Dose enhancement effects of gold nanoparticles specifically targeting RNA in breast cancer cells

Critical parameters to translate gold nanoparticles as radiosensitizing agents into the clinic

Radiotherapy is an inevitable choice for cancer treatment that is applied as combinatorial therapy along with surgery and chemotherapy. Nevertheless, radiotherapy at high doses kills normal and tumor cells at the same time. In addition, some tumor cells are resistant to radiotherapy. Recently, many researchers have focused on high-Z nanomaterials as radiosensitizers for radiotherapy. Among them, gold nanoparticles (GNPs) have shown remarkable potential due to their promising physical, chemical, and biological properties. Although few clinical trial studies have been performed on drug delivery and photosensitization with lasers, GNPs have not yet received Food and Drug Administration approval for use in radiotherapy. The sensitization effects of GNPs are dependent on their concentration in cells and x-ray energy deposition during radiotherapy. Notably, some limitations related to the properties of the GNPs, including their size, shape, surface charge, and ligands, and the radiation source energy should be resolved. At the first, this review focuses on some of the challenges of using GNPs as radiosensitizers and some biases among in vitro/in vivo, Monte Carlo, and clinical studies. Then, we discuss the challenges in the clinical translation of GNPs as radiosensitizers for radiotherapy and proposes feasible solutions. And finally, we suggest that certain areas be considered in future research. This article is categorized under: Therapeutic Approaches and Drug Discovery > NA.

Nanoscopic biodosimetry using plasmid DNA in radiotherapy with metallic nanoparticles

Nanoscopic lesions (complex damages), are the most lethal lesions for the cells. As nanoparticles have become increasingly popular in radiation therapy and the importance of analyzing nanoscopic dose enhancement has increased, a reliable tool for nanodosimetry has become indispensable. In this regard, the DNA plasmid is a widely used tool as a nanodosimetry probe in radiobiology and nano-radiosensitization studies. This approach is helpful for unraveling the radiosensitization role of nanoparticles in terms of physical and physicochemical effects and for quantifying radiation-induced biological damage. This review discusses the potential of using plasmid DNA assays for assessing the relative effects of nano-radiosensitizers, which can provide a theoretical basis for the development of nanoscopic biodosimetry and nanoparticle-based radiotherapy.

Incorporation of Low Concentrations of Gold Nanoparticles: Complex Effects on Radiation Response and Fate of Cancer Cells

(1) Background: In oncology research, a long-standing discussion exists about pros and cons of metal nanoparticle-enhanced radiotherapy and real mechanisms behind the tumor cell response to irradiation (IR) in presence of gold nanoparticles (GNPs). A better understanding of this response is, however, necessary to develop more efficient and safety nanoparticle (NP) types designed to disturb specific processes in tumor cells. (2) Aims and Methods: We combined 3D confocal microscopy and super-resolution single molecule localization microscopy (SMLM) to analyze, at the multiscale, the early and late effects of 10 nm-GNPs on DNA double strand break (DSB) induction and repair in tumor cells exposed to different doses of photonic low-LET (linear energy transfer) radiation. The results were correlated to different aspects of short and long-term cell viability. SkBr3 breast cancer cells (selected for the highest incidence of this cancer type among all cancers in women, and because most breast tumors are treated with IR) were incubated with low concentrations of GNPs and irradiated with ⁶⁰Co γ-rays or 6 MV X-rays. In numerous post-irradiation (PI) times, ranging from 0.5 to 24 h PI, the cells were spatially (3D) fixed and labeled with specific antibodies against γH2AX, 53BP1 and H3K9me3. The extent of DSB induction, multi-parametric micro- and nano-morphology of γH2AX and 53BP1 repair foci, DSB repair kinetics, persistence of unrepaired DSBs, nanoscale clustering of γH2AX and nanoscale (hetero)chromatin re-organization were measured by means of the mentioned microscopy techniques in dependence of radiation dose and GNP concentration. (3) Results: The number of γH2AX/53BP1 signals increased after IR and an additional increase was observed in GNP-treated (GNP(+)) cells compared to untreated controls. However, this phenomenon reflected slight expansion of the G2-phase cell subpopulation in irradiated GNP(+) specimens instead of enhanced DNA damage induction by GNPs. This statement is further supported by some micro- and nano-morphological parameters of γH2AX/53BP1 foci, which slightly differed for cells irradiated in absence or presence of GNPs. At the nanoscale, Ripley’s distance frequency analysis of SMLM signal coordinate matrices also revealed relaxation of heterochromatin (H3K9me3) clusters upon IR. These changes were more prominent in presence of GNPs. The slight expansion of radiosensitive G2 cells correlated with mostly insignificant but systematic decrease in post-irradiation survival of GNP(+) cells. Interestingly, low GNP concentrations accelerated DSB repair kinetics; however, the numbers of persistent γH2AX/53BP1 repair foci were slightly increased in GNP(+) cells. (4) Conclusions: Low concentrations of 10-nm GNPs enhanced the G2/M cell cycle arrest and the proportion of radiosensitive G2 cells, but not the extent of DNA damage induction. GNPs also accelerated DSB repair kinetics and slightly increased presence of unrepaired γH2AX/53BP1 foci at 24 h PI. GNP-mediated cell effects correlated with slight radiosensitization of GNP(+) specimens, significant only for the highest radiation dose tested (4 Gy).

