Recent Advances in Brachytherapy Using Radioactive Nanoparticles: An Alternative to Seed-Based Brachytherapy

Navigating the landscape of theranostics in nuclear medicine: current practice and future prospects

Theranostics refers to the combination of diagnostic biomarkers with therapeutic agents that share a specific target expressed by diseased cells and tissues. Nuclear medicine is an exciting component explored for its applicability in theranostic concepts in clinical and research investigations. Nuclear theranostics is based on the employment of radioactive compounds delivering ionizing radiation to diagnose and manage certain diseases employing binding with specifically expressed targets. In the realm of personalized medicine, nuclear theranostics stands as a beacon of potential, potentially revolutionizing disease management. Studies exploring the theranostic profile of radioactive compounds have been presented in this review along with a detailed explanation of radioactive compounds and their theranostic applicability in several diseases. It furnishes insights into their applicability across diverse diseases, elucidating the intricate interplay between these compounds and disease pathologies. Light is shed on the important milestones of nuclear theranostics beginning with radioiodine therapy in thyroid carcinomas, MIBG labelled with iodine in neuroblastoma, and several others. Our perspectives have been put forth regarding the most important theranostic agents along with emerging trends and prospects.

Brachytherapy at the nanoscale with protein functionalized and intrinsically radiolabeled [169Yb]Yb2O3 nanoseeds

PURPOSE

Classical brachytherapy of solid malignant tumors is an invasive procedure which often results in an uneven dose distribution, while requiring surgical removal of sealed radioactive seed sources after a certain period of time. To circumvent these issues, we report the synthesis of intrinsically radiolabeled and gum Arabic glycoprotein functionalized [169Yb]Yb2O3 nanoseeds as a novel nanoscale brachytherapy agent, which could directly be administered via intratumoral injection for tumor therapy.

METHODS

169Yb (T½ = 32 days) was produced by neutron irradiation of enriched (15.2% in 168Yb) Yb2O3 target in a nuclear reactor, radiochemically converted to [169Yb]YbCl3 and used for nanoparticle (NP) synthesis. Intrinsically radiolabeled NP were synthesized by controlled hydrolysis of Yb3+ ions in gum Arabic glycoprotein medium. In vivo SPECT/CT imaging, autoradiography, and biodistribution studies were performed after intratumoral injection of radiolabeled NP in B16F10 tumor bearing C57BL/6 mice. Systematic tumor regression studies and histopathological analyses were performed to demonstrate therapeutic efficacy in the same mice model.

RESULTS

The nanoformulation was a clear solution having high colloidal and radiochemical stability. Uniform distribution and retention of the radiolabeled nanoformulation in the tumor mass were observed via SPECT/CT imaging and autoradiography studies. In a tumor regression study, tumor growth was significantly arrested with different doses of radiolabeled NP compared to the control and the best treatment effect was observed with ~ 27.8 MBq dose. In histopathological analysis, loss of mitotic cells was apparent in tumor tissue of treated groups, whereas no significant damage in kidney, lungs, and liver tissue morphology was observed.

CONCLUSIONS

These results hold promise for nanoscale brachytherapy to become a clinically practical treatment modality for unresectable solid cancers.

177Lu-Labeled Iron Oxide Nanoparticles Functionalized with Doxorubicin and Bevacizumab as Nanobrachytherapy Agents against Breast Cancer

The use of conventional methods for the treatment of cancer, such as chemotherapy or radiotherapy, and approaches such as brachytherapy in conjunction with the unique properties of nanoparticles could enable the development of novel theranostic agents. The aim of our current study was to evaluate the potential of iron oxide nanoparticles, coated with alginic acid and polyethylene glycol, functionalized with the chemotherapeutic agent doxorubicin and the monoclonal antibody bevacizumab, to serve as a nanoradiopharmaceutical agent against breast cancer. Direct radiolabeling with the therapeutic isotope Lutetium-177 (177Lu) resulted in an additional therapeutic effect. Functionalization was accomplished at high percentages and radiolabeling was robust. The high cytotoxic effect of our radiolabeled and non-radiolabeled nanostructures was proven in vitro against five different breast cancer cell lines. The ex vivo biodistribution in tumor-bearing mice was investigated with three different ways of administration. The intratumoral administration of our functionalized radionanoconjugates showed high tumor accumulation and retention at the tumor site. Finally, our therapeutic efficacy study performed over a 50-day period against an aggressive triple-negative breast cancer cell line (4T1) demonstrated enhanced tumor growth retention, thus identifying the developed nanoparticles as a promising nanobrachytherapy agent against breast cancer.

