Clinical Perspectives of Theranostics

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.

Lessons learned in application driven imaging agent design for image-guided surgery

To meet the growing demand for intraoperative molecular imaging, the development of compatible imaging agents plays a crucial role. Given the unique requirements of surgical applications compared to diagnostics and therapy, maximizing translational potential necessitates distinctive imaging agent designs. For effective surgical guidance, exogenous signatures are essential and are achievable through a diverse range of imaging labels such as (radio)isotopes, fluorescent dyes, or combinations thereof. To achieve optimal in vivo utility a balanced molecular design of the tracer as a whole is required, which ensures a harmonious effect of the imaging label with the affinity and specificity (e.g., pharmacokinetics) of a pharmacophore/targeting moiety. This review outlines common design strategies and the effects of refinements in the molecular imaging agent design on the agent's pharmacological profile. This includes the optimization of affinity, pharmacokinetics (including serum binding and target mediated background), biological clearance route, the achievable signal intensity, and the effect of dosing hereon.

In vivo-stable bis-iminobiotin for targeted radionuclide delivery with the mutant streptavidin

Targeted delivery of radionuclides to tumors is significant in theranostics applications for precision medicine. Pre-targeting, in which a tumor-targeting vehicle and a radionuclide-loaded effector small molecule are administered separately, holds promise since it can reduce unnecessary internal radiation exposure of healthy cells and can minimize radiation decay. The success of the pre-targeting delivery requires an in vivo-stable tumor-targeting vehicle selectively binding to tumor antigens and an in vivo-stable small molecule effector selectively binding to the vehicle accumulated on the tumor. We previously reported a drug delivery system composed of a low-immunogenic streptavidin with weakened affinity to endogenous biotin and a bis-iminobiotin with high affinity to the engineered streptavidin. It was, however, unknown whether the bis-iminobiotin is stable in vivo when administered alone for the pre-targeting applications. Here we report a new in vivo-stable bis-iminobiotin derivative. The keys to success were the identification of the degradation site of the original bis-iminobiotin treated with mouse plasma and the structural modification of the degradation site. We disclosed the successful pre-targeting delivery of astatine-211 (211At), α-particle emitter, to the CEACAM5-positive tumor in xenograft mouse models.

Blood-brain barrier disruption in dementia: Nano-solutions as new treatment options

Candidate drugs targeting the central nervous system (CNS) demonstrate extremely low clinical success rates, with more than 98% of potential treatments being discontinued due to poor blood-brain barrier (BBB) permeability. Neurological conditions were shown to be the second leading cause of death globally in 2016, with the number of people currently affected by neurological disorders increasing rapidly. This increasing trend, along with an inability to develop BBB permeating drugs, is presenting a major hurdle in the treatment of CNS-related disorders, like dementia. To overcome this, it is necessary to understand the structure and function of the BBB, including the transport of molecules across its interface in both healthy and pathological conditions. The use of CNS drug carriers is rapidly gaining popularity in CNS research due to their ability to target BBB transport systems. Further research and development of drug delivery vehicles could provide essential information that can be used to develop novel treatments for neurological conditions. This review discusses the BBB and its transport systems and evaluates the potential of using nanoparticle-based delivery systems as drug carriers for CNS disease with a focus on dementia.

Precision peptide theranostics: developing N- to C-terminus optimized theranostics targeting cholecystokinin-2 receptor

Peptides are ideal for theranostic development as they afford rapid target accumulation, fast clearance from background tissue, and exhibit good tissue penetration. Previously, we developed a novel series of peptides that presented discreet folding propensity leading to an optimal candidate [68Ga]Ga-DOTA-GA1 ([D-Glu]6-Ala-Tyr-NMeGly-Trp-NMeNle-Asp-Nal-NH2) with 50 pM binding affinity against cholecystokinin-2 receptors (CCK2R). However, we were confronted with challenges of unfavorably high renal uptake. Methods: A structure activity relationship study was undertaken of the lead theranostic candidate. Prudent structural modifications were made to the peptide scaffold to evaluate the contributions of specific N-terminal residues to the overall biological activity. Optimal candidates were then evaluated in nude mice bearing transfected A431-CCK2 tumors, and their biodistribution was quantitated ex vivo. Results: We identified and confirmed that D-Glu3 to D-Ala3 substitution produced 2 optimal candidates, [68Ga]Ga-DOTA-GA12 and [68Ga]Ga-DOTA-GA13. These radiopeptides presented with high target/background ratios, enhanced tumor retention, excellent metabolic stability in plasma and mice organ homogenates, and a 4-fold reduction in renal uptake, significantly outperforming their non-alanine counterparts. Conclusions: Our study identified novel radiopharmaceutical candidates that target the CCK2R. Their high tumor uptake and reduced renal accumulation warrant clinical translation.

