Industrial-Scale Synthesis of Intrinsically Radiolabeled 64CuS Nanoparticles for Use in Positron Emission Tomography (PET) Imaging of Cancer

Diagnosis of Melanoma with 61Cu-Labeled PET Tracer

Until the recent years, substances containing radioactive 61Cu were strongly considered as potential positron-emitting radiopharmaceuticals for use in positron emission tomography (PET) applications; however, due to their suitably long half-life, and generator-independent and cost-effective production, they seem to be economically viable for human imaging. Since malignant melanoma (MM) is a major public health problem, its early diagnosis is a crucial contributor to long-term survival, which can be achieved using radiolabeled α-melanocyte-stimulating hormone analog NAPamide derivatives. Here, we report on the physicochemical features of a new CB-15aneN5-based Cu(II) complex ([Cu(KFTGdiac)]-) and the ex vivo and in vivo characterization of its NAPamide conjugate. The rigid chelate possesses prompt complex formation and suitable inertness (t1/2 = 18.4 min in 5.0 M HCl at 50 °C), as well as excellent features in the diagnosis of B16-F10 melanoma tumors (T/M(SUVs) (in vivo): 12.7, %ID/g: 6.6 ± 0.3, T/M (ex vivo): 22).

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.

Bioimaging guided pharmaceutical evaluations of nanomedicines for clinical translations

Nanomedicines (NMs) have emerged as an efficient approach for developing novel treatment strategies against a variety of diseases. Over the past few decades, NM formulations have received great attention, and a large number of studies have been performed in this field. Despite this, only about 60 nano-formulations have received industrial acceptance and are currently available for clinical use. Their in vivo pharmaceutical behavior is considered one of the main challenges and hurdles for the effective clinical translation of NMs, because it is difficult to monitor the pharmaceutic fate of NMs in the biological environment using conventional pharmaceutical evaluations. In this context, non-invasive imaging modalities offer attractive solutions, providing the direct monitoring and quantification of the pharmacokinetic and pharmacodynamic behavior of labeled NMs in a real-time manner. Imaging evaluations have great potential for revealing the relationship between the physicochemical properties of NMs and their pharmaceutical profiles in living subjects. In this review, we introduced imaging techniques that can be used for in vivo NM evaluations. We also provided an overview of various studies on the influence of key parameters on the in vivo pharmaceutical behavior of NMs that had been visualized in a non-invasive and real-time manner.

Anchoring Group-Mediated Radiolabeling of Inorganic Nanoparticles─A Universal Method for Constructing Nuclear Medicine Imaging Nanoprobes

Nuclear medicine imaging has aroused great interest in the design and synthesis of versatile radioactive nanoprobes, while most of the methods developed for radiolabeling nanoprobes are difficult to satisfy the criteria of clinical translation, including easy operation, mild labeling conditions, high efficiency, and high radiolabeling stability. Herein, we demonstrated the universality of a simple but efficient radiolabeling method recently developed for constructing nuclear imaging nanoprobes, that is, ligand anchoring group-mediated radiolabeling (LAGMERAL). In this method, a diphosphonate-polyethylene glycol (DP-PEG) decorating on the surface of inorganic nanoparticles plays an essential role. In principle, owing to the strong binding affinity to a great variety of metal ions, it can not only endow the underlying nanoparticles containing metal ions including some main group metal ions, transition metal ions, and lanthanide metal ions with excellent colloidal stability and biocompatibility but also enable efficient radiolabeling through the diphosphonate group. Based on this assumption, inorganic nanoparticles such as Fe₃O₄ nanoparticles, NaGdF₄:Yb,Tm nanoparticles, and Cu_2-xS nanoparticles, as representatives of functional inorganic nanoparticles suitable for different imaging modalities including magnetic resonance imaging (MRI), upconversion luminescence imaging (UCL), and photoacoustic imaging (PAI), respectively, were chosen to be radiolabeled with different kinds of radionuclides such as SPECT nuclides (e.g., ^99mTc), PET nuclides (e.g., ⁶⁸Ga), and therapeutic SPECT nuclides (e.g., ¹⁷⁷Lu) to demonstrate the reliability of the LAGMERAL approach. The experimental results showed that the obtained nanoprobes exhibited high radiolabeling stability, and the whole radiolabeling process had negligible impacts on the physical and chemical properties of the initial nanoparticles. Through passive targeting SPECT/MRI of glioma tumor, active targeting SPECT/UCL of colorectal cancer, and SPECT/PAI of lymphatic metastasis, the outstanding potentials of the resulting radioactive nanoprobes for sensitive tumor diagnosis were demonstrated, manifesting the feasibility and efficiency of LAGMERAL.