Cancer Brachytherapy at the Nanoscale: An Emerging Paradigm

Brachytherapy is an established treatment modality that has been globally utilized for the therapy of malignant solid tumors. However, classic therapeutic sealed sources used in brachytherapy must be surgically implanted directly into the tumor site and removed after the requisite period of treatment. In order to avoid the trauma involved in the surgical procedures and prevent undesirable radioactive distribution at the cancerous site, well-dispersed radiolabeled nanomaterials are now being explored for brachytherapy applications. This emerging field has been coined "nanoscale brachytherapy". Despite present-day advancements, an ongoing challenge is obtaining an advanced, functional nanomaterial that concurrently incorporates features of high radiolabeling yield, short labeling time, good radiolabeling stability, and long tumor retention time without leakage of radioactivity to the nontargeted organs. Further, attachment of suitable targeting ligands to the nanoplatforms would widen the nanoscale brachytherapy approach to tumors expressing various phenotypes. Molecular imaging using radiolabeled nanoplatforms enables noninvasive visualization of cellular functions and biological processes in vivo. In vivo imaging also aids in visualizing the localization and retention of the radiolabeled nanoplatforms at the tumor site for the requisite time period to render safe and effective therapy. Herein, we review the advancements over the last several years in the synthesis and use of functionalized radiolabeled nanoplatforms as a noninvasive substitute to standard brachytherapy sources. The limitations of present-day brachytherapy sealed sources are analyzed, while highlighting the advantages of using radiolabeled nanoparticles (NPs) for this purpose. The recent progress in the development of different radiolabeling methods, delivery techniques and nanoparticle internalization mechanisms are discussed. The preclinical studies performed to date are summarized with an emphasis on the current challenges toward the future translation of nanoscale brachytherapy in routine clinical practices.

The Impact of Nanomedicine on Soft Tissue Sarcoma Treated by Radiotherapy and/or Hyperthermia: A Review

This article presents a comprehensive review of nanoparticle-assisted treatment approaches for soft tissue sarcoma (STS). STS, a heterogeneous group of mesenchymal-origin tumors with aggressive behavior and low overall survival rates, necessitates the exploration of innovative therapeutic interventions. In contrast to conventional treatments like surgery, radiotherapy (RT), hyperthermia (HT), and chemotherapy, nanomedicine offers promising advancements in STS management. This review focuses on recent research in nanoparticle applications, including their role in enhancing RT and HT efficacy through improved drug delivery systems, novel radiosensitizers, and imaging agents. Reviewing the current state of nanoparticle-assisted therapies, this paper sheds light on their potential to revolutionize soft tissue sarcoma treatment and improve patient therapy outcomes.

Water-soluble endohedral metallofullerenes: new horizons for biomedical applications

Endohedral metallofullerenes (EMFs) offer a safe avenue to manipulate metals important to biomedical applications such as MRI contrast, X-ray contrast, radiolabeling, radiotherapy, chemotherapy, and the control of inflammation by scavenging reactive oxygen species (ROS). Moreover, functionalizing the double bonds on the surface of EMFs modifies their solubility, supramolecular behaviour, binding, targeting characteristics, and physical properties. While most existing water-soluble derivatives possess a statistical mixture of appended functional groups, progress has been made in creating molecularly-precise derivatives with a defined number of surface functional groups, leading to potentially more nuanced control of their behaviour and properties. Further elucidation of the structure-function relationships of these materials is expected to enhance their utility in biomedical applications and possibly broaden their use in diverse areas of science and technology.