Implementing Ac-225 labelled radiopharmaceuticals: practical considerations and (pre-)clinical perspectives

BACKGROUND

In the past years, there has been a notable increase in interest regarding targeted alpha therapy using Ac-225, driven by the observed promising clinical anti-tumor effects. As the production and technology has advanced, the availability of Ac-225 is expected to increase in the near future, making the treatment available to patients worldwide.

MAIN BODY

Ac-225 can be labelled to different biological vectors, whereby the success of developing a radiopharmaceutical depends heavily on the labelling conditions, purity of the radionuclide source, chelator, and type of quenchers used to avoid radiolysis. Multiple (methodological) challenges need to be overcome when working with Ac-225; as alpha-emission detection is time consuming and highly geometry dependent, a gamma co-emission is used, but has to be in equilibrium with the mother-nuclide. Because of the high impact of alpha emitters in vivo it is highly recommended to cross-calibrate the Ac-225 measurements for used quality control (QC) techniques (radio-TLC, HPLC, HP-Ge detector, and gamma counter). More strict health physics regulations apply, as Ac-225 has a high toxicity, thereby limiting practical handling and quantities used for QC analysis.

CONCLUSION

This overview focuses specifically on the practical and methodological challenges when working with Ac-225 labelled radiopharmaceuticals, and underlines the required infrastructure and (detection) methods for the (pre-)clinical application.

Multifunctional Carbon Dots for Biomedical Applications: Diagnosis, Therapy, and Theranostic

Designing suitable nanomaterials is an ideal strategy to enable early diagnosis and effective treatment of diseases. Carbon dots (CDs) are luminescent carbonaceous nanoparticles that have attracted considerable attention. Through facile synthesis, they process properties including tunable light emission, low toxicity, and light energy transformation, leading to diverse applications as optically functional materials in biomedical fields. Recently, their potentials have been further explored, such as enzyme-like activity and ability to promote osteogenic differentiation. Through refined synthesizing strategies carbon dots, a rich treasure trove for new discoveries, stand a chance to guide significant development in biomedical applications. In this review, the authors start with a brief introduction to CDs. By presenting mechanisms and examples, the authors focus on how they can be used in diagnosing and treating diseases, including bioimaging failure of tissues and cells, biosensing various pathogenic factors and biomarkers, tissue defect repair, anti-inflammation, antibacterial and antiviral, and novel oncology treatment. The introduction of the application of integrated diagnosis and treatment follows closely behind. Furthermore, the challenges and future directions of CDs are discussed. The authors hope this review will provide critical perspectives to inspire new discoveries on CDs and prompt their advances in biomedical applications.

Pursuing excitonic energy transfer with programmable DNA-based optical breadboards

