs also affect their cellular uptake. [39] Chithrani et al. studied size-dependent Au NPs uptake in mammalian cells and found that 50 nm Au NPs showed higher cellular uptake when compared to 14 and 70 nm Au NPs. [40] Similarly, NBTXR3 was engineered with a size of 50 nm to enhance cancer cell uptake. [41] We recently reported the design of nanoscale metal-organic frameworks (nMOFs) comprising metal-oxo cluster secondary building units (SBUs) and organic bridging ligands and examined their potential use as a novel class of nanoradiosensitizers. [42][43][44][45] We hypothesized that highly porous nMOFs might afford unprecedentedly high radiosensitization with an Nanoscale metal-organic frameworks (nMOFs) have recently been shown to provide better radiosensitization than solid nanoparticles (NPs) when excited with X-rays. Here, a Monte Carlo simulation of different radiosensitization effects by NPs and nMOFs using a lattice model consisting of 3D arrays of nanoscale secondary building units (SBUs) is reported. The simulation results reveal that lattices outperform solid NPs regardless of radiation sources or particle sizes via enhanced scatterings of photons and electrons within the lattices. Optimum dose enhancement can be achieved by tuning SBU size and inter-SBU distance.

MCHP (Monte Carlo + Human Phantom): Platform to facilitate teaching nuclear radiation physics

“…For the energy range of photons considered in the current example (where the original source was 137 Cs), incoherent (Compton) scattering is a main photon-matter interaction mechanism [8][9][10][11][12][13][14][15] (see the cross-section data shown in Fig 2 ), and the dose will be delivered…”

Monte Carlo Simulation‐Guided Design of a Thorium‐Based Metal–Organic Framework for Efficient Radiotherapy‐Radiodynamic Therapy

“…We have recently discovered nanoscale metal–organic frameworks (nMOFs) with heavy metal secondary building units (SBUs) and photosensitizing ligands as a novel class of radiosensitizers via a unique radiotherapy‐radiodynamic therapy (RT‐RDT) mode of action [27–30] . With three‐dimensional (3D) arrays of ultrasmall heavy metal SBUs, nMOFs afford superior radiosensitization over nonporous NPs by more efficiently scattering secondary photons and electrons (Figure 1a) [31] . It was further revealed that nMOFs with larger mass attenuation coefficients exhibited stronger dose enhancement effects [31–34] …”

Nanoscale Metal–Organic Layers for Biomedical Applications

“…Ni et al reported Hf 6 -DBA and Hf 12 -DBA nMOFs (DBA = 2,5-di­( p -benzoato)­aniline) as efficient radioenhancers using the electron-dense Hf 6 O 4 (OH) 4 and Hf 12 O 8 (OH) 14 SBUs as X-ray absorbers to generate reactive oxygen species (ROS) and the open channels as well as small nMOF dimensions to facilitate ROS diffusion . The nMOFs showed a much higher radioenhancement than HfO 2 , a clinically investigated radioenhancer based on in vitro and in vivo antitumor efficacy studies as well as Monte Carlo simulations. , In 2014, Wang et al observed energy transfer from M 6 clusters to anthracene ligands in M 6 -anthracene MOFs (M = Hf and Zr) and X-ray scintillation properties of these MOFs . In 2018, Lu et al reported nMOF-mediated RT–RDT by combining X-ray absorption by Hf 12 -SBUs and photosensitizing bridging ligands. ,, The periodically arranged heavy-metal SBUs deposit X-ray energy and enhance radiolysis, leading to the RT effect, while transferring some of the absorbed energy to the photosensitizing ligands to generate singlet oxygen ( 1 O 2 ) and other ROSs, realizing the RDT effect.…”