Prospects of nanoparticle-based radioenhancement for radiotherapy

Radiotherapy is a key pillar of solid cancer treatment. Despite a high level of conformal dose deposition, radiotherapy is limited due to co-irradiation of organs at risk and subsequent normal tissue toxicities. Nanotechnology offers an attractive opportunity for increasing the efficacy and safety of cancer radiotherapy. Leveraging the freedom of design and the growing synthetic capabilities of the nanomaterial-community, a variety of engineered nanomaterials have been designed and investigated as radiosensitizers or radioenhancers. While research so far has been primarily focused on gold nanoparticles and other high atomic number materials to increase the absorption cross section of tumor tissue, recent studies are challenging the traditional concept of high-Z nanoparticle radioenhancers and highlight the importance of catalytic activity. This review provides a concise overview on the knowledge of nanoparticle radioenhancement mechanisms and their quantification. It critically discusses potential radioenhancer candidate materials and general design criteria for different radiation therapy modalities, and concludes with research priorities in order to advance the development of nanomaterials, to enhance the efficacy of radiotherapy and to increase at the same time the therapeutic window.

Gold-Enhanced Brachytherapy by a Nanoparticle-Releasing Hydrogel and 3D-Printed Subcutaneous Radioactive Implant Approach

Brachytherapy (BT) is a widely used clinical procedure for localized cervical cancer treatment. In addition, gold nanoparticles (AuNPs) have been demonstrated as powerful radiosensitizers in BT procedures. Prior to irradiation by a BT device, their delivery to tumors can enhance the radiation effect by generating low-energy photons and electrons, leading to reactive oxygen species (ROS) production, lethal to cells. No efficient delivery system has been proposed until now for AuNP topical delivery to localized cervical cancer in the context of BT. This article reports an original approach developed to accelerate the preclinical studies of AuNP-enhanced BT procedures. First, an AuNP-containing hydrogel (Pluronic F127, alginate) is developed and tested in mice for degradation, AuNP release, and biocompatibility. Then, custom-made 3D-printed radioactive BT inserts covered with a AuNP-containing hydrogel cushion are designed and administered by surgery in mice (HeLa xenografts), which allows for measuring AuNP penetration in tumors (≈100 µm), co-registered with the presence of ROS produced through the interactions of radiation and AuNPs. Biocompatible AuNPs-releasing hydrogels could be used in the treatment of cervical cancer prior to BT, with impact on  the total amount of radiation needed per BT treatment, which will result in benefits to the preservation of healthy tissues surrounding cancer.

Radiation therapy-activated nanoparticle and immunotherapy: The next milestone in oncology?

Radiotherapy (RT) is a fundamental treatment at the locoregional or oligometastatic stages of cancer. In various tumors, RT effects may be optimized using synergistic combinations that enhance tumor response. Innovative strategies have been designed that explore the radiation mechanisms, at the physical, chemical and biological levels, to propose precision RT approaches. They consist in combining RT with immunotherapy to revert radiation immunosuppressive effects or to enhance radiation-induced immune defenses against the tumor to favor immunogenic cell death. Radiotherapy-activated nanoparticles are another innovation. By increasing radiation response in situ, nanoparticles improve tumor control locally, and can trigger systemic immune reactions that may be exploited to improve the systemic efficacy of RT. Strong clinical evidence of improved outcomes is now available for combinations of RT and immunotherapy on one hand and RT and nanoparticles on the other hand. The triple combination of RT, immunotherapy and nanoparticles is promising in terms of tolerance, local and systemic anti-tumor control. Yet, significant challenges remain to unravel the complexity of the multiscale mechanisms underlying response to this combination and their associated parameters. Such parameters include patient characteristics, tumor bulk and histology, radiation technique, energy, dose, fractionation, immunotherapy targets and predictive biomarkers, nanoparticle type, size, delivery (intratumoral/intravenous), distribution. The temporal combination is another critical parameter. The mechanisms of response of the combinatorial approaches are reviewed, with a focus on underlying mechanisms based on preclinical, translational and clinical studies. Opportunities for translation of current understanding into precision RT trials combined with immunotherapy and nanoparticles are also discussed.