DNA nanotechnology has now enabled the self-assembly of almost any prescribed 3-dimensional nanoscale structure in large numbers and with high fidelity. These structures are also amenable to site-specific modification with a variety of small molecules ranging from drugs to reporter dyes. Beyond obvious application in biotechnology, such DNA structures are being pursued as programmable nanoscale optical breadboards where multiple different/identical fluorophores can be positioned with sub-nanometer resolution in a manner designed to allow them to engage in multistep excitonic energy-transfer (ET) via Förster resonance energy transfer (FRET) or other related processes. Not only is the ability to create such complex optical structures unique, more importantly, the ability to rapidly redesign and prototype almost all structural and optical analogues in a massively parallel format allows for deep insight into the underlying photophysical processes. Dynamic DNA structures further provide the unparalleled capability to reconfigure a DNA scaffold on the fly in situ and thus switch between ET pathways within a given assembly, actively change its properties, and even repeatedly toggle between two states such as on/off. Here, we review progress in developing these composite materials for potential applications that include artificial light harvesting, smart sensors, nanoactuators, optical barcoding, bioprobes, cryptography, computing, charge conversion, and theranostics to even new forms of optical data storage. Along with an introduction into the DNA scaffolding itself, the diverse fluorophores utilized in these structures, their incorporation chemistry, and the photophysical processes they are designed to exploit, we highlight the evolution of DNA architectures implemented in the pursuit of increased transfer efficiency and the key lessons about ET learned from each iteration. We also focus on recent and growing efforts to exploit DNA as a scaffold for assembling molecular dye aggregates that host delocalized excitons as a test bed for creating excitonic circuits and accessing other quantum-like optical phenomena. We conclude with an outlook on what is still required to transition these materials from a research pursuit to application specific prototypes and beyond.

Current use and future potential of (physiologically based) pharmacokinetic modelling of radiopharmaceuticals: a review

Rationale: Physiologically based pharmacokinetic (PBPK) and population pharmacokinetic (PK) modelling approaches are widely accepted in non-radiopharmaceutical drug development and research, while there is no major role for these approaches in radiopharmaceutical development yet. In this review, a literature search was performed to specify different research purposes and questions that have previously been answered using both PBPK and population PK modelling for radiopharmaceuticals. Methods: The literature search was performed using the databases PubMed and Embase. Wide search terms included radiopharmaceutical, tracer, radioactivity, physiologically based pharmacokinetic model, PBPK, population pharmacokinetic model and nonlinear mixed-effects model. Results: Eight articles and twenty articles were included for this review based on this literature search for population PK modelling and PBPK modelling, respectively. Included population PK analyses showed to have an added value to develop predictive models for a population and to describe individual variability sources. Main purposes of PBPK models appeared related to optimizing treatment (planning), or more specifically: to find the optimal combination of peptide amount and radioactivity, to optimize treatment planning by reducing the number of measurements, to individualize treatment, to get insights in differences between pre-therapeutic and therapeutic scans or to understand inter-patient differences. Other main research subjects were regarding radiopharmaceutical comparisons, selecting ligands based on their peptide characteristics and gaining a better understanding of drug-drug interactions. Conclusions: The use of PK modelling approaches in radiopharmaceutical research remains scarce, but can be expanded to obtain a better understanding of PK and whole-body distribution of radiopharmaceuticals in general. PK modelling of radiopharmaceuticals has great potential for the nearby future and could contribute to the evolving research of radiopharmaceuticals.

The Chemical Scaffold of Theranostic Radiopharmaceuticals: Radionuclide, Bifunctional Chelator, and Pharmacokinetics Modifying Linker

Therapeutic radiopharmaceuticals have been researched extensively in the last decade as a result of the growing research interest in personalized medicine to improve diagnostic accuracy and intensify intensive therapy while limiting side effects. Radiometal-based drugs are of substantial interest because of their greater versatility for clinical translation compared to non-metal radionuclides. This paper comprehensively discusses various components commonly used as chemical scaffolds to build radiopharmaceutical agents, i.e., radionuclides, pharmacokinetic-modifying linkers, and chelators, whose characteristics are explained and can be used as a guide for the researcher.

Radioiodination of Modified Porous Silica Nanoparticles as a Potential Candidate of Iodine-131 Drugs Vehicle

There are challenges related to cancer treatment, namely, targeting and biocompatibility associated with a drug vehicle. This research aims to prepare a theranostic cancer vehicle based on porous silica nanoparticles (PSN) with controllable nanoparticle size, supporting targeting properties, and biocompatible. The synthesis method combined the Stöber process and liquid crystal templating using a dispersant and pore expander. Triethanolamine (TEA) and Pluronic F-127 were combined as a steric stabilizer and dispersing agent, while n-hexane was used as a pore expander. The amine functionalization was carried out using the 3-aminopropyl-triethoxysilane solution. Furthermore, radiolabeling of PSN using Iodine-131 and iodogen as oxidizing agents was carried out. The results showed that the best achievable PSN size was 100-150 nm with a polydispersity index of 0.24 using TEA-Pluronic F-127. The functionalization results did not significantly affect the radioiodination result. Radiochemical purity (RCP) values up to 95% were obtained in the radioiodination, while the labeled compounds were relatively stable with 12 mCi radioactivity, indicating the absence of radiolysis. The synthesized PSN was not toxic to normal cell samples up to a concentration of 150 μg/mL for PSN and 170 μg/mL for PSN-NH2. The cellular uptake testing results of the PSN-131I in cancer cell samples showed promising uptake ability.