A Paradigm Revolution or Just Better Resolution-Will Newly Emerging Superresolution Techniques Identify Chromatin Architecture as a Key Factor in Radiation-Induced DNA Damage and Repair Regulation?

DNA double-strand breaks (DSBs) have been recognized as the most serious lesions in irradiated cells. While several biochemical pathways capable of repairing these lesions have been identified, the mechanisms by which cells select a specific pathway for activation at a given DSB site remain poorly understood. Our knowledge of DSB induction and repair has increased dramatically since the discovery of ionizing radiation-induced foci (IRIFs), initiating the possibility of spatiotemporally monitoring the assembly and disassembly of repair complexes in single cells. IRIF exploration revealed that all post-irradiation processes-DSB formation, repair and misrepair-are strongly dependent on the characteristics of DSB damage and the microarchitecture of the whole affected chromatin domain in addition to the cell status. The microscale features of IRIFs, such as their morphology, mobility, spatiotemporal distribution, and persistence kinetics, have been linked to repair mechanisms. However, the influence of various biochemical and structural factors and their specific combinations on IRIF architecture remains unknown, as does the hierarchy of these factors in the decision-making process for a particular repair mechanism at each individual DSB site. New insights into the relationship between the physical properties of the incident radiation, chromatin architecture, IRIF architecture, and DSB repair mechanisms and repair efficiency are expected from recent developments in optical superresolution microscopy (nanoscopy) techniques that have shifted our ability to analyze chromatin and IRIF architectures towards the nanoscale. In the present review, we discuss this relationship, attempt to correlate still rather isolated nanoscale studies with already better-understood aspects of DSB repair at the microscale, and consider whether newly emerging "correlated multiscale structuromics" can revolutionarily enhance our knowledge in this field.

Exploring Diffusion and Cellular Uptake: Charged Gold Nanoparticles in an in Vitro Breast Cancer Model

Gold nanoparticles have emerged as a prominent tool in nanomedicine, particularly for applications in cancer diagnostic and treatment. One of the challenges for the successful implementation of gold nanoparticles in cancer therapy is their delivery to the specific cancer area within the tumor microenvironment. The presence of cancer enables a poorly organized vascularization system, increasing the pressure with the microenvironment, limiting the uptake of particles. The physicochemical properties of the gold nanoparticles (size, shape, and surface charge) also have a significant effect on diffusion to the tumor site and cellular uptake. In this work, we analyzed the transport of 10 nm gold nanoparticles with different surface charges (neutral, negative, and positive) through a hydrogel composite. Three-dimensional in vitro models composed of breast cancer cells loaded in the hydrogel composite were used for the qualitative and quantitative evaluation of cellular uptake of the gold nanoparticles. Surprisingly, an inverse correlation between the diffusion coefficients of the nanoparticles and cellular uptake was demonstrated. Positively charged gold nanoparticles displayed high cellular uptake, although their diffusion coefficient indicated slow transport through the hydrogel matrix. Neutral particles, on the other hand, displayed fast diffusion but the lowest cellular uptake. The results obtained indicate that nanoparticle diffusion and cellular uptake should be studied together in realistic in vitro models for a true evaluation of transport in tumor microenvironments.

Nuclear-targeted gold nanoparticles enhance cancer cell radiosensitization

Radiation therapy aims to kill or inhibit proliferation of cancer cells while sparing normal cells. To enhance radiosensitization, we developed 40 nm-sized gold nanoparticles targeting the nucleus. We exploited a strategy that combined RGD and NLS peptides respectively targeting cancer cell and the nucleus to initiate cell-death activated by x-ray irradiation. We observed that the modified gold nanoparticles were either translocated in the nuclei or accumulated in the vicinity of the nuclei. We demonstrated that x-ray irradiation at 225 kVp energy reduced cell proliferation by 3.8-fold when the nuclear targeted gold nanoparticles were used. We determined that the radiation dose to have a 10% survival fraction was reduced from 11.0 Gy to 7.1 Gy when 10.0 µg ml^-1 of the NLS/RGD/PEG-AuNP was incubated with A549 cancer cells. We conclude that the peptide-modified gold nanoparticles targeting the nucleus significantly enhance radiosensitization.