Radiolabeling strategies and pharmacokinetic studies for metal based nanotheranostics

Radiolabeled metal-based nanoparticles (MNPs) have drawn considerable attention in the fields of nuclear medicine and molecular imaging, drug delivery, and radiation therapy, given the fact that they can be potentially used as diagnostic imaging and/or therapeutic agents, or even as theranostic combinations. Here, we present a systematic review on recent advances in the design and synthesis of MNPs with major focuses on their radiolabeling strategies and the determinants of their in vivo pharmacokinetics, and together how their intended applications would be impacted. For clarification, we categorize all reported radiolabeling strategies for MNPs into indirect and direct approaches. While indirect labeling simply refers to the use of bifunctional chelators or prosthetic groups conjugated to MNPs for post-synthesis labeling with radionuclides, we found that many practical direct labeling methodologies have been developed to incorporate radionuclides into the MNP core without using extra reagents, including chemisorption, radiochemical doping, hadronic bombardment, encapsulation, and isotope or cation exchange. From the perspective of practical use, a few relevant examples are presented and discussed in terms of their pros and cons. We further reviewed the determinants of in vivo pharmacokinetic parameters of MNPs, including factors influencing their in vivo absorption, distribution, metabolism, and elimination, and discussed the challenges and opportunities in the development of radiolabeled MNPs for in vivo biomedical applications. Taken together, we believe the cumulative advancement summarized in this review would provide a general guidance in the field for design and synthesis of radiolabeled MNPs towards practical realization of their much desired theranostic capabilities. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Cation Exchange Protocols to Radiolabel Aqueous Stabilized ZnS, ZnSe, and CuFeS2 Nanocrystals with 64Cu for Dual Radio- and Photo-Thermal Therapy

Here, cation exchange (CE) reactions are exploited to radiolabel ZnSe, ZnS, and CuFeS2 metal chalcogenide nanocrystals (NCs) with 64Cu. The CE protocol requires one simple step, to mix the water-soluble NCs with a 64Cu solution, in the presence of vitamin C used to reduce Cu(II) to Cu(I). Given the quantitative cation replacement on the NCs, a high radiochemical yield, up to 99%, is reached. Also, provided that there is no free 64Cu, no purification step is needed, making the protocol easily translatable to the clinic. A unique aspect of the approach is the achievement of an unprecedentedly high specific activity: by exploiting a volumetric CE, the strategy enables to concentrate a large dose of 64Cu (18.5 MBq) in a small NC dose (0.18 µg), reaching a specific activity of 103 TBq g-1. Finally, the characteristic dielectric resonance peak, still present for the radiolabeled 64Cu:CuFeS2 NCs after the partial-CE reaction, enables the generation of heat under clinical laser exposure (1 W cm-2). The synergic toxicity of photo-ablation and 64Cu ionization is here proven on glioblastoma and epidermoid carcinoma tumor cells, while no intrinsic cytotoxicity is seen from the NC dose employed for these dual experiments.

Radiolabeling nanomaterials for multimodality imaging: New insights into nuclear medicine and cancer diagnosis

Nuclear medicine imaging has been developed as a powerful diagnostic approach for cancers by detecting gamma rays directly or indirectly from radionuclides to construct images with beneficial characteristics of high sensitivity, infinite penetration depth and quantitative capability. Current nuclear medicine imaging modalities mainly include single-photon emission computed tomography (SPECT) and positron emission tomography (PET) that require administration of radioactive tracers. In recent years, a vast number of radioactive tracers have been designed and constructed to improve nuclear medicine imaging performance toward early and accurate diagnosis of cancers. This review will discuss recent progress of nuclear medicine imaging tracers and associated biomedical imaging applications. Radiolabeling nanomaterials for rational development of tracers will be comprehensively reviewed with highlights on radiolabeling approaches (surface coupling, inner incorporation and interface engineering), providing profound understanding on radiolabeling chemistry and the associated imaging functionalities. The applications of radiolabeled nanomaterials in nuclear medicine imaging-related multimodality imaging will also be summarized with typical paradigms described. Finally, key challenges and new directions for future research will be discussed to guide further advancement and practical use of radiolabeled nanomaterials for imaging of cancers.