Emerging microfluidics-enabled platforms for osteoarthritis management: from benchtop to bedside

Osteoarthritis (OA) is a prevalent debilitating age-related joint degenerative disease. It is a leading cause of pain and functional disability in older adults. Unfortunately, there is no cure for OA once the damage is established. Therefore, it promotes an urgent need for early detection and intervention of OA. Theranostics, combining therapy and diagnosis, emerges as a promising approach for OA management. However, OA theranostics is still in its infancy. Three fundamental needs have to be firstly fulfilled: i) a reliable OA model for disease pathogenesis investigation and drug screening, ii) an effective and precise diagnostic platform, and iii) an advanced fabrication approach for drug delivery and therapy. Meanwhile, microfluidics emerges as a versatile technology to address each of the needs and eventually boost the development of OA theranostics. Therefore, this review focuses on the applications of microfluidics, from benchtop to bedside, for OA modelling and drug screening, early diagnosis, and clinical therapy. We first introduce the basic pathophysiology of OA and point out the major unfilled research gaps in current OA management including lack of disease modelling and drug screening platforms, early diagnostic modalities and disease-modifying drugs and delivery approaches. Accordingly, we then summarize the state-of-the-art microfluidics technology for OA management from in vitro modelling and diagnosis to therapy. Given the existing promising results, we further discuss the future development of microfluidic platforms towards clinical translation at the crossroad of engineering and biomedicine.

Theranostics – present and future

Theragnostics in nuclear medicine constitute an essential element of precision medicine. This notion integrates radionuclide diagnostics procedures and radionuclide therapies using appropriate radiopharmaceutics and treatment targeting specific biological pathways or receptors. The term theragnostics should also include another aspect of treatment: not only whether a given radioisotopic drug can be used, but also in what dose it ought to be used. Theragnostic procedures also allow predicting the effects of treatment based on the assessment of specific receptor density or the metabolic profile of neoplastic cells. The future of theragnostics depends not only on the use of new radiopharmaceuticals, but also on new gamma cameras. Modern theragnostics already require unambiguous pharmacokinetic and pharmacodynamic measurements based on absolute values. Only dynamic studies provide such a possibility. The introduction of the dynamic total-body PET-CT will enable this type of measurements characterizing metabolic processes and receptor expression on the basis of Patlak plot.

Obstacles and Recommendations for Clinical Translation of Nanoparticle System-Based Targeted Alpha-Particle Therapy

The rationale for application of nanotechnology in targeted alpha therapy (TAT) is sound. However, the translational strategy requires attention. Formulation of TAT in nanoparticulate drug delivery systems has the potential to resolve many of the issues currently experienced. As α-particle emitters are more cytotoxic compared to beta-minus-emitting agents, the results of poor biodistribution are more dangerous. Formulation in nanotechnology is also suggested to be the ideal solution for containing the recoil daughters emitted by actinium-225, radium-223, and thorium-227. Nanoparticle-based TAT is likely to increase stability, enhance radiation dosimetry profiles, and increase therapeutic efficacy. Unfortunately, nanoparticles have their own unique barriers towards clinical translation. A major obstacle is accumulation in critical organs such as the spleen, liver, and lungs. Furthermore, inflammation, necrosis, reactive oxidative species, and apoptosis are key mechanisms through which nanoparticle-mediated toxicity takes place. It is important at this stage of the technology's readiness level that focus is shifted to clinical translation. The relative scarcity of α-particle emitters also contributes to slow-moving research in the field of TAT nanotechnology. This review describes approaches and solutions which may overcome obstacles impeding nanoparticle-based TAT and enhance clinical translation. In addition, an in-depth discussion of relevant issues and a view on technical and regulatory barriers are presented.