Delivery of Nanoparticle-Based Radiosensitizers for Radiotherapy Applications

Nanoparticle-based radiosensitization of cancerous cells is evolving as a favorable modality for enhancing radiotherapeutic ratio, and as an effective tool for increasing the outcome of concomitant chemoradiotherapy. Nevertheless, delivery of sufficient concentrations of nanoparticles (NPs) or nanoparticle-based radiosensitizers (NBRs) to the targeted tumor without or with limited systemic side effects on healthy tissues/organs remains a challenge that many investigators continue to explore. With current systemic intravenous delivery of a drug, even targeted nanoparticles with great prospect of reaching targeted distant tumor sites, only a portion of the administered NPs/drug dosage can reach the tumor, despite the enhanced permeability and retention (EPR) effect. The rest of the targeted NPs/drug remain in systemic circulation, resulting in systemic toxicity, which can decrease the general health of patients. However, the dose from ionizing radiation is generally delivered across normal tissues to the tumor cells (especially external beam radiotherapy), which limits dose escalation, making radiotherapy (RT) somewhat unsafe for some diseased sites despite the emerging development in RT equipment and technologies. Since radiation cannot discriminate healthy tissue from diseased tissue, the radiation doses delivered across healthy tissues (even with nanoparticles delivered via systemic administration) are likely to increase injury to normal tissues by accelerating DNA damage, thereby creating free radicals that can result in secondary tumors. As a result, other delivery routes, such as inhalation of nanoparticles (for lung cancers), localized delivery via intratumoral injection, and implants loaded with nanoparticles for local radiosensitization, have been studied. Herein, we review the current NP delivery techniques; precise systemic delivery (injection/infusion and inhalation), and localized delivery (intratumoral injection and local implants) of NBRs/NPs. The current challenges, opportunities, and future prospects for delivery of nanoparticle-based radiosensitizers are also discussed.

Physical, chemical and biological enhancement in X-ray nanochemistry

X-ray nanochemistry studies how to use nanomaterials and particularly how to create new nanomaterials to increase the effects of X-rays such as chemical reactivity, damage to cells, tumor destruction, scintillation and more. The increase, also called enhancement, can be categorized into several groups, and the current categorization of enhancement follows a natural division of physical, chemical and biological enhancement based on how nanomaterials behave under X-ray irradiation. In physical enhancement, electrons released from atoms in the nanomaterials upon X-ray ionization interact with the nanomaterials and surrounding media to increase the effects. Scintillation also belongs to this category. Chemical enhancement results when reactive oxygen species (ROS) or reactive radical intermediates (RRI) produced in aqueous solutions under X-ray irradiation interact with the surface of catalytic nanomaterials to increase the effects. When the damage of cells is enhanced through biological pathways beyond the abovementioned physical or chemical enhancement due to the presence of nanomaterials under X-ray irradiation, the enhancement is called biological enhancement. Works supporting this systematic categorization, the reported values of these enhancements, and important aspects of the development of enhancement in the X-ray nanochemistry framework are given and discussed in this perspective.

Challenges and Contradictions of Metal Nano-Particle Applications for Radio-Sensitivity Enhancement in Cancer Therapy

From the very beginnings of radiotherapy, a crucial question persists with how to target the radiation effectiveness into the tumor while preserving surrounding tissues as undamaged as possible. One promising approach is to selectively pre-sensitize tumor cells by metallic nanoparticles. However, though the "physics" behind nanoparticle-mediated radio-interaction has been well elaborated, practical applications in medicine remain challenging and often disappointing because of limited knowledge on biological mechanisms leading to cell damage enhancement and eventually cell death. In the present study, we analyzed the influence of different nanoparticle materials (platinum (Pt), and gold (Au)), cancer cell types (HeLa, U87, and SKBr3), and doses (up to 4 Gy) of low-Linear Energy Transfer (LET) ionizing radiation (γ- and X-rays) on the extent, complexity and reparability of radiation-induced γH2AX + 53BP1 foci, the markers of double stand breaks (DSBs). Firstly, we sensitively compared the focus presence in nuclei during a long period of time post-irradiation (24 h) in spatially (three-dimensionally, 3D) fixed cells incubated and non-incubated with Pt nanoparticles by means of high-resolution immunofluorescence confocal microscopy. The data were compared with our preliminary results obtained for Au nanoparticles and recently published results for gadolinium (Gd) nanoparticles of approximately the same size (2⁻3 nm). Next, we introduced a novel super-resolution approach-single molecule localization microscopy (SMLM)-to study the internal structure of the repair foci. In these experiments, 10 nm Au nanoparticles were used that could be also visualized by SMLM. Altogether, the data show that different nanoparticles may or may not enhance radiation damage to DNA, so multi-parameter effects have to be considered to better interpret the radiosensitization. Based on these findings, we discussed on conclusions and contradictions related to the effectiveness and presumptive mechanisms of the cell radiosensitization by nanoparticles. We also demonstrate that SMLM offers new perspectives to study internal structures of repair foci with the goal to better evaluate potential differences in DNA damage patterns.