Clinical scale synthesis of intrinsically radiolabeled and cyclic RGD peptide functionalized 198Au nanoparticles for targeted cancer therapy

INTRODUCTION

The emerging concept of intrinsically radiolabeled nanoparticles has the potential to transform the preclinical and clinical studies by improving the in vivo stability and demonstrating minimal alteration in the inherent pharmacokinetics of the nanoparticles. In this paper, a simple and efficient single-step method for clinical scale synthesis of intrinsically radiolabeled ¹⁹⁸Au nanoparticles conjugated with cyclic arginine-glycine-aspartate peptide (¹⁹⁸AuNP-RGD) is reported for potential use in targeted cancer therapy.

METHODS

Large radioactive doses (>37 GBq) of ¹⁹⁸AuNP-RGD were synthesized by reaction of ¹⁹⁸Au-HAuCl₄ with cyclic RGD peptide. The synthesized nanoparticles were characterized by various analytical techniques. In vitro cell binding studies were carried out in B16F10 (murine melanoma) cell line. Biodistribution studies were carried out in melanoma tumor bearing C57BL/6 mice to demonstrate the tumor targeting ability of ¹⁹⁸AuNP-RGD. The therapeutic efficacy of ¹⁹⁸AuNP-RGD was evaluated by carrying out systematic tumor regression studies in melanoma tumor bearing mice after intravenous administration of the radioactive doses.

RESULTS

Well dispersed and biocompatible nanoparticles (~12.5 nm diameter) could be synthesized with excellent radiochemical and colloidal stability. In vitro studies exhibited the cell binding affinity and specificity of ¹⁹⁸AuNP-RGD towards melanoma cell line. A high uptake of 8.7 ± 2.1%ID/g in the tumor was observed within 4 h post-injection (p.i.). Significant decrease in tumor uptake of ¹⁹⁸AuNP-RGD (2.9 ± 0.8%ID/g) at 4 h p.i. on co-injection of a blocking dose of the peptide suggested that tumor localization of the intrinsically radiolabeled nanoparticles was receptor mediated. Administration of 37.0 MBq of ¹⁹⁸AuNP-RGD resulted in significant regression of tumor growth with no apparent body weight loss over a period of 15 d.

CONCLUSIONS

Overall, these promising results demonstrate the suitability of ¹⁹⁸AuNP-RGD as an advanced functional nanoplatform for targeted cancer therapy.

External stimulus responsive inorganic nanomaterials for cancer theranostics

Cancer is a highly intelligent system of cells, that works together with the body to thrive and subsequently overwhelm the host in order for its survival. Therefore, treatment regimens should be equally competent to outsmart these cells. Unfortunately, it is not the case with current therapeutic practices, the reason why it is still one of the most deadly adversaries and an imposing challenge to healthcare practitioners and researchers alike. With rapid nanotechnological interventions in the medical arena, the amalgamation of diagnostic and therapeutic functionalities into a single platform, theranostics provides a never before experienced hope of enhancing diagnostic accuracy and therapeutic efficiency. Additionally, the ability of these nanotheranostic agents to perform their actions on-demand, i.e. can be controlled by external stimulus such as light, magnetic field, sound waves and radiation has cemented their position as next generation anti-cancer candidates. Numerous reports exist of such stimuli-responsive theranostic nanomaterials against cancer, but few have broken through to clinical trials, let alone clinical practice. This review sheds light on the pros and cons of a few such theranostic nanomaterials, especially inorganic nanomaterials which do not require any additional chemical moieties to initiate the stimulus. The review will primarily focus on preclinical and clinical trial approved theranostic agents alone, describing their success or failure in the respective stages.