Image-Guided Nanodelivery of Pt(IV) Prodrugs to GRP-Receptor Positive Tumors

Over the last decades, gold nanoparticles (AuNPs) have proven to be remarkable tools for drug delivery and theranostic applications in cancer treatment. On the other hand, Pt(IV) prodrugs have been employed as an interesting alternative to the more common Pt(II) complexes, such as cisplatin, for cancer chemotherapy. Searching to design an image-guided nanocarrier to deliver selectively Pt(IV) prodrugs to tumors expressing the gastrin releasing peptide receptor (GRPR), we have synthesized small core AuNPs carrying a thiolated DOTA derivative, a GRPR-targeting bombesin analog (BBN[7-14]) and a Pt(IV) prodrug attached to the AuNPs without (AuNP-BBN-Pt1) or with a PEGylated linker (AuNP-BBN-Pt2 and AuNP-BBN-Pt3). In the GRPR+ prostate cancer PC3 cell line, the cytotoxic activity of the designed AuNP-BBN-Pt nanoparticles is strongly influenced by the presence of the PEGylated linker. Thus, AuNP-BBN-Pt1 displayed the lowest IC₅₀ value (9.3 ± 2.3 µM of Pt), which is comparable to that exhibited by cisplatin in the same cell line. In contrast, AuNP-BBN-Pt1 showed an IC₅₀ value of 97 ± 18 µM of Pt in the non-tumoral RWPE-1 prostate cells with a much higher selective index (SI) towards PC3 cells (SI = 10) when compared with cisplatin (SI = 1.3). The AuNPs were also successfully labeled with ⁶⁷Ga and the resulting ⁶⁷Ga-AuNP-BBN-Pt were used to assess their cellular uptake in PC3 cells, with AuNP-BBN-Pt1 also displaying the highest cellular internalization. Finally, intratumoral administration of ⁶⁷Ga-AuNP-BBN-Pt1 in a PC3 tumor-bearing mice showed a prolonged retention of the nanoparticle compared to that of cisplatin, with optimal in vivo stability and 20% of the injected platinum remaining in the tumor after 72 h post-injection. Furthermore, microSPECT imaging studies confirmed the uptake and considerable retention of the ⁶⁷Ga-labeled AuNPs in the tumors. Overall, these results show the potential of these targeted AuNPs loaded with Pt(IV) prodrugs for prostate cancer theranostics.

Novel Implications of Nanoparticle-Enhanced Radiotherapy and Brachytherapy: Z-Effect and Tumor Hypoxia

Radiotherapy and internal radioisotope therapy (brachytherapy) induce tumor cell death through different molecular signaling pathways. However, these therapies in cancer patients are constrained by dose-related adverse effects and local discomfort due to the prolonged exposure to the surrounding tissues. Technological advancements in nanotechnology have resulted in synthesis of high atomic elements such as nanomaterials, which can be used as radiosensitizers due to their photoelectric characteristics. The aim of this review is to elucidate the effects of novel nanomaterials in the field of radiation oncology to ameliorate dose-related toxicity through the application of ideal nanoparticle-based radiosensitizers such as Au (gold), Bi (bismuth), and Lu (Lutetium-177) for enhancing cytotoxic effects of radiotherapy via the high-Z effect. In addition, we discuss the role of nanoparticle-enhanced radiotherapy in alleviating tumor hypoxia through the nanodelivery of genes/drugs and other functional anticancer molecules. The implications of engineered nanoparticles in preclinical and clinical studies still need to be studied in order to explore potential mechanisms for radiosensitization by minimizing tumor hypoxia, operational/logistic complications and by overcoming tumor heterogeneity in radiotherapy/brachytherapy.