Recruitment of 53BP1 Proteins for DNA Repair and Persistence of Repair Clusters Differ for Cell Types as Detected by Single Molecule Localization Microscopy

DNA double stranded breaks (DSBs) are the most serious type of lesions introduced into chromatin by ionizing radiation. During DSB repair, cells recruit different proteins to the damaged sites in a manner dependent on local chromatin structure, DSB location in the nucleus, and the repair pathway entered. 53BP1 is one of the important players participating in repair pathway decision of the cell. Although many molecular biology details have been investigated, the architecture of 53BP1 repair foci and its development during the post-irradiation time, especially the period of protein recruitment, remains to be elucidated. Super-resolution light microscopy is a powerful new tool to approach such studies in 3D-conserved cell nuclei. Recently, we demonstrated the applicability of single molecule localization microscopy (SMLM) as one of these highly resolving methods for analyses of dynamic repair protein distribution and repair focus internal nano-architecture in intact cell nuclei. In the present study, we focused our investigation on 53BP1 foci in differently radio-resistant cell types, moderately radio-resistant neonatal human dermal fibroblasts (NHDF) and highly radio-resistant U87 glioblastoma cells, exposed to high-LET ¹⁵N-ion radiation. At given time points up to 24 h post irradiation with doses of 1.3 Gy and 4.0 Gy, the coordinates and spatial distribution of fluorescently tagged 53BP1 molecules was quantitatively evaluated at the resolution of 10⁻20 nm. Clusters of these tags were determined as sub-units of repair foci according to SMLM parameters. The formation and relaxation of such clusters was studied. The higher dose generated sufficient numbers of DNA breaks to compare the post-irradiation dynamics of 53BP1 during DSB processing for the cell types studied. A perpendicular (90°) irradiation scheme was used with the 4.0 Gy dose to achieve better separation of a relatively high number of particle tracks typically crossing each nucleus. For analyses along ion-tracks, the dose was reduced to 1.3 Gy and applied in combination with a sharp angle irradiation (10° relative to the cell plane). The results reveal a higher ratio of 53BP1 proteins recruited into SMLM defined clusters in fibroblasts as compared to U87 cells. Moreover, the speed of foci and thus cluster formation and relaxation also differed for the cell types. In both NHDF and U87 cells, a certain number of the detected and functionally relevant clusters remained persistent even 24 h post irradiation; however, the number of these clusters again varied for the cell types. Altogether, our findings indicate that repair cluster formation as determined by SMLM and the relaxation (i.e., the remaining 53BP1 tags no longer fulfill the cluster definition) is cell type dependent and may be functionally explained and correlated to cell specific radio-sensitivity. The present study demonstrates that SMLM is a highly appropriate method for investigations of spatiotemporal protein organization in cell nuclei and how it influences the cell decision for a particular repair pathway at a given DSB site.

Enhancing radiotherapy effect in breast cancer with nanoparticles: A review

Amongst all efforts for improving oncological management outcomes, nanoparticles enhanced radiation for breast cancer patient's treatment is a novel approach that has grown interest for research in the last decade. Multiple preclinical data has been published, from all around the globe; however, clinical evidence is still insufficient for implementing the method in routine practice and in disease specific management. Gold nanoparticles (AuNP), which may be among the most studed materials, account for the majority of available data; however, some new materials have also been used in preclinical settings. Without any safety data available at the moment to support an active use, dosimetric in vitro and in vivo information seems to be consistent with a very promising and hopeful panorama for clinical applications. This review evaluates existing dosimetric data in breast cancer tissue, and a probable future impact in treatment choices and patient outcomes, as further investigation is required in a clinical setting.