Preliminary Evaluation of Iron Oxide Nanoparticles Radiolabeled with 68Ga and 177Lu as Potential Theranostic Agents

Theranostic radioisotope pairs such as Gallium-68 (⁶⁸Ga) for Positron Emission Tomography (PET) and Lutetium-177 (¹⁷⁷Lu) for radioisotopic therapy, in conjunction with nanoparticles (NPs), are an emerging field in the treatment of cancer. The present work aims to demonstrate the ability of condensed colloidal nanocrystal clusters (co-CNCs) comprised of iron oxide nanoparticles, coated with alginic acid (MA) and stabilized by a layer of polyethylene glycol (MAPEG) to be directly radiolabeled with ⁶⁸Ga and its therapeutic analog ¹⁷⁷Lu. ⁶⁸Ga/¹⁷⁷Lu- MA and MAPEG were investigated for their in vitro stability. The biocompatibility of the non-radiolabeled nanoparticles, as well as the cytotoxicity of MA, MAPEG, and [¹⁷⁷Lu]Lu-MAPEG were assessed on 4T1 cells. Finally, the ex vivo biodistribution of the ⁶⁸Ga-labeled NPs as well as [¹⁷⁷Lu]Lu-MAPEG was investigated in normal mice. Radiolabeling with both radioisotopes took place via a simple and direct labelling method without further purification. Hemocompatibility was verified for both NPs, while MTT studies demonstrated the non-cytotoxic profile of the nanocarriers and the dose-dependent toxicity for [¹⁷⁷Lu]Lu-MAPEG. The radiolabeled nanoparticles mainly accumulated in RES organs. Based on our preliminary results, we conclude that MAPEG could be further investigated as a theranostic agent for PET diagnosis and therapy of cancer.

Therapeutic Advancements in Metal and Metal Oxide Nanoparticle-Based Radiosensitization for Head and Neck Cancer Therapy

Although radiation therapy (RT) is one of the mainstays of head and neck cancer (HNC) treatment, innovative approaches are needed to further improve treatment outcomes. A significant challenge has been to design delivery strategies that focus high doses of radiation on the tumor tissue while minimizing damage to surrounding structures. In the last decade, there has been increasing interest in harnessing high atomic number materials (Z-elements) as nanoparticle radiosensitizers that can also be specifically directed to the tumor bed. Metallic nanoparticles typically display chemical inertness in cellular and subcellular systems but serve as significant radioenhancers for synergistic tumor cell killing in the presence of ionizing radiation. In this review, we discuss the current research and therapeutic efficacy of metal nanoparticle (MNP)-based radiosensitizers, specifically in the treatment of HNC with an emphasis on gold- (AuNPs), gadolinium- (AGdIX), and silver- (Ag) based nanoparticles together with the metallic oxide-based hafnium (Hf), zinc (ZnO) and iron (SPION) nanoparticles. Both in vitro and in vivo systems for different ionizing radiations including photons and protons were reviewed. Finally, the current status of preclinical and clinical studies using MNP-enhanced radiation therapy is discussed.

Radiolabeled Gold Nanoseeds Decorated with Substance P Peptides: Synthesis, Characterization and In Vitro Evaluation in Glioblastoma Cellular Models

Despite some progress, the overall survival of patients with glioblastoma (GBM) remains extremely poor. In this context, there is a pressing need to develop innovative therapy strategies for GBM, namely those based on nanomedicine approaches. Towards this goal, we have focused on nanoparticles (AuNP-SP and AuNP-SPTyr8) with a small gold core (ca. 4 nm), carrying DOTA chelators and substance P (SP) peptides. These new SP-containing AuNPs were characterized by a variety of analytical techniques, including TEM and DLS measurements and UV-vis and CD spectroscopy, which proved their high in vitro stability and poor tendency to interact with plasma proteins. Their labeling with diagnostic and therapeutic radionuclides was efficiently performed by DOTA complexation with the trivalent radiometals ⁶⁷Ga and ¹⁷⁷Lu or by electrophilic radioiodination with ¹²⁵I of the tyrosyl residue in AuNP-SPTyr8. Cellular studies of the resulting radiolabeled AuNPs in NKR1-positive GBM cells (U87, T98G and U373) have shown that the presence of the SP peptides has a crucial and positive impact on their internalization by the tumor cells. Consistently, ¹⁷⁷Lu-AuNP-SPTyr8 showed more pronounced radiobiological effects in U373 cells when compared with the non-targeted congener ¹⁷⁷Lu-AuNP-TDOTA, as assessed by cell viability and clonogenic assays and corroborated by Monte Carlo microdosimetry